A111D7 lT7fl&2

<2

(/) Q4- NBS SPECIAL PUBLICATION 615

U.S. DEPARTMENT OF COMMERCE / National Bureau of Standards

Sensor Handbook for Automatic Test,

Monitoring, Diagnostic, and Control

Systems Applications to Military

Vehicles and Machinery
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards' was established by an act of Congress on March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and technology

and facilitate their effective application for public benefit. To this end, the Bureau conducts

research and provides: (1) a basis for the Nation's physical measurement system, (2) scientific and technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety. The Bureau's technical work is per- formed by the National Measurement Laboratory, the National Engineering Laboratory, and

the Institute for Computer Sciences and Technology.

THE NATIONAL MEASUREMENT LABORATORY provides the national system ot physical and chemical and materials measurement; coordinates the system with measurement

systems of other nations and furnishes essential services leading to accurate and uniform

physical and chemical measurement throughout the Nation's scientific community, industry,

and commerce; conducts materials research leading to improved methods of measurement,

standards, and data on the properties of materials needed by industry, commerce, educational

institutions, and Government; provides advisory and research services to other Government

agencies; develops, produces, and distributes Standard Reference Materials; and provides

calibration services. The Laboratory consists of the following centers:

Absolute Physical Quantities 2 — Radiation Research — Thermodynamics and

Molecular Science — Analytical Chemistry — Materials Science. THE NATIONAL ENGINEERING LABORATORY provides technology and technical ser- vices to the public and private sectors to address national needs and to solve national problems; conducts research in engineering and applied science in support of these efforts; builds and maintains competence in the necessary disciplines required to carry out this research and technical service; develops engineering data and measurement capabilities;

provides engineering measurement traceabili-ty services; develops test methods and proposes

engineering standards and code changes; develops and proposes new engineering practices;

and develops and improves mechanisms to transfer results of its research to the ultimate user. The Laboratory consists of the following centers:

Applied Mathematics — Electronics and Electrical Engineering 2 — Mechanical

Engineering and Process Technology 2 — Building Technology — Fire Research —

Consumer Product Technology — Field Methods.

THE INSTITUTE FOR COMPUTER SCIENCES AND TECHNOLOGY conducts

research and provides scientific and technical services to aid Federal agencies in the selection,

acquisition, application, and use of computer technology to improve effectiveness and

economy in Government operations in accordance with Public Law 89-306 (40 U.S.C. 759), relevant Executive Orders, and other directives; carries out this mission by managing the Federal Information Processing Standards Program, developing Federal ADP standards

guidelines, and managing Federal participation in ADP voluntary standardization activities; provides scientific and technological advisory services and assistance to Federal agencies; and

provides the technical foundation for computer-related policies of the Federal Government.

The Institute consists of the following centers:

Programming Science and Technology — Computer Systems Engineering.

'Headquarters and Laboratories at Gaithersburg, MD, unless otherwise noted; mailing address Washington, DC 20234. 'Some divisions within the center are located at Boulder, CO 80303.
Sensor Handbook for Automatic Test,

Monitoring, Diagnostic, and Control

Systems Applications to Military

Vehicles and Machinery

Paul S. Lederer

Center for Electronics and Electrical Engineering

National Engineering Laboratory

National Bureau of Standards

Washington, DC 20234

°» STA.VOAHOs

Llfi/f A ((

y

NOV 2 1981

Sponsored by: U.S. Army Material Command

CORADCOM/DRDCO-TCS

Fort Monmouth, NJ 07703

, U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Issued October 1981
Library of Congress Catalog Card Number: 81-600127

National Bureau of Standards Special Publication 615

Nat. Bur. Stand. (U.S.), Spec. Publ. 615, 450 pages (Oct. 1981) CODEN: XNBSAV

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1981

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402

Price $9.00

(Add 25 percent for other than U.S. mailing)
Sensor Handbook for Automatic Test,

Monitoring, Diagnostic, and

Control Systems Applications to

Military Vehicles and Machinery

Paul S. Lederer

National Bureau of Standards

Washington, DC 20234

Abstract

The Sensor Handbook is intended as a guide for those who design, specify,

use, and test military automatic test equipment containing sensors. The

handbook addresses measurands and principles of measurement, data acquisition,

sensor calibration and testing, environmental considerations, stability,

durability, reliability, and error assessment. Sensor manufacturers and sensor calibration and evaluation resources are included, as is an annotated

bibliography. The handbook is based largely on the present, proved

state-of-the-art. Possible future trends are briefly discussed. The handbook

is addressed to the general engineer, system designer, or manager with an engineering background. It does not provide the highly detailed technical

information needed by the measurement engineer, although ample references are included for further study.

Key words: automatic test equipment; ATE; calibration; data acquisition;

durability; dynamic calibration; environmental testing; evaluation;

measurand; reliability; sensor; transducer

i i i
FOREWORD

The increasing complexity and cost of weapons and other military systems

and the need for greater operational readiness in a world of rapidly changing

events, combined with decreases in skilled personnel, dictate the integration

of automatic testing into those systems. Following the recommendations of

industry /joint-services groups, a Joint Logistics Commanders Panel on Automatic

Testing (JLC-AT) was chartered in early 1978. The Panel prepared a study plan

defining tasks in all areas of automatic testing [3]. The tasks are divided

into three major areas: management, acquisition support, and testing

technology, with these objectives:

a. Optimize definition, application, and support of automatic testing

hardware and software in the system acquisition management process;

b. Develop systems engineering and logistics tools to enhance the

application of automatic testing to the design and support of

weapons systems; and

c. Coordinate R&D planning and execution in testing technology and

associated software to minimize duplication of effort and achieve

common testing technology objectives.

All subtasks needed to make these objectives are described in detail in

the "Subtask Descriptions" (Joint Logistics Commanders Panel on Automatic

Testing, September 30, 1980). Tasks under the second objective will provide

the tools necessary to integrate Automatic Test Equipment (ATE) electronics

into military and weapons system acquisition. The tools will include

standards, specifications, and guides for controlling the interfaces between

automatic test hardware and the systems to be tested. Sensors not only

represent a critically important type of interface in these systems, they may

be part of the unit-under-test itself.

Task 20600 (Acquisition support-hardware interface) has two subtasks with

these objectives:

Subtask 20601: To develop specifications for on-line and off-line ATE

interfaces.

Subtask 20602: To develop a Sensor Handbook, including state-of-the-art

techniques and devices for electronic and non-electronic testing.

There is a critical need to provide information on the selection,

application, testing, and use of sensors as part of ATE systems. This led to

an assignment to the NBS staff who had conducted the NBS program on transducers,

"InterAgency Transducer Project," to develop a Sensor Handbook to meet the

objectives of Subtask 20602. The material which follows comprises the Sensor

Handbook (Subtask 20602) as prepared by staff of the National Bureau of

Standards at the request, and with the support, of DARCOM-U.S. Armv.

i v
The NSIA ATE project "Non-Electronic Testing Task Group" has recommended

that this document be revised periodically to keep the information current.

Comments and suggestions on the handbook should be addressed to the

author, Electrosystems Division, Center for Electronics and Electrical

Engineering, National Bureau of Standards, Washington, DC 20234.

The use of trade names or company products in

this publication does not constitute endorsement

or recommendation by the National Bureau of

Standards and does not imply that the products

are necessarily the best available for the

purpose.

v
TABLE OF CONTENTS

Page

Abstract iii

FOREWORD iv

LIST OF TABLES . . x

ACKNOWLEDGMENTS xi

1. INTRODUCTION .1-1

1.1 Purpose and Scope of Sensor Handbook 1-1

1.2 Contents 1-1

2. AUTOMATIC TEST EQUIPMENT AND SENSORS 2-1

3. SENSORS 3-1

3.1 Introduction 3-1

3.2 Sensor Selection Factors 3-3

3.3 Sensor "Accuracy" 3-6

3.4 Sensor Cost Considerations 3-7

3.5 Sensor Materials Compatibility 3-8

3.6 Future Trends in Sensors 3-9

4. MEASURANDS AND PRINCIPLES OF MEASUREMENTS 4-1

4.1 General Considerations 4-1

4.2 Specific Measurands 4-1

4.2.1 Pressure 4-1

4.2.1.1 Introduction 4-1

4.2.1.2 Pressure References 4-2

4.2.1.3 Units of Pressure 4-3

4.2.1.4 Pressure Ranges 4-3

4.2.1.5 Pressure Sensing Technologies 4-4

4.2.1.6 Pressure Sensing Elements 4-5

4.2.1.7 Transduction Elements 4-5

4.2.1.8 Vacuum Sensors 4-15

4.2.1.9 Current Problems and Future Trends .... 4-17

4.2.2 Motion 4-23

4.2.2.1 Introduction 4-23

4.2.2.2 Materials and Environmental Factors .... 4-26

4.2.2.3 Displacement 4-26

4.2.2.4 Linear Velocity 4-28

4.2.2.5 Angular Velocity (Tachometer) 4-29

4.2.2.6 Acceleration 4-33

4.2.2.7 Sensing Technologies 4-35

4.2.2.8 Angular Acceleration 4-36

4.2.2.9 Jerk 4-37

4.2.2.10 Current Problems and Future Trends .... 4-37

4.2.3 Flow 4-39

4.2.3.1 Introduction 4-39

4.2.3.2 Material Compatibility Factors 4-39

vi
TABLE OF CONTENTS (cont.)

Page

4.2.3.3 Units of Flow 4-40

4.2.3.4 Range Considerations 4-40

4.2.3.5 Sensing Techniques in General 4-41

4.2.3.6 Differential Pressure Flow Sensors .... 4-41

4.2.3.7 Fluid Velocity and Mass Responding Sensors 4-45

4.2.3.8 Flow Sensors Based on Physical

Characteristics of the Fluid 4-48

4.2.3.9 Current Problems and Future Trends .... 4-50

4.2.4 Temperature 4-53

4.2.4.1 Introduction 4-53

4.2.4.2 Materials Compatibility 4-54

4.2.4.3 Units of Measurement 4-54

4.2.4.4 Temperature Sensors (Non-Electr1cal ) . . . 4-57

4.2.4.5 Thermocouples 4-58

4.2.4.6 Resistance Thermometers 4-61

4.2.4.7 Radiation Temperature and Heat Flux Sensors 4-64

4.2.4.8 Selection of Temperature Sensors 4-65

4.2.4.9 Summary 4-70

4.2.5 Force and Torque 4-72

4.2.5.1 Introduction 4-72

4.2.5.2 Materials Compatibility 4-73

4.2.5.3 Units of Measurement 4-73

4.2.5.4 Range Considerations 4-74

4.2.5.5 Sensing Principles 4-74

4.2.5.6 Application Considerations and Problems . . 4-78

4.2.5.7 Future Trends 4-81

4.2.6 Level 4-81

4.2.6.1 Introduction 4-81

4.2.6.2 Materials Compatibility 4-81

4.2.6.3 Units 4-81

4.2.6.4 Level Device Principles 4-81

4.2.6.5 Float and Displacer Devices 4-83

4.2.6.6 Head or Pressure Devices 4-84

4.2.6.7 Electrical or Electronic Devices 4-85

4.2.6.8 Application Considerations 4-89

4.2.6.9 Future Trends 4-89

4.2.7 Humidity and Moisture 4-89

4.2.7.1 Introduction 4-89

4.2.7.2 General Considerations 4-90

4.2.7.3 Non-Electrical Hygrometers 4-90

4.2.7.4 Electrical Hygrometers 4-92

4.2.7.5 Application Considerations 4-95

4.2.7.6 Current Problems and Future Trends .... 4-96

4.2.8 Other Measurands 4-96

4.2.8.1 Wear 4-96

4.2.8.2 Lubricating Oil Analysis 4-96

5. DATA ACQUISITION AND SIGNAL CONDITIONING 5-1

5.1 General Considerations . 5-1

5.1.1 Data Acquisition System (DAS) Parameters 5-4

vii
TABLE OF CONTENTS (cont.)

Page

5.1.2 Sensors 5-5

5.1.3 Signal Conditioning 5-5

5.1.4 Multiplexing and Anal og-to-Digi tal Conversion (ADC) . 5-7

5.1 . 5 Sample Rate 5-7

5.1.6 Bit Rate and Data Resolutions 5-8

5.1.7 Sample and Hold 5-9

5.1.8 Transmission Media 5-9

5.1.9 Demultiplexing 5-10

5.1.10 Data Distribution 5-11

5.1.11 Data Compression 5-11

5.1.12 Computer Interfacing 5-12

5.1.13 Computer Processing 5-12

6. SENSOR CALIBRATION 6-1

6.1 Performance Characteristics 6-1

6.1.1 General Considerations 6-1

6.1.2 Qualification Testing 6-4

6.1.3 Acceptance Testing 6-9

6.2 Laboratory Measurement Tests 6-9

6.2.1 Static Calibration 6-9

6.2.1.1 Basic Considerations 6-9

6.2.1.2 Number of Calibration Points in Single

Calibration 6-10

6.2.1.3 Number of Calibration Cycles 6-12

6.2.1.4 Static Calibration Procedures 6-13

6.2.2 Dynamic Calibration 6-16

6.2.2.1 Basic Considerations 6-16

6.2.2.2 Sinusoidal Stimuli 6-21

6.2.2.3 Step Function Stimuli 6-29

6.2.2.4 Random Stimuli 6-37

6.3 Operating Environments and Tests 6-37

6.3.1 General Considerations 6-37

6.3.2 Simulation of Environmental Conditions 6-40

6.3.3 Environmental Test Procedures 6-47

6.3.3.1 Extreme Steady-State Temperatures 6-47

6.3.3.2 Thermal Transients 6-49

6.3.3.3 Acceleration, Vibration, and Shock .... 6-50

6.3.3.4 Electromagnetic Radiation 6-53

6.4 Stability, Durability, and Reliability Testing 6-54

6.4.1 General Considerations 6-54

6.4.2 Stability, Durability, and Operating Life 6-55

6.4.2.1 Storage Life Tests 6-55

6.4.2.2 Operating Life Tests at Room Conditions . . 6-56

6.4.2.3 Operating Life Tests at Elevated

Temperatures 6-57

6.4.3 Re-Calibration Considerations 6-58

6.4.3.1 Re-Calibration Intervals . 6-59

6.4.4 Reliability 6-61

6.4.4.1 Infant Mortality 6-62

6.4.4.2 Useful Life 6-62

v i i i
TABLE OF CONTENTS (cont.)

Page

6.4.4.3 Wearout 6-64

6.4.4.4 Failure Rate 6-64

6.4.4.5 Reliability Degradation 6-65

6.4.4.6 Reliability Growth 6-66

6.4.5 Failure Mechanisms 6-67

6.4.6 Accelerated Life Testing 6-70

6.4.7 Fail -Safe Considerations in ATE Systems 6-76

7. ERROR ASSESSMENT AND ACCURACY 7-1

7.1 General Considerations 7-1

7.2 Sensor Error Analysis 7-1

7.2.1 Straight Line Data Reduction 7-1

7.2.2 Selection of Straight Line 7-1

7.2.3 Calibration Parameters Obtained From Data Reduction . 7-2

7.2.4 Number of Significant Digits for Reporting

Calibration Results 7-3

7.2.5 Expression of Uncertainties of Final Results 7-4

7.2.6 Sampling Considerations in the Performance Testing

of Sensors 7-6

7.2.7 Error Band Concept 7-8

8. SENSOR-RELATED STANDARDS DOCUMENTS 8-1

8.1 Introduction 8-1

8.2 Voluntary Standards Listing 8-3

8.3 Government Standards 8-31

8.3.1 Civilian Standards Listings 8-32

8.3.2 Military Standards Listings 8-32

9. REFERENCES AND BIBLIOGRAPHY 9-1

9.1 References 9-1

9.1.1 Cited References 9-1

9.1.2 Non-Referenced Useful Sources 9-7

9.2 Bibliography of Sensor-Related Books 9-9

10. GLOSSARY 10-1

11. RESOURCES c. 11-1

11.1 Manufacturers of Sensors and Related Items 11-1

11.2 Sensor Calibration and Evaluation Resources 11-79

11.2.1 Government Sensor Laboratories, Contacts and

Functions 11-80

11.2.2 Private Industry Sensor Laboratories, Contacts and

Functions 11-89

11.2.3 Miscellaneous Sensor Information Resources 11-102

11.2.3.1 Periodicals 11-102

11.2.3.2 Courses 11-103

11.2.3.3 Conferences 11-103

12. INDEX 12-1

APPENDIX A. TABLES OF COMMERCIALLY AVAILABLE SENSORS A-1

ix
LIST OF TABLES

Page

1. Pressure Sensors - Comparison of Pressure Sensing Elements 4-19

2. Pressure Seniors - Comparison of Transduction Elements 4-20

3. Comparison 4>f Transduction Elements 4-21

4. Quality Ratings of Transduction Elements 4-22

5. (Motion) Displacement Sensors - Comparison of Transduction Elements 4-38

6. Flow Sensors - Comparison of Common Operating Principles 4-51

7. Flow Sensors - Comparison of Common Operating Principles 4-52

8. Fixed Points on International Practical Temperature Scale 4-56

9. Commonly Used Thermocouples 4-59

10. Accuracy Characteristics of Thermocouples From

ANSI Standard MC96. 1-1975 4-60

11. Temperature Sensors - Comparison of Sensing-Transduction Elements . 4-71

12. Torque Sensors - Comparison of Transduction Elements . 4-80

13. Summary of Characteristics of Electrical and Electronic Level Sensors 4-88

14. Typical Wear Monitoring Techniques » 4-98

15. Considerations in Selecting Data Acquisition Systems and Components 5-3

16. Student's "t" Values 6-13

17. Environments and Typical Effects 6-41

18. Illustration of Interacting Environmental Effects 6-45

x
ACKNOWLEDGMENTS

Appreciation is expressed for the guidance and assistance provided by

Wsewolod Hnatczuk, DRDTA-RGD, U.S. Army Tank Automotive Research and

Development Command, who serves as lead coordinator for this JLC Subtask, and

the members of his committee: J. E. Hart, H. R. Hegner, W. R. McWhirter,

F. Micka, and W. Prather.

H. K. Whitesel, DTNSRDC, U.S. Navy, A. F. Pi tsenbarger, ASD/ENEGP, U.S.

Air Force, and R. R. Hoi den, Hughes Aircraft Company, reviewed handbook drafts

and made many valuable suggestions.

The following technical personnel of the National Bureau of Standards made

noteworthy contributions to this effort: Carol F. Vezzetti, George Rogers (now

retired), and Thomas F. Leedy. Barry A. Bell, Leader, Electronic

Instrumentation and Metrology Group, NBS, and J. Vogt, Office of Measurement

Services, NBS, provided management support and coordination.

The cooperation and contributions of many staff members of government

agencies and industry are also gratefully acknowledged. In particular, the

author would like to recognize the following individuals who gave permission

for the inclusion in this handbook of material from their own publications:

Frederic S. Cushing, Director of Publishing Services,

Instrument Society of America

Harish C. Suluja, Managing Editor, Measurements and Control

Robert W. Myers, Manager, Technical Writing, CEC Division,

Bell and Howell

S. Kent Morgan, Director, EMR Data Systems, Schlumberger Corporation.

Last, but not least, the author would like to express his appreciation to

the four secretaries who deciphered his handwriting and typed the

manuscript: Brenda Yankey, Bonnie Smith, Jenny Pal la, and Betty Oravec.

xi

1. INTRODUCTION

1.1 Purpose and Scope of Sensor Handbook

The Sensor Handbook is intended primarily as a guide and reference for

systems engineers who design, specify, procure, review, and manage Automatic

Test Equipment (ATE) systems. The book will address such areas as measurands

and principles of measurement, ancillary equipment, sensor calibration and

testing, error assessment, list sensor-related standards documents, and contain

a bibliography and a listing of sensor manufacturers.

The handbook is not intended for measurements engineers and specialists;

it is specifically addressed to the general engineer or manager with an engineering background. It will try to provide that type of material which

will give reasonable assurance of proper sensor selection, application, and use

in military ATE systems. This book will also attempt to point out possible

unsuspected pitfalls and problem areas in the use of the sensors. A minimum

amount of mathematics and graphics will be used; additional information can be

gained from the references cited. It is the author's hope that this book will

provide a realistic assessment of the role and characteristics of sensors as critical components of ATE systems.

To achieve optimum continuing usefulness, it is planned to update the

handbook periodically. Corrections, comments, and suggestions are welcomed and

will be incorporated whenever, in the judgment of sponsors and author, they

will tend to enhance the usefulness of the book.

1.2 Contents

The focus of this handbook is on the sensors in their role as interfaces

for military ATE systems. As such, the performance of the sensors, to a major

extent, determines the performance of the ATE system itself. By extension,

the performance of the sensors also has a major bearing on the performance of

the military system which is monitored by the ATE system. When they are allowed to be the weakest links in the entire chain, sensors critically

influence major military systems and the fulfillment of their missions.

The handbook will attempt to address those sensor considerations which are most likely to influence their selection and use in .the ATE systems themselves

or in the validation and troubleshooting of ATE. The information in this

handbook is also applicable to machinery and process control equipment

containing sensors.

In addition to some general coverage of Automatic Test Equipment and sensor selection, major sections will deal with the measurands most likely to

be encountered by military ATE systems; these include pressure, motion, flow,

temperature, force and torque, level, and humidity. The sections will deal

with units, ranges, and principles of measurement in some detail, as well as other factors which must be considered when selecting sensors. Also included

are tables listing advantages and disadvantages of the sensing principles

discussed. In addition, a sampling of the characteristics of typical

commercial sensors is presented in tabular form in an appendix. The sensor

output, an electrical signal, generally needs to be conditioned prior to its

1-1
input to the main part of the (usually minicomputer-controlled) ATE system. A

section of the book deals with data acquisition and conditioning systems.

In view of the importance of the knowledge of the performance

characteristics of sensors, considerable emphasis will be placed on the factors

bearing on this. Sensor calibration and testing, including static and dynamic

calibration, operating environments, stability, durability, and reliability

will be addressed in some detail. The assessment of sensor errors completes

this approach which can help select the proper sensor, calibrate and test it

realistically, and obtain a measure of the quality of its performance.

To further aid in the process, the handbook contains sections which list

pertinent sensor standards documents and sensor resources. The latter includes

a listing of sensor laboratories located in government and private industry, as well as a listing of manufacturers of sensors. Finally, for those who desire

additional, more detailed theoretical and practical information, an annotated

bibliography of sensor-related publications is added, as well as an extensive

list of references.

To keep the size of the handbook reasonable, most treatments are kept as concise as practicable by avoiding unnecessary duplication of existing and

otherwise readily available information.

The major thrust of this handbook is to cope with the fact that sensors

are not the simple, stable devices they appear to be, and are not necessarily

easy to select and use in complex systems and military environments. Careful

and realistic considerations of measurands, operating environments, ATE system

requirements, calibration needs, and desired durability are absolutely

essential to achieve ATE mission goals. The handbook attempts to provide the

information needed to assure this achievement.

The reader might well bear in mind the old quotation which states "for the

want of a nail ... . etc.

!"

1-2
2. AUTOMATIC TEST EQUIPMENT AND SENSORS

As the number of components in a system increases, reliability tends to

decrease. Hence increasingly complex electronic systems with many circuit

elements, including large-scale integrated microcircui ts , make it increasingly

difficult to assure continuing proper functioning of all system elements. The

incorporation of microcomputers and microprocessors, of increasing complexity

themselves, in these systems, however, made possible greater levels of

self -testing of the electronic system or its components. This was the genesis

of ATE.

The field of ATE encompasses a broad spectrum of scientific/engineering

disciplines and hardware/software technologies. ATE systems generally consist

of a digital computer with its attendant software operating system, application

programs and peripheral storage, and input/output (I/O) equipment, programmable

stimulus and measurement instrumentation, and a network of sophisticated

interfacing, switching, signal -conditioning, and routing interconnections.

Essential to the operation and functions of any ATE system is the reliable

performance of a variety of active and passive electrical /electronic modules,

devices, and components.

Considerable efforts are expended on the design and development of

automatic test equipment for electronic systems. The initial approach was the

addition of automatic test functions to existing, or about-to-be-developed,

equipment. Subsequently, the ATE functions were incorporated into the original

design of the equipment. The success of the ATE concept has made possible

tremendous advances in the capabilities and functions of electronic equipment

(for communication, measurement, and control) while assuring continuing

reliability of operation.

The military has long had an interest in the strategic importance of ATE.

The increased electronic complexity of prime weapons systems requires better

and more automatic means of testing the operational readiness of avionics,

missiles, tanks, and shipboard electronic assemblies. A high turnover of

personnel and a more limited training budget have compounded the military's

test and support problems. To make matters worse, ATE bought by the services

lacks the standard packaging and modularity (hardware and software) requisite

for logistic support economics.

Automatic testing of non-electronic systems, such as machinery-monitoring

instrumentation, is a logical extension of the state-of-the-art ATE for

electronic systems. Military hardware, such as ordnance, automotive vehicles,

ships, aircraft, and missiles, requires large amounts of spare parts and efficient

repair of defective components. Maintenance time and costs naturally increase

with the size and complexity of the equipment involved. A major contributor

is the high cost of staffing, combined with difficulties of acquiring and re- taining the skilled personnel needed. Automation provides the opportunity of

reducing maintenance time and costs.

Ultimately, automation will control much, if not most, military machinery.

To achieve this, it will be necessary to develop machinery performance

monitoring systems to provide information on operation status as well as maintenance requirements. In the case of naval vessels, machinery performance

monitoring will make it possible to attain the benefits of ship automation, re- duction of human operations, and improved continuity of operation. The same

2-1
considerations apply to military land vehicles, aircraft, missiles, and other

weapons systems.

The performance monitoring of large, basically mechanical systems with the use of ATE requires the use of sensors (often called transducers) as the

interfaces between the system to be monitored and the electronic ATE. A

variety of performance monitoring and failure prediction approaches exists.

They are based on the sensing of certain parameters, and a comparison between

the measured values and those thought to establish limits of acceptable

performance, whether singly or in combination. Any operating component has a mechanical, electromagnetic, or chemical "signature." Any change in this

signature may indicate incipient failure before any other external indications

exist. Physical parameters sensed include: vibration and motion, pressure,

temperature, flow, force, torque, strain, etc. Thermal signals, chemical

signatures, and electromagnetic signals are also used. Many approaches are

under investigation.

A fundamental consideration for the ATE system and its interfaces, such as sensors, is that the ATE system must itself perform properly, otherwise, its

output is worthless . Purely electronic systems are achieving a very high

degree of reliaoility and predictability of operation. With the extension of

ATE applications to non-electronic systems, the role of the necessary sensor interface between the system to be tested and the electronic ATE becomes

critically important. Figure 1 shows a generalized concept of the sensor-ATE

system matrix and the factors which influence sensor selection and operation.

These sensors which provide an electrical output signal in response to a physical (or chemical) input are potentially the weakest link in the

measurement chain essential to the proper functioning of the entire ATE system.

This is often due to inherent 1 imits in the performance of the sensors and/or

because of 1 i mi ted knowledge concerning their performance. Two factors may

exist: a lack of information by the sensor designer of the sensor performance

needed by the user, and/or a lack of adequate information on sensor performance

to guide system designers. Information on sensor performance in adverse

environments, over long periods of operating time and to measure rapidly

varying quantities, is not readily available. Users frequently have been

forced to devise and carry out laboratory tests of their own to supplement the

often meager information supplied by manufacturers, or to check the

manufacturer's claim on performance. Methods and equipment for such tests,

particularly for determining performance under dynamic conditions, have not

always been available. Existing test methods may not be standardized

adequately, leading to different results when used in different laboratories.

Sensor test method development and standardization has been scattered among

government agencies and private industry and the information on them is hard to uncover. To the author's knowledge, only one comprehensive, long-term program

on transducers (sensors) was carried on: the "InterAgency Transducer Project"

at the National Bureau of Standards from 1951 to 1979. Its major objectives

were: investigating the performance characteristics of transducers required

for making meaningful measurements of physical quantities, and the development

of techniques and apparatus for the determination of those characteristics [1].

The purpose of this handbook then is to present, in one volume, pertinent

information on sensors and their performance. This information is aimed at sensors used in, or in conjunction with, automatic test equipment of military

systems. However, much of the information is also pertinent to other sensor application, including machinery monitoring and process control.

Numbers in brackets refer to the literature references listed in section 9.

2-2
2 S z 1— l— oo < uj I OO h— h- O

zd zd i dc

I— a. li, h- <2 JZ i— O LU O oo c_> oo o

22a

I—

C3 cC Q- CC CD O I— i—' LU cC —II

1 1— I— CC < O _I _l o < Q Z Ll OO

tSi >

V3

CCo

00

60

CCo o

I—oUJ

—J

LU00

CCo

00

LUoo

oo

z:

<c

LU h-z: < LU z: 1— o _J a; (— o zd cC 1— > o DC < LU

NT NT z:

LU

u =r < C3 X ST ST 1 U_ LU z:o O CJ C_> LU o CJ CC a oo CO

_J

a.

CJ LU z: —

Q- CCCc

<_> z: z:

2: o o o

CC 1— 1—

Q- h- CC =C

<_> CC CJ

=>

—

a CD U_ oo

C/l z: Ll_ _J h2: Z: cC OO

LU

O =5 OO o o- o

C3

a:

zd z:

[— CD >- LU l-cc

CC I— 1—i ZD

LU CC

O OO

a. cc oo s m s u

m q:

u LU i—i ZD DC ET ZD I— h>ID.UQlil

CO

Xi—

cc: <

O0

5-

O0oO0

oo

CCI

oo

a

oo<

CD

z:

CC

CC ES LU IE a h- i

ZD CD

CCLU 1

3 LU ex. 1 Q D_ o D. z: >- CC s: CC

h- Cc cC CO

CD

i-Z5CD

V)

LU

O

s: i

cC i—i dc z: cC O

2-3

3. SENSORS

3.1 Introduction

A sensor is a device that responds to a physical stimulus (such as heat,

light, sound, pressure, magnetism, or motion) and transmits a resulting signal

(for measurement or control). The term "sensor" is a general term commonly

used to mean one, or some combination of, sensing element and transduction

element. The term "transducer" is often used interchangeably with "sensor"

(although it has a more specialized meaning in fields such as acoustics and

electrical machinery: a device which converts energy from one form to another). In the field of measurements, a transducer can be defined as a device which converts information from one form to another, a generalization

which includes the above definition of sensor. The term "transmitter" is

frequently used to describe the sensor or transducer which is used in process

control applications.

In this handbook, the term "sensor" will be used and its meaning will be

restricted to devices which transmit a signal in the form of an electrical

quantity, either by means of a change in a passive parameter like resistance,

inductance, or capacitance or by the generation of an active output like

voltage, current, or charge.

As indicated above, the sensor consists of two parts: the sensing

element, which responds directly to the physical stimulus (measurand), and the

transduction element, which converts the sensing element response to the

electrical signal suitable for transmission and/or measurement. It should be

noted that sometimes the two parts are combined and are not separable: a thermocouple which converts temperature differences directly to voltage is one example. See figure 2 for a schematic of a sensor.

The terminology used and most definitions in this handbook are based on a very comprehensive ANSI standard, originally developed by the Instrument

Society of America: ANSI/ISA S37.1 "Electrical Transducer Nomenclature and

Terminology" [2]. A selection of sensor terms is contained in the glossary,

section 1U. It should be noted that it is always better to give detailed

descriptions rather than to rely on imperfect (or imperfectly understood)

definitions.

The most common sensing elements for the measurement of physical

quantities convert these measurands into mechanical force, or by use of an intermediate elastic element into mechanical displacement. The latter, in

turn, acts on the transduction element to produce the electrical signal.

Exceptions are thermocouples or resistance temperature sensors, radiation

detectors, certain types of flowmeters, humidity and conductivity sensors, sensors of chemical composition, and a few others.

Sensors are usually analog devices, i.e., the electrical output is a continuous function of the measurand input. Certain quasi-digital devices

exist in which the output is a frequency which is a function of the measurand.

Since frequency is the measure of the input, by stipulating a time interval

during which the frequency is measured, the output is "digitized." An example

of a fully digital output is provided by an optically encoded shaft position

sensor which produces an unambiguous digital code for any angle of rotation.

3-1
3 , J

<I en O —

z CO

<

I—

CO

3-2
It is also possible to convert the electrical analog output of a sensor to

digital form by means of an electrical analog-to-digital (a-d) converter.

The "performance characteristics" of a sensor contain the information

needed to assess the quality of the measurements made by the sensor. Later

sections will describe in detail methods for establishing these

characteristics. Sensor manufacturers generally supply performance information

but this information may not be complete or up-to-date. It is highly

desirable, and recommended, to be able to independently establish these

characteristics upon acceptance or during later re-calibrations. It is

particularly important to retest the sensor periodically, preferably as a part

of the ATE system, to be assured of continuing quality of performance. The

concept of "end-to-end" calibration requires a known, actual, or simulated

measurand input to the sensor and a measurement of the system output.

Repeating this at prescribed re-calibration intervals is an important "self

test" feature of operational ATE systems. This will be discussed later.

A number of factors need to be considered in the selection of sensors to

meet the requirements of a particular system. These factors are discussed

briefly in the following parts of this section. Factors of particular

importance are covered in greater detail in separate sections of this

handbook.

3.2 Sensor Selection Factors

The selection of sensors requires the consideration and weighing of a variety of factors. External system constraints may make it impossible to

select a sensor which is optimum for all factors. It is highly likely that

compromises will be needed. Here are some of the items of importance:

The measurand which is to be sensed, the quality which is required of the

measurements, and the particular type of sensor (principle of sensing)

constitute major factors. These are discussed in detail in other sections of

this handbook (section 4, Measurands and Principles of Measurements, and

section 6, Sensor Calibration).

Selecting the right sensor to obtain data from a measurement requires an understanding of sensor performance characteristics and a clear idea of the

effects which occur within the measurand before, during, and after the

measurement. Successful specification of sensors may not require a comprehensive investigation of the measurement problems, but certainly the user

will want to guard against pitfalls and surprises. In the case of ATE systems,

the requirements posed by the rest of the system are of great importance to

insure the compatibility needed for reliable functioning of the entire system.

Excitation supplies, physical location, data format requirements, and

accessibility of sensors must be considered.

Measurement objectives often dictate "impossible" locations for the

placement of sensors. Available sensor size and operating environments are

major considerations. Selection of a sensor which can be placed within minimum

space envelopes may lead to performance compromises. Success in using sensors with limited accuracy for such installations requires the test engineer to

fully understand the selected sensor's characteristics within the operating

environment. Data analysis, with allowances for individual sensor performance

3-3
as installed and used, can provide adequate information from sensors which

could not otherwise be used for the measurement. The subject of "accuracy" is

not only important but so frequently misunderstood that it deserves discussion

in a section of its own: section 3.3.

Pressure sensors must be placed very close to the pressure sensing point

to obtain wide band dynamic data. Vibration sensor mass may affect the

vibration characteristics of the object under investigation. Regardless of sensor size, proper sensor installation is often the key to making accurate

measurements.

Attention must be paid to installation torque or force and mounting

position. Most sensors exhibit some sensitivity to deformation or torque on the exterior case. Often, zero shifts in the electrical output result from

torque applied to pressure fittings or bolting fixtures. Recommended

installation torque requirements should be obtained from the manufacturer.

Zero shifts should be checked in a post-installation calibration.

Temperature also may cause subsequent tension or compression within an installation, resulting in output shifts beyond those anticipated in

manufacturers' temperature error specifications. Temperature effects due to sensor installation can be reduced by selecting materials of similar

coefficients of expansion and by allowing for physical dimension changes of the

attachments.

Some sensors exhibit different performance characteristics with respect to

gravity or acceleration in various positions. Mounting position information is

usually included in manufacturers' specifications.

Operating and storage environments can have very large effects on sensor performance and are treated in more detail later. Here are some things to

consider: Operating temperatures may be more restrictive than storage or nonoperating temperatures. Materials used in sensors may show temperature

hysteresis which can influence measurement accuracies. The shutdown of

equipment being tested may produce high "temperature soak" conditions which

result in sensor calibration shifts.

Thermal lag between the test media and sensing elements has been worked

out successfully for many applications. For example, baffles and multipath

pressure ports with high thermal conductivity materials are used for hot gas

pressure measurements. Water-cooled jackets are successfully employed in high

temperature environments for both transient and steady temperature problems.

Transient temperature changes may cause errors quite different from

manufacturers' specified temperature errors. The specified temperature errors usually are based on testing sensors within ovens which stabilize sensors at a given temperature before determining temperature effects on the output. When a transient temperature problem is known to exist, transducer case designs often are altered to accommodate the situation.

Vibration and shock during measurements will add uncertainty to the data.

Persistence of such environments in excess of manufacturers' specifications may

lead to sensor damage and ultimate failure. Shock mounting may provide

protection against shock but may, in turn, cause other problems like thermal

3-4
lag. Other environmental factors include humidity, electromagnetic and nuclear

radiation. The subjects of environments and durability are treated in greater

detail later on. Corrosion and erosion are factors which can greatly affect sensor durability. The compatibility of the sensor materials with the

measurand and with the operating environment must be considered carefully.

Section 3.4 will address this in more detail.

The characteristics of the electrical output of the sensor must also be

considered with care. High level versus low level sensor output signals must

be considered for many measurement installations. Local noise, cable length

effects, and grounding considerations for power supplies, sensors, signal

conditioning amplifiers, and record/display devices have been treated in the

literature in some detail [9].

While detailed recommendations in all these areas are beyond the scope of

this endeavor, certain basic choices in proper selection of a sensor are offered. In the case of strain gage sensors, full-scale outputs may range from

0-20 mV to 0-5 V, depending on the type of sensing element employed. Integral

amplifiers are used to obtain outputs of 0-1 V or greater. Sensors for process

control applications, commonly called transmitters, usually provide full-scale

output signals of 4-20 mA in two-wire systems.

With the good, stable amplifiers available today, there is little

significant difference in use of sensor output levels over the range of 0-20 mV

to 0-100 mV. System compatibility with existing equipment may or may not be a consideration. Selection of a sensor with an integral amplifier to provide a high level output is generally made because of either severe operating noise or limited installation space available for amplifiers. Knowledge of electrical

noise at the sensor location is important, since signals from a low level sensor operating at the low end of its range may be masked by electrical

interference. One must remember, however, that integral semiconductor

electronics may be more sensitive to harsh environments than the sensor

itself.

Another factor, often overlooked, involves handling and mounting. From

the time a sensor is disconnected after a test at the maker's plant until data

is taken during an actual test by the customer, careless handling and lack of

protection against environmental exposure may have changed some sensor characteristics. Proper practices in handling and packing of sensors for

shipment must be used.

Different levels of protection against handling shock, vibration, and

temperature are required for various sensor types. Engineering and test

personnel installing and using the sensor must fully understand the sensors and

their limitations. Installation of a sensor can be relatively simple, yet care

in handling is required to ensure that the expected performance accuracy is

achieved.

Cost is a factor, different in kind from the other factors discussed in

this section, but of sufficient importance to be treated in section 3.4 in

detail. In summary, the selection of a sensor for a particular function in a particular ATE system requires the weighing of many factors. The most

important of these are discussed in this handbook. User experience, an

3-5
intangible, may be more important than any other factor, but no handbook can provide this!

3.3 Sensor "Accuracy"

It seems logical that sensor accuracy should be one of the primary factors

governing sensor selection. Yet the concept of accuracy is frequently

misunderstood, often misapplied, and never simple. It deserves discussion.

"Accuracy" basically means the degree with which a measured quantity

approaches the "true" value (which may be defined by a "national standard").

Since the "true" value is unknowable, accuracy is often taken as a measure of

the deviation of measured values from the calibration values as referred to (or

"traceable" to) national standards. Purists prefer the term "uncertainty,"

since it involves no direct reference to "true" values, but is an estimate of

the error bounds of the measured quantity.

Nevertheless, "accuracy" is loosely used to try to convey an idea of

quality in a quantitative manner. One major cause of confusion is the fact

that a device like a sensor cannot really be "accurate." "Accuracy" in its

proper interpretation can only apply to the act of measurement. This

immediately shows that such "accuracy" (uncertainty is really a better term to use so as to eliminate confusion) is a function of many factors. These include

the characteristics of the sensor, the signal conditioning system,

environmental factors, the type of measurement process (steady-state or dynamic), and others.

Error assessment of a measurement system is a lengthy, complicated

process, detailed in section 7 of this handbook. It is, however, the essential

and only way to establish the quality and validity of the measurements. Many

factors need to be considered and the basic laboratory performance of the sensor is only one. Laboratory performance, usually based on one or more

static calibrations, is the basis of a manufacturer's claim of specified

"accuracy" for the sensor.

A sensor with less deviation from linearity, smaller hysteresis, and

better repeatability, in theory, can produce better measurements. However, it

must be emphasized that those values are usually based on careful static

calibrations at laboratory ambient conditions. Those values alone are not

sufficient to indicate actual measurement quality in a real-world situation.

Hence sensor "accuracy" is a misleading term and subsequent tables showing

comparisons of sensing and transduction principles and systems do not

specifically indicate "accuracy."

A major factor bearing on "accuracy" is the proper selection of the range

of the sensor. Almost all uncertainty figures for sensors or systems from

manufacturers or users are referred to the "Full -Scale Range" (FSR) or

"Full -Scale Output" (FSO). This means that such figures apply only when the sensor measures measurand amplitudes at, or very close to, full-scale values.

What one is really interested in, however, is the actual uncertainty of a reading anywhere within the sensor's range. If the sensor system has, for

example, an uncertainty of +1 percent of full-scale range , but senses a measurand value of 10 percent of full scale, the uncertainty of that particular

measurement is +10 percent of the actual reading . 3-6
Thus, to achieve optimum quality of measurement, the sensor's range must

be selected to just slightly exceed the maximum expected values of the

measurand. Improper range selection or incomplete knowledge of anticipated

measurand values can seriously degrade the quality of the measurements.

Continuing "accuracy" of measurement is another factor often taken for granted.

As the sensor system is used, subjected to measurand variations and varied

environmental conditions, its performance will change. This is covered in

detail under "Stability and Durability" in section 6.4. It can be stated

briefly that sensor performance generally deteriorates with time, increasing

the uncertainty of the measurements.

The best way to be assured of continuing adequate measurement performance

is by the use of periodic, in-place, sensor-system re-calibrations.

Self-calibrating sensors would be highly desirable, but none appears to be

commercially available now. Other ways must be found to assess, at regular

intervals, the quality of the measurements. Section 6.4 has more details on field calibrations. This is another area where considerable research and

development efforts appear desirable.

The reader should develop an appreciation for the many factors which need

consideration to assure good measurements with sensors. The reader is urged to

study section 7 carefully to become familiar with the essentials of error analysis.

3.4 Sensor Cost Considerations

Finally, there are cost considerations, although, generally speaking, the

cost of the measurement is far greater than the cost of the individual sensor.

If one tries to evaluate the effect, or cost, of an incorrect measurement on the Unit-Under-Test (UUT), the sensor cost may not be significant.

However, costs need to be considered, at least initially, and in conjunction

with costs of auxiliary equipment (signal conditioners, power supplies) which a particular sensor type may require.

Sensor performance specifications include a margin for yield which often

influences the price. There are variables in materials which go undetected

until late in the manufacturing or test sequences. Tight control on processes

and close inspection of materials used cannot eliminate all variations in

performance characteristics. The cumulative effects may cancel and result in sensors with outstanding performance; at other times, performance may be below

permitted specifications. This "good," "better," "best" yield deserves to be

recognized and large volume manufacturers can price performance accordingly.

A review of the manufacturing processes and material costs for each of the

various sensor principles establishes many common costs. Although sensor designs and materials vary greatly, the labor to assemble and range an instrument involves much of the same effort.

Factory calibration against a known measurand and temperature testing

takes about the same length of time, regardless of the method of transduction.

Temperature compensation is accomplished by environmental testing, the addition

of components, and retest. Tight specifications are met by repeated adjustment

and verification of performance. Such practices cost nearly the same regardless of the type of sensing element employed. Therefore, selection of a sensor by preference of sensor type, in general, cannot be made on price

alone.

3-7
It cannot be emphasized too strongly that the initial cost of the sensor

itself may only be a small part of the cost of the entire installationcalibration-measurement-decision continuum; "life-cycle costs" must also be

taken into account. While sensor cost is a selection factor, in the author's

opinion, it should not be allowed to adversely affect quality of measurements.

3.5 Sensor Materials Compatibility

The compatibility of the sensor materials with the measurand and with the

operating environment has a great effect on the durability of the sensor. Measurands like fluid pressure and flow may cause corrosion and erosion of sensor materials in contact with the measurand. This, in turn, may lead to changes in sensor performance and the reduction of sensor life.

The sensor design engineer may have only a limited selection of materials

available if the sensor has to have certain performance characteristics.

Temperature coefficients must be carefully matched for minimum temperature

effects and for good mechanical repeatability and hysteresis. Sensing elements

must be made from metals which exhibit very stable characteristics and long

life.

The user must also determine media effects in the selection of a sensor.

An investigation into the materials exposed to the measurand and ambient

environment exposure of the external sensor case may be needed. Materials used

in the construction of sensors are usually listed in the literature or such

information is available from the manufacturer. For example, pressure sensors may be made from one or more of the materials listed below.

t Sensing elements may use various types of stainless steels, copper,

and nickel alloys. Those may be generic types with published

characteristics or proprietary ones. In the latter case, it may be more difficult to learn their limitations.

t Sensor cases may be made from a wide variety of steels, aluminum

alloys, or even plastics.

• Sensor gaskets and seals may be metallic or nonmetallic ranging from

copper, aluminum, and stainless steels through rubber compounds to a large variety of polymers.

• Transduction elements and integral amplifiers may be affected by

corrosive elements in the environment, even if those components are

not in contact with the measurand.

The ambient environment may affect other exposed portions of the sensor. Adhesives, lead-tin solder, and various potting compounds are employed to assemble electrical connectors and wires into cables. Wire insulation

compatibility must also be considered.

Corrosion of materials in contact with the media and the external

environment is a concern. The effects go beyond cosmetics. Corrosion of the

pressure-sensing diaphragm will cause calibration shifts and changes in

sensitivity. Structural strength of both the diaphragm and sensor case,

including pressure fittings, can be affected.

3-8
Unfortunately, materials suitable for good sensor performance

characteristics are not the most compatible with some media. Careful selection

of sensor materials satisfies many installation requirements.

Isolation of the sensing elements is practical in many applications and is

often done by using oil or water in the case of liquid media. Vacuum filling

of the pressure cavity and plumbing is often employed to insure that no air is

trapped which can cause an apparent reduction in frequency response of the

measurements.

Even with considerable care, such isolation practices are limited in

application, owing to the effects of gas diffusion or level change and

temperature effects for liquid isolators. Media isolation using bellows or a diaphragm between the corrosive media and a liquid-filled sensor is

successfully employed by some manufacturers. Even high-line low-differential

pressure measurements are possible.

A major problem with pressure isolation systems is their ability to

accommodate all expansion and contraction as temperature changes. The

nonlinearity and hysteresis of media isolators under such conditions also may

add error to the measurement.

Another problem posed by media isolators, including particle screen and

diaphragm coatings, is the resultant reduction of quality of dynamic

measurements. The latter must be assessed experimentally to assure that system

requirements can still be met.

Sensor manufacturers offer configurations for differential pressure

measurement which differ in their ability to accept conductive or corrosive

media. A fully isolated sensor is often described as acceptable for wet-wet

service. A differential sensor which exposes the sensing element's electrical

circuits to the media on one side of the differential pressure is often

described as acceptable only for wet-dry service. The user must protect this

second pressure port connection so that no conductive or corrosive media

reaches the sensor interior [3].

Quite similar considerations apply to temperature sensors like

thermocouples. This is particularly true of measurements in hot gases, which

may have oxidizing or reducing effects on the sensor materials. This may

result in incorrect measurements and lead to complete deterioration of the sensor itself.

Flowmeters may show corrosion and erosion if used in streams of corrosive

or particulate-laden fluids. If the flow measurement depends on the stability

of dimensions of an orifice, measurement errors may increase with time.

3.6 Future Trends in Sensors

Sensor technology developed rather slowly during the 1940 's and 1950 's until it was spurred on by space age requirements in the 1960's. At that time,

semiconductor technology began the development of silicon sensors fabricated

using integrated-circuit batch-processing, high volume methods. Taken with

advances in large-scale integration (LSI) fabrication techniques, the

3-9
development held the promise that a family of sensors for a variety of

parameters could be fabricated in silicon at extremely low cost. Some of the

devices fabricated include: temperature sensors, Hall -effect devices,

differential and absolute pressure sensors, thermal conductivity sensors,

specific gas detectors, and others. The automotive industry, with its need for

inexpensive engine control systems, is playing a leading role in this area as outlined in an excellent paper, "Sensor Development in the Microcomputer Age"

[4]. In the automotive field, cost considerations are a prime concern, with

durability and reliability of somewhat less importance. Thus other sensing

approaches have not been discarded if they are cost effective. A major

disadvantage of silicon sensors is that they operate only between -100 °C and

200 °C. Fabrication problems exist as well: aluminum wire bonding is not

always suitable for rugged environments; methods must be developed for

protecting sensors in applications where the chip must be "naked," as in

measuring gas flow; and the integration of sensors and signal processing

circuits on the same chip may lead to undesirable feedback effects [5].

Silicon is known to be a highly effective material for transducing many

physical effects, including light levels, force, and temperature. The use of

microcomputers has changed the emphasis in sensor design away from requirements

for sensor output to be a simple function of the measurand. This, in the past,

has required a linear output and minimum sensitivity to environments such as temperature. With the advent of the microcomputer, the emphasis has shifted to

predictability and stability. Nonlinearity and sensitivity to other variables

can be corrected by the processor, as long as the secondary variables can be

independently measured. Thus one can expect the development of sensing systems

incorporating single or multiple groups containing several sensors and the

associated signal processing and correcting circuitry. Sensors are being

designed from the start to work with microcomputers to achieve the best in

overall system performance. Two-way communication between the sensor and the

microcomputer will offer the possibilities of remote testing, auto calibration,

and multiparameter measurements [4,5].

Thus it is likely that the future trend in sensor development will be

toward "smart" sensors with integral signal processing. The two references

cited, [4] and [5], give a very comprehensive overview of this field.

Two points must be emphasized, however. One, the developments cited can be described as "near future"; i.e., current efforts which should lead to

viable, commercially available devices in the "near" future. They are not

available now, certainly not in quantity, to the ATE system designer. Two,

there is almost no information given in either survey on the performance of

these devices. There is no mention of tests or test methods required to

establish their performance characteristics.

Great caution must be used when incorporating new and promising

developments into military systems. There is no doubt that new systems

(including ATE) are apt to be more reliable if they retain those components of

old systems which have proved reliable in the past. Newness is no guarantee of

durability or reliability!

3-10
4. MEASURANDS AND PRINCIPLES OF MEASUREMENTS

4.1 General Considerations

Previous sections have shown the importance of good sensor performance on the proper functioning of measurement systems in general, and ATE systems in

particular. Section 3 discusses the subject of sensors, in general, and

outlines some of the factors which should influence sensor selection. Those

factors can, then, have considerable influence on sensor performance.

The sensor selection process is, of necessity, an iterative one if one expects optimum system performance, and should take into account the factors

outlined above which are detailed in this handbook.

The primary selection (and classification factor) is the measurand. This

section of the handbook presents a discussion of sensors arranged by

measurands. It should be noted that in the selection of sensors for a specific

measurand, two important factors must be considered: the effect of the

measurand on the sensor and the effect of the sensor on the measurand.

For example, in the case of a pressure measurement, it is important to

know whether the pressure is that of a liquid or gaseous medium, as well as the

exact nature of the medium. Certain media are corrosive and incompatible with

the materials of certain sensors; others may be abrasive. A pressure sensor designed for gaseous media may have totally different dynamic characteristics

when used with a liquid medium. If it is an active sensor and dissipates heat,

its long-term stability may be different with different media.

Temperature sensors will have different time constants when used with

different media. Temperature sensors may also conduct heat away from the

medium, thus producing erroneous readings. Flowmeters may reduce pressure and

flow in a system because they introduce obstructions to the flow. There are many other situations in which it is important to consider carefully the mutual

effects of measurand and sensor in the selection process. It is generally true

that the introduction of any sensor into any system will disturb the system and

produce uncertainties in the data. It is equally true that any measurand will

ultimately have a degrading effect on the sensor. It is almost always

possible, however, with knowledge and judgment, to select a sensor which can approach the optimum desired for a given system.

4.2 Specific Measurands

Sensor principles and considerations appear in the sections below arranged

by measurand. The order is based on the author's experience and indicates his

assessment of the relative importance of the measurands listed. In a number of

cases, the same transduction principle may be used for a variety of measurands;

such principles will be covered in detail only once, and then referenced.

4.2.1 Pressure

4.2.1.1 Introduction

A large fraction of all mechanical measurements is concerned with pressure,

particularly in propulsion systems, process control systems, and ordnance

4-1
systems. Pressure is the actual quantity required in many instances; however,

in other cases the desired parameter is inferred from pressure measurements.

Thus flow may be measured in terms of the differential pressure across a deliberate flow obstruction or in terms of the force exerted against a deflection plate.

As indicated before, the concept of pressure as measurand refers to a fluid medium (pressure in a solid medium as a measurand is commonly referred to as "force" or "stress"). Fluid media can be either liquid or gaseous (a

mixture of the two can usually be classified, for pressure measurements, as either of the above depending on the location of the sensing end of the

sensor). The selection of pressure sensors is Influenced by the type of

medium, primarily in regard to compatibility of materials and dynamic

characteristics of the sensor. Much of the material in the following sections

has been excerpted, with permission of the CEC Division of Bell and Howell,

from their "Pressure Transducer Handbook" [3].

4.2.1.2 Pressure References

All pressure measurements are made with reference to a specified datum

pressure and the range of the sensor (and the pressure units used) is normally

expressed to reflect this.

There are four possible cases:

ABSOLUTE PRESSURE. The reference is to a vacuum. Typically, the

interior of the sensor case is evacuated and sealed. Some absolute transducers

are referenced to a sealed bellows or capsule, the exterior of which is acted

upon by the active measurand.

GAGE PRESSURE. The reference is to ambient atmospheric pressure. The sensor uses essentially the same configuration as an absolute pressure sensor with the case vented to atmosphere rather than evacuated.

SEALED GAGE PRESSURE. Sealed reference pressure is offered in sensor designs to prevent ambient media from entering the sensor case. Usually these

instruments are of such range that atmospheric pressure change does not affect

the measurement. This configuration is usually built with a partial atmosphere

of helium or nitrogen sealed within the instrument, following practices applied

to absolute pressure sensor construction.

DIFFERENTIAL PRESSURE. Two pressure ports are incorporated in this

design to permit application of pressure to both sides of the pressure sensing

element. This permits measurement of small pressure differences even at high

line pressures with accuracies superior to those obtainable by measuring each

pressure independently.

Ranges for differential pressure measurement include bidirectional and

unidirectional pressure sensing capability. A bidirectional or plus/minus

pressure measuring sensor offers additional flexibility for monitoring pressure

changes in which prior identification of the higher of the two pressures is

unknown or changing. The bidirectional pressure sensor is offered in two basic

configurations depending on the application. Based on which of the pressure

ports is to be exposed to the liquid medium, the sensor may be classed

4-2
as wet-dry and wet-wet media acceptance. The considerations in regard to

corrosive pressure media were discussed above in section 3.5.

4.2.1.3 Units of Pressure

In technological applications, the units of pressure customarily used are different for different portions of the pressure domain. Absolute pressures

less than atmospheric may be expressed in millimeters of mercury, or torr, or inches of water, or pounds per square inch absolute^or dynes per square

centimeters. Pressures above atmospheric are commonly expressed as pounds per

square Inch (absolute, gage, or differential, as outlined in section 4.2.1.2)

or pascals, bars or atmospheres, and torr.

Despite efforts at unification and standardization, it 1s likely that this

profusion of pressure units will continue. The Eleventh General Conference on Weights and Measures (CGPM) in 1960 formally promulgated a rationalized

selection of units from the metric system known as the International System of

Units, abbreviated "SI," based on the four MKSA units (meter-kilogram-secondampere) plus the kelvin as the unit of temperature and the candela as the unit

of luminous intensity. This system includes a unit of force (the newton) which

was introduced in place of the kilogram- force to indicate by its name that it

is a unit of force and not of mass. The preferred metric SI unit of pressure

is the pascal (newton per square meter).

A brief table of conversion factors appears below, extracted from ANSI

Standards Z210.1 "Standards for Metric Practices" [6]. The current edition of

this document should always be consulted prior to any conversion calculations

requiring great accuracy.

1 pound per square inch (psi) = 6894.76 pascals (Pa)

1 kilo pascal (kPa) = 0.145048 pounds per square inch

1 millimeter of mercury (mm Hg)(0°C) = 133.322 Pa

1 bar = 100 kPa

1 inch of water (in HoO)(39.2°F) = 249.082 Pa

1 atmosphere (Standard) = 101.325 kPa

1 torr (mm Hg) (°0C) = 133.322 Pa

4.2.1.4 Pressure Ranges

Practical pressure measurements cover approximately 18 orders of

magnitude. For example, measurements of pressure may be higher than

10° pounds per square inch (about 10° millimeters of mercury) in studies of

the properties of materials and geology. Vacuum metallurgy, on the other hand,

may involve measurements as low as 10~1° millimeters of mercury. This

vast domain of pressures can be divided into two major sectors, vacuum and

pressure. For most practical applications, the sectors can be further

subdivided into convenient classes as follows:

Pressure Vacuum

A) 0 to 100 psi E) <10-° mmHg

B) 100 to 1000 psi F) 10" 3 to 10"6 mmHg

C) 1000 to 10 000 psi G) 10" 1 to 10" 3 mmHg

D) >10 000 psi

4-3
4.2.1.5 Pressure Sensing Technologies

Pressure measuring systems probably vary over a greater range of

complexity than any other type of measuring system, extending from simple

manometers to the very complex systems used in vacuum measurements. The

majority of pressure measuring instruments with electrical output, however, are devices operating on the principle that the deflection or deformation of a sensing element may be used as a measure of pressure.

Major types of elastic sensing elements are: diaphragms, Bourdon tubes,

capsules, and bellows. One or more of these are useful over most of the

pressure ranges cited, as well as for low vacuum. In order to produce an electrical output, the elastic element must act in conjunction with electrical

transduction elements, which will exhibit a change in some electrical parameter

in response to the deflection or deformation of the elastic element. Sometimes

the two functions are combined as in the piezoelectric pressure sensor.

Commonly used electrical transduction elements include metallic and

semiconductor strain gages, potentiometers, piezoelectric elements, variable

capacitance and variable inductance devices, and differential transformers. A

few transducers employ more esoteric principles: vibrating wire,

magnetostriction, ionization, photoelectricity, and electrokinetic potential.

Devices employing these principles are generally used only in highly

specialized applications and may not be suitable for ATE systems.

For the measurement of high pressure, above 10^ psi , the mechanical

element may be dispensed with and the pressure applied directly to a resistance

wire. The wire will undergo an elastic size change and a corresponding change

in resistivity and will produce a measurable resistance change in response to

the change in hydrostatic pressure. Manganin wire is frequently used for this

purpose, as is an alloy of gold and chromium. Similarly, dynamic pressures may

be sensed by the direct application of the pressure to a hydros tatical ly

sensitive material like lithium sulfate or barium titanate. Such materials

generate an electrical charge in response to a change in pressure.

Very low pressure (vacuum) may be measured by systems which infer the

pressure from the density and other characteristics of the gases present. The

temperature of a heated wire depends on the power supplied to it and the amount

of heat lost through radiation and conduction of the medium surrounding it.

The conduction heat loss is a function of the density of the gas and its

composition. At a known temperature, the density of the gas is a measure of

its pressure. The temperature of the wire may be determined by means of an attached thermocouple or inferred from its resistance, as in a "Pirani" gage.

Such thermal conductivity devices generally use a second sealed compensating

element to minimize variations caused by ambient temperature changes.

For extremely low pressures, less than 10" 3 torr, Bayard-Al pert- type

ionization gages are used. This device is similar to an electronic vacuum

tube. It uses a heated filament emitting electrons which ionize some of the

molecules of the gas whose pressure is to be measured. The ionized molecules

are attracted to the plate of the tube causing a current flow in the external

4-4
circuit which is a measure of the number of molecules present (the density),

and therefore a function of the pressure.

To aid the user of this handbook, several tables are provided in the

appendix which summarize the pertinent properties of some current commercial

sensors. It is to be noted that this sampling is not complete and is intended

only to illustrate the kinds of devices on the market and their performance

trade-offs.

The inclusion of particular devices does not constitute endorsement by the

author, nor does omission show disapproval. The user who wants to procure

pressure sensors should contact sensor manufacturers to get the latest

information on these devices.

4.2.1.6 Pressure Sensing Elements

As previously mentioned, a pressure sensor consists basically of the

pressure sensing element which converts the pressure to a force or displacement

and the transduction element which converts the force or displacement to an electrical signal. Although these are usually two separate elements, there are exceptions.

The most common pressure sensing force-summing element is the diaphragm.

This is generally a planar metallic component which, when subjected to

pressure, deflects predictably and thereby activates the transduction element.

Many variations to the basic diaphragm exist. Diaphragms may be flat or convoluted, stretched, or slack. A capsule consists of two corrugated

diaphragms. A bellows is essentially a series of capsules. Metals used in the

fabrication of diaphragms include copper and nickel alloys and a variety of

stainless steels. In modern semiconductor sensors, the diaphragm may be

silicon. Diaphragms may be welded to their supports to minimize hysteresis.

Sensors machined from solid blanks of metal also show low hysteresis, but are difficult to produce and are expensive.

Bourdon tubes are basically curved or twisted tubes whose ends rotate when

pressure is applied to the inside of the tube. Straight tubes change body

dimension when subjected to internal or external pressure. Bourdon tubes are made of the same alloys as diaphragms. They can be made with thick walls to

withstand high pressures.

These are the major types of pressure sensing elements used in sensors with electrical output signals. General advantages and disadvantages of these

elements are tabulated in table 1. It should be noted that some of those are relative and design compromises are possible.

Finally, as indicated in section 4.2.1.5, there are those elements which

combine sensing and transduction functions due to bulk properties of their

materials. They will be discussed in more detail below.

4.2.1.7 Transduction Elements

There are a variety of approaches to convert the pressure-derived force or displacement into an electrical signal. They are discussed in some detail

4-5
below. Advantages and disadvantages of these approaches are presented in

tables 2 and 3 in section 4. Again proper design, engineering, and trade-offs

can reduce or eliminate some disadvantages to emphasize the advantages of

particular types. Table 4 in section 4 shows approximate ratings in a number

of categories for commonly used transduction elements. This table can be used

as a general guide, but should not be used for absolute choices between two

adjacent items in a column.

(1) Strain Gage Sensing Elements

It is interesting to note that engineering test measurements are taken

with strain gage sensors more frequently than with any other type of pressure

sensor. There are several general reasons for this: They include the need for

high accuracy, capability for flat frequency response from steady state to

several thousand cycles, reliable operation over extended periods of time,

known performance characteristics, ready commercial availability, and

standardization of data signal conditioning and power supplies. Within the

strain gage sensor family, there are several types of transduction elements.

They are divided into two major classes: metallic and semiconductor gages,

each with a variety of configurations.

Force or diaphragm displacement causes a change in position or change in

length of the sensing element. In the unbonded strain gage sensing element, a short length of wire is stressed by pulling on one end of the wire or deflecting the position of its mounting posts. Bonded strain gages are attached to the diaphragm or bending beam by means of an adhesive. Thin film sensors are a special example of the bonded strain gage. They generally employ

a metal substrate and vacuum deposited layers of insulation and circuit

elements. The diffused semiconductor gage consists of a single silicon chip

into which an impurity, such as boron, has been diffused to produce

piezoresi stive elements.

Strain or shear is induced by the sensing element upon the wire or crystalline strain gage element. Each active element exhibits a resistance

change, which can be measured by a Wheatstone bridge circuit.

The resistance change, compared to the unstrained element resistance, is

often referred to as gage factor. It is a measure of the electrical

sensitivity of the gage to mechanical strain.

Gage factor is expressed as

rc _ AR/R

GF " ALA

is change in resistance

is unstrained element resistance

is change in element length

is unstrained element length.

Different types of gages exhibit different gage factors. Gage factor is an important element in proper design of the sensors, since it defines the

requirements for the signal conditioning of the sensor output. High amplitude

where AR

R AL

L

4-6
output signals are desirable provided other performance characteristics such as temperature sensitivity are acceptable to the measurement.

Typical gage factors of the various types of strain gages are compared

below:

Characteristics of the different types of strain gages are discussed

below. The gage factor determines output level and sensitivity of the sensor,

but variances from unit to unit can be adjusted to a nominal value with

resistors placed in series with the gages. Gage factor is not normally

specified in any sensor performance characteristics since it is "internal" to

the sensor.

By proper adjustments, manufacturers can set the sensor output to achieve

some or all of the following: changes in zero output level, in full-scale

level (sensitivity or span), temperature effects on zero, temperature effects

on full scale (sensitivity or span), and in input or output impedance

matching.

Effects of temperature change and the time required for the transducer

output to restabilize after a temperature transient are important design and

use considerations. Good design practices incorporate low thermal resistance

paths among sensor elements and compensation resistors to quickly restabilize

errors due to transient temperature changes. The effects of transient

temperature changes and tests to establish them will be discussed in a later

section.

It seems proper to discuss in more detail the different types of strain

gages now.

The unbonded wire gage consists of metallic wire, usually 0.3 mils to

0.5 mils in diameter, wrapped around nonconducti ve posts. In some designs, the

tension in one winding is increased while tension in a second winding is

decreased as positive pressure is applied. The two windings have precise

adjustments of tension to insure that optimum sensitivity and balanced

characteristics are obtained. Some designs cause only one element to move,

resulting in one-half the output sensitivity of a four-active arm Wheatstone

bridge. A rod transmits the force from the pressure sensing diaphragm to the

flexure or bending platform on which the strain wire is mounted. Both

unidirectional and bidirectional pressure measurements can be taken with

properly designed unbonded gages. This design can accommodate stops to prevent

mechanical over- travel for over-pressure protection in both the positive and

negative directions. Table 2 shows the advantages and disadvantages of the

unbonded strain gage as a transduction element.

The bonded strain gage consists of metallic wire, foil, or ribbon coated

with a thin layer of insulation and cemented to the rear of the diaphragm or

Type of Sensor Gage

Unbonded wire

Bonded foil

Thin film

Diffused semiconductor

Bonded bar semiconductor

Gage Factor (Approximate)

4

2

2 80-150

80-150

4-7
cantilever beam which is deflected by changes in the pressure sensing

diaphragm.

Strain sensing elements, similar in composition to the unbonded gage, are

laid out in special patterns to be sensitive in a single axis of deformation.

They are mounted directly to the pressure sensing diaphragm in medium and high

pressure range sensors. Low pressure range designs may incorporate a rod

to transmit the force between the pressure sensing diaphragm and a beam to

which the strain gages are bonded. In bonded gage designs, greater force is

required than for the unbonded gages to deflect the material on which the gages

are mounted. For this reason, foil gage sensors are limited to a 0-10 psi

minimum range. To obtain more sensitivity at low pressures, larger diaphragms

or bellows are required. The trade-offs between sensitivity and environmental

effects on accuracy (vibration, acceleration, temperature) set the lower

practical range limit for their pressure sensitivity.

The bonded gage exhibits a characteristic related to the bonding to the

diaphragm or beam which is not present in the thin film and diffused

semiconductor gages. The adhesive between the gage and the surface to which it

is attached may plastically deform, resulting in slight shifts or repositioning

of the gage at elevated temperatures; this characteristic can be minimized to

achieve good repeatability and stability specifications.

The rugged construction of bonded strain gage sensors permits considerable

abuse in handling and use where transient over-pressure might destroy other

types of sensors. After rough handling and use, the sensors may require

re-calibration, however, as zero and sensitivity shifts will occur. Temperature compensation and shunt calibration techniques are similar to those

employed in unbonded gages. Table 2 lists advantages and disadvantages of the

bonded strain gage sensors.

Vapor deposition (sputtering) of insulation and strain gages results in a thin film strain sensor with improved performance. The good features of

unbonded and bonded strain gage sensors are combined. However, this method of

transduction does not solve all application problems. To construct such a sensor, a metal substrate, which can be either the sensing diaphragm or bending

beam^is polished to a mirror finish. The substrate forms are placed in a high vacuum chamber for deposition either by vacuum deposition or the sputtering

process.

First, an electrical insulator such as silicon monoxide is deposited over

the substrate. Next, the metal employed for strain gage elements is deposited

on the insulator using sputtering or vacuum deposition. Multi-step operations

are required to mask and deposit gages and electrical terminals. The

fabrication of thin film devices requires careful control of cleaning,

polishing, and etching to build satisfactory gages. Although the same processes are used to make IC's, etc., performance requirements of pressure

sensors are unique and require special care.

The geometric patterns of strain gages are defined in one of two ways.

The first uses a punched mask placed between the source of evaporant and the

substrate to shadow the substrate in those regions where deposition is not

required. The second method uses a photosensitive polymer, or photomask, to

protect those areas where the pattern is desired. The unwanted deposit is then

4-8
chemically etched. Laser trimming of the strain gage pattern is employed to precisely adjust the resistance of each element. Once a gage is built and

tested, it can be installed within a sensor case following practices employed

with other kinds of bonded strain gages.

The thin film gage exhibits little creep or set. Effects of linearity,

hysteresis, repeatability, and stability are almost all limited by materials

employed in the sensor case, diaphragm, and any beams or flexures to which the

gage is attached. The best gage offers no better performance than the

materials from which it is assembled. Also temperature hysteresis and case distortion due to torque, etc., may cause errors much greater than those

developed within the gage itself.

The gage and other sensor components must be considered carefully to

properly design a sensor which exhibits good stability during temperature

changes. It is possible to closely match the temperature coefficients of the

gage elements and the pressure sensing diaphragm through proper selection of

materials. Sensor specifications for thin film gages list thermal sensitivity

shifts of 0.005 percent FS/°F, which is typical of a good unbonded strain gage.

However, less temperature compensation is required due to better coefficient

match between gage and the sensing diaphragm.

The thin film processes used in microcircui try and pressure sensors employ, as the name suggests, thin films of both conductors and insulators.

For operating conditions within the manufacturer's specifications, such

elements are quite satisfactory. However, excessive voltages can cause the

insulation to break down.

Transient voltages in adjacent circuits or radio frequency interference

may cause voltages greater than the dielectric layer between gage elements and

their mounting surfaces can withstand. The resulting punchthrough from the

elements to diaphragm or beam usually produces a permanent path of low

resistance, rendering the unit worthless. The voltage at which this occurs poses no problem in most installations. Unbonded or bonded strain gages can withstand much higher voltage than thin film types. As transistor and

integrated circuit technology improves, thin film strain gages will be

developed with higher dielectric strengths. It is good practice to review the

installation requirements for potential failure due to dielectric overstress.

Thin film gage sensors offer the promise of good long-term stability and

uniformity of characteristics. As with all other metallic strain gages, their

voltage output is relatively low.

The latter disadvantages have been overcome with the introduction of the

semiconductor strain gage.

The technologies developed for manufacture of transistors and integrated

circuits are now applied to pressure sensors. Integrated circuit manufacturing

techniques can be employed to build, calibrate, and test pressure sensors. These techniques can be used to produce high accuracy, stable pressure sensors

in high volume at very low costs.

Within the semiconductor or piezoresisti ve family of strain gages , two

types of sensors are employed: the bar gage and the diffused gage. The bar

4-9
gage sensor is nearly identical in concept to the bonded foil strain sensor.

Bars of silicon are individually bonded with epoxy to a mechanical structure,

such as a beam or diaphragm, to act as transduction elements. The diffused gage sensor uses a silicon element, but the active region of the gage is diffused

into the silicon.

In the bar gage, an impurity such as boron is introduced into the silicon

crystal as it is grown. In a bar gage, the entire piece of silicon is an active gage. The individual gages are then electrically matched, as nearly as possible, and the four legs of a bridge circuit are cemented to the pressure sensor (either a diaphragm or bending beam). Although the four-gage elements

made from silicon-based semiconductors exhibit high gage factor levels

(20 mV/V), they suffer the inherent limitations associated with other bonded

gages: zero shift and creep from variations in elasticity and differing

expansion coefficients of bonding cement and sensor materials. Although the

bar gages are somewhat easier to produce, considerable assembly labor and

element matching is required to produce a good sensor.

The diffused semiconductor strain gage employs a multi-step process of

polishing and cleaning of the sensor surface, and the application of

photoresist, the masking and diffusion of this active area, electrical terminal

deposition, and lead attachment. Automation of gage manufacturing process

provides consistent results at relatively low cost. If the pressure diaphragm

and sensor are properly designed, excellent performance characteristics are obtainable.

The diffused semiconductor gage offers excellent long-term stability. The

diffused gage is integral to the silicon crystal and therefore exhibits no creep or set relative to the silicon base material. Relatively high gage

factors may be attained resulting in large electrical signals with a given

strain. Thus the stress level within the pressure sensing element or diaphragm

can be lower than in other strain gage sensors. This results in improved

hysteresis, linearity, repeatability, and long-term stability provided good sensor case design practices are followed. However, achieving a stable bond

between the silicon base material and the case structure requires specialized

techniques. Unfortunately, commercial designs do not always achieve the levels

of stability and performance which are theoretically possible in a diffused

element system.

In theory, a zero temperature coefficient should be attained for a four-arm diffused gage. That is, with equal temperature coefficients and equal

element resistance characteristics, a diffused four-gage element should exhibit

equal changes in each bridge leg, thereby canceling resistance changes due to

temperature variations. In practice, however, minor differences in geometries,

etching, depositing, and lead attachment resistance result in some residual zero unbalance within the bridge. However, very good temperature coefficients

can be achieved with minor amounts of additional compensation.

Temperature sensitivity (change in full-scale output with change in

temperature) can be compensated by including temperature sensitive voltage or current regulation in the strain gage excitation. Typically, thermistors, zener diodes, or transistors may be employed. Recently developed compensation

networks incorporate hybrid circuits which can be trimmed to required values

with a laser beam. Temperature compensation elements are usually located near

4-10
the pressure sensing element within the sensor case. A possible thermal lag

between step-temperature changes at the pressure port and the location of

compensation must be considered.

The stability of recent amplifier designs and incorporation of complete

circuits on a single chip makes it practical to manufacture sensors providing

high level dc output. These units offer excellent performance at low costs in

volume production.

Utilization of the semiconductor pressure sensor is generally limited to

applications where temperature does not exceed 125 °C. Short exposure to

higher temperatures (150 °C) is permissible in some designs, but rapid

deterioration in performance and permanent damage can be expected. With proper

design, the semiconductor gage can be successfully used in cryogenic

temperature applications down to -270 °C (liquid helium).

Apart from temperature-imposed limitations and some sensitivity to nuclear

and electromagnetic radiation, semiconductor strain gage sensors offer the

greatest potential for inexpensive high quality sensors.

(2) Potentiometer Elements

The potentiometer is one of the earliest transduction elements used for a variety of sensors. Typically, a force-summing pressure bellows or Bourdon

tube is linked to a potentiometer wiper which travels across a multi-turn wire

coil or deposited resistor. Usually some mechanical amplification is employed

between the force-summing element and the wiper which tracks across the

resistance element to increase resolution. Balancing masses may be employed to

minimize acceleration error. Friction between the wiper and resistance element

plus pivot bearing friction and wobble result in considerable hysteresis for

measurements taken in a vibration-free environment. A taut band movement shows

less hysteresis. Vibration and pressure fluctuations cause dither of the wiper

resulting in fast wear of the resistor. For short-term measurements where

moderate accuracy is adequate, the potentiometric sensor offers several

advantages. The resistor can be shaped to provide specialized output

linearities such as linear, sine, cosine, and exponential transfer

characteristics. Since potentiometers are basically used as voltage ratio

devices, close regulation of the excitation voltage is not required. High

level output is inherent in the potentiometer concept, but output load

impedance must be kept high to limit loading effects.

Potentiometer- type pressure sensors can be produced inexpensively, but

their short life expectancy makes them an expensive selection for repeated or medium duration test measurements.

(3) Variable Reluctance and Inductance Elements

Variable reluctance or variable inductance transducers indicate pressure

changes by changes in output impedance. One approach uses a pair of coils that

changes their magnetic coupling by means of a pressure-driven armature which

displaces, or rotates, between the two coils. When the coils are excited by a carrier frequency, changes in the ratio of reluctance of the two coils can produce output levels of the order of 40 mV per volt of carrier voltage. Thus

a 25 V signal can produce output levels of one volt with no amplification.

Some designs include dc-to-ac inverters to supply the carrier output amplifiers

and demodulators for direct operation from unregulated 28 V dc supplies to

4-11
produce an output of 0-5 Vdc. Two basic designs have been developed using the

variable reluctance principle. One type uses a Bourdon-tube-driven armature

which rotates above a single "E" core with two coils or a pressure-displaced

diaphragm positioned between two "E" cores which alters the effective

inductance of each coil on the "E" core. The armature-driven system is massive

and is primarily used in secondary standard stationary applications.

The other type of variable-reluctance sensor uses a diaphragm

configuration with a high natural frequency; it is extremely rugged. Because

the diaphragm itself is part of the inductive loop, a compromise is made

between good mechanical linearity and magnetic sensitivity. Among the

trade-offs to be considered in choosing reluctance transducers are high output,

the requirement for ac excitation, ruggedness, vibration sensitivity, and

sensitivity to external magnetic fields.

(4) Linear Variable Differential Transformers

Somewhat similar to reluctive sensors in their requirement for ac excitation and demodulating circuitry are linear variable differential

transformers (often abbreviated LVDT). For these transduction elements the

force-summing device is often a diaphragm. Bellows and Bourdon tube designs

are used where applications do not require exposure to high levels of shock or

vibration. In most designs, a push rod or linkage displaces a magnetic core within a three-coil transformer to produce unbalance within two secondary

windings. AC excitation of the transformer primary can be as low as 50-60 Hz

from the power line. Aircraft applications may require operation at 400 Hz.

Moreover, an excitation frequency of 10 kHz or higher is frequently employed to

reduce the size and mass of sensor components and permit higher frequency

dynamic measurements. The sensitivity of the transduction elements is a design

trade-off between the displacement of the transformer core and the transformer

turns ratio. Due to the relative large core displacement required, this type

of sensor is not employed where acceleration or vibration is present or where

high frequency response is needed. Servo-type force-balance sensors discussed

below often employ this type of transduction element.

(5) Variable Capacitance Elements

Variable capacitance transduction elements can have a very simple

geometry, and therefore more readily predictable mechanical characteristics.

One design has a stretched flat diaphragm positioned between two fixed plates;

its deflection causes a capacitance change in two circuits. In some sensor designs only a single capacitance element is employed. The change in

capacitance can be used to vary the frequency of oscillators or null a capacitance bridge. If the dielectric of the capacitor is stable with

temperature and time or compensated for its variations, a very repeatable

sensor is achieved. The small displacements of the capacitor-diaphragm system

result in low hysteresis, good linearity, and good response to high

frequencies.

The dual element concept can be employed to drive two oscillators: one increases, the other decreases in frequency as pressure increases. The

difference signal from a mixer fed by the two oscillators is highly linear.

Capacitance-type sensors are ideally suited for pressure sensor ranges up to

100 psi and down to the medium vacuum region. Capacitance sensors require

signal processing circuitry with short leads from the high impedance output of

4-12
the sensor. This may cause mechanical configuration problems in some applications.

(6) Force Balance Elements

Force balancing (servo) sensors produce a signal in response to the

sensing element's deflection, which generates the force needed to oppose that

deflection exactly. By balancing the force caused by the applied pressure and

restoring the sensing element to its original position, hysteresis and

nonlinearity are practically eliminated.

Two types of transduction elements (capacitive or differential

transformers) are usually employed within these sensors. However, the forcesumming element diaphragm or capsule can be coupled to any of the various ty.pes

of sensors compatible with properly designed electronics to produce a restoring

force which returns the system to a null condition.

The force-restoring element typically consists of an electromagnetic coil or servo motor, which produces the necessary null displacement or balancing

torque. Leverage is often incorporated into a balance beam to amplify the

restoring force applied to the force-summing pressure sensing element.

The magnitude of power required to restore the force balance to null

condition is usually measured as the voltage across a series dropping resistor

in the servo loop. Various resistor values can be selected to change

sensitivity or adjust output levels to correspond to engineering units as read

on a dc voltmeter. A high level output of 0-10 volts (or even higher) makes

possible a high resolution system for secondary standard applications.

The massive element and balance beam construction drastically reduce the

frequency response. In fact, the bandwidth of the electronics is intentionally

limited from dc to approximately 5 Hz. Despite their potentially superior

accuracy, force balance devices are usually too large, delicate, and expensive

for other than laboratory applications.

While there are no true digital pressure sensors, two approaches to obtain

digital pressure data do exist. The most common is the use of an electronic A-D converter to change the analog output of the above described

sensors into digital form. This will be more widely used in the future in

order to meet the needs of computerized ATE systems. Section 5 on Data

Acquisition will discuss this approach in more detail.

The other approach makes use of a digital position encoder linked to the

sensing element. Such an approach commonly uses a sectored disk to generate a digital code that describes its angular position with respect to a reference

point. Such encoders are described in more detail later. However, such

digital encoders have relatively poor resolution and large mass of moving

parts. Both factors severely curtail the dynamic measurement capability of

such devices.

(7) Vibrating Wire or Cylinder Elements

There are also quasi -digital transduction systems based on the vibrating

wire or cylinder principles which are described below.

4-13
A force-summing diaphragm causes a change in tension of a fine wire or

cyl indrically configured element. The wire, or cylinder, is excited by a varying magnetic field and is in resonance. As tension changes in the wire or tube, the resonant frequency changes. The frequency deviation can be counted

with digital circuitry or handled as an analog signal with discriminator

circuits. The low-mass vibrating system has good frequency response and is

quite insensitive to steady acceleration. However, it is very sensitive to

shock and vibration which tend to modulate the vibrating element's natural

frequency. Unlike the dual element capacitive gage which employs two

oscillators, this "single element" design generates a variable frequency from a mechanical system which is very sensitive to temperature change and requires a long time to stabilize after temperature changes.

(8) Piezoelectric Elements

The piezoelectric system is based on the principle that strain applied to

asymmetrical crystalline materials generates an electrical charge. The

piezoelectric effect has been used in a variety of instruments. The most

common crystals employed include barium titanate, quartz, Rochelle salt, and

tourmaline. Special ceramics polymers and other salts have been developed for

special applications by various sensor manufacturers, but the basic principles

are observed. Piezoelectric sensors produce an electric charge in response to

changes in pressure (force) with respect to time and cannot respond to static

pressures or forces.

A pressure sensing diaphragm is coupled to a selected axis surface of the

crystal to induce strain. The high impedance output of piezoelectric devices

requires a voltage or charge amplifier to match the sensor output with signal

conditioning before transmission beyond a few feet from the sensor.

Dynamic pressure measurement with flat frequency response from below 10 Hz

to over 50 kHz can be obtained from well -designed sensors. High frequency data

and dynamic calibration of other kinds of pressure sensors are dependent upon

these sensors.

Piezoelectric sensors have two major advantages: They are self -generating, requiring no external electrical excitation, and they are capable of response to very high frequencies. They also have great drawbacks:

Piezoelectric sensors have no steady-state response and therefore can only be

calibrated dynamically. They are frequently temperature-sensitive (quartz is

relatively immune to this, but has low sensitivity). Such sensors are also

high impedance devices, requiring appropriate signal conditioning.

Other Transduction Elements . The above described elements are those which

are being used in commercially available pressure sensors. At various times

other transduction elements have been introduced, but have proved less viable

because their disadvantages outweigh their advantages, technically or economically. They include electro-kinetic, photoelectric, and nuclear

radiation elements, to name a few. Undoubtedly other new principles will be

introduced in the near future and one or more may prove superior to existing

ones. Section 4.2,1.9 discusses new developments and looks at future trends in

this area. Until new developments have thoroughly proved themselves, it is

likely that the above described major transduction principles will be the ones used.

4-14
4.2.1.8 Vacuum Sensors

Although vacuum is, theoretically, a space devoid of matter, the term is

used in the field of pressure measurements to denote, generally, pressures

below one standard atmosphere. Conventional pressure sensors of the absolute

type can be used to measure such pressures provided the absolute pressure is a substantial fraction of an atmosphere, perhaps 1 psia or greater, in order to

achieve reasonable output signals.

When it is necessary to measure much lower pressures, different types of sensors must be used. It is customary to refer to vacuum sensors when

pressures below one torr (1/760 of standard atmosphere) are involved. Vacuum

sensors do not use pressure sensing elements distinct from the transduction

elements. Instead they generally sense properties other than pressure of the

gaseous medium whose pressure (vacuum) is to be measured.

Vacuum sensors as a class are more delicate than most conventional

pressure sensors and are not often used for field measurements. Several

different types exist which are briefly described below based on information in

the "Handbook of Transducers for Electronic Sensors" [7].

(1) Thermoconducti ve Vacuum Sensors

Thermoconducti ve vacuum sensors measure pressure as a function of heat

transfer by a gas. They are of two basic forms as discussed below. Heat flow

originates at the surface of an electrically heated wire (filament) and is

transferred by a gas in an enclosed vessel to the inside wall surface of this

vessel. The quantity of heat transferred is proportional to the number of gas

molecules and, hence, to the pressure in the vessel. A decrease in pressure

causes the filament to get hotter, because fewer gas molecules transfer less

heat away from the filament and to the wall of the vessel. At low pressures

the heat conductivity of a gas decreases linearly as pressure decreases. The

actual conductivity depends on the composition of the gas.

Thermoconducti ve vacuum sensors require a well-regulated filament supply

for their excitation. The filament is typically of tungsten or platinum wire.

The filament and its end supports must be carefully designed to minimize heat

losses from radiation from its surface and from conduction through the vessel,

preferably down to cryogenic temperatures. The normal measuring range of these sensors is from 10~ 3 to 1 torr.

The first type of thermoconducti ve vacuum sensor is the resistive

thermoconducti ve vacuum sensor . This type of sensor is characterized by a filament that changes resistance due to heating. The temperature of the

filament is determined, in turn, by gas pressure. An increase in filament

temperature causes an increase in filament resistance. The sensor is usually

connected so that the hot filament forms one arm of a Wheatstone bridge. A

second sensor of the same configuration, but sealed so as not to respond to any

pressure changes, is often connected as a second arm of the bridge. This can compensate for changes in the temperature of the vessel or chamber.

This type of sensor is commonly referred to as the "Pi rani" gage. It

operates from a constant-voltage filament supply. The filament is normally

heated to a temperature of about 400 U C at the lower end of the measuring

4-15
range. A design variation (operating at lower temperature, but higher

sensitivity) uses a thermistor instead of a filament.

The second type of instrument is the thermoelectric thermoconducti ve vacuum sensor sometimes called the thermocouple gage, which uses a thermocouple

as transduction element. The thermocouple's sensing junction is welded to the

center portion of the filament and measures the filament temperature. The sensor operates from a constant-current filament supply. It is somewhat less

accurate than the resistive type. Design variations use a thermopile or multiple thermocouples connected in series instead of a single thermocouple for

increased output voltage. One design uses a center-tapped thermopile both as heat source and as transduction element.

(2) Ionizing Vacuum Sensors

The ionizing vacuum sensor measures pressure as a function of gas density

by measuring ion current. The ion current results from positive ions which are collected at a negatively charged electrode when the gas is ionized by a stream

of electrons or other particles. The ion current is proportional to gas

density (molecular density) and, hence, proportional to pressure. This is true

only when the number of electrons and their average path length are cons cant

and all ions are collected. Because these sensors measure density, however,

their calibrations are different for different gases. Nitrogen is most

frequently used as reference gas.

The thermionic ionizing vacuum sensor often referred to as the ion gage or ionization gage resembles a triode-type radio tube and differs from it

primarily by having an opening in the bulb. In a typical design the

filamentary cathode is surrounded by a helical grid around which a cylindrical

anode is placed. Positive ions are collected at the grid, which is kept at a low negative voltage with respect to the filament; the anode collects the

secondary electrons.

Tungsten or iridium filaments are used in most designs. Thoriated

tungsten is used in some designs to allow operation at low temperatures and to

prolong filament life. The pressure port for tubing connection (the

tubulation) is kept short and of relatively large (typically 0.75 in) diameter.

To further reduce tubing effects, some thermionic ionizing vacuum sensors are furnished without glass envelopes, for direct installation in vacuum vessels.

The normal measuring range of the triode-type sensor is from 10"8 to

10" 3 torr. At pressures higher than this the space charge effect and the

recombination of ions due to a reduction in the mean free path of the ions cause extreme nonl ineari ty; this tends to limit the range to that given. A

variation, the Shulz-Phelps ion gage, is designed to minimize space charge

effects and yields a usable range from 10~5 to 1 torr.

Radioactive ionizing vacuum sensors use particles other than electrons to

ionize gas. One example is an alpha-particle ionizing vacuum sensor, the

"Alphatron." The radioactive-particle source is a small thin plaque usually

containing radium, tritium, polonium, or a similar radioactive material which

is in equilibrium with its daughter products. In a typical design a radioactive source of Ra"6 with a strength of 200 microcuries is used to

provide a relatively constant alpha-particle flux. When the average path

length is fixed, the average energy is constant, and all ions which are formed

4-16
are collected. The ion-current-vs-pressure relationship is linear up to about

50 torr. One design variation contains an auxiliary, smaller, ionization

chamber for use at higher pressures. Although this sensor is most commonly

used over the range from 10"! to 10U torr, its range capability is from

1U"5 to 1000 torr. When the higher range is available on a given design,

the ambient atmospheric pressure level can be used as a convenient calibration

checkpoint. Ion current can be amplified and read out in terms of voltage,

current, or pulse frequency. Output readings can differ for different gases or

gas compositions which have different ionization cross sections for alpha

particles. It should be noted, however, that calibrations for different gases are closer to each other for this type of sensor than for any other type of

ionizing vacuum sensor.

There are other types of vacuum sensors primarily intended for even lower

pressures than the above [8], not likely to be of concern for ATE applications

and not discussed in this handbook. Of interest in validational

troubleshooting may be devices like partial pressure analyzers which are useful

in detecting leaks.

4.2.1.9 Current Problems and Future Trends

While section 3.6 addresses future trends in the field of sensors in a general way, some remarks on pressure sensors and pressure measurements

fol low.

It is highly likely that increased emphasis will be placed on sensors with

digital output signals, particularly for use in ATE equipment. Practical

problems of data transmittal in the presence of extraneous noise require true

conversion to digital form as close to the sensor as possible. Sensors are being developed with integral digital encoders in the body of the sensor. Developments of this kind may be expected to increase greatly as the use of

electronics in the sensor may impose more stringent limits on the sensor's

operating environments than would apply to the sensing element alone.

In pressure sensors, insufficient output and large size may have a considerable effect on measurement quality. The former makes the effects of

system noise more critical and requires additional signal conditioning which

increases the complexity of the system. The size of the sensing element may

have a considerable effect on the pressure which can be measured and on the

dynamic fidelity with which pressure variations can be sensed. The whole area

of the fidelity of dynamic pressure measurement is one which has not been fully

explored and needs further investigation. The durability of sensors operating

for extended periods of time and in harsh environments is another area requiring additional work. One area of considerable potential trouble is the

lack of agreement among manufacturers and users on performance characteristics,

test methods, and data interpretation regarding pressure (and other) sensors. Continuing efforts by the entire sensor community are necessary to correct this

situation.

The most important advance in the last decade in pressure sensors was undoubtedly the introduction of the semiconductor strain gage, which resulted

in signal levels greater by at least one order of magnitude than previously

known. Clever temperature compensation schemes, combined with artificial

cooling, permit operation of pressure sensors at very high temperatures. The

4-17
operation of sensors at high temperatures, however, has only partially been

solved, as has the need for improved materials compatible with some of the

exotic fluids whose pressures are to be measured.

Miniaturization of components, rapid advances in silicon sensor technology, and wideband, stable microcircuitry begin to show the way to better

and cheaper sensors for measurement of dynamic pressure. Better evaluation

techniques and equipment are needed to attain a better understanding of the

capabilities of these sensors as parts of measurement systems.

Future trends, as far as can be discerned, will be essentially extensions

of present efforts. Increased knowledge of material characteristics and

increased use of microcircuitry should lead to smaller, cheaper, and better

sensors. Based on silicon technology, new principles or designs will appear at

times, but their long-range success will depend on their being significantly

better than existing devices. The advantages of fiber-optics ( immunity to

electrical noise and small size) encourage the development of sensors based on variable light intensity as a measure of deflection of a surface (such as a diaphragm). The optics must be compensated for changes in light source intensity.

Information on trends can be gathered from annual articles in technical

journals. A very informative article on silicon sensors, in general, appeared

in the November 6, 1980 issue of Electronics [59].

4-18
r0

ne E

me c Cn 3 cu E o rd i— > 3

0) •r~ s_

O o r—

s_ j» P > X>

fd s 3 O >» "S CL tO >

to 4—

U i- rd

p to

to

C XI •r~ c c >> •t- +-> cu -o r— CU T3 CU u <d u to c

s- cu rO 3 > i E c cu x: cu cu c cu cu CL-P C cu cu cu > p E > cu s- E

i_ -rw ZeB rd «— 3 -r- 3 r" 3 cu cu

CU E CU E x: *aJ a> cr P >» +-» cr -P r- > <- J= CU <-t— O) CDP cu •<- •p 9

°f— cu cu l/) cu o .— 4-> c f© CU rd cn cn s- to •r— > to L. > >>

in o i— s- > s- cu c C <4-

C s- c: <+- x: cn

CU

q +j

to +3

fO -C -i- -c E •r- CU id cu •p c

CD P c CL S- Q.+J CL 3 to </) i— to cu o </} r— [ r— cu <-

(0 CD 3 <0 •!— P •- to fd i— c c ro c to to re to s- to +> cu = to CU c cu CU i- c •r— +J e: c c 3 C c > CU c > o <o "O c ••o 5 to tO 3 O c: cu o 3 cu P CU

•i- o o !-

C CU P !- cu i/i •1— i t—

to ra to > P ro Q-+-> to c to SL

s_ <d P S- E p rd S- X3 tO T- o s- re re cu CU C 1X3 cu cu cu fd c cu cu

ed </) CL CU CO s- cu x: cu cn s_ S- cr> sa Q. cn

</> c to s_ c S- 3 -P i- P s- s- $ -a o 'a> %. jd o E i- •r CU o o o <d fO O •'- o re o CU ro Q 00 Q 00 o -J s _i _i _j > a. _J > _1 00 I— _J

to Pc

cuE to

cu co

UJ

p

o> •r" c -a

'r— c

to to o

s- c o o cu

to 00

p c

cu cu 3 J 00 s- </> J 3

cu to c i- to 3 cu

t/i i- CU

to Q.

cu

s- rd oc fd o >

to fd

•rL. to

rd

ro. fd

•r-S_ o CU

to

i.cu>coo

cu

cn| fd +jc

rd> p

CU

sro

CU nfd

cu cu i— o

rd

tO Q.

to cu o s- CL P r— c cu 3 -r~ O <4- E

to

to i

i- rd c o

(O -C 5- a p

cu

u E CU CD CU c

•I- +J

to

a c cu

cu s- tO -r- >> ^ U r— C ID L DUO 3 -i- <f- CT S_

CU P C

iO

O

4- CU

U

r— •r- i— CU i

rd •!- J- <4- IO 3 O p -a

rd >> CU C P «/> CU 3

x: •>- 4- cn s_ i- rd •- e > a c

cu> CUu

cn c

cu to

s_ i. E

«£

cu i/>

cu c E s- ro cn x:

fd cu o

&.

p cu x: 3 E

CL

rd 'o cn

r- to c o <0 to c c

rd CU cu x: 1/) p > P o to ro

rz sU

cu Cl ro 'r— E

CU i- P o CU o

rd P cu -a fO CL cu E "a; to

t- cu re O i» cu 3 tO

i_ to

cu to cu CU -Q CL C

re o o o

cu cu

•r- t—

rd fd

to rd E rd s_ to O 3

•r—

O

C

a

fd % 4-> ro x: SI 3 u CL-O

cu &. 4->

C E o 3 ro O

cn s- c rd X)

rd ro -i- to 3 CL P r—

-p c cn rd c cu re O cnxi

cu to fd •r- ro E CU o +J

cu t- cn ro o to 'id O c to

fd r—

u <+- fd i— 3 s.

i— fd S- <d cu CL'I- Z. to C i- to J_ P cu cu Z o

•r- CU o Cl s- cu •i- x: a +-> cu- rd 3 P to cn

rd x: c to fd i- •!- S- E a; </> a» to E cu x:

fd E CU >

cu •+- 4- CU S~ i+-

C 4- c o o o u Cl O o o

r" fO o

I— >> >> P ^ P p Q. 1/) -P •P r—

cu cu to CU cua xj

•f— x: •!- CU ro

%. iL s- -o cn i. t- CL

fd rd fd <d •i- rd •r- ro —1 5» > > zn. > a o E

cn

re

scuQJ

CM

(0 ^ s

<4-oc to SI+-> <d

fd 4-

cu c x: to

•l- CL

x» rd o

1/) E T- a o -a t— u cu O CO

cuo

•o

S-o

CD

s.a> o

fZ CU

£_ "5

cn CD c c

•I— PfO ro

t- S-Cl

•r— > >

4-19
O.

a>

It

S~

(-> qj

^=

4-* i

•r- >

co CO CO

QJ o> Co <L> JC

(0 +J S- P a P 3 3 3 IB c Cl-P QJ CL

(0 4-> 03 -P -P cn > 3 S- 03 3 c O <U U O •(— 03 -a

CO c O ^ 111 O o Q —II— Q _J CQ | >- (O O- 03 cn

to Qj QJ CD 'r— Q~ ' QJ CO t3 o £- QJ O 2 ° 3 S- CD QJ C QJ & qj *» os ^

QJ *

St

QJ * O E P > (_) >> > CO

•1— »|— r" •I- ' r~ JC •r~ CO +->+-> ai co -P -p

©

w c r- a> > <uC •i- ai CO

'r~ QJ co e •- > an CO C o co CO C CO CO •!- CO C CO i_ sc a> <o a> +> qj <o p "3 QJ as

O

CD QJ 1/1 E £ 'r QJ co e 3 4- co f0 -P •.- £- O "O co i- o r" +J 3 -C 3 c s- 03 c 3 c t_ o c £= CL P o +-> qj P o +-> CO C o O

03 •i— (J CO CO 03 •i- <_> QJ o "O •1— o

$- P QJ

C s_ 4-> cv s- r- QJ +J

O 4-> qj n3 i— •!- Q.-I— 0) "O o

a> 03 i— P P 03w

•i" CL •r- QJ i_O s_ QJ E -o c o E "O — o 'r- E JD C5l

O -r- 01 <a o jc a> o s- _J _1 1— 0£ CQ 00 l— cc o_ L±_

—I > 3

CO

4-» c

QJE

QJ r—

LUc

co o

$- »r- o P tfl O c 3

QJ "O UJ OO co _J c

CQ QJ «

Su

1— \—

CO

CO 4-

QJ o

S_ CL co

CO

°r= i.03a.Eoo

QJ QJ QJ QJ a>

CO 10 co CI co c c C o o O o o

CL QJ D. QJ "O D. QJ CL OJ CL 0) co co CO co ai co CO CO CO CO CO

aj c c QJ

C c -a 0)

C c QJ c c QJC c

i- o o SO o c JO o S- o o s- o o P

CL CL c o CLC CL c CL

C E C

O -P CO

O P co o -Q

O -P CO

O

u +J co o O P CO

O co 03

•r- 3 QJ •i- 3 QJ -r- r- 3 QJ -r- QJ f- 3 QJ -r- 3 E ^ s_ E r- S- P c E S- P E t- p E •— l- P Cr

(TJ

O njO 03 03 03

O 03 r- 03 OS 03

O 03

C CO >-

C CO >,P J=

C CO >>P jQ

C CO P C CO >>p CO QJ

C

>> QJ

u

O -i- P >, QJ

a •- 03 >> 0) o •<- '1— > a s_ c c o T3 S_ c u P C u TD l_ C O co

QJ a>

x -o QJX CO +J QJ

X P QJ

X QJ 8QJ

co "O CO 3 "O CO 3 QJ QJ T3 CO 3 Q) 3 a CO 3 QJ 3 "O CO 3 QJ i. >

QJ

C 3 CTC 3 cr co

C 3 cr -o CL 3 cr a.C 3 cr QJ 03 •rC7> n3 O a> ro O QJ O CO >o o QJ U o -P 03 o QJ U p 03 O QJ O P E co

fO 3 i_ 3 S- -O 3 3 S_ "O o 3 3 S- -o 3 3 S- -o CO c

+J

O

C 4-

O c '4- i_u c <*- •O CO

O (J

C

O

U

C 4- >> QJ QJ c •iTM "r— f— *r- s_ J- QJ i- S- JC a CL p -p -C P P JC O QJ p -p JC o co >, JC P P JC o _c P P JC o X > (O c 03 C co i- 03 C CO co i_ cn 03 c cn CO 03 C CO c QJ P o i— P O •r- U O P O r- o 3 QJ P o °ff— CJ P O r- <_) O 03 C

00 o 00

O I 00

O 03 cn > CO o 03 :c 00

O re 03 _J

O i

j

QJ JO

03

03>

03

CO

QJ>3 QJ O COc P o 3 CL CL CO P QJ 3 SC O O U

03 -P

•i— O P X 3 QJ CL P O 3 "O O

s_ JC o

CO

•I- <_J a: 03

O E

03

COC

a> >, ClXJ

03 QJ J= -o >

CO

C •!- 03 CO i— C

03 <_> oj

•r- CL O +-> X

QJ 03 QJ CLP C

O0 00

—i

SCO o CO

QJ -o +-> QJ CO o QJ u CO

03 QJ E %, 3 03

u cn

O QJ o QJ

d

C •r— P c CO QJ r— c o O ct- P o c 03 co ( •r- QJ 3 u f— CO 3

>T3 03 CJ

C CL •1— 03 4- P !- 3 'r— co E t- s_ '+- QJ P Q JC QJ P 03 •i— 2 OO CQ 1— wl 00 CQ a

s- p

QJEo

QJ PO

Q_ 4-20
CD cd cd CD "O > >

•r- > > o P P p

<D 'ai •r- •ii_ P •r— 00 o 00 oo oo CD

•r— <+- e e +J e c oo £ >> cd 03 CD CD 03 ai CD 00 CD o (J 00 00 00 4) oo oo 00 o

'|— e 3 > oo E 00 > c

CD +-> "O o "O "O Q-r— Q

• CD •J— Q_ 3 0) U o >, Cl U o 03 P 03 (_) D. S_ o CD p > CD oo cr e O E i

00 o E Cl» 3 E o oo c <D o 00 •f— 3

c c O) o.e CD -o e <U JE n> o

oo O O .e CD o +J _c o c 00 P o -Q o o s_ 03 00 o S- oo e •r— oo s_ 00 oo o •r— CD no Q-'-t- E CD P ai p p >, +3 CL CD O0 > CD c 00 "O cd e >>T3 O) OO S- to -o >) OO o •r oo 00 oo c r- O

o CD c c t- o u e s- o e -o o e -o u c -o o CD oj P C

•r- t- o 03 •1" E 03 •r— <u <o -o •r— 03 e -a CD -a •r— S- ai O0 •i- (O

+-> •r— 3 +-> <D 3 s. oo a <o e cd O) <n c t_ C s- 00 "O

03 >>P cd e CT" 03 3 C CT" 3 a> o N E 3 o 3 i- o _o 3 c C CD CD p U 03 > o CD p cr o 0) P 00 CL 00 s_ i

o CT 00 i. +J fO o O0 i- > P o CD CL >

r— c P •1— •f— 5- 0> -r- S- <o o> E a> P 00 a> CD •p <0 CD p •r- p (13 •1

00 E o <D p +-> o s- p s- s_ •i- t. u> p 1- i. u s_ c P s_ OO (O S- p 'i— P

X (J 03 &

<+- 03 <u r- oj <u 03 <+- •r- CD CD 13 CD C p •r- o> CT" X S_ CD s_ CL 3 -C 3 CD S- 3 CL (— %. 5 r

CD oo 00 0) CD c -Q E E CT" en cr cd s- -Q cr cd c JD cr a' CL E -O O CT) o J- Oi cj O i- CD •r- CD o CD o a> X o CD A3 -E •!- CD

10 ll. CO > 03 _J 5» h- _J >» _1 CC >= cc: LU 1— co a: OO

a;

00

00o

CL

CD <a CD

oo p to c i

c

o CT) o

CL CL

00 o to c CD C CD c

o S- o s_ o •1" 'T— p u p o > p 3 •r— c 3 '1

3

E o E p

'o f0 •1

'o (O *rTM 'o

00 c oo 00 c to oo oo

CD s- CD C CD •r" i- ai S- CD S_ OO p > p 10 p at s_ 3 00 o c 3 oO o 3 oo s- 13 CL 3 o CL 3 c -C CL 3 CD CD P O fO o P O (0 CT) P O P C

3 3 3 3 •i- 3 3 00 r" O o p O C o x: o •(— <J r" "1

-E P p CD P P P CT CD fO s_ CT) c 03 C CT) c S O

•i— o p 1— •r- O P CD -r- o o o

3: o O0 Q o CO > 3: o _l CJ3

ITS P

CT) •r- CT

>) ^

s.3

U

<_> p A3 1— 3

cl x: P .a P CT) C 3 03 3-i- CD OP O Tr- I- Ifl E >)-£.

CT) t. O 5- CT)

•r- CD X CD Tr- tO

S- CD 03 tCD CD >, C P P

r- 00 -l- >)•—

•r— C i— O -I- I-P 03 3 P

r— 03 O CD 00 Q.

CD CD

C CD O r—

•i- XI

10 -r- S- 00

CD to > O

C CL o

U P

3 P CL U P CD 3

S- O

a: 3: a

CDooco

CL

00 P CD 3 S- CL p >) 3 O

O C

CD

CT) 3

C CT

- •i- CD P i03 <••- S_

CD -E E CT) CD -r- CTl-E

I <*- >) i— S- CD CD co >

03

CD E

CT) 00 E

03 >>

i~ S-CD O >

E CD

03 "CT E 03 ^

E

CD -S

CT) E

03 03 —I O

CD !o <U

03 O

•r— 03 S- E

s_ •r- CD CD 03

CD 03 P E >

> > E s_ i— 03 o

CD o P n

-P S_ t. '->- I

O 03 CD oo CJ a» OJ 3 CD *4- c 03 u oo E 4- 03 Cl s-

'ai • r— S- 03 o

1 CT P O LU 4-21

CT) CT) E

S- P

o

CD

ajo

N

CD
TABLE 4

Quality Ratings of Transduction Elements

In Order of Decreasing Quality (Approximate)

lutput Static Frequency Vibration Small Low Cost High Temperature

evel accuracy Stability response immunity size quantity operation, °F

FRr d PE PE PE SD r 850

ru FRr D vr SD SD SD SB u 600

VP TFi r TFi r vc M u VR 600

V w TFi r TFi r SR PO TF 525

U 1 OU •sR iiu RFDr TFi r DT PE 400

V/D VK u RFDr <\R 1

1

VR TF PO

PE SB u BF SB BF VR DT 300

SD BF VR VR VR PO PE BF 300

SB VR DT VW VW VC SB SD 250

U DT PE DT DT DT VC SB 250

TF PE PO PO PO VW VW VW 200

BF PO FB FB FB FB FB FB 165

BF Bonded foil strain gage

DT Differential transformer

FB Force balance

PE Piezoelectric

PO Potentiometer

SB Semiconductor bar strain gage

SD Semiconductor diffusor strain gage

TF Thin film strain gage

U Unbonded strain gage

VC Variable capacitance

VR Variable reluctance

VW Vibration wire/tube

4-22
4.2.2 Motion

4.2.2.1 Introduction

Measurements need to be made either of the motion of objects in inertial

space or of the motion of certain parts of objects with respect to other parts.

The type of measurement, the amplitude and frequency response requirements, as well as certain environmental considerations usually dictate the particular

aspect of motion sensed and the type of sensor used. Motion can also be

considered equivalent to position as a function of time.

Much of the following discussion is taken, with permission, from material

in the ISA Transducer Symposium [8].

Motion sensors discussed in this section convert linear and angular

displacement, and their time derivatives: velocity, acceleration, and jerk, to

electrical signals. Each of the motion parameters may be directly sensed and

converted in one or more steps to the desired electrical signal, or the desired

signal may be derived by differentiation or integration from a signal

transduced from one of the related motion parameters.

Motion may be measured relative to a reference point on a material object

or with respect to inertial space. In the latter case the measurement is

sometimes referred to as "absolute." Absolute displacement and absolute

velocity cannot be measured directly, independent of reference objects, but

only by integration of acceleration. The integration is often accomplished

electrically or mechanically without explicit recognition or disclosure of the

process.

"Absolute" measurement of acceleration is based on Newton's second law for

constant mass:

F = m dt

= m

To measure acceleration by application of the second law, one measures the

force required to impress upon a "known" mass (the mass may be inferred by

calibration) motion identical to the motion to be measured. The most commonly

used method is elastic deformation as embodied in a spring-mass system. To measure acceleration by this method, the motion to be measured is transmitted

to the known mass through a spring of known stiffness. The displacement

representing compression of the spring is, by Hooke's law, a measure of the

force exerted by the spring on the mass. Figure 3 shows a schematic of such a system.

The measurement of motion is basically one of displacement and tables 5 and 6 summarize the advantages and disadvantages of various transduction

elements which may be used for this. These tables are quite similar to

tables 2, 3, and 4 for pressure sensors. Unlike the latter, motion sensing

does not involve a variety of force-summing elements, except in the case of

piezoelectric sensors. In this case the piezoelectric crystal serves both as

the sensing (force-summing element) and the transduction element.

4-23

The measurement of acceleration and its time integrals is more complex

than the measurement of displacement. For example, two conflicting

requirements are apparent when changing accelerations are to be measured: On

the one hand the spring must be stiff in order to faithfully transmit the

measurand motion to the mass. On the other hand, the deformation of the spring

must be sufficient to be susceptible to accurate, noise-free transduction to an electrical signal. In practice, the capability for transducing rapidly

changing accelerations is limited by the stiffness of available "spring"

materials and by the need to sense very small relative displacements.

Application of other force fields is strictly analogous to the spring-mass

system.

If the measurand is motion relative to a reference point, displacement and

velocity can be transduced directly to an electrical magnitude. For example,

the proportionality of induced voltage to velocity and the frequency modulation

provided by the Doppler effect are often used. A wide variety of relationships

between electrical phenomena and displacement are utilized, to determine

displacement including piezoelectricity and piezoresistivi ty, dependence of

electromagnetic induction upon proximity, change of resistance with length of

conducting path, change of capacitance with electrode separation, and change of

illumination with distance. Transduction of relative displacement to an electrical signal is commonly the final step of the transduction chain leading

from other measurands to an electrical signal. (See tables 5 and 6.)

Periodic motion is measured by the same means as other displacements,

within the limits of dynamic response capabilities of the sensors.

In the foregoing discussion, the measurement of motion has been discussed

in terms of change of position with time. The general relationship between

position and time can be expressed as the sum of sinusoidal components

described by specifying their frequency, amplitude, and phase. These data in

the frequency domain contain all of the information required to describe the

motion in the time domain. For some purposes such as observation of vibration,

not all of the frequency domain parameters are of interest. It may sometimes

be desired to know only the frequency of the vibration; more often, frequency

and amplitude are required with phase omitted. Vibration sensors that make

these more limited measurements are included within the scope of this section

although, in a strict sense, they do not transduce motion as such. Also

included are sensors for either time domain or frequency domain that indicate

only peak values of the measurand occurring during the interval of interest.

In general, the reaction of the sensor upon the measurand object must be

considered in applying sensors. In the measurement of acceleration with

spring-mass system sensors, for example, the force required to move the

accelerometer comes from the measurand structure and, hence, the sensor mass

reacts upon the structure. Since the measurand structure is neither perfectly

rigid nor infinitely massive, the measurand motion may be modified appreciably

by reaction of the sensor. Sensors that must measure rapidly changing

accelerations must therefore be of small mass and their attachment to the

measurand surface must be rigid.

4-25
4.2.2.2 Materials and Environmental Factors

Considerations discussed in sections 3.5 and 6.3 apply to motion sensors insofar as environmental factors are concerned. There is generally no effect

of the measurand itself, in this regard. The exception might be an accelerometer designed to measure extremely small accelerations, whose sensing

element might acquire a permanent deformation when subjected to very large

acceleration. An example might be a navigational acceleration sensor subjected

to high-g launch accelerations.

4.2.2.3 Displacement

It should be recognized that sensors for a variety of measurands convert

that measurand, such as pressure, into a displacement. In those cases,

displacement is an intermediate step. In this chapter, motion (or

displacement) is the primary quantity to be sensed. There is then a certain

amount of overlap (and duplication) in the discussions on transduction

considerations for displacement in several chapters of this handbook. The

author believes, however, that the approach chosen is more useful for the

reader. Tables 2, 3, and 4 summarize transduction principles and should be

consulted. Additional ones are covered in table 5.

Changes of resistance, inductance, and capacitance are prominent among the

large number of physical effects used to sense displacement in commercially

available displacement sensors.

For motions that take place very slowly or in steps with long stationary

periods potentiometric devices have the advantages of large electrical output,

availability at any desired displacement range, generally low cost, and simple

associated instrumentation.

For the measurement of strain displacement, there are commercial strain

gages made of fine wire or foil, with refinements such as noninductive

windings, compensation for use with particular materials under conditions of

changing temperature, and special mounting materials and techniques to allow

the measurement of strain in the plastic range up to a strain of several

percent. Dimensions of strain gages range from 1/16 to 6 in. (1.6 mm to 0.15

m) long, and 1/16 to 1/2 in. (1.6 to 12.7 mm) wide. These gages are generally

mounted in pairs such that tension acts on one gage and compression on the

other. The two gages are connected in adjacent arms of a resistance bridge for

better temperature compensation and somewhat increased output.

An increase in sensitivity by almost two orders of magnitude

may be attained by piezoresistive (semiconductor) strain gages which have

become commercially available in the past few years. At the present time,

these are made of silicon with various amounts of impurity doping to improve

the temperature characteristics. Strains up to three parts per thousand (and,

for selected devices, somewhat more) can be sensed. For larger strains,

adaptors are available which reduce the strain at the element.

"Absolute" displacement measurements can be made with spring-mass systems

for motions whose frequency components are sufficiently far above the resonant

frequency of the spring-mass system. In effect, the spring-mass system under

4-26
these circumstances performs a double integration of acceleration. In making

such measurements, as in seismometers, an extremely low resonant frequency is

required and the mechanical spring may be further weakened by electrical

feedback. Since these systems have extremely small restitution forces, a non-contacting electrical sensing system must be used to obtain the best

low-frequency characteristics.

The advantage of little or no friction is characteristic of sensors based

either on optical principles or on change in self -inductance, mutual

inductance, electrical coupling, or capacitance.

Other transduction elements include linear variable differential

transformers having ranges from a few hundredths of an inch to several feet

(from tenths of a mm to several meters). Excitation may be directly from the

60 Hz, 120 V line or, for better frequency response, from carriers having

frequencies from a few hundred to several thousand hertz. The linearity

generally depends upon the excitation frequency, and both are usually specified

by the manufacturer.

Capacitive devices are available that offer high displacement sensitivity,

but these often require somewhat more complicated associated instrumentation.

Thus cylindrical capacitors with a small cylindrical air gap may be used over considerable ranges with good linearity, while parallel -pi ate capacitors with a spacing of 0.001 in. (0.025 mm) or less have been used to measure full-scale

displacements of the order of lCr? in. (approx. 2.5 x 10~ 9 m) or

less.

Piezoelectric devices can be used to measure displacement in situations

where high reactive forces can be tolerated. A piezoelectric crystal or ceramic generates a charge that is very nearly proportional to a rapidly

occurring compressional bending or shear strain. If it is not required that

very-low-frequency components of motion be reproduced accurately, then this

charge may be measured with the help of a charge amplifier or a high input

impedance amplifier such as a cathode follower or emitter follower.

Piezoelectric devices have comparatively large outputs and very high resonant

frequencies. Their major disadvantage is the fact that they have no response

at zero frequency and cannot be calibrated statically .

Another class of sensors which measure motion in terms of position and

provide a digital output are usually referred to as "encoders." They can be

applied to either linear or angular motion (position). These devices use graphic digital codes patterned on discs, plates, drums, or wheels. The

position of the moving plate or disc is detected either mechanically (brushes

on conductive elements of the coded surface), optically (photo cells sensing

light transmitted through, or reflected from, the coded surface) or through

inductive or capacitive coupling. The major advantage of "encoders" is the

direct digital output; major disadvantages are size, vulnerability to vibration

and shock, and limited high frequency response. The latter is due to the

comparatively large mass of the moving components and the limits of optical

resolution of the coded disc which may necessitate significant disc or plate

motion.

Optical displacement sensors are available which measure displacement in

terms of light intensity reflected from a moving surface. Such sensors are 4-27
linear over only small displacement ranges and require close control of light

source intensity [60].

Quite recently, a class of semiconductor photoelectric position

(displacement) sensors have become available. They sense the location or movement of a spot of light on the sensitive surface. With displacement ranges

up to several centimeters and frequency responses of kilohertz, they offer

interesting design possibilities, although their environmental performance may

be limited.

A resistive displacement transducer based on the conductivity of an electrolyte has been used commercially for phonograph pickups, as well as in

horizontal -sensing angular-displacement transducers. The motion changes the

cross-sectional area available to the flow of current through the electrolyte,

generally increasing the area in one path and decreasing it in the other. Two

other devices having large outputs and, in addition, the ability to follow

extremely low frequencies are the electronic displacement gage and the

capacitive "ionization transducer." In the electronic displacement gage, an element of a vacuum tube is moved relative to the other elements by means of a linkage extending through the shell. In the capacitive ionization transducer,

the position of the plasma surrounding two electrodes in a gas tube is affected

by the displacement of metallic rings or plates external to the tube. The

environmental vulnerability of the last three devices may outweigh their

potential usefulness except in special applications.

In certain applications where a direct measurement is not advantageous, an output that is proportional to displacement may be obtained by performing an electrical integration of the velocity output. This integration is readily

performed by means of a simple resistor-capacitor circuit, providing the

available velocity signal is sufficiently large. This approach has inherent

frequency limitations which must be carefully considered in its use. A thorough survey of displacement sensing principles, their advantages and

disadvantages, applications, and other considerations can be found in

reference [61].

In general, a simple, well-proven principle of sensing is almost always to

be preferred to a more exotic one which may exhibit unanticipated

deficiencies.

4.2.2.4 Linear Velocity

Measurement of velocity is most readily made by means of a sensor that

follows the motion and whose output system has a response proportional to the

first time-derivative of the displacement, i.e., to the velocity. The most

commonly used electrical devices use the relative motion of a coil with respect

to a magnetic field so that the magnetic flux linking the coil changes as a result of the motion. This may be accomplished either by having a small coil move in a very concentrated magnetic field or by moving a magnet past a stationary coil. In either case, nonlinearity effects will occur unless the

displacement range is limited such as by mechanical stops.

A mass isolated from accelerating forces can be used as a reference

against which to measure changes in velocity, since the velocity of such a mass

will remain constant. Such an isolated mass may be approximated by a 4-28
spring-mass system whose undamped natural frequency is well below the

frequencies associated with the rate of velocity change of interest. The

velocity of the base of the sensor relative to the "stationary" mass may be

transduced to a proportional electrical signal by electromagnetic induction as indicated above. Devices of this type are commonly used for vibration and

shock measurement. The low-frequency limit of such a sensor is set by the

natural frequency of the spring-mass system. As frequency increases, the

reaction forces of electromagnetic induction (including eddy currents)

increase, thus imposing an upper frequency limit on the sensor. In applications involving large displacements, such as in the shipboard

measurements of shock caused by waves or enemy action, the design of

instruments within these limits leads to devices that are quite bulky and

heavy.

It is possible to overcome some of these difficulties by means of a different type of velocity -measuring system involving electrical integration of

the output of a piezoelectric accelerometer. The range limitation becomes

trivial (cable length effects can be eliminated by using charge amplifiers)

with such a system and the low-frequency response is readily extended to

frequencies of the order of one hertz or less with an amplifier of proper

design. To achieve integration with a reasonable signal-to-noise ratio, a relatively large mass is required to load the piezoelectric element and to

produce a sufficiently large signal. Such a device is likely to be bulky.

Quite different approaches are used in the determination of rotary speed.

The discussion which follows describes some of the methods used for this type

of measurement.

4.2.2.5 Angular Velocity (Tachometer)

Rotary speed sensors may be classified into analog and digital types [9].

In analog types, the amplitude of the intelligence signal is a function of

rotary speed (usually linearly proportional over the useful speed range). In

digital types, the frequency or the time interval between peaks of the signal are proportional to the rotary speed. Many conventional tachometer systems are highly developed analog types.

For many industrial applications, conventional analog tachometer systems

are adequate and have many desirable features, including long development and

service histories, and a minimum of auxiliary circuitry. Needs arose for

improved techniques for measurement of shaft speed, particularly for operation

in severe temperature and nuclear radiation environments, operation over wider

speed ranges, and with greater accuracy requirements. Digital tachometer

sensors which are much less sensitive to environmental variations are meeting

these needs.

Rotary speed analog sensors include the ac induction tachometer, which is

essentially a variable coupling transformer in which the coupling coefficient

is proportional to rotary speed. One winding of the transformer is excited by

an ac voltage at either the line- or a carrier-frequency. An ac voltage at

excitation frequency, and proportional in amplitude to the rotary speed, is

obtained at the output phase winding. Rotation of the shaft of a rugged

squirrel -cage or drag-cup rotor produces the shift in flux distribution which

4-29
is the principle of operation of this device. This tachometer type requires a source of excitation voltage that is stable in amplitude and frequency.

DC tachometer generators are similar to the ac types but these devices can

be excited by a small permanent magnet, or separately excited from a dc source. One of the chief advantages of the dc tachometer is its high sensitivity (10 to

20 V per 1000 rpm) in a very small size. One of the main disadvantages is that

a commutator and brushes are required. The brushes vibrate and arc creating

electromagnetic interference, and associated maintenance problems of deposits

from the brushes on the commutator, and brush and commutator wear.

For applications where the direction of shaft rotation must be determined,

the dc tachometer generator is useful since its output polarity is dependent

upon rotational direction. The output voltage of the permanent-magnet type may

be calibrated to provide an accuracy of 0.25 percent to 0.1 percent of the

full-scale range.

Another analog device for measuring rotary velocity is the

permanent-magnet alternator. This rotary speed sensor is similar to a constant-field synchronous generator and produces a linear output voltage

proportional in amplitude and frequency to shaft speed. Performance tends to

be poor at low speeds. With an auxiliary rectifier circuit on the output, a dc

voltage proportional to speed over a wide range can be obtained without the

disadvantages of brushes or sliding contacts. However, these devices are not

suitable for measuring very low angular velocities.

The frequency characteristic of the alternator output provides a more accurate measurement of rotational speed. It is essentially unaffected by

loading, temperature variations resulting from ambient conditions and

self-heating, and armature misalignment caused by shock and vibration. Through

the use of signal conditioning circuits, the frequency may be converted to a proportional dc voltage.

With the greater use of digital converters and signal processing, the

desirability of using sensors with digital outputs has increased. This is true

in the area of rotary speed measurements.

The units of measurement of shaft speed are events per unit time, most

often expressed as revolutions per minute (rpm). Digital measurement of shaft

speed is facilitated by using electronic counting circuits and precise

time-interval measurement. If a reference mark in a readily measurable

form is placed on a rotating shaft, the number of passages of the reference

mark past a sensing element per unit time will provide a measure of shaft

speed. If a number of reference marks are placed uniformly around the

periphery of the shaft, fractions of a revolution can be detected and counted.

An ideal digital tachometer system would consist of a sensor that produces

one pulse each time a shaft discontinuity passed the fixed sensor element, with

signal amplitude constant and independent of shaft speed and circuit variables.

If signals are nearly constant in amplitude, the pulse recognition circuits can

be much simpler in design than if the signals vary widely in amplitude.

Appropriate optional circuits are available to count and display, to encode, or

to convert the signal repetition rate to an analog voltage amplitude.

4-30
The signal amplitude may vary due to factors such as environmental

changes. The system will remain operative and accurate as long as the signal

amplitude does not drop below the level of system noise or below the threshold

of the recognition circuits, and as long as the signal amplitude does not

increase to the point where amplifiers are overloaded. A digital tachometer

system inherently has a wider range of operating conditions than has an analog

tachometer system. In addition, feedback techniques may sometimes be employed

to extend the operating range by adjusting sensor excitation or signal

preamplifier gain to maintain a constant signal level.

Important criteria for digital shaft speed sensors are the signal-to-noise

ratio and amplitude difference between the two states of the signal (pulse and

no-pulse, or maximum and minimum values of alternating signals). As long as the auxiliary circuits can distinguish between the two states, shaft

revolutions or sub-intervals of a revolution can be counted per unit time.

Therefore, the accuracy, resolution, and dynamic range of the tachometer system

will depend to a greater extent on the characteristics of the auxiliary

circuits rather than those of the sensor. Although the sensor may be subjected

to environmental extremes, the auxiliary circuit can be located in a more moderate and controlled environment. Degradation of signals due to losses in

the transmission of the pulses between sensor and circuits will not affect

performance as long as the degradation is not so extreme as to mask the signals

entirely.

There are a number of ways of producing digital electrical signals

proportional to speed. Two techniques can be used to produce capacitance

variation as a function of shaft position: The relative position of a pair of

capacitor plates can be varied or, alternately, the dielectric constant between

the stationary plates can be varied.

A commonly used configuration has a capacitor formed by a metallic stator

plate and a rotor attached to the shaft the speed of which is to be sensed.

The capacitance rotor consists of a modification of a portion of the shaft.

Since shafts may have smaller diameters, lower electrical conductivity, or higher interfering magnetic permeability than desired for the sensor, a geometry modification can be obtained by attaching a disc of appropriate shape

and material to the shaft.

A variable dielectric-constant sensor operates on the principle of a rotor

of variable dielectric constant moving between the fixed plates. In this case,

the effective dielectric constant is a function of rotor position, and

the capacitance varies cyclically for every revolution or fraction of a revolution. These types of sensors are more affected by changes in environment

than are those based on moving capacitor plates.

Another system uses variations in magnetic permeability for the sensing of

rotary speed. This is generally referred to as a variable reluctance sensor. A gear-type chopper (driven by the shaft) may act in the air gap of a variable

reluctance sensor to change the inductance of a passive circuit element or the

induced voltage for an active circuit. A form of magnetic sensor consists of a cylindrical permanent magnet and, extending from it, a pole piece surrounded by

a pickup coil of copper magnet wire. The sensor generates a voltage whenever

the permanent magnet field around it is disturbed. When a piece of magnetic

material is brought near the head of the sensor, the lines of magnetic force

4-31
shift and, in doing so, cut across the pickup coil and generate a voltage in

it.

The output voltage depends upon the rate of change of the magnetic field.

This, in turn, is dependent on three factors: (1) the amount of clearance

between the sensor and actuating element, (2) the rate of movement of the

latter, and (3), the size of the element. Output voltage tends to be inversely

proportional to the clearance between the head of the sensor and the actuating

element. For a given clearance and rate of interruption, sensor output is

linear with the surface speed of the magnetic actuator.

The sensor can be actuated by the teeth of a gear, the blades of a turbine, spokes of a wheel, or a steel part, such as a screw, mounted on a moving nonmagnetic material. The most common application is the measurement of

rotary speed from the teeth of a gear. Small-tooth gears (20-pitch or higher)

produce an output that is approximately a sine wave. Coarser teeth produce a more distorted output, but the peak-to-peak voltage values are higher. The

outputs for single activating masses produce waveforms similar to the

coarse-tooth gear. Peak-to-peak voltages are roughly proportional to the width

of the single tooth.

It is preferable to actuate a magnetic sensor with a protrusion from a metallic surface rather than with a keyway or slot in the surface. In the

latter case, the sensor is closer to the entire mass of the exciting

material, and consequently more vulnerable to unwanted background signal due to

varying density or eccentricity of the material. On the other hand, when

excitation is from a protrusion, the sensor is at a relatively greater distance

from the exciting material and less likely to pick up stray signals between

excitation periods. With any given speed and clearance conditions, maximum

power and output results when the field of the sensor is filled with what

amounts to an infinite mass of magnetic material at one instant and a complete

absence of such material at the next.

It is possible to excite magnetic sensors through thin sections of a nonmagnetic substance. Such a barrier may be needed when the exciting means is

in hot or corrosive environments or when it is necessary to provide a seal

against pressure. With nonmagnetic separators, the output of the sensor is

affected only by the increased clearance due to the separator thickness.

Metallic separators between the sensor and the actuating device reduce the

output appreciably. This is due to a shortened-turn effect, since eddy

currents are induced in the metallic separator. Loss of output increases with

output frequency and becomes prohibitive at about 5 kHz.

Another type of sensor operates on the eddy current principle. The

parameters of interest in eddy -current sensors are the inductance and

resistance of air-core coil sensors. A highly conductive element attached to, or part of, a rotating shift causes parameter variations with shaft rotation.

The electromagnetic field created by the sensor coil induces eddy currents in

the conductive element as it passes near the coil. The eddy currents, in turn,

create a magnetic field which opposes the original field. The superposition of

the two fields reduces the effective inductance of the coil. For an element

with finite conductivity, there is a power loss due to the eddy currents. As a result of this power loss, the effective resistance of the coil is increased.

4-32
In common with other magnetic sensors, the Hall effect permits the

transduction of mechanical quantities to an electrical output without physical

contact. When a magnetic field is applied perpendicularly to the current in a conductor, the moving charges which constitute the current are deflected by

the Lorentz force in a direction perpendicular to both the current and the

applied magnetic field. This deflection results in a potential gradient within

the conductor, and a voltage appears between the two edges of the semiconductor

parallel to the current direction. This voltage is proportional to the

vector cross-product of the magnetic flux density and the current. It is

independent of the rate of change of flux, at least for changes occurring in

time intervals greater than 10 ns. A semiconductor device employing the Hall

effect can be used to sense the change of position of mechanical assemblies

independent of their velocity.

Where it is undesirable to connect a tachometer mechanically to a device

because of the small energy (torque) available, or when the measurand speed is

very high, an optical tachometer pickup may be used. Such devices are capable

of measuring speeds from a few rpm to 300 000 rpm (5000 rps) or even higher. A

typical device includes a light source which illuminates the rotating part

provided with alternate reflecting and absorbing surfaces and a phototube which

converts the reflected light into electrical pulses. Alternate opaque and

translucent surfaces can also be used.

While incandescent lamps and phototubes can be used as sources of light

and light detectors, recent developments in solid state light sources (LED,

lasers) and solid state light sensors make these preferred components. Solid

state components can be physically small, rugged, use little energy, and are relatively inexpensive. They may, however, be more vulnerable to environmental

conditions such as high temperature, humidity and nuclear radiation.

The most current manufacturers literature should be consulted prior to the

selection of the components for any optical tachometer system to determine

their environmental degradation.

4.2.2.6 Acceleration

The measurement of acceleration is of great importance in many

technologies. In general, acceleration is measured by means of a spring-mass

system, with the spring fixed to the case of the instrument which is in turn

attached to the structure to be tested as shown in figure 3. Jt is readily

shown that, for frequencies which are low with respect to the undamped natural

frequency of the system, the displacement of the mass with respect to the frame

of the instrument is proportional to the acceleration imparted to this frame.

As the frequency is increased, the displacement per unit acceleration, and

hence the sensitivity of the accelerometer, changes in a manner which depends

on the damping of the spring-mass system. The theoretical relationships are sufficiently important to warrant the following detailed treatment.

The relative displacement, x, in such a system is given by a second-order

differential equation with constant coefficients, mx + cx + kx = F, where m, c,

and k are the mass, damping coefficient, and spring constant, respectively,

and F is the external force applied to the system. (The dot denotes

4-33
differentiation with respect to time.) The following terms are commonly used

as a measure of the degree of damping:

Damping Coefficient (c) : The damping force per unit velocity, in the

above differential equation.

Damping Constant (a) : The Napierian logarithm (base e = 2.718...) of the

ratio of the first to the second of two values, separated by unit time, of an exponentially decreasing quantity; a = c/2m.

Logarithmic Decrement (6) : The Napierian logarithm of the ratio of two

successive peak amplitudes in the same direction;

6 = 2 ire/ 4 mk_ c

2 >

Damping Ratio (c/q.) : The ratio of the damping force per unit velocity, c, to the value cc

= ZJftK. of this force which would make the system critically

damped. This ratio is often expressed as "percent of critical damping."

Damping Factor (e-et) : The ratio of the first to the second of two values

separated by time t, of an exponentially decreasing quantity having a damping

constant a.

(Q) : A measure of the sharpness of resonance, by analogy with electrical

systems. For small damping, Q is nearly equal to the magnification at resonance. At the undamped natural frequency, Q = (2c/cc

) _1

.

A measurement of acceleration by a spring-mass system is thus converted to

a measurement of relative displacement, and the methods available include in

principle all the methods discussed in connection with displacement

measurements. The most commonly used transduction principles include

potentiometers, bonded and unbonded strain gages, devices based on changes in

self-inductance, linear variable differential transformers, vibrating wires,

capacitive, piezoresistive, and piezoelectric devices.

Tables 2, 3, 4, and 5 outline the advantages and disadvantages of these

transduction elements.

Acceleration is usually measured in terms of g -units (where g is the

acceleration of gravity: approximately 32.2 F/s2 or 0.81 m/s2 ). In case

of high accuracy measurements, the actual local gravitational acceleration

value which g represents must be specified.

It is well to think in terms of two types of acceleration measurements:

slowly changing, or quasi-static, accelerations such as are encountered in

moving vehicles of all types; and vibratory and shock accelerations associated

with machinery and explosions, and also with certain biomedical phenomena. In some tests, the two types of acceleration occur simultaneously and the demands

on the instrumentation may become quite severe.

Measurements of slowly changing acceleration are often related to guidance

or other high-accuracy functions and hence require sensors and associated

instrumentation of the highest accuracy. Force-balance or servo types are well

4-34
suited to this application. Accuracy is attained, however, at the expense of

high-frequency response and ability to withstand large shocks.

On the other hand, measurements of vibration and shock often do not

require accuracy better than 5, 10, or even 20 percent. In view of the large

range of vibration and shock amplitudes at different points of a structure or vehicle, particularly for frequency components above several hundred hertz,

high accuracy at a single point may have little value. The requirements for

accelerometers suitable for vibration and shock measurements generally include

a high resonant frequency, extremely rugged construction free of subsidiary

resonances, very low response to accelerations at right angles to the sensitive

axis, a mass that is negligible in its reaction upon the structure to be

tested, small temperature effects, small sensitivity to sound and to ambient

pressure changes, and low electrical noise generation by motion of the

connecting cable. These characteristics may be achieved in a number of designs

of piezoelectric accelerometers but always at the expense of the ability to

follow very-low-frequency acceleration changes.

Measurement requirements for the two types of acceleration are fundamentally incompatible. Considerable compromise of performance in the

fundamental requirements would have to be made to use a single instrument for

both types of measurements. Thus it is a common practice in missile

technology, for example, to use separate devices for the two types of

acceleration measurements. Since these devices generally have different masses

and cannot be mounted at the same position, the records may not agree in the

range of frequencies in which both devices measure correctly. Considerable

effort has been made to develop accelerometers having compromise specifications

that make them suitable for low-frequency accelerations and for vibration and

shock applications. These include strain-gage types having resonant

frequencies above 1500 Hz and capacitive devices with frequency -response

characteristics controlled by air damping.

4.2.2.7 Sensing Technologies

The discussion above pointed out that acceleration sensors produce output

signals in response to displacements or forces due to the acceleration. The

transduction principles used are then the same as those discussed in the

chapters on pressure and displacement and summarized in tables 2, 3, 4, and 5.

Nevertheless, it is useful to discuss in more detail some transduction

principles as they apply specifically to acceleration sensors. It has already

been pointed out that piezoelectric sensors essentially combine to force acting

on the piezoelectric crystals. The geometry of the sensors is relatively

simple, involving in each case a seismic mass acting on the piezoelectric

transduction element. Three principal designs are used: compression design

(excellent temperature characteristics, high sensitivity), shear design

(insensitive to base bending), and bender design (high sensitivity with small

mass).

As pointed out earlier, piezoelectric sensors are self-generating and

require no external excitation. On the other hand, they have no output for a constant acceleration and therefore cannot be calibrated statically. This can

be a distinct handicap when accurate calibrations are required. The high

frequency capabilities of piezoelectric sensors make them useful for the

4-35
measurement of environmental vibration and shock. Such measurements do not

require high accuracies because other factors cause measurement uncertainties

which are often much greater than the errors associated with the sensor itself.

They include effects of the sensor on the system to be measured uncertainties

of high frequency dynamic calibrations, lack of inherent damping, and

non-homogeneities of materials.

Damping of an accelerometer is an important subject. Most sensors are basically single or multiple spring-mass systems with little damping.

Consequently, their amplitude response increases as the resonant frequency is

approached. It is necessary to have a flat amplitude-frequency response and

constant (or linear) phase-frequency response in order to measure transient

accelerations without distortion. If the lowest resonant frequency of the

system is far above the frequency range of interest, as is usually the case with piezoelectric acceleration sensors, there is not much of a problem. If, on the other hand, the frequencies of interest extend close to, or even beyond,

the resonant frequency of the sensor, damping must be provided.

The most common approach to damping is the use of a liquid to provide

(viscous) shear damping between the moving seismic mass and the enclosure of

the acceleration sensor. Silicone oils are frequently used because of their

stability, chemical inertness, and small temperature coefficient of viscosity.

It can be shown that damping ratio is directly proportional to the viscosity.

Thus as viscosity decreases (with rising temperatures) damping decreases as well. This results in changes in the dynamic characteristics with changes in

temperature, a factor which cannot be overlooked in evaluating the dynamic

performance of accelerometers . For shear damping to be effective, significant

movement between seismic mass and case is required, consequently, it can only

be applied to low frequency accelerometers. Piezoelectric sensors cannot be

effectively damped.

One other type of acceleration sensor deserves mention: namely, the servo

(or force balance) accelerometer. In operation, a linear or pendulum

acceleration-sensitive element feeds a servo amplifier that provides a torque

or force balance to the input. Motion of the acceleration sensing element

generates an error signal which is amplified to generate the electromagnetic

restoring force which counteracts the motion and restores the sensing element

to its undisturbed position. The output signal is thus proportional to the

restoration force and is a measure of the applied acceleration. Electrical

damping is inherent to servo systems and can be varied to suit the requirement.

This type of damping is not dependent on temperature.

Servo accelerometers can be highly accurate, stable, and sensitive, and

often serve as secondary standards. They also tend to be large, delicate,

expensive, and have a limited frequency range.

4.2.2.8 Angular Acceleration

The previous discussion has been generally applicable to both linear and

angular acceleration measurements. Angular acceleration is more difficult to measure primarily because such accelerometers are more difficult to design and

calibrate. Generally, the calibration of angular motion sensors is more difficult since they are also sensitive to linear motions in certain planes.

Angular accelerometers tend to be large devices, with low natural frequencies.

4-36
One design uses a balanced beam, able to rotate about a center suspension.

Springs keep the beam in a fixed position normally. The beam deflects when

angular acceleration acts on it and thus deflection (displacement) produces an output signal. Liquid damping is provided between beam and enclosure. In another design, liquid in a ring-shaped enclosure, in response to angular

acceleration, provides a reaction force on a fixed "paddle." The deflection of

this paddle is sensed electrically.

Very few calibration methods have been developed for angular

accelerometers. In some cases, it is possible to sense angular motions with

the aid of two linear accelerometers mounted equidistant from the axis of

rotation about which motion is to be measured.

The general subject of the measurement of angular acceleration (torsional

vibration) is covered in detail in reference [62].

4.2.2.9 Jerk

The characteristic of motion which is of interest under conditions of

rapidly changing forces is sometimes the rate of change of acceleration, or

jerk. As indicated by the above definition, jerk is expressed in g -units per

second, meters per second^, or feet per second-^. The major applications

for jerk measurements have been in connection with physiological measurements,

where it appears that discomfort and injuries from transient motions correlate

well with the measured jerk. Ballistocardiographic measurements render

additional detail by time differentiation of the more usual velocity or acceleration traces.

An output proportional to jerk is readily obtained by electrical

differentiation of the output of an accelerometer. This process is

particularly simple for piezoelectric accelerometers, because these devices

represent capacitive sources that require only a resistive load to perform the

required differentiation.

4.2.2.10 Current Problems and Future Trends

Current problems in the measurement of motion (particularly acceleration)

are reflected in the desires to have smaller and cheaper sensors, producing

greater output signals and showing greater tolerance to adverse environmental

conditions. This is a common desire in the transducer community.

In response to these desires, one would expect continuation of the

following: the use of new piezoelectric and semiconductor materials with

greater sensitivity and lower temperature effects and the increasing use of

integral microelectronic signal conditioners in the sensor body.

The use of integral adaptive filters, self-calibration features, integral

digitizing, and the use of fiber optics as a data link between the motion

sensor and its associated signal conditioning circuitry appear as possibilities

in the more distant future.

4-37
"0

fa

oo oo pc «

(/) CO CM

s- E o CD </) 00 r- CD c UJ r—

co -Q 00 C <0 O h~ Pc P c

aja t- E 3

cou

f0 c s- rO CO a. 4- >

oo i— oo O 4-O CD00 C c o O O -C

'r- oo (— Po E o Z CO P CLO 'rO o cop

"O

•o<

>1, oCO p

to -o

QJ E

•rO

O

>> CO r— 00 c c

CD P CD 3 CO >

CT

C -r- co cnp

O

O t- ClUpTM

00 00 c 00 C

CO

O CO c CO cn •r— s- o to

A3 P +J re >>p CD C -t-> u re > o

•rC P r" > (J co <- a X 3 O °p-= ra

rs CO cr

x 00

00 CO CO e:

'p- (_> i- CD Q rC U_ 00 >

4J

rs

CD>

00 r- c ro

CO E

oo oo C P o <o P c

ro

O

CO "OP O CO ro 3

S_ > i~ p- 3 ••- O O P i- 00

00 •!- o CO

oo

p ' p c a C CO CO CD 00 P

CO

00 a

co

ra

U E

•i- oo p

CO P C ro cn

oo ro

C P E O C -r- co q p E P 3

CO p— O CO o

ra > oo oo Q QCL P 00 •!-

•r- 00 -a c

CO

a

CO

ro

U E

•r- 00 P

CO P C ro

CT) 00 ro

C P E O C >r- 0) O +J E P 3

CO r—

<J 4)

O ro > oo

oo a.

CLP

00 -r-

•r- 00 -o c

0) oo

00 QCO> P "I- C P

CO «i- "O 00 c c

CO CO CL 00 ftw -CO

J- >> 3

00 <J P p C ro c CO s- i 3 CO E CT CL

CO <U E u i- CO

ro 4- P r— CO

U«L P P >

00 3 0) •r- •p— CL C a P cn to 3 ro re o z z

If, QJcn

rs P

re>

-a<

CO

c:o

CL

QJ

s_

p

u 3 •!- r- E O ro

oo

C

CO >, P3 00 TO

CL 3 C P O re 3 3 O C O

JC P P

cn c <o

•rO P

JC

O 00 ca

oo

CO>c co O r- O jG P oo

(_) 00

CO o

S_ CL

CO CO CO cn cn cn c c c

re ro ro

s_ $- L.

CO CO CO cn cn cn

&_ i- s-

<0 ra re P3

i- CL

S_ s- P o o 3

4-

O

C c c cn P o P o P o c 3 •!- 3 •!- 3 -r- »rTM CLP ClP CLP P P 3 P 3 P 3 ro 3 i— 3 r— 3 r— S- O O o o O O co oo oo 00 c

i— CO i— CO CO ro S- ro t- cn

p P P i •r- "O •r- "O •p- T3 cn o cn o cn o

•rO •p- o •i- o 'co Q C3 Q 'J O U3 00

COCL

,>1 T3

p

Cl

enj o p

COe

cn

roE

4-38 >u3

TOc

roP

COc

cn

ro pc

a»c

reE

Ia> a.
4.2.3 Flow

4.2.3.1 Introduction

Fluid flow measurements are of great importance in propulsion systems and

vehicles, chemical process industries, and in the transfer of certain types of

goods. The flowing media may be liquid, gaseous, a granular solid, or a combination of these. The flow may be laminar or turbulent, steady-state or transient.

Flow measurement methods may be categorized into two basic methods.

The first method uses devices to measure quantity of fluid such as weight or volume tanks or positive displacement meters. This method is frequently used

as a means of calibrating flow rate devices, or in applications involving

relatively steady flow and the need for direct output indication. Examples are gasoline pumps and home gas meters. Flowmeters using this method are unlikely

to be used in conjunction with ATE systems and are not discussed further in

this section.

The second method uses devices such as obstruction meters, velocity

probes, and certain other special methods. Brief descriptions of common types

of these flowmeters follow in later sections.

Rate meters may be defined as those in which the fluid stream continuously

passes through the meter without being interrupted or broken up into discrete

quantities and counted. The flow rate is inferred because of some action of

the fluid on the primary metering element; hence, these meters are sometimes

referred to as inferential meters. Established laws of fluid behavior and, in some cases, empirical data form the basis for predicting the flow rate from the

measured action.

It is conventional to consider a flow sensor as divided into two parts, a primary element and a secondary element. The primary element is that portion

which is in contact with the fluid stream and upon which the steam acts. The

secondary element is the device that measures the action. For example, an orifice plate is the primary element in an orifice type meter and the

differential pressure sensor which measures the flow-induced pressure drop across the orifice plate is the secondary element. In the measurement of gas

pressure, the static line pressure sensor is also part of the secondary

element. Thus a complete flow sensor may consist of more than one actual sensor.

Other meters have only one secondary element as the flow sensor. For

example, a transverse-momentum mass flowmeter's primary element, a turbine, is

acted upon by the steam to produce a force that is directly proportional to the mass rate of flow. The secondary element must detect the magnitude of the

force and provide an output signal.

4.2.3.2 Material Compatibility Factors

The same considerations which were discussed in section 3.5 for

pressure sensors also apply to flowmeters. In addition, abrasion becomes an important factor in the selection of materials of construction for flowmeters.

Additionally, the presence of particles in the fluid may deposit debris at

4-39
pressure taps or interfere with the rotation of turbine impellers. Thus the

selection of a flow sensor should take into account possible long-term

deleterious effects of the measurand fluid on the performance of the sensor.

4.2.3.3 Units of Flow

Fluid flow, or more correctly rate of flow, is measured and expressed in

two different ways: as volumetric flow rate or as mass flow rate. The choice

depends partly on the use made of the measurement and partly on the type of sensor.

Volumetric flow rate is most commonly expressed in gallons per minute for

liquids and in cubic feet per minute, or cubic feet per second for gases. In the SI system, volumetric flow rate units are cubic meters per second. The

term liter (cubic decimeter) as applied to the volume of liquids and gases is

permitted by the SI system; hence, volumetric flow rate could also be given in

terms of liters per minute or second.

To facilitate conversion of units, the following conversion table is given

for volumetric flow rates [5]:

1 gallon per minute (gpm)

1 liter per minute (1pm)

1 cubic foot per minute (ft3 /min)

1 liter per minute (1pm)

100 000 gallons per minute (gpm)

1 cubic meter per second (m3 /s)

= 3.78541 liters per minute (1pm)

= 0.264172 gallons per minute (gpm)

= 28.317 liters per minute (1pm)

= 0.035314 cubic foot per minute

(ft3/min)

= 6.30902 cubic meters per second

(m3 /s)

= 15 850.3 gallons per minute (gpm)

Mass flow rate is usually expressed in terms of pounds (mass) per minute

or kilograms per second in the SI system. In the case of gases, mass flow rate

may be expressed as equivalent volume flow at "standard" conditions (20 X and

14.7 psia) in "standard" units as standard cubic feet per minute or standard

cubic centimeters per minute.

A brief conversion table for mass flow rate follows:

1 pound per minute ( lb/mi n) = 0.00755987 kilograms per second (kg/s)

1 kilogram per second (kg/s) = 132.277 pounds per minute (lb/min)

1 standard cubic foot per minute (ft3 /min) = 28 316.9 standard cubic

centimeters per minute (cm3 /min)

100 000 standard cubic centimeters per minute (cm 3 /min) = 3.53146

standard cubic feet per minute (ft3/min). -

4.2.3.4 Range Considerations

It is difficult to classify flow sensors into specific ranges, since most

flow measuring principles can be applied to most ranges. Generally,

restrictive (orifice) type sensors can be used in very large diameter pipes for

the measurement of very large flow rates. Variable area and vortex-shedding

sensors are normally used at intermediate flow rates and pipe diameters.

4-40
Turbine meters can be used in very small diameter pipes, however, a minimum

flow rate is required for proper operation of the turbine. Manufacturers

literature should be consulted for specific information.

4.2.3.5 Sensing Techniques in General

The sensing elements which respond directly to the flow rate of a fluid

fall into three general categories:

(a) A section of a pipe or duct with a restriction of some sort which

produces a differential pressure proportional to flow rate. This

differential pressure can then be measured by a pressure sensor.

(b) A freely moving, or elastically restrained, mechanical member which

responds to the moving fluid either by rotating (such as a turbine

impeller), by deflecting (such as a canti levered or drag body), or by

a vertical displacement in a tapered tube (such as a float in a variable-area flowmeter).

(c) The fluid itself, with one of its physical characteristics

interacting with the transduction element (such as the cooling of a heated wire by the fluid).

A flow rate measurement may be required in terms of mass flow rate when

volumetric flow is actually measured. However, if the fluid density is known,

the mass flow rate can be computed from the volumetric flow rate.

The description of flow sensors which follows is based largely on the

chapter "Flow" by R.L. Galley in the ISA Transducer Compendium [8]. Additional

information can be found in two other publications dealing with

flowmeters [10,11].

Table 6 presents a comparison of some of the advantages and disadvantages

of the most common types of flow sensors. These are also discussed in the

following sections.

4.2.3.6 Differential Pressure Flow Sensors

Classified as obstruction meters, the orifice plate, the flow nozzle, and

the venturi all operate on the principle of an obstacle placed in the path of

the flowing fluid, causing localized changes in the velocity of flow.

Concurrently with the velocity change, there will be a pressure change in

accordance with Bernoulli's law. At points of maximum restriction, hence

maximum velocity, minimum pressures are found. From the measurement of the

pressures at fixed locations on either side of the obstruction, the flow rate

can be calculated. A certain amount of pressure is lost by the fluid when

passing through any obstruction meter.

(1) Thin-Plate Orifice Meters

The thin-plate orifice meter consists of a thin, flat plate with a circular hole (orifice) bored through and mounted in the flow conduit

perpendicular to the flow. Most often, the plate is held in place between pipe

flanges.

4-41
This is the most widely used flow rate sensor. Calibration factors

(discharge factors) are widely known and have contributed to a relatively high

degree of accuracy for concentric orifices in a wide variety of flow line

sizes, from 2 inches through 42 inches.

As previously mentioned, the orifice is usually mounted concentric with

the bore of the pipe because (1) this configuration is easiest to manufacture;

and (2) the empirical factors are most exactly known. However, in some cases,

eccentric or segmental orifice plates may be useful. They are usually

recommended where solid matter in the fluid stream might collect in front of a concentric plate, resulting in inaccurate metering.

Pressure taps are precisely located in the conduit. The standard location

of the taps may vary from one industry to another or even within an industry.

Some of the more common terms used to describe tap locations are flange taps,

pipe taps, vena contracta taps, and corner taps. Each set of standard tap

locations is associated with a particular set of discharge coefficients. The

most extensive data are available for flange or pipe tap locations. The use of

either of these standardized sets of coefficients will facilitate computation

because of existing step-by-step calculation tables.

For accurate measurements, a method must be applied to assure laminar flow

of the fluid. This is commonly done with a long, straight length of pipe

upstream of the orifice plate, sometimes aided by straigtening vanes. A

shorter length of straight pipe downstream of the plate is provided to reduce

the effect of downstream disturbances.

The pressure drop or differential head across the orifice plate must be

measured. This is performed with instruments ranging from ordinary manometers

to more sophisticated differential pressure sensors of various types. The

"dry-type" differential pressure sensors are gaining in popularity, since the

fluid does not contact the sensor and they reduce corrosion problems of the

pressure sensor. A variety of pressure sensors are used for the differential

pressure measurements required for flow sensing. Section 4.2.1 gives detailed

information on pressure sensors and their characteristics.

The basic orifice meter is not inherently a wide-range meter because the

flow rate is directly proportional to the square root of the differential

pressure. Therefore, if the differential pressure sensor has an effective

sensing range of twenty to one, the orifice flow sensor as a whole will have a range of the square root of twenty or only about four and one-half to one. Various techniques and methods have been developed to increase the range.

One of the standard techniques is that of multiple meter runs. As the

flow changes, by-pass pipes (meter runs) are either opened or closed

automatically to keep the flow and hence the pressure differential within the

necessary range for accurate metering. Major suppliers specializing in orifice

meters can provide such equipment.

Another method automatically changes the size of the orifice plate. This

method, traditionally done manually, has been mechanized such that the orifice

assemblies will be substituted from a selection of plates automatically. These

assemblies are made in several ranges and sizes and for various working

pressures; therefore, they may prove to be quite popular.

4-42
The detailed calculations necessary to obtain useful information regarding

flow rate or total flow have often caused the engineer to use some type of

automatic method to provide direct readings of flow. A variety of analog

electronic circuits now exist which can perform the desired functions; some are integral with the flow sensor. The use of electronic digital computers has

introduced digital methods for calculating flow from pressure

differentials.

(2) Flow Nozzles

The flow nozzle operates on the same theory as the orifice, the principal

distinction being that the entrance is streamlined. This tends to produce

discharge coefficients much nearer to unity than those of an orifice meter. It

has been suggested that this is an advantage, because higher flow rates can be

measured.

The International Standards Organization (ISO) has done a great deal to

standardize the flow nozzle. Another standard configuration includes the ASME

long-radius flow nozzle. It differs from the ISO flow nozzle in that the ASME

inlet shape is a quadrant of an ellipse, while the ISO nozzle shape is composed

of sections of two arcs. The ISO nozzle is also shorter. As with orifice

meters, various tap locations have been proposed and offered. These include

pipewall taps, throat taps, and corner taps.

Any secondary elements that are applied to orifice meters are also suited

to most flow nozzle applications. One exception to the rule comes from the

fact that many flow nozzles are employed for free discharge to the atmosphere,

while thin-plate orifices are not usually used in this manner. The effect of

entrance conditions is much the same for a flow nozzle as for a thin-plate

orifice meter.

(3) Venturi Meters

The venturi meter has both the entrance and the exit streamlined. Its

purpose is to provide a measurable change in static pressure between the

entrance and the throat; however, it must create a minimum of disturbance in

order that a significant portion of the energy of the stream may be recovered,

i.e., to minimize permanent pressure losses.

Simplified, the convergent entrance may have an included angle of about

20 to 25 degrees, followed by a straight throat and a divergent exit (diffuser)

with an included angle of from 5 to 15 degrees. Normally either six or seven degrees of divergence will provide excellent recovery. Wider angles are used

primarily to shorten the total length of the venturi, but at some expense in

lost energy.

Various modifications of the venturi have been employed. In all cases,

however, the venturi depends upon the diffuser to recover kinetic energy as pressure. Contrary to some beliefs, Venturis are not more accurate than

orifices or nozzles. Again, secondary sensors are similar to those used for

orifice plates or flow nozzles.

Although the basic form of the venturi has not changed radically in over

50 years, it is still widely used in various water and steam applications; its

design is not likely to undergo drastic change in the future.

4-43
Relative merits of the three obstruction devices can be briefly summarized

as follows:

Orifice meters

Advantages:

Inexpensive

Low space requirements

Moderate cost

Flow nozzle meter

Advantages:

High accuracy

Moderate pressure recovery

Low space requirements

Venturi meter

Advantages:

High accuracy

Good pressure accuracy

Resistance to abrasion

Di sadvantages

Poor pressure recovery

Inaccuracy due to wear

Prone to damage by transients

Disadvantages:

More expensive than orifice

Difficult to install properly

Disadvantages:

More expensive than others

High space requirements

(4) Pi tot Tubes and Pi tot-Static Tubes

The pitot tube consists, in its simplest form, of a small, open-ended tube

that is parallel to the line of flow. The impact of the flowing stream

produces a change in pressure, above static pressures, that is proportional to

the kinetic energy of the stream.

This holds true for subsonic flow, for example, mach numbers below 0.4

where the mach number is the ratio of flow velocity to the velocity of sound in

the fluid. As sonic velocity is approached and exceeded, other, more complex

laws apply. They are predictable, however, and are routinely employed in all

phases of wind tunnel testing, in-flight tests, etc.

The pitot tube is a valuable research tool, but it has not been widely

applied as an industrial flow transducer. This is simply because the

conventional forms are intended to measure the fluid velocity at a particular

point. Some specialized designs have been adapted to infer total stream flow

by individual calibration.

Specialized forms of pitot tubes have been adapted to determine the

direction, as well as the magnitude of the flow. Again, these are very useful

in research work.

4-44
(5) Linear Resistance Flowmeters

All previously discussed flow sensors were based on Bernoulli's theorem

and are basically nonlinear devices. The linear resistance flowmeter

(sometimes referred to as friction meter) has a very different characteristic.

In it, the pressure differential across the primary element is linearly related

to the flow rate. This is due to the fact that the flow is maintained in the

laminar flow range. Capillary tubes and porous plugs form the primary elements

and their small passages and low velocities result in low Reynolds numbers, or laminar flow.

Linear resistance flowmeters are most useful at low flow rates. They are commonly used in laboratory work where clean fluids are being metered.

Particles in the fluid may cause the primary element to act as a filter and

thereby cause a change in the linear relationship with flow.

The linear resistance meters are usually calibrated for each particular

application, a procedure necessitated in part by the fact that pressure

differential is also related to the fluid viscosity.

(6) Critical Flow Nozzles

These are similar to flow nozzles in appearance. They are used only in

gas flow applications. Critical flow nozzles may be defined as those that

have a sufficiently low pressure ratio between the throat static pressure and

the upstream total pressure to produce a stream velocity at the throat that is

equal to the sonic velocity (at throat conditions). The critical pressure

ratio for a given gas is determined by the ratio of specific heats, usually

somewhere between 0.5 and 0.6 for most gases. At any pressure ratio below the

critical value, the sonic velocity exists at the throat.

Suppose that the upstream pressure is maintained constant and the

downstream pressure is gradually reduced. The flow rate will increase until

the critical pressure ratio is attained, but no further increase in mass flow

will be obtained by decreasing the downstream pressure to pressure ratios that

are below the critical value. On the other hand, suppose that the downstream

pressure is maintained constant and the upstream pressure is gradually

increased. In this case the flow rate will increase as well. Below the

critical pressure ratio, the velocity at the throat increases with increasing

pressure. This causes the flow rate (either mass flow rate or "standard"

volume) to increase. This point is commonly misinterpreted by those who are

not familiar with critical flow nozzles.

Critical flow nozzles have been employed to calibrate large and remotely

located gas meters. They have been used for years in steam work, or in any

other place where an expansion exists to the extent that the critical pressure

ratio is obtained. Steam tables list the sonic velocity at various conditions.

A recent survey of pressure and velocity head flowmeters appears in

reference [63].

4.2.3.7 Fluid Velocity and Mass Responding Sensors

The second major group of flow sensors is based on the force exerted by

the flowing fluid on some fixed or moving member, the deflection or movement of

which is an indication of the flow rate. A recent survey discusses some of

these [63].

4-45
1. Area Meters

Area meters may be defined as fluid meters that have a constant pressure

differential and in which the area is changed with varying flow rate. The area change is usually brought about by a change in level of a float in the fluid

condui t.

There are two types of area meters: (1) the tapered tube and float type

(rotameter); and (2) the cylinder and piston type. Because of the wider

acceptance of the tapered tube and float, only that type will be discussed.

2. Tapered Tube and Float Meters

This meter consists of a float (or bob) suspended in a tapered tube. The

flow is upward, causing the float to assume a particular position for a specific flow rate. The position of the float is also a function of the fluid

density and viscosity. This consideration is most important in gas metering.

The tube is made of a wide variety of materials, including glass, plastic,

and metals. Glass tubes provide a simple method of visually observing the

position of the float and therefore the relative flow rate. Opaque materials

require a more elaborate secondary element. A common approach is to detect the

float position with a magnetic follower. Plastic or resin-coated tubes may be

used for applications involving corrosive materials. Metal tubes may be used

where high pressures are encountered. Different ranges can be achieved in the same tube by using floats of different densities.

Much of the art of designing a satisfactory float and tapered tube meter

has been associated with the material and shape of the float. Manufacturers

are able to provide special designs for various applications.

3. Force Meters

Force meters are available for both open-channel flow (hydraulic pendulum

used to determine velocity of liquids) and closed-channel flow. Those used in

closed-channel flow depend upon some force being exerted on the primary element

by a change in the momentum of the stream. This discussion will be limited to closed-channel flow. There are various types.

4. Drag (or Lift) Meters

These may be defined as meters that are acted upon by the stream to

generate a force, which is measured and from which the flow rate can be

inferred. In practice, the configuration is such that the force is directly

proportional to the kinetic energy of the fluid stream and therefore to the

square of the flow velocity. Hence the output is nonlinear.

The principle underlying this type of meter is very old, but has not been

widely used except in hydraulics. This could possibly be attributed to the

past lack of good force sensors. The principle employed in this primary

element is also commonly used as a method for detecting flow in. "off-on" type

switch systems.

5. Velocity Meters

Velocity meters are fluid meters whose primary element is driven at a constant rotational speed by the fluid stream, but which does not break the

4-46
stream into nominally discrete segments (as in quantity meters). The secondary

elements may be similar to those used on quantity meters, because either rotor

speed (for flow rate sensing) or cyclometers (for totalized flow) may be used.

This classification includes at least two types for open flow, the cup

anemometer (for measuring wind velocity) and propeller meter, neither of which

has great industrial significance.

6. Turbine Meters

The sensing element is a rotor with blades (usually helical) which is

mounted in the flowing stream with its center of rotation corresponding with

the centerline of the pipe. When freely suspended, the rotor will turn at a speed directly proportional to the velocity of the stream. Special designs

that tend to minimize bearing drag or friction are available. The transducing

element is usually a magnetic pickup of some type, e.g., a magnet in the tip of

each rotor blade may energize a coil in the pickup at the wall of the conduit.

These meters are available in a wide range of sizes, from laboratory sizes to

very large pipeline sizes. Generally, they are employed in liquid measurement;

however, gas models are also available.

7. Mass Flowmeters

A mass flowmeter represents another classification of force-sensing flow

devices and may be defined as a flow-measuring device in which the action upon

the primary element by the fluid stream is nominally proportional to the mass

rate of flow. In the three main categories, which collectively may be called

"transverse-momentum mass flowmeters," a force or torque is produced that is

linearly related to the mass flow rate. To fulfill this requirement, fluid

stream properties such as density, pressure, temperature, viscosity, and

Reynolds number (which determines whether flow is laminar or turbulent) should

have a negligible effect upon the meter within its design operating range.

Transverse-momentum mass flowmeters all operate on some momentum or inertia principle. Newton's second law of motion (force being proportional to

the product of mass and acceleration) is universal to all head meters. The

principle of these meters makes them true mass flowmeters. They all require

power to drive some part of the meter.

8. Axial Flowmeter

This meter is composed of two parts, a turbine and an impeller, that

comprise the primary (sensing) element. The impeller is driven by a motor at a constant speed, imparting an angular momentum to the stream. The turbine is

stationary, and it extracts angular momentum. This causes a torque on the

turbine shaft that is directly proportional to the mass rate of flow.

These meters were originally developed about 1950 for military

applications. Since then, they have been applied to many industrial

applications over wide flow and pressure ranges for both gases and liquids.

9. Gyroscopic Mass Flowmeter

In this type of meter, the liquid measurand is made to flow around a circular loop of pipe which is in a plane perpendicular to the input line.

Following one pass around the loop, the fluid is returned to the input axis.

During the rotation, the fluid develops angular momentum. When the loop is

vibrated through a small angle about an axis in the plane of the loop, an

4-47
alternating gyro-coupled torque is developed. The peak amplitude of this

torque is directly proportional to the mass flow rate. By measuring the torque

or converting it into a measurable displacement, mass flow rate can be sensed.

Such directly sensing mass flow rate sensors tend to be more complicated,

delicate, and expensive devices than the other types discussed above.

Another approach to mass flow measurements is discussed below.

10. Inferential Mass Flowmeters

This type of mass flowmeter consists of two or more sensor sections that

may be combined in a prescribed manner to provide an output that is a function

of the mass flow rate.

For example, a velocity meter output may be multiplied by the output of a density sensor. When properly calibrated, this combination will give a single

output linearly related to the mass flow rate. Other types of inferential mass flowmeters exist.

There is a great deal of interest in these schemes at present. Suitable

secondary elements may be connected to existing primary elements (such as orifice plates) to provide an indication of mass flow rate or to measure total

flow. Computing circuits or mechanisms are an inherent part of these meter

types.

4.2.3.8 Flow Sensors Based on Physical Characteristics of the Fluid

1. Electromagnetic Meters

These are based on the principle that an electromotive force is generated

when a conductor is moved through a magnetic field so as to cut the magnetic

flux lines. The fluid stream acts as the conductor and the magnetic field is

maintained electrically. The electromotive force is directly proportional to

the velocity of the conducting fluid stream and is measured with the aid of two

electrodes across the conduit.

This type of meter is now widely accepted. It is necessary that the fluid

be a conductor of electricity, and this has limited its application. One of

its more interesting applications is for slurry measurements, a difficult task

for most meters. By the use of plastic coatings, this meter can be rendered

very resistant to corrosion.

2. Acoustic (Sonic/Ultrasonic) Flowmeters

In the acoustic flowmeter, sound waves are propagated downstream and

upstream. The time interval required for the waves to move known distances is

measured. The velocity of the stream may be computed by using the time

interval, the distance, and the velocity of sound in the fluid. This

computation is usually performed electronically.

They are good for corrosive fluids, slurries, and other difficult metering

problems. Acoustic flowmeters have the important advantage of being able to be

clamped on the outside of the pipe carrying the flow to be measured without

altering the structure in any way except to clean the outside surface.

4-48
Acoustic flowmeters using Doppler principles and others which use electronic cross-correlation to measure fluid-transit time are in various

stages of development.

3. Tracer Type Meters

These introduce a foreign substance into the fluid stream and measure the

time required for the substance to travel a known distance. The distance

traveled, divided by the elapsed time, is the average velocity of the fluid

stream.

Salt is the foreign substance commonly used in water measurements and

detection is achieved with conductivity measuring devices. In petroleum

pipeline work, a ball or "pig" may be introduced and its passage detected

mechanically. This basic method is used in "pipe-type" meter provers for

quantity meters in petroleum applications. It is an acceptable secondary

standard.

In gas and liquid measurement, radioactive material may be introduced and

its passage detected by radiation detectors.

4. Thermal Flowmeters

Thermal flowmeters are of two types. The first type is known as the

hot-wire anemometer. It operates on the principle of the fluid cooling a heated temperature sensor. It is used to determine fluid velocities in

experimental work. It is especially sensitive to small velocity changes.

Hot-wire anemometers must be calibrated if good accuracy is to be achieved.

They are somewhat delicate and are not widely used in commercial applications.

The second type of thermal flowmeter uses the transport of heat by the

fluid over a known distance as a measure of the fluid velocity.

5. Magnetic Resonance Meter

Flowmeters using nuclear magnetic resonance are commercially available.

They have produced excellent results for applications in petroleum products,

pipelines, chemical processing plants, in the measurement of jet and rocket

propel 1 ants, and liquid hydrogen.

Using nuclear magnetization imparted to the fluid, the flow measurement is

made from outside the pipe wall; no electrical, mechanical or optical contact

with the fluid is required although the pipe wall must be nonconducti ve. This

results in a straight through, nothing-in-the-stream design and a flowmeter

that has the appearance of a thick-walled pipe spool. The direction of the

nuclear magnetization in the fluid is modulated at one point and a component of

the magnetization is detected downstream at a distance equal to one diameter.

The frequency of the modulating signal is controlled in order to maintain a fixed phase difference between the modulation signal and the detected signal by means of an external, phase-locked, solid-state, servo loop. The modulating

frequency is, therefore, proportional to the flow velocity and is read out on

an electronic counter for totalization.

6. Laser-Operated Meter

The Doppler shift of laser light scattered from a moving fluid is a precise measure of the velocity of the fluid. The Doppler shift is detected by

4-49
optical mixing (heterodyning) of the scattered beam with a reference beam from

the same laser. The difference or "beat" frequency is equal to the Doppler

shift and is detected with conventional electronic gear. Velocities down to

1U~ 3 cm/sec may be measured in volume elements as small as 10" 3 cm in

diameter.

7. Vortex-Shedding and Swirl Meters

A more recent development in flow measuring instruments is based on a natural phenomenon known as vortex shedding. When a fluid flows past an obstruction, boundary layers of slow-moving viscous fluid are forced along the

outer surfaces. If the obstruction is a bluff body, the flow cannot follow the

obstacle contours on the downstream side; the boundary layers become detached

and develop into vortexes which are shed from alternate sides of the body. The

frequency at which they are shed are directly proportional to fluid velocity.

As this vortex sheds from the bluff body, the pressure distribution also

changes at that point. It is possible then to sense vortex generation through

the sensing of pressures on sections of the bluff body or by means of a microphone which senses the passage of the vortexes downstream from the

obstruction [10]. A somewhat similar principle is used in the swirl meter in

which an obstruction causes rotating helium vortexes. The velocity of their

passage is sensed by heated thermistors or microphones to yield a measure of

flow rate. The principal advantage of these devices is their relative

ruggedness due to a lack of moving parts.

8. Corona Discharge Mass Flow Sensor

Somewhat similar to acoustic flowmeters, the corona discharge flow sensor

uses the time of a passage (or distance from its source to its detection) or ionized particles in the fluid. It's a relatively recent development [64].

There are probably more schemes for measuring fluid flow than for any

other measurand. It should be kept in mind that many of the schemes are somewhat experimental, not fully proven and may not have the dependability and

predictability required of components of military ATE systems. Advantages and

disadvantages of the common flow measuring systems are summarized in tables 6

and 7.

4.2.3.9 Current Problems and Future Trends

There are areas of fluid metering that pose special problems. One of

these is pulsating flow. Although pulsating-flow theory has been advanced by

research in recent years, no ideally suited meter is yet available. Within

certain ranges of pulsation amplitude and frequency, meters such as turbine

meters and certain mass flowmeters may be applied. Hot-wire anemometers have

been used in some area of pulsation research.

Another problem area is two-phase flow. There are many applications in

chemical, petroleum, and petrochemical industries in which the fluid exists in

both the gas and the liquid phase. For processes involving chemical reactions,

it is very desirable to know the total fluid rate (the most useful form would

be either mass or weight per unit time).

Slurry measurement still poses problems in many cases. There are flow

transducers available for certain slurries, but all of the problems are not

yet solved.

4-50
to

<uo.

•i—uc

•r-S- a.cdc

i"p 00 ro

s- &. o

CO CL c o0) CO coE 1 EO

u. o

<4- oco

00

•r-i-roa.Eoo

(1)

x Q)

»r" 4—

O

(/) o ^ w /II i_ u E

QJ •p— W +^ jO r"— (/) fO <+- CO

</> at

t/) CD©

w

W *-

fil VI/ c

t» d. ro o *o O- J- wrtv fli w miQJ x:

f—rv Wi +* QJ

(Vt «V

W c o o t •rTM *»

C t- f— (Si Q)

+->

u C?o > > ai CO a> fO (O O O

-a S- t L (/)

u

ta 3 rs a>

</) 3 ro «du

u > $- cr 00 u u c Q co =3 < < =>

to "O -O Q>

•r- P 3 rO cr w.

•r- Xl

rOU

to

a;, CD

ro pc

<0>

-o<

to Pc

a>c c o ro §- e o c a -i- CD a> c r- at oc

rC

10

O

at r—

00 '+- rOCD Qj X) T3 p a*

CO 4-> -C Q O CO

at

at

•i- xi > rO

<0 o > z <

atu

<4- a>

•r- -a

1, > CDc

(/S >r~ o

CJ at

I/) at c CL >

to#>—

at "O 1 >o 3 1? o cr >- w iW

»XI edCO CO

C 4J to c

=u .2 S c E

,rj 4) -s

to P l/l i % c to -a «T3 +-> o »o 3 I- O CL &

CD

O0 3 jd a>

•r- -r-j

litO s-

+-> M- i— X3 o a o O (O 3 «o

C_5 CO o co u•p— +J

s-§i

at

+-> c3

at

i-3

CO

to

at

s_o. oc

(O

to o 3 -r- c

a>

to "O

<a a> co $_

S- 3 5 >» S- O +J O

r- 0J T3 XJ rat »c £i

>,4-> Q. <C

4-> ^ -i- <0 +J

CO i— E O 3 3-i- 3

S! CQ

—I CO

i-

+-> O

01

"aj

a> at

4-> > I— c

CO •<- xj o E O 4-> -P 3 -r- fO

•iC to _Q 3 O -r- ff U+Jr-

•rO iQ —I z o

113 a> o

<_> +* o CL

at

S_

me i>p

to3E

CO

at at at > i— -a

•r- T- TO

CO P C -r- a> co CL C x a> lu co o +j

$-

u

cl at 3

8L

CO -a

at P

to >

•p— at CO •p— c p ro CO

•p— <B 2

s- c

01 8

s- CO

<o 3 co

O -a

p to o c o

(TJ to ro

at a> $ . CL u at to •r- at at CL £. o at to 1-

s0) 3

CO

•p—i.

O 3

(Jp

T3 X3 CO i. co ro C a> 3 •r- i.

rtJ 'i P^ at s- at to > at

E-r, •p— CD CL > p to CL >>P s- a> p c S- P >> E O 3 01 to to 3 r0 5 s_ (O T3 3 J- xi a« ro cl s- > c c XI a. s- 5 o CL at CL O p

i~ 4-> o o o <o P r— 4- P P M- 3 3 Q. 3 5 CD U 3 O O 1

01

p to P OOP a>

C 3 o a>p at

U to r—

C •r- S- o s- ro S- xi -o t- O 1_ 4- fO X) > P S- XI a> 3

f0 (0 c u ro P ro

O CO ro ro 4- CO jz at «-h p o P x: Oi t—» to P E X) a> p 4- co CD C °r— o CO CD c c *p— o C -r- ro at r- *r— to o •p- o o 3 o c •p- 3 C i- 3= _l T—

Lu _J _l r-H

O CO ZZ)_ICO zs a.

atCL

at

i/i to

atCL

ro Pc

at

s-0)

at

XJ

roat

i~

ro

at X)

ro

s.

ro o

COc

at

CO patc

CD

rOEO

s- pu

at

4-51

At ordinary process temperature and pressures, certain gases depart

dramatically from the ideal gas laws. The departures are not always well known

or predictable. This makes computations from quantity, inferential, and

volumetric meters extremely difficult and of doubtful accuracy.

The more commonly encountered problems of extremely low temperatures

(cryogenic) or high fluid and/or ambient temperatures and the problem of

developing corrosion-resistant meter bodies depend largely upon advances in

construction materials rather than advances in the science of fluid flow

measurement itself. Certainly the increasing use of microcomputers as integral

parts of sensing devices will be applied to flow sensors. In view of the fact

that flow rate, in the case of a number of the described sensing principles, is

inferred rather than directly measured, signal processing and computation

within the sensor appears a logical aim.

As in other areas of sensing, the environment in which such combined

mechanical and electronic systems are forced to operate will have a critical

effect on the overall performance and durability of flow sensors. It is likely

that sensors without moving parts (such as acoustic, electromagnetic, and

vortex-shedding types) will be used increasingly because of their greater

ruggedness.

4.2.4 Temperature

4.2.4.1 Introduction

Temperature is among the most widely measured parameters. It is also

probably that physical quantity which has been measured for the longest span in

the history of technology. Liquid-in-glass thermometers, bimetallic elements,

thermocouples, and resistance thermometers are widely used and of great

importance to the monitoring of industrial processes, machinery, and the health

of human beings.

Apart from the specific application considerations, which will be

discussed later, the most important factor about temperature measurements is

that a temperature sensor can only measure its own temperature. To some

extent, the introduction of any sensor into a measurand system will disturb

that system and modify the measured parameter. This is particularly true in

the case of temperature measurements.

The temperature of the measurand must be inferred from the output of the sensor by carefully considering all the factors which may influence the

sensor's ability to measure correctly, as the following example indicates.

A thermocouple in a hot gas stream will report an apparent temperature

which will have an additional impact energy (stagnation) component, modified by

radiation loss from the tip of the couple and conduction loss along the

thermocouple wire. In addition, both chemical and physical, time-related

processes will change the thermoelectric voltage generated as a function of

time. The use of a protective thermal well will further modify the

measurements made by the thermocouple.

Careful consideration of the sensors and measurement system is necessary

to assure continuing and meaningful measurement. In this handbook, discussion

4-53
will be restricted to temperature sensors with an electrical output. These

include thermocouples, metallic resistance thermometers (RTD), metal -oxide

resistance temperature sensors (thermistors), and semiconductor temperature

sensors.

Table 10 shows some of the advantages and disadvantages of different

sensing-transduction elements.

4.2.4.2 Materials Compatibility

Materials compatibility is of particular importance in the case of

temperature sensors with electrical outputs. High temperature measurands can affect the materials of a thermocouple (particularly) of other temperature

sensors by causing changes 1n physical and electrochemical characteristics.

These result in changes in the temperature-sensitivity characteristics,

resulting 1n measurement errors. A more subtle effect, investigated at NBS, concerns the catalytic action of some thermocouple materials 1n hot gas

streams, resulting in increased temperatures at the thermocouple due to

catalyst-enhanced oxidation [12J.

The selection of temperature sensor materials to insure compatibility with

the measurement environment can be critical. Often thermal wells or protective

sheaths are used to avoid the effects discussed. In these cases, however, the

temperature sensor may no longer indicate the desired measurand temperature and

its response time may be degraded as well.

4.2.4.3 Units of Measurement

Units of temperature are probably better known than for any other

measurand. The most common units are degrees Celsius (1.8 degrees Fahrenheit)

and degrees Fahrenheit (0.5555 degrees Celsius). Some equivalent references

follow:

0 degrees Celsius (C) =32 degrees Fahrenheit (F)

0 degrees Celsius (C) = 273.15 degrees kelvin (K)

0 degrees Fahrenheit (F) = 459.67 degrees Rankine (R)

It seems desirable to discuss briefly temperature scales based on the section

on temperature in the "ISA Transducer Compendium" [8].

The experimental basis for the concept of temperature is the zeroth Law of

Thermodynamics: Two systems in thermal equilibrium with a third are in thermal

equilibrium with each other. To establish an empirical temperature scale, some system is selected arbitrarily as the basis for a standard thermometer and a set of arbitrary rules is adopted for assigning numbers (temperatures) to its

isotherms. The number (temperature) assigned to any isotherm of the standard

thermometer is also assigned to the corresponding isotherm for every other

system. Then, for any two systems connected through a conducting wall,

difference of temperature means that heat will flow and equality of temperature

means thermal equilibrium.

The International Practical Temperature Scale is an operational procedure

designed to solve the problem of referring measurements by actual instruments

to the thermodynamic scale. The International Practical Temperature Scale is

4-54
based on a series of fixed points (freezing and boiling points) to which

specified values of temperature have been assigned, and on the use of specified

means of interpolation and extrapolation. This scale, as adopted in 1968, is

based on eleven fixed and reproducible equilibrium states to which are assigned

numerical values according to their respective thermodynamic Celsius

temperatures as follows:

4-55
TABLE 8

Fixed Points on International Practical Temperature Scale

Fixed Point Temperature (°C)

t.p.*

b.p.

b.p.

b.p.

t.p.

b.p.

t.p.

b.p.

f .p.

f .p.

f .p.

f .p. f .p. b.p.

f .p. f .p.

Hydrogen

Hydrogen

Hydrogen

Neon

Oxygen

Oxygen

Water

Water

Zi nc Silver

Gold

Tin

Lead

Sulfur

Antimony

Al umi num

(25/76 atm.

)

Secondary Fixed Points

-259.34

-256.108

-252.87

-246.048

-218.789

-182.962

+ 0.01

100

419.58

961.93

1064.43

231.9681

327.502

444.674

630.74

660.37

* t.p. - triple point

b.p. - boiling point

f.p. - freezing point

The International Practical Temperature Scale is divided into four ranges

using three different instruments for interpolation. The range from the triple

point of hydrogen (-259.34 °C) to the freezing point of water (0 °C), is

measured using a standard platinum resistance thermometer and the resistance

value is corrected to temperature using a special equation with values of

deviations from other fixed points in the range for relating temperature to

resistance. The next higher temperature range from the freezing point of water

(°C) to the freezing point of antimony (630.74 °C) also uses the standard

platinum resistance thermometer, but the resistance is converted to temperature

with a modified Callendar formula. For the third range of the scale, from the

freezing point of antimony to the gold point (1064.45 °C), a standard platinum

and platinum-rhodium thermocouple is used and parabolic formula relates

temperature to electromotive force when one junction of the thermocouple is at

the temperature being measured and the other is at 0 °C. The fourth part of

the range is above the gold point where temperature measurements are made with

a narrow-band radiation pyrometer. The Planck radiation formula is used.

The present lower limit of the International Practical Temperature Scale

at the oxygen point leaves a region below this point of less than 14 Celsius

degrees where there is no defined scale. The present International Practical

Temperature Scale also has no upper limit and the use of a radiation pyrometer

4-56
for modern high temperatures leaves much to be desired from a practical

standpoint.

4.2.4.4 Temperature Sensors (Non-Electrical )

Instruments used to measure temperature are classed as either pyrometers

or thermometers. Originally the term "pyrometer" was applied only to

instruments that measured temperatures above the range of the mercury

thermometer. Since some of these "pyrometers" have also been used to measure temperatures in the range of the mercury thermometer, the terms "thermometer"

and "pyrometer" became somewhat interchangeable. Today different meanings are attached to the two terms. If the device for measuring temperature is inserted

into or attached to the body or substance that is to be measured, the device is

called a "thermometer." If the device is located some distance away from the

temperature source, it is classified as a "pyrometer." This concept

practically limits the term "pyrometer" to radiation and optical devices. The

term "pyrometric" is often applied to paints, cones, etc., and other devices

used to determine maximum or minimum temperatures sustained during a given time

period.

Although temperature sensors with an electrical output are of primary

importance of ATE application, other types will be briefly discussed since they are often used as reference standards for calibration purposes.

In a liquid-in-glass thermometer, the differential expansion of a liquid

in a closed glass system is used to indicate the temperature. The device

consists of a thin-walled glass bulb attached to a glass capillary system

closed at the other end, with the bulb and a portion of the stem filled with an expansive liquid. Temperature is indicated by a scale marked on or attached to

the capillary. Working range is from -165 to 620 °C, the upper fixed by glass

properties. Other limits are dependent upon the liquid used as follows:

organic liquids (typically -200 °C to +230 °C), mercury-thallium mixture

(typically -60 °C to +120 °C), and mercury(from -39°C to +620°C).

Accuracy attainable with these thermometers varies, but can be as good as +0.01 °C, depending on precision of manufacturer, calibration, scale length,

and range. Similar in nature are fil led-system thermometers, all-metal

assemblies of bulb, capillary tube, and a Bourdon tube pressure sensor. The

latter is usually provided with a dual readout. The system is filled with a liquid which changes its state or phase with temperature. This is communicated

through the capillary to the Bourdon tube which provides an indication of the

temperature. Such system may be filled with various gases, vapors, or liquids.

Mercury is also used. Temperatures sensed by such systems may extend from as low as -240 °C to as high as 815 °C, depending on system design and materials.

They generally have uncertainties of about +1 percent of the range.

Another type of mechanical thermometer is the bimetallic thermometer.

The operation of these thermometers depends on the difference in thermal

expansion of two metals. The instruments consist of an indicating or recording

device, a sensing element called a bimetallic thermometer bulb, and a means for

operatively connecting the two. Bimetallic thermometers are available in

ranges from -130 to 540 °C. For continuous operation an upper limit of 430 °C

4-57
1s more suitable. The Industrial type has a nominal error of 1 percent and the

laboratory type has an error of 0.5 percent of span.

4.2.4.5 Thermocouples

Among temperature sensors with electrical output, thermocouples are probably the most widely used and useful devices.

In these devices the electromotive force developed in a circuit comprised

of two dissimilar metals is used to measure temperature. The voltage developed

across a thermocouple junction is uniquely established by the materials of the

junction of the two metals. The system consists of a sensing element

(thermocouple), which produces the electromotive force, a device for measuring

electromotive force, and electrical conductors for connecting the two. The

range of these devices depends on the materials used in their construction as shown in table 9 which follows.

4-58
TABLE 9

Commonly Used Thermocouples L8]

Nominal

ANSI Thermocouple Temperature Range (°C) Approximate Sensitivity

Type Material Lower Upper mV/100 °C

B PLATINUM, 30% 870 1650 0.45

RHODIUMPI atinum, 6%

Rhodium

E CHROMEL- 0 870 7.6

Constantan

J IRON-Constantan -185 760 5.6

K CHR0MEL-A1 umel 0 1260 4.1

R PLATINUM, 13% 0 1480 1.0

Rhodium-Platinum

S PLATINUM, 10% 0 1480 0.90

Rhodium-Platinum

T COPPER- -185 370 4.7

Constantan

*Positive material in capital letters

The accuracy of thermocouple wire (deviation of emf -temperature

relationship from standard tables) depends on the material of the wires, the

range, and the grade used. Two grades are available commercially, "standard"

and "special." Special wire is that which has been selected from standard

grade and matched to provide emf -temperature relationships that match the

tabular values with a deviation about one-half that of the standard grade. T National Bureau of Standards has published extensive tables with these

values [68]. For greater accuracy either grade of thermocouple wire may be

calibrated.

The accuracy characteristics of commercial thermocouples appear in the

following table.

4-59
TABLE 10

Accuracy Characteristics of Thermocouples From ANSI Standard MC96.1-1975 [13]

ANSI Temperature

Range, °F

Limits of Error

Standard

J 32 to 530 +4 °F

530 to 1400 +3/4%

K 32 to 530 +4 °F

530 to 2300 +3/4%

-300 to -75 + - -150 to -75 +2%

T -75 to 200 +1-1/2 °F

200 to 700 +3/4%

E 32 to 600 +3 °F

600 to 1600 +1/2%

32 to 1000 +2-1/2 °F

S,R 1000 to 2700 +1/4%

6 1600 to 3100 +1/2%

Special

+2 °F

+3/8%

+2 °F

+3/8%

+1%

+1%

+3/4 °F

+3/8%

+2-1/4

+3/8%

+2-1/2

+1/4%

Some of the characteristics of the different thermocouples are discussed

in this section, extracted from the "1979 Temperature Measurement Handbook" by

Omega Engineering [14].

( 1 ) I ron-Constantan (ANSI Symbol J ) The Iron-Constantan "JJ" curve thermocouple with a positive iron wire and a negative constantan wire is recommended for reducing atmospheres. The

operating range for this alloy combination is 1600 °F for the largest wire

sizes. Smaller size wires should be used only at the lower temperatures

because of the large surface-to-volume ratio; chemical effects due to

temperature which can change thermocouple characteristics become apparent after

shorter periods of time [65], This is true of all types of thermocouples.

(2) Copper-Constantan (ANSI Symbol T)

The Copper-Constantan "T curve thermocouple with a positive copper wire

and a negative constantan wire is recommended for use in mildly oxidizing and

reducing atmospheres up to 750 °F. It is suitable for applications where

moisture is present. This alloy is recommended for low temperature work since

the homogeneity of the component wires can be maintained better than other base

metal wires. Therefore, errors due to inhomogeneity of wires in zones of

temperature gradients are greatly reduced.

(3) Chrome! -Alumel (ANSI Symbol K)

The Chromel -Constantan thermocouple may be used for temperatures up to 1600 °F in a vacuum or in an inert, mildly oxidizing or reducing atmosphere.

At sub-zero temperatures, the thermocouple is not subject to corrosion. This

thermocouple has the highest emf output of any standard metallic thermocouple.

(4) Platinum-Rhodium Alloys (ANSI Symbol S, R and B)

Three types of "noble-metal" thermocouples are in common use; they are:

1) a positive wire of 90% platinum and 10% rhodium used with a negative wire of

4-60
pure platinum, 2) a positive wire of 87% platinum and 13% rhodium used with a negative wire of pure platinum, and 3) a positive wire of 70% platinum and 30%

rhodium used with a negative wire of 94% platinum and 6% rhodium. All have a high resistance to oxidation and corrosion. However, hydrogen, carbon, and

metal vapors contaminate a platinum-rhodium thermocouple. The recommended

operating range for the platinum-rhodium alloys is up to 2800 °F, although

temperatures as high as 3270° can be measured with the Pt-30% RH vs Pt-6% RH

alloy combination.

(5) Tungsten-Rhenium Alloys

Three types of tungsten-rhenium thermocouples are in common use for

measuring temperatures up to 5000 °F. These alloys have inherently poor

oxidation resistance and should be used in vacuum, hydrogen, or inert

atmospheres.

4.2.4.6 Resistance Thermometers

The basis for resistance thermometry is the fact that most metals and some semiconductors change resistivity with temperature in a known, reproducible

manner. A resistance thermometer consists of a sensing element called a resistor, a resistance measuring instrument, and electrical conductors for

connecting the two. A resistor may consist of a metallic sensing element,

usually in wire form, having known reproducible and stable temperatureresistivity characteristics. More recently semiconductor devices have become

available, which are basically variations of silicon transistors with special

output current-temperature characteristics. They are small, inexpensive, with

good linearity, but have a somewhat limited temperature range.

A thermistor is a special type of resistor (semiconductor) comprised of a mixture of metallic oxides. These are substances whose electrical conductivity

at or near room temperature is less than that of metals but greater than that

of typical insulators. Thermistors have a high negative temperature

coefficient, in contrast with most metals, which have a positive coefficient.

Their measurement range depends on the materials used in construction.

The most commonly used metallic resistance thermometer is made of

platinum. Of all usable metals, platinum best meets the requirements of

thermometry. It can be highly refined. It resists contamination. It is

mechanically and electrically stable. The relationship between temperature and

resistance is quite linear. Production units can be made closely

interchangeable in calibration. Drift and error with age and use are negligible.

(1) Platinum Resistance Thermometers

Platinum resistance thermometers are used for temperature measurements in

the range -220 to +600 °C (standard), to 750 °C (special order). The maximum

temperature is determined by the type of insulation material used to enclose

the platinum winding. The heart of the platinum resistance thermometer is the

sensing element, made of high-purity platinum wire wound upon a ceramic core. The sensing element is carefully stress relieved and immobilized against strain

or damage. It is normally protected by a stainless steel sheath.

4-61
Production units supplied by most manufacturers are closely

interchangeable in calibration. To achieve stability of measurement, elements

are artificially aged during fabrication, hence no further aging is observed

with elements in glass up to 500 °C and ceramic up to 600 °C. Either glass or

ceramic encapsulated resistances can be used up to 600 °C.

In its laboratory form the platinum resistance thermometer is the world

standard for temperature measurement from -270 °C to +660 °C. In its

industrial version, performance approaching that of laboratory standards can be

achieved in instruments rugged enough to withstand difficult process

environment.

Commercial thermometers are typically of reference grade platinum

(99.999+% pure), strain free, with interchangeabili ty between units of 0.25 °C

at 0 °C, and long-term drift less than 0.050 °C up to about 500 °C. They are generally supplied with a nominal resistance of 100 ohms at 0 °C, although 50,

200, 400 and 500 ohms are also available. The temperature coefficient of

resistance change ("Alpha") is 0.003902 ohms per ohm per degree C ("American"

curve, used in the U.S.).

Precautions and compromises encountered in using other types of electrical

temperature sensors are less important for platinum sensors. Connecting leads

may be platinum, nickel, or copper depending on temperature environment and

application. Since the calibration is absolute, cold junction compensation is

not necessary. The linear response eliminates corrective networks and errors

in interpretation. Freedom from drift makes frequent calibration unnecessary.

In the application of platinum resistance thermometers, attention must be

paid to the time constant of the sensor-sheath system if rapidly changing

temperatures are to be measured. Other factors to be considered include the

self heating due to the current through the resistor and error signals due to

electromagnetic induction.

(2) Thermistors

Another major class of resistance temperature sensors is represented by

thermistors. Most of the following information is extracted from the "1979

Temperature Measurement Handbook" by Omega Engineering [14].

Thermistors are essentially metallic oxide semiconductors which behave as "thermal resistors "--that is, resistors with a high (usually negative)

temperature coefficient of resistance. In some cases, for example, the

resistance of a thermistor at room temperature may decrease by almost 6 percent

for each degree C rise in temperature.

In use thermistors operate as either "self heated" or "externally heated"

units. When externally heated they convert changes in ambient or contact

temperatures directly to corresponding changes in voltage or current. They are

well suited for precision temperature measurement, temperature control, and

temperature compensation because of their very large change in resistance

with temperature. This provides a degree of resolution, or of gain, not

available with other sensors. Externally heated thermistors are widely used

for such applications in the range of -100 °C to over 300 °C.

Self-heated units employ the heating effect of the current flowing through

them to raise and control their temperature, and thus their resistance. Under

4-62
normal operating conditions the temperature may rise 200 °C to 300 °C, and the

resistance may be reduced to 0.001 of its value at low current. This operating

mode is useful in such devices as voltage regulators, microwave power meters,

gas analyzers, vacuum gauges, flowmeters, and automatic volume and power level

controls, but not in temperature measurements.

Probably the most familiar property of the thermistor is the fact that,

within certain limits, its electrical resistance is almost entirely a function

of its temperature. More important, this temperature dependence is so great

that, over the range of -100 °C to 400 °C, there may be a change of as much as 10 million to one in its resistance. The result is an extremely high

sensitivity (many times greater than that of thermocouples and resistance

bulbs, for example). This makes the thermistor an unusally effective sensor

for temperature measurement, control, and compensation, particularly where

accuracy and high resolution are important.

The temperature coefficient of resistance of a thermistor (which, unlike

that of most materials, is negative) may be expressed as:

l ar

a

=

"r AT ohms/ohm/°C, or %/°C

The resistance-temperature behavior of individual thermistor types is

usually specified by the ratio of the resistance at 0 °C to the resistance at

50 °C.

In temperature measurement applications the thermistor's relatively large

resistance change per degree change in temperature provides good accuracy and

resolution. A typical 2000-ohm thermistor with a temperature coefficient of

3.9%/C @25 °C will exhibit a resistance change of 178 ohms per degree C change

in temperature, compared to only 7.2 ohms for a platinum resistance bulb with

the same basic resistance. Connected in a simple bridge circuit with an indicating galvanometer, a thermistor will readily indicate a temperature

change of as little as 0.0005 °C. It is a simple matter with such a circuit to

obtain a 1 °C full-scale output. This high sensitivity, together with the

relatively high thermistor resistance which may be selected, makes the

thermistor ideal for remote measurements or control, since changes in contact, , resistance, or transmission line resistance, due to ambient temperature effects

have a negligible effect on the measurements. For example, 400 ft of #18 AWG

copper wire transmission line subjected to a 25 °C temperature change will

affect the accuracy of measurement or control by less than 0.05 °C.

One of the drawbacks of thermistors is their nonlinear resistancetemperature characteristics. For narrow ranges of sensing this is less

critical. For wider ranges of measurement thermistor linearizing networks can

be designed in the form of resistance bridges. Current work is leading to

thermistors with greater long-term stability, the ability to operate at higher

temperatures, and thermistors with positive temperature coefficients of

resistance [66].

(3) Semiconductor Temperature Sensors

A relatively new class of sensors makes use of the properties of

semiconductors like silicon. These devices may be in the form of two terminal

4-63
resistors of heavily doped p-type silicon with a positive temperature

coefficient of 0.7 percent per degree C. This type of sensor is quite linear over its measuring range from -65 °C to about 200 °C without resort to any

linearizing network.

Another type of semiconductor temperature sensor makes use of an actual

transistor defect: junction instability. In this device the highly

predictable correlation between temperature and transistor base-to-emitter

voltage of a bipolar transistor, which is roughly 2 millivolts per degree C, is

used to sense temperature. There are also integrated circuits which act as constant-current elements. The current through the circuit is dependent on temperature. Such circuits are capable of good linearity and a temperature

range up to about 150 °C.

The field of semiconductor temperature sensors is rapidly changing and

growing. Future trends appear to lead to such sensors of smaller size, faster

response, better linearity and interchangeable i ty , and lower cost [67].

4.2.4.7 Radiation Temperature and Heat Flux Sensors

All the temperature-measuring methods discussed so far require the

temperature sensor to be in contact with the body whose temperature is to be

measured. There are applications where it is not possible or desirable to have

this direct contact. There are methods for inferring the temperature of an object from its thermal radiation. Such sensors are called radiometers,

radiation pyrometers, or radiation thermometers. Another consideration is that

there are measurement situations in which measurement of heat transfer rates

(heat flux) are required. This is further complicated by the fact that heat

transfer can be by radiation alone or by convection (in gas or liquid media) or

by a combination of the two.

Radiation-temperature sensors operate on the principle that every body

above absolute zero in temperature emits radiation dependent on its

temperature. The radiant intensity varies with wavelength, with peaks of

radiative power occurring at wavelengths inversely related to temperature. The

total radiated power is directly proportional to the fourth power of the

absolute temperature. In radiation thermometers, the radiation is focused on a detector which produces an electrical signal. Thermal detectors are blackened

elements designed to absorb a maximum of incoming radiation at all wavelengths.

The absorbed radiation causes the temperature of the detector to rise until

equilibrium is reached with heat losses to the surroundings. Thermal

detectors, such as resistance thermometers or thermocouples, measure this

temperature. Photon detectors also are used to sense thermal radiation. They

operate on the principle that incoming radiation (photons) frees electrons in

the detector structure and thereby produces an electrical output. Through

photoconducti ve or photovoltaic effects, proton detectors have a sensitivity

that varies with wavelengths, and they must be taken into account in radiation

measurements [69].

Heat flux measurements are somewhat similar in that one measures the

temperature rise of a body, such as an insulated metallic slug of known mass or

a thin foil. The rate of rise of temperature of the slug is proportional to

the rate of heat transfer to the slug. The thin foil sensor is bonded at its

periphery to a metallic body. Usually foil and body meterials are chosen so as

4-64
to produce a thermocouple which measures the temperature difference between the

center and the edge of the foil. This temperature difference is directly

proportional to the rate of heat transfer to the foil. The section "Heat Flux"

in the ISA Transducer Compendium [8] provides more detail.

Optical temperature measurements and heat flux measurements are quite

complex. Disadvantages of the former are difficulty of correcting for

emissivity in converting from measurements of emitted radiation to a measurement of temperature, the need for line of sight measurements, and

difficulties with radiation-transmitting windows covering the sensor.

Heat flux measurements are also strongly influenced by knowledge of the

emissivity of the sensing body by the heat leakage from the sensor to its

surroundings and by the mode of heat transfer (radiative, convective, or a combination). There are also a number of other factors, some of them

time-variant, discussed in the above-cited reference [8],

Calibration of optical and heat flux sensors is difficult as well, but

essential to obtain an indication of the validity of the measurements. As

indicated above, radiation temperature and heat flux measurements are usually

resorted to only when it is not possible to make contacting temperature

measurements.

4.2.4.8 Selection of Temperature Sensors

The many secondary phenomena associated with changes in temperature often

tend to be confusing for engineers. Where the object is the measurement or

control of temperature itself, however, the broad assortment of effects (and of sensors that detect them) is a decided advantage and the problem often becomes

simply a matter of selecting the optimum sensing technique from among a number

of possibilities.

Frequently, for industrial or military applications where continuous

temperature ranges are to be monitored, the choice is limited by practical

considerations to three familiar devices: thermistors, resistance thermometers,

and thermocouples.

Some general considerations in the selection of sensors are discussed in

section 3.2. In the case of temperature sensors, some additional factors need

to be considered in their selection and are discussed below.

Type of Measurement - Resistance-temperature devices such as thermistors

and resistance thermometers provide a direct indication of absolute

temperature. Thermocouples, on the other hand, which measure the temperature

differential between two junctions of dissimilar metals, provide a relative

measure. For direct temperature indication, one thermocouple junction must be

accurately maintained at, or compensated to, a known reference temperature.

Temperature Range - Thermistors are available for measuring temperatures

from a few degrees above absolute zero to about 315 °C. They can be used at

higher temperatures but tend to decrease in stability above 300 °C. Platinum

resistance thermometers normally have a range of -183 °C to about 1100 °C,

while platinum-irridium alloys can be used up to about 2200 °C. Nonlinearity

of resistance change increases, of course, at temperature extremes.

4-65
Thermocouples are available for use up to more than 3300 °C. Accuracy at

extremely high and low temperatures is usually limited.

Sensitivity - The sensitivity of resistance-temperature transducers is a function of the temperature coefficient of resistance or the change in

resistance resulting from a unit change in temperature. A typical platinum

resistance bulb will exhibit a change of less than 0.06 ohm/°C at room temperature. Thermistors, on the other hand, provide changes of from about

6 ohms to 6 x 104 ohms/°C under the same circumstances. (Between -100 °C and

400 °C the resistance of a thermistor may change by ten million to one,

compared with a change of about four to one in the resistance of platinum over

the same temperature range.)

Due to the large voltage outputs provided by a typical thermistor bridge

or by a typical thermistor telemetering circuit, no amplification is required.

The voltage output of a thermistor bridge at 25 °C will be 18 mill1volts/°C

using a 4000 ohm thermistor; 450 times greater than that of a Chromel /Alumel

thermocouple whose output is only 0.040 millivol ts/°C.

Thermistor control systems are inherently sensitive, stable, and fast

acting, and require relatively simple circuitry. Neither polarity nor lead

length is significant, and no reference temperature or cold junction

compensation is required, as with thermocouples.

Accuracy - In general, thermistors and resistance thermometers provide

relatively high absolute accuracies. Ordinary commercial -grade thermocouples

are normally of specified accuracies of +1 °C or less over the measurement

range. Both thermistors and resistance bulbs will provide accuracies of

+0.01 °C or better. Repeatability of thermistor measurements 1s such that

variations 1n repeated readings are within the overall accuracy of the

measuring circuit.

Installation Effects - As indicated earlier a temperature sensor can only

sense its own temperature. To what extent this value represents the

temperature that is desired to be known depends on a number of factors.

The installed accuracy (indicated vs measurand temperature) is the result

of complicated heat transfer effects produced by the measurand, sensor,

protective housing, measurand vessel, environment, and steadiness of state.

When the measurand is a moving gas or vapor, several temperatures exist

simultaneously, and it is necessary to decide which should be or are being

measured.

The indication of a calibrated sensor is thus subject to many influences

from installation effects. In general, it is not good practice, nor are the

necessary data usually available, to correct a poor installation by the use of

computed "correction factors." Such factors can be in error by a greater

amount than the magnitudes of the effects that they are attempting to rectify.

In-place calibration, or checking by a known standard, will simply verify the

correctness of the transfer function because the standard will indicate its own temperature as it too will be subject to installation effects. For realistic

temperature measurement, it is necessary to make an analysis of each proposed

installation, select a suitable sensor, and install it in such a manner that

undesired heat transfer effects are minimized.

4-66
Sometimes the physical or chemical conditions of the measurand require

that the sensor be housed in a protection device such as a tube or thermometer

well. In such cases this housing becomes the "measurand" to the sensor. Since

usually the true measurand temperature is the one whose measurement is desired,

and since the two interact, in the discussions that follow, the term "probe" is

used to mean both the sensor and its protective housing, if any. This approach

considerably simplifies the discussion of some of the more common installation

effects. Again, the intent is to present highlights as a reminder; for any

work in depth, the references cited should be consulted.

The following discussion on factors influencing temperature measurements

is extracted from the "ISA Transducer Compendium" [8].

Kinetic Energy

In a gas at rest, temperature is a measure of the random motion of the gas

molecules. In a moving gas, the directed velocity may be appreciable compared

with the mean velocity of random motion. In such cases two temperatures are of

Interest, the static or stream temperature Ts and the total or stagnation

temperature Tf For an Ideal gas these two temperatures are related as follows:

Tt

- Ts = V

2 /2gJc

p where V 1s the gas velocity, g is the acceleration due to gravity, J is the

mechanical equivalent of heat, and c

p 1s the specific heat of the gas at

constant pressure.

The attainment of T s requires that the probe move with the same velocity

as the gas; the attainment of T^ requires a probe that brings the gas to rest

by 1sentrop1c compression. Neither probe can be physically constructed, so that stationary probes 1n fluid streams will show neither Ts nor T^ but some Indicated temperature T-j. This Indicated temperature depends not only

on how the directed kinetic energy 1s brought to rest, but also on viscous and

heat transfer effects 1n the boundary layer of the probe. The capability of a probe to affect this conversion is its recovery factor r, defined as

r =

Although each Installation should be judged on its own merits, it is

generally desirable to use a probe of special design described in the

literature as "total temperature" or "stagnation" when the gas or vapor

velocity is in excess.

For example, the difference in Tt

- T

s in air at a velocity of about

100 m/s is of the order of 4° C, while at about 160 m/s it 1s 11 °C. An

ordinary round thermometer well has a recovery factor of about 0.7, so that the

kinetic energy error (Tt

- T-j) is about 1 °C at 100 m/s and about 3.5 °C at

160 m/s. It is possible to reduce this error by increasing the size of the

pipe at the point of measurement, thus reducing the fluid velocity. However,

the heat transfer effects discussed in the next paragraph should be considered.

In some installations the kinetic error may be insignificant, and it may

actually be desirable to increase the velocity to overcome other effects.

4-67
Steady State

Heat transfer equations for probe located in a moving fluid stream where

the directed kinetic energy is negligible are so complicated as to be of little

value in a discussion of correction of installation effects. An approximate

relationship for a probe installed in a vessel may be obtained by considering a heat balance at equilibrium: WV MVV % (W

(Convection) (Radiation) (Conduction)

where hc is the convection coefficient of heat transfer, hr is the

radiation heat transfer coefficient, k is the thermal conductivity of the probe

materials, A is the cross-sectional area of the probe at the wall, L is the

length of the probe in the stream, T-j is the indicated temperature at L, T

g is the true gas temperature, T5 is the temperature of the probe at the wall,

and Tw

is the temperature of the vessel wall.

For purposes of analysis, the equation may be rewritten as

j j MW +

< kA/ L

> <YT

b>

It becomes readily apparent that hg should be as large as possible. The

value of hc may be increased by increasing the mass velocity of the gas

(aspiration of the measurand past the probe, or reducing the size of the duct);

however, kinetic energy effects must then be considered. The convection

coefficient may be increased by reducing the diameter of the probe, which

within strength limitations is always good practice.

The effects of radiation may be discussed from the following elementary

definition:

X

h r

< T

i - V = Qa f cdx (T T M

0

where Q is the emissivity of the probe surface, a is the Stefan-Bol tzmann

constant, C is the circumference of the probe, x is the distance from the wall,

and T

x is the temperature at x.

The emissivity of a blackbody is unity and that of a perfect reflector is zero. If the probe can be maintained in the fluid stream in a bright and shiny

condition, the effects of radiation will be negligible. If the temperature of

the vessel wall is the same as the gas temperature, radiation is no problem.

This is usually accomplished by insulating the pipe wall at least as far as the

probe can "see," and farther if possible. The smaller the probe diameter and

hence its circumference C, the smaller the radiation error. When it is not

practical to maintain a shiny surface, nor to insulate or reduce size, then the

probe may be shielded. When shields are used, the shield temperature is higher

4-68
than that of the wall (Tw

< T

g

), and the more shields used, the smaller the

radiation error.

Conductivity effects may be minimized by selection of probe materials of

low thermal conductivity, reducing probe cross-sectional area, and increasing

the insertion length. Often in making an installation, the insulation in the area where the probe is to be inserted is removed and not replaced, with a consequent lowering of lb(Tw

< T

g

), and a corresponding increase in the

conductivity effect. Sometimes this is done deliberately to keep the external

portions of the sensor at a low temperature. Therefore, care should be

exercised in the application of a sensor that makes this a necessary

requirement. The insulation should always be replaced and the external

portions of the probe lagged to maintain Tb as near as possible to Tg.

Dynamic Effects

It is a common practice to characterize the response of a thermal element

to a nonisothermal state change by a thermal time constant. No one time

constant can describe the response characteristics of anything but a simple,

idealized element. For purposes of discussion, consider a probe with

first-order response. Within the probe there is no resistance of heat flow, so that the probe itself is pure capacitance. Resistance to heat flow is in the

fluid film only. The only mode of heat transfer is by convection. The thermal

time constant of this idealized probe is

t = wc/hc

S

where t is the thermal time constant, w is the mass of the probe, c is the

specific heat capacity of the probe, hc is the convection coefficient of heat

transfer, and S is the surface area of the probe.

This equation indicates that for fast response the mass of the probe

should be as small as possible, the specific heat small in value, and the

surface area and heat transfer coefficient large. It should be noted that

weight, specific heat, and surface area are properties of the probe itself, but

that the convective heat transfer coefficient is dependent upon properties of

the fluid, its mass velocity, and the diameter of the probe. The requirements

of low mass and small diameter are not compatible with large surface area unless fins are used.

Although no actual probe has a time constant described by the equation,

many approximate it closely enough for engineering measurement purposes. It

should be noted that the time constant for a probe consisting of a protective

housing and a sensor is not the same as that for either component, nor is it

equal to the sum of the two. It should be further recognized that the actual

time constant of the probe is a function of the installation conditions as well

as of the probe. The time constant data for a sensor given in this chapter

cannot be used directly unless they were determined for the exact conditions

for which the sensor is to be used.

Strength Effects

Two kinds of probes are equally useless, those that measure temperature

inaccurately and those that fail due to lack of strength. Factors that tend to promote accurate measurement are also those that tend to reduce strength as shown by the tabulation which follows.

4-69
It is apparent from all the above discussion that sensor selection and

probe design necessarily result from a series of engineering compromises.

Ideal for Measurement Ideal for Strength

Long-conductivity errors

reduced. Active portion

must be in the flow stream.

Length

Strength

Short-impingement forces

reduced. Higher natural

frequency.

Thin-reduced conductivity loss, (cross-section Thick-greater moment of

Faster response. area)

Mass Velocity

inertia, less stress.

Higher natural frequency.

High-increased heat transfer.

Faster response.

Low-reduced impingement forces

Lower vortex trail

frequency.

4.2.4.9 Summary

Temperature measurement is unique in that a primary standard for

temperature cannot be realized. There are two basic temperature scales--one

theoretical, the other empirical. Over a period of years a number of widely

used temperature measuring instruments have been highly developed commercially.

It is not possible to separate the performance of a temperature sensor from

installation effects.

Two important areas vital to the knowledge needed for intelligent

selection and application of sensors were not discussed. There are industrial

and/or commercial installation "rules of thumb" and the purpose for which the

temperature is being measured, which in turn creates the measurement

requirement. These two areas are related because the installation practices

were developed in order to meet the measurement requirement. Where experience

has demonstrated that a measurement requirement is being satisfied by a "rule

of thumb" such as "insert the thermometer at least x diameters into the flow

stream," an analysis of the type suggested in the section on Installation

Effects is a waste of both time and money.

It should be obvious from the discussion above and the theoretical

relations shown that accurate temperature measurements are quite difficult.

Accordingly, it is very important to carefully and realistically assess the

temperature measurement accuracy required before money, time, and effort are expended on the actual measurement system. This caution applies to all

sensors, but perhaps more so to temperature sensors because of their

deceptively simple nature.

4-70
00 p

00 P S- (J O 3

CO "O C CO

0) c

co <o

s- UJ £T _J 3 CD

CO P C < <0 -r- 1— i- CO

a* c

cl ai E co

0) 1— 4-

00aicn

<o

+-» c

(O>

<0

oo

CO

CD c Q_ O CO 3

•i—CU SO P "U 1) O (O •!- o c s- a» t*- 3 CDM- >i—

»r"S CD 'i— r— Or- a he P 0» E p O 00 "O <0 Cl C 0) c c P CD S- fO OJ fO O 0) -3 CD !o p

CD <U Cn S- rd P 00 i— a3 5 cr o cu —I Q£

2LE

CD

O

p <p

-C CD Cn CL O"

•i- CD o <o C P

(O CO

CO

CD

sp -a

CO CD O CT> u en

CD -C 00 Cn 00

•i- CD

CDCD

(O

CD

<0

i-8.E

CD PaCD p

CD CD CD cn C c

to <0

i- S_

a> CD

s. J- 3 3 P P

<o fO

s_ J- en

pe 4!a.

in E CD

CD re

p P S_

fO 00 -o a* CD "S CD c L.

+-> P •r-

•rTM »r" 3 E E cr

•r- rTM o 0) _J _J z 0* o

00

•Ii-

<dClEOo

CD

oo cn

CD e

CL ro $

i- j >

CD

O

rd [I

'4- E- s- fO o 3 3 >» <u S- oo P -P c »S 0) > 3 C CD

A3 (_) •r— »r*

O -r- 00U CD 00

p <o i~ <o &. fO S- re

p

U CO

C

00 CD S- CD rO S- rO o <o

O

QJ •i- 3 ClP -S T3 CD 3 CD Cl co P Cl cn p s- u E c rC O C <_> C P 00 c CD C 00

id co <0 <_> CD a> -P

O

O •!- OO CD P CD CD

p o CD > <0 P oo cn rO r—

O 00 (Or- S- c o u S- i—

CL CD "O 8 OJ T3 >, 13 -a -a

p -o CD CD P > E -O O u O 4? O o o 00 O a (_> to o o •i- •- o X O CD O o o 8 o O X A3 < _l CO 3 CD 2 LU CD > CD CD CD _j u_ CD

CD

5-3P(13 U

CDego E

CD PICDUc

ro Poo

OO

CD E O 3

•r- 0) Pf0 O op00

•r» 00c

id

CD

4-71
4.2.5 Force and Torque

4.2.5.1 Introduction

Force and torque measurements find application in industrial and military

systems. The thrust of rocket propulsion systems, the torque generated by

internal combustion engines, the weight of a liquid-filled tank in a chemical

plant are generally measured with sensors which measure force in terms of the

displacement of an elastic element. This displacement, in turn, is converted

into an electrical signal.

The homogeneity of the material of the sensor, the mechanical design and

workmanship, and the transduction elements used all have a bearing on the

quality of measurement of which the sensor is capable* The following material

has been excerpted with permission from the ISA Transducer Compendium [8].

An understanding of the general area of force and torque measurement must

be based on a familiarity with the two terms. The following are commonly

accepted definitions for force and torque.

Force is either a push or pull exerted on a body. It may produce motion

of the body or cause deformation of the body, or it may be balanced by an opposing force so that no motion occurs.

Torque is a force that tends to produce rotation about an axis. If the

body referred to is a system of particles which is not deformed by any system

of forces acting on it and the fixed distances between these particles are maintained, then the body may be considered a rigid body. Thus all particles

of the body experience the same motion (provided rotation is not permitted).

This allows one to consider the mass of the body as being concentrated at its

center (center of gravity) and the total force as acting at this point.

Applying a force at an off-center point of a rigid body tends to produce

rotation about an axis through that center. This tendency is the moment of

that force, or the torque exerted by that force. Expressed mathematically,

torque (T) is the product of the force (F) and the perpendicular distance (L)

from the axis of rotation to the line of action of the force.

In a non-rigid or elastic body, the force or torque will result in a deformation of that body. The body will return to its original state after the

removal of the force or torque, provided that the elastic limit of the material

has not been exceeded. Under these conditions, the stress developed within a body to withstand an outside load is proportional to the strain to which the

body is subjected by that load (Robert Hook's law).

Sir Isaac Newton's observations and interpretations of the relation

between motion and the action of forces on bodies led to his deduction of the

three fundamental laws of motion which bear his name. Force sensing is

generally based on his second law : "An unbalanced force acting on a body causes the body to accelerate in the direction of the force; the acceleration

being directly proportional to the unbalanced force and inversely proportional

to the mass of the body." Expressed mathematically this becomes

a " F/m
where a is the acceleration of the body, F is the unbalanced force acting on the body, and m is the mass of the body. Solving equation for F, we find

F

a ma

F = kma

where k is a constant of proportionality whose value depends on the units

employed. By the proper choice of units, k will be unity, and the force is

then

F = ma

where m = W/g (W = weight, g = acceleration due to gravity); thus,

r W

F g

It will be noted that this relation permits the measurement of acceleration in

terms of force or force in terms of acceleration. See section 4.2.2 on the

measurement of motion (acceleration).

The validity of Newton's laws depends on the particle concept and on the

assumption of rigidity. An unbalanced force system acting at the center of

gravity will thus result in a linear acceleration of the body as indicated by

the relation above. Similarly, angular acceleration is related to torque by

the expression

where a is the angular acceleration of the body, T is the unbalanced torque

action on the body, and I is the moment of inertia.

Thus, in summary, it can be stated that an unbalanced force acting on a body will cause either a distortion or a displacement on that body, depending

upon the rigidity of the body. The distortion or displacement occurs in

accordance with Hook's and Newton's laws governing the behavior of elastic or non-elastic bodies. The conversion of this distortion (deformation) or motion

to an electrical signal provides the means to determine the value of the force.

The instrument or device that performs this conversion is the force or torque

sensor.

4.2.5.2 Materials Compatibility

Unlike the cases of pressure and flow, force or torque cannot inherently

be corrosive or abrasive. Nevertheless, there are still compatibility problems

in regards to the operating environment of the sensors and section 3.5 should

be consulted for information on this.

4.2.5.3 Units of Measurement

Having defined force and torque, it is now appropriate to discuss the

units in which these quantities are measured.

4-73
In the International System of Units (SI) the unit of force is the newton.

The newton thus replaces the kilogram force unit and is the force which gives

an acceleration of 1 meter per second2 to a mass of 1 kilogram.

In the English system, the unit of force is the poundal, which is defined

as the force required to give a mass of 1 pound an acceleration of 1 foot per

second2.

In the gravitational or technical system of units (used extensively in

engineering), it is the usual practice to measure forces by scales and balances

calibrated by comparing them with the pull of the earth upon standard masses.

Thus a mass of n pounds (weight) is equal to ng poundal s, where g is the local

acceleration of gravity in feet/s2.

1 pound force (Ibf) = 4.44822 newtons

1 poundal = 0.138255 newtons

1 newton = 7.23300 poundal

s

The unit of torque in SI units would be the newton-meter or ^eter-kil ogram

force. In the English system it would be the poundal -foot while the technical

units would be the pound (force)-foot. It is interesting to note that the

units of torque and energy or work have the same dimensions in their respective

systems (length times force in mass units). They are differentiated by

reversing the force and length units in the product. Unfortunately, the units

in the English and metric systems are interchanged which leads to confusion.

Commercial torque transducers, which one would expect to be categorized in

force-length units (technical units), are generally categorized in length-force

units such as inch-pounds.

1 pound (force) foot = 1.35582 newton meters

1 poundal -foot = 0.0421402 newton meters

1 newton-meter = 23.7303 poundal -foot

4.2.5.4 Range Considerations

Practical measurements of force range from fractions of newtons to

5 x 10' newtons (more than 10 million pounds).

Torque measurements range from about 7 x 10" 2 to 10^ newton-meters

(10 ounce-inches to 750 000 pound-feet).

4.2.5.5 Sensing Principles

A great many sensors are commercially available for monitoring force or

torque. They accomplish the conversion of these phenomena to an electrical

signal. Typical of the kind of parameters which are changed due to these

phenomena are resistance, inductance, and capacitance. In addition, changes in some of the electro-mechanical properties of the materials themselves

(permeability, dielectric strength, magnetostriction, electrostriction, and the

piezoelectric effect) are also employed to produce signals related to the

physical change or motion of the sensing device.

4-74
Force Sensors

Most of the force sensors presently in use are designed for the

measurement of load or weight. The sensor, or load cell, is inserted between

the body to be weighed and a reference platform. Since the body is at rest, a force equal in magnitude but opposite in direction to the downward pull of

gravity must be balancing the weight of the body.

This balancing force, so extensively used for calibration purposes, exists

in the stored molecular energy of the deformed element of the sensor. The

efficiency of the mechanical -to-electrical conversion depends upon the method

used to monitor this deformation (displacement).

The deformation of the load column of the sensor results in a strain at

its surface. Either foil or wire strain gages are bonded to the surface of the

load-bearing column. The strain is transmitted to the wire or foil strain

gages via the bonding cement, changing their resistances in accordance with the

relation shown in section 4.2.1.7, and given in this form:

AR _ rcc _ AL -r

- GF? = T

where AR is the change in resistance of the gage, R is the original gage

resistance, GF is the gage factor supplied by the manufacturer, and £ is the

strain or elongation set up in the load column and is equal to the change in

length of the column divided by its original length, orAL/L.

The usual arrangement for strain gages on such a load member is to have

them "back to back," with two gages mounted axial ly and two radially (at right

angles). The latter indicates only the lateral contraction in accordance with

Poisson's ratio. This arrangement permits the electrical connection of the

gages to be made in a full Wheatstone bridge circuit, thereby increasing the

signal output. Any changes in the dimensions of the gages due to ambient

temperature changes will affect all four gages similarly and will be cancelled

out electrically.

Changing the mechanical features of the attachment devices permits the use

of this type of load cell for the measurement of tension loads as well as compression loads. Other types of load cells make use of different

sensing elements. Two such configurations involve the use of a load beam and

the use of a proving ring. The former is usually a simple cantilever beam with

strain gages bonded adjacent to the fixed end. The latter is a circular ring

with gages mounted on the surface.

Various sensitivities and ranges are obtained by changing the material as well as its thickness. Ranges of the loads which can be measured vary from

about a tenth of a pound force to over twelve million pounds (0.4 newton to

about 50 x 106 newton). The use of unbonded strain gages, careful

calibration, and benign environments can result in an accuracy of this type of

load cell between 0.1 percent and 0.25 percent.

Factors which affect the accuracy are hysteresis, repeatability, and

thermal sensitivity. Contributing to the hysteresis effect is the creep which

occurs both between the gage wire and its carrier and between the carrier and

the member to which it is bonded.

4-75
This type of load cell is capable of both steady-state and dynamic load

measurement. Either dc or ac excitation may be provided the gage or gages,

depending on the type of instrumentation system being employed. It should be

noted that metallic wire or foil strain gages as well as semiconductor strain

gages can be used as transduction elements. In addition, variable capacitance

or reluctance, or differential transformers can also be used. These

transduction principles are discussed in more detail in the section on pressure, 4.2.1; the advantages and disadvantages of the transduction

principles are summarized in tables 2, 3, and 4.

Force gages using a piezoelectric element for the sensor are suitable only

for dynamic work. Deformation of the crystal results in the generation of an electrical charge. This type of gage has a range capacity of from 1/2 ounce to over 5000 pounds (1.4 x 10"^ to 2.2 x lO^N). The frequency range is

from 2 Hz to beyond 15 000 Hz and the linearity is approximately +1 percent.

The sensor is essentially very stiff, ensuring a very high natural frequency of

the system and permitting the gage to be a load-carrying member in the

structure.

Torque Sensors

The most common of the torque sensors consists of an elastic member,

usually in the form of a short accurately machined shaft, which is inserted in

a line of shafting between the rotating driving unit and the rotating load. In

transmitting the torque, this shaft deforms (twists) and sets up shear forces

normal to and along the same axis as the load. These shear forces have tension

and compression components at 45° to the axis. By bonding foil or wire strain

gages along these 45° components, the torque or twist is measured in relation

to the tension or compression at the surface of the shaft. The gages are positioned and connected into a bridge circuit, cancelling the effects of

bending and thrust strains. The bridge unbalances linearly with the amount of

torsional strain.

The sensitivity of torque sensors is a function of the design. Thus, by

reducing the diameter of the portion of the shaft on which the gages are mounted, the sensitivity is increased.

The torque developed in such sensors is related to the physical dimensions

of the sensing portion and to the material used. Thus

Torque = 6

where C is the modulus of rigidity of the material, e is the angle through

which the shaft twists, and D and L are the diameter and length of the sensing

portion of the sensor. The use of a full bridge eliminates temperatureunbalance problems in the strain gages themselves, but temperature still

affects the sensitivity.

The limiting items in the use of this type of torque gage are the

temperature limits of the bearings, the bearing speed and the slip-ring surface

speed. Until recently, a rotational speed of 5000 to 7000 rpm was maximum, and

a slip-ring surface speed of 5000 ft/mi n was not to be exceeded if noise

4-76
problems were to be avoided. For conventional slip-ring assemblies, operation

to 12 000 rpm is now practical. Special designs can operate at higher speeds.

Other techniques to obtain the torque signal and eliminate the use of

slip-rings involve more complex electronic circuitry and larger sensors. Two

of these are magnetically coupled and optically coupled sensors. A

magnetically coupled device adapts a linear differential transformer pick-off

to sense the twist of one end of the torque bar with respect to the other. A

primary winding of the magnetic circuit is located on the input end of the sensor. The circuit is excited by means of a carrier oscillator. As the

winding (or magnetic core to which it is attached) approaches one of the

secondary windings of the sensor, it moves away from the other. The induced

voltage increases in the closer winding and decreases in the other, resulting

in an output amplitude that is proportional to the magnitude of the torque.

The relative phase of the output will depend upon the direction of rotation of

the input shaft. Processing this signal through a phase-sensitive converter

will result in a dc voltage whose amplitude is proportional to the torque and

whose polarity is related to the direction of rotation. The frequency response

of such a system is limited to frequencies up to approximately 10 percent of

the carrier frequency.

Two types of optical transduction elements are available for use with

torque sensors. In one of these,, photocel Is are used to develop two separate

and identical pulse trains, one from the input end of the torque shaft and one from the output end. As torque is transmitted and the sensing part of the sensor twists, a time displacement (or phase displacement) occurs between the

two pulse trains. The leading edges of one train of pulses causes an electronic gate to open and allows oscillator clock signals to operate an electronic counter. The leading edges of the second train of pulses stops the

counter. For a given shaft speed, the counter total is then proportional to

the time displacement between the pulse trains, and thus is proportional to the

torque.

In the second type of optical torque sensor, two matched sectioned or segmented discs are mounted so that one is attached to the input end of the

torque shaft and the other to the output end of the shaft. Light sources and

photocells are arranged and the optical discs positioned so that the light

passing through the clear sectors of one disc is partially obscured by the

opaque sectors of the other disc. This provides a zero- torque quiescent

current. The application of torque will then vary the photocell current from

this quiescent level. The quiescent current can be adjusted so that the cell

output range is in the most linear portion of its characteristic range.

Table 12 shows a comparison of transduction elements commonly used in torque

sensors.

An additional technique which is sometimes employed to circumvent the

slip-ring problem in torque sensors is by the use of small radio-frequency,

telemetry transmitters mounted in the rotating member. Here the power source

for both the torque sensor and the transmitter must be entirely self-contained

and a suitable antenna provided for radiating the energy to a nearby receiving

antenna and receiver.

I 4-77
4.2.5.6 Application Considerations and Problems

In the preceding discussion of typical force and torque sensors, there is

brief mention of the accuracy to be expected from them. It is appropriate to

expand on this aspect of the ability to measure force and torque and on the

factors which limit accuracy. The accuracy of the system depends upon both the sensor and its associated instrumentation.

Nonlinearity Effects

In the conventional load cell, the load-supporting element is usually a column, loaded in compression. Within the elastic limit of the material, the

length of the element decreases linearly with the load. The cross-sectional

area increases in accordance with Poisson's ratio. Load cells are designed so that the compression of the supporting member is small compared to its length.

The strain gage bonded to its member also functions in its linear range. By

operating in this region, almost no nonlinearity is experienced. When larger

portions of the range of a sensor are used, the high end of the loading curve

is approached. Here a larger deformation results from each corresponding

loading increment. This nonlinearity of deformation accounts for the major

share of the load cell's nonlinearity. Strain gages mounted to the column will

exhibit similar nonlinear behavior themselves at large loads. In addition,

they will also be measuring the nonlinearity of column deformation. Special

load cells with a deviation curve close to +0.5 percent can be obtained.

Hysteresis Effect

Another factor affecting the accuracy of a sensor is hysteresis. This is

characterized by a sensor output which is not the same for identical values of

load, but depends upon whether the load is increasing or decreasing.

Hysteresis, the maximum separation between the full -range average hysteresis

loop and the calibration curve, for typical load cells, may vary between

+0.01 percent and +0.05 percent of full scale, but can be reduced if the

loading is applied in only one direction and the cell calibrated in the same direction.

Temperature Effects

A third factor affecting the accuracy of load cells is temperature, which causes two effects. The first is a change in output sensitivity due to a change in the modulus of elasticity of the load member. Nominal values for

this error are approximately 0.02 percent for a 1 °C change in temperature.

Second, temperature variations will cause unequal changes in the resistance

of the bridge arms, changes which can affect the no-load readings by

approximately 0.001 percent of full-scale output per 1 °C.

Temperature-compensating resistors are often added to the cell input

circuitry to compensate for this condition. The net thermal error can be

reduced to +0.001 percent of the applied load per 1 °C. Temperature transients

may also cause errors and extreme caution is required to keep them to a minimum.

Load Alignment Effects

Alignment of the load on the cell is another factor which can result in errors. The load cell can only measure the load component which is normal to

4-78
its base. Thus a misalignment of the force vector by 2.5° will result in a vector force normal to the sensor base which is 0.1 percent less than the force

desired to be measured (cos 2.5° = 0.999).

Repeatability and Dynamic Behavior

Repeatability of this type of load cell is approximately +0.01 percent of

the applied load, because the only moving part is the deformed load member.

It can be seen that load cells can be capable of greater accuracy than

most other types of sensors, largely because as a class they are very simple

mechanical systems. However, it should be noted that this is a static

accuracy. The dynamic behavior of load cells has received little attention and,

to the author's knowledge, there are no existing facilities for the dynamic

calibration of force sensors.

In general, one would expect their dynamic behavior to be not too

dissimilar to pressure sensors. That is, one would expect to find multiple

resonances and little damping. The section on dynamic calibrations (6.2.2)

should be consulted.

4-79
CL

OJ

CU

i~o

"O ft? CU £

t- > sz c

O" o o

CO <D 10

cu &- 0)

p

p ai f 3 3

to CO -P "O p cn 3 «3 o o c c CL CO co P Cn CD O) > 3 C S- S- -o >> O •!- A3 Q, CO a s- SCO •f— °r- * sz o o

°fTM r— o o o o o Q 00 Z _! CO a.

CO pc

ajE

0J UJco

co •«- S- P o o

CM CO 3 c -o

0) CO UJ 00 c

_J

CO CU S- <£ 3 1—

H- CT

S- <+_ O O

I— co

com

a.B©

CO

OJ

(0 pc>

-o 3

'o

CO

cusCOcoa>,c CO P O

CD -i— •!— S- S- P

cop o c •- C -i- o

<L! r—

X

©

crp

CD

C

J- CU

x: a» Cn U

•rX o

coCO

s-Q.

CO >,

S- -P

•r- 'r- 3 >

CT-r0) P Poc

CO

CUoQ

COcn

a.

cu >,

s- -p

•1— "I- 3 >

CT-rCU P

COd

at

co "O

cu •o cn o cn o 3

c3 a; Poc

to

CUoa

cu

co "O

CU o cn o cn o 3

J3 oc:

CUcr

(0On I

CU

"cuupCUc

cn

fO 2

4-80
4.2.5.7 Future Trends

Study of possible future trends in force or load sensors suggests the use of integral microcomputers to correct for nonl inearity and temperature effects,

combined with the use of semiconductor strain gages.

Exploration of other sensing principles will continue.

4.2.6 Level

4.2.6.1 Introduction

The discussion which follows is based largely on the chapter "Level" in

the ISA Transducer Compendium [8] and is concerned primarily with liquids.

The measurement and control of liquid level is probably the simplest and

oldest achievement in man's instrumentation progress. Level devices can be

found wherever there are vessels that require measurement or control of liquid

level. They range from the simplest toilet bowl float valve to sophisticated

systems used on spacecraft. Level devices may either sense the presence of the

level or measure the actual location of the level or surface.

Level devices are used frequently to control liquid levels at a specific

point within a narrow band, or to comply with a programmed demand. The success

or failure of a chemical process may depend upon the accurate control of two

immiscible liquids. Savings of valuable space and vessel costs are realized by

the accurate level control of boiler water programmed to steam demand.

Level devices are also used to maintain an inventory of stored liquids.

In this regard, the accuracy of measurement may represent considerable profit

or loss.

4.2.6.2 Materials Compatibility

The remarks made in this regard in section 3.5 in the chapter on pressure

apply here as well. The compatibility considerations generally apply to all

types of sensing systems and those parts (or components) of sensors which are

in direct contact with the measurand.

4.2.6.3 Units

Level is frequently only an intermediary, i.e., that indication from which

the desired measurand is inferred. A simple example is the familiar gas gage

of the automobile. It is a float device which sends an electrical signal

proportional to the level at which the float rides in the gasoline above the

bottom of the gas tank. The dashboard indicator reading converts that into,

basically, a fraction of the volume of gasoline still in the tank. Level is

measured in terms of length above a specified datum plane. As will be

indicated later, pressure is often used to indicate level.

4.2.6.4 Level Device Principles

Level devices are classified as either Direct Method or Inferential Method

instruments.

4-81
In the Direct Method, the actual physical position of the medium is sensed

or observed in relation to some datum point. The visual observation of level

in a gage glass, as measured by an "inch and foot" scale, is an example of

direct measurement.

In the Inferential Method, the physical position of the medium is implied

by the measurement of another variable that can be related to the actual level.

An example is a bubbler system as discussed in the section on head devices.

Level devices are more commonly classified by a common physical

characteristic as follows:

1. Visual Devices

Dip stick, hook gage, plumb bob and tape, open-end manometer, gage

cock and gage glass.

2. Float (Power) Devices

Floats connected by rod or tape to pointer and scale readout; rod or gear-driven switch mechanism; rod to magnetically actuated switches; rod

to a pneumatic amplifier (pilot), then to an indicator or a final control

element; or rod to hydraulically driven pointer.

Floats that travel up and down a center post and either make

electrical contact with a resistor wound on the center rod or are magnetically coupled to a tape and dial indicator.

3. Displacer Devices

Hollow cylinder or sphere connected through a packless pressure

barrier to a pneumatic amplifier (pilot), then to an indicator or a controller, an electrical switch, or a motor-driven tape.

4. Head Devices

Bubbler-pressure gage, direct connected pressure gage or differential

pressure detector, diaphragm box (entrapped air and pneumatically force

balanced), dip tube to fluidic element.

5. Electrical or Electronic Devices

Current through liquid-conduction, nuclear radiation, capacitance,

sonic or ultrasonic, thermistor, photoelectric, radio frequency.

This handbook is concerned primarily with sensors that produce an electrical output signal. Visual devices normally do not have an electrical

output. Float and displacer devices convert the level sensor into a displacement which is then transduced into an electrical signal, while

devices use pressure sensors to achieve the desired output. The large number

of level sensors falling under all of the above classifications are too

extensive for detailed coverage in this section. Readers are referred to the

technical literature for such coverage [8,9]. The following material is

intended to summarize some of the pertinent characteristics of commonly used

level sensors with electrical outputs.

4-82
4.2.6.5 Float and Displacer Devices

These two types of level sensors can provide an electrical output by the

use of displacement or force transduction elements. Except for the fact that

the actual displacements involved are usually very large, ranging from inches

to tens of feet, the characteristics of the displacement sensors are quite

similar to those used for other measurands. Tables 2, 3, and 4 show some of

the characteristics. In view of the large physical displacements involved,

speed of response tends to be slow. Absolute resolution is poor, although

resolution in terms of the full-scale ranges can be quite good. A discussion

of the characteristics of the sensing element follows.

In the float (power) sensor a hollow sphere is designed to float in the

liquid. The vertical motion of the float is translated to an external

rotational element through a bearing and stuffing tube. The rotational motion

can actuate a displacement sensor, such as a potentiometer or an electro-optical encoder. A variation has the float attached to a taut

perforated tape which turns a sprocket wheel, which actuates the displacement

sensor.

Floats connected to tapes are primarily used to indicate level over the

full range of depth of a container. Floats connected to tapes have been used

to measure level in vessels to a depth of over 70 feet. Float devices are used

where moving mechanical parts can be tolerated. Float devices are also well

suited for applications in which level changes are slow and subject to a minimum of perturbations.

Float-to-tape devices are generally used on atmospheric or low pressure

tanks and where temperatures are below 250 °F. Float-to-rod devices can be

used over wide pressure and temperature ranges. A typical high

temperature-pressure rating would be 600 °F and 800 psi

Corrosive media are handled by the selection of corrosion-resistive

metals, plastics, or elastometers in the manufacture of the wetted parts.

In general, float devices are simple and when properly applied and

maintained will provide many years of reliable service. Many new devices

appear on the market with novel techniques for coupling to switches or controls. Instead of sensing displacement, one can measure the force required

to keep the float in position to overcome changes in buoyancy or the liquid

caused by changes in level. Some devices use the force balance mechanism.

Displacement devices came into prominence in the late 1930's. It is

thought that over 80 percent of all process type level controls employ

displacement devices. They are offered by many companies. A wide variety of

innovations is noticeable, particularly in the packless mechanisms, the

transduction elements, and the materials of construction; however, the basic

design features are similar.

These devices are essentially steady-state sensors with long response

times.

4-83
4.2.6.6 Head or Pressure Devices

The approach is different depending on whether the liquid level to be

sensed is in an open (to ambient pressure) vessel or a closed one. For the

open vessel, a pressure indicator or sensor is connected either directly to the

lower level of the vessel or through an extension tube that transmits the

pressure exerted by the overhead liquid. The pressure device is calibrated in

level units. The relationship is simply pressure = liquid density x liquid

height above the point of measurement. It is obvious that density changes will

result in erroneous readout.

A pressure sensor connected to the lower section of a vessel is a very

direct and simple application. Such an installation is not suitable for media

that are either corrosive or contain solid particles. A buffer fluid between

the vessel connection and the pressure sensor connections is sometimes useful

for these conditions.

An air bubble device may be used to avoid the problems of directly

connected pressure devices. In this system air from a pressure source higher

than the maximum possible vessel head pressure is bubbled through a dip tube

resulting in a pressure buildup equal to the level head, because the excess air

is free to flow out of the bottom of the tube. Bubbler systems are subject to

clogging and air flow pressure drop errors due to operational faults.

The entrapped air diaphragm box may be used for media that are adversely

affected by bubbling air. The liquid overhead pressure acting on the flexible

diaphragm compresses the air entrapped in the connecting tube. The resultant

increased pressure is sensed by a pressure device calibrated in level units.

For a closed vessel, a differential pressure (D/P) sensor is connected to

a low level sensing point and to a point above the liquid in the vapor phase of

the vessel through a reference leg. This technique is used to cancel the

vessel pressure effect, because both sides of the D/P device are subject to the same pressure. The success of this technique depends upon the maintenance of a constant reference leg. One technique is to locate the D/P device above the

vessel and to provide a piping installation designed to avoid the accumulation

of either liquid or solid deposits in the reference leg. In a technique used

in a nuclear plant pressurized water vessel, the reference leg is filled with

water and is maintained at a fixed height, because steam will condense to keep

the condensate pot filled to the spillover level. This technique, like all

others, is subject to system errors that are best seen by an examination of the

equation describing the differential pressure to level relationships:

AP = P

2

- Pi where:

Ap - Differential pressure measured by the D/P device in psid.

?2 ~ Pressure exerted on the high side of the D/P device by the

reference leg R|_.

P-| -- Pressure exerted on the low side of the D/P device by the liquid

uncompensated vapor heads.

4-84
DRL • HRL

p l = DML • HML + D VL • HVL

W = DRL • HRL - (DML . Hml + DVL • HVL )

where:

Drl - density of the reference leg.

H RL " height of the reference leg.

Dml - density of the measurand leg.

H^l - height of the measurand leg.

Dy|_ - density of the uncompensated vapor leg.

Hvl - height of the uncompensated vapor leg.

From this relationship, various factors must be considered or the

operational variations from calibration values will result in errors.

The special considerations include:

(1) The density of the reference liquid will depend upon the temperature

gradient from the condensate pot to the detector. Vessel temperature

changes and the resultant gradient changes or reference leg ambient

changes will affect the reference leg density.

(2) The density of the measurand and the vapor leg will also vary with

vessel temperature and pressure changes.

(3) Sudden vessel pressure decreases may cause the reference leg liquid

to vaporize.

Other considerations pertaining to direct-connected pressure-type level sensors follow. Such devices are limited only by the vessel height because

they are available in pressure ranges from several inches of water to over

10 000 psi. The air bubbler systems may be limited by the air pressure

services available. An air supply of over about 120 psig is not commonly

available.

The diaphragm box is usually applied to low head systems of 10 to

20 feet of water, but can be applied to systems of up to 100 feet of water.

Reference leg differential pressure (D/P) systems can be used in systems

of up to many thousands of psi, but are often limited by the range availability

of industrial D/P devices—several inches of water to several hundred psid.

Despite the system design problems associated with the use of D/P detectors for

level sensing, it still remains a popular solution for systems at elevated

temperatures and pressures.

4.2.6.7 Electrical or Electronic Devices

Electrical or electronic level devices are characterized as sensors that

generally have no moving parts, wherein a change in level results in a change

in an electrical property such as current flow, capacitance, resistance,

voltage, or inductance. A brief discussion of some of these devices follows.

4-85
(1) Conductivity

A current-through-liquid conduction device operates on the principle that

the electrical path between a probe (electrode) and a conducting tank wall can

be completed by the medium contained in the tank. The consequent current flow

is used either to operate relays directly or solid-sta

Dte amplifiers that are used to operate final control elements.

This type of sensor is used for media that will not ignite by arcing and

that have resistivities less than 20 000 fi-cm. Two probes can be used either

for high and low level control or for narrow band control for media whose

surfaces are turbulent. A sensing system with a solid-state amplifier is used

for poorly conducting media with resistivities of up to 20 x 10° ft-cm. The

devices generally incorporate a sensitivity adjustment to accommodate one thousand to one or greater ratio of media resistivities. The current level in

the electronic systems is well within the safe limits prescribed for flammable

vapors. These devices are used primarily for control purposes with municipal

water systems, a variety of chemical solutions, and boiler feed water systems.

They are not proportional devices suitable for measurement of continuously

changing levels.

(2) Nuclear Radiation

There are several types of nuclear radiation devices that are currently

available. One consists of a gamma source (cesium 137, cobalt 60, or radium 226) located on one side of a tank, a detector located on the opposite

side of the tank, and electronic circuitry for signal conditioning and

indication. The intensity of the radiation received by the detector is

directly proportional to the source strength and the thickness of the materials

between the source and the detector. The gamma radiation absorbed by the

vessel walls is a constant that is cancelled by the circuitry. The gamma

absorption characteristics of the gas or vapor above the medium change the

amount of gamma radiation striking the detector. The detector consists of one

or more self -quenching Geiger-Muller detector tubes that convert incident

pulsed gamma energy into proportional pulsed direct current. The solid-state

circuitry associated with the detector provides for: regulated voltage

(required to bring the detector to its operating plateau of 800 to 1100 volts),

pulse shaping, integrating network (for averaging the statistical noise

inherent in the system), and an output amplifier that includes gain and zero adjustments. A typical output range would be from 0 to 10 mV to 0 to 50 mV.

Re-calibration may be necessary to account for half life of the radioactive

source.

Nuclear radiation devices were initially developed to measure difficult

media, i.e., highly viscous, or corrosive substances or media at high

pressures. These devices may now be economically applied to some routine

problems. These are also not proportional measurand devices.

(3) Capacitance

The capacitance level device consists basically of a large capacitor

formed by the tank and a metallic sensing element (probe), with the medium

(and/or gas or vapor) as the dielectric between the two metallic elements.

Changes in level change the capacitance of the tank-probe capacitor, which is a part of an oscillator circuit. For single point sensing or control, the

oscillator circuit is detuned when the level rises to the probe. The RF output

of the oscillator circuit is converted to a rectified voltage, which is

4-86
amplified and used to operate a relay or solid-state switch. If the medium has

a dielectric constant between 2 and 100, a bare metal rod insulated from the

tank can be used. If the medium is conducting, the probe must be insulated.

This is usually done with a plastic, elastomer, or ceramic coating over the

probe. An example is a plate type probe that senses the variable air

capacitance between the sensing plate and the medium surface. The circuitry

compares this capacitance with a reference capacitor in the sensing circuit.

The measurement accuracy of capacitance devices may be adversely affected

by conditions that change the dielectric constant of the medium such as temperature, entrained gases, or suspended solids.

Capacitance level devices are applicable for a wide variety of

media-water, jet fuel, ammonia, oil, paint, sewage, beer, gasoline, and a host

of other products. A suitable probe insulator does not appear to have been

found that will permit using a capacitance probe in high pressure water

service.

(4) Sonic and Ultrasonic

There are two basic types of sonic or ultrasonic level devices. One is

the acoustical loading, point-sensitive type with a sensor probe containing

a driver coil wound around a magnetostricti ve rod and powered by an ultrasonic

oscillator. The sensitive surface of the probe attached to the rod

acoustically propagates at an ultrasonic frequency only when the surface is

exposed to compressible medium (gas or vapor above the liquid). The sensor

probe also contains a pickup or signal coil wound around the rod that generates

a sympathetic ultrasonic signal. The signal is fed into a circuit that

triggers a relay or solid-state switch for indication or control. This occurs

when the medium contacts the sensitive probe and dampens its oscillation.

Devices of this type are available that operate at sonic frequencies as low as 120 Hz. Such devices are available with wet to dry signal ratios of 1000:1 and

a sensitivity of 0.002 inch of level change. They are not affected by changes

in dielectric constant, viscosity, temperature, resistivity, pressure, density,

clinging droplets, coating buildup, or foam.

The second type of sonar device can be used for continuous level sensing.

In this system a pulsed sound wave is generated and beamed to the target (the

medium interface). The sound wave bounces off the interface and is reflected

to the sensor's receiver. The device measures the time for the pulse to travel

from the transmitter to the receiver and provides a signal that is related to

level. Sonar devices are available with sensitivities of 0.01 inch per foot of

distance from the transmitter receiver to the level surface. The receivertransmitter head may be designed for locating at the bottom of the tank or at

the top of the tank. The accuracy of this device may be adversely affected by

changes in the density of either the liquid medium or the gas, which in turn

affects the speed of sound through the sound-carrying medium.

Sonic and ultrasonic devices have a range of applicability similar to that

of capacitance devices.

(5) Thermistor

The thermistor level device senses a point change through a change in

the resistance of a self-heated, probe tip mounted thermistor. This is due to

4-87
the ability of the medium to conduct heat away from the sensor probe as the

level rises to cover it. An ac voltage is impressed across the thermistor to

produce sel f -heating. Changes in ambient temperature around the probe are a source of error and must be compensated for in the design. A technique used to

eliminate a source of error employs a second thermistor that is not

self -heated, but which changes its resistance in response to temperature

changes. This resistance is used in the measuring circuit to cancel out the

effect of ambient temperature change. The circuitry consists of a differential

amplifier that compares the resistance at the self-heated thermistor to a set

point resistance selected with the sensitivity control potentiometer.

Since the thermistor is basically a temperature device, its accuracy will

be affected by those conditions that adversely affect the heat transfer rate of

the probe. The response time is also slower than other point-level devices but

is reported to be nominally one second.

Thermistor level devices are applicable to most media that will not

experience wide variations in temperature. Other temperature sensors such as thermocouples and resistance thermometers using similar techniques have been

applied successfully. Most recently silicon semiconductor sensors have become

available, using sel f -heating-induced resistance changes as indicators of the

presence or absence of liquids.

(6) Other Sensor Types

Similar in principle to sonic level sensing are techniques which use other

types of propagating waves. Optical light-sensing devices are used to seek the

location of interface levels using reflection or transmission of light.

Radio-frequency and microwave techniques have also been described in

applications whose opaque materials prevent optical sensing.

The characteristics of electrical and electronic devices discussed are summarized below.

Summary of Characteristics of Electrical and Electronic Level Sensors [8]

TABLE 13

Device Type

Point Sensing

Typical

Accuracy

Continuous Sensing

Typical Typical

Range Accuracy

psi

Typical Rating

Degrees F

Current probes +1/16 in

Nuclear radiation +1/8 in

Capacitance +1/8 in

Sonar

Ultrasonic better than 0.1 in

Thermistor +1 in

8-72 in

1 in-12 ft +2% FS

1-25 ft 2-3% FS 600 -40 to +350

1000 0 to 500

3000 15 to 300

500 400

-14 to +160 unlimited

1000 -100 to +450

4-88
4.2.6.8 Application Considerations

The calibration requirements influence the selection and use of level sensors to some extent. One can briefly summarize this.

Calibration of point level sensing devices used at low pressures and for

most media can be made with a gage glass or open end manometer, while the

calibration of continuous level sensing devices used at low pressure and for

most media can be made with a plumb bob and tape.

Calibration of sensing devices at elevated pressures and temperatures

requires special, and usually individual, treatment depending upon the medium

and the operating conditions. A typical solution to the calibration of a continuous device is to install high and low point sensors using a completely

different principle of operation.

In general, the electrical and particularly the electronic devices have

offered the greatest area for advancing the art in the past ten years. The

acceptance of new level devices is slow, particularly if the simpler and older

devices are working well. The pneumatic varieties require no special attention

in hazardous areas. New devices are making entry into industry primarily where

the media are difficult to measure or to accommodate a new overall plant system

(all electronics or computer). In addition, there has been some reluctance to

introduce new devices, because this would add to the training and stocking

burden of the user.

4.2.6.9 Future Trends

Future trends in level sensing are divided into two broad categories [70].

One involves the development of solid-state (no moving parts) sensors which

sense levels either discretely or continuously and all of which have electrical

outputs suitable for transmission to remote control centers. Various

techniques are now being researched, including electromagnetic, radar, and time

domain ref lectometry, focused and broad beam acoustics, and optical and laser

devices. It is also likely that there will be future developments of

electrochemical devices.

The second category will involve the incorporation of electronics

technology as an integral part of the system including analog signal

processing, digital logic, and microprocessor control to accomplish a number of

functions. These will include linearization, conversion (e.g., level to

volume; pressure to level, etc.), automatic calibration, multiple sensor array

switching, control, display, logging, and maintenance and fault diagnosis.

4.2.7 Humidity and Moisture

4.2.7.1 Introduction

The measurement of moisture in gas has in recent years become increasingly

important in industrial applications and in engineering research. In military

ATE applications, humidity (moisture) is primarily an environmental parameter

influencing device life and operation by way of corrosion. In certain

combustion-related applications, the moisture content of all combustible gases

influences the efficiency of burning. The following discussion is based,

4-89
largely, on the section "Humidity and Moisture" in the ISA Transducer

Compendium [8].

Humidity, in many cases, is measured with mechanical instruments designed

for this purpose a century ago. This discussion will focus on humidity sensing

devices with an electrical output, although mechanical hygrometry will be

discussed briefly in section 4.2.7.3 below.

4.2.7.2 General Considerations

The methods, devices, and instruments designed or proposed for determining

the water vapor content in a gas are legion. They range in complexity from

simple mechanical hygrometers that function through dimensional changes,

through the routine gas analysis apparatus of the gas chemist, to instruments

that measure one or more of the physical characteristics of a gas. It is from

this wide variety that a choice must be made for a particular application—a

choice that is governed by such factors as range, sensitivity, accuracy, cost,

portability, speed of response, commercial availability, continuous or intermittent operation, and indicating or recording operations.

4.2.7.3 Non-Electrical Hygrometers

It seems appropriate to briefly cover two non-electrical methods

(psychrorneters and mechanical hygrometers) since they are useful for the

environmental humidity measurements.

(1) Psychrometer

In its elemental form, the psychrometer is comprised of two thermometers.

The bulb of one thermometer is covered with a moistened wick and is referred to

as the "wet bulb"; the bulb of the other thermometer is left bare and is called

the "dry bulb." Evaporative cooling depresses the temperature of the wet-bulb

thermometer below that of the dry-bulb thermometer. From the wet and dry bulb

temperatures and the ambient pressure, the vapor pressure or relative humidity

can be determined.

The sling psychrometer, using two mercury-in-glass thermometers, is the common form of this instrument. Ventilation is obtained by swinging the

thermometers. Unventilated psychrorneters are unreliable and hence rarely used

for scientific, engineering, or technical work.

Among the factors influencing the performance and accuracy of the

psychrometric method are (a) the sensitivity, accuracy, and agreement in

reading of the thermometers, (b) the speed of air past the wet bulb

thermometer, (c) the incident radiation on the thermometers, (d) the size,

shape, material, and wetting of the wick, (e) the relative positions of the

wet and dry bulb thermometers, (f) the temperature of the water used to wet the

wick, and (g) the purity of the water.

The psychrometer is a simple, relatively inexpensive instrument which can

be used for either intermittent indication or continuous recording of wet and

dry bulb temperatures. Since it does not yield the moisture content of a gas

directly, computations must be made, or alternately, recourse must be had to

tables, charts, nomograms, or curves. These computational aids are available

only for water vapor-air mixtures.

4-90
The psychrometric method may be used over a dry bulb temperature range of

0 to 100 °C. At lower temperatures there is a marked decrease in sensitivity

and accuracy. In addition, there is an increase in lag due to the ice that

surrounds the wet bulb in place of the film of water. Over the range of

dry bulb temperatures of about 5 to 40 °C, it is possible to achieve an accuracy of about +2 percent relative humidity. Under normal operating

conditions, the accuracy is more apt to be of the order of +3 to 4 percent

relative humidity.

(2) Mechanical Hygrometer

Mechanical hygrometers are based on the fact that many hygroscopic

materials undergo dimensional changes with changes in ambient relative

humidity. These dimensional changes, through suitable simple lever systems,

may be made to actuate a pointer or move a pen across a chart. Instruments of

this type are known as mechanical hygrometers. Such materials as hair, cotton,

wool, silk, wood, goldbeater's skin, nylon, plastic, paper, and whalebone have

been used as the dimensionally variable humidity elements. Of these, hair is

probably the most widely used material.

The main virtues of the mechanical hygrometer are its simplicity of design

and construction and its low cost. It indicates relative humidity directly over a moderate range of temperatures. Its reliability decreases with

decreasing temperature. Its chief defects are a lack of stability under normal

conditions of use and appreciable hysteresis.

At best, the mechanical hygrometer has an accuracy of about +3 percent

relative humidity at room temperature under stable conditions. It has a time

lag of the order of minutes, so that with changing humidity the accuracy of

indication decreases. For optimum performance it should be re-calibrated at

frequent intervals.

(3) Dew-point Hygrometer

A principle that is basically mechanical but lends itself to electronic

control, with electrical output, is that of the dew-point hygrometer.

When water vapor is cooled, a temperature is reached at which condensation

occurs to liquid or solid. The dew-point method provides a convenient

technique for ascertaining this temperature. The procedure is to alter the

temperature, pressure, or volume of a water vapor-gas mixture in such a fashion

that condensation just occurs. The temperature at which condensation is

initiated, for a given pressure and volume, is defined as the dew-point

temperature.

Condensation may be detected by the appearance of dew or frost on a surface, usually a polished metallic mirror, or as a fog or cloud. By far the

most common method of inducing condensation is to lower the temperature of a mirror and to observe the condensation thereon by reflected or scattered

light. The formation of dew or frost on a mirror surface can be detected

visually, photoelectrically, or electrically through a change in surface

resistance.

In theory, the dew-point measurement is influenced by several factors

which are of such indeterminate nature as to make an estimate of the accuracy

difficult. It is not always possible to measure the temperature of the mirror

4-91
at the surface or to assure that no gradients exist across the surface. The

visual detection of the inception of condensation cannot be made with complete

assurance nor is it probable that two different observers can detect dew or frost at the same instant. The automatic photoelectric detection of the dew

point usually depends upon achieving an equilibrium condition on the mirror

surface during which the amount of dew or frost remains constant.

At temperatures below freezing, the initial formation of a condensate on a mirror may be either liquid or ice. Condensates of supercooled water have been

observed as low as -27 °C. At extremely low temperatures, the deposition of

frost assumes a glossy appearance which is difficult to detect visually.

The use of the dew-point method presupposes that no other component of the

gas mixture under test will preferentially deposit or condense before water

vapor and hence yield an erroneous answer. One decided advantage is that the

dew-point method may be used at high pressures.

4.2.7.4 Electrical Hygrometers

Instruments of this type consist of two parts: a humidity-responsive

resistor, the sensor, and an electrical or electronic circuit for detecting and

indicating the magnitude of the resistance of the sensor.

(1) Electrolytic Solution Sensor

The most common form of sensor is one in which an aqueous electrolytic

solution serves as the variable resistor. The electrical resistance of this

type of sensor is a function of the concentration of the solution, which in

turn is a function of the ambient relative humidity and temperature. The

solution can be applied directly to an impervious insulating surface on which

electrodes have been affixed. However, this combination is relatively unstable

so that frequent calibration is needed to assure accuracy of indication.

(2) Surface Resistivity Sensor

Another form of sensor utilizes the surface resistivity of selected

impervious materials like glass, porcelain, and plastics. Water is absorbed on the surface of these materials and retained by physical bonding forces, forming

a thin film whose thickness, and possibly continuity, is a function of relative

humidity. This film of moisture provides a leakage path for current flow.

There probably are minute quantities of soluble salts or gases present on the

surface which contribute to the conductivity of the film. The net effect is

that as the relative humidity changes from 0 to 100 percent, the surface

resistivity may decrease six or more decades. One interesting version of this sensor comprises an insulating surface on which a thin film of salt is

deposited under vacuum. A second version consists of a plastic surface

converted into a thin film of ion exchange resin.

(3) Volume Resistivity Sensor

In a manner analogous to the use of the variation with relative humidity

of the surface resistivity of impervious solids, the variation of the volume

resistivity of some porous materials can be used for humidity sensing. There

are many substances which absorb water vapor, but relatively few that do so with sufficient reversibility and reproducibility. Highly porous substances,

as, for example, underfired clays, natural fibers, and textiles have a high

capacity for moisture absorption. Water vapor diffuses and permeates into the

4-92
pores and capillaries of these substances, greatly affecting their volume

resistivities. Unfortunately, the porous nature of these materials, which

makes them so highly hygroscopic, often contributes undesirable characteristics

that seriously detract from their usefulness as sensors. For one, the time

involved for a porous material to reach equilibrium with change in relative

humidity is often excessively long. Then too, a porous material too often

possesses appreciable hysteresis and drift. In spite of their shortcomings,

porous solids find some application as sensors. Typical of this class of sensor are sintered ceramics, underfired clays, and plaster of Paris.

There is a class of electric hygrometer sensors that depends on dimensional changes to produce changes in resistance. Many materials change in

length or volume or both as they absorb or desorb water vapor. The classic

examples are hair, vegetable fibers, and wood. These materials are routinely

used in hygrometry to actuate mechanical systems that move pointers over dials

for indicating relative humidity, or operate switches in humidity control

systems. Dimensionally variable materials may be coated or impregnated with

conductive substances. The latter will expand and contract as the

humidity-sensitive material expands and contracts. By the proper choice of the

conductive substance, a measurable change in resistance is achieved. The most

successful version of this type of sensor is the so-called carbon film element.

It consists of an insulating base, with electrodes, which is coated with a mixture comprising a dimensionally variable plastic binder, carbon particles as

the conductive medium, a moisture retaining agent, and a nonionic dispersing

agent.

The electric hygrometer has certain features which make it useful for a wide variety of applications. The sensor is usually small and relatively

inexpensive, although the cost of the measuring circuit may not necessarily be

low. The indications are in terms of electrical quantities so that remote

indicating or recording is feasible. On the other hand, the electric

hygrometer is an empirical device that requires calibration. It has an appreciable temperature coefficient so that the calibration must cover a range

of temperatures and with each measurement with the hygrometer there must be an auxiliary temperature measurement. To a limited extent, circuitry can be

designed to correct or compensate for the temperature coefficient.

The performance of a sensor may be influenced by polarization, exposure

to fog, clouds, or saturated gas, and contamination of the sensitive surface.

Those sensors that use an aqueous solution without binder on an impervious

surface are inherently faster in response but less stable than the binder

type or the impregnated fiber, fabric or ceramic types. Of all the sensors,

those that depend on surface adsorption, like the salt film sensor, have the

fastest response, but to measure the high resistances of such sensors requires

special circuitry and handling. Sensors whose operation is based on volume

resistivity tend to be very sluggish in response and to exhibit hysteresis and

drift. The carbon element usually displays a "hump" or reversal in its

relative humidity-versus-resi stance characteristics which makes it bi -valued in

relative humidity at high resistances.

(4) Thermal Conductivity Sensor

Another approach to humidity sensing with an electrical output uses a thermal -conductivity bridge. A change in thermal conductivity with composition

4-93
is used as the measure of the relative proportion of one component of a binary

gas mixture. A typical apparatus involves the use of two concentric cylinders

in a cell, one heated and the other maintained at constant temperature. If the

design is such that radiation and convection are eliminated, then the rate. of

heat transfer from the hot to the cold cylinder will be proportional to the

thermal conductivity of the gas in the space between the two cylinders. The

inner cylinder is normally a heated wire whose resistance varies with its

temperature and whose temperature, in turn, varies with the rate of heat

transfer to the outer cylinder, which usually is the wall of the cell. If two

cells, one filled with an invariant reference gas and the other with the test

gas, are arranged in opposite arms of a Wheatstone bridge circuit, the bridge

output will yield the percentage composition of the binary gas mixture.

Further, if the binary mixture consists of water vapor and a dry gas, then the

reference cell can be filled with the dry gas, the test cell with the mixture,

and the output will be a function of the water vapor content.

The method has the obvious advantage of giving a continuous indication or recording of moisture content. It is limited by the fact that it is not

specific for water vapor but indicates any change of composition of the gas

entering the instrument. Then too, slight changes in physical dimensions of

the cells, oxidation of the inner surfaces, and changes in wire resistance

contribute to drift and instability in indication and lack of reproducibility

in calibration.

(5) Refractive Hygrometer

A more sophisticated and complex approach to humidity sensing by

electronic means involves refractive hygrometers.

The refractive hygrometer utilizes the change in refractive index with

change in water vapor concentration to measure the moisture content of a gas.

The refractive index of a gas is defined as the ratio of the velocity of a given radiation (i.e., radiation of a given frequency) in vacuo to that of the same radiation in the gas. Since the velocity of electromagnetic radiation in vacuo is constant, only the velocity in the gas needs to be measured. The

latter can be accomplished by measuring either wavelength or frequency, keeping

the other constant and using the relationship Vg = fx. Radiation at optical,

radio, or microwave frequencies may be used. At optical radiation, wavelength

is measured. At radio and microwave frequencies, wavelength is usually fixed

and the refractive index of the gas is allowed to determine the frequency

of radiation measured as the resonance frequency of a circuit or cavity.

At radio frequencies, a small capacitor is used in the resonant circuit of

a variable oscillator. Changes in refractive index, and hence in dielectric

constant, are reflected as changes in the resonance frequency of the circuit.

The variable frequency is compared with a reference frequency and the small

difference is detected, measured, and related to vapor pressure.

At microwave frequencies, two identical cavity resonators are employed.

Into one of these cavities, the test sample is introduced, into the other, dry

gas. The resulting difference in resonance frequency between the cavities is

then a measure of the vapor pressure.

4-94
The refractive hygrometer is capable of detecting the vapor pressure with

high sensitivity. By using an appropriate servo system, the instrument may be

made completely automatic and recording, with a speed of response limited only

by the flushing time and the lags in the electronic and recording devices. Its

basic limitation arises from the fact that it may be used only with binary gas

mixtures, for it does not uniquely distinguish changes in water vapor content

from changes in content of other vapors or gases.

(6) Electrolysis Humidity Sensor

Yet another type of humidity sensor uses electrolysis.

Water is electrolyzed into gaseous oxygen and hydrogen by the application

of a voltage in excess of the thermodynamic decomposition voltage, that is, more than 2 volts. The mass of water electrolyzed per unit time is directly

related to the electrolysis current by Faraday's law. Thus it can be shown

that the current flow is directly proportional to the volume ratio of water

vapor to air and to the mass flow of gas. Therefore, given a constant mass

flow rate, the current uniquely determines the water vapor concentration.

The electrolytic hygrometer continuously and quantitatively electrolyzes

the water vapor content of water vapor-gas mixture and indicates its magnitude.

It does this by maintaining a constant mass flow rate of the test gas through a electrolysis cell. Within the cell, the water vapor is adsorbed by partially

hydra ted phosphorus pentoxide. Voltage is applied to spirally wound platinum

wires embedded in the absorbent, and the electrolysis current is measured.

At a pressure of 760 mm Hg and a temperature of 25 °C, a flow rate of

100 cm3 /min results in an instrument sensitivity of 13.2 MA/ppm. Vapor

concentrations of 1 ppm can be detected. The commercial instrument normally

has scale ranges of 10 to 1000 ppm, although with special techniques, higher

concentrations can also be measured.

It is claimed that the instrument has an accuracy of 5 percent of the

indication from 1 to 1000 ppm. It is relatively slow in response and requires

long and continuous flushing with extremely dry gas before low vapor

concentrations can be reliably determined.

There are other, less commonly used, methods for sensing humidity or moisture content of gases. More detailed information on all methods of

moisture measurements can be found in the literature [9].

4.2.7.5 Application Considerations

As is evident from the discussion above, there are many different ways of

measuring the moisture content of gases. Some are very complicated, others are simple but less accurate or reliable. In the selection of a sensor, the

overall performance required must be carefully considered. It may be more

practical, in the long run, to select a simple, although potentially less

accurate method, possibly with a second sensor for redundancy, over a more sophisticated system.

In any case for most ATE applications, humidity is probably just an environmental parameter which needs only to be measured with moderate

accuracy.

4-95
4.2.7.6 Current Problems and Future Trends

Problems with humidity and moisture sensors can be summarized briefly:

their dynamic response tends to be slow; their performance at low temperatures

is not always adequate; they are generally quite temperature-sensitive; and

their calibration characteristics change with time.

A variety of sensing principles are under continuing investigation. Solidstate sensors of monolythic construction using a variable impedance

transduction element with integral temperature sensor appear promising, as do

piezoelectric devices in which absorbed moisture changes the resonant frequency

of a crystal [71].

4.2.8 Other Measurands

In addition to the measurands discussed in some detail earlier in this

handbook, there are some others which may play growing roles in future military

ATE systems. Some of them are essentially physical parameters like

concentration, viscosity, or density; others are of a chemical nature like ph

level, oxygen content, or salinity. Sensors with electrical output do not

exist in some cases or are only experimental at present. The measurement of

many of these parameters is treated with reference to industrial (process

industry) applications in a publication such as the "Handbook of Applied

Instrumentation" [15]. Finally, it is somewhat desirable to monitor other

parameters which require very specialized instrumentation techniques. This

includes the detection of cracks in components and materials, the detection of

leaks, and of corrosion and fouling. Discussion of most of these is beyond the

scope of this present volume. Some areas, pertinent to military ATE system

applications, are discussed briefly in the following section.

4.2.8.1 Wear

"Wear" is not a measurand as such, but it is one of the most important

characteristics of any operating mechanism, vehicle, and propulsion system.

One of the primary functions of ATE for such systems is to ascertain "wear," to

anticipate malfunction or failure, and to indicate remedial action required.

Many factors determine "wear" including equipment design, material

selection, operational parameters, environment, and others. A great body of

detailed knowledge has been accumulated and is available in the literature.

For the purposes of this handbook, it seems instructive to refer to a recent

article on "Materials Selection for Wear Resistance" [16], which contains a table of typical wear monitoring techniques. This table, which follows, is a state-of-the-art summary. It is clear that while sensors can be used to

ascertain some of the characteristics, analytical laboratory techniques are required for others. A case in point is the analysis of lubricating oil.

4.2.8.2 Lubricating Oil Analysis

An important area of concern in the operational life and maintainability

of military prime movers lies in the characteristics of the lubricating oils of

turbines and internal combustion engines. Future military ATE systems for

ships and other vehicles are likely to require the development of special

4-96
sensors which can respond to these physical and chemical properties of the

lubricants.

At present, analytical methods are generally used to monitor used marine

circulating oils to detect contamination and oxidation and to determine the

effectiveness of shipboard purification practices [17]. In turbine service,

water contamination may be present but significant quantities of dirt and wear

metal are seldom evident. In diesel engines, on the other hand, it is possible

to find water, fuel, soot, cylinder lubricant residues, dirt, and system metal.

The reference [17] describes some of the test procedures used to examine the

lubricating oils and thereby to assess the condition of the prime mover and the

location of any source of impending trouble. Tests include appearance and

odor, water content, density, flash point, viscosity, and the amount of

insolubles present; graphic analysis has also been used on oil samples to

attempt to assess the degree and source of contamination.

An approach to the analysis of bearing performance through the examination

of wear particles from rear axle bearings of vehicles is described [18]. In this case an electron microscope and a scanning electron microscope (SEM) were

used on particles extracted from a sample of rear axle lubricants. While the

data indicate the methods to be useful in locating the wear particles, the

report states "...no attempt is made to explain the mechanism of wear."

4-97
TABLE 14

Typical Wear Monitoring Techniques

Method Remarks

Techniques dependent on effects of wear

Temperature changes

Vibration

Optical

"Kurtosis 1

Operation analysis

Measurement of temperature changes between a moving surface and its surroundings; a rise

may indicate increased wear.

Increase in vibration follows increased

clearances due to wear; e.g. the use of

accelerometers or vibration analysis with

numerical readout can automate techniques.

Spatial measurement (often incorporating

holography) can be applied in some cases using

special ports built into machinery.

Advanced form of noise and vibrational

analysis where the output over a range of

frequencies is compared with recordings from

the prior history of the equipment;

significant changes occur as wear proceeds.

Changes in torque, blowby, fuel consumption or exhaust gas analysis may be symptomatic of wear (but can also have other causes).

Techniques dependent on wear products

Spectrographs oil analysis

to particles

Can incorporate activation analysis, atomic

absorption etc. as analysis method, regular

samplings and analyses are made and increases

in metal build-up in oil can be related to wear.

Magnetic chip detection

Ferrography

Thin-layer activation analysis

Small magnets collect ferrous metal chips from

the oil pipline and are periodically removed

and inspected; can be automated.

A sample of oil from the sump is diluted and

magnetically separated over an inclined plane;

metal lographic examination of debris can

reveal the amount and type of wear.

Part of the wearing surface is exposed to

beams from a linear accelerator; induced

radioactivity (which is kept to small levels) can be used to measure wear.

4-98
5. DATA ACQUISITION AND SIGNAL CONDITIONING

5.1 General Considerations

Although this is a Sensor Handbook, addressing sensor considerations in

ATE Systems, the sensor cannot stand alone. The sensor is an important

component of a Data Acquisition System (DAS), and while it may be the most

critical and yet weakest link of such a system, it is appropriate to briefly

discuss some of the other components of Data Acquisition Systems.

The following discussion of such systems is extracted, with permission,

from "How to Configure a Data Acquisition System" by S. Kent Morgan [19].

The task of configuring such a system is difficult, with a vast selection

of available hardware, an often confusing set of terminology, and the

inevitable challenge of optimizing the performance /cost ratio for a specific

appl ication.

No two DAS users have exactly the same requirement. A DAS specifically

configured to meet today's measurement needs can be obsolete tomorrow if it has

inadequate flexibility. Therefore, a prime consideration for the DAS is growth

capability for future needs.

In the case of ATE Systems, two major factors will influence the selection

of data acquisition systems. One is the need for a number of measurements of

the desired parameters of the Unit-Under-Test (UUT). Second is the need for

acquired data to be processed by means of a computer programmed to achieve the

objectives of the ATE in an optimum manner.

The trends toward computer entry and processing of data, greater

automation, and improved data accuracy have led to digital DAS for dynamic as well as static data. A digital DAS is basically a system involving one or several analog- to-digital converters, and in the case of multi -channel inputs,

circuitry for multiplexing, i.e., time-sampling the channels. Such a system is

often referred to as a pulse-code-modulation (PCM) system, since the analog

information is converted into an array of pulses. The location within the

chosen time frame of a given pulse, pulse-position-modulation (PPM), or the

pulse length, pulse-duration-modulation (PDM) represent quantitative values of

instantaneous samples of the analog signal.

A pulse-code-modulation multiplex DAS can be thought of as a sophisticated

data logger; it is also a time division multiplex system. In time division

multiplex (TDM), the various measurands are sampled in time sequence, and the

pulse-coded data for all measurements transmitted sequentially over the same transmission lines. Such a system offers high throughput capability as well as flexibility in sampling rates and sampling sequences; the operating parameters

of each element can be under computer control, offering "hands off" flexibility

in reconfiguring the system between tests and even during testing.

A major reason for using a PCM DAS system is that a considerable

improvement in data accuracy can be realized over instrumentation recorders or frequency division multiplex (FDM) techniques. (In FDM each measurand is

transmitted at a different frequency, modulated by the measurand 's dynamic

5-1
frequency.) This technique requires complex demodulators (discriminators) with

potential stability and linearity problems.

Once the input signals have been digitized, the PCM serial bit stream is

essentially immune from noise in the instrumentation or transmission systems.

With 10- , 12- and even 14-bit encoding available, system accuracies of better

than 0.1 percent can be achieved for dynamic as well as static data. Note that

such accuracy claims can be made, and verified, only for the electrical signal

portion of the DAS. The error contribution of the sensor is the subject of

much of this handbook.

Another advantage of the digital approach is that it is most amenable to computer control. This approach can provide a rapid and efficient means of

reconfiguring the system for different test requirements.

It should be noted that such digital systems will probably require an intermediate analog signal conditioner (amplifier) between the sensor

(basically an analog device) and the digital data processing components of the

DAS.

In the selection of the DAS, ten basic questions need to be answered; all or most of these need also be addressed in the selection of system components,

including the sensor. The particular factors to be considered in regards to sensors form the major portion of this handbook. The questions and factors are summarized in table 15.

5-2
TABLE 15

Considerations in Selecting

Data Acquisition Systems and Components

Questions

1. What , are the given system inputs?

2. What are the desired system outputs?

3. What are the system environments?

4. What is the useful life goal?

5. What are current budget constraints?

6. What is the total useful life cost?

7. What are availability goals?

8. What data processing is required?

9. What system configuration changes are required?

10. What expansion capability is required?

Factors

Type, quantity, duration, signal level,

bandwidth, dynamic range.

Type, quantity, accuracy, format, display,

storage.

Thermal, mechanical, electromagnetic

interference, portability, meteorological.

Life span, duty cycle, environment,

mission profile.

Capital funds, program funds, lease or buy,

make or buy.

Initial cost, operational cost, maintenance

cost, down-time cost, expansion cost.

Mean Time Between Failures (MTBF),

Mean Time to Repair (MTTR), vendor vs in-house maintenance, required spares

inventory.

Real-time, off-line, arithmetic, monitor

and alarm, compression, display, storage.

Degree, frequency, turnaround time,

automation, adaptive.

Input: quantity, level, bandwidth, range.

Output: quantity, display, storage.

5-3
The answers to these ten questions describe what the system has to do; it is

then up to the designer to determine how to arrive at the best mix of hardware,

software, and systems integration to meet his requirement.

5.1.1 Data Acquisition System (DAS) Parameters

Once the general system has been defined, the next step is to quantify the

following system parameters:

1. Number of channels

2. Data bandwidth per channel

3. Test event duration

4. Required dynamic range

5. Total system accuracy.

The (data bandwidth x number of channels) - product provides a quantitative measure of the system speed. In sampled data systems, such as the

data logger or PCM multiplex described above, the system speed is generally

expressed in terms of the (sampling rate of each channel x the number of

channels) - product. This product is called the system "throughput rate." As

the system throughput rate increases, the cost per channel also increases.

The event duration for a specific test may last from milliseconds to

years. For short-term transient testing, data are often recorded on analog

tape or stored in a digital memory for subsequent playback, processing, and

display. Long-term data, such as operation or mission history, are usually

recorded on digital cassette tapes at timed intervals and collected on a periodic (e.g., quarterly) basis for processing. Between these two extremes,

the more typical application involves real-time monitoring and quick-look

display of events lasting up to an hour, with off-line processing and analysis

performed within a one-day turnaround time.

In recent years, the ability to gather large volumes of raw data has

exceeded the capability to fully process these data. As a result,

instrumentation engineers may be inundated with stacks of computer

printouts and cabinets filled with magnetic tapes. In some cases these data

are required for archival retrieval purposes. In many cases the data volume

could be reduced significantly through the use of data compression techniques.

Caution must be used, however, to avoid loss of significant information. In configuring the processing portion of the DAS, the design engineer must

consider carefully the volume of expected data.

"Dynamic range" and "accuracy" are often confused, but there is a definite

distinction. "Dynamic range" refers to the ratio of the maximum input signal

for which the system is useful, to the noise floor of the system. The

"accuracy" figure for a system is impacted by the noise floor, nonlinearity

,

temperature, time and power supply instabilities, crosstalk, etc. In selecting

an 8-, 10- or 12-bit analog-to-digital converter (ADC), the design engineer

must not assume that the system accuracy will necessarily be determined by the

resolution of the encoders; i.e., 0.4 percent, 0.1 percent and 0.025 percent,

respectively. In fact, if the sensor or the signal conditioning equipment

preceding the ADC is limited to 1 percent full-scale accuracy, for example, no significant benefits are gained by utilizing a 10- or 12-bit system over using

aji 8-bit system and suppressing the least significant bit.

5-4
Although the cost of increasing the dynamic range of a system is

often relatively modest, the cost of achieving comparable "accuracy" may

become progressively prohibitive.

In discussing the selection of the components of a DAS system, the

reference cited [19] makes an important statement in regard to sensors. It is

quoted below to emphasize the basic goal of the Sensor Handbook: to enable

careful selection of the optimum sensor for its mission, optimum being adequate

in every sense.

5.1.2 Sensors

"The importance of selecting the right sensor cannot be overemphasized.

You can spend $100 000 to obtain a high-quality, 0.01 percent accuracy DAS that

is a complete overkill if the sensor accuracy is only +5 percent.

"Although 90 percent of all sensors employed in data acquisition are either strain gage, thermocouple, or resistance devices, it is still necessary

for the design engineer to be familiar with other sensor types. These sensors

are described in the general technical literature; additionally, transducer

manufacturers publish a large body of specifications as well as some application literature. Essential as the fundamental theory of sensor

operation is, it is also necessary to know how to install, cable, terminate,

and calibrate these devices. There is definitely an art to their proper

implementation in a physical system.

"Despite the quest for the 'Universal Digital Sensor,' it just has not

been discovered and is not likely to become an economic reality in the next few

years. Although all of the elements required for this digital sensor exist in

separate chip form, it remains for the semiconductor people to put it all

together. The technology certainly exists to do this, but the non-recurring

investment to develop the extremely large number of different sensors required

vs the number of sensors purchased each year does not now make this a viable

investment. Therefore, for the foreseeable future, the design engineer must

interface with conventional sensors."

5.1.3 Signal Conditioning

In order to convert the sensor output to a signal suitable for further

processing, signal conditioning is required to provide:

1. Excitation

2. Completion networks

3. Calibration

4. Amplification

5. Filtering

With the exception of sel f -generating elements such as thermocouples, most

sensors require some form of excitation. This is generally in the form of a constant voltage or constant current source and can be either dc or ac depending on the particular sensor. Although constant voltage excitation has

certainly been the most popular for strain gage excitation, constant current

excitation offers advantages in transfer function linearity. DC excitation

usually provides acceptable excitation accuracy, but where long leads are 5-5
involved and dc offsets are anticipated, the use of ac excitation can provide

improved accuracy.

Completion networks are passive components, external to the sensor, which

complete the electrical network to form a complete bridge to enhance signal

conditioners. They provide the user with flexibility in selecting different

types of sensors. For instance, the user can change the completion networks to

accommodate one, two, or four active arms in a strain gage network. For

maximum flexibility, these completion networks should be on plug-in cards, to

facilitate system changes.

Some form of system calibration is mandatory in most DAS. In addition to

providing at least two-point calibration for system drift correction, the

calibration feature provides verification of proper system operation before,

during, and after a test event. Many types of calibration are available,

ranging from simple, manual, zero, and full-scale calibration to automatic zero

and automatic gain correction within the signal conditioning unit. Although

the linearity of state-of-the-art amplifiers is typically as good as the

tolerance of the calibration resistors, multi -point calibration is still

desirable to provide positive assurance that the entire electrical system is

operating properly over its full dynamic range.

It should be emphasized that these calibrations do not include the sensor.

At best, the transduction element is included, for example in a "shunt"

calibration. A complete end-to-end system calibration, from measured to final

output, is the only valid system verification. This is discussed more fully in

later sections.

The output of most sensors is in the order of millivolts and amplification

may be required to raise the signal amplitude to a level suitable for further

processing. Additionally, because the common-mode electrical interference may

be much higher than the desired signal level, differential input amplifiers are often essential. One of the most difficult things for the engineer to

determine is exactly how large the common mode environment will be in the final

system installation. Values may range from 1 V to 150 V peak, usually

60 Hz ac, while some special applications may run as high as a few thousand

vol ts.

From a cost standpoint, there is a significant crossover point for common mode voltages greater than the power supply voltage of the amplifier. This is

typically +15 V and falls in the middle of the normal commond mode bounds.

Unfortunately, even if the common mode voltage is just slightly greater than

the specified level (e.g., 20 V), this can render the amplifier quite useless.

Therefore, if a marginal condition is anticipated, the prudent designer will

select the higher common mode capability.

In straight analog DAS, filtering at the output of the signal conditioner

is sometimes employed to band limit the required signals. In digital sampleddata systems where broadband data are encountered, presampling filters (PSF)

should be used ahead of the multiplexer to limit the maximum signal frequency

to the minimum necessary for adequate definition of the measurand. This helps

to reduce aliasing errors, which occur when the measurand is sampled at too low

a rate relative to the highest signal frequency to permit the signal to be

accurately reproduced by the sampled data.

5-6
The importance of aliasing errors in a system is often underestimated by users not familiar with sampled data systems. It can be shown when considering

aliasing error with sampling frequency for various low-pass filters that even when sampling at five samples per data cycle, a five-pole low-pass output

filter is required to achieve less than 1 percent rms aliasing error for a sinusoidal signal. Note that this error is independent of the number of bits

of encoding by the ADC.

5.1.4 Multiplexing and Anal og-to-Di gi tal Conversion (ADC)

In selecting a multiplexer /ADC, the designer can choose from either

low level or high level multiplexer systems. Using differential switching, the

low level system samples the analog inputs and presents these signals to a single programmable-gain amplifier prior to digital conversion. The high level

multiplexer utilizes a single amplifier for each channel to raise the signal

level prior to high level single-ended analog multiplexing and digital

conversion.

Since the low level approach requires only one amplifier, it enjoys a considerable cost advantage over the high level approach. However, the

low level approach has disadvantages, such as a limit on throughput rate. In switching from a high to low input signal, the multiplexer and the programmable

gain amplifier must be given time to allow switching transients to settle out.

For a system with wide-range gain control, the throughput rate is typically

limited to about 10 000 samples-per-second (sps). With a single amplifier per

channel, the rate can exceed 1 000 000 sps.

Although active filters can be used for low level inputs, they must be

correctly leveled, offset, or dc-decoupled. If this is not done, active

devices can introduce unacceptable dc errors at low level inputs. The

presampling filters used in many low level multiplexers are passive.

Practically, this limits the input filter to a two-pole configuration which

requires a normalized sampling rate of 30 times the data rate to ensure less

than 1 percent aliasing error with broadband noise. A DAS system with a 10 kHz

throughput rate and 100 channels would have a maximum data rate of 3.3 Hz per

channel. Other disadvantages of the low level approach are that failure of the

programmable amplifier results in complete system failure; also, an overload on one channel can cause errors on sequential channels until the amplifier

recovers.

5.1.5 Sample Rate

"How fast do I really need to sample?" is probably the most frequently

asked question by users of digital DAS. Nyquist's well known theorem, often

quoted and usually misused, states that an ideally bandlimited signal can be

perfectly reconstructed from samples taken at a uniform rate equal to or greater than twice the highest signal frequency. Unfortunately, ideally

bandlimited signals are rather hard to come by in practical applications. If

ideal "boxcar" filters (filters with flat amplitude and linear phase response,

and with infinite attenuation at frequencies beyond the design filter limits),

are not used in a system using a sampling rate of twice the highest signal

frequency, sidebands created by the sampling process will overlap, producing

aliasing errors.

5-7
A "boxcar" filter can be represented by a presampling filter with an infinite number of poles. However, for practically realizable filters, there

is a direct tradeoff between the number of poles required and the minimum

sampling rate required for a constant error. For example, to achieve less than

1 percent aliasing error, a system using presampling filters with two, three,

or five poles must be sampled at about thirty, ten, and five samples per data

cycle, respectively.

If a particular physical phenomenon has a natural bandlimiting roll off,

this effect can be added to the presampling filter roll off to achieve the net

overall effect. If a phenomenon has a natural roll off of 12 dB per octave

above the highest frequency, a three-pole filter with a similar cutoff will

give the overall effect of a five-pole filter. As a general rule of thumb, the

five-times per cycle sampling rate with a five-pole filter yielding less than

1 percent aliasing error is a good guideline. Filter design is a sophisticated

subject and the examples are given only as approximations for discussion

purposes. Obviously, if the bandwidth and sampling rate capabilities are available, the higher sampling rates should be utilized.

It is an unusual system in which all channels have identical data

bandwidths, thus requiring identical sampling rates. Typically, there may be a wide disparity between the highest- and lowest-frequency channels of the

system. In order to accommodate these efficiently, faster commutation rates

and slower subcommutation can be used for those channels which are higher or lower, respectively, than the average rate.

5.1.6 Bit Rate and Data Resolutions

In selecting the number of bits of encoding, a reduced quantization error

(i.e., greater resolution) must be weighed against the resultant higher cost

and lower speed. If the signal to the multiplexer/ADC can be kept near the

rated full-scale input by the preceding signal conditioner/amplifier circuits,

the quantization error is merely +1/2 of the least significant bit (LSB) or

1 part in 2 times 2m where m is the number of bits. However, if the actual

signal is only 1/8 of full scale, the resultant quantization error has the same impact as a +2-bit error on a full-scale signal.

A common problem in strain gage systems is one of a relatively small

dynamic signal of interest superimposed on a large static offset. If the

signal conditioning amplifier does not have programmable offset, the ADC must

have additional resolution to yield a quantization error equivalent to full

scale. For example, with a design full-scale input of +5 V, a 10-bit ADC

operating with up to +3.75 V compensated offset and only +1.25 V of dynamic

signal is equivalent to a 12-bit unit operating at +5 full scale with no offset

compensation.

As noted before, ADC resolution is not the same as system accuracy, but

most ADC manufacturers try to keep the ADC accuracy consistent with the ADC

resolution. From a practical standpoint, 10 to 12 bits ought to be adequate

for most applications, where errors of +1 LSB represent +0.1 percent to

+0.024 percent of full scale, respectively. Eight-bit ADC's may be adequate

Tor quick-look or high speed systems, while 14 bits (and greater) are typically

reserved for slow-speed or wide-dynamic-range systems. The ADC has a limit for

throughput which is usually specified in terms of conversion time. Exceeding

5-8
the throughput rate of the ADC is obviously to be avoided. Generally, for a given cost, the greater the number of bits, the slower the ADC. For a given

throughput rate, the cost of the ADC may increase nonli nearly with the number

of bits.

Although a multiplexer/ADC may indeed have a +1/2 LSB accuracy with static

inputs and low throughput rates, the absolute accuracy of any system will be

degraded with dynamic input signal and higher throughput rates. For example,

multiplexers using solid-state switching have a number of dynamic error sources

that increase with throughput rate, including:

1. Turn on/turn off time of multiplexing switches.

2. "Pump back" or charge injection into the input signal path.

3. Multiplexer settling time.

4. Output amplifier settling time.

5. Cross-talk between channels.

5.1.7 Sample and Hold

In most multiplex/ADC systems, a sample-and-hold circuit is used at the

output of the multiplexer buffer amplifier to store the output of one channel

while the multiplexer is sequencing to the next channel. The sample-and-hold

module also has time-sensitive errors which include:

1. Sample-to-hold errors, including aperture time uncertainties and

settling time errors, and

2. Hold-to-sample errors, including acquisition and settling time

uncertainties.

3. The change of input signal with time in the "hold" mode.

These errors can become significant as the throughput rate increases, since

each of these times is a fixed value for a specific module.

The sequential sampling of channels in the DAS will result in a definite,

but predictable, time skew of the sampled values of different channels. This

may be negligible in many cases, but for systems in which accurate time

correlation between channels is important (such as for phase relationships

between vibration channels), simultaneous sample-and-hold's can be inserted

between the presampling filter and the multiplexer. These sample-and-hold's,

operating from a common command circuit, will provide a simultaneous sample of

all channels at the frame rate of the multiplexer. Although time deskewing can

be performed offline using a computer system, the hardware sample-and-hold

provides a straight-forward, real-time solution to time correlation.

5.1.8 Transmission Media

The physical location of the DAS is seldom identical to that of the data

reduction system. The previous discussions have assumed that a serial

communication link over a single conductor pair is required. For distances up

to a few hundred feet, a parallel link using a multiconductor bus structure may

be used between the acquisition and reduction systems. Although there have

been a myriad of different bus structures, recently three standards have

emerged: the CAMAC, the IEEE-488 bus (HPIB-HP, GPIB-Tektronix ), and ARINC 429

(MIL-STD-1533). The IEEE-488 appears to have the greatest potential for

5-9
universal acceptance. Although originally conceived as a common communication

link between instruments, this bus can also serve for setup and control as well

as the transmission of acquired data from one subsystem to another.

For relatively short, fixed-point communication links of up to a mile or

so, either twisted-shielded pair or coaxial cable is generally used. The

bandwidth and signal-to-noise ratio over relatively short lengths are extremely

good. For greater distances, the signal losses and high-frequency attenuation

as well as installation costs become quite significant. For longer distances,

either an RF link or telephone link is required. Because both of these systems

are bandlimited carrier systems, some form of modulator/demodulator (MODEM) is

necessary.

All of the transmission media listed add some noise and distortion to the

transmitted signal. For relatively slow data rates with a limited number of

channels, the degradation in an analog transmission scheme such as FM may not

be significant. For large systems with high data rates, the natural noise

immunity of digital transmission techniques is unquestionably superior. In any

event, the designer must determine the key characteristics of the transmission

media prior to configuring the system. These include bandwidth, distortion,

noise, and dynamic range. The fundamental limiting parameters for any

transmission link are available bandwidth and practical transmission distances.

Typical limiting parameters appear below.

Medi urn Typical Distance Bandwidth

Parallel Bus 50 feet 250 kilobits/s

Twisted-Pair 1000 feet 100 kilobits/s

Coaxial Cable 1 mile 10 megabits/s

Fiber Optic Cable Several Miles 10 megabits/s

The last-named is commercially available, at reasonable cost, and immune to

electrical and electromagnetic interference.

5.1.9 Demultiplexing

At the receiving end of the transmission link, data channels using

frequency division multiplexing (FDM) or time division multiplexing (TDM) must

be demultiplexed (to sort out each channel) from the parallel or serial data

stream. In FDM, each channel has a unique frequency assignment, while in TDM

each channel has a specific time slot assignment relative to the start of each

frame.

In FDM systems, demultiplexing is accomplished with frequency-to-voltage

converters called "discriminators" (frequency discriminators). These select

each channel from the transmitted subcarrier frequency spectrum with bandpass

filters and convert the selected frequency to an analog voltage that is

proportional to the instantaneous frequency of the subcarrier. After the

subcarrier frequency is selected by the bandpass filter, it is limited,

detected, and filtered. The output is an analog voltage that is typically

within 1 or 2 percent of the actual data source input voltage.

For improved accuracy, direct digital outputs, and reduced costs in large

systems, TDM offers significant advantages over FDM. In order to extract each

5-10
data channel from a serial TDM data stream, the demultiplexing equipment must

synchronize with the incoming data. In a PCM system, this attraction includes

bit synchronization to accurately derive the bit clock, frame synchronization

to determine the start of each frame of data, and word counting to identify

each data word within the frame.

These functions are performed with a PCM demultiplexer (usually called a "decommutator" or "decom") which can be obtained in either fixed or tunable and

manual or computer-controlled hardware. Although it is possible to use a computer to assist in decommutati ng a TDM signal, it is usually faster and more cost effective to use dedicated hardware. This hardware includes a direct

bit-parallel, word-serial output to a computer interface as well as quick-look

analog or digital display. In either a manual or computer-controlled system,

random selection of either single or multiple channels for quick-look display

is usually available.

5.1.10 Data Distribution

In most systems, it is not necessary or even desirable to take all of the

incoming data and distribute it to all of the recording, computing, and display

peripherals. A few critical parameters are usually monitored in real time by

the test directors to check for out-of-1 imits conditions. Some direct "pseudo"

real-time displays of parameters are required by instrumentation analysts, but

most of the data are recorded on mass storage devices for off-line analysis and

archival history. In order to route various data channels to the required

computer/storage/display peripherals, some form of data distribution is

requi red.

Although a computer is capable of performing this function, it may

seriously limit the data throughput rate as well as the number of other

different processing functions that the computer is called upon to perform. A

dedicated data distributor is in essence a hard-wired special -purpose computer

designed to efficiently distribute data from a single (or multiple) input

port(s) to various output devices. In doing so, the distributor can also

provide either a time tag or special identification tag to aid in processing or reconstruction of the original data. This function can be manually or computer

controlled, but is most often implemented in a computer control mode because of

the variety of test requirements.

5.1.11 Data Compression

As the number of data channels and throughput rates have increased, the

major problem in DAS has become what to do with all of the data. For example,

even a medium-speed DAS operating with a sampling rate of 50 000 sps will

accumulate almost 1.5 billion words of data in a single 8-hour day. Rather

than supply storage capacity for all of the data, it may be desirable to perform some data compression which can reduce the amount of storage

requirements by one to two orders of magnitude.

The essential function of the data compressor is to pass only those data

which represent changes from previous data; redundant data should be rejected.

Data compression can be performed under either software or hardware control.

Although software control provides the most flexibility, the maximum throughput

capability is usually lower than that of a hardware compressor.

5-11
There are many different algorithms which can be selected for data

compression. These algorithms are simply different formulas which set the

criteria for whether or not a data word should be passed or rejected. One

example would be to pass a data word if its value is outside two preset limits;

another example would be to pass the data word if the difference between the

previous data word and the current data word is greater than a preset amount.

Each compressed data point must be accompanied by the channel identification,

and the time corresponding to the sample, in order to completely reconstruct

the data. For data channels that have a significant amount of data point

redundancy, data compression can be very efficient. However, because of the

additional data required for channel identification and time tagging, data

compression may actually result in decreased throughput if the input data are changing at high rates.

Data compression can be extremely important where real-time analysis of

high throughput rates is required. If the input data rate is in the

neighborhood of 250 000 words per second (wps), most computer systems simply

cannot ingest the full amount of data, process it, and provide real-time

feedback to test observers. With a hardware data compressor, the throughput

rate can be reduced to 10 000 to 20 000 wps which can be easily accommodated by

a typical minicomputer subsystem.

5.1.12 Computer Interfacing

The outputs of most large DAS ultimately interface with a computer system.

All computer manufacturers offer standard computer digital interfaces which can accept low- to medium-speed data from the system and/or control the DAS. A

typical minicomputer interface consists of a 16-line data bus with a few

accompanying "handshake" lines.

For high-speed data transfers, some form of buffered data channel computer

interface is required. For example, a DAS with a 200 000 word per second

throughput to the computer system would require a high-speed buffered data

channel that can either load the computer memory or disk storage directly.

These buffered data channels can absorb data bursts of short durations at a high throughput rate and retransmit blocks of data .to the computer at a reduced

average rate. These buffered data channels also have multiple ports available

that allow program-controlled switching from one source to another. This

switching enables merging of housekeeping information, such as time code, along

with the main data stream.

5.1.13 Computer Processing

Detailed configuration of a DAS computer system is beyond the scope of

this section, but the major questions that must be answered by the engineer in

his computer system selection are as follows.

1. Processing Power and Speed Requirements

What arithmetic capabilities are required? Are floating point and

hardware multiply/divide required? What processing must be done in

real time, and how much time is allowed after the test for complete

offline analysis?

5-12
2. Memory Requirements

Basically, what size and what cycle times are required? Must all

memory be non-volatile, or is a mixture of volatile and non-volatile

memory acceptable?

3. Input/Output Requirements

What is the maximum average throughput rate? What is the maximum

burst mode throughput rate? Will standard or special input/output

circuits be required to handle the data rates?

4. Options

What main frame options will be required? What type of system clock

is required (fixed, programmable, internal, external, etc.)? Is additional solid-state memory expansion required?

In summary, it should be obvious that the capabilities of the DAS have a major

role in establishing the capabilities of a sensor-based measurement system.

5-13

6. SENSOR CALIBRATION

6.1 Performance Characteristics

6.1.1 General Considerations

The primary requirement imposed on any sensor is that it measure the

parameter (measurand) it was designed to measure within the required limits of

uncertainty. How well the sensor is likely to meet this requirement depends on the performance characteristics of the sensor, which are obtained from a series

of calibrations and evaluation tests. Sensor performance can be predicted or verified depending on the completeness of the knowledge of its performance

characteristics. Calibration and evaluation tests must exist to establish all

the needed performance parameters.

It cannot be emphasized too strongly that the continuing ability of a sensor to perform its measurement function acceptably must be established

through periodic re-calibrations. It is not sufficient to perform only initial

acceptance calibrations prior to installation of the sensor in the UUT. It is

also necessary to be able to perform periodic in-place (field) calibrations in

the actual operational environment. Field calibrations are greatly facilitated

by sensors with self-test capabilities so as to assure that such calibrations

test the entire measurement chain. In many cases, sensors with comprehensive

self-test capabilities do not exist yet.

For the purposes of this handbook, the operating environments in which

sensors are used may be categorized into three regimes as follows: (1)

operation at laboratory conditions, (2) operation in severe environments, and

(3) operation over an extended period of time. Practical experience with

sensors suggests that this order of listing also represents the order of

increasing performance degradation. It also represents the order of decreasing

knowledge of the actual type and magnitude of performance degradation.

Operation at laboratory ambient conditions, for short periods, and in a well controlled environment, eliminates the need for concern over the effects

of severe environments or the effects of long periods of operation. The concerns are with the two major modes of measurement which the sensor is called

upon to perform: static (or quasi -static) measurements and dynamic

measurements.

(1) Static Characteristics

The performance characteristics which determine the sensor's ability to measure static (or quasi -static, i.e., very slowly changing) measurands are established by means of static calibrations. These characteristics include

such parameters as sensitivity, zero output, linearity, hysteresis,

repeatability, resolution, creep, and dead band. Static calibration procedures

for many sensors have been published and incorporated in standards documents,

and although gaps exist in some areas, the general field of static calibration

for sensors is covered reasonably well.

(2) Dynamic Characteristics

With rare exceptions, sensors are called upon to measure time-varying

quantities. It is necessary not only to know the amplitude of the measurand at

6-1
a given time, but how it is changing at that time, since such changes may

require rapid corrective action.

If the sensor is to be used to measure (or follow) such dynamic changes,

the dynamic characteristics of the device must be known. Calibrations to

establish the dynamic characteristics such as amplitude response, phase

response, resonant frequency, and damping are less well developed than static

calibrations. Those dynamic calibrations that are available tend to cover relatively narrow amplitude- and frequency-ranges and may have other

restrictions.

(3) Other Factors

Even at laboratory ambient conditions, there are factors external to the . sensor which can affect its performance. Power supply variations, electrical

noise, mechanical vibration, and lead resistance variations will tend to

degrade the measuring ability of the sensor.

It is evident that a considerable number of performance characteristics

must be known before one can estimate the quality of measurements performed by

the sensor in a benign operating environment such as at laboratory ambient

conditions.

(4) Operation in Severe Environments

The majority of sensors do not operate in a benign environment. They are subjected to a variety of harsh environmental conditions which can greatly

influence their performance.

Such environments affect sensors in two major ways. Measurement

performance is adversely affected while the sensor is subjected to the specific

environment. Such changes in performance are generally reversible and

disappear when the particular environment no longer acts on the sensor. An

example is extremes in temperature which can change sensitivity. However, the

action of the environment of the sensor may also result in an irreversible, and

thus permanent, change in performance such as a zero shift.

It is essential to be aware of both types of effects to adequately assess sensor performance. Environmental parameters that have proven to be important

are briefly discussed in the following paragraphs and will be covered in more

detail later.

Temperatures above and below laboratory ambient are the most frequently

encountered environments which influence sensor performance. It is often

possible to compensate the sensor output for temperature effects, provided the

operating temperature is known and constant. This is true whether the entire

sensor is at the operating temperature or only a part of it, such as the

diaphragm of a pressure sensor. In the latter case, however, a temperature

gradient may exist between the sensor and the surrounding environment, causing

errors. If this gradient is stable, compensation can still be effective. If

the process or environmental temperature varies, temperature compensation

cannot be effective. In fact, compensating networks within the sensor may

actually degrade the output. Thermal transients can cause unexpectedly large

measurement errors unless sensors are specially selected or are protected

against them. It is also known that sensors last longer at constant

6-2
temperatures within their rated range than those exposed to wide temperature

excursions.

As with temperature, measurements performed by a sensor can be severely

affected by the presence of shock and vibration environments which may generate

spurious signals and otherwise interfere with sensor performance.

The presence, of moisture may cause undesirable shunting of resistive and

capacitive elements, as well as current leaks to ground. More important,

however, exposure to humidity can result in corrosion of metal parts and

components and can lead to component failures.

There are a number of other environmental parameters which may affect the

measurement performance of sensors, including dust and sand, salt spray, highlevel acoustic excitation, electromagnetic radiation, magnetic fields, and

ionizing radiation. More details of their effects appear in later sections.

In many cases, the electrical connector of the sensor has been a source of

problems and apparent sensor failures. A connector of proven reliability, but

extra cost, is a worthwhile investment to assure good sensor performance.

(5) Operation Over Extended Periods of Time

In some aerospace and defense applications, sensors are expected to

perform properly and reliably over short periods of time, from minutes to

hours. In industrial applications and defense ATE applications, on the other

hand, the periods of time over which these devices are expected to operate may

range from days to years.

When extended-time operation is considered, durability (stability) and

reliability are particularly important factors. The reliability of many

devices can be computed from knowledge of component failure rates. This

information has been applied to critical aerospace applications and expressed

as meantime between failures. This concept of reliability, however, is usually

concerned with the total failure of the device, but does not address the

deterioration of the sensor performance. The sensor's lack of stability or durability has received relatively little attention, but is of vital importance

in the case of ATE systems.

It is good practice to calibrate all measurement systems before each use.

It is not sufficient, however, to verify only once the performance of any

measurement system that is used over an extended period of time. Continuing

operation of any measurament system tends to lead to degradation of

performance. Consequently, it is necessary to recheck system operation and sensor calibration at selected limits. At present there seems little agreement

as to the proper time intervals for such field calibrations. Economic

considerations play a large role in the decision, particularly when such

re-calibrations require interruption of the process or disassembly of systems.

There are a large number of factors which have a bearing on the

performance characteristics of sensors. The factors can be grouped into (a)

those inherent to the sensing or transducing principle, design, and

fabrication, (b) those due to the environment in which the sensor operates, and

(c) those due to the continued, long-term operation. Comparatively little work

has been done, or at least published, to thoroughly establish these factors.

6-3
There is also a lack of adequate test methods or theoretical concepts to attempt to predict the influence of these factors. Later sections will discuss,

in more detail, sensor characteristics and existing test methods used to

determine those characteristics.

(6) Anticipated Needs

It should be apparent, however, that additional resources will be needed

in the following two-fold approach to assure optimum performance for sensor- based ATE systems:

9 The development of performance concepts and test methods to verify sensor performance under the variety of operational and environmental

conditions.

• The design and installation of measurement systems with the capability

of in-place calibration is highly desirable for any kind of industrial

process application. It is particularly critical for any system or process meeting national defense needs, including ATE systems for

military applications.

In view of the importance of sensor calibrations to the proper functioning

of ATE systems, and because of the scattered nature of information in this

area, the handbook section on calibrations is more detailed than other

sections.

6.1.2 Qualification Testing

The purpose of qualification tests is to establish the suitability of a type or class of sensor for a particular application. Sensors for use in

military applications are almost always required to be qualified according to

prescribed military standards, such as those listed in section 8.3.2 of this

handbook.

Qualification tests are intended to thoroughly explore all those

characteristics of the sensor which might have a bearing on the sensor's proper

performance of its measurement function. Qualification tests are usually

performed on a selected sampling of the type or group which they are intended

to represent. Once such a type or group of sensors has been "qualified,"

individual devices must still undergo acceptance tests, which are discussed

below. In addition, depending on the number of sensors being procured, it may

still be desirable to subject new samples periodically to complete

qualification tests to assure that quality has not deteriorated since the

first samples were qualified.

Qualification testing is exhaustive, complicated, extensive, and

expensive. Not all laboratories are equipped to carry out such a qualification

test program. Sophisticated test methods are used (and sometimes new ones must

be developed if existing ones are inadequate). Qualification testing by its

nature requires expertise, since it involves not only static and dynamic

calibrations, environmental tests, durability and reliability investigations,

but also proper interpretation of test results. Examples of some of the test

methods developed for such testing are provided by the work of the NBS

InterAgency Transducer Program [1], and are discussed below.

6-4
Qualification testing includes procedures which are covered under Static

Calibration (section 6.2.1), Dynamic Calibration (section 6.2.2), Operating

Environment (section 6.3), and Durability and Reliability (section 6.4).

However, there are some test procedures which do not really fall within any of

these sections and these are discussed here.

(1) Visual Examination

The first step of any qualification test procedure is a thorough visual

examination of the sensor. Check for defects in workmanship: loose parts and

connections, missing screws, damaged surfaces, improper fit with mating

connectors, missing labels, etc. If sensor dimensions are critical, such as for proper fit into a tight location, they must be verified.

(2) Mechanical Inspection

The next step is a check of the mechanical aspects of the sensor. For

example, in the case of a pressure sensor check for absence of leaks or, in the case of a turbine flowmeter, verify the freeness of rotation of the wheel.

Other checks include flatness of mounting surface for accelerometers and fit of screws for mounting. This type of inspection is typically performed as one mounts or connects the sensor to the calibration system for the basic static

calibrations, and prior to the electrical tests. Clearly, if any mechanical

problem is present, it is best to eliminate it prior to investing any further

efforts, such as the electrical tests.

It may be desirable, following the visual examinations, to examine the

sensor's electrical system by checking for open connections and shorts, and

measuring input and output impedances. Sometimes it is less time consuming to actually connect and prepare the sensor for the basic static calibration and

discern any electrical problems from the calibration data.

In any case, certain types of electrical tests are needed to establish

operating characteristics.

(3) Tests for Effects of Excitation Variations

Most sensors exhibit changes in sensitivity and zero-measurand output when

operated at excitation values other than the nominal values recommended by the

manufacturer.

The tests consist of static calibrations at laboratory ambient conditions

and at excitation values both above and below nominal values. If the

manufacturer gives a maximum allowable value for the excitation, in addition to

the nominal value, the former poses the upper limit for the tests. In the

absence of a maximum value, tests are usually performed at excitation values

from 50 percent of nominal to 125 percent of nominal.

The test starts with an initial static calibration at the nominal value of

excitation to serve as reference. The sensor is then disconnected from the

excitation source and permitted to cool down for two hours. At the end of this

time, the power supply output is adjusted to deliver 50 percent of the nominal

excitation value and the sensor is reconnected. After a stabilization period

of about 45 minutes, a static calibration is run. The procedure is repeated

for 75 percent, 100 percent, and 125 percent of the nominal excitation (and,

possibly, at the "maximum allowable excitation") if that is not likely to cause

6-5
any damage. When the data are evaluated, one can then determine the effects of

variations in excitation on the performance characteristics of the sensor.

(4) Tests to Establish "Warm-up" Effects

Sensitivity and zero-output of sensors may change somewhat from the time

the sensor is connected to the excitation source until complete internal

thermal equilibrium is reached. For this reason, a stabilization period of

about 45 minutes is considered good practice before static calibrations and

other tests. Under certain conditions of use, however, a sensor may be

expected to perform measurements shortly after being energized. In order to

evaluate the performance under such conditions, the following test procedure is

followed.

The test equipment, including excitation power supply, is turned on and

permitted to stabilize with the sensor disconnected from the excitation source.

The sensor is connected and a series of three-point static calibrations is

started one minute later. The calibrations are made at zero-measurand, at full

range, and at zero-measurand again. NBS experience suggests calibrations at

b-minute intervals during the first half-hour, at 10-minute intervals during

the next half-hour, at 15-minute intervals during the following hour, and

half -hour intervals during the following hours.

These calibrations monitor closely the expected initially rapid changes

in the sensor and permit data work-up and plotting after the first hour. The

tests are stopped when sensitivity and zero output have been stable for about

one hour.

(5) Test for Contact Noise for Potentiometric Sensors

Contact noise is the result of the variations of contact resistance at the

sliding contact of the potentiometric element. The importance of this

characteristic depends on the current level, the magnitude of the change in

contact resistance, the nominal resistance of the winding, and the resistance

of the load circuit. The higher the load impedance, the less will be the

effect of a given contact resistance change.

A circuit for this test is shown in figure 4. With switch S closed, the

potentiometer slider is moved over the resistance winding by means of a sinusoidal measurand input. The height on the oscilloscope of the noise pips

generated is noted. With the slider at rest, i.e., no input, the resistance

required to produce a vertical signal on the CRO equal to that of the noise

pips when switch S is opened, and closed, is determined. This resistance is

then the same as the change in slide contact resistance during the sinusoidal

input. This test may be performed at one or more specified levels of current.

The test described next is really a combined mechanical -electrical test

and should be performed before the basic static calibrations.

(6) Tests for Effects of Mounting Force or Torque

Pressure sensors, particularly flush-diaphragm instruments, may exhibit

changes in sensitivity and zero-pressure output as a result of case deformation

in mounting when they are mounted in fixtures. Sensors with integral pressure

fittings for tubing are not normally subject to this effect.

6-6

The tests to determine effects of mounting torque are static calibrations

at various levels of mounting torque. (Manufacturers' literature generally

gives no information on recommended mounting torque.) It is prudent to perform

this test early in the evaluation sequence. It is possible to proceed by

mounting the sensor in the test fixture and using a calibrated torque wrench to

tighten it in increments while running a static calibration at each level of

mounting torque (these may be abbreviated calibrations; five points are adequate). The maximum torque used for many commercial sensors should not

exceed 30 inch-pounds, in the absence of any information from the

manufacturer.

Similarly, mounting force and torque may have an effect on the

characteristics of force sensors, flowmeters and accelerometers. A judgment

should be made in the case of each sensor application as to whether mechanical

mounting conditions are likely to have an effect on the performance of the sensor. Appropriate tests should then be devised to verify the effects.

(7) Proof or Overload Tests

Proof or overload tests are part of the qualification procedures. They are used to verify the integrity of the sensing element (or sensor case,

depending on the device) to measurand amplitudes well above the rated range.

In the case of pressure sensors, such a test is designed to assure that no safety hazard exists when the pressure exceeds the rated value. This test is

usually referred to as a proof test, a term used for such tests for ordnance

i terns

.

The overload test using amplitudes only 10 percent or 20 percent above

rated is used to check the effects of such an overload on the calibration of

the sensor and its subsequent performance. Overload or proof tests may destroy

or permanently damage the sensor and are therefore used only in qualification

testing, never in acceptance tests.

(8) Tests for Effects of Position

Some sensors may be position sensitive, that is, their output may be

influenced by gravity acting along a particular axis of the device. An example

is a turbine flowmeter which can show different amounts of bearing friction

depending on its orientation. Low range acceleration sensors and low range

pressure sensors may also be position sensitive. It is desirable to establish

the uncertainty due to position (or orientation) by calibrations performed with

the sensor in each of three orthogonal orientations in the earth's

gravitational field.

If this test cannot be carried out due to time or resources constraints,

the reference static calibrations must always be performed with the sensor having the same orientation as it will in the final installation.

(9) Tests of Directional or Transverse Sensitivity

Acceleration sensors are prone to errors due to vibrational inputs along

axes other than the sensitive one. It is not practical to construct a sensor

which has no transverse sensitivity. Fabrication tolerances and

inhomogeneities in materials will result in erroneous output signals due to

transverse inputs. For this reason it is very important, in the calibration of

accelerometers, to make sure that the input motion is free of transverse

components.

6-8
Transverse sensitivity is not easy to determine experimentally. One

approach is a constant frequency and amplitude mechanical motion applied to an acceleration sensor at right angles to its sensitive axis. Measuring the

resultant output at a number of points of a 360° coverage can produce a plot of

transverse sensitivity. From this, the least transverse sensitive orientation

can be established and used in the selection of subsequent installation

orientation.

There seems to be some indication that transverse sensitivity,

particularly of piezoelectric accelerometers, is also a function of vibration

amplitude and frequency. It may not be economical to run a complete evaluation

program to pin this down in detail. One should consider the possibility of errors due to this when reducing vibration data.

In a similar manner, the application of force to a load cell at an angle

to its sensitive axis can also cause output errors. This effect can be checked

for by deliberate and controlled variations of input angles during static

cal ibrations.

6.1.3 Acceptance Testing

Even when a sensor type has been "qualified," it is still necessary to assure the proper performance of each individual sensor. This is done with

an acceptance test, sometimes referred to as "Individual Acceptance Test"

(I AT).

Acceptance tests, in contrast to the qualification tests discussed above,

are kept as brief as practicable, since often large numbers of sensors must

undergo these tests. The tests are used to establish function (i.e., proper

signal output, no internal shorts), and static calibration parameters like

sensitivity, linearity, hysteresis, and repeatability. If the application is a critical one, additional tests from the qualification sequence may also be

performed. Subjecting specified samples to additional tests is another

option.

Generally speaking, the acceptance test is also an integral part of any

qualification test program. The main component of the acceptance test is the

static (base or reference) calibration which will be treated in more detail in

section 6.2.1

6.2 Laboratory Measurement Tests

6.2.1 Static Calibration

6.2.1.1 Basic Considerations

Static calibrations of sensors at laboratory ambient conditions constitute

the fundamental calibrations to which all further tests are referenced. The

established performance characteristics (defined in the glossary) are established from the results of these static calibrations. This approach is

used for all types of sensors, except those which inherently cannot respond to

zero frequency (steady-state) stimuli. Piezoelectric sensors fall into this

category and their characteristics must be evaluated with the aid of dynamic

calibrations, which will be covered later.

6-9
The high cost of acquiring calibration equipment, and the high labor cost

for the skilled personnel necessary to operate it, make it imperative that the

static calibration procedure adopted is the most efficient and practicable one. The procedure must be one which produces the greatest amount of useful

information about the sensor with a minimum expenditure of calibration- and

data analysis-time. The recommendations in this section will help to realize

these objectives.

Finally, the following discussion and recommendations are based on the

assumption that the overwhelming majority of sensors are designed to be

inherently linear devices, i.e., the electrical output-measurand input relation

is essentially linear over the entire operating (calibration) range

of the sensor.

6.2.1.2 Number of Calibration Points in Single Calibration

(1 ) Zero Output

The recommended calibration sequence starts with a measurement of sensor output with zero measurand applied to the input. There are three reasons for

thi s:

t In most measurement situations, the sensor is exposed to zero measurand

first, before the process is started which produces the actual

measurand amplitudes which are to be measured.

• In case of gage pressure and differential pressure sensors, zero measurand means simply ambient pressure on both sides of the sensing

diaphragm. This does not require a separate controlled source of

pressure and simplifies the test. In other types of sensors, zero measurand means no flow, no vibration, no force, or no displacement

from rest. This test can also apply when a constant and well known

measurand near one end of the range exists. Examples are laboratory

ambient pressure, temperature, humidity, position, or acceleration

(gravitational ).

• Electrical malfunctions of sensors will frequently show up when the

output is measured with zero measurand or constant input. Some types

of drift can also be checked in this manner.

(2) Full -Scale Output

The next most important point is the full-scale point, i.e., the measured

output with the full-scale value of the measurand applied to the sensor. In all measurement situations, the sensor should be chosen so that the maximum

measurand will not likely exceed the full-scale range of the sensor.

In those cases where measurand amplitudes might exceed the full-scale

value, it is desirable to check the sensor's characteristics beyond this value.

Manufacturers' recommendations should be followed and caution exercised to

prevent permanent sensor damage due to overranging. In normal calibration

practice, however, the full-scale measurand input should not be exceeded.

(3) Three Point Calibration

If the sensor has previously been found to be a linear device with a known, or acceptable, amount of hysteresis, a three-point calibration may be

6-10
adequate for many purposes. Among them are: in-place calibration immediately

before use, and quick checks of sensor stability during extended storage or during operation in hostile environments. A three-point calibration starts

with zero measurand input, then full-scale input, followed by zero input again.

Such a calibration will yield values of zero output, zero shift (hysteresis at zero input) and sensitivity (assuming linear input-output relation). It will

not yield information on linearity or hysteresis, nor will it establish

confidence in the sensitivity, since that value is based on a single point

above zero input.

(4) Eleven Point Calibration

A calibration sequence commonly used involves eleven points with equal

intervals between them. Each interval corresponds to 20 percent of the

full-scale range for a unidirectional sensor (0% to +100% FSR). The eleven

calibration points of a single calibration for this sensor are attained by a sequence which starts with zero measurand, then increases input in steps of

20 percent of full scale to 100 percent FS (full scale) and retraces the

points until zero measurand is reached. For bidirectional sensors (-100% FSR

to 0% to +100% FSR), and some full-scale ranges of unidirectional sensors, it

may not be feasible to calibrate at cardinal 20 percent FS points or to manage

an eleven -point calibration; it may be necessary to use additional points.

Nevertheless, the eleven-point static calibration of a unidirectional sensor

will probably be the most commonly encountered basic calibration.

(5) Twelve-Point Calibration

In theory, data reduction from an eleven-point calibration by means of the

least-squares straight line computation is biased slightly since there are two

output values corresponding to each measurand input, except at the full-scale

point. To give equal weight to the latter point, a twel ve- poi nt calibration

has been proposed. In this, after the full-scale point has been reached and

the corresponding output read, the input is raised a little more, reaching

perhaps 105 percent FS or 110 percent FS. Then the input is dropped again

until the full-scale point is reached again and the corresponding output is

read again. The remainder of the procedure follows as before in the standard

eleven-point calibration. Since there are now two output values corresponding

to full-scale input, all points have equal weight in this twelve-point

calibration. An experiment carried out at NBS comparing eleven-point

calibrations to twelve-point calibrations on the same sensor indicated only

insignificant differences in the computed slope (sensitivity) of the sensors.

It should be noted that a twelve-point calibration may put additional stress on

the sensor, since it is actually overranged by 5 percent or 10 percent during

this calibration.

(6) Twenty-One Point Calibration

A calibration sequence sometimes used involves twenty -one points with

equal intervals between them, with each interval equal to 10 percent of the

full-scale range for a unidirectional sensor. The calibration points, in

sequence, follow that for the eleven-point calibration described above except

at the smaller intervals, ending at zero measurand.

For a bidirectional sensor, with equal spans about zero measurand, a twenty-one point calibration is also possible. The sequence for this starts at

zero measurand, proceeds in 20 percent FS steps to full scale, returns to zero measurand, continues in the negative direction to minus full scale, and returns

6-11
to zero measurand again. An experiment carried out at NBS comparing elevenpoint calibrations with twenty -one point calibrations on the same sensor indicated that differences between calculated parameters were insignificant for

the two sets of data. In view of the doubled calibration time, it is not

recommended to use a twenty-one point calibration sequence for most

unidirectional sensors.

(7) Twenty -Two Point Calibration

In a similar manner to the twelve-point calibration above, an additional

full-scale point can be added to a twenty -one point calibration by increasing

the input to 105 percent FS or 110 percent FS and then dropping back to the

full-scale value. Again, this does not offer any noticeable advantage over the

twenty -one point calibration.

(8) Recommended Calibration

The eleven-point calibration sequence is recommended for the static

calibration of unidirectional sensors on the basis of the discussion above.

For the less common bidirectional sensors, a twenty -one point calibration is

suggested.

6.2.1.3 Number of Calibration Cycles

It is necessary to perform more than one static calibration on a sensor in

order to be able to predict anything about the future performance

characteristics of the device. "Repeatability" is the term used to describe

the short-term variations in parameters with time; "stability" refers generally

to long-term changes over periods of months or years. The basic parameters of

interest are the slope of the best straight line through the calibration

points: the sensitivity, the intercept of this line on the output axis, the

linearity (frequently given as the largest deviation from the best straight

line), and the hysteresis: the maximum deviation in output readings at the same value of measurand. These terms, and others, are defined in the

glossary.

It seems desirable at this point to delve briefly into some statistical

considerations on repeat calibrations. The material is derived from the NBS

"Handbook on Experimental Statistics" [20].

A value derived from a single calibration run can be considered a sample

in a "population of calibrations" for a particular device under certain

well-defined test conditions. It is desirable to be able to make statements

about expected future values of the significant parameters. One would,

ideally, like to state the average value of a particular parameter for the

entire "population of calibrations." Since this population is infinite, this

cannot be done. It is, however, possible to obtain an average value of this

parameter from a limited number of calibrations and then set up a stated

tolerance interval about this average. One can then assert with some numerical

confidence that the population average will fall within this interval.

The statistics for this have been worked out in some detail in available

tables. The only assumption is that the "population of calibrations" follows a normal distribution. The average value of a parameter A, A, from the original

calibrations is used as an estimator for the "true" value. To go from A to the

6-12
confidence interval, within which the "true" value is expected to lie, one uses Student's "t" distribution [20],

The bounds of the confidence interval are:

|A + t -^_| and Ik - t — \

\ / N/ \ / N/

where N is the number of calibrations and S a is the standard deviation of the

parameter average . The value of "t" depends on the desired confidence level

and the number of degrees of freedom of the data. In this case the latter is a number which is one less than the number of calibrations from which the data are obtained.

Values of "t" extracted from reference [20] are shown below for two-sided

confidence intervals at the 90 percent, 95 percent, and 99 percent confidence

level s.

TABLE 16

Student's "t" Values

Degrees of Freedom Value of "t" at various confidence levels

90% 95% 99%

673T4 127706 63.657

2.920 4.303 9.925

2.353 3.182 5.841

2.132 2.776 4.604

2.015 2.571 4.032

The table shows that the interval does not shrink much beyond two degrees of

freedom, except for the 99 percent level where the turning point is three

degrees.

For most calibrations, a confidence level of 95 percent should be adequate

and reasonable. The true population average would then be expected to be

inside the interval 95 percent of the time. Based on those considerations

three static calibrations performed in succession are recommended. They yield

the desired data on repeatability and stability within acceptable confidence

intervals and without the use of excessive calibration time.

Section 7 contains additional information on the data reduction and error

analysis to establish the sensor's performance characteristics.

6.2.1.4 Static Calibration Procedures

Calibration procedures for different types of sensors are different but

certain common features exist. It is possible to briefly describe general

principles for such procedures in roughly the sequence in which the

calibrations are to be carried out. It is important that the particular

procedures for a given sensor must be carefully specified based on measurement

needs, user experience, and good professional judgment. The accurate

establishment of the sensor's characteristics and, therefore, its ultimate

6-13
ability to measure correctly depend entirely on the quality of the calibration.

The following discussion is designed to illustrate the general principles

involved.

(1) Equipment

The basic equipment necessary for the static calibration of a sensor consists of the measurand, a source of electrical excitation for passive

sensors, and the device which measures the electrical output of the sensor. The combined errors or uncertainties of the entire calibration system should be

sufficiently smaller than the anticipated tolerance of the performance

parameter under investigation to result in meaningful values. Conservative

practice in a calibration hierarchy specifies a ten-fold quality ratio, i.e.,

use of a "0.1 percent" pressure gage to calibrate a "1.0 percent" pressure

sensor. This approach may be unrealistic in the case of the better and more "accurate" sensors coming into the market. A three-to-one ratio represents a reasonable approach in view of the customary root-sum-square combination of

uncertainties.

Measuring instruments should be checked against standards periodically,

and traceability to the National Standards must be provided for. Environmental

conditions during the static calibration must be constant (laboratory ambient

for baseline calibrations), and specified, to permit possible corrections to

the data from the calibrations.

The source of the measurand should be continuously variable over at least

the full-scale range of the sensor. Alternately, the measurand may be provided

in discrete levels as long as the transition from one level to the next during

calibration is accomplished without creating a hysteresis error due to

measurand overshoot.

Procedure

1. The sensor is first inspected visually for mechanical defects, poor

finish, improper identification markings, and such other flaws as may

make it unacceptable. The electrical connector and the input port,

mounting base, or similar measurand interface are also inspected.

2. The sensor is connected to (mounted on) the calibration system

component from which the measurand is applied to the sensor. In

connecting (or mounting) the sensor, care must be taken that the

recommended force or torque is not exceeded. Case distortions from the use of excessive force or torque may lead to incorrect calibration

data. It is good practice to check the entire setup for proper

connections and fit. In case of pressure sensors or flowmeters, the

system must be checked for leaks. The excitation source and output

measuring (readout) device are connected to the sensor via cabling.

Then the sensor is energized. It is good practice to turn on everything except the sensor's excitation, sufficiently ahead of the

calibration procedure to permit adequate time for warm-up of the

calibration components. One hour is customary for this; a half-hour is

the minimum recommended time. (See section 6.1.2 for "tests to

establish warm-up time.")

3. It is good practice to permit a similar warm-up period for the sensor

as well, prior to the calibration and to watch all components and

6-14
indicators for any signs of malfunction. The "warm-up period" (see

glossary) of the sensor, an important performance characteristic, is

usually established through separate qualification tests prior to this

static calibration.

4. The static calibration sequence is performed next. As explained in

detail in sections 6.2.1, three eleven-point static calibration cycles

are carried out sequentially (for bidirectional sensors --twenty -one points) and the data reduced as explained in section 7.2 below.

Those calibrations yield information such as sensitivity, zero measurand output, linearity, hysteresis, repeatability, and resolution

(see glossary).

5. Additional repeated calibration cycles, at specified time intervals,

can be used to establish stability , as indicated by zero shift- and

sensitivity shift- with time.

6. The application of the full-scale value of the measurand for a specified short period of time and measurements of sensor output during

and following this period of time can be used to establish creep .

7. Application of a specified value of measurand above the full-scale

range, followed by a static calibration cycle, will indicate the

overload capability of the sensor.

8. In the case of differential pressure sensors (such as used in flowmeter applications), both input ports may be fed from the same high

pressure source to determine the effect of line pressure on the zero measurand output. The effect of line pressure on sensitivity requires

application of an accurately known pressure differential between the

pressure ports in the presence of a constant high line pressure at both

ports. This is a very difficult procedure requiring sophisticated

equipment.

9. It may be desirable to establish electrical characteristics of the sensor such as input impedance , output impedance , and insulation

resistance . Conventional techniques are used for this.

It should be noted that for sensors which interface with computers, sensor linearity may be a critical parameter, if calibration points can

be stored in memory for look-up and the software provides

interpolation. The static calibration procedures at laboratory ambient

conditons described above are the Individual Acceptance Test (IAT)

(section 6.1.3) for each sensor. They are also an integral part of the

Qualification Tests (section 6.1.2). Similar procedures at other than

laboratory ambient conditions are used to establish environmental

performance and durability and will be discussed in more detail in

sections 6.3 and 6.4.

6-15
6.2.2 Dynamic Calibration

6.2.2.1 Basic Considerations

Sensors are almost always required to measure physical quantities which

vary with time. A purely static measurement is a rarity; furthermore, certain

types of sensors, such as piezoelectric devices, have no static (zero

frequency) response at all. For these devices, and to correctly evaluate the

performance of sensors which measure time-varying measurands, dynamic

calibrations are required.

As in the case of static calibrations, one must apply a measurand with

accurately known characteristics and measure the resulting sensor output with

comparable accuracy. It is generally difficult to generate measurands with

accurately known (or well controlled) dynamic characteristics. Consequently,

dynamic calibration procedures are less well developed than static

calibrations. Also dynamic calibration procedures are not available for

certain amplitude and frequency ranges of some measurands.

One approach to dynamic calibration (and sometimes to static calibration)

of sensors is the use of a "reference" sensor mounted close to the sensor to be

calibrated and subjected to the same measurand. This procedure has merit only

if one has a stable, dependable reference sensor with well known

characteristics. Even under such circumstances, it is highly desirable to be

able to verify the dynamic performance of this sensor periodically. Also, the

concept of both sensors being subjected to exactly the same measurand becomes

less tenable when measurands have high amplitudes or high frequencies.

Ultimately, then, to assure adequate knowledge of the dynamic characteristics

of any sensor, it is necessary to subject it to some form of a dynamic

cal ibrationo

There are a number of considerations applying to dynamic performance

characteristics and the methods used to establish them.

Much of the following discussion is based on material in ANSI

Standard B88. 1-1972, Guide to the Dynamic Calibration of Pressure

Transducers [21], but it can be applied to sensors in general.

The sensor properties or characteristics of interest to a user will depend

to a large extent on the application involved. This section defines and

discusses some of the properties most often required. These properties

sometimes can be described in terms of the "transient" response of the device

to a step input, or in terms of its "steady-state" response to sine wave excitation, or both.

In defining sensor properties related to dynamic response, the transfer

function of the sensor provides valuable information. The transfer function is

the ratio of output to input (expressed in the frequency domain), and forms the

basis for the frequency response parameters. Once the transfer function is

known, the input vs time for any output can also be calculated. These topics

have been treated by those working in the fields of servo mechanisms and

network theory, where it is often necessary to describe system behavior in both

transient and steady-state terms. This approach, using the transfer function

6-16
concept, has much to offer in the consideration of dynamic calibration of sensors.

Because of the limitations of periodic generators, responses to aperiodic

generators must be depended upon to provide much of the needed information of sensors. Measurements of frequency response using sine wave inputs are easily

defined and understood, whereas, the necessity to convert from the time to the

frequency domain makes analysis with aperiodic inputs more difficult.

Single Degree of Freedom System

A description of sensor dynamic properties is usually based on the

assumption that the sensor is a linear second-order system with a single degree

of freedom, e.g., a simple spring-mass system with damping. Some sensors may

be found to be more complex than such a simple system and their analysis is

correspondingly more difficult. Since a large percentage of sensors now in use

can be treated as simple single-mass and single-spring systems, a detailed

analysis of such a system is justified.

It must be emphasized, however, that the assumption of a simple

single-mass spring (single degree-of -freedom) system does not always apply and

the assumption must be carefully considered in the case of measurements of

high-frequency phenomena. In such cases, one must consider not only the fact

that the sensor may be a complex multi -degree-of -freedom system, but also that

the interface between sensor and measurand (i.e., the connecting plumbing for a pressure sensor, or the mounting surface for a vibration sensor) may interpose

additional spring-mass systems.

With this caveat in mind, one can then consider the assumed underdamped

single degree of freedom system.

The typical spring-mass mechanical system (see fig. 3) which provides the

first resonance of a sensor, is described by a linear second-order differential

equation:

d*x

+

c dx

+ kx f_Ul

dt 2 m dt m " "m (6,1)

where c indicates the damping, k the spring constant, m the mass, and f(t) the

forcing function (provided by the dynamic calibrator). The use of the Laplace

transform allows the formation of the transfer function from equation (6.1):

OUT(s)

Ra)o (6.2) ~m^

J ~ s

2 + 2fao

ftO

s + <0

where

OUT(s) is the Laplace transform of the output,

IN(s) is the Laplace transform of the input,

K is the steady -state sensitivity

o> 0 ls the natural frequency of the system in radians

per second = j~Y • t m

6-17
The natural frequency is the frequency of free (not forced) oscillations

of the sensing element of the sensor without damping (c = 0). In practical

terms, it is the measured frequency at which the sensor has a 90° phase shift,

s is the complex variable = j

0-* = j (27rf), where f is frequency

? is the damping ratio (ratio of actual damping to critical damping).

The response of an underdamped second-order system is treated in numerous

texts; the "Shock and Vibration Handbook" [22] is noteworthy.

The model of eq. (6.2) assumes that the sensor can respond to static measures (put s = J

XI= 0 into eq. (6.2) with sensitivity K. Often sensor

systems with their associated electronics cannot respond to static measures and

in this case the model can be modified by incorporating the equivalent of a high-pass RC stage with the transfer function. For example, a piezoelectric

sensor with a dominant mechanical resonance can be approximated by the transfer

function:

koo

2 OUT s ^ = s* + 2CV u> s + 1/RC

<6- 3)

Now when s = 0, the response is zero.

Equations (6.2) and (6.3) are written in terms of the variable s, and

describe the system behavior in the frequency domain. When the input function

is specified, the inverse Laplace transform can be used to derive an equation

yielding the time domain function. Assume the application of a pressure step

of height A to the sensor described by eq. (6.2). The time response of the

output voltage is

B(t) = A [1 - —i— e ( ^ ) S i n ( rft + arc tan jOiC)]

(fi ^

A—2 where d

= u

o

? • This equation yields the time response B(t) of the

system to a specified input.

Based on the equation describing this model of the sensor, one can then

describe certain properties of the sensor in the frequency and time domains.

Amplitude response is the amplitude of the transfer function versus frequency (often called the "frequency response"). It can be computed from

eqs. (6.2) or (6.3) by substituting jw for s and computing the resultant

magnitude. When this is plotted, it is frequently normalized (by dividing by

the value of the sensitivity) to show deviations from a flat amplitude

response.

The amplitude response contains a great deal of information relative to

the sensor, such as resonant frequencies, bandwidth, and the damping of the resonance (or resonances of the real system). It is most desirable to

determine this experimentally using an accurately known sinusoidally varying

measurand. This is also true of the other parameters discussed below.

6-18
Slew rate is another dynamic property, describing the maximum change in

amplitude of the output as a function of time.

Phase response shows phase variations of the transfer function versus

frequency. It can be derived from eqs. (6.2) or (6.3) by substituting w for s and computing the phase as u is varied. In the time domain, phase influences

the instantaneous shape of the response to an input signal and contributes to a time lag in sensor response.

Resonant frequency ( w

r

) is the measured frequency at which a sensor

responds with the maximum output amplitude. Most sensors have more than one resonance, and the lowest in frequency, or "first" resonance, is usually

considered important. If the first resonance is the dominant one, the

second-order system approximation may be valid. The normalized amplitude

response at resonance is governed by the amount of damping in the system.

Dynamic nonlinearity . As indicated in the discussion of static

calibrations, sensors are almost always designed to be inherently linear

devices. Deviations from linearity are normally established from the static

calibrations. Dynamic responses can also show deviations from linearity, due

to additional factors like overranging, nonlinear elasticity, and other

factors. Dynamic nonlinearity is best described by a family of

frequency-response curves. If present, such nonlinearity can degrade

measurements considerably. In general, sensors with dynamic nonlinearities

should not be used at all.

The discussion thus far has assumed that sinusoidal stimuli are used for

the derivation of these frequency-response curves.

There are some other dynamic characteristics such as creep, sag, and

hysteresis, which are essentially time-dependent factors. To determine these

most effectively, the dynamic calibration requires a somewhat different

approach. Quite frequently, a step function, ramp function, or other transient

measured input is used. Such approaches must be used in cases where it is not

possible to generate the necessary sinusoidal measurand. In such cases,

techniques exist by means of which the transient output of the sensor can be

manipulated to yield the transfer function of the sensor.

The following properties in the time domain are descriptions of the

sensor's response to a specified transient input, usually a step function.

Ringing frequency (w^), sometimes referred to as damped natural

frequency, is the frequency of free oscillations in the sensor output resulting

from a step change in measurand. The ringing frequency is indicated by the

number of oscillations per unit time. For the linear second-order sensor, the

ringing frequency (w^) is related to the resonant (^

r ) by

Damping is the energy dissipating characteristic which, together with

natural frequency, determines the upper limit of frequency response and the

response time characteristics of a sensor. In response to a step change of

(6.5)

6-19
measurand, an underdamped (periodic) system oscillates about its final steady

value before coming to rest at that value. An overdamped (aperiodic) system

comes to rest without overshoot, and a critically damped system is at the point

of change between the underdamped and the overdamped conditions.

Damping ratio (f) is the ratio of the actual damping to the damping

required for critical damping. In eq. (6.2) the coefficient f is the damping

ratio. Typical sensors have damping ratios much less than unity, consequently,

values of and <*> r very nearly coincide. The damping ratio is defined

specifically for a linear second-order system. Sensors with more resonances

are approximated by associating a "damping ratio" with each resonant

frequency.

The damping ratio is a useful parameter in both the time and frequency

domain. In the time domain, T is related to the amount of overshoot and

influences the number of ringing cycles present after a shock excitation. In the amplitude response, f is related to the height of the peak at the resonant

frequency.

Rise time is the length of time required for the output of a sensor to rise from a small specified percentage of its final value to a large specified

percentage of its final value when excited by a step change in measurand. Rise

time is related to sensor frequency response.

Overshoot is the amount of output measured beyond the final steady output

value in response to a step change in the measurand. The maximum theoretical

overshoot of an ideal second-order sensor is 100 percent; this occurs when f is zero. Overshoot is determined as: jlL

percent overshoot = 100 e U/l -f 2

J (6.6)

for the conditions f 50.1.

Settling time is the time required after the application of a step change

in measurand for the sensor output to settle within a small specified

percentage of its final value (5% is often used). For the ideal second-order

sensor with small T :

t = I/tZETL

s ?wd (6.7)

The settling time increases with smaller f and <^j. The number of

oscillations at required to settle within 5 percent of final value for the

ideal second order transducer is:

N = 2ttc (6.8)

The major disadvantage of the use of transient stimuli is the fact that

they are less well controlled or known and that certain modifying assumptions

must be made for data reduction.

6-20
In the case of the most commonly used transient stimulus, the step

function, the inherent assumption in data reduction is that it is indeed a mathematically precise step. Actual measurand stimuli produced by dynamic

calibrators cannot be true step functions with infinitely fast rise times. In actuality, the input is a form of ramp-function with a finite rise time and

frequently a slightly tirne-varyi ng amplitude as well.

The advent of Fast Fourier transform analysis capability in dedicated

analyzers or the use of FFT-programmed computers has greatly reduced the

efforts of deriving frequency response curves from transient calibrations. The

resultant increasing use of non-sinusoidal dynamic calibration techniques

requires increased care in data reduction and interpretation, however, because

the underlying assumptions and limitations are not always understood or clearly

stated.

Summary information on the more commonly used dynamic calibration

techniques appears in the following sections.

6.2.2.2 Sinusoidal Stimuli

(1) Dynamic Pressure Calibrations

While there are similarities in dynamic calibrations using sinusoidal

stimuli for most types of sensors, it is helpful to treat the different sensor

types separately.

In the case of pressure sensors, ANSI Standard B88. 1-1972 [21] provides

considerable detail on their dynamic calibration using sinusoidal and transient

input stimuli. The following is abstracted from that document.

The dynamic calibration of pressure sensors requires that the measurand

produced by a dynamic pressure generator vary in time in both a known and an appropriate manner. With some generators the pressure-time relationship can be

predicated quite accurately. With others, the pressure-time relationship can

be established accurately only with the aid of comparison to reference pressure

sensors. Reproducibility is a highly desirable characteristic of the dynamic

pressure generator, but it is not an essential characteristic. When it is

lacking, full dependence on the reference sensor is required.

Dynamic pressure generators fall into two basic classes: aperiodic and

periodic. The aperiodic generators are characterized by the pulse shapes they

produce, such as the step or the peaking pulse. Quick-opening valve devices

and pulse generators produce pressure rise times generally in the millisecond

range or less. The rise times and the pressure amplitudes generated by these

devices vary markedly from one type of aperiodic pressure generator to another.

The shock tube, for example, is capable of generating pressure steps having

rise times in the nanosecond range. The pressure step, as used in this

treatment, is defined as a change in measurand in which the rise time is less

than one-fifth the rise time of the sensor measuring it.

(2) Sinusoidal Pressure Generators for Gaseous Media

Sinusoidal pressure generators are the most useful of the various periodic

pressure generators available. Although these devices are adjustable over some

range of frequency, they are limited in dynamic pressure ratio, dynamic

amplitude, and in their useful frequency range. Non-sinusoidal pressure

6-21
generators of significant usefulness include the square wave or rectangular

wave generators, which may be considered as a special case of the aperiodic or step-function generators.

The dynamic calibration of a pressure sensor can ideally be accomplished

by sensing known inputs from a periodic pressure generator at known frequencies

and amplitudes. The observed response, including the magnitude, waveform, and

phase lag, can then be compared with the known input at various conditions. In

order to calibrate with only one frequency at a time for accuracy and

simplicity, a sinusoidal pressure generator (SPG) is required. In practice,

there are limitations to this approach. First, the applied average pressure

levels and dynamic amplitudes generally are not known by absolute means and

must be measured by another sensor. The SPG generates a pulsating pressure in

a small chamber which can be monitored simultaneously, both by a reference

standard sensor and by the sensor being calibrated. The two sensors must be

sufficiently close that they sense the same pressure, including amplitude,

shape, and phase lag. Analysis of the output of the sensor being calibrated is

thus entirely dependent on the performance of the reference sensor, and what is

known about its performance. Currently this basic limitation of SPG

utilization in a comparison process is not serious because available

high-quality reference sensors have response characteristics exceeding the

pressure, pressure amplitude, and frequency which can be obtained with

available SPGs.

The governing limitations are associated with the ability of the SPG to

provide the desired signal. An SPG, when used for calibrating a pressure sensor for a specific use, should satisfy the following:

• The pressure generated is sinusoidal such that frequencies, other than

the fundamental one, are negligible.

• The frequency range generated covers the frequencies of pressure

expected in the intended application.

• The operating pressure range covers the sensor's full-scale range or a large portion of the range.

• The dynamic pressure amplitude generated is large enough to identify

possible nonl ineari ties in the sensor amplitude response.

t The SPG is operated with the same medium (gas or liquid) with which the sensor is to be used.

Often, all of these criteria cannot be met, and a less-than-desired match

is obtained between the dynamic pressure measurand applied during calibration

and that encountered in use of the sensor.

Many devices have been proposed and developed as SPGs. The widely used

SPGs can be categorized as acoustic resonators, variable-volume generators, or variable-mass generators.

Any of several driving devices can be used to establish acoustic resonance within the chamber of an acoustic resonator. The frequency of resonance is

fixed by the geometry of the chamber and the properties of the working fluid.

6-22
To obtain a specific frequency, the chamber length must be a multiple of the

acoustic half wavelength. When another frequency is required, the geometry

must be changed, or harmonics of the fundamental frequency must be used.

At resonance, the pressure waves may be distorted to a significant degree

from the pure sinusoidal excitation because of gas dynamic phenomena. As the

amplitude or frequency is increased, the nonl ineari ties associated with real

gas, wall, and friction effects also become significant. At low dynamic

pressure amplitudes, these generators can provide pressure pulses that are sufficiently sinusoidal for many uses.

In the variable-volume pressure generator , a relatively fixed mass of

working fluid is alternatively compressed and expanded within a small chamber.

The chamber is deliberately made small such that its natural frequencies are always higher than the frequencies imposed, and thus resonant effects are eliminated. A piston or diaphragm driver is used to vary the chamber volume

and thereby the pressure in a repetitive manner.

Usually the gas compression is isentropic and the pressure, p, follows the

piston position, & , as follows:

P ~o

p 0 is the equilibrium pressure

^ 0 is the driver (piston or diaphragm) position at the equilibrium

pressure

y= ratio of specific heats at constant pressure and volume (Cp /C v

).

Thus, as the piston travels in a sinusoidal manner, the pressure amplitude is

represented by the expression:

p =

p0

(1 + a sin u>t)"7 (6.10)

and the dynamic pressure amplitude by the expression:

Ap = p - P = p [1 + a sin a)t)~ Y

]

(6.11)

a

2 = ayp

Q

sin cot - ^ P0 y(y+1 ) sin 2 cut ...

where a = modulation factor which is always < 1.

Considering subsequent terms in the expansion with realistic coefficients,

this dynamic pressure is clearly non-sinusoidal. The effects of fluid motion

and viscosity also introduce nonl ineari ties in the waveform.

This class of generators is generally limited by the amplitude -frequency

characteristics of the driving unit. In theory, non-sinusoidal input from the

driving device could compensate for nonl ineari ties and thus a sinusoidal

(6.9)

6-23
pressure pulse shape could be approximated. However, the dynamic

characteristics of practical driver systems (e.g., crystal diaphragm or electromagnetical ly driven piston) naturally degrade into sinusoidal

displacements as the frequency is increased, thus limiting the effectiveness of

this approach.

The variable-mass pressure generator utilizes a fixed chamber volume and

the rate of fluid flow into or out of the chamber is cyclically varied to

develop the dynamic pressure pulsations. These flow-modulated devices provide

a fast response so that relatively larger pressure amplitudes are available at

high-frequency conditions compared to the variable-volume generators. The

critical frequency limitation associated with acoustic dimensions of the

chamber still apply. Operation is limited to frequencies appreciably below the

natural frequency of the chamber which is dependent on the properties of the

fluid used and the chamber dimensions.

A siren-type device is often used for this class of SPG with the gas

entering the chamber through a critical flow orifice or nozzle from a constant

pressure source and leaving the chamber through a larger critical flow nozzle.

The throat of one of these nozzles is interrupted by a rotating disc or cylinder with throat-sized holes. The pressure in the chamber is dependent on both the rate of mass addition and the rate of mass discharge:

H

- n (A, - A

e 2- ) p

s (6.12)

where n is a constant given by

= 7

^

(6-13)

a = gas speed of sound

v = chamber volume

y = ratio of specific heats of constant pressure and volume

Ai = inlet orifice area

Ae

= outlet orifice area

p s = stagnation pressure of supply gas.

In order for the dynamic pressure inside the chamber to be sinusoidal, two

conditions must be met:

2A

as—1 and ... ±-AP<

. *e «1

A - - 2oj e P where Ap is the dynamic pressure component

A

Ae

= maximum exit area

"p = average chamber pressure.

6-24
When these conditions are met, the expression for the dynamic pressure

component becomes:

nA p

- Ap = - sin cot (6.14)

2u)

Developments in fluidic devices provide the basis for a new generation of

dynamic pressure generators. Fluidic pressure generators are, typically, low

amplitude devices but are capable of wide dynamic range. The devices described

so far make use of gaseous media and depend on the use of accurately

characterized reference sensors.

For liquid media there is a fundamental dynamic calibration technique

which produces sinusoidal stimuli. The following description summarizes the

method [23,24].

(3) Sinusoidal Pressure Generators for Liquid Media

A dynamic pressure source intended for the dynamic calibration of pressure

sensors can be used to produce sinusoidal ly varying pressures of up to 34 kPa

zero-to-peak, over the frequency range of approximately 50 Hz to 2 kHz. The

source consists of a liquid-filled cylindrical vessel, 11 cm in height, mounted

upright on the armature of a vibration exciter which is driven by a sinusoidally varying voltage. The sensor to be calibrated is mounted near the

base of the thick-walled tubular vessel with the pressure-sensitive element in

contact with the liquid in the tube. A section of the tube is filled with

small steel balls to damp the motion of the dimethyl siloxane working fluid

with a viscosity of 10 stokes. This helps to extend the useful frequency range

to higher frequencies than would be provided by an undamped system.

For the geometry described, both the amplitude of the sinusoidally varying

pressure and the natural frequency of the liquid column may be calculated to

first approximations by simple relations.

Damping is an important consideration because a damped system may have a higher useful frequency range than the same system undamped. With an undamped,

si ngle-degree-of-freedom system, the amplitude -frequency response remains

constant within +5 percent up to approximately 20 percent of the natural

frequency. In a system with optimum damping (a damping ratio of about 0.6 of

critical), the amplitude-frequency response remains constant within +5 percent

to about 80 percent of the natural frequency. To maintain a flat response to

2 kHz thus requires an undamped system with a natural frequency of 10 kHz or an optimally damped system with a natural frequency of 2.5 kHz. Other degrees of

damping would require natural frequencies between those values to achieve the

desired flat response to 2 kHz.

Four factors, in combination, determine the pressure levels attainable

over the frequency range of interest. They are: (1) the force and

displacement capabilities of the vibration exciter, (2) the density of

available working fluids, (3) the height of the liquid column, and (4) the

degree of damping. The last factor interacts with the others and depends on geometry, on the bulk modulus, and viscosity of the fluid. As noted above,

damping need not be considered at frequencies below about 20 percent of the

system's natural frequency because the amplitude-frequency response is flat up

6-25
to this limit. Up to that limit, the amplitude of the sinusoidal pressure

generated within the liquid column and acting on the sensor is given by:

P = ahc

p (6.15)

where

P = pressure (Pa zero-to-peak),

a = acceleration amplitude (g zero-to-peak),

hc

= liquid-column height above the center of the transducer

diaphragm (m), and

p = density of liquid (kg/m3

).

The natural frequency of a liquid column is directly proportional to the

square root of the velocity of sound in the liquid and inversely proportional

to the height of the column. For an infinitely stiff, open- topped vessel

containing the liquid, the system has one degree of freedom with a natural

frequency given by:

f = 0.25 1 /X~ (6.16)

h (-) ,

where

fn = natural frequency (Hz),

h = total height of liquid column (m), and

B = bulk modulus (Pa).

The quotient of B and p is proportional to the velocity of sound in the

1 i qui d.

In practice the tube is not infinitely stiff, but has some elasticity.

For thick-walled vessels, a volume change in the tube itself is small enough

compared to other volume changes that it may be neglected for practical

calibrations. More important, the sensor diaphragm forms part of the tube

wall, and since this diaphragm is displaced in response to pressure, an overall

volume change occurs. The effect of this change is to lower the natural

frequency as the effective bulk modulus is reduced. The effective bulk modulus

may be defined by the relation:

b' - (6.17)

where

b' = effective bulk modulus (Pa),

V = volume of liquid in the tube (m3

), and

dVt = change of volume resulting from unit pressure change (nr/Pa).

In the NBS calibrator, steel balls are used for damping and the volume of

the liquid is reduced by an amount equal to the total volume of the balls,

although the column height remains unchanged. Damping can be adjusted by

changing the number of steel balls and/or their size and/or the viscosity of

the liquid medium as described in reference [24].

6-26
Taking the above factors into account, the natural frequency of the

sensor-calibrator system is given by:

n h

V

B < v

c

- V

p(V

c

- V

b + BdV

t

) (6.18)

where

Vc

= volume available for liquid with no balls present (m3

),

Vb = volume occupied by balls (m3

), and

h, B, p , and dV t are as given above.

It is estimated that this dynamic pressure source has a total calibration

uncertainty of about +5 percent when calibrating a typical pressure sensor with

a flush diaphragm [24"J.

(4) Dynamic Motion Calibrations

The basic considerations for the dynamic calibration of motion sensors are quite similar to those for pressure sensors and are outlined in section

6.2.2.1. Motion sensor principles are discussed in section 4.2 (additional, more detailed coverage can be found in references [22] and [25]). The motion

sensor, in its common form of a damped spring-mass system, responds to a motion

of its case by a corresponding displacement (or force) between the mass and the

base. This displacement (or force) is transduced into an electrical signal

which is proportional to displacement, velocity, or acceleration, depending on the relation of measurand frequency to the natural frequency of the spring-mass

system.

The dynamic calibration of such sensors is then a matter of applying a known sinusoidal motion to the case of the sensor and measuring the resultant

output. For sensors with very large full-scale ranges of acceleration,

limitations of sinusoidal motion generators require another approach: This is

the use of a transient input, such as a step or pulse input. Such methods will

be discussed in section 6.2.2.3.

The most common dynamic sinusoidal calibrator for linear motion is the

Electro Dynamic Vibration Excitor . It is a readily available commercial device

similar to a large loudspeaker (without its cone) driven by an electronic

amplifier. Typical systems can generate undistorted sinusoidal linear

displacements with amplitudes up to about one inch peak-to-peak, frequencies

from about 5 Hz to 10 kHz, and peak-to-peak accelerations up to 100 g's. At

low frequencies, those systems are limited in displacement and therefore only

capable of generating low amplitude accelerations. At high frequencies they

are acceleration-(force)-! imited, thus capable only of small displacements.

Within these limitations, they are good working systems with the motion of the

sensor easily determinable. The motion is calculated from measurements of

displacement (optically or electronically) and frequency. Alternately, a "reference" sensor can be used, back-to-back, with the sensor to be calibrated.

As discussed in section 6.2.2.1, the "reference" sensors must have stable and

well known characteristics, and must be mounted as close to the sensor under

test as practicable. The latter is particularly important at high frequencies.

If this is not assured, the motions applied to the two sensors may not be

identical and the resulting calibration erroneous.

6-27
For angular motion similar considerations apply. A device capable of

generating angular sinusoidal displacements was developed at NBS about twenty

years ago. It was an electrically driven torsion pendulum with a vertical

axis. Its frequency range was about 0.5 Hz to 30 Hz, with a maximum angular

acceleration of 40 rad/sec^ [27].

The " Earth's Field Dynamic Calibrator for Accel erometers " was developed to calibrate ac eel erometers at frequencies from about 30 Hz down to about 0.1 Hz,

by rotating the sensor at uniform velocity in the earth's gravitational field,

the magnitude of which is well known. The electrical connections to the sensor

are made through low noise sliprings. Air bearings and a magnetic coupling

insure low friction and constant speed. This device has the limitation that

the exciting force cannot exceed +_lg n

, and the further limitation that the

accelerometer under test must have negligible response to transverse excitation

[26].

The "dual centrifuge" was developed in order to generate large

acceleration amplitudes at low frequencies and overcome the limitations of the

earth's field device.

It is capable of generating large amplitudes of acceleration in the

frequency range from 0.5 Hz to about 30 Hz. It consists essentially of a small

turntable mounted on a large one, each turning in a horizontal plane. The

accelerometer is mounted on the small table with its sensitive axis in a horizontal plane. When the turntables are rotating with constant angular

velocities, the seismic mass in the accelerometer responds to a sinusoidal ly

varying component of the centrifugal force field generated by the rotation

of the large table. A system of pulleys and timing belts is arranged so that

the small turntable has zero absolute angular velocity in inertial space at all

times (its motion is like that of the connecting rods for the drivewheels of a steam locomotive). The equation of motion of the seismic mass of the

accelerometer is the same as for sinusoidal linear motion. Due to the

character of the motion, the accelerometer is also subjected to transverse

acceleration during each cycle and the output will reflect this in its

departure from the ideal. The magnitude of the generated acceleration can be

varied by locating the small turntable at various distances from the center of

the large one.

The dual centrifuge can generate accelerations of +1 gn at 1 Hz,

increasing to +100 g n at 10 Hz to 25 Hz [27],

It is possible to generate very large amplitude sinusoidal acceleration

amplitudes through resonant amplification by driving beams or rods at their

resonant frequencies [22]. This subjects the sensors, which are mounted at the

end of the beam or rod, to large amplitudes of motion. Optical sensing of

displacements or the use of reference sensors are employed to establish values

of applied acceleration. Disadvantages of this method include limitation to

operation at a resonant frequency, fatigue failures of beams or rods after a short time, and uncertainties in the measurement of displacement amplitudes.

(5) Dynamic Calibrations for Other Sensors

Dynamic calibration techniques for sensor types, other than the above, may

be under development in measurement laboratories, although little information

appears available. Low range force sensors can be tested similarly to

6-28
acceleration sensors by generating inertial forces. If a heavy, known mass is

mounted on the force sensor and the whole system is vibrated at known

acceleration amplitudes, the corresponding dynamic force can be calculated.

Due to force limitations of commercial vibration exciters, this approach is

feasible only for relatively low range force sensors.

Clearly in the area of dynamic sinusoidal calibration methods for sensors,

much more work needs to be done to meet test requirements.

6.2.2.3 Step Function Stimuli

As pointed out in section 6.2.2.1, the preferred method for dynamic

calibration of sensors is the application of sinusoidal measurands.

Limitations of this method, particularly when large amplitudes are required,

call for other approaches.

The application of a well characterized transient such as a step function

(actually a ramp function with very fast rise) can be used for dynamic

cal ibrations.

(1) Dynamic Pressure Calibrations

Again, as in the previous sections, it is helpful to treat separately the

step function calibrations for different types of sensors.

In the case of pressure sensors, ANSI Standard B88. 1-1972 [21] provides

details, which are summarized below.

A shock tube , in its simplest form, consists of two sections of tubing

separated by a thin diaphgram. When these two sections are pressurized to

different pressure levels and the diaphragm is suddenly ruptured, the higher

pressure gas will immediately begin to flow into and compress the gas at lower

pressure. At a distance of approximately 10 to 15 tube diameters downstream

from the diaphragm, a well formed shock wave is established. This shock wave

continues to move through the remainder of the gas in the low pressure section

at approximately a constant velocity. Behind the shock wave the pressure

suddenly rises to a new value resulting in a positive pressure step. The

length of time the pressure remains constant behind the shock wave depends on several factors. These include the dimensions of the shock tube, the position

in the low pressure section at which the pressure is being monitored, the

degree of smoothness of the inner walls of the low pressure section, the type

and design of the diaphragm, and the type, temperature, and initial pressure of

the gas in each section.

When a shock tube is utilized for pressure sensor calibration, several

parameters must be measured before the amplitude of the pressure step can be

ascertained. These parameters include the shock wave velocity, V s

, and the

initial absolute pressure, Pj_, and temperature, T^, of the gas in the low

pressure section.

If a pressure sensor is mounted flush in the sidewall of the low pressure

section, it will sense a change in pressure, Ap, when the shock wave passes

over it. The equilibrium pressure and particle velocity behind the shock wave

are determined from the Rankine-Hugoniot relations [7]. When air is used as

6-29
the working gas in the low pressure section, the amplitude of the pressure step can be computed from the following equations:

where V

s is expressed in meters per second, T in degrees kelvin, and Ms is the shock wave mach number. When gases other than air are used, equations

(6.19) and (6.20) do not apply.

Since the working gas temperature must be known, a convenient method of

determining it is from a measurement of the static wall temperature of the

shock tube. Except at very low pressures, the temperature of the working gas

closely approaches that of the wall.

The shock wave velocity, V

s

, is determined by measuring the time

necessary for the shock wave to pass between points spaced a known distance

apart along the path of the velocity vector. Because the velocity of the shock wave tends to decrease with distance, the last pair of points should be in

close proximity (less than one tube diameter) from the sensor undergoing

calibration. Several different types of sensors can be used to detect the

passage of the shock wave past these points, the most common being pressure

sensors, thin-film heat-transfer gages, and light screen photo-electric gas

density sensors. The shock wave transit time, Ats

, between pairs of sensors

is measured with electronic timers or with calibrated oscilloscope sweeps. The

shock wave velocity, V

s

, is computed from the equation V

s - spacing between

sensors/Ats

. Because of the squared relationship between V

s and P, an uncertainty of 0.5 percent in the measurement of the shock wave velocity

produces an uncertainty of at least 1 percent in the determination of pressure

step amplitude.

When the pressure sensor is mounted flush in the sidewall of the shock

tube, the rise time of the pressure step resulting from the passage of the

shock wave depends on the shock wave velocity and the transverse length, d, of

the sensor diaphram, in the direction of shock wave propagation. The time

required for the pressure on the sensor to change from Pi to ?2

(?2 - p l +AP) is given by the expression

(6.19)

with Ap and p^ in compatible pressure units

and

(6.20)

(6.21)

6-30
The maximum theoretical rise time (1U to 90 percent) for pressure sensors with

circular diaphragms mounted flush in the sidewall of a shock tube can be shown

to be:

t 0.687d

r (6.22)

where d and V

s must be in consistent units.

The side-mounted mode of operation is recommended when:

• This is the manner in which the sensor will be used in the actual

appl ication.

• Maximum accuracy in the determination of the pressure step amplitude is

desi red.

• It is desirable to minimize sensor ringing.

• The incident wave is considerably "cleaner" than the reflected wave.

If the end of the low pressure section of the shock tube is sealed off

with an end plate, the moving shock wave, in striking the plate, will be

reflected by it. A pressure sensor mounted flush in the end plate will detect

only the reflected shock wave. The reflected shock wave is characterized by a much shorter rise time (usually nanoseconds) and a higher pressure as compared

to the incident shock wave (sidewall measurement). The rise time of the

pressure step associated with the reflected shock wave is sufficiently short to

excite all the ringing frequencies associated with any flush-mounted pressure

sensor. When air is used as the working gas, the amplitude of the pressure

step behind the reflected shock wave is

where Ms and Pj_ are defined as in equations (6.19) and (6.20).

Because of the complex relationship between AP and Ms in

equation (6.23), any uncertainty in the measurement of the shock wave velocity,

M2, may produce an uncertainty in the determination of the pressure amplitude

AP several times larger.

The pressure behind the incident and reflected shock waves remains

constant for a period of time which is dependent on the design of the shock

tube and on the type, the temperature, and the pressure of the gases initially

in the two sections. For a given shock tube geometry, the longest duration of

constant pressure behind the reflected shock wave is obtained when the shock

tube is operated under "tailored" conditions. Depending on the operating

conditions and shock tube geometry, the period of constant pressure behind the

reflected shock wave may vary from a few hundred microseconds to several

milliseconds.

The end-plate mounted mode of operation is recommended when:

• Ringing frequencies must be determined.

AP (6.23)

6-31
• This is the manner in which the sensor is to be used in the actual

appl i cation.

• The maximum pressure step amplitude is required in calibration.

e The maximum duration of constant pressure behind the shock wave is

desired.

Vibration of the walls and end plate of the shock tube occurs during

operation. In order to determine the effect of this "ground shock"

acceleration on the sensor output, the sensing end of the sensor must be

blanked off from the pressure wave without significantly altering the

acceleration components, and the resultant output measured. Acceleration

effects can be minimized by utilizing heavy -walled tubing for the low pressure

section of the shock tube, by using a heavy end plate and by shock-mounting the

tube.

When a shock wave passes through the working gas, the temperature of the

gas is suddenly raised. The new temperature, T2, varies with the square of

the shock wave mach number, Ms

, as well as with the type and initial

temperature of the gas. If the sensor is sensitive to transient temperatures,

then the temperature step produced by the shock wave may cause errors in the sensor calibration.

To determine the extent of such errors and to reduce their effect, a temperature shield may be employed. Thin coatings of opaque insulating

materials sprayed on or bonded to the diaphragm make good shields but may alter

the sensor characteristics. A sensor should always be checked for transient

temperature sensitivity. This will be covered in more detail in

section 6.3.3.2.

A typical example of a shock tube built for, and used by, the National

Bureau of Standards generates a pressure step function with a rise time of less

than 10"° seconds. The shock tube is 20 ft long and is divided by a cellulose acetate diaphragm into two chambers, 12 ft long and 8 ft long. The

12 ft section is filled with helium and the 8 ft section with dry air; the

ratio of respective absolute pressures in these sections is set to be 2.7 to 1 over the entire range of operation of the shock tube. The pressure of the

helium is set to a value approximately equal to the desired pressure amplitude

of the step function. Upon rupture of the diaphragm, helium pushing into the

air chamber generates a shock wave in the air which travels the length of the

8 ft section, and is then reflected from the rigid end wall at an increased

pressure. The amplitude of the step function pressure to which a sensor in the

end wall is exposed ranges from about 6 psi to 1000 psi and the duration of the

pressure step at these values is about 4.5 milliseconds.

Shock! ess Step Pressure Generators form another class of devices for the

dynamic calibration of pressure sensors. A number of devices have been

developed which generate a rapidly rising pressure step between two pressure

levels. Most of these units employ a quick-opening valve. At least one utilizes a burst diaphragm. The geometry of the generator and the opening time

of the valve or burst diaphragm are chosen to preclude the formation of shock waves when the device is operated. Shockless step generators have been

designed and successfully used to produce both increasing and decreasing

6-32
pressure steps. Although most of these generators employ gaseous media, a few

liquid devices have been developed and used. The shockless pressure step

generator has the following advantages over other dynamic pressure

cal i bra tors.

• The magnitude of the pressure step generated by the device is

determined by measurements of static pressure before and after the

quick-opening valve is opened, thereby permitting good accuracy.

• The duration of the state of constant pressure following the pressure

step can be made of any chosen time duration.

t Both the initial pressure on the sensor and the magnitude of the

pressure step are controllable over very wide pressure ranges.

• This calibrator is superior to the shock tube from the standpoint of

operational speed and simplicity of technique.

The dynamic characteristics of a shockless pressure step generator are determined by measurement with a calibrated reference sensor possessing a rise time of no more than one-fifth that of the measurand. The following

dynamic characteristics of the generator should be known: rise time,

overshoot, undershoot, and the inherent ringing frequencies with their

associated damping ratios. Also of interest is the stability of both static

pressure levels ?i (initial pressure) and P% (final pressure).

When the pressure rise time is one-fifth that of the sensor undergoing

test or calibration, the error in the measured value of sensor rise time is

less than 1 percent. If this criterion cannot be met, the composite rise time

must be analyzed carefully to determine each component of the rise time.

Vibration present during the operation of the shockless pressure step

generator should be minimized by careful design. In general, the shorter the

rise time of the device, the greater is the level of vibration acceleration

(ground shock). In those units which utilize poppet values, it may be necesary

to open the poppet valve more slowly when calibrating at very low pressures in

order to keep the vibration effects on low range sensors to a minimum.

Associated with the pressure step produced by these generators is a dynamic temperature change whose amplitude is related directly to the pressure

change, ?2 - P\, and inversely to the rise time of the measurand. The

effect of this dynamic temperature pulse on the response of both the test and

reference sensor must be determined. When a gaseous medium is used in the

shockless step generator, the rise time of the measurand is inversely related

to the speed of sound in the gas. For this reason helium is used when very

short rise times are desired.

The following is a brief description of several shockless step pressure

generators developed in recent years. The first one was developed at the

National Bureau of Standards [28]. The range of pressures of this pneumatic

calibrator is from about 2 psi to 100 psi

The rise time of the generated pressure is about 0.9 ms (much longer than

that of the shock tube) and the initial oscillation superimposed on the step

6-33
decreases to less than 2 percent of the step amplitude within 15 ms. The heart

of the calibrator is a pneumatically operated quick-opening valve which applies

air pressure from a large storage tank to the sensor under test. The tank

pressure is set to the desired value by a pressure regulator and measured by a precision dial pressure gage. Since the volume of the storage tank is more

than 100 times that of the combined internal volumes of the quick-opening valve

and the fixture holding the sensor, gas flow and temperature change are held to a minimum. The pressure in the storage tank after the step is applied to the

sensor, as indicated on the dial gage, is then equal to the amplitude of the

pressure step within about +1 percent. This calibrator is most useful for the

inspection of sensors for dynamic errors at low frequency such as those due to

hysteresis and creep.

Another type of step function pressure calibrator was developed at the

U.S. Naval Ordnance Laboratory [29]. It is also based on a quick-opening valve

mechanism, using a gaseous medium. It consists of a poppet valve with a long

rod which quickly opens the passage between a pressure storage vessel and the sensor to be calibrated. The quick-opening action is accomplished by means of

a weight which is dropped onto a plate attached to the far end of the valve rod

stem. This device is capable of rise times as short as 50 ms and pressure

amplitudes up to 1000 psi.

A liquid medium step function pressure calibrator was also developed at

the National Bureau of Standards [30]. This calibrator consists of a conical

valve with a long stem in a large pressure vessel. The sensor to be tested is

mounted to face a small cavity in front of the conical valve. Application of

pressure to a piston at the end of the long stem of the conical valve causes

the latter to close. Pressure of the desired amplitude is built up in the

large pressure vessel. The sensor cavity is brought to zero measurand and

ambient pressure by a bleeder valve which is thereafter kept closed. A fast

release of the pressure on the valve stem piston relieves compressive stress in

the valve stem and the conical valve begins to open. As the pressure in the sensor cavity builds up, opening of the valve accelerates, so that a pressure

step of short rise time is applied to the sensor. As in the pneumatic step

function calibrator, the ratio of the volume of the large pressure vessel to

that of the sensor cavity is very large. Like the pneumatic step function

generator, static measurement of the amplitude of the pressure step to within

about +0.2 percent is possible using a precision dial gage. By the selection

of cavity size, oil viscosity, and the diameter of the valve stem, a nearly

optimum step function of pressure with a rise time of less than 3 ms can be

obtained at most pressures from 500 psi to 3000 psi.

This device also is most useful for the inspection of sensors for dynamic errors at low frequency such as those caused by hysteresis and creep.

Pressure pulse generators have been developed to provide single peaking

pulses of reasonably controlled amplitudes [31]. These pulse generators

produce a dynamic measurand which is not a step function, but which may

resemble a single half cycle of a sine wave. One technique employed to

generate such a pulse is to drop a mass onto a piston in contact with the

surface of an "incompressible" fluid contained within a fixed volume. The

amplitude of the pulse is dependent on the fluid compressibility, the mass, its

initial height above the piston, and the piston area. The pulse generator is

not an absolute calibration device and requires a reference pressure sensor of

6-34
known characteristics to monitor the pulse and provide a peak value measurement

for the sensor under test. The greatest advantage of the pulse generator is

the comparative ease with which very high pressure pulses can be generated.

Care must be taken in the selection and location of the reference sensor used

since results of the calibration are dependent on this comparison standard.

The recommended conditions of operation of section 6.2.2 relative to the

comparison sensor apply equally well to these generators. In order to achieve

accuracy in calibration using a liquid medium pulse generator, it is essential

that no pockets of gas exist in the vicinity of either the reference or test

sensor.

(2) Dynamic Acceleration Calibrations

Several methods are available for the dynamic calibration of acceleration

sensors.

Step acceleration (shock) calibrators are used to overcome some of the

amplitude and frequency limitations of sinusoidal calibrators. The situation

is similar to that for dynamic pressure calibrators.

Impact methods for high-acceleration calibration generate sudden velocity

changes with reproducible amplitudes and time durations. They can be used to obtain calibrations up to about 30 000 g n (where gn is the acceleration of

gravity). These methods make use of the fact that the velocity change during a transient pulse is equal to the time integral of acceleration:

v - J adt (6- 24 >

a = acceleration

where the initial or final velocity is taken as reference zero and the

integration is performed to, or from, the time at which the velocity is

constant. The voltage output of the sensor can be described as:

r _ Sa

L

" gn (6.25)

s a

= the calibration factor in volts per g

g n = acceleration of gravity.

When the two relations (6.25) and (6.26) are combined, one gets

T,

/

T

i

2 Egm dt

(6.26)

S

a

" v Methods for determining the integral are described in the "Shock and Vibration

Handbook" [22] and other texts. With the integral determined and the velocity

known, the calibration factor of the acceleration sensor can be found.

6-35
Various devices for such impact calibration are described in the

literature [22,32]. The Ballistic Pendulum consists of two masses suspended by

wires or metal ribbons. These restrict the masses to motion in a common

vertical plane. The sensor to be calibrated is mounted on the far end of the

anvil mass. The hammer mass is raised to a predetermined height and then

released, striking the anvil mass. The resultant velocity of the anvil mass

can be calculated from optical displacement measurements as a function of time.

The duration of the pulse input can be varied by the use of different contact

materials between hammer and anvil. Typical times range from about 0.5 ms to

5 ms.

Another calibrator used a vertically Dropping Hammer Mass on which the sensor is mounted, impacting on a fixed anvil. The velocity change for this

system can be calculated from the height of the hammer drop and the height of

the subsequent rebound [22,32].

In the Drop-Ball Calibrator , the sensor is mounted on the bottom flat of an anvil mass held in position by magnets. A large steel ball is dropped from

the top of the calibrator to impact the anvil. The anvil and sensor are accelerated in a short free-flight path until they are caught by a soft

cushion. The anvil passes through an optical timing gate to enable measurement

of the velocity after impact. Acceleration amplitudes and pulse durations can be varied by selecting the proper anvil mass, ball mass, and contact materials

between ball and anvil. Attainable shock acceleration and durations range from

100 g n at 3 ms to 10 000 g n at 0.1 ms. Calibration uncertainties are estimated at about 5 percent to 10 percent [22].

There appears to be little information on dynamic calibrators for other

types of sensors than those for pressure and motion. It would seem practical

to adapt certain types of step pressure calibrators for the dynamic

calibration of force sensors . A quick-opening valve pressure calibrator of the

type developed at NBS L28J was modified so that the generated step pressure

drove a piston against the input end of a force sensor. The electrical output

signal indicated a compression force input with a rise time of shorter than

2 ms and an amplitude equivalent to the product of the pressure and the piston

area. Such calibrators warrant future development. A variation of this

approach could be used to apply a step force in tension, as well as

in compression.

An experimental system for the dynamic calibration of flowmeters (turbine

types) was reported by NASA several years ago. In it the flowmeter was elastically coupled to a pipe in which liquid flowed at a constant speed. The

flowmeter was vibrated longitudinally along the axis of flow, thus modulating

the flow, as seen by the meter. With constant meter displacement over a specified frequency range, a measure of the dynamic performance could be

obtained. No commercial version of the system is available.

Temperature sensors are basically first-order systems, having no resonances. Their dynamic characteristics can be obtained from step function

measurand inputs. The time constant of the sensor is generally all that is

required. The time constants of most temperature sensors used in engine or ordnance monitoring ATE systems are relatively long, typically on the order of

seconds. Consequently, it is probably only necessary to rapidly move the

sensing end of the device from a medium at one known, steady-state temperature

6-36
to another at a different steady-state temperature. No commercial version of

such a dynamic calibrator is believed to exist.

6.2.2.4 Random Stimuli

Dynamic calibrations of sensors can be performed in a variety of ways, as discussed in the sections above. For ease of data reduction, and, usually,

ease of generating the stimuli, preference is given to sinusoidal wave shapes,

since all the energy of the stimulus is concentrated at one frequency. This

simplifies the data reduction process as well. Other important dynamic stimuli

are step and ramp functions, pulse (square, triangular, half sine) and random

or white noise inputs.

The choice of method is normally dictated by the amplitude and frequency

range (or rise time) required to characterize the sensor. The most desirable

methods, however, may not be usable for other reasons.

The use of random input signals for dynamic calibrations of sensors is a more recent development. It became practical with the advent of sophisticated

spectrum analyzers and computer based data reduction equipment. Random

stimuli ideally contain signals with all frequency and phase components, thus

the power spectral density of a white noise source is constant throughout its

bandwidth. The term "white noise" is used in analogy to white light which also

contains frequency components throughout the optical spectrum. The usefulness

of random stimuli is primarily due to the fact that if they are applied to a lightly damped resonant system, that system acts as a narrow band-pass filter

near the resonance. Thus the resonance (or resonances) of a physical system

can be excited by random inputs and therefore identified. Random stimuli sources can often excite resonances far beyond those excitable from other

dynamic calibration sources.

Random stimuli are used primarily in vibration testing at this time. A

random vibration can be considered to be a sum of a large number (tending to

infinity) of harmonic vibrations of appropriate amplitude and phase. The total

power is the sum of the powers in the individual components. Power spectral

density describes the power per unit frequency interval. For white noise the

power spectral density is a constant at all frequencies making it especially

suitable for dynamic calibration purposes. In addition, some environmental

vibration testing using random signals has come into favor due to more realistic and shorter duration test possibilities. This is discussed in

section 6.3.3. The "Shock and Vibration Handbook" [22] provides a good

coverage of the subject of "statistical concepts in vibration."

The application of random stimuli to pressure sensors has been suggested,

but no known commercial devices are marketed.

6.3 Operating Environments and Tests

6.3.1 General Considerations

Most military systems are designed for operation while being subjected to

a wide variety of operating environments. To assure proper operation, the

6-37
systems (and/or their individual components) must be tested. The discussion

below is extracted from an engineering design handbook promulgated by the

U. S. Army Material Command [33].

Environmental testing consists of subjecting equipment to various

conditions such as temperature, vibration, radiation, and humidity, in order to

determine or verify its capability to operate satisfactorily when subjected to such stresses. Strength, life, and performance tests, as well as other basic

test types, may all involve environmental testing.

The effect of environmental conditions is an important consideration in

reliable design of equipment. Environmental testing may be performed during

the initial stages of equipment manufacture to determine its ability to

withstand adverse use conditions.

Generally, there is a deliberate attempt to simulate as closely as possible the environmental conditions expected during equipment operation.

Such simulations are performed, for example, in reliability demonstrations with

samples of prototype hardware. Usually, certain critical features of the total

operational environment are simulated at specific severity levels in order to uncover design and material weakness and those workmanship errors not uncovered

during inspection. In still other cases (such as development tests), the

operational environment may not be known and test conditions consequently cover a wide range.

All environmental tests have the common objectives of determining the

effect of the environmental conditions on an item or verifying that the item is

capable of proper operation under these conditions.

Environmental testing ranges in sophistication from very crude methods,

such as using an improvised temperature chamber, to testing in very elaborate

facilities permitting many combinations of conditions to be simulated. Tests

may be purposely destructive (as in strength and life testing) or nondestructive (such as proof tests and burn-in).

The appropriate test conditions must be carefully selected. Basic factors

to consider are:

• The possible environmental conditions during intended use of the

equipment.

t The subset of these that must be used in testing.

• The capability for generating and controlling these test conditions.

The environmental factors that can affect the behavior of the item during

field operations must be determined and simulated to the extent feasibile

within the constraints of cost, schedule, and testing capability. Not all

environmental conditions that affect behavior can be readily simulated, and

very rarely can all be generated simultaneously to account for interaction

effects. Trade-offs therefore must be made when selecting the test

conditions.

6-38
It should be noted that environmental testing must consider all the

environments encountered in manufacturing, storage, transportation, and

handling, as well as those experienced during operational use.

The environmental conditions to be encountered by equipment are not always

known in exact form. No one knows precisely, for example, the environmental

profile that a field artillery rocket will experience throughout its life,

including all types of environmental factors and their severity levels. It is

only possible to select representative characteristics, such as averages or maximum levels, or major factors which adequately describe conditions for a test.

Environmental conditions of greatest interest from the reliability

viewpoint are those that have detrimental effects on equipment operation.

Table 17 lists typical detrimental effects of environmental factors. In many

cases, effects not detectable when the factors are encountered singly appear

when two or more are present simultaneously. For example, some electronic

components function properly in either a low temperature or a vibrational

environmental environment, but when the environments are combined, component

leads break. Some possible combined effects on several environmental factors

are illustrated in table 18. Combined environments do not always have adverse

effects. For example, low temperature inhibits the growth of fungi and rain

dilutes the corrosion effects of salt spray.

A less frequent effect occurs when one environmental condition creates

another, e.g., when arcing between switch or relay contacts causes the

formation of ozone, thus changing the environment and its effect.

Some conditions cause cumulative, nonreversible changes in the equipment;

therefore, when considering equipment behavior, the history of environmental

exposures must be considered. For example, heating from welding and soldering

can cause permanent shifts in device characteristics; mechanical shock can result in permanent dislocation of a lead or a part; and nuclear radiation can cause permanent defects in semiconductor devices.

The need for conditioning items prior to environmental testing to simulate

the historical effects must be considered. This conditioning is sometimes

necessary to assure that the response during the test is representative of that

in operational use. Knowing the environmental history is less important when

the effects are reversible, but the reversibility of all important responses

can be determined only through careful analysis. Ignoring the nonreversible

effects that have occurred in previous tests and operations can result in

misleading environmental test results. Of course, these effects may be

difficult to assess or simulate, but just knowing of their existence can be

very valuable for the test designer.

Experience is frequently the most useful guide for selecting the

environmental factors and the severity levels and combinations of them to be

used in a test. This prior knowledge based on experience can help reduce the

number of environmental tests to those needed to ensure the successful

operation of the item. This is an extremely important point: Testing is very

expensive, both in terms of equipment cost and personnel time and cost. This

point should be kept in mind also when being guided by one of the Standard

Testing Documents. Best known among these are MIL-STD-202E (Test Methods for

6-39
Electronic and Electrical Component Parts), MIL-STD-810C (Environmental Test

Methods), and, related, MIL-T-28800B (Test Equipment for Use with Electrical

and Electronic Equipment, General Specification for). All three documents

include, in the specified tests, various levels of severity. There is always a tendency to specify, or use, a more severe level (or a wider frequency range,

or a longer test duration) than may be really necessary--"To be on the safe

side!" In view of the costs and time involved in testing, test conditions

should only be selected through close and continuing coordination between

system designer and service user.

The difficulties associated with common environmental factors—such as temperature, vibration, and thermal shock —nearly always receive attention.

Less familiar factors can sometimes be equally or even more important, e.g.,

hail and insects demand special attention to determine what characteristics and

severity levels are required.

Hail, for example, may cause mechanical impact damage and the size, shape,

velocity, and number per unit area of the simulated hailstones are the

important characteristics. On the other hand, the vibration induced by the

incident hail may be the most significant factor. Insects can cause both

mechanical and chemical damage; both characteristics must be evaluated.

When there is little available knowledge about the operational environment

or its effect on an item, it is often simpler and more economical to test and

see what happens than to spend a great deal of time and money on an independent

study. This is essentially the "buil d-and-test" approach, which has limited

value for large and expensive items, but when used with discretion it can be

useful for new designs or for new applications of old designs.

Tables 17 and 18 listing "Environments and Typical Effects" [33] follow.

The experimental simulation of environmental conditions is discussed in section

6.3.2.

6.3.2 Simulation of Environmental Conditions

The need for environmental tests to simulate all or some of the conditions

listed above has led to the development of sophisticated and detailed test

methods. These include MIL-STD-202E, MIL-STD-810C, MIL-T-28800B, and others

listed in section 8.3. These documents should be used for guidance in the

specification and performance of environmental tests.

Several factors should be considered. It is not always possible to

generate complex conditions, even with the most elaborate facilities. Air

turbulence, gases, or insect conditions can be difficult to simulate. Many

facilities are even limited in their capability to generate complex temperature

profiles.

A great deal of effort has been devoted to developing sophisticated

simulation facilities. But there may be other ways to determine if a device

can withstand a hostile environment. First of all, it is the effect of the

environmental conditions that is of interest, not just the conditions

themselves. Therefore, substitutes should be considered. For example, pebbles

might be used as a substitute for hailstones if mechanical damage from impact

6-40
TABLE 17

Environments and Typical Effects

Envi ronment Effects

High temperature Parameters of resistance, inductance,

capacitance, power factor, dielectric

constant, etc., will vary; insulation may

soften; moving parts may jam due to expansion, finishes may blister; devices

suffer thermal aging; oxidation and other

chemical reactions are accelerated; viscosity

reduction and evaporation of lubricants are problems; structural overloads may occur due

to physical expansion.

Low temperature Plastics and rubber lose flexibility and

become brittle; electrical constants vary;

ice formation occurs when moisture is

present; lubricants gel and increase

viscosity; high heat losses; finishes may

crack; structures may be overloaded due to physical contraction.

Thermal shock Materials may be overstressed instantaneously

causing cracks and mechanical failure;

electrical properties may be altered

permanently.

Thermal radiation Causes heating and possible thermal aging;

surface deterioration; structural weakening;

oxidation; acceleration of chemical

reactions; and alteration of physical and

electrical properties.

Acceleration Mechanical overloading of structures; items

may be deformed or displaced; mechanical

functions may be impaired.

6-41
TABLE 17 (continued)

Mechanical strength may deteriorate due to

fatigue or overstress; electrical signals may

be mechanically and erroneously modulated;

materials and structures may be cracked,

displaced, or shaken loose from mounts;

mechanical functions may be impaired;

finishes may be scoured by other surfaces; wear may be increased.

Mechanical structures may be overloaded

causing weakening or collapse; items may be

ripped from their mounts; mechanical

functions may be impaired.

Vibration applied with sound waves rather

than with a mechanical couple; can cause the same damage and results as vibrational

environment, i.e., the sound energy excites

structures to vibrate.

Penetrates porous substances and causes leakage paths between electrical conductors;

causes oxidation that leads to corrosion;

moisture causes swelling in materials such as gaskets, excessive loss of humidity causes embrittlement and granulation.

Salt combined with water is a good conductor

which can lower insulation resistance; cause galvanic corrosion of metals; chemical

corrosion of metals is accelerated.

Structures such as containers, tanks, etc.,

may be overstressed and fractured; seals may

leak; mechanical functions may be impaired.

Structures such as containers, tanks, etc., are overstressed and can be exploded or fractured; seals may leak; air bubbles in

materials may explode causing damage;

internal heating may increase due to lack of

cooling medium; insulations may suffer arcing

and breakdown, ozone may be formed;

outgassing is more likely.

6-42
TABLE 17 (continued)

Zero gravity Disrupt gravity-dependent functions;

aggravates high- temperature effects as convective heat removal ceases.

Magnetic fields False signals induced in electrical and

electronic equipment; interference with

certain functions; can induce heating; can alter electrical properties.

Electromagnetic Interference Causes spurious and erroneous signals from

electrical equipment and components; may cause complete disruption of normal

electrical and electronic equipment such as communication and measuring systems.

Sand and dust Finely finished surfaces are scratched and

abraded; friction between surfaces may be

increased; lubricants can be contaminated;

clogging of orifices, etc.; materials may be

worn, cracked or chipped.

Nuclear/cosmic radiation Causes heating and thermal aging, can alter

chemical, physical, and electrical properties

of materials; can produce gases and secondary

radiation; can cause oxidation and

discoloration of surfaces; damages electrical

and electronic components, especially

semiconductors

Solar radiation Effects similar to those for sunshine,

nuclear/cosmic radiation; and thermal

radiation.

Albedo radiation Albedo radiation is reflected electromagnetic

(EM) radiation; amounts depend on the

reflection capabilities of illuminated object

such as a planet or the moon; effects are the same as for other EM radiation.

Winds, gust and turbulence Applies overloads to structures causing

weakening or collapse; interferes with

function such as aircraft control;

convectively cools surfaces and components at

low velocities and generates heat through

friction at high velocities; delivers and

deposits foreign materials that interfere

with functions.

6-43
TABLE 17 (continued)

Applies overloads to structures causing

weakening or collapse, removes heat from

structures and items; aids corrosion, causes

electrical failures; causes surface

deterioration; and damages protective

coating.

Can interfere with optical and visual

measurements; deposition of moisture,

precipitation, etc.; enhances contamination;

can act as an insulator or attenuator or radiated energy.

Sunshine (ultraviolet radiation) Causes colors to fade; affects elasticity of

certain rubber compounds and plastics;

increases temperatures within enclosures; can cause thermal aging; can cause ozone formations.

Chemical contaminants Corrosion of metals may be accelerated;

dielectric strength may be reduced; an explosive environment can be created; heat

transfer properties may be altered; oxidation

may be accelerated.

Insects, fungi Can cause surface damage and chemical

reactions; can cause clogging and

interference with function; can cause contamination of lubricants and other

substances.

Precipitation: sleet, snow,

rain, hail, dew, frost

Clouds, fog, smog, smoke,

haze, etc.

6-44
TABLE 18

Illustration of Interacting Environmental Effects

Salt Spray Vibration

Low

Temperature

High

Temperature

High

Temperature

Low

Temperature

Vibration

Salt Spray

Accelerate

Corrosion

Decelerate

Corrosion

No

Interaction

Increase Rate

of Wear

Intensity,

Fatigue,

Rupture, etc.

Mutual ly

Exclusive

6-45
is of interest. Or, if vibration induced by hailstones is of interest, then a vibration test already scheduled may be adequate.

Some effects are investigated more easily at a more fundamental level.

Also, the environmental conditions sometimes may be separated into fundamental

components. For example, a temperature profile may be simulated by high and

low temperature levels and thermal shock. In such cases, effects such as nonreversible ity, interactions, and aging must be accounted for.

Elaborate environmental test facilities are not always required. Simply

heating individual circuit components with a soldering iron or hair dryer may

in some cases be more informative than testing the entire circuit or assembly

in an oven, since the contribution to temperature instability of each component

may be examined. And, in the absence of certain capabilities, an improvised

test may be better than none at all. For example, mechanical shock may be

simulated by dropping the item from a prescribed height.

When facilities do not exist for generating combined environments,

combined environmental effects must be simulated by using single environments

in sequence. If the severity levels of the environments are set not to

deliberately damage the equipment, the order of application is determined by

whatever is most convenient. When tests cause damage, the order of

environments must be considered carefully. First, one should apply those

conditions least likely to damage the specimen. For mechanical parts, humidity

and salt spray tests logically would usually be applied before vibration or a mechanical load test. An electronic part usually would be tested by applying

vibration before high temperature. Such test sequencing allows the maximum

amount of information to be obtained before damage occurs.

Ordering of environments for items composed of both mechanical and

electrical parts is not clear-cut. The same basic criteria still apply, and

the ability to repair the item can greatly influence the ordering.

If both single and combined environmental conditions can be generated, it

does not necessarily follow that the combined testing is preferable. The final

choice of an approach depends on what is to be accomplished with the test and

is influenced strongly by factors such as time, cost, skills, and

instrumentation.

Combined environmental testing has two significant advantages over single

environmental testing:

• The ability to investigate the combined effects of multiple conditions

since combined testing, in most cases, more closely approximates the

real environment.

o Several conditions usually can be applied simultaneously in a short

time, rather than in sequence, due to savings in setup and test time.

Therefore, combined testing often saves money. The major disadvantage

of this approach is that the initial equipment cost for combined

testing may be higher.

In qualification and acceptance testing, combined environments are preferable. The increased confidence derived from the knowledge that

6-46
synergistic effects are accounted for frequently permits the use of smaller

safety factors.

When testing to relate cause and effect, combined environmental testing is

used as an extension of single environmental testing. During the development

phase, initial testing usually is applied to determine the effects of single

environments. Combined environments are employed after single environmental

effects have been determined and combined effects become of interest. Single

environmental testing also may be preferable in long duration tests due to the

impractical ity of committing combined environmental test facilities for long

periods of time.

The following section describes some of the environmental test methods in more detail.

6.3.3 Environmental Test Procedures

Environmental test procedures for military systems are described in great

detail in the documents cited in section 8.3, specifically in MIL-STD-202E and

MIL-STD-blOC. It is instructive, however, to state considerations applying to

test methods for the most common environments and summarize these methods.

6.3.3.1 Extreme Steady -State Temperatures

Temperature is the environmental parameter most likely to change during a sensor's application life, and it is necessary to evaluate the effects of

thermal changes on the performance characteristics of the sensor.

All environmental conditions vary with time, to some degree, but for

practical purposes it is possible to divide the regime into steady -state

conditions and dynamic conditions. "Steady-state" represents changes that are long with reference to the time constant of the sensor, typically, times from

hours to days, and "dynamic" implies changes that are short with reference to the time constant, typical time span from minutes down to fractions of a second. Two totally different approaches are called for in the test procedures

for temperature environments, and they are treated separately.

The steady-state temperature test procedure consists of static

calibrations of the sensor (dynamic in the case of sensors that do not have

zero-frequency responses, such as piezoelectric sensors) after it has become

stabilized at each of several prescribed test temperatures. Military

specifications and standards must be consulted for the applicable parameter

values. These tests are usually carried out with the aid of temperature

chambers. Such chambers are equipped with controllers which permit the

attainment and regulation of the desired temperatures either above or below

laboratory ambient conditions, with heating and refrigeration elements in the

walls of the chamber. A wide variety of temperature chambers are commercially

available, depending on the temperature range desired and on the size of the

object which is to be tested.

For the tests, the sensor is mounted in the chamber and connected to the

measurand whose source is usually external to the chamber. For accelerometers

a vibration exciter can be used to apply the desired acceleration by means of a column or rod protruding into the chamber through a flexible seal.

6-47
It is often possible (depending on available chamber space) to test

several sensors simultaneously. This can greatly reduce overall testing time.

One should attach a temperature sensor to one or more of the test sensors

in the chamber to measure chamber temperature, and to indicate when the sensors have reached a stabilized temperature level. The typical dial thermometer on the chamber can be used as a rough indicator of the temperature.

The test procedure involves eleven-point static calibrations performed at

each test temperature. When testing two or more sensors of the same type and

range, fewer points are sometimes taken for the static temperature calibrations

of the second and subsequent sensors.

Unless otherwise specified, the temperature range over which the sensors

are tested should leave a margin of safety of about 10 °C (18 °F) at the ends

of the claimed operating range of the instrument. The testing is done in two

parts with tests below laboratory ambient temperature followed by tests at

elevated temperatures. This assures evaporation of any moisture which may have

condensed inside the sensors during the low temperature tests.

An initial static calibration is performed (after the sensor has been

mounted in the test chamber and permitted to stabilize at room temperature).

For the low temperature tests, the desired low end of the range is reached in

steps, usually of about 25 °C each. Then the chamber is permitted to warm up

and an additional calibration is performed about halfway between the lower

range limit and room temperature. A final calibration at room temperature

completes this part. At each temperature, the sensor is allowed to stabilize

for about 45 minutes, and the sensor case temperature is measured by the

attached temperature sensor before, during, and immediately after each

cal ibration.

Tests at elevated temperatures follow immediately, using as initial

calibration the one just performed at room temperature. Again, the high

temperature end of the range is reached in equal 25 °C steps. The majority of

presently available sensors have an upper limit of about 120 °C (248 °F). If

the limit is higher, additional steps are taken. After this, the chamber is

permitted to cool down with one calibration performed halfway down to room temperature. A final calibration is then performed at room temperature.

Results from this calibration will indicate if any permanent changes in

performance characteristics have occurred as a result of the temperature

tests.

Sensitivity at each test temperature is computed, and these values, as well as the zero measurand outputs, can be plotted as a function of the test

temperature.

The testing and calibration of strain gage sensors is usually performed

with constant voltage excitation. Some semiconductor strain gage sensors may

show quite different temperature characteristics when excited from a constant

current source. Where manufacturers' literature indicates that either type of

excitation may be used, static temperature tests should be run with both types

of excitation.

6-48
6.3.3.2 Thermal Transients

The temperature tests described above will not establish the performance

characteristics of sensors operating in a rapidly changing thermal environment.

Many sensors contain temperature compensating components that are designed to

minimize changes in sensitivity and zero measurand output over a wide range of

temperatures. Temperature compensation is effective only when these components

and the sensing elements of the device are at the same temperature. Rapidly

changing environmental temperatures will set up thermal gradients in the sensor. These may cause large zero shifts due to the temperature difference

between sensing and compensating elements.

Tests for the effects of thermal transients are more difficult to perform

than those for steady-state temperatures. At present techniques exist only for

testing flush-diaphragm pressure sensors and piezoelectric accel erometers

[34,35]. It is not known whether thermal transient test techniques for other

types of sensors are under development.

Dynamic temperature effects are most pronounced in small, flush-diaphragm

pressure sensors. A technique was developed at NBS for observing dynamic

temperature effects in such sensors [36]. Briefly, it consists of immersing

the sensing end into a pool of molten Woods metal at a temperature slightly

below the upper limit of the sensor's operating temperature range. The output

of the sensor during immersion may be displayed on an oscilloscope with an adequately slow sweep or recorded on a strip chart recorder for longer time

periods. The testing time varies with the instrument, but generally three

minutes are adequate from the initiation of immersion. During the test the sensor zero-pressure output will usually show a rapid initial negative shift

lasting for a few seconds. This shift reverses and becomes positive,

increasing until a maximum is reached, typically after about one minute. After

this, the shift will decrease until ultimately the zero shift will reach the

value expected from its static temperature characteristics for the temperature

at which the sensor finally stabilizes.

Tests may be performed at other temperatures within the operating range of

the sensor. For tests at low temperatures, the sensor can be dipped into ice

water, as an example. This technique cannot be used effectively for other than

flush-diaphragm devices due to the difficulties of introducing the liquid

medium into the sensor cavity rapidly enough." It sould be noted that the

thermal transient stimulus sets up a "thermal gradient," i.e., a heat flow

condition, in the sensor which causes different parts of the sensor to be at

different temperatures until stability is reached, thereby producing transient

output signals.

Pressure sensors which measure gaseous pressures require testing for the

effects of thermal transients in this medium by a different test procedure.

The procedure using thermal radiation stimuli can also be applied to piezoelectric acceleration sensors, and probably to other types of sensors as

well

A simple and repeatable testing technique was developed at the National

Bureau of Standards to obtain information on the zero shift and change in

sensitivity of a pressure sensor by subjecting it to a thermal transient

generated by a mechanically chopped cw laser beam [37]. In the NBS tests,

6-49
commercial flush-diaphragm pressure sensors with ranges up to 50 psi (345 kPa) were tested. Zero shifts and changes in sensitivity of the order of

20 percent FS were measured due to thermal transients with power densities up

to 10 W/cm^. In this technique the sensor can be pressure-cycled while it is

irradiated. In this way, zero shifts and sensitivity changes may be directly

displayed in a procedure which requires a testing time of only about one minute

for each sensor.

NBS also developed another test method for evaluating the effects of

short-duration, thermal radiant-energy transients on pressure sensors [34]. In

this method sensor output (zero-shift with the sensor at atmospheric pressure)

is measured as the sensor is exposed to thermal radiation from the ignition of

a photographic flashbulb or from the discharge of an electronic flash. Thermal

energy pulses up to 0.1 J/cm^ with durations of about 6 ms were generated

using an electronic flash; pulses of up to 2.2 J/cnr and duration up to about

37 ms were generated using No. 22 flashbulbs. In the latter tests a sampling

of 25 commercial pressure sensors showed zero shifts ranging from 0.5 percent

to about 400 percent of the full-scale output.

A simple, inexpensive method was developed at NBS for determining the

effects of thermal transients on the zero output and sensitivity of

piezoelectric accel erometers [35]. Thermal transient stimuli were generated by

mechanical chopping of the beam of an incandescent lamp, and were aimed to heat

the top or side of the test accel erometer. In tests of 14 commercial

accel erometers, zero shifts were observed with magnitudes as high as 640 gn representing up to 7 percent FS. These results were obtained at a radiation

power density of 1.8 W/cnr with 15 s transients. No changes of accel erometer

sensitivity were found to exceed experimental uncertainties in these thermal

transient tests.

It should be emphasized again that sensors in operational environments are highly likely to be subjected to thermal transients and should be tested

accordingly. At the conclusion of such tests, a static calibration is

recommended to check on possible damage sustained during the tests. In view of

this possibility, dynamic temperature tests should be performed last in the

evaluation of sensors.

6.3.3.3 Acceleration, Vibration, and Shock

Military systems are subject to environmental motions which can be divided

into the three regimes of acceleration, vibration, and shock. It is generally

understood that acceleration represents a steady-state, unidirectional

measurand; vibration is the measurand acting over a range of frequencies; shock

represents a single transient application of the measurand.

A variety of test methods are used to simulate each of the regimes.

Military specifications of each service specify different amplitudes,

frequencies, shock shapes, and durations; in addition, specific types of test

equipment may also be called for. These must be followed when so specified.

Tests to establish the acceleration sensitivity of the sensor are carried

out by mounting the instrument on a centrifuge and subjecting it to

acceleration forces for various orientations of the sensor.

6-50
The sensor is usually tested along three orthogonal axes:

1. The cylindrical axis of sensor in line with the applied

acceleration and its sensing end away from centrifuge center of

rotation.

2. The cylindrical axis of sensor in line with the applied

acceleration and its sensing end toward centrifuge center of

rotation.

3. The cylindrical axis of sensor perpendicul ar to the applied

acceleration.

4. Same as (2) with radial position changed 90°.

Typically in such tests, accelerations of 5, 10, 15, and 20 g« are applied in

each of the positions with zero measurand input, and the resulting output

measured. The results are reported in terms of percent FS/g n

.

Two precautions must be taken. The pressure ports of a pressure sensor must be covered, otherwise in one of the testing positions the air impact

pressure due to centrifuge rotation may cause erroneous outputs. Sensors which

dissipate much electrical energy (certain high-voltage bonded strain gage sensors in particular) must be covered with a box to prevent air cooling due to

rapid centrifuge spinning. The latter may result in outputs not representative

of normal use.

Inadvertent effects, similar to those on other types of sensors, must be

considered prior to the planning of the tests to assure proper interpretation

of the test data.

Tests which establish the vibration sensitivity of the sensor are carried

out by mounting the instrument on the table of an electromagnetic shaker and

subjecting it to vibrational acceleration fields along the three axes used for

the steady acceleration tests (1, 3, 4 above). Tests usually involve

vibrational accelerations with a maximum amplitude of 40 g n peak-to-peak over

a frequency range wide enough to include those frequencies which the sensor is

likely to encounter in actual use. The frequency range and amplitudes

obtainable by typical commercial equipment are: frequencies between 2 Hz and

20 000 Hz, and acceleration levels up to about 100 gn peak-to-peak.

During the test, the sensor output is displayed on an oscilloscope which

is watched while the frequency of vibration is slowly varied through the

desired range. The vibration amplitude is monitored and adjusted to keep the

amplitude relatively constant within equipment limitations. Resonances appear

as peaks in the output at certain frequencies. It may be difficult at times to

ascribe such peaks to the sensor rather than to the shaker-sensor combination.

The fact that peaks appear simultaneously in the sensor output and in the

shaker motion does not necessarily indicate a shaker resonance. One possible

way of identifying the origin of resonances is to use a piece of metal of the

weight and size of the sensor as shaker load. If a peak in shaker motion

appears at the same frequency as before, this frequency is a shaker resonance.

Frequently, no peaks are discernible. The vibrational acceleration

response is then described simply as not exceeding the maximum trace broadening

(in terms of the sensor sensitivity) observed (due to internal noise,

vibration, electrical pickup) over the frequency and amplitude range tested.

6-51
In potentiometric sensors a mechanical resonance of the slider may manifest

itself by complete loss of output signal.

A static calibration at the conclusion of the vibrational acceleration

tests is desirable to indicate any possible permanent change in the performance

characteristics caused by the tests.

It should be noted that there are two ways of considering acceleration and

vibration tests. They can be used to indicate what kind of errors may result

if the sensor must make measurements whil

e

being subjected to those

environments. Such tests can also be used (and this can be part of the same

test) to indicate what kind of permanent effects may have occurred in the sensor due to exposure to this environment.

Shock tests, on the other hand, are almost exclusively used to establish

the permanent effects on sensor performance (survivability). There is

generally no requirement to exactly duplicate the real environment which the sensor may encounter. The shock test is specified to assure the ability of the sensor to survive the assumed shock environment. Shock theory, tests, and data

interpretation are covered in great detail in the "Shock and Vibration

Handbook" [22].

Shock test parameters and the shock test equipment to be used are usually

specified in military specifications and test standards such as MIL-S-901 Navy.

Shock test specifications contain the shape of the shock pulse, its amplitude,

and its time duration. The axis of the test item along which the shock is

to be applied may also be given, as well as the number of shock pulses which

are to be applied.

There are three major types of shock test machines. In one the test

specimen is mounted on a table structure which is hoisted vertically to a predetermined height and then dropped onto a platform. The material and shape

of that platform as well as the material and mass of the table will determine

the shape and duration of the shock pulse. The height of drop will control the

amplitude of the shock. Half -sine, rectangular, and saw tooth acceleration

pulses are most commonly employed.

A second type of machine uses a hydraulic ram with a shaped piston and

damping orifice to generate the desired shock pulse and shape. The third

system uses a mechanical hammer which is released from a specified height and

strikes a plate on the other face on which the test item is mounted. In this

setup the plate properties will influence the shock pulse shape, duration, and

ampl i tude.

In shock tests, three successive shocks are usually applied along three

orthogonal axes of the sensor to be tested. After these tests also, at least

one static calibration is performed to assess the effect of the shock test on the performance characteristics of the sensor.

Test procedures for other environmental parameters listed in tables 17 and

18 tend to be more specialized and less commonly required. Details on those

procedures can be obtained from the military documents cited.

6-52
6.3.3.4 Electromagnetic Radiation

The increasing use of electronics in the automotive and process industries

led to the recognition of problems caused by susceptibility to undesired

electromagnetic interference by conduction or radiation. In military vehicles,

the need for measurement of the susceptibility of electronic components to

electromagnetic sources has recently become more critical as more electronic

components are used in vehicle applications. Electronic and electrical

equipment may be susceptible to temporary or permanent malfunctions when

subjected to electromagnetic sources, either of a transient or steady-state

nature.

Electromagnetic interference (EMI) may be either transient, intermittent,

or continuous in nature arising from sources such as transmitters or other

equipment located either on board or adjacent to the vehicle, or from component

parts of the vehicle ignition or electrical power systems [38].

In the process industries, electromagnetic radiation can arise from

various sources. This radiation is frequently generated by the small hand-held

radio transceivers that are used by maintenance and security personnel. The

susceptibility of process control instrumentation to the radiation of the

hand-held transceiver is of great concern. There are other sources of

electromagnetic radiation of concern, such as fixed radio and television

transmitters, vehicle radio transmitters, and various industrial

electromagnetic sources [39].

In addition to the continuous forms of electromagnetic energy deliberately

generated, there are also spurious radiations caused by devices such as welders, contactors, and motors. These sources can also cause difficulties in

the operation of equipment. Methods employed to prevent effects from

continuous radiation will normally also reduce the effects from these sources.

The electromagnetic environment is determined by the strength of the

electromagnetic field (field strength in volts per, meter). The field strength

is not easily measured without sophisticated instrumentation and is not readily

calculated by classical equations and formulae because surrounding structures

or the proximity of other equipment will distort and/or reflect the

electromagnetic waves. The most direct method of specifying the EMI

environment limits is to measure the actual fields, voltages, currents, and

impedances around the component or system of interest under all hazardous

conditions. This will require a large enough sample of installations to

determine possible variations.

Another approach to setting limits on levels of EMI would be to establish

experimentally the maximum levels of electric and magnetic field strength

existing with the actual interconnecting wires and field impedance levels

expected during operation of the system. One would use sources of maximum

power levels expected for on-board transmitters, transient sources, and

external transmitters. All of these constitute the ambient level of EMI. Data

of this type are being collected in the automotive industry. They may be

available later as special reports on EMI characteristics and test limits.

Test methods for measuring the effects of electromagnetic radiation on the

instruments of concern are designed to establish repeatability of results at

6-53
various test sites. However, electromagnetic radiation will be affected and

distorted by the proximity of conductive objects, including the walls of any

test chamber. There will undoubtedly be some differences in results for tests

conducted at various sites. These results must be taken into account when

verification testing is conducted.

Caution must be exercised in carrying out the test procedure where high

voltages or intense fields may be present. "... present maximum allowable

field for human exposure is 10 mW/cm 2 averaged over six min, which is

equivalent to about 194 V/m electric field strength in the far field ..."[38].

A few definitions follow:

Conducted emission - desired or undesired electromagnetic energy which

is propagated along a conductor. Such an emission is called conducted

interference if it is undesired.

Radiated emission - radiation- and induction-field components in space.

(For many test purposes, induction fields are classed together with

radiation fields.)

Field strength - This term can be applied to either the electric or the

magnetic component of the field, and may be expressed as V/m or A/m.

When measurements are made in the far field and in free space, the

power density in W/m2 may be obtained from field strengths

approximately as (V/m) 2 /377 or (A/m) 2

x 377 [38].

Information is available in the literature on design for electromagnetic

compatibility [72]. The measurement of electromagnetic interference

characteristics and the requirements are discussed in great detail in the

literature [38,39,73,74]. Although the first two documents [38,39] were

written for two specific industries, automotive and chemical processes, the

principles and test methods described are applicable to other areas of use as well

.

Three generally used military standards documents for testing of

electrical components, MIL-STD-810C [40], MIL-STD-202E [41] and

MIL-T-28800B [42], do not specifically address electromagnetic interference.

6.4 Stability, Durability, and Rel iabil ity Testing

6.4.1 General Considerations

The operating conditions in which sensors are used, and which influence

their performance characteristics, may be categorized into several major areas. These are: operation at laboratory conditions, operation in harsh

environments, operation over extended periods of time, and, finally, operation

in harsh environments over extended time. Degradation of sensor performance

tends to increase in the order in which the areas are listed.

Determination of performance at laboratory ambient conditions is covered

in section 6.2, and the effects of environment in section 6.3. The effects of

time on sensor performance are addressed in this section. The terms

reliability, stability, and durability are similar in that all indicate

6-54
quantitatively "how long it will work." There is a distinction between the

terms which is tacitly accepted by most measurement engineers. "Reliability"

is used to show the time to failure of the device (expressed in a variety of

ways). "Stability" and "durability" are more concerned with the manner in

which the performance of the device deteriorates prior to total failure. Of

course, failure itself can also be defined as the point at which performance

deteriorates beyond all specified boundaries. Nevertheless, the distinctions

in meaning between these concepts are considered useful and the discussion

which follows will be based on these.

Durability is too general a term to be useful in specifications and test

procedures. The glossary defines stabil i ty as "the ability of a sensor to

retain its performance characteristics for a relatively long period of time."

The definition also states: "Unless otherwise stated, stability is the ability

of a sensor to reproduce output readings obtained during its original

calibration, at room conditions, for a specified period of time. It is

typically expressed as within percent of full-scale output for a period

of months."

The implication in this statement is that the output readings obtained

during re-calibrations are taken at room temperature as during the original

calibration. In a real-world application, such as a military ATE system, one

is really concerned whether the sensor continues to operate within established

bounds in its operational environment . This suggests the desirability of

in-place calibrations, or self -testing sensors.

The next section will discuss test methods and will attempt to clarify

this, further.

6.4.2 Stability, Durability, and Operating Life

In order to establish the stability, durability, or operating life of

sensors, one must re-calibrate them at specified intervals. There are a number

of considerations which will dictate the kinds of tests which are to be

conducted.

6.4.2.1 Storage Life Tests

While section 6.4.1 describes four operating regimes, actually, there is

also a fifth one: non-use storage with zero measurand input. In this case there are two possible situations: storage at "room conditions" (laboratory

environment) or at some other conditions, perhaps simulating spare parts

storage at an equatorial island base (high temperatures, high humidity, fungus)

or in the artic (very low temperatures, low humidity).

This handbook has repeatedly emphasized that the performance

characteristics of the sensor, as determined through careful calibrations,

indicate the "health" of the sensor, i.e., its ability to properly perform its

specified measurement function. Knowledge of the continuing health of the sensor is derived from re-calibrations which are compared to the initial

acceptance tests, as well as subsequent ones. Static calibrations are usually

sufficient (except in the case of sensors with no response at zero frequency,

such as piezoelectric devices). It is also reasonable to perform abbreviated

6-55
calibrations in many cases; i.e., five point, instead of eleven- or twenty-one

point. Engineering judgment will dictate the choice.

For sensors stored at room conditions and zero measurand, calibrations at

yearly intervals are probably adequate. This assumes that sensor characteristics have previously been established through extensive

qualification tests and thorough acceptance tests. If the temperature and/or

humidity environments are significantly different from room conditions, check

calibrations should be performed at more frequent intervals, perhaps even monthly when stored at environmental extremes. The check calibrations

themselves should be performed at room conditions to provide a proper base of

comparison with the initial calibrations. An indication of the changes

observed in such tests follows.

A limited investigation was conducted at NBS on the effects of storage at

elevated temperatures on the performance of strain gage pressure sensors [43].

Seven types of these sensors were kept at temperatures of 107 °C, and three

others at 91 °C, for five weeks, followed by a three-week period at laboratory

ambient conditions again. Excitation voltage was applied during the entire

test period. Test results at the end of the test program indicated permanent

changes of up to 0.5 percent in sensitivity and up to 4.5 percent of full-scale

output at zero pressure for the sensors tested. It should be noted the storage

temperature in all cases was below the maximum specified operating temperature

for the sensors tested. The largest portion of the changes appeared to occur during the first five days of the test, suggesting such temperature "annealing"

may be useful prior to high temperature use. These conclusions are valid only

for the actual sensors tested and may not apply to other pressure sensor

types.

While information should be available from sensor manufacturers on the

shelf life of sensors, proprietary considerations often make it difficult to

obtain this information. Again, as in the other areas discussed earlier,

considerable work remains to be done to explore the shelf life of sensors. Shelf life or storage life, however, is the most benign regime to which a sensor may be subjected, provided storage is at "room conditions."

6.4.2.2 Operating Life Tests at Room Conditions

A more severe regime is sensor operation at room (laboratory ambient)

conditions. It is not possible to generalize the effects of operational life

on the stability of any sensor. The effects depend on factors like type of

measurand, its amplitude and rate of application, the type, operating

principle, and construction of the sensor and the amount of time it is

energized. Very little work has been done (or at least published in readily

accessible form) on what is often called "life-cycling" (operating life)

effects on sensor performance.

A limited investigation was conducted at NBS on the effects of a million

pressure cycles on the performance characteristics of several types of strain

gage pressure sensors [44]. The test sensors were subjected at laboratory

ambient conditions to pressure pulses with amplitudes of 80 percent to

90 percent FS at a rate of about once per second until a total of 10° cycles

had been completed. The three main conclusions from this investigation were: zero pressure output and sensitivity changed more during the first 105 cycles

6-56
than subsequent ones; after 10^ cycles, the zero pressure output had shifted

about 1 percent from its initial value; and linearity and hysteresis changes

due to cycling were minor compared to the changes in zero output and

sensitivity.

6.4.2.3 Operating Life Tests at Elevated Temperatures

A more extensive investigation was conducted at NBS on a group of bonded

wire strain gage pressure sensors [45], Near full-scale values of pressure

were applied five times per second at laboratory ambient conditions until

40 x 10° cycles had been completed.

Some of the sensors were also cycled at 66 °C (150 °F). Conclusions drawn

from these tests were: The sensitivities of sensors tested at ambient

conditions decreased with cycling as well as time; sensitivities increased at

the elevated temperatures; and zero pressure outputs decreased with cycling and

time at both temperature levels. Changes in hysteresis and linearity were very

small overall, although somewhat larger changes in characteristics occurred

during the first 10° cycles (the first three for four days of testing) than

subsequently. Cycling at pressures higher than full scale produced total

failures or radical changes in characteristics within the first 105 cycles.

It should be noted that the conclusions obtained from those investigations were based on a small number of specimens of a few types of pressure sensors which were subjected to a particular type of durability testing concept.

Nevertheless, the test results point to the type of behavior which other

sensors might be expected to exhibit and which should be investigated.

Certain general guidelines can be stated although the particular kind of

life-cycling (durability) test procedure selected will depend on the particular

type of sensor, measurand, use, and environmental conditions. In such lifecycling tests, the measurand should be applied with an amplitude ranging from

zero to the full-scale value (or close to it). It should be applied at a rate

slow enough not to excite sensor resonances, but at a frequency which results

in a reasonably short testing time. Thus a cycling rate of 3 Hz results in an accumulation of about 1.8 million cycles per week of continuous testing. The

effects of this cycling are established from static calibrations following

ever-increasing periods of cycling, such as after 10 000, 20 000, 50 000, and

100 000 cycles.

Rest periods during which no cycling occurs, followed by static

calibrations, will give indications on permanent, versus temporary, changes in

performance characteristics. In all cases, control sensors should be used

which are not cycled, but only calibrated statically whenever the test sensors

are calibrated. This should permit correct assignment of performance changes

to the cycling test itself.

Life cycling under specified environmental conditions: temperature,

humidity, vibration, etc., singly or in combination, may furnish additional

information on the stability and durability of the sensors in the actual

operational conditions. Clearly, all tests of this nature are qualification

tests and are not to be performed on each individual specimen, since such tests

are ultimately destructive in nature.

6-57
It should be emphasized that this is an area about which little

information exists and much work needs to be done to establish valid sensor evaluation methods.

6.4.3 Re-Calibration Considerations

As stated in section 6.1, the continuing ability of the sensor to make

measurements within acceptable limits of error must be checked throughout the

operational life of the measurement system. Qualities such as stability,

durability, and to some extent, reliability, are established with the aid of

re-calibrations of the sensing system. Unfortunately, it is very difficult to

specify the intervals at which such re-calibrations are to be performed since a variety of factors needs to be considered.

The redl problem with major significance to the overall performance of the

measurement system is that knowledge of the sensor's performance, al one , is

insufficient. It is necessary to assess repeatedly the performance of the

enti re measurement system in order to be continuously assured of obtaining

meaningful data.

The two major considerations are: How realistically can one re-calibrate

the entire measurement system, and how frequently should this be done? The

major trade-offs for the latter are availability for service and cost

effectiveness. To re-calibrate the system, it must be taken out of service,

i.e., the measurement system (whether it is in the UUT or ATE system) is

normally not operational while re-calibrations are performed. This lack of

service availability time, in itself, raises the operational cost of the UUT or ATE. The process of re-calibration adds costs as well. Those trade-offs

require careful study by engineering management.

There are other considerations for meaningful calibration of sensors. The most realistic approach is to apply one or more known values of measurands

to the sensing end of the sensor and record the corresponding output at the

output end of the entire system. This presents several difficulties, including

problems of generating measurands with the proper characteristics, injecting

them at the right point of the sensing chain. Of necessity, the sensor and

system (or channel) must be taken out of service during calibration. This

approach is not widely used, largely because it is uneconomical. However, it

is possible, for example, to apply a known pressure to the backside of the

diaphragm of a pressure sensor without removing the sensor. Other types of sensors cannot use this approach, notably acceleration or force transducers.

An alternative is to dismount the sensor from the UUT, mount it in a portable

calibration unit, and apply the measurand in that manner. Inaccessibility of some sensors in the UUT, the possibility of damage to those sensors during

dismounting, the lack of suitable portable calibrators for some measurands, and

the time involved make this approach unattractive.

"Self -calibrating" sensors with a built-in mechanism to apply the

measurand to the sensing element have been developed. The fact that no such sensors are commercially available now suggests that they are not satisfactory.

However, the trememdous demand for long-term reliable measurements in complex

systems such as ATE did not exist when those sel f-cal ibrati ng sensors were

first developed. Perhaps interest in self-calibrating sensors will be renewed

for specialized applications. It appears that this field deserves serious

6-58
investigation and research to develop a variety of self-calibrating sensors to serve ATE needs.

The next best approach to calibration of a measurement system is to employ

a substitute signal for the output of the sensor. One can disconnect the sensor and feed in this approach electrical signals which represent the sensor output (corresponding to specified measurands) into the next part of the chain,

generally the signal conditioner. This method is relatively easy to carry out,

and, in the case of ATE, can take advantage of the ATE software to integrate

this kind of check calibration of the measurement chain into the overall ATE

test schedule.

This approach, however, cannot check the integrity and quality of the sensor. In the case of strain gage sensors, a compromise measure is frequently

used known as "shunt calibration" [46]. In this technique, one or more of the

elements of the strain gage bridge are shunted by known resistance values.

During previous laboratory calibrations of the sensor, shunt resistance values

have been determined which produce signals corresponding to specified measurand

values. By shunting the elements during a system calibration, a simulated

measurand is generated. This method also lends itself to ATE software

implementation, but again, it does not totally assure intrinsic sensor

integrity. Similar approaches of known perturbations of electrical parameters

can be applied to sensors using other transducing principles, such as differential transformers and variable capacitance devices.

Another largely qualitative approach to overall measurement system

calibration can be taken if the sensors in the UUT see a significantly

different value of measurand when the UUT is operating than when it is not.

For example, a temperature sensor in the cooling system of an engine during

operation normally may sense a temperature of 90 °C, and during non-operation

the ambient environment of 25 °C. If the system output signals for these two

conditions correspond roughly to the calibration values, at least a gross

verification of proper system operation exists.

Present approaches to quantitative performance checks of the total

measurement system (including the sensor) appear inadequate, This calls for

generic investigations of a thorough nature. Past experience shows that it is

difficult to find adequate support and resources for this type of research

activity. Yet without it, knowledge of measurement system performance,

particularly in critical applications such as ATE, can never be adequate to the

needs.

6.4.3.1 Re-Calibration Intervals

Despite the limitations of the various approaches to system

re-calibration expressed above, it is essential to carry out the task in some manner.

Section 6.4.2, which describes limited life tests performed on some selected sensors, suggests re-calibration at yearly intervals for sensors

stored at ambient laboratory conditions and more frequent (monthly) tests if

the storage environment departs significantly from laboratory conditions. The

Navy's "Metrology Requirements List" [47], for example, in discussing pressure

gages (i.e., fully mechanical devices), quotes "... pressure gages that have

6-59
been treated as follows: for a period up to and including six months, the

storage time shall not be considered as part of the calibration interval; that

is the date the gage is removed from storage and will be used as the 'date

calibrated'." It goes on to indicate that for storage periods from six months

to one year, samples of the stored gages shall be check-calibrated to determine

the probable status of the entire lot. It is also stated that for storage

periods greater than one year, all gages must be re-calibrated. Finally the

reference states "...whether a gage requires calibration depends on the use of

the gage in the equipment or system in which it is installed." It should be

noted that the above discussion does not address sensors with electrical

outputs. The same document [47] has a listing of "calibration intervals by

type of TMDE, (generic)" where TMDE is "test, measurement and diagnostic

equipment." Here are some examples from this listing of devices and their

"generic calibration interval s' accelerometers, 12 months; gage, vacuum,

electronic, 12 months; manometer, capacitance, 6 months; transducer, pressure,

6 months; transducer, force, 12 months; transducer, vibration, 6 months.

The National Conference of Standards Laboratories has issued a Recommended

Practice [48] which addresses the subject of calibration intervals. It cites

from MIL-C-45662B "Calibration System Requirements" this passage: "Measurement

and test equipment and standards shall be calibrated at intervals established

on the basis of stability, purpose, degree of usage, precision, accuracy and

skills of personnel utilizing the equipment. Intervals shall be shortened as required, to assure continued accuracy, as evidenced by the results of

preceding calibrations and may be lengthened only when results of previous

calibrations provide definite indications that such action will not adversely

affect the accuracy of the system." The recommended practice continues by

outlining five general methods in use today for the establishment of

calibration intervals and gives advantages and disadvantages of each. The

methods are: fixed interval through engineering intuition, fixed interval

through data, variable or floating intervals, interval by use time, and

interval by in-use testing. The conclusion states "...there is considerable crossover in these techniques and portions of each may be used in constructing

a satisfactory program." This supports the introductory statement of this

document that "...establishment of calibration intervals has long been a weak

technical link in the calibration chain. At the present time there appears to

be no definite single solution to this problem."

If there appears to be no single definite solution what should be done?

First, as stated earlier, it seems reasonable to re-calibrate stored sensors at

no greater than yearly intervals. Such re-calibrations, although requiring

certain resources, generally pose no major problems since sensors in storage can be calibrated individually, as in qualification or acceptance tests.

Certainly, they must be re-calibrated immediately prior to issue for

installation (or replacement) and the data from this re-calibration compared to the original acceptance calibration (or the previous re-calibration). If

discrepancies exist beyond specified limits, the particular sensor should not

be issued. Whether it should be tested further, returned to the manufacturer,

or discarded will depend on cost-benefit considerations for the particular

system.

Second, in the case of system tests of UUTs or acceptance tests of UUTs,

the entire ATE measurement chain, including the sensor, should be calibrated

(in place, preferably) immediately prior to those tests and immediately after

6-60
the tests. Comparison of these calibration data with previous system

calibrations should generate valid information on the short-term stability of

the sensor systems.

Third, for operational applications, in-place calibrations should be

performed at those intervals which are selected by the experienced engineering

staff directly concerned with the design and operation of the ATE/UUT.

Conservatively, the initial (early in the operational life) intervals should be

shorter than those considered optimum for the total life of the system. As re- calibration data are gathered and compared, and if the system stability appears

to be within specified bounds, the re-calibration intervals may be

incrementally lengthened. Experience and expertise are needed to evaluate the

data on system performance and decide the best course of action.

In a system where a sensor is used to measure a parameter that is adjusted

to a single value or checked to be within a narrow tolerance band as compared

to the full output range, a single point calibration may suffice for periodic

checks of the installed sensor.

It must be emphasized, again, that the above recommended in-place

("field") system calibrations are difficult to achieve, at best. Much work

remains to be done to develop "self-calibration" (or "in-place cal ibratable"

sensors and systems. But without a reasonable continuing assurance that the sensor system performs within specifications, the function and value of the

entire ATE system are compromised.

6.4.4 Reliability

The following information is largely extracted from the "Reliability

Design Handbook" [50], Other detailed information on reliability can be found

in a series of five handbooks: "Design for Reliability," AMCP 706-196;

"Reliability Production," AMCP 706-197; "Reliability Measurement,"

AMCP 706-198; "Contracting for Reliability," AMCP 706-199; and "Mathematical

Appendix and Glossary," AMCP 706-200. These are published by the U.S. Army

Material Command [33].

Reliability has been described as "quality in the time dimension." It is

classically defined as the probability that an item will perform its purpose

satisfactorily for a period of time under a stated set of use conditions. From

a functional point of view, in order for an item to be reliable it must do more

than meet an initial factory performance or quality specification--it must also

operate satisfactorily for an acceptable period of time in the field

application for which it is intended.

The classical definition of reliability, stated above, stresses four

elements, namely: probability, performance requirements, time, and use conditions. Probability is that quantitative term which expresses the

likelihood of an event's occurrence (or non-occurrence) as a value between 0

and 1. Performance requirements are those criteria which clearly describe or define what is considered to be satisfactory operation. Time is the measure of

that period during which one can expect satisfactory performance. The use conditions are the environmental conditions under which one expects an item to

function.

6-61
Determining reliability, therefore, involves the understanding of several

concepts which relate to these four definitional elements. Among such concepts

is that of a failure rate which can vary as a function of age. A failure rate

is a measurement of the number of malfunctions occurring per unit of time. In order to show the variation in failure rate, separate consideration is given to

three discrete periods when viewing the failure characteristics of a product or item over its life span (and then considering a large sample of its

population). This is illustrated in figure 5.

6.4.4.1 Infant Mortality

Initially, the item population exhibits a high failure rate. This failure

rate decreases rapidly during this first period (often called the "infant

mortality," "burn-in," or "debugging period"), and stabilizes at an approximate

value when the weak units have failed. It may be caused by a number of things:

gross built-in flaws due to faulty workmanship or manufacturing deviations from

the design intent, transportation damage, and installation errors. This

initial failure rate is unusually pronounced in new equipment. Many

manufacturers provide a "burn-in" period for their product, prior to delivery,

which helps to eliminate a high portion of the initial failures and assists in

establishing a higher level of operational reliability. Examples of

workmanship deficiencies which contribute to early failures of a system are:

Poor wel ds or seal s Poor solder joints

Poor connections

Dirt or contamination on surfaces or in materials

Chemical impurities in metal or insulation

Voids, cracks, thin spots in insulation or protective coatings

Incorrect positioning of parts

Missing heat sinks.

Many of these early failures can be prevented by improving the control over the

manufacturing process. Sometimes improvements in design or materials are required to increase the tolerance for these manufacturing deviations, but

fundamentally these failures reflect the "manufacturability" of the component

or product and the control of the manufacturing process. Consequently, these

early failures would show up during:

In-process and final tests

Process audits (to uncover potential for failure)

Life tests

Environmental tests.

6.4.4.2 Useful Life

The item population, after having been burned in, reaches its lowest

failure rate level, which is normally characterized by a relatively constant

failure rate accompanied by negligible or very gradual changes due to wear. This second period is called the useful 1 ife period , and is characterized

mainly by the occurrence of stress-related failures. The exponential failure

distribution is widely used as a mathematical model to approximate this time

period. This period varies among hardware types and is the interval usually

given for reliability prediction and assessment activities.

6-62
6-63
For electronic devices and components, experience has shown that excessive

temperature and voltage levels, either steady state, transient, or changing at

rapid rates, are the two most destructive stresses. Humidity, vibration, shock,

and altitude also contribute to the failure of these devices.

6.4.4.3 Wearout

The third and final life period occurs when the item population reaches

the point where the failure rate starts to increase noticeably. This point is

identified as the end of useful life or the start of wearout. Beyond this

point on the time axis, the failure rate increases rapidly. When the hardware

failure rate due to wearout becomes unacceptably high, replacement or repair of

the item should be made. Replacement schedules (of critical short-life

components) are based on the recognition of this failure rate.

Wearout failures are due primarily to deterioration of the design strength

of the device as a consequence of operation and exposure to environmental

fluctuations. Deterioration results from a number of familiar chemical and

physical phenomena:

Corrosion or oxidation

Insulation breakdown or leakage

Ionic migration of metals. in vacuum or on surfaces

Frictional wear or fatigue

Shrinkage and cracking in plastics.

Optimizing reliability involves the consideration of each and all of these

three life periods. Early failures must be eliminated by systematic procedures

of controlled screening and burn-in tests. Stress-related failures must be

minimized by providing adequate design margin. Wearout must be eliminated by

timely preventive replacement of short-life component parts. Thus all major

factors which influence (and degrade) a system's operational reliability must

be addressed during design (using appropriate techniques described later) to

optimize and control system reliability.

6.4.4.4 Failure Rate

During the "useful life" time period, reliability is described by means of

the single parameter exponential distribution:

R(t) = e _xt

where

R(t) is the probability that the item, which has a constant failure

rateX, will operate without failure for the time period, t

(usually expressed in hours), under stated operating conditions;

e is the base of the natural logarithms, equal to 2.7182...;

X is the item failure rate (usually expressed in failures per hour),

and is a constant for any given set of stress, temperature, and

quality level conditions. It is determined for parts and

components from large-scale data collection and/or test programs.

When the values of X and t are inserted into the above expression, the

probability of success (i.e., reliability) is obtained for that time period.

6-64
The reciprocal of the failure rate is defined as the mean time between

failures (MTBF)

MTBF = 1/x

The MTBF is primarily a figure of merit by which one hardware item can be

compared to another. It is a measure of the failure rate (X) during the useful

life period. The procedures used to establish failure rates for the

constituent electronic parts (resistors, semiconductors, etc.) used in systems

and equipment is given in MIL-HDBK-217B [49]. For non-electronic parts,

information appears in the "Non-Electronic Reliability Notebook" [75],

6.4.4.5 Reliability Degradation

Reliability estimates prepared in accordance with MIL-HDBK-217B techniques

reflect the inherent (or potential) reliability of a system as defined by its

engineering documentation, its stress and safety factors and gross

environmental application, and manufacturing and quality factors. These

estimates are indicative of the upper limit or reliability potential as applied

to the useful 1 ife period . However, these estimates do not reflect expected

performance when operated and maintained in its actual field environment.

The results of numerous data collection efforts have shown that the

reliability of fielded equipment and systems is degraded from three to ten

times the potential predicted during design . The transition from a paper

design to production to field operations introduces degradation factors which

constrain the expected reliability.

In order to assess the magnitude of the reliability degradation due to manufacturing, the impact of manufacturing processes (i.e., the process-induced

defects, the efficiency of conventional manufacturing and quality control

inspection, and the effectiveness of reliability screening techniques) must be

considered. In addition to the latent defects attributable to purchased parts

and materials, assembly errors can account for substantial degradation.

Assembly errors can be brought about by operator learning, motivational , or fatigue factors.

A decrease in reliability may occur at the onset of production. This is

primarily due to workmanship errors resulting from unfamiliar operations,

process discrepancies, and quality oversights which drive reliability below

expected levels. As production continues and skill increases, measured

reliability again approaches the inherent value.

Manufacturing and quality control inspections and tests are provided to

minimize degradation from these sources and to seek out the more obvious

defects. No inspection process can remove all defects which are contained in an item presented for inspection. A certain number of defective items will

escape the process, be accepted, and be placed in field operation. More

important, these gross defects are overshadowed by unknown numbers of latent

defects, the results of weakened parts, which can fail under the proper

conditions of stress—usual ly during field operation. Factory screening tests

are designed to apply a stress of given magnitude over a specified duration to remove these kinds of defects. As in the case with conventional inspection

processes, screening tests are not 100 percent effective.

6-65
Degradation in reliability also occurs as a result of system operation.

Wearout, with aging as the dominant failure mechanism, can shorten the useful

life. Situations also occur in military systems where the system is operated

beyond its design capabilities because of an unusual mission requirement or to

avoid a threat. These situations could cause ill effects to the constituent

parts of systems. Operational abuses due to rough handling, extended duty

cycles, or neglected maintenance can contribute materially to reliability

degradation, which eventually results in failure. The degradation can be a result of the interaction of man, machine, and environment. The translation of

the factors which influence operational reliability degradation into corrective

procedures requires a complete analysis of functions performed by man and

machine, plus fatigue and/or stress conditions which could degrade operator

performance.

Degradation in inherent reliability can also occur as a result of

maintenance activities. Indeed, studies have shown that excessive handling

brought about by frequent preventive maintenance or poorly executed corrective

maintenance (e.g., installation errors) have degraded system reliability.

Several trends in system design have reduced the need to perform adjustments or make continual measurements to verify peak performance. Extensive replacement

of analog with digital circuitry, inclusion of more built-in test equipment,

and use of fault- tolerant circuitry are indicative of these trends. These

factors, along with greater awareness of the cost of maintenance, have brought

changes for ease of maintenance whose by-product has been increased system

reliability. In spite of these trends, the maintenance technician remains a primary cause of reliability degradation. The effects of poorly trained,

poorly supported, or poorly motivated maintenance technicians on reliability

degradation require careful assessment and quantification.

6.4.4.6 Reliability Growth

Reliability growth represents the resultant action taken to hasten a hardware item toward its reliability potential either during development or during subsequent manufacturing or operation. During early development, the

achieved reliability of a newly fabricated item, or an off-the-board prototype,

is much lower than its predicted reliability. This is due to initial design

and engineering deficiencies as well as manufacturing flaws. The reliability

growth process, when formalized and applied as an engineering discipline,

allows management to exercise control, allocate resources, and maintain

visibility into activities designed to achieve a mature system prior to full

production or field use.

The basic concepts associated with a reliability growth process and its

application to newly fabricated hardware involve consideration of hardware

test , failure, correction, and retest activities. Specifically, reliability

growth is usually an iterative test-fail -correct process. There are three

essential elements involved in achieving reliability growth, namely:

(1) Detection and analysis of hardware failures.

(2) Feedback and redesign of problem areas.

(3) Implementation of corrective action and retest.

The rate at which hardware reliability grows is dependent on how rapidly these

three elements can be accomplished and, more importantly, how well the

6-66
corrective action solves the problem identified. During early development and

test activities, the achieved reliability (or MTBF) is well below that

predicted on the basis of design analyses and analytical predictions. As

development and test efforts progress and problem areas become resolved,

measured reliability values approach the inherent (design based) value.

6.4.5 Failure Mechanisms

The failure (or deterioration of performance) of sensors can be caused by one or more factors. One of the factors is simply the operating life of the

device, another factor is the environment in which the sensor must operate, a third factor (less easily taken into account) is inappropriate selection, or application, of the sensor. In considering the effects of the operating life

on the mechanical components of a sensor, fatigue failure and its precursing

effects need to be taken into account. Well established engineering practice

assigns lower values of maximum allowable stress to those parts which may be

subjected to repeated stress. It is generally assumed that fatigue needs to be

considered if the repetitions of the stress are of the order of one million

cycles or more. Corrosion and defects in the material under stress can materially affect the fatigue life.

One notable effect of repeated stress application, known as "cold

working," actually tends to increase the fatigue strength, although the process

may also introduce internal strains and minute cracks [51]. Thus it may be

possible to increase the fatigue life by subjecting the component to stress

cycling at low stress levels. A possible side effect of this is that work

hardening may result, which in case of a sensor may result in decreased

sensitivity with time and cycling. Repeated stress cycling may also decrease

friction and decrease hysteresis of the stressed components.

The environmental factors which affect the life (and contribute to failure)

of sensors and similar devices are manifold and are listed in tables 17 and 18.

Some examples follow [50].

High temperatures impose a particularly severe stress on most electronic

components. They can cause not only catastrophic failure, such as melting of

solder joints and burn out of solid-state devices, but also slow progressive

deterioration of component performance levels due primarily to chemical

degradation effects. It is often stated that excessive temperature is the

primary cause of poor reliability in military electronic equipment.

In present day electronic systems design, great emphasis is placed on

small size and high component part densities. This generally requires a cooling system to provide a path of low thermal resistance from heat-producing

elements to an ultimate heat sink of reasonably low temperature.

Solid-state components are generally rated in terms of maximum junction

temperatures, and the thermal resistances from this point to either the case or

to free air are usually specified. The specification of maximum ambient

temperature for which a component is suitable is generally not a sufficient

method for component selection with densely packaged parts since the surface

temperatures of a particular component can be greatly influenced by heat

radiation or heat conduction effects from other nearby parts. These effects

can lead to overheating above specific maximum safe temperatures even though

6-67
the ambient temperature rating appears not to be exceeded. It is preferable,

therefore, to specify thermal environment ratings such as equipment surface

temperatures, thermal resistance paths associated with conduction, convection

and radiation effects, and cooling provisions such as air temperature, pressure,

and velocity. In this manner, the true thermal state of the temperaturesensitive internal elements can be determined.

Low temperatures experienced by electronic equipment can also cause reliability problems. These problems are usually associated with mechanical

elements of the system and include mechanical stresses produced by differences

in the coefficients of expansion (contraction) of metallic and nonmetallic

materials, embrittlement of nonmetallic components, mechanical forces caused by

freezing of entrapped moisture, stiffening of liquid constituents, etc.

Typical examples include cracking of seams, binding of mechanical linkages, and

excessive viscosity of lubricants.

Additional stresses are produced when electronic equipment is exposed to

sudden changes of temperature or rapidly changing temperature cycling.

These conditions generate large internal mechanical stresses in structural

elements particularly, when dissimilar materials are involved. Effects of the

thermal shock-induced stresses include cracking of seams, del amination, loss of

hermetic! ty, leakage of fill gases, separation of encapsulating components from

components and enclosure surface leading to the creation of voids, and

distortion of support members.

A thermal shock test is generally specified to determine the integrity of

solder joints since such a test creates large internal forces due to

differential expansion effects. Such a test has also been found to be

instrumental in creating segregation effects in solder alloys leading to the

formulation of lead-rich zones which are susceptible to cracking effects.

Electronic equipment is often subjected to environmental shock and

vibration both during normal use and testing. Such environments can cause

physical damage to components and structural members when deflections produced cause mechanical stresses which exceed the allowable working stress of the

constituent parts.

The natural frequencies of subsystems comprising the equipment are important parameters which must be considered in the design process. A

resonant condition can be produced if a natural frequency is within the

vibration frequency range. The resonance condition will greatly amplify the

deflection of the subsystem and may increase stresses beyond the safe limit.

The vibration environment can be particularly severe for electrical

connectors since it may cause relative motion between members of the connector.

This motion, in combination with other environmental stresses, can produce fret

corrosion which generates wear debris and causes large variations in contact

resi stance.

Humidity and salt air environments can cause degradation of equipment

performance., They promote corrosion effects in metallic components and can foster the creation of galvanic cells, particularly when dissimilar metals are

in contact. Another deleterious effect of humidity and salt air atmospheres is

the formation of surface films on nonmetallic parts. This causes leakage paths

6-68
and degrades the insulation and dielectric properties of these materials.

Absorption of moisture by insulating materials can also cause a significant

increase in volume conductivity and dissipation factor of materials so affected.

Electromagnetic and nuclear radiation can cause disruption of performance

levels and, in some cases, permanent damage to exposed equipment. It is

important that such effects be considered in determining the required

environmental resistance for electronic equipment to achieve a specified

rel iabil i ty goal

Electromagnetic radiation often produces interference and noise effects

within electronic circuitry which can impair the functional performance of the

system. Sources of these effects include corona discharges, lightning

discharges, sparking, and arcing phenomena. These may be associated with high

voltage transmission lines, ignition systems, brush-type motors, and even the

equipment itself. Generally, the reduction of interference effects requires

incorporation of filtering and shielding features or the specification of less

susceptible components and circuitry.

Nuclear radiation can cause permanent damage by alteration of the atomic

or molecular structure of dielectric and semiconductor materials. High energy

radiation can cause ionization effects which degrade the insulation levels of

dielectric materials. The mitigation of nuclear radiation effects typically

involves the use of materials and components possessing a higher degree of

intrinsic radiation resistance and the incorporation of shielding and hardening

techniques.

In addition to the aforementioned stress factors, other environmental

factors must be considered in the design to assure adequate environmental

resistance for the equipment. These additional factors include:

Sand and dust

Fungus

Acoustic noise

Electric fields

Magnetic fields

Presence of reactive liquids and gases.

The effect of each of these stress factors on the operation and reliability of

the materials and components of the ATE equipment being designed must be

determined. This entails the identification of material, component, and

packaging techniques that afford the necessary protection against such

degrading factors.

In the stress identification process preceding the selection of

environmental resistance techniques, stresses associated with all life

intervals of the equipment must be considered. This includes not only the

operational and maintenance environments but also the preoperational

environments. Stresses imposed on the parts during manufacturing assembly,

inspection, testing, shipping, and installation may have significant impact on

the eventual reliability of the equipment. Stresses imposed during the

preoperational phase are often overlooked, but they may represent a particularly harsh environment which the equipment must withstand. Often the

6-69
shock and humidity environments to which commercial and military systems are exposed during shipping and installation are more severe than those it will

encounter under normal operating conditions.

6.4.6 Accelerated Life Testing

The preceding sections discussed the factors which tend to influence the

stability, durability, and reliability of sensors. They also touched briefly

on failure mechanisms and test methods used to establish stability, durability,

and reliability of the sensors. It should be clear that the subject is very

complex and relatively unexplored; certainly no easy answers exist.

Nevertheless, test methods exist in some areas which, by subjecting the sensors

to postulated operating conditions (and environments), make an attempt to

simulate the operational life of the sensor. One problem common to these

methods is that they generally require a testing time close to the real

operational life.

When such a test method really simulates the actual operating life of the

sensor, it then becomes desirable for economical and logistical reasons to

shorten the test period required. This brings in the concept of "accelerated"

testing, which is treated in AMCP 706-198, "Development Guide for

Reliability" [33]. The following discussion is excerpted from that reference.

"Accelerated" testing is a very loosely defined concept; attempts to make

it rigorous generally run into difficulties. Loosely speaking, accelerated

testing started when someone said: "Let's shoot the juice to it and see what

happens." This means, roughly, "Let's treat it worse than we expect it to be

treated in ordinary practice and then see what happens." One difficulty is

that treating it worse does not always mean "shooting the juice to it." For

example, electrical contacts behave better as voltage and current are increased

(up to a point) and some warmth may improve matters for electronic equipment by

helping to reduce the moisture problem.

Accelerated testing in this qualitative sense is something that anyone can

do and that everyone does. There is a reasonably firm qualitative foundation

for much of it. It is in the quantitative interpretation that troubles begin.

These qualitative and quantitative uses of accelerated testing can conveniently

be put into four classes:

1. Qualitative - to see what kinds of failures are generated and to

decide then if a modification is worthwhile,

2. Qualitative - to get a rough, quick idea of whether or not something

can stand the "gaf,"

3. Qualitative - to see what happens when the user maltreats the device,

as he probably will, and

4. Quantitative - to make a prediction about the life under actual

operating conditions.

There is little question that accelerated testing is useful for the three

qualitative measures, so it is mainly the quantitative problem to which this

chapter is addressed.

Several definitions for "true" acceleration appear in the literature, some

of which are not very explicit, although most engineers associate true

6-70
acceleration with behavior over time. The definition below is chosen for its

generality and applicability. Acceleration need not be "true" to be useful even though untrue acceleration is more difficult to analyze, even

qual itatively.

Acceleration is true if, and only if, the system under the accelerated

conditions passes reasonably through equivalent states and in the same order it

does at the usual conditions. In addition to verifying that true acceleration

exists, a great deal of effort must be expended in determining the acceleration

function. It is virtually always presumed that the acceleration function is a constant.

Some gross failure modes which can be accelerated for mechanical parts are fatigue, corrosion, creep-rupture, stress corrosion, and various combinations

of them. In electronics, one does not ordinarily specify the gross failure

modes for acceleration, but, rather, specifies the "stresses" which are being

increased. Some of these are temperature, supply voltage, power dissipation,

vibration, humidity, and corrosive environments. There is a large body of

material in the mechanical and metallurgical fields dealing with those gross

failure modes. Since the behavior of electronic components is organized

differently, there is no organized body of literature which deals with gross

failure modes that cut across all components or applies to complex devices such

as sensors.

Several accelerated tests are in use. One of them is the constant

severity-level method, a traditional type of test in which the severity level

remains constant throughout the life of the items on test. It is customary to run tests at several severity levels and to plot a curve of some parameter such

as failure rate vs severity level. A sample of several items usually is put on test, and the test stopped when some fraction of the original sample has failed

or a specified test time has elapsed. For reliability prediction purposes, the

early fraction that fails is most important because only the short-lived items

are going to affect the reliability seriously.

Other approaches involve "step-stress" and "progressive-stress" methods.

The word "stress" is used in the sense of severity level. In this method, the

severity applied to a sample of items is increased in steps or increments until some criterion is met for terminating the test. All steps do not have to be

the same size, even though this is a common practice.

The term "step-stress" as used in the literature is ambiguous. It is

convenient to classify step-stressing into three categories:

1. Large steps in which the steps are presumed high enough and long

enough so that, for a given step, the damage accumulated at all

previous steps is negligible.

2. Small steps in which the steps are small enough so that in the

analysis one can presume with negligible error that the severity level

is steadily increasing. This is the progressive-step case in which

the stress increases at a constant rate.

3. Medium steps for which the assumptions for neither small nor large

steps are valid. The cumulative damage at previous steps must be

6-71
taken into account, but the steps are not small enough that the

severity level can be considered to be continuously increasing.

The following terminology is used: 1 a rge/step -stress , medium/ step -stress, and

small /step-stress. The size designations are not absolute, but are relative to

the kind of analysis that must be performed.

Large/step-stress tests are analyzed as if they were constant-stress tests

being run at the severity level of the last step. Parts that are very

expensive or otherwise difficult to acquire or test often are treated in this

way. Often a sample of only one is used. It is wise to consider the results

as "ballpark" figures, since the necessary assumption that the effects of

previous steps are negligible is likely to be in error. Preliminary tests

often are run in this way and are followed by a more comprehensive set of tests

later on.

Smal 1 /step-stressing is analyzed in the same way as progressive-stressing,

and, in fact, there is really no distinction between them. In many cases,

there may be an economic advantage to choosing very small step increments over

a continuously increasing stress. For example, if extremely accurate voltage

steps are desired, a stepping switch might be used with a voltage divider;

otherwise, a slow motor might be used to turn a multi-turn potentiometer.

Less testing time is the major advantage of step -stress tests over constant-stress tests. A direct comparison of the methods requires an assumption of a theory of cumulative damage; for example, metal fatigue is

attributed to a variety of such theories. In electronics, a simple linear

model is assumed most often because of its simplicity and the lack of knowledge

of the actual processes.

A linear model of cumulative damage is a gross approximation. In some circumstances, it consistently underestimates, and in other circumstances

consistently overestimates, the correct results. Regardless of these

deficiencies, it offers the advantages of being tractable, easily remembered,

and widely used. One should use the linear model unless some other, better

model is known. But one must remember the arbitrariness of any assumption .

An important parameter in step-stress testing is the ratio of severity

step size to the time at each level. This controls the rate of increase of the

stress severity and is the parameter that is varied when running several tests

on a particular population of items.

For some kinds of items, the maximum useful severity level will be

exceeded before the device fails in the proper mode. For example, on thermally

stressed transistors there are sometimes eutectic points where melting occurs

and the transistor essentially ceases to be a transistor. If this happens, the

rate of increasing the stress severity must be decreased. The slope of the

steps during the course of the tests also can be modified. The severity level

limits (i.e., the level where the device ceases to function in its usual

manner) are an important limitation to step-stressing. There are other cases where the failure mode changes so drastically at some level that it is

senseless to continue testing above that level.

6-72
Another advantage of step-stress testing is the elimination of "switch-on"

problems, such as initial transients and failures due to high stress rates.

This is because the severity level is low at the beginning and the severity

increase is gradual. The severity level need not begin at "zero" (i.e., a level near benign). This can save time and reduce the amount of cumulative

damage at severity levels other than the failure level. Some programs

concerned with investigating cumulative damage theories may change the severity

level only once during a test. For example, the initial part of one test may

be at a high severity level and the remainder at a low severity level; a subsequent test reverses the procedure. Not much work of this sort is done in

electronics, but metallic fatigue is a field in which these methods of

programming stresses have received considerable attention.

In order to compare tests (or field experience) run under different

severity level programmings, some model of cumulative damage is necessary . No

particular model is required, merely some model. In electronics there are very

few theories of cumulative damage, regardless of the part, but in mechanical

fatigue, for example, there are many models of cumulative damage. Most often

such a model uses "constant stress" test as its basis. The most common

conceptual model, in almost any field, for cumulative damage is the so-called

linear model. It has one basic assumption, i.e., the rate of doing damage is

1/MtF where MtF is the Median-time-to-Fail ure. The MtF is for the particular

severity level at which damage is accumulating. There are several corollaries

to this assumption which often are (but improperly) stated as additional

assumptions.

• The rate of doing damage does not depend on the amount of damage

already done.

• The order in which the severity levels are applied makes no difference.

• The total damage is the simple sum or integral of the damage done at

each stress level.

• The rates of doing damage are independent of each other for different

severity levels.

• The Median endurance at constant severity level is unity.

The use of a cumulative damage model does not necessarily mean that the

failure modes/mechanisms were the same at each severity level, although such a case may help the validity of the model.

Accelerated life tests can be used in programs operating under tight and

critical schedules. If production begins before research and development is

completed, some assurance must be obtained quickly that the equipment has an adequate lifetime and that no gross design weakness exists. Conventional life

tests often take too long to be used under these conditions.

Accelerated testing also is used when repair parts must be manufactured

simultaneously with a short run production program. In this case, failure rate

data cannot be provided quickly enough by life testing to influence the

analysis of the repair complement.

6-73
In some cases (explosives, for example), the earliest times to failure in

the storage environment and variations in times to earliest failure must be

known with high accuracy. A large sample would have to be kept in storage in a usual life test. This would be very expensive and time consuming. Accelerated

testing of critical failure modes can be used to determine the range of

variability of the time to failure, with useful accuracy, with a smaller sample

than that required for usual life testing. For example, solid rocket

propellants are subject to catastrophic failure modes that may result in

explosions. The remaining life in a stored lot must be subjected to

accelerated aging in order to determine whether some critical failure mode is

about to be triggered.

Accelerated tests can be implemented by speeding up the duty cycle or the

environmental level, or both. The environments must be cycled from extreme to

extreme in order to reproduce in a short time the degradation expected over the

period of actual service life. The environmental factor selected for

acceleration is determined by the item tested and its failure modes. For

example, for many mechanical components, failure is caused by mechanical wear;

hence the acceleration is obtained by increasing the frequency and severity of

stress.

The failure data at usual environmental levels and those at accelerated

environments must correlate in some way with the stresses actually applied. A

precise statistical correlation frequently cannot be obtained because much of

the theory of accelerated testing is still very crude. In such cases accelerated environmental tests may permit a great deal of intuitive

information to be developed.

Statistical correlation often can be obtained with accelerated duty cycle

testing. The expected number of cycles of actual service in a given time

period often can be estimated. Accelerated testing is performed by increasing

the number of cycles in a given time period and measuring the

mean-cycles-to-fail ure. The mean-cycles-between-fail ures (MCBF) at the

accelerated duty cycle frequently can be related to the MCBF at normal duty

cycles as a function of the ratio of cycles per time period.

The ideal accelerated test should include the following information:

• An algorithm for converting the reliability data observed at

accelerated conditions to reliability data at normal conditions.

e A statistically sound empirical proof of the algorithm.

t A physical model explaining the algorithm.

Unfortunately, most accelerated test techniques do not meet these criteria.

They tend to be approximate and require a great deal of engineering judgment in

the absence of precise physical models or statistical techniques. Some

discussions in the literature are vague and ambiguous; the word "life" may

mean the random variable, or may refer to the mean life, or may not mean anything specific. One must beware of using acceleration factors from the

literature for specific components. The state-of-the-art in components changes

rapidly enough so that failure modes and their acceleration factors can be

expected to change in nonapparent ways.

6-74
Temperature is the most common method of accelerating a test; usually the

scale parameter of the distribution is presumed to follow the Arrhenius

law [54]. Voltage can be increased for some kinds of capacitors, and power

dissipation can be increased to shorten the life of many electronic components.

Mechanical excitation, such as vibration and shock, are sometimes used.

In the parametric approach, the parameters of the failure distribution are presumed to change in a "deterministic fashion" with the "stress." The

functional relationship of the "deterministic fashion" is presumed known, and

the purpose of the test is to evaluate the parameters in that relationship.

The most common situation is the constant failure rate and the Arrhenius

temperature law, which describes the rate of increase of chemical reactions

with increasing temperature [52].

When a failure distribution has two parameters, it is most common to assume that one of them is independent of the accelerating "stresses." Other

assumptions tend to be tractable, even if more realistic. In the s-normal or

log normal distributions, the median usually is assumed to be a function of the

"stresses," and the other parameter to be a constant.

No matter what distribution is assumed, it is essential that the

statistical uncertainty in the results be estimated and clearly stated--

because this uncertainty is usually so large as to greatly reduce the impact of

the nominal conclusions. In fact, one is often tempted to remark, "I could

have guessed that close without the tests!" For example, in some reasonably

high temperature tests, the uncertainty in failure rate at operating

temperatures might be a factor of 10 or so. At this point it may be useful, in

summing up accelerated testing, to cite appropriate remarks from an NBS study

of life-cycle testing [53].

"Accelerated testing, in the absence of historical data is inherently

risky--by making a use condition or environmental factor more severe than

normal, failure mechanisms different from those which would occur normally may

be brought on; further, it is difficult to predict the performance at the

normal stress level. There should be justification for predicting what the

characteristic would be at normal use conditions and environmental factors.

Otherwise, predictions are little more than guess work. Justification can take

the form of historical data or a quantitatively calculable knowledge of the

processes governing the predominant failure mechanisms.

"Because of the risk involved in accelerated testing it is advisable to do

normal testing when practical; except if historical data are available. If the

product class were rapidly evolving, or the time to complete testing were excessively long, or the cost were prohibitive, the normal test would be

considered impractical. A way to reduce clock time while still doing a normal

stress test may be to increase the frequency of use (an example where this

should work is an appliance such as the vacuum cleaner).

"In summary, where historical data are not available, because of the risk

in making accelerated tests, normal tests are advisable wherever practical.

Where normal tests are not practical, then accelerated tests should be

considered, but accelerated tests will not always be feasible and the specific

product class must be considered and evaluated. A necessary condition for

6-75
making credible accelerated tests is (1) historical data or (2) a calculable

knowledge of the main failure mechanisms."

6.4.7 Fail -Safe Considerations in ATE Systems

There are two major, but overlapping, failure problems in relation to ATE

systems. One is the failure of a component in the ATE system which will not

result in damage to the remainder of that system or affect its performance so that it can no longer perform all, or most, of its ATE functions. The

implication here is that the ATE system would continue to operate, although at

less than the total effectiveness desired.

The second failure problem is one in which another type of component, such

as a sensor monitoring a critical parameter in the UUT, fails. If ATE data are used as inputs to an automatic control system, the UUT itself could conceivably

be destroyed or damaged beyond repair. An example might be a rotary speed sensor with a voltage output amplitude proportional to speed. If the sensor output were to drop due to increased temperature or leakage currents, the ATE

might not detect anything amiss and an automatic control might feed more power

to the rotating device to bring its speed up to "normal."

The answer to both problem areas, of course, is proper planning and

execution of fail-safe design practices.

Again, there are two overlapping areas to achieving a reliable fail-safe

system: redundancy and part selection. The reliability of a system can be

significantly enhanced through the use of redundancy. Redundancy involves

designing one or more alternate signal paths into the system through addition

of parallel elements. Redundancy has been extensively applied to airborne

systems. For example, the electronic multiplexing system may use a redundant

design. In such a system, redundant computers control the main switching

buses. Normally, one of two computers is active and feeds the two main buses

which control all switching functions while the other continuously performs the same function and compares its output with the active computer. If the active

computer malfunctions, the standby automatically takes over.

Another example of a redundant configuration is provided in a weapon

control system in which two major sensors are used to achieve the same goal

.

An example is a pulse Doppler search, track, acquisition, and guidance radar

with a gimbal -mounted infrared search/acquisition sensor. The infrared system

provides a backup to the radar if the latter is inoperable due to malfunctions

or jamming. Additionally, it may operate in a dual mode to augment the radar

search volume.

Depending on the specific applications, a number of approaches are available to improve reliability through redundant design. These design

approaches can be classified on the basis of how the redundant elements are introduced into the circuit to provide a parallel signal path. In general,

there are two major classes of redundancy.

Active redundancy —External components are not required to perform

the function of detection, decision, and switching when an element or path in the structure fails.

6-76
Standby redundancy —External elements are required to detect, make a decision, and switch to another element or path as a replacement for

a failed element or path.

Additional details can be found in the literature [5u].

The other approach involves part selection and control from the

diversified complement of electronic parts which is available to structure

modern military electronic systems. These parts constitute the building blocks

from which systems are fashioned and greatly impact hardware reliability.

Since the reliability of the end item is dependent upon these building blocks,

the importance of selecting and applying the most effective parts cannot be

overemphasized.

The task of selecting, specifying, assuring proper design application,

and, in general, controlling parts used in complex electronic systems is a major engineering task. Part selection and control is a multi -disciplinary

undertaking involving the best efforts of component engineers, failure analysts,

and reliability engineers, as well as design engineers. Numerous controls,

guidelines, and requirements must be formulated, reviewed, and implemented

during the development effort.

Part control activities comprise a large segment of the total effort for

part selection, application, and procurement. The effort encompasses tasks for

performance, reliability, and other requirements of the evolving design. Other

subsections of the handbook provide further details with regard to these

control tasks, indicate their importance within the part selection process, and

provide appropriate design guidance.

Electronic parts that comprise any electronic equipment constructed for

military purposes are under the cognizance of the Military Parts Control

Advisory Group, located in the Directorate of Engineering Standardization at

the Defense Electronics Supply Center (DESC). This group promotes

standardization in part selection and application. By using standard parts in new equipment design and development programs, much time and effort can be

saved while obtaining better equipment performance, in addition to simpler and

better logistics support. DESC promotes usage of standard parts and manages

standardization problems for parts which are initially characterized as nonstandard but whose repetitive usage makes their standardization necessary.

Department of Defense standardization managers work closely with the military

services and industry in developing an effective standardization program for new systems.

The general rule for part selection is that wherever possible, "standard"

devices should be used. "Standard" devices may be defined as those which, by

virture of systematic testing programs and a history of successful use in

equipment, have demonstrated their ability to consistently function within

certain specific electrical, mechanical, and environmental limits and, as a result, have become the subject of Military (MIL) Specifications. MIL

Specifications which thoroughly delineate a part's substance, form, and

operating characteristics exist, or are in preparation, for practically every

known type of electronic component. Military Standards also cover the subject

of testing methods applicable to MIL-specified components. A listing appears

in section 8.3.

6-77
In addition, Military Standards exist which list by MIL designation those

parts or devices which are preferred for use in military equipment. In regard

to sensors, there are only a few MIL Standards (see section 8.3), but a larger

number of "Civilian" Standards (see section 8.2). Since there are significant

gaps in coverage, sensors generally must be subjected to qualification tests

tailored to the specific application as outlined below.

In conjunction with part standardization, nonstandard part approval must

be considered. Nonstandard part approval is comprised of activities to

document and secure authorization to use the part in the system.

Mil itary-STD-891 outlines the functions of a Part Advisory Group or a Part

Control Board operating under both government and contractor cognizance and

which provides the necessary mechanism for securing approval of nonstandard

parts.

The qualification of nonstandard parts must include detailed and formal

submittal of data to support approval request. This data must be:

(1) statistical test data, (2) analytical data for components that are similar

to a standard part, or (3) a combination of statistical and analytical data.

(Note: Those components that require formal statistical test data for

qualification should be identified as critical items.)

The selection process must include design evaluation, reliability history

review, construction analysis, failure mode and effects analysis, and cost

effectiveness studies as necessary. The control effort should include the

development of meaningful procurement specifications which, when completed,

reflect a balance between design requirements, quality assurance, and

reliability needs consistent with apportionment studies and vendor

capabil ities.

A well controlled parts program involves establishing a vendor control

program, audits of vendor processes, the establishment of source inspection

where applicable, and the preparation of associated documentation. The parts

control effort includes identifying all critical parts, equipment/components,

and other items considered critical from any of the following standpoints:

Mission and safety sensitive (failure impacts mission success

and personnel safety),

Reliability sensitive (from early reliability studies,

apportionments, etc.),

Have limited life,

Are high cost items,

Have long procurement lead times,

Require formal statistical qualifications testing.

Planning for critical item control must include controls for special handling,

the identification of critical item characteristics to be inspected or measured

during incoming inspection, material review procedures, traceability criteria,

and periodic audits. All items considered safety critical must be coded.

Detailed documentation must be prepared that describes procedures, tests, test

results, and efforts to reduce the degree of critical ity of each item.

In order to realize fully the benefits of a rel iabil ity -oriented design

and to assure fail-safe provisions, consideration must be given early in the

6-78
design process to the required environmental resistance. Whether intrinsic or provided by specifically directed design features, it will singularly determine

the ability of the equipment to survive the deleterious stresses imposed by the

operational environment. The initial requirement for determining the required

environmental resistance is the identification and detailed description of the

environments in which the equipment must operate. The next step is the

determination of the performance of the components and materials that comprise

the equipment when exposed to the degrading stresses of the environments so identified. This had been discussed in much detail in the preceding sections.

When such performance is inadequate or marginal, with regard to the equipment

reliability goals, corrective measures such as derating, redundancy, protection

from adverse environments, or selection of more resistant materials and

components are necessary to fulfill the reliability requirements of the

equipment.

6-79

7. ERROR ASSESSMENT AND ACCURACY

7.1 General Considerations

The primary function of the ATE system is to monitor the health of the

UUT. To do this the health of the ATE system itself must be superior to that

of the UUT. The quality of performance (continuing health) of the ATE system

is established from an assessment of the errors within the system.

Two things must be kept in mind: First, ATE system outputs ultimately

require decisions to be made in regard to the health of the UUT. The validity

of these decisions depends largely on all the errors inherent in the total ATE

system. Second, the errors in the total ATE system include the errors of the sensor and the errors inherent to the remainder of the electronic portion of

those systems.

Error analysis for the sensor is discussed in the following sections.

Error analysis for the electronic components has similar considerations, based

on calibration and test results of those components. Discussion of the latter

is outside the scope of the Sensor Handbook.

7.2 Sensor Error Analysis

7.2.1 Straight Line Data Reduction

In order to establish the quality of measurements performed by the sensor,

it is necessary to establish its "accuracy" by an error analysis. This

analysis is largely based on the reduction of data obtained from sensor calibrations and evaluations.

In the process of data reduction, it is incumbent to extract the maximum

amount of useful information from the calibration data of the sensor. This

information is generally given in terms of a number of performance parameters,

the numerical values of which permit interpretation of measurements performed

by the sensor. These values also permit the quantitative comparison of

different sensors. Such parameter values, obtained from calibration data, must

be the "best" values, that is, those which best represent the actual character

of the sensors. "Best" in this connotation requires a preconceived basis of

judgment for comparison. As indicated previously, for the vast majority of sensors this basis is the assumed straight-line relationship between sensor output and measurand input.

Thus sensor calibration data are generally reduced so as to obtain the

parameters of, and show deviations from, the "best" straight line.

7.2.2 Selection of Straight Line

There are a number of straight lines which may be chosen to represent the

sensor's calibration characteristic. ANSI Standard MC6. 1-1975 [2] lists five:

"end-point" line, "best straight" line, "terminal" line, "theoretical slope"

line, and "least squares" line. They are defined in the glossary, section 10.

The line most commonly used is the one based on the mathematically rigorous

criterion of least squares. It is based on the principle: "The most probable

value of an observed quantity is such that the sum of the squares of the

7-1
deviations of the observations from this value is a minimum" [20], This is

based on the fact that most measurements of physical quantities show a normal

distribution with positive and negative deviations from the mean equally likely

and very large deviations less likely than small ones.

The "least squares" straight line is the most desirable one to use in

reducing data from static calibrations of sensors. The line can be defined

unequivocally in terms of the quantities measured. This line is also

statistically significant and standard deviations can be assigned to estimates

of the slope, intercept, and other parameters derived from it.

Accordingly, the "least squares" straight line is recommended for data

reduction. Laboratories that have digital computers or modern desk calculators

can frequently obtain all parameters of this line with the use of a standard

"least squares" straight line program supplied with these devices.

7.2.3 Calibration Parameters Obtained From Data Reduction

As indicated earlier, the general simplified assumption in data reduction

is that the sensor calibration is a straight line, with the customary equation

y = bx + a, where y represents the electrical output parameter and x the input

measurand. Calibration data are normally tabulated and from this the data can readily be reduced.

There are five resulting numerical calibration parameters describing the

straight line relation which is assumed to represent the sensor performance for

each calibration. They are:

a - the y-intercept (intercept on the output axis)

S a

- the standard deviation of the y-intercept

b - the slope (sensitivity of the transducer)

Sb

- the standard deviation of the slope

S t

- the standard deviation of the "deviations of experimental points

from the theoretical line" (the "goodness of fit").

In addition two other parameters commonly used to describe performance

characteristics may be obtained from the data or from a graph plotted with the

aid of the tabular data from one calibration.

Hysteresis - the maximum difference in output, at any measurand value

within the specified range, when the value is approached

first with increasing and then with decreasing

measurand [2].

Linearity - the closeness of a calibration curve to the specified

straight line, expressed as the maximum deviation of any

calibration point from that line during any one calibration

cycle [2].

From the data obtained from three static calibrations performed consecutively,

an additional parameter can be derived.

Repeatability - The ability to reproduce output readings when the same measurand value is applied to it consecutively, under the

same conditions, and in the same direction [2].

7-2
Repeatability is expressed as the maximum difference between corresponding

values in the three calibrations. There is no universal agreement as to the

particular values selected. Full-scale output is a commonly used one, as is zero measurand output. Derived values are also used, like slope (sensitivity)

or the y-intercept. Deviations in full-scale output values are likely to be

greatest, and therefore probably the best indicators of repeatability. The

total time involved for the three calibration cycles must be reported also,

since time has a significant effect on repeatability.

It should be pointed out that modern computers make it relatively easy to

represent calibration data by polynomial expressions of varying degrees of

complexity. The advantages of obtaining a major conformance ("fit") of such a theoretical curve to the actual calibration points must be weighed carefully

against the ellipse of uncertainty which in reality represents each calibration

point. It is the author's opinion that the straight-line assumption of sensor characteristics in the vast majority of cases is the most realistic approach.

A notable exception to this are flow measurements based on differential

pressures where the output corresponding to flow is given by the square root of

the differential pressure.

7.2.4 Number of Significant Digits for Reporting Calibration Results

Data reduction of a calibration run ordinarily produces the pertinent

parameters which describe an instrument being tested. The number of

significant digits which should be used is important in order to neither

overspecify nor underspecify a parameter value.

As might be anticipated, computation cannot be expected to lead to values

of greater precision than that of the input data. Thus the accuracy of the

measuring instruments in the calibration system and, in particular, the

precision of the measurements (as measured by the number of significant digits

indicated) are the principal factors which limit the precision to which one should properly report derived (i.e., computed) parameters, e.g., the

sensitivity.

Using a pressure sensor as an example, the input data in a pressure sensor calibration is ordinarily the pressure applied (in Pa or psi), the output

response (in mV/V), and the power supply voltage (in volts). If a temperature

correction is needed, the temperature (in °C) is also part of the input data.

Thus a number of significant digits to which each measurement (mentioned above)

can be reported is of paramount importance in determining the precision to

which the computed parameter can be reported.

The rules for handling significant digits in the common arithmetic

operations are as follows (according to section 22-2, "Rounding in Statistical

Computation," NBS Handbook 91 [20].

1. For addition - record and report to the number of decimal places in

the addend with the fewest number of decimal places. Before summing,

round more precise addends to 1 decimal place more than this. Round

the sum one more place where required.

2. For subtraction - both numbers should be rounded to the same number of

places before subtracting. Keep as many decimal places as possible to

7-3
avoid error in differences between two nearly equal numbers. Where

possible, approximate to more places before subtracting.

3. For multiplication and/or division - if the less precise of two

approximate numbers (for division - divisor or dividend) contains n significant digits, the product (or quotient) can be relied on for n significant digits at most. Keep all digits until the final results

and then round as indicated.

4. For power and roots - the power (root) of a number is good at best to

the same significant number of digits as the number.

The gist of the rules given, as they apply to the statistical parameters

presented as a result of a calibration, is that the number of significant

digits to be used in the value of any parameter should be no more than that of

the least precise value which entered into the calculation of the parameter.

There are certain considerations which appear to represent (but do not)

exceptions to the rules. An integer such as 10, which is a counting number, is

exact and therefore has not two significant digits but an infinite number.

Another consideration which has a two-fold benefit is Berk son's premise

with regard to an ordered laboratory experiment [20]. This premise, first

described by Joseph Berkson in 1950, can be summarized briefly as follows.

An exception to the normal precision requirement is available in a planned

physical experiment where both variables, x (measurand) and y (output voltage),

could be expected to have some associated random error in their measurement.

If the normal independent variable is given a set of ordered p reassigned

values called nominal or target values and then set to these target values as well as possible (assuming only randomness and independence of errors), the

resultant data will give a valid underlying linear structural relationship

where measurement errors are assumed in the y measurements but not in the x measurements. In this procedure, the x measurements are assumed to be without

error and therefore precise to as many places as desired. According to this

premise, which has had wide acceptance in statistical circles, not only does one not have to consider the random error in the x measurement (measurand), but

because, in effect, there is no random error, precision can be added to this

measurement to equal that of the next least precise measurement made and used

in parameter calculation. Thus the lack of precision of the x measurement does

not degrade the precision of the result.

One can thus state the simple rule—parameters derived from a calibration

(of a sensor, for example) should be expressed to the same precision (i.e.,

significant number of digits) as that of the output voltage reading, not more

and not less. Thus an accurate output reading voltmeter is most significant.

7.2.5 Expression of Uncertainties of Final Results

Most of the following material was obtained from chapter 23, "Experimental

Statistics" by Mary G. Natrella, NBS Handbook 91 [20].

The actual error of a reported value, the magnitude and deviation from the

true value, is usually unknowable. Limits to this error can generally be

inferred from the precision of the measurement process and from reasonable

7-4
limits of the possible bias of the measurement process. The bias, or systematic error of a measurement process, is the magnitude and direction of

its tendency to measure something other than what was intended; its precision

(actually imprecision) refers to the typical closeness of successive

independent measurements of a single magnitude generated by repeated

application of the process under specified conditions. Its accuracy is

determined by the closeness to the true value characteristic of such

measurements. Precision and accuracy are inherent characteristics of the

measurement process employed.

The uncertainty of a reported value is indicated by giving credible limits

to its likely inaccuracy. No single form of expression for these limits is

universally satisfactory. Different forms are recommended, depending on the

relative magnitudes of imprecision and likely bias. Four distinct cases are possible:

1. Both systematic error and imprecision are negligible in relation to the requirements of the intended and likely uses of the result.

2. Systematic error is not negligible, but imprecision is negligible in

relation to the requirements.

3. Neither systematic error nor imprecision are negligible in relation to the requirements.

4. Systematic error is negligible, but imprecision is not negligible in

relation to the requirements.

In general, it is recommended that two numerics relatively expressing the

imprecision and the bounds to the systematic error to the results should be

used whenever (a) the margin is narrow between ability to measure and the

accuracy or precision requirements of the situation; or (b) the imprecision and

the bounds to the systematic error are nearly equal in indicating possible

differences from the true value (case 3).

Also it is desirable that expressions of uncertainty be given in sentence

form whenever feasible. Finally, the form "a + b" should be avoided as much as possible, and never used without an explicit explanation of its connotation.

It is very likely that most practical static calibration situations can be

represented by case 3 above, i.e., neither systematic error nor imprecision

negligible. In this case, recommendations are that the reported numerical

result be qualified by a statement that places bounds on its systematic error

and a second statement identifying its measure of imprecision.

In the statements of values, the bounds of systematic error and the measure of imprecision should be stated to no more than two significant

figures. Furthermore, the reported numerical result should be stated, at most,

to the last place affected by the more precise of the two qualifying

statements. It is also desirable to give the qualification in sentence form.

The term "standard error" may be used to signify the standard deviation of

the reported value itself, such as the sensitivity and the y-intercept computed

from the static calibration data by the method of "least squares." The

7-5
recommendations above do not exclude, however, the presentation of the type of

statement placing bounds on an overall uncertainty, provided separate

statements of its imprecision and possible systematic error are included also.

Such bounds indicating the overall uncertainly of the repeated value should not

be numerically less than the corresponding bounds placed on the systematic error outwardly increased by at least two times (and preferably three times)

the standard error. An example of such a statement is "...with an overall

uncertainty of +3 percent, based on a standard error of 0.5 percent and an allowance of +1.5 percent for systematic error." The uncertainty might

alternatively be described as: "...the standard error of this value is less

than 0.5 percent, and the systematic error is thought to be less than

+1.5 percent." It is also desirable to state that the standard error was obtained from a "least squares" evaluation of an n-point static calibration.

7.2.6 Sampling Considerations in the Performance Testing of Sensors

The sections above have been concerned with the error analysis of data

obtained from one or more calibrations of a single sensor. In qualification

testing in particular, but also in certain cases of acceptance testing, one desires to gain some understanding of the performance of a group or class of sensors. While it would seem desirable to evaluate the performance

characteristics of every single sensor, this is not practical for at least two

reasons: the high expense of testing in terms of personnel, equipment, and

time makes such evaluation economically unsound. Furthermore, the performance

tests themselves may cause deterioration of the sensor's performance.

Accordingly, it is an established practice to select some sensors from a group for evaluation and to consider their performance characteristics as representative of the entire group. The use of certain statistical principles

makes it possible to draw mathematically valid inferences from the experimental

data. For any particular performance characteristic, one would like to be able

to state numerical 11 imits between which one has a certain confidence (p%) that

a given proportion (p) of all the values will lie. The limits are based on two

factors derived from the numerical values of the particular performance

characteristic of a number (sample) of selected sensors. The two factors are

X, the arithmetic mean of the values and S, the standard deviation of these

val ues.

Extensive tables in "Experimental Statistics," NBS Handbook 91 [20] enable

one to find for (N), a desired number of samples, the factor K such that the

proportion (P) of the values lie within the range X +KS, with a confidence

level p percent where_ i N

X ~

N ^

X

L^ Arithmetic mean of sample

VNl (x - X) 2 Standard deviation of sample

- 1 = 1

N - 1 It is extremely important to realize that the tables cited and the

validity of values derived from them are based on two fundamental assumptions:

7-6
(1) The particular characteristic has a normal distribution in the entire

group of sensors.

(2) The samples tested are selected in a random manner.

To gain an idea of the numerical values involved, the following is

extracted from a table of "Factors for Two-Sided Tolerance Limits for

Normal Distribution" [20].

Confidence Level 75% 75% 75% 90% 90% 90% 95% 95% 95%

Proportion of 0.99 0.95 0.90 0.99 0.95 0.90 0.99 0.95 0.90

Group P

Number of Samples "K"

N

2 9.53 7.41 6.30 24.2 18.8 16.0 48.4 37.7 32.0

3 5.43 4.19 3.54 8.97 6.92 5.85 12.9 9.92 8.38

4 4.47 3.43 2.89 6.44 4.94 4.17 8.30 6.37 5.37

5 4.03 3.09 2.60 5.42 4.15 3.49 6.03 5.08 4.28

It is apparent from the table that a considerable shrinking of the limits

of the range of values X +KS occurs when three samples are tested, as compared

to two. The improvement possible varies from 1.8 to 3.8 fold, depending on proportion and confidence level selected. The testing of four samples results

in a much smaller additional improvement, the total ranging from about 2.2 to

5.8 fold, as compared to the values based on two samples, while adding

appreciably to testing time and expense.

It is quite practical to perform static calibration, and similar tests, on three sensors (including data reduction) within one day or less. Four or more

sensors may require testing time extending over several days with the added

possibility of different laboratory conditions, warm up etc., which would make

data comparison less valid.

More important, however, under the present system of procurement of

sensors, there is no assurance that the samples received are randomly selected.

The numerical validity of the inferences as to the characteristics of the group

is therefore doubtful, although this may be offset somewhat by the fact that

quality control of the sensors during manufacture may result in a distribution

closer to the mean than described by the normal curve.

It is quite feasible for the large-scale user of sensors to assure himself

of random sampling by ordering a large number of sensors and then selecting

random samples.

In general, it seems that the testing of three sensors is the most

practical procedure to establish most performance characteristics. If a particular characteristic contributes only a small error to the measurement,

tests on two and sometimes even one unit seem adequate. Experience and

judgment help to make these decisions.

7-7
If the three sensors tested are known to be, or assumed to be, random

samples, the value of K for P = 90 percent (P = 0.90), K = 5.85 appears a reasonable one to use. With this value the computed limits of the particular

characteristic can be said to represent the actual limits nine times out of ten

for nine out of ten specimens of the group.

7.2.7 Error Band Concept

The discussions to this point have been directed at base line (static or reference) calibrations of sensors. These are the fundamental calibrations to

establish sensor performance at laboratory conditions. Actual sensor operation, however, as elaborated earlier, is not normally in such benign

circumstances and the performance is expected to be "poorer." Thus the numbers

expressing the uncertainty (or error) of a particular characteristic of the sensor are likely to be larger when the conditions of sensor operation are less

favorable.

Calibrations yield a number of parameters which measure the quality of

performance of the sensor, among them linearity, hysteresis, repeatability,

stability, friction error, creep, etc. (see section 3.3 for definitions). It is difficult to compare the qualities of several sensors using values of these

individual parameters.

In 1957, the error band concept was developed at an aerospace

company [29]. In brief, it postulates that individual tolerances assigned to

repeatability, hysteresis, friction error, and linearity could be replaced by a single set of tolerances on the maximum deviation of any data point from a specified performance line which represents the ideal calibration curve of the sensor.

The introduction of error band specifications resulted in higher

production yields by sensor manufacturers since more leeway was permitted in

the tolerances of individual parameters. In addition, this approach led to

interchangeable calibration records. If the error band specified for a given sensor was sufficiently narrow for overall data accuracy requirements, the

calibration records of all sensors having an equal or smaller error band were

considered interchangeable within error band tolerances. The data obtained

from any of the sensors could then be reduced on the basis of the ideal

calibration curve and the uncertainties associated with it.

The base line (static) error band can be obtained from the static

calibrations discussed in section 6.2.1, in which the measurand is applied in

increasing and then decreasing manner. The author' of this handbook feels that

a more realistic approach would involve the application of the specified

measurand amplitudes in a random sequence during the calibrations and believes

this to be a subject worthy of experimental investigation.

For sensor operation under other than laboratory conditions, the error

band concept is logically extended to describe the deviations of data points

from the ideal line or curve when the sensor is calibrated at the specified

environment or following a specified exposure or cycling, etc. Thus the error

band is a very useful and realistic concept since it focuses attention on the

overall quality of the data obtained from the sensor as a measuring device,

i.e., its ultimate quality of performance.

7-8
8. SENSOR -RELATED STANDARDS DOCUMENTS

8.1 Introduction

The aim of standards documents is to enhance communications and

understanding concerning particular items among the community making or using

those items. There are several groups of standards extant in the field of sensors and their applications. These standards fall into two major

subdivisions: voluntary standards and mandatory standards. The former are generally promulgated by professional or trade associations, the latter by

governmental bodies.

Standards are generally not of a static nature, that is, they are supposed

to be reviewed and revised after specified intervals of time. New standards

are being worked on as well, consequently, there is a continuing state of flux

and a completely up-to-date listing of standards documents, even in a restricted field, is difficult to achieve. The field of sensors is no exception. It is felt, however, that a listing of such documents applicable to sensors would be of considerable benefit in the planning, design, use, and

testing of ATE systems. A quotation from the preface to a sensor standard by

the Instrument Society of America outlines quite clearly the aims of such a document.

"This standard is intended as a guide for technical personnel at user facilities as well as by manufacturers' technical and sales personnel whose

duties include specifying, calibrating, testing or showing performance

characteristics of pressure transducers. By basing users' specifications as

well as technical advertising and reference literature on this Standard, or by

referencing portions thereof, as applicable, a clear understanding of the

users' needs or of the transducers' performance capabilities, and of the

methods used for evaluating or proving performance, will be provided. Adhering

to the specification outline, terminology and procedures shown will not only

result in simple, but also complete specifications; it will also reduce design

time, procurement lead time, and labor, as well as material costs. Of major

importance will be the reduction of qualification tests resulting from use of a commonly accepted test procedure and uniform data presentation" [54].

Government standardization documents are almost always of a mandatory

nature and are frequently used as regulatory documents. The two major

subdivisions are federal (civilian) and military documents, although some overlaps exist. No federal standards pertaining to sensors with electrical

output were located. As expected considerable numbers of military documents

exist. They fall into several classes and it seems useful to define the types

of standards documents which exist. The definitions which follow are extracted

from Defense Standardization Manual DoD 4120.3-M [55].

Specifications

Specifications are documents prepared specifically to support procurement

and cover items which vary in complexity from paper clips to missile weapon

systems. They establish requirements in terms of complete design details or in

terms of performance, but in most instances in terms of both design and

performance. Specifications may cover a single item, such as a camera, or

thousands of items, such as bolts, and for each single style there may be

8-1
several finishes and hundreds of sizes. When invoked, specifications should be

tailored to their application consistent with basic program requirements.

Standards

Standards are documents that establish engineering and technical

requirements for processes, procedures, practices, and methods that have been

adopted as standard. They are prepared to provide the designer with the

descriptions and the data normally required for selection and application.

Their purpose is to control variety. They may cover materials, items, features

of items, engineering practices, processes, codes, symbols, type designations,

definitions, nomenclature, test, inspection, packaging and preservation

methods, items, parts and components of equipment. Standards represent the

best solution(s) for recurring design, engineering, and logistics problems. It

is intended that they be up-to-date records of the decisions and

recommendations of experts in each field or area. When applied by design and

procuring agencies, standards should be tailored to the application consistent

with basic program requirements.

Standard and Specification Relationship

Standards function in procurement through the medium of specifications. Thus

they are used to standardize one or more features of an item such as size,

value, or detail of configuration. In equipment specifications, they are referenced to standardize on those design requirements which are essential to

achieving the design objectives, e.g., interchangeability, compatibility,

reliability, and maintainability. Standards disclose or describe the technical

features of an item in terms of what 1t is and what it will do. In contrast,

the specification for the same item describes it in terms of requirements for

procurement.

Federal and Military Standards and Specifications

Federal standards and specifications are developed when the document will be

used by two or more federal agencies, at least one of which is an agency other

than the Department of Defense. Military standards and specifications cover items or services which are intrinsically military in character, commercial

items which meet special requirements of the military, or commercial items with

no present or known potential use by federal agencies other than military.

Where requirements warrant it, there may be both federal and military

specifications and standards covering the same items or services.

Military specifications and standards are issued as either coordinated or limited coordination documents. Coordinated specifications and standards are used to cover items or services required by more than one military department.

Limited coordination documents cover items or services of interest to a single

department, or those which are prepared by a department or activity to meet an immediate procurement need where urgency does not permit coordination to be

effected.

Handbooks

A handbook is a reference document which brings together procedural and

technical or design information related to commodities, processes, practices,

and services. A handbook may serve as a supplement to specifications or standards to provide general design and engineering data. The use of handbooks

as references is optional.

8-2
8.2 Voluntary Standards Listing

Standards on sensors (transducers) and related subjects promulgated by

professional societies or trade organizations are listed below. They are arranged by the organization which sponsored the work or which issued the

standards. Prospective users are urged to contact the listed organization to

obtain the most up-to-date version of any given standard or to obtain

information on other pertinent documents.

There is some lack of uniformity in the designation of ANSI Standards.

All ANSI Standards are actually prepared by other organizations. Some are initially prepared under ANSI auspices and, when issued, carry the ANSI

designation only. Others are issued as standards by other standards

organizations, then accepted by ANSI, issued also (later) as ANSI Standards,

and may carry dual designations. Some ASTM Standards may also carry multiple

designations.

Voluntary standards concerned with sensors (transducers) were among those

compiled in a very comprehensive column: "Standards and Practices for

Instrumentation," Sixth Edition, 1980, published by the Instrument Society of

America, Research Triangle Park, NC 27709. The following sensor-related

standard titles and abstracts were taken, with permission, from this volume.

They are arranged, in alphabetical order, by the organization which developed

or published the document. Most of these organizations have active committees

working on additional standards documents. No efforts were made to list these

since such information becomes rapidly obsolete.

It should be noted that the completeness and applicability of these

documents varies widely. They were developed for a wide variety of uses by a variety of organizations. Constraints on time and other resources preclude

attempts to critically evaluate these documents in this handbook.

8-3
AMERICAN NATIONAL STANDARDS INSTITUTE (ANSI

)

(Formerly United States of America Standards Institute - USASI)

The following publications have been approved as American National Standards

and are available from the American National Standards Institute, Inc.,

1430 Broadway, New York, NY 10018. Many standards approved by ANSI are published by sponsoring organizations. These standards may be found listed

under the sponsoring organization, but the ANSI number is indicated. These

are available from either ANSI or the sponsoring organization.

ANSI: C39. 3-1976, Specifications for Light-weight Shock-Testing Mechanism for

Electrical Indicating Instruments, 24 pp, $5.50.

Describes and specifies the design and construction of a shock testing

mechanism for testing electrical indicating instruments. Includes general

design, theory of operation, use, construction, mounting of mechanism,

calibration curves, and maintenance. (Sponsored by Electrical and

Electronics Standards Board)

ANSI: C39. 4-1966 (R1973), American Standard Specifications for Automatic Nullbalancing Electrical Measuring Instruments, 2nd edition, 26 pp, $5.50.

Provides classifications, definitions, general requirements, test

conditions and procedures for instruments of the dc potentiometer and dc

bridge types. Performance guides are provided for three types of

operating conditions: reference, rated, and extreme. (Sponsored by

Electrical and Electronics Standards Board)

ANSI: C39. 5-1974, American Standard Safety Requirements for Electrical and

Electronic Measuring and Controlling Instrumentation, 13 pp, $3.75.

Provides maintenance classification, general and particular test

requirements to assure safe electrical operation of measuring and

controlling instrumentation. (Sponsored by Electrical and Electronics

Standards Board)

ANSI: C39. 6-969, Requirements for Automatic Digital Voltmeters and Ratio

Meters, 20 pp, $5.50.

Provides classifications, definitions, detailed reference standards, test

conditions, procedures for instruments intended to indicate dc voltages

and voltage ratios in decimal units. (Sponsored by Electrical and

Electronics Standards Board)

ANSI: C42. 100-1977 (IEEE Std. 100-1977) Standard Dictionary of Electrical and

Electronics Terms, 882 pp, $37.50.

Consolidates and supersedes all previous C42 Series Standards. Defines

20 000 technical words from every area of electrical and electronics

engineering. (Sponsored by IEEE)

8-4
ANSI: C57. 13-1978, Requirements for Instrument Transformers, 68 pp, $7.00.

Applies to current and potential instrument transformers, including

general requirements, terminology; and miscellaneous measurement devices.

(Sponsored by Electrical and Electronics Standards Board)

ANSI: C83. 17-1970, Methods of Definitions and Measurement for Piezoelectric

Vibrators, 18 pp, $4.00.

Defines piezoelectric vibrator and equivalent circuit and provides methods

for measuring electrical parameters of the equivalent circuit. (Sponsored

by IEEE)

ANSI: MCI. 1-1975, IEEE Standard Digital Interface for Programmable

Instrumentation, 80 pp, $10.00.

This standard applies to interface systems used to interconnect both

programmable and nonprogrammable electronic measuring apparatus with other

apparatus and accessories necessary to assemble instrumentation systems.

ANSI: SI. 2-1962 (R 1976), Method for Physical Measurement of Sound, 23 pp,

$5.50.

Covers methods for measuring and reporting the sound presure levels and

sound powers generated by a source of sound using a sound-level meter

and octave-band filter set as minimum equipment. (Sponsored by Acoustical

Society of America)

ANSI: SI. 6-1967 (R 1976), Preferred Frequencies and Band Numbers for

Acoustical Measurements, 11 pp, $3.25.

Provides guide to the design of new acoustical equipment and to the

selection of frequencies to make comparison of the results of acoustical

measurements most convenient. (Sponsored by Acoustical Society of

America)

ANSI: SI. 8-1969 (R1974), Preferred Reference Quantities for Acoustical Levels,

10 pp, $3.75

Concerned with the reference quantities and the definitions of some levels

for acoustics, electroacoustics and mechanical vibrations. Purpose to to

provide a preferred reference quantity of convenient magnitude for a given

kind of acoustical level. (Sponsored by Acoustical Society of America and

ASME)

ANSI: SI. 10-1966 (R 1976), American Standards Methods for Calibration of

Microphones, 33 pp, $7.00.

Methods are described for performing absolute and comparison calibrations

of laboratory standard microphones. Absolute calibration is based on reciprocity; pressure, free field, and random field calibration are desired.

8-5
ANSI: SI. 13-1971 (R 1976), Methods for the Measurement of Sound Pressure

Levels, 34 pp, $6.00.

General recommendations to assist in the development of noise

measurement techniques that are satisfactory for use under various

environmental conditions. Intended to assist in the preparation of test

codes for: 1) determining compliance with a specification, ordinance, or

acoustical criterion; and 2) obtaining information to assess the effects

of noise on people or equipment. (Sponsored by Acoustical Society of

America)

ANSI: SI. 20-1972, Procedures for Calibration of Underwater Electroacoustic

Transducers, 40 pp, $7.00.

Establishes measurement procedures for calibrating underwater

electroacoustic transducers and describes forms for presenting the

resultant data, determining the sound power level produced by a source. Contains test room requirements, source location and operating conditions,

instrumentation and techniques. For measurements that can be used in test

codes for particular types of equipment. (Sponsored by Acoustical Society

of America)

ANSI: S2. 2-1959 (R 1976), Calibration of Shock and Vibration Pickups, 33 pp,

$5.50.

Covers definitions of letter symbols and technical terms,

characteristics to be measured, and methods for the calibration of

acceleration, velocity, and displacement pickups. (Sponsored by

Acoustical Society of America and ASME)

ANSI: S2. 4-1960 (R 1976), Method for Specifying the Characteristics of

Auxiliary Equipment for Shock and Vibration Measurements, 11 pp, $2.75.

Provides a uniform terminology and format for the presentation of the

performance and other characteristics of auxiliary equipment for shock and

vibration measurement. (Sponsored by ASME and Acoustical Society of

America)

ANSI: S2. 10-1971 (R 1976), Methods for Analysis and Presentation of Shock and

Vibration Data, 28 pp, $6.50.

Designed to acquaint the user with general principles of the

analysis and presentation of shock and vibration data and to describe

concisely several methods of reducing data to forms that can be applied

and used in subsequent analyses. (Sponsored by Acoustical Society of

America and ASME)

ANSI: S2. 11-1969 (R 1973), Selection of Calibration and Tests for Electrical

Transducers Used for Measuring Shock and Vibration, 19 pp, $4.75.

Includes considerations relevant to commonly employed

electromechanical shock and vibration measurement transducers, but not to

8-6
those transducers pri marly designed for measurement of acoustic or pressure phenomena. (Sponsored by Acoustical Society of America and

ASME)

ANSI: Y32. 2-1975, Graphical Symbols for Electrical and Electronics Diagrams,

111 pp, $8.00.

Provides graphical symbols for electrical and electronic devices

suitable for all drafting purposes. (Sponsored by IEEE and ASME)

ANSI: Z24. 21-1957 (R 1971), Method for Specifying the Characteristics of

Pickups for Shock and Vibration Measurement, 19 pp, $4.50.

Applies to pickups that, over a specified amplitude and frequency range,

are capable of producing outputs which are known functions of the linear

or angular accelerations, velocities, or displacements of objects whose

motions are being measured. (Sponsored by Acoustical Society of America)

AMERICAN PETROLEUM INSTITUTE (API) .

The following API Publications, Recommended Practices, Standards, and Bulletins

are available from the American Petroleum Institute,

1801 K Street, N.W., Washington, DC 20006.

API: Manual of Petroleum Measurement Standards: Measurement of Liquid

Hydrocarbons by Turbine Meter Systems, 1970, chapter 5.3, $5.00.

Covers the design, installation, operation, and proving procedures for

turbine meter systems. Also presents informational material on the

application of statistical methods to metering systems, troubleshooting

charts, explanation of electronic readout devices, and glossary of terms.

API: Std. 2543 (ASTM D1036-64), Method of Measuring the Temperature of

Petroleum and Petroleum Products, 1965, (ANSI. Zll. 172-1971) $1.00.

Describes the procedure and apparatus used in the determination of

temperatures of petroleum liquids.

AMERICAN SOCIETY FOR TESTING AND MATERIALS (ASTM)

The following ASTM Standards are available from the American Society for

Testing and Materials, 1916 Race Street, Philadelphia, PA 19103. Joint

ASTM-API Standards are available from either organization.

ASTM: Index to Standards; The 1979 Annual Book of ASTM Standards, Part 48,

1979, 292 pp, $5.00.

This book is a key reference volume. It lists by number designation and cross indexed title every one of over 5500 ASTM Standards. The index

refers the reader to the exact part of the 48 Part Annual Book of ASTM

Standards where a particular standard may be found.

8-7
ASTM: D 1085-65 (1975) - (API: STD 2545), Standard Method of Gaging Petroleum

Products, 39 pp, $2.00. Published as reprint only.

Describes the procedure for gaging crude petroleum and its liquid products

in various types of tanks, containers, and carriers.

ASTM: D1142-63 (1975), Standard Methods of Test for Water Vapor Content of

Gaseous Fuels by Measurement of Dew-Point Temperature, 13 pp, $4.00.

Covers the determination of the water vapor content of gaseous fuels by

measurement of the dew-point temperature and the calculation therefrom of

the water vapor content.

ASTM: D1589-60 (1974) Standard Methods of Test for Dissolved Oxygen in Waste

Water, 6 pp, $1.75.

Covers four methods of determination of dissolved oxygen in waste water in

the presence of certain interfering substances. Includes a description of

the use of the polarograph in determination of dissolved oxygen in wastes

after dilution with natural water by a factor of 4 to 100.

ASTM: E177-71, Standard Recommended Practice for Use of the Terms Precision

and Accuracy as Applied to Measurement of a Property of a Material, 1971, 18

pp, $4.00.

The purpose of this recommended practice is to outline some general

concepts regarding the terms "precision" and "accuracy", to provide some standard usages for ASTM committees in reference to precision and

accuracy, and to illustrate some important features of the experimental

determination of precision.

ASTM: E220-72E, Standard Method for Calibration of Thermocouples by Comparison

Techniques, 1972, 18 pp, $1.75.

Covers the techniques of thermocuple calibration based on the comparisons

of thermocouple indications with those of a standard thermometer, rather

than those using fixed temperatures. Method applies to common types of

thermocouples which can be exposed to a clean oxidizing atmosphere.

ASTM: E230-72, Standard Temperature-Electromotive Force (EMF) Tables for

Thermocouples, 1972, 100 pp, $7.00.

Consists of temperature-emf tables for thermocouple types B, E, J, K, R,

S, and T,; standard and special limits of error and upper temperature

limits. All intervals are 1°.

ASTM: E235-76, Standard Specification for Thermocouples, Sheathed, Type K, for

Nuclear or for Other High Reliability Applications, 1976, 7 pp, $4.00.

Presents the material, operating, and environmental requirements of

two-wire thermocouples intended for nuclear service. Provisions for

temperatures up to 900 °C (1650 °F) are covered.

8-8
ASTM: E251-67 (.1974) - (ANSI: Z168. 7-1969 )

, Standard Methods of Test for

Performance Characteristics of Bonded Resistance Strain Gages, 1967, 7 pp,

$4.0U.

Describes procedures for determining: gage factor at a reference

temperature; variation of gage factor with temperature; transverse

sensitivity; temperature sensitivity*

ASTM: E344-74, Standard Definitions of Terms Relating to Temperatuare

Measurement, 1974, 4 pp, $1.75.

ASTM: E380-76, Standard for Metric Practice, 1976, 37 pp, $4.00.

Gives guidance for application of the International System of Units (SI).

Includes information on SI, a limited list of non-SI units recognized for

use with SI, a list of conversion factors from non-SI units recognized for use with SI units, and general guidance on proper style and usage.

AMERICAN SOCIETY OF HEATING, REFRIGERATING, AND AIR CONDITIONING

ENGINEERS, INC. (ASHRAE)

The following ASHRAE Standards may be obtained from the American Society of

Heating, Refrigerating, and Air Conditioning Engineers, Inc.,

345 East 47th Street, New York, NY 10017.

ASHRAE: Std. 41.1-74, Part I, Standard Measurements Guide: Section on Temperature Measurements, 1974, 18 pp, $10.00.

Provides methods for accurate temperature measurement for the particular

needs of heating, refrigeration, and air conditioning. The rates of heat

flow, both to and from moving volatile and non-volatile fluids, in the

range of -40 to 400 °F are covered. The use of thermometers,

thermocouples, and thermistors and the effect of changes in enthalpy are

di scussed.

AMERICAN SOCIETY OF MECHANICAL ENGINEERS (ASME)

The following ASME and ANSI Standards may be obtained from the American Society

of Mechanical Engineers, 345 East 47th Street,

New York, NY 10017.

ASME: PTC 9, Displacement Compressors, Vacuum Pumps, and Blowers, 1970, 41 pp,

$8.00.

Describes tests for determining the performance of positive displacement,

compressors, blowers, and vacuum pumps whether reciprocating or rotating.

ASME: PTC 19.2, Instruments and Apparatus: Pressure Measurement, 1964, 58 pp,

$9.00.

8-9
Discusses the technology of pressure measurement: general considerations

and definitions, pressure connections, liquid-level gages, deadweight

gages and testers, elastic gages, and low-pressure measurement.

ASME: PTC 19.3-1974, Instruments and Apparatus: Temperature Measurement,

1974, 118 pp, $16.00.

Presents a revision, expansion, and consolidation of all earlier pamphlets

on temperature measurement instruments, with particular emphasis on basic sources of errors and means of coping with them.

ASME: PTC 19.5, Interim Supplement on Instruments and Apparatus: Application,

Part II, Fluid Meters, Sixth Edition, 1971, 140 pp, $14.00.

Presents the recommended conditions, procedures and data for measuring the

flow of fluids, particularly with the three principal differential

presssure meters: the orfice, the flow nozzle, and the venturi tube.

ASME: PTC 19.6, Electrical Measurements in Power Circuits, 1965, 40 pp,

$7.00.

The methods given include measurements made with either indicating or integrating instruments of power voltage and current in direct-current and

alternating current single-phase and poly-phase rotating machinery,

transformers, induction apparatus, arc and resistance heating equipment,

and mercury arc rectifiers.

ASME: PTC 19.7, Measurement of Shaft Horsepower, 1961, 29 pp, $5.00.

Shows how measurement of shaft horsepower of rotating machines can

be accomplished either by the direct method of utilizing dynamometers or

the indirect method of using calibrated motors or generators, heat

balance, or heat exchangers.

ASME: PTC 19.13, Measurement of Rotary Speed, 1961, 17 pp, $5.00.

Covers commonly used instruments and methods, and discusses

characteristics and limitations of commercially available instruments used

for testing rotating machinery, turbine, blower, or electric motor.

The following Standards, identified by their ANSI number are ANSI approved, but

published by ASME. They are available from either ASME or ANSI.

ANSI: B88. 1-1972 (R1979), Guide for Dynamic Calibration of Pressure

Transducers, 1972, 20 pp, $5.00.

The intent of this document is to provide the user with a comprehensive

guide to current techniques and to identify possible pitfalls associated

with the dynamic calibration of pressure transducers.

8-10
ANSI: C85. 1-1963, Terminology for Automatic Control, 1963, 65 pp, $5.25

(includes supplements C85.1a-1966 and C85. lb-1972) . (Individual supplements

$1.50 each)

Terminology pertaining to systems such as: automatic process control,

feedback control, regulating, and other related systems not requiring

human intervention as a part of the regulating procedure.

AMERICAN VACUUM SOCIETY (AVS)

The following tentative Standards are available from the American Vacuum

Society, 335 East 45th Street, New York, NY 10017.

AVS: 6.2-1969, Procedure for Calibrating Vacuum Gages of the Thermal

Conductivity Type, 1969, 4 pp, $1.00.

Procedures are given and apparatus described for calibrating vacuum gages

of the thermal conductivity type of direct comparison with measurements

made with an absolute reference instrument such as the McLeod gage. The

pressure range considered is of the order of 10"4 to several Torr.

AVS: 6.4-1969, Procedure for Calibrating Hot Filament Ionization Gauges

Against a Reference Manometer in the Range of 10"2-10" 5 Torr, 1969,

5 pp, $1.00.

Procedures are given for the calibration of hot cathode ionization gauges

and gauge tubes by direct comparison against a McLeod gauge or other

absolute manometer in the pressure range of 10" 2 -10" 5 Torr.

ELECTRONIC INDUSTRIES ASSOCIATION (EIA)

The following EIA Standards are available from the Electronics Industries

Association, 2001 Eye Street, N.W., Washington, DC 20006. In addition,

EIA and NEMA have jointly prepared several standards. The joint standards may

also be listed under EEI or NEMA and may be ordered from any of the three.

EIA: RS-186-E, (ANSI RS-186-E-78), Standard Test Methods for Passive

Electronic Component Parts, $3.00.

Establishes uniform methods for testing electronic component parts. The

methods provide a number of test conditions of varying degrees of severity

so that appropriate test conditions may be selected for any component.

Contains index of individual test methods.

EIA: RS-232-C, Interface Between Data Terminal Equipment and Data

Communication Equipment Employing Serial Binary Data Interchange, $6.90.

Applicable to the interconnection of data terminal equipment (DEC)

employing serial binary data interchange. It defines Electrical Signal

Characteristics, Interface Mechanical Characteristics, Functional

Description of Interchange Circuits and Solid Interfaces for Selected

Communication System Configurations. Included are thirteen specific

8-11
interface configurations intended to meet the needs of fifteen defined

system applications. (A companion document to RS-232-C is Industrial

Electronics Bulletin No. 9, $2.60. It provides the application notes to

RS-232-C.)

EIA: RS-253 (Also NEMA: SK 56-1961), Standard Temperatures for Electrical

Measurement and Rating Specification - Semiconductor Devices,

1961, 2 pp, $2.0U.

To provide the specification writer with a list of temperatures in common

usage, and for which testing equipment will be more readily available; and

to reduce the number of temperatures at which semiconductor device

electrical measurements and ratings are specified to a minimum consistent

with electronic equipment requirements, thus minimizing the diversity of

equipment required for environmental testing.

EIA: RS-275-A (ANSI: C83. 68-1972 )

, Thermistor Definitions and Test Methods,

1972, $3.50.

Covers definitions of terms and test methods for measurement of the

performance characteristics of thermistors. The following are defined:

Zero Power Temperature Coefficient, Maximum Operating Temperature,

Dissipation Constant, Zero Power Resistance Temperature Characteristic,

Temperature Wattage Characteristic, Current-Time Characteristic,

Resistance Ratio, Beta, Stability, and Maximum Power.

EIA: RS-309 (ANSI: C83. 27-1968) (R 1977), General Specification for

Thermistors, Insulated and Non-Insulated, 1972, 12 pp, $4.70.

Covers insulated and non-insulated thermistor disks and rods with leads.

INSTITUTE OF ELECTRICAL AND ELECTRONICS ENGINEERS (IEEE)

Publications of the former American Institute of Electrical Engineers (AIEE)

and Institute of Radio Engineers (IRE) are identified by the IEEE number. All

of these publications are available from the Institute of Electrical and

Electronics Engineers, 345 East 47th Street, New York, NY 10017.

IEEE: STD 85-1973, Test Procedure for Airborne Noise Measurements on Rotating

Electric Machinery, 34 pp, $5.00.

Outlines practical techniques and procedures which can be followed for

conducting and reporting tests on rotating electrical machines of all

sizes to determine the airborne noise characteristics under steady-state

conditions.

IEEE: STD 118-1978, Master Test Code for Resistance Measurement, 31 pp,

$6.00.

Provides instructions for those measurements of electric resistance which

are commonly needed in determining the performance characteristics of

electric machinery and equipment.

8-12
IEEE: STD 120-1955 (REAFF 1972), Master Test Code for Electrical Measurements

in Power Circuits, 40 pp, $3.6U.

Gives instructions for those measurements of electrical quantities

which are commonly needed in determining the performance characteristics

of electric machinery and equipment.

IEEE: STD 121-1959, Recommended Guide for the Measurement of Rotary Speed, 12

pp, $3.00.

Describes the instruments and methods commonly used for the measurement of

rotary speed or slip and gives information regarding the characteristics

and limitations of commercially-available instruments ordinarily employed

in connection with the testing of electric machinery.

IEEE: STD 151-1965 (REAFF 1971), Terms of Audio and Electroacoustics, 2nd

edition, 12 pp, $3.00.

Contains definitions for 174 terms used widely in audio and

electroacoustic techniques.

IEEE: STD 162-1963 (REAFF 1972), Definitions of Terms for Electronic Digital

Computers, 2nd edition, 12 pp, $3.00.

Contains nearly all important terms related to electronic digital

computers. Analog and programming terms are not included because they are covered in other standards.

IEEE: STD 165-1977, Definitions of Terms for Analog Computers, 12 pp, $5.00.

Contains definitions for 172 terms common to analog computing techniques

and associated hardware.

IEEE: STD 169-1955, Definitions of Industrial Electronics Terms, 4 pp, $3.00.

Defines 76 terms for techniques and equipment used in dielectric and

induction heating.

IEEE: STD 170-1964, 170, Definitions of Terms for Modulation Systems, 2nd

edition, 8 pp, $3.00.

Contains 75 items important in modulation systems, including those terms

on the borderline of information theory.

IEEE: STD 196-1951, Definitions of Terms for Transducers, 4 pp, $3.00.

Defines 32 terms related to theory and devices for converting or transmitting energy.

IEEE: STD 216-1960 (REAFF 1971), Definitions of Semiconductor Terms, 4 pp,

$3.00.

8-13
Provides definitions of important terms relating to the physical aspects

of semiconductor materials and basic components developed from them.

IEEE: STD 221-1962 (REAFF 1971), Definitions of Terms for Thermoelectric

Devices, 8 pp, $3.00.

Defines 55 terms related to thermoelectric effects and the application and

evaluation of them in devices.

IEEE: STD 223-1966, Standard Definitions of Terms for Thyristors, 6 pp,

$3.00.

Includes classes of thyristors, physical structure nomenclature and

electrical characteristic terms.

IEEE: STD 251-1963 (REAFF), Proposed Test Procedure for Direct-Current

Tachometer Generators, 1963, Reaffirmed 1972, 12 pp, $3.00.

Covers instructions for conducting and reporting the more generally

applicable and acceptable tests to determine the performance

characteristics of direct-current tachometer generators.

IEEE: STD 337-1972 (REAFF 1978), Specification Format Guide and Test Procedure

for Linear, Single-Axis, Pendulous, Analog Torque Balance Accel erometer, 47 pp,

$10.00.

Defines the requirements for a linear, single-axis, pendulous, analog

torque balance accel erometer. The instrument is equipped with a permanent

magnet torquer and is used as a sensing element to provide an electrical

signal proportional to acceleration.

The following ANSI-approved Standards are published by IEEE and are available

from either IEEE or ANSI. They are identified below by their ANSI number with

the IEEE number (if available) in parentheses.

ANSI: C83.23 (IEEE: STD 178), Method for the Determination of the Elastic,

Piezoelectric and Dielectric Constant of Piezoelectric Crystals, 1960, 16 pp,

$3.50.

Provides equations, diagrams, and charts for calculating important

parameters for piezoelectric crystals.

ANSI: C83.24 (IEEE: STD 179), Measurement of Piezoelectric Ceramics, 1962,

Reaffirmed 1971, 11 pp, $3.50.

Covers definitions, relations, and measurement methods developed for

piezoelectric crystals in general, including ferroelectric ceramics.

Includes measurement methods, signal response, pyroelectric effects, and

aging.

ANSI: C83.3 (IEEE: STD 176), Piezoelectric Crystals, 1972, 20 pp, $4.00.

8-14
Defines areas for piezoelectric crystals, specifies, orientation of

crystal plates; provides symbols, units, and relations for piezoelectric

components.

INSTRUMENT SOCIETY OF AMERICA (ISA)

The following ISA Standards and Recommended Practices are available from the

Instrument Society of America, 67 Alexander Drive, P.O. Box 12277, Research

Triangle Park, NC 27709. The price given for each Standard is the

non-member, single-copy price. ISA members are entitled to a reduced price and

bulk-quantity discount prices are provided on request.

ISA-RP2.1, Manometer Tables, 1962 (R1978), 31 pp, $9.00.

Presents abbreviations and fundamental conversion factors commonly used in

manometry, recommended definitions of pressure in terms of a column of

mercury and water, and for a large number of liquids, tables of pressure

indicated by, or equivalent to, heights of columns at various

temperatures.

ISA-S5.1 (ANSI Y32. 20-1975), Instrumentation Symbols and Identification, 1973,

54 pp, $10.00.

Establishes a uniform means of designating instruments and instrumentation

systems used for measurement and control. The differing established

procedural needs of various organizations are recognized, where not

inconsistent with the objectives of the Standard, by providing alternative

symbolism methods. A number of options are provided for adding

information or simplifying the symbolism, if desired.

ISA-RP25.1, Materials for Instruments in Radiation Service, 1957, 15 pp,

$9.00.

Intended to serve as a guide to the selection of materials for use in

intense radiation fields such as those encountered in and around nuclear

reactors.

ISA-S26 (ANSI MC4. 1-1975), Dynamic Response Testing of Process Control

Instrumentation, 1968, 26 pp, $9.00.

Incorporating four revised ISA recommended practices, the standard

establishes the basis for dynamic response testing of measurement and

control equipment with pneumatic output and electric output, and for

closed loop actuators for externally actuated control values and other

final control elements. Pulse testing techniques as well as methods for

sine wave, step, and pulse-type signals are included.

ISA-RP31.1 (ANSI ISA RP 31.1-1977), Specifications, Installation, and

Calibration of Turbine Flowmeters, 1972, 23 pp, $9.00.

Establishes minimum ordering information, recommended acceptance and

qualification test methods including calibration techniques, uniform

8-15
terminology and drawing symbols, and recommended installation techniques

for volumetric turbine flow transducers having an electrical output.

ISA-S37.1 (ANSI: MC6. 1-1975), Electrical Transducer Nomenclature and

Terminology, 1975, 15 pp, $9.00.

Establishes uniform nomenclature for transducers and uniform simplified

terminology for transducer characteristics.

ISA-RP37.2, Guide for Specifications and Tests for Piezoelectric Acceleration

Transducers for Aero-Space Testing, 1964, 19 pp, $9.00.

Covers piezoelectric acceleration transducers, primarily those used in

Aero-Space test instrumentation. Terminology used in this document

follows ISA-537.1, Electrical Transducer Nomenclature and terminology,

except that additional terms considered applicable to piezoelectric

vibration transducers are defined.

ISA-S37.3 (ANSI: MC6. 2-1975), Specifications and Tests for Strain Gage Pressure

Transducers, 1976, 20 pp, $9.00.

Establishes for strain gage pressure transducers: uniform minimum

specifications for design and performance characteristics; uniform

acceptance and qualification test methods, including calibration

techniques; uniform presentation of minimum test data; and a drawing

symbol for use in electrical schematics.

ISA-S37.5 (ANSI: MC6. 3-1975), Specifications and Tests for Strain Gage Linear

Acceleration Transducers, 1976, 18 pp, $9.00.

Establishes uniform minimum specifications for design and performance

characteristics, uniform acceptance and qualification test methods

including calibration techniques, uniform presentation of minimum test

data, and a drawing symbol for use in electrical schematics for strain

gage linear acceleration transducers.

ISA-S37.6 (ANSI: MC6. 5-1976), Specifications and Tests of Potentiometric

Pressure Transducers, 1976, 26 pp, $9.00.

Establishes for potentiometric pressure transducers: uniform minimum

specifications for design and performance characteristics; uniform

acceptance and qualification test methods, including calibration

techniques; uniform presentation of minimum test data; ana a drawing

symbol for use in electrical schematics.

ISA-S37.8 (ANSI ISA S37.8-1977), Specifications and Tests for Strain Gage Force

Transducers, 1977, 16 pp, $9.00.

Outlines uniform general specifications, acceptance and qualification

methods, methods for data presentation, and includes a drawing symbol used

in electrical schematics for tension, compression, and combination

tension/compression transducers.

8-16
ISA-S37.10 (ANSI: MC6. 4-1975), Specifications and Tests for Piezoelectric

Pressure and Sound-Pressure Transducers, 1976, 25 pp, $9.00.

Establishes uniform specifications for describing design and performance

characteristics, acceptance and qualification test methods and

calibration techniques, and procedures for presenting test data for

piezoelectric (including ferro-electric) pressure and sound-pressure

transducers.

ISA-S37.12 (ANSI ISA S37.1 2-1 977 ) , Specifications and Tests for Potentiometric

Displacement Transducers, 1977, 21 pp, $9.00.

Establishes uniform specifications for potentiometric displacement

transducers for design and performance characteristics, acceptance and

qualification test methods and calibration test methods and calibration

techniques; uniform presentation of minimum test data and a drawing symbol

for use in electrical schematics.

ISA-S50.1 (ANSI: MC12. 1-1975) , Compatibility of Analog Signals for Electronic

Industrial Process Instruments, 1975, 11 pp, $5.00.

This Standard applies to analog dc signals used in process control and

monitoring systems to transmit information between subsystems or separated

elements of systems. Its purpose is to provide for compatibility between

the several subsystems or separated elements of given systems.

ISA-S51.1 (ANSI/ISA-551. 1-1979), Process Instrumentation Terminology, 1979, 41

pp, $9.00.

Intended to include all specialized terms used to describe the use and

performance of the instrumentation and instrument systems used for

measurement, control, or both in the process industries.

ISA-RP52.1, Recommended Environments for Standard Laboratoaries, 1975, 20 pp,

$9.00.

Recommendations for three levels of standardization are presented - from

the more general National Bureau of Standards, through commercial,

industrial and government laboratories. Requirements for nine

environmental factors are discussed.

The following Standard, identified by its ANSI number was sponsored and

published by ISA, approved by ANSI and is available from either ISA or ANSI.

MC96. 1-1975, Temperature Measurement Thermocouples, 42 pp, $9. ,00.

Covers coding of thermocouple wire and extension wire; coding of insulated

duplex thermocouple extension wires; terminology, limits of error and wire

sizes for thermocouples and thermocouple extension wires; temperature EMF

tables for thermocouples; plus appendixes that cover fabrication, checking

procedures, selection, and installation.

8-17
NATIONAL BUREAU OF STANDARDS (NBS)

U.S. DEPARTMENT OF COMMERCE

The National Bureau of Standards had consolidated the Standards Application and

Analysis Division which has two units of interest to those concerned with

engineering standards.

Standards Development Services (SDS)

Administers the Department of Commerce Voluntary Products program as set

forth in NBS Policy Bulletin No. 4 (November 29, 1971). Basically this

program is now operated as a supplement to the activities of the private

sector standards-writing bodies. It is the process of transferring, where

appropriate, the responsibility for the continued maintenance of older

NBS Standards on industrial products to private sector organizations.

Standards Information Services (SIS)

NBS-SIS maintains a reference collection of engineering and related

standards which includes over 200 000 standards, specifications, test

methods, codes, and recommended practices issued by U.S. technical

societies, professional organizations, and trade associations, state and

federal agencies, foreign national standards bodies, and international

organizations.

NBS-SIS also functions as a referral activity by directing inquiries to

appropriate standards-issuing organizations.

For requests for lists of Standards, together with names of organizations

where copies of the Standards can be obtained, write to:

Standards Information Services, Room B162, National Bureau of Standards,

Washington, DC 20234, or call (301) 921-3272.

The following NBS Publications may be ordered by SD Catalog Number from the

Superintendent of Documents, U.S. Government Printing Office, Washington, DC

20402. Add 25% to SD prices for foreign mailings.

An Index of U.S. Voluntary Engineering Standards, Supplement 1, 1972, to

NBS Special Publication 329. Price $8.25; SD catalog number C13. 10:329

Supplement 1; Supplement 2, 1975 to NBS Special Publication 329. Price

$9.35; SD catalog number SN003-003-01362J.

Index of International Standards NBS Special Publication 390, 1974. Price

$7.25; SD catalog number COM 74-56352.

Directory of U.S. Standardization Activities NBS Special Publication 417,

Price $6.75; SD catalog number SN 003-003-01395-1.

Order by COM Number from the National Technical Information Service, 5285 Port

Royal Road, Springfield, VA 22161.

8-18
An Index of U.S. Voluntary Engineering Standards, NBS Special Publication

329, 1971. Price $26.25 Domestic; $52.50 Foreign. COM 71-50172.

World Index of Plastics Standards, NBS Special Publication 352, 1971,

Price $11.75 Domestic; $14.25 Foreign COM 75-10291.

An Index of State Specifications and Standards, NBS Special Publication

375, 1973 Price: $10.75 Domestic; $13.25 Foreign. COM 73-50839.

Tabulation of Voluntary Standards and Certification Programs for

Consumer Products, under revision.

NATIONAL ELECTRICAL MANUFACTURERS ASSOCIATION (NEMA)

The following NEMA Standards publications are available from the

National Electrical Manufacturers Association, 155 East 44th Street,

New York, NY 10017. In addition, NEMA, EIA, and EEI have jointly prepared

several standards, which may be ordered from any of the three organizations.

(Remittance required with all orders.)

NEMA: EI 2-1966, Instrument Transformers, 2nd edition 1966, 12 pp,

$1.25.

Covers all instrument transformers except bushing current

transformers which are mounted inside circuit breakers and power

switchgear assemblies; supplements ANSI: C57.13 and NEMA:

E121-1973, $1.25.

NEMA: EI 21-1973, Instrument Transformers for Metering Purposes, 15 KV

and less, 1973, 20 pp, $1.75.

Covers general requirements, ratings, accuracy classifications, burdens

and pertinent dimensions applicable to dry-type instrument current and

potential transformers for metering purposes on circuits up to and

including 15 KV.

NEMA: II 2-1972, Electrical Indicating Instrument-Relays, 1972, 63 pp,

$5.50.

Developed to meet the need for Standards for electrical -indicating

instrument-relays, which are known colloquially as "meter-relays."

The term "instrument-relay," therefore, is used herein to conform

to American National Standards and International standards

practice. Contains definitions, general requirements, and test

procedures.

8-19
NATIONAL FLUID POWER ASSOCIATION (NFLDP)

The following NFPA and ANSI Standards are available from the National Fluid

Power Association, 3333 N. Mayfair Road, Milwaukee, WI 53222. Note: the

acronym NFLSP is used above and in the index section to distinguish from the

National Fire Protection Association.

NFPA: T2.9.6 (ANSI: B93. 28-1973), Standard Method for Cal ibration of

Liquid Automatic Particle Counters Using "AC" Fine Dust Test, 1973, 15

pp, $7.50.

Provides procedures for calibration of a liquid automatic particle

counter which is used for determination of particle size

distribution of contaminants encountered in hydraulic fluid power

appl i cations.

NFPA: STD T3. 9. 12-1975, Recommended Standard Method of Measuring Sound

Generated by Hydraulic Fluid Power Pumps, 8 pp, $5.50.

Establishes a uniform basis for measuring, reporting, and comparing the

sound levels of hydraulic fluid power pumps.

NFPA: STD T3.9.14-R 1976, Recommended Standard Method of Measuring

Sound Generated by Hydraulic Fluid Power Motors, 9 pp, $5.50.

Establishes a uniform basis for measuring, reporting, and comparing the

levels of sound generated by hydraulic fluid power rotary motors.

RANGE COMMANDERS COUNCIL (RCC)

The following IRIG and RCC Standards have been prepared and published

by the Range Commanders Council for use by governmental agencies, and

industries under contract to them, for use in the fields of missiles,

rockets, and associated equipment. Limited copies are available to

authorized non-government agencies from the Secretariat, Range

Commanders Council, STEWS-SA-R, White Sands Missile Range, NM 88002.

Authorization is identified by the supporting governmental service for

its associate agencies and industries.

RCC: 106-77, Telemetry Standards, Revised 1977, 90 pp.

These current Standards provide development and coordination

agencies with the necessary criteria on which to base equipment

design and modification. The ultimate purpose is to ensure efficient spectrum and interference-free operation of the radio

link for telemetry systems at the RCC member ranges.

RCC: 118-73, Test Methods for Telemetry Systems and Subsystems, 1975,

336 pp.

8-20
Developed by the Telemetry Group and the Inter-Range

Instrumentation Group. Complements RCC Document 106-77,

"Telemetry Standards," by defining standard test methods for

telemetry ground systems and related subsystems. Utilization of

the methods as described in this document will enable the exchange

of test results which are derived and expressed in a common

manner.

RCC: 119-71, Error Analysis and Methods for Estimating Errors in

Position, Velocity, and Acceleration Data, 1971, 122 pp.

Developed by the Data Reduction and Computing Working Group and the

Inter-Range Instrumentation Group. Mathematical models, methods, and

techniques which are useful and appropriate for estimating the accuracy of

position (in some coordinate systems); velocity, and acceleration data are presented in this document. The development and use of the techniques

discussed have evolved through the years and in some cases out of work not

related to missile testing.

IRIG: 126-73, Physical Constants and Conversion Factors, 1973, 24 pp.

Prepared by the Data Reduction and Computing Working Group and the

Inter-Range Instrument Group. The objective is to present a compilation of the more commonly used physical constants,

mathematical constants, unit conversion factors, and other fixed numerical

values as may be required at the various member installations for data

processing.

SCIENTIFIC APPARATUS MAKERS ASSOCIATION (SAMA)

The following SAMA and ANSI publications are available without charge

from the Scientific Apparatus Makers Association; 1140 Connecticut

Avenue, N.W., Washington, DC 20036.

SAMA: MTI 1 and 2, Load Cell Terminology and Recommended Test

Procedures, second edition, 1964, 16 pp.

Provides recommended terminology and definitions for hydraulic,

pneumatic, and mechanical load cells used for measurement of

weight and force. Also provides recommended general purpose test

procedures for qualification and acceptance testing of these types

of load cells.

The following SAMA publications are available from: Scientific

Apparatus Makers Association, Process Measurement and Control Section,

370 Lexington Avenue, New York, NY 10017.

SAMA: PMC 5-10, Resistance Thermometers, 2nd edition, 1963, 6 pp,

$1.00.

8-21
Establishes uniformity of terminology (including symbols),

definitions, and dimensions for resistance thermometers.

SAMA: PMC 8-10, Thermocouple Thermometers (Pyrometers), 2nd edition,

1963, 11 pp, $1.00.

Establishes uniformity of terminology (including symbols),

definitions for thermocouple thermometers.

SAMA: PMC 8-10, Thermocouples-Thermometers (pyrometers), 2nd Edition,

1963, 11 pp, $1.00.

Establishes uniformity of terminology (including symbols),

definitions, and dimensions for thermocouple thermometers.

SAMA: PMC 17-10, Bushings and Wells for Temperature Sensing Elements,

1963, 6 pp, $1.00.

Establishes uniformity of terminolgy (including symbols),

definitions for bushings and wells. Also establishes a series of

preferred sizes with dimensions and tolerances such that bushings

and wells of the same nominal dimensions are completely

interchangeable. Dimensions given in this Standard provide

bushings and wells suitable for bimetallic thermometers, resistance

thermometers, filled system thermometers and thermocouple thermometers in

accordance with other SAMA Standards.

SAMA: PMC 20.1-1973, Process Measurement and Control Terminology,

1973, 44 pp, $2.00.

Applies to terminology associated with industrial process

instrumentation used in industries such as chemical, petroleum,

metallurgical, power, food, textile and paper. It includes terms

relating to measurement and control, and the static and dynamic

performance of indicators, recorders, controllers, indicating

controllers, recording controllers, transmitters and transducers.

SAMA: PMC 21-4-1966, Temperature-Resistance Values for Resistance

Thermometer Elements of Platinum, Nickel and Copper, 1966, 14 pp,

$2.00.

Purpose is to establish standard temperature resistance values for

platinum, nickel, and copper resistance thermometer elements.

SAMA: PMC 22-111-1966, Functional Diagramming of Instrument and

Control Systems, 1966, 20 pp, $2.00.

Presents both symbols and diagramming format for use in

representing measuring, controlling, and computing systems as used in

industrial practice. The purpose is to establish uniformity of symbols

and practices in diagramming such systems in their basic

8-22
functional form, exclusive

equipment detail.

of their operating media or specific

SOCIETY OF AUTOMOTIVE ENGINEERS INC. (SAE)

The following and numerous other SAE publications are available from

the Society of Automotive Engineers, 400 Commonwealth Drive,

Warrendale, PA 15096.

Aerospace Information Reports (AIR)

SAE: AIR 46, Preparation and Use of Chromel -Al umel Thermocouples for

Turbojet Engines, 1956, 50 pp, $5.00.

Reviews the precautions which must be taken and the corrections

which must be evaluated and applied if the experimental error in

measuring the temperature of a hot gas stream with a thermocouple is to be

kept at a practicable minimum.

SAE: AIR 65, Thermoelectric Circuits and The Performance of Several

Aircraft Engine Thermocouples, 1958, 36 pp, $3.50.

Covers theory of thermoelectric circuits; thermocouple corrections

for radiation, conductions, velocity and response rate; and

thermocouple materials. Also included is a section on nomenclature and performance charts.

Aerospace Standards (AS)

SAE: AS 407B, Fuel Flowmeters, 3rd edition, 1960, 7 pp, $1.50.

Specif ices minimum requirements for fuel flowmeters for use primarily in reciprocating engine powered civil transport

aircraft, the operating of which may subject the instruments to

specified environmental conditions. Covers two basic types: Type

I - measures rate of flow of fuel used; and Type II - totalizes

amount of fuel consumed or remaining.

SAE: AS 428, Exhaust Gas Temperature Instruments, 1966, 11 pp, $2.25.

Establishes essential minimum safe performance standards for

electrical -servo, null -balance-type exhaust gas indicating

instruments for use in turbine-powered subsonic aircraft. Covers

a null balance system actuated by vary-emf output of a chromel -al umel thermocouple.

SAE: AS 431A, True Mass Fuel Flow Instruments, 2nd edition, 1962, 12

pp, $2.25.

Establishes essential minimum safe performance standards for true mass fuel flow instruments for use in turbine powered subsonic

8-23
transport aircraft. Covers three basic types of true mass flow

indicating instruments as follows: Type - rate indication. Type

II - integration. Type III - rate indication and integration.

Each may consist of an indicator, transmitter and other auxiliary

items such as a power supply or amplifier as required.

SAE: AS 432A, Tachometer Instruments, 2nd edition, 1963, 12 pp,

$2.25.

Establishes essential minimum safe performance standards for

tachometer instruments 0-110% rpm and 0-120% rpm indicators and generators

for remote indication of engine speed.

SAE: AS 793, Total Temperature Measuring Instruments (Turbine Powered

Subsonic Aircraft), 1966, 9 pp, $2.25.

Establishes essential minimum safe performance requirements for

the subject instrument, operation of which may subject it to

environmental conditions specified. Covers three basic types of

total -temperature-measuring instruments: Type I - flush-type

total -temperature sensor, and Types II and III - probe-type

total -temperature sensors (electrically heated and unheated,

respectively).

SAE: ARP 175, Temperature Measurement, Well Insert Type, 1948, 4 pp,

$1.50.

Covers the detail installation requirements and the temperature

response characteristics of various types of temperature

responsive elements intended for well-type installation in

aircraft engine cylinder heads. May also be applied to

temperature measuring applications other than air-cooled aircraft

engine cylinder heads.

SAE: ARP 427, Pressure Ratio Instruments, 1958, 12 pp, $1.50.

Recommends requirements for electrical pressure ratio indicating

instruments for use in aircraft. Covers two unit-pressure ratio

instruments each of which consists of a transducer and an indicator. The transducer computes the ratio of two pressures and

converts this ratio to synchro-electrical signal which is

transmitted to the indicator.

SAE: ARP 464, Thermocouple Mount, 1958, 1 pg, $1.50.

Dimensional drawing with tolerances.

SAE: ARP 465A, Flange - Thermocouple, 1971, 4 pp, $1.50.

Supersedes and cancels ARP 465 and ARP 466, issued 2-15-58.

Flanges described in this ARP are used for mounting temperature

sensing probes in gas turbine engines. The probes are welded or

8-24
brazed to the flange for positive support. The flanges are bolted

or secured by nuts and studs to mounting bosses located on the

engine case.

SAE: ARP 485, Nomenclature for Temperature Measuring Devices, 1957, 8

pp, $1.50.

Establishes the nomenclature and related terminology of

temperature measuring devices as applied to aircraft,

gas-reaction-type power plants for use by: (a) power plant

manufacturers, (b) airframe manufacturers, (c) procurement

organizations, (d) equipment organization, (e) service and

maintenance personnel, and (f) other interested organizations.

Surface Vehicle Documents (J)

The SAE surface vehicle (J) documents can be purchased for prices listed. A

lower case "a," "b," etc., appended to the (J) document number indicates

successive revisions of that document.

SAE: J 211b, Instrumentation for Impact Tests, 1976, 2 pp, $2.00.

Provides guidelines for instrumentation used in motor vehicle and

motor vehicle component impact tests. It is intended to

supplement impact test procedures such as those described in SAE

J850, J944, J117, etc.

SAE: J254, Instrumentation and Techniques for Exhaust Gas Emissions

Measurement, 1976, 11 pp, $3.50.

Establishes uniform laboratory techniques for the continuous and

grab sample measurement of various constituents in the exhaust gas

of the gasoline engines installed in passenger cars and light

trucks. The report concentrates on the measurement of the

following components in exhaust gas: hydrocarbons (HC), carbon

monoxide (CO), carbon dioxide (CO2), nitric oxide (NO), nitrogen

dioxide (NO2), and oxygen (O2).

SAE: J390, Dual Dimensioning, 1976, 8 pp, $3.50.

Establishes a uniform method of combining U.S. customary (inch)

units and metric units of measure on the same engineering drawing.

In this document "metric units" means the International System of

Units (abbreviated SI) as described in ISO Recommendation R 1000,

which includes certain units in addition to the formal SI.

8-25
THE SOCIETY OF NAVAL ARCHITECTS AND MARINE ENGINEERS (SNAME)

The following ship testing codes are available from The Society of

Naval Architects and Marine Engineers, 74 Trinity Place, New York, NY 1UU06.

SNAME: Code C-l, Code for Shipboard Vibration Measurements, 1975.

Establishes standard procedures for gathering and interpreting

data on hull vibrations in single-screw commercial ships. These

data are needed to compare the vibration characteristics of

different ships of a given class, to establish vibration reference

levels, and to provide a basis for the improvement of individual

ships.

SNAME: Code C-2, Code for Sea Trials, 1973.

Includes a section which describes the instruments and apparatus

commonly used for making measurements of the performance of

various items of machinery in ships' trials.

SNAME: T&R Bulletin 3-23, Guide for Centralized Control and Automation

of Ship's Steam Propulsion Plant, 1970, 54 pp.

Gives technical guidance in establishing the desired degree and

methods for employing centralized control and for automating a ship's steam propulsion plant.

INTERNATIONAL STANDARDIZATION

Standards of two international organizations are available from the

American National Standards Institute (ANSI), 1430 Broadway, New York,

NY 10018. ANSI also has an office in Europe: American National

Standards Institute, 16 Chemin de la Voie Creuse, 1211 Geneva,

Switzerland. ISO and IEC Standards are also available from their

respective Secretarial Headquarters. The number of

instrumentation-related international standards is so extensive that

only representative titles are listed in this section. In addition the

listing has been limited to reference number, title and price (ANSI

price as of 1976). Additional information on individual standards or a complete listing of international standards from the following

organizations may be obtained from ANSI.

INTERNATIONAL ORGANIZATION FOR STANDARDIZATION (ISO) - The American

National Standards Institute is the Member Body representing the United

States in the International Organization for Standardization (ISO).

Fifty-six national standards bodies comprise the world membership and

cooperate in formulating the technical program in which each member

maintains a status as a participant or observer in accordance with the

interest of the member in the specific standard under consideration.

8-26
INTERNATIONAL ELECTROTECHNICAL COMMISSION (IEC) - The American

National Standards Institute has administrative and technical

affiliation with the U.S. National Committee of the IEC. This

committee, in turn, represents the U.S. in the IEC. The IEC holds the

international responsibility for the coordination and unification of

all national electrotechnical standards and it is affiliated with the

ISO. It also acts as the coordinating body for the activities of other

international organizations whose responsibilities relate to or overlap

the electrotechnical field.

In addition to the national organizations listed above, two other

international organizations actively participate in standardizing

activities in the area of automatic control through cooperation with

their member societies. They are: Secretariat, International

Federation of Automatic Control (IFAC), Postfach 1139, D-4000

Duesseldorf 1, FRG, (West Germany); and Secretariat, International

Federation for Information, Processing (IFIP), 3, rue du Marche,

1204-Geneva, Switzerland.

INTERNATIONAL ORGANIZATION FOR STANDARDIZATION (ISO)

The following Standards are available from ANSI, 1430 Broadway, New

York, NY 10018. In the titles, the number in parentheses refers to a similar ANSI Standard.

Note: Prices given are approximate and may change at anytime due to

international currency fluctuation.

ISO: 31/1-1978, Quantities and Units of Space and Time, $18.90.

ISO: 31/11-1978, Quantities and Units of Periodic and Related

Phenomena, $10.50.

ISO: 31 /I I 1-1 978, Quantities and Units of Mechanics, $23.10.

ISO: 31/IV-1978, Quantities and Units of Heat, $18.90.

ISO: 31/V-1965, Quantities and Units of Electricity and Magnetism,

$21.00.

ISO: 31 /VI -1973, Quantities and Units of Light and Related

Electromagnetic Radiations, $14.70.

ISO: 31/VII-1978, Quantities and Units of Acoustics, $18.90.

ISO: 31/VIII-1973, Quantities and Units of Physical Chemistry and

Molecular Physics, $18.90.

ISO: 31/IX-1973, Quantities and Units of Atomic and Nuclear Physics,

$16.80.

8-27
ISP: 31/X-1973, Quantities and Units of Nuclear Reactions and Ionizing

Radiations, $21.00.

ISO: 31 /XI -1 978, Mathematical Signs and Symbols for Use in the

Physical Sciences and Technology, $31.50.

ISO: R1680-1970, Test Code for the Measurement of the Airborne Noise

Emitted by Rotating Electrical Machinery, $23.10.

ISO: R2186-1973, Fluid Flow in Closed Conduits - Connections for Pressure Signal Transmissions Between Primary and Secondary Elements,

$35.70.

INTERNATIONAL ELECTROTECHNICAL COMMISSION (IEC)

The following Standards are available from ANSI. An asterisk (*)

following the year of publication indicates that later amendments or supplements are included. In the titles, the number in parentheses

refers to a similar ANSI Standard.

Note: Prices given are approximate and may change at any time due to

international currency fluctuations.

IEC: 27-1 (1971)* Letter Symbols to be Used in Electrical Technology,

Part I: General, $73.50.

IEC: 27-2 (1972)* Letter Symbols to be Used in Electrical Technology,

Part II: Telecommunications and Electronics, $51.10.

IEC: 38 (1975) Standard Voltages, $17.50.

IEC: 50-00 (1975), International Electrotechnical Vocabulary, General

Index, $63.00.

IEC: 50-08 (1960), Electro-Acoustics, $24.50.

IEC: 50-12 (1955), Transductions, $7.00.

NOTE: IEC: 68, Basic Environmental Testing Procedures.

Describes a standard general procedure for climatic and mechanical

robustness tests, designed to assess the durability, under various

conditions of use, transport, and storage, of components used in equipment

for telecommunication and in electronic equipment employing similar

techniques. This publication is issued in two parts, viz.

IEC: 68-1 (1978)* Part I, General $28.00.

8-28
General description of the framework of the test procedure and how

it is to be used.

IEC: 68-2, Part 2. Tests.

This part describes the different tests in detail. Each test is

identified by a letter of the alphabet and is issued in the form

of a separate booklet.

IEC: 68-2-1 (1974), Test A: Cold, $39.20.

IEC: 68-2-2 (1974) , Tet B: Dry Heat, $51.45.

IEC: 68-2-3 (1969), Test C: Damp Heat, Steady Heat, $8.00.

IEC: 68-2-4 (1960)., Test D: Accelerated Damp Heat, $5.60.

IEC:

IEC:

69-2-6

68-2-7

(1970),

(1968),

Test Fc:

, Test Ga:

Vibration, (Sinusoidal), $23.10.

Acceleration, Steady State, $7.35.

IEC: 68-2-13 (1966 1, Test M: Low Air Pressure, $4.90.

IEC: 68-2-14 (1974'1, Test N: Change of Temperature, $28.00.

IEC: 68-2-17 (1978 1, Test Q: Sealing, $50.40.

IEC: 68-2-27 (1972

1 1, Test Ea: Shock (includes supplement), $24.15.

IEC: 68-2-28 (1968'1, Guidance for Damp Heat Tests, $7.35.

IEC: 68-2-29 (1968 1, Test Eb: Bump, $14.00.

IEC:

$6.3U.

68-2-30 (1969'1, Test Db: Damp Heat, Cyclic (12+ 12-Hour Cycle),

IEC: 68-2-31 (1969

Equipment-Type Speci

i, Test Ec: Drop and Topple, Primarily for

mens, $3.50.

IEC: 68-2-32 (1975'1, Test Ed: Free Fall, $11.20.

IEC: 68-2-33 ( 1971 1 , Guidance on Change of Temperature Tests, $14.70.

NOTE: All above tests should be used in conjunction with 68-1.

IEC: 160 (1963), Standard Atmospheric Conditions for Test Purposes,

$7.00.

IEC: 164 (1964), Recommendations in the Field of Quantities and Units

Used in Electricity, $13.50.

8-29
IEC: 184 (1965), Methods for Specifying the Characteristics of

Electro-Mechanical Transducers for Shock and Vibration Measurements,

$21.00.

IEC: 185 (1966), Current Transducers, $48.30.

IEC: 190 (1966), Non-Wi rewound Potentiometers Type 2, $31.50.

IEC: 222 (1966), Methods for Specifying the Characteristics of

Auxiliary Equipment for Shock and Vibration Measurement, $14.00.

IEC: 271 (1974) Preliminary List of Basic Terms and Definitions for

the Reliability of Electronic Equipment and the Components Used

Thereof, $60.20.

IEC: 272 (1968) Preliminary Reliability Considerations, $3.50.

IEC: 351 (1971) Expression of the Functional Performance of Electronic

Measuring Equipment, $25.20.

IEC: 605 (1978) Equipment Reliability Testing, Part 1, General

Requirements, $47.60.

8-30
8.3 Government Standards

The documents listed below are standards documents developed and

issued by agencies of the United States government. The Office of

Standards Information of the National Bureau of Standards has a "Visual

Search Microfilm File" which contains copies of more than 100 000

standards and specification documents. A file search of documents

considered pertinent to this handbook was made and the information

summarized below.

In addition, for military standards documents, the "Index of

Specifications and Standards" July 1, 1978 edition, put out by the

Department of Defense, was checked for pertinent references. The

supplement of November 1, 1979 to this index was also checked. It is

possible that some documents may have been left out or that some will

be superseded by the time this handbook appears in print.

It should be noted that the search was confined to material

bearing on sensors with electrical output and test methods for such

components. Gages and mechanical indicators generally are not listed.

In case of doubt on the applicability of a particular document,

however, we normally chose to include it.

8-31
8.3.1 Civilian Standards Listings

GG-G76D, 4 December 1975

Gages, Pressure and Vacuum, Dial Indicating (for Air, Steam, Oil,

Water, Ammonia, Chi oro-Fl uoro Hydrocarbon Gases, and Compressed

Gases). ...covers dial gages which indicate pressure or vacuum on

a graduated dial by means of a pointer, utilizing an elastic

element (Bourdon Tube or cell) and actuating linkage, as required,

for measuring pressure or vacuum.

8.3.2 Military Standards Listings (Standards, Specifications, and

Handbooks

)

MIL-STD-105D, 29 April 1963

Sampl i ng Procedures and Tables for Inspection by_ Attributes

...establishes sampling plans and procedures for inspection by

attributes... intended primarily for a continuing series of lots or batches. (Inspection by attributes is inspection whereby either

the unit of product is classified as defective or nondefecti ve, or

the number of defects in the unit of product is counted with

respect to a given requirement or set of requirements).

MIL-STD-198E, 4 August 1966

Definitions of and Basic Requirements for End osures for El ectric

and Electronic Equipment Enclosures ...establishes definitions and

basic requirements for equipment. The use of these definitions

for parts intended for mounting in enclosures is also described.

MIL-STD-109B, 4 April 1969

Qua! i ty Assurance Terms and Definitions ...provides a standardized

interpretation of quality assurance terms and definitions to be

applied throughout the determination of product quality.

MIL-STD-143B, 12 November 1969

Standards and Specifications, Order of Precedence for the

Selection of ...sets forth the order of precedence for the

selection of standards and specifications to identify and describe

items, materials, and processes used by design activities in the

design and construction of military material for the DoD.

Requirements for approval of standards and specifications by the

Government Command or agency concerned prior to use are excluded

from the coverage of this standard. Requirements for approval or release, if any, or the use of documents stating applicability of

standards and specifications for special applications are subject

to contract provisions.

MIL-STD- 167-1, 1 May 1974

8-32
Mechanical Vibrations of Shipboard Equipment (Type 1^ - Environmental and Type II - Internally Excited) . . .covers the

requirements of Naval equipment including machinery as regards

both internally excited vibrations and externally imposed

vibrations. In some special machinery, equipment, or installations, such as antennas, large machinery items, and

certain unique designs it may be necessary to deviate from this

standard. In those cases, special modifications shall be subject

to approval by the command or agency concerned. All other

deviations from, or waivers of this standard, are prohibited.

MIL-HDBK-172A, 11 March 1964

Electronic Test Equipment (Volume I - Unclassified and Volume I_I - Classified ) ...contains information on electronic test equipment

of the Army, Navy, and Air Force used in calibration, adjustment,

maintenance, and repair of communication, radar, countermeasures,

meteorological, photographic, power, and other technical equipment

employed for military purposes. ...presents data and information

on technical physical, operational, and logistical characteristics

of electronic test equipment. ...primarily for use by

standardization, design, development, and procurement activities,

and technical planning and coordinating use and maintenance of

equipment.

MIL-STU-188C, 24 September 1969

Military Communication System Technical Standards ...provide

technical design standards for military communications systems.

These provide the basic technical parameters of communications

equipment and systems. The parameters have been chosen for future

state-of-the-art values wherever these can be determined with

reasonable accuracy as well as to define the minimum acceptable

performance values for interim use. The standards are to be used

in development of new equipment as well as procurement of

production models of standard equipment.

MIL-STD-202E, 16 April 1973

Test Methods for Electronic and Electrical Component Parts

...establishes uniform methods for testing electronic and

electrical component parts, including environmental test,

physical, and electrical test. ...includes capacitors, resistors,

switches, relays, transformers, and jacks. ...intended for small

parts (transformers over 300 lbs or rms test voltages over

50 000 V are excluded).

MIL-STD-210B, 15 December 1973

Climatic Extremes for Military Equipment ...(a) establishes

uniform climatic design criteria for that military material which

is intended for world-wide usage (excluding the air, land, and ice

8-33
shelf areas south of 60° S). ...does not apply in design of

material to be used only in specific areas or environments. ...(b)

provide sets of climatic design conditions for land, sea, and air

in which military materiel may be required to operate. ...also

provides separate sets (land and sea) of climatic design

conditions which materiel exposed to nature may be required to

withstand without damage, (c) If equipment failure due to weather

extremes. . .could endanger life of personnel, the design criteria

should be established so as to result in a percentage of

inoperability which is as close to zero as possible.

MIL-HDBK-235-1, 23 June 1972

Electromagnetic (Radiated) Environment Considerations for Design

and Procurement of Electrical and Electronic Equipment . Part I

.

...to provide guidance and establish a uniform approach for tHe

protection of Navy electronics from adverse effects of the

electromagnetic environment. Examples of systems, subsystems and

equipments for which this handbook may be applicable are: (a)

aerospace and weapons, (b) ordnance, (c) support and checkout

equipment and instrumentation for (a), (b), and (d). Any other

electronic equipment which may be subjected to high intensity

electromagnetic environments.

Purpose: provides (a) information on electromagnetic environments

for design and procurement of equipment exposed to electromagnetic

radiation, (b) information for use in tailoring the radiated

susceptibility requirement R503 of MIL-STD-461 and MIL-E-6051.

Part I- ...general information; Part 2- ...describes

electromagnetic levels encountered from friendly emitters; Part 3-

... levels from hostile emitters. Table I furnishes an index of

locations from which electromagnetic radiation environment levels

are provided in Parts 2 and 3.

MIL-HDBK-217B, 20 September 1974

Reliability Prediction of Electronic Equipment . ...provides two

methods of reliability prediction: (1 ) Parts Stress Analysis and

(2) Parts Count. Mathematical expressions for part failure rates

are provided for use in computer programming. Tables are used for

base failure rates. ...is oriented toward reliability prediction

of military electronic equipment; ...provides a common basis for

prediction and comparing predictions on military contracts and

proposals. It is not a complete guide to reliability

engineering.

MIL-HDBK-251, 19 January 1978

Reliability /Design - Thermal Applications . ...recommends and

presents electronic parts stress analysis methods which lead to

8-34
the selection of maximum safe temperatures for parts so that the

ensuing thermal design is consistent with the required equipment

reliability.

MIL-STD-415D, 1 October 1969

Test Provisions for Electronic Systems and Associated Equipment , Design Criteria for, ...establishes design criteria for test

provisions that permit the functional and static parameters of

electronic systems and associated equipment to be monitored,

evaluated, or isolated. These test provisions consist of the

following: (a) external test receptacles for connecting

automatic; semi-automatic, or manual checkout equipment or automatic monitoring equipment, (b) a built-in test capability,

and (c) test points.

MIL-STD-441, 20 June 1958

Reliability of Military Electronic Equipment . Superseded by

MIL-STD-785

MIL-STD-454F, lb March 1978

Standard General Requirements for Electronic Equipment . ...covers

the common requirements to be used in military specifications for

electronic equipment.

MIL-STD-461A, 1 August 1968

Electromagnetic Interference Characteristics, Requirements for

Equipment. ...covers the requirements and test limits for the

measurement and determination of the electromagnetic interference

characteristic (emission and susceptibility) of electronic,

electrical, and electromechanical equipment, subsystems, and

systems. The requirements shall be applied for general or multi -service procurements and single service procurements as specified in the individual equipment specifications.

MIL-STD-462, 31 July 1967

Electromagnetic Interference Characteristics , Measurement of.

...establishes techniques to be used for the measurement and

determination of the electromagnetic interference characteristics

(emission ana susceptibility) of electrical, electronic, and

electromechanical equipments, subsystems, and systems as required

by MIL-STD-461A, Notice 4.

MIL-STD-463A, 1 June 1977

Definitions and Systems of Units, Electromagnetic Interference and

Electromagnetic Compatibility Technology . ...is designed to assTit

in reaching a more common understanding of the meaning of terms

8-35
used in the various military standards which provide a basis for

assuring electromagnetic compatibility within the operational

military environment. Definitions of terms and abbreviations are limited to statements of meaning related to this and applicable

standards, rather than encyclopedia or textbook discussions.

MIL-STD-469, 1 December 1966

Radar Engineering Design Requirement , Electromagnetic

Compatibility . Cancelled 28 February 1975.

MIL-STD-470, 21 March 1966

Maintainability Program Requirements ( for Systems and Equipments )

.

...provides requirements for establishing a maintainability

program and guidelines for the preparation of a maintainability

program plan. The requirements of this standard are applicable to

the development of other systems and equipment when specified.

MIL-STD-704C, 3u December 1977

Aircraft Electric Power Characteristics . ...establishes

requirements for electric power characteristics on aircraft at the

interface between the electric power system and the input to

electric utilization equipment. The electric power

characteristics covered... are of duration longer than 50

microseconds or less than 20 kilohertz. Electric power

characteristics of duration less than 50 microseconds.. .are covered by MIL-E-6051.

MIL-HDBK-705B, 26 June 1972

Generator Sets , Electrical , Measurements and Instrumentations . ...covers a compilation of electrical term definitions and two

series of methods of measurements for testing and determining the

characteristics of electric generators, generator sets, and

associated equipment. Illustrations and descriptions of the test

instruments together with instructions for their use are included

as applicable under each method.

MIL-STD-705B, 26 June 1972

Generator Sets , Engine Driven Methods of Tests and Instructions . ...explains, establishes and standardizes specific methods for

measurements associated with the evaluation of electric

generators, generator sets, and related components. This standard

is closely allied with MIL-HDBK-705.

MIL-STD-706A, 25 November 1960

Power Supply Voltages , Regulated , D.C. , Within Electronic

Equipment. ...establishes nominal values of regulated direct

8-36
current voltages within the range of 0 to 600 volts from power

supplies that are contained within military electronic equipment.

Voltages shall be selected from the following list: 1.5, 3, 6,

12, 25, 50, 100, 150, 250, 300, 450, and 600; or 6.3, 9.0, 12.6,

18.0, 26.5, 75.0, and 125 when required by electron tube

filaments. Other values may be used as required or approved by

the agency concerned.

MIL-STD-735A, 6 May 1965

Test Methods and Test Equipment for Thermometers Used i_n Machinery

and Piping Systems . ...describes methods and equipment for testing

of thermometers used in machinery and piping systems.

...Liquid-in-glass, Bimetallic, and filled systems.

MIL-STD-740B, 13 January 1965

Ai rborne and Structureborne Noi se Measurements and Acceptance

Criteria of Shipboard Equipment . ...covers acceptable

instrumentation and procedures for the measurement of and

acceptance criteria for, airborne and structureborne noise of

Naval shipboard equipment. ...Basic method for airborne noise

measurement is determination of sound power. (Second pressure may

be specified for certain items.) Basic method for structureborne

noise testing is measurement of vibrational acceleration of

resiliently mounted equipment at its mounting points.

MIL-STD-750B, 27 February 1970

Test Methods for Semiconductor Devices . ...establishes uniform

methods for testing semiconductor devices, including basic

environmental tests to determine resistance to deleterious efforts

of natural elements and conditions, and physical and electrical

tests. Devices include: transistors, diodes, voltage regulators,

rectifiers, and tunnel diodes. ...applies only to semiconductor

devices.

MIL-STD-781C, 21 October 1977

Reliability Design Qua! i fi cation and Production Acceptance Tests : Exponential Distribution . ...covers the requirements for

reliability qualification tests (preproduction) and reliability

acceptance tests (production) for equipment that experiences a distribution of tirne-to-fail ure that is exponential. These

requirements include: test conditions, procedures, and various

fixed length and sequential test plans with respective

accept/ reject criteria.

Appendix E- ...sets forth minimum requirements for test equipment

and facilities for the performance of reliability qualification

and production acceptance tests.

8-37
MIL-STD-785A, 28 March 1969

Requirements for Reliability Program for Systems and Equipments

Development and Production . ...establishes uniform criteria for

reliability programs, and provides guidelines for the preparation

and implementation of a reliability program plan.

MIL-STD-810C, 10 March 1975

Environmental Test Methods . ...establishes uniform environmental

test methods for determining the resistance of equipment to the

effects of natural and induced environments peculiar to military

operations. It provides environmental test methods in order to

obtain, as much as possible, reproducible test results. The test

methods described are intended to be applied by the contractual

documents.

MIL-STD-843, 1 April 1965

Altimeters , Pressure , General Test Requirements for . ...defines

those tests which should be performed on pressure altimeters prior

to acceptance, after extended periods of storage, or after

servicing.

MIL-STD-883B, 31 August 1977

Test Methods and Procedures for Microelectronics . ...establishes

uniform methods and procedures for testing microelectronic

devices, including environmental, ...physical, and electrical

tests. Includes monolithic, multichip, film, and hybrid

microcircuits, microcircuit arrays, and the elements from which

the arrays and circuits are formed.

MIL-S-901C, 15 January 1963

Shock Tests , H.I. ( High-Impact ) ; Shipboard Machinery and Systems , Requirements for. ...covers the shock testing requirements for

shipboard machinery, equipment, and systems which are required to

resist High Impact (HI) mechanical shock. The requirements are for the purpose of determining the suitability of machinery,

equipment, and systems for use under the effects of the severe

shock which may be incurred in war-time service.

MIL-E-917D, 28 January 1965

Electric Power Equipment , Basic Requirements . ...covers the

general requirements applicable to the design, materials, and

construction of Naval shipboard electric power equipment

(exclusive of communications equipment and electronic equipment

other than that used in electric power applications).

MIL-STD-976, 31 August 1977

8-38
Certification Requirements for JAN Microcircuits . ...establishes

the minimum requirements for the certification of and maintenance

of certification for manufacturing facilities/line(s) in

fabricating, assembling, and testing high reliability JAN

microcircuits per MIL-M-38510. This includes plant facilities,

equipment, personnel training, process controls, testing, and

documentation.

MIL-I-983E, lb August 1966

Interior Communication Equipment , Naval Shipboard ; Basic Design

Requirements for. ...covers the basic design requirements, test

and operating conditions for interior communications equipment to

be used in Naval ships. The purpose is to secure uniformity of

practice, quality of materials and workmanship necessary to meet

the special requirements for equipments to be installed in ships

of the U.S. Navy.

MIL-STD-1309B, 30 May 1975

Definitions of Terms for Test , Measurement , and Diagnostic

Equipment. ...contains definitions of terms for test,

measurement, and diagnostic equipment most commonly used. 438

definitions are given.

MIL-STD-1313A, 8 December 1967

Microelectronic Terms and Definitions . Cancelled - 22 May 1977.

MIL-STD-1326, 15 January 1968

Test Points , Test Point Selection and Interface Requirements for

Equipments Monitored by_ Shipboard On-Line Automatic Test

Equipment . ...establishes the requirements for providing test

points in prime equipments for monitoring by on-line automatic

test equipment (ATE). ...provides criteria for guidance in optimum

test point selection. ...defines interface and data requirements,

a system of test point data generation, and procedures for

submission of data disclosing the selections of these test

points.

MIL-E-415E, 11 January 1973

Electronic Equipment , Ground : General Requirements for . ...covers

the general requirements of the design and manufacture of ground

electronic equipment.

MIL-S-4456, 12 March 1953

Shock , Variable Duration , Method and Apparatus for . Obsolete.

8-39
MIL-E-5272C, 13 April 1959

Envi ronmental Testing , Aeronautical and Associated Equipment . Cancelled - Superseded Dy MIL-STD-810.

MIL-E-5400R, 31 October 1975

Electronic Equipment , Airborne , General Speci fi cation for . ...covers the general requirements for airborne electronic

equipment for operation primarily in piloted aircraft. The

detailed performance and test requirement for a particular

equipment shall be specified in the detail specification for that

equipment. The appendix lists the specifications, standards, and

publications to be used in the design and construction of airborne

electronic equipment.

MIL-T-5422F, 30 November 1971

Testing , Envi ronmental , Ai rborne Electronic and Associated

Equipment. ...contains procedures for testing airborne electronic

and associated equipments under environmental conditions to

demonstrate compliance with MIL-E-5400, MIL-T-21200, other general

design specifications, and applicable detailed equipment

specifications. The procedures contained herein specify, modify

as necessary, and provide the required detail data for the

applicable test method of MIL-STU-810 for Navy airborne electronic

and associated equipment.

MIL-T-5494A, 28 November 1956

Thermocouples , Contact Aircraft Engi ne Spark Plug basket-Type . ...covers i ron-constantan gasket-type thermocouples (14mm & 18mm

gasket) Range: -55° to +300 °C; Intended use: on aircraft to actuate a thermocouple-type of indicator for the cylinder head

temperature of air-cooled engine cylinders. Qualified Products

List - 13 September 1974.

MIL-P-5640, 1 February 1950

Pickups ; Strain Gage Types . ...covers equipment designed to

provide a means of converting various flight test data of

conventional and pilotless aircraft into electrical intelligence

for injection into a telemetering transmitter. * The various

pickups shall utilize a strain-gage type of electrical pickoff to

provide an electrical output. ...Types: pressure gage - 0 to 40

and 0 to 5U0 psia for non-corrosive liquids and gases;

accelerometer - 2, 5, 10, and 20 g (dynamic and static).

MIL-E-6051D, 7 September 1967

Electromagnetic Compatibility Requirements , Systems . ...outlines

the overall requirements for systems electromagnetic

compatibility, including control of the system electromagnetic

environment, lightning protection, static electricity, bonding,

8-40
and grounding. It is applicable to complete systems, including

all associated subsystems/equipments.

MIL-S-15U3D, 3 August 1961

Salinity Indicating Equipment . ...covers salinity indicating

equipment designed to indicate the amount of dissolved salts in

boiler feed water, fresh water, distillate and submarine battery

cooling water, and to warn operating personnel when predetermined

values of salinity have been exceeded, [uses electrolytic cells].

Includes Qualified Products List - 8 March 1978.

MIL-T-16377F, 26 April 1979

Temperature Monitor Equipment . ...covers temperature monitoring

equipment which continuously monitors and selectively indicates at

a central location, a number of temperatures at remote equipment

locations on board Naval ships. ...Temperature sensing techniques:

resistance element - platinum; or thermocouple element - type K.

MIL-S-195U0F, lb December 1977

Semiconductor Devices General Specification for . ...establishes

general requirements for semiconductor devices. Detail

requirements and characteristics are specified in the detail

specifications. Four levels of assurance requirements are provided for in this specification: JAN, JANTX, JANTXV, and

JANS.

MIL-R-19610, lb September 1966

Reliability of Production Electronic Equipment , General

Specifications for . Cancelled 21 February 1966

MIL-I-19646, b December 19b6

ihermometers , Remote Reading , Sel f-Indi eating Dial , Gas Actuated . ...covers distant reading sel f-indi eating dial thermometers of the

gas-filled type for those applications and temperature ranges

specified. Includes Qualified Products List - 23 December 1977.

MIL-A-22145B, 22 May 196/

Accel erometer Group , Counting Type , Designation MS26477 and

MS26448 . ...covers the design and performance requirements for a single-axis four load-factor counting accel erometer. ...consists

of: (a) hermetically sealed force-balance accelerometer ...which

furnishes a voltage proportional to applied acceleration, provides

filter circuitry for required dynamic response and test circuits;

(b) a display with electromagnetic counters to indicate number of

times the aircraft is subjected to load factors of pre-set levels,

8-41
power supply and regulator (18.5V), delay circuit, and a digital

lock-out circuit.

MIL-T-231200L, 2 July 1973

lest Equipment of Use With Electronic and Electrical Equipment , General Specification tor . Inactive for new equipment, 27 June

1977.

MIL-R-22256, 20 November 1959

Kel i abi 1 i ty Requirements for Design of Electronic Equipment or Systems. Superseded by MIL-STD-/85.

MIL-R-22/32C, 12 November 19/3

Reliability Requirements for Shipboard Electronic Equipment . ...covers the procedures and requirements for achieving and

verifying adequate levels of reliability during the design,

feasibility study, development, test and evaluation, and

production phases in the acquisition of shipboard electronic

equipment.

MIL-A-23395, 15 August 1962

Altimeter , Pressure , Counter-Pointer Type MC-3 and MC-4 . Cancelled, 9 May 19/8.

MIL-T-23588C, 23 May 1974

Transducer , Pressure . ...establishes the requirements for the

procurement of a pressure transducer, NAVORD Outline Drawing

1803636. ...Range to 500 psig; transduction Bourdon tube with wire

strain gages in bridge circuit. ...must meet MIL-E-82590

...specifies performance characteristic, environment.

MIL-T-23648A, 1 March 1966

Thermistor , ( Thermally Sensitive Resistor ), Insulated , General

Specification for. ...covers the general requirements for general

purpose insulated thermistors to be used for temperature

compensation, control, and measurement over the temperature range

specified. ...includes Qualified Products List, 9 February 1978.

MIL-L-23886A, 4 February 1965

Liquid Level Indicating Equipment ( Electrical ) ( Naval Shipboard

Use ). ...covers the requirements for electrical liquid level

indicating equipment for Naval shipboard use in fresh water, sea water, diesel fuel oil, lubricating oil, waste oil, refrigerants,

and jet propulsion fuel in low pressure and high pressure tanks.

...Sensing technique; magnetic float, differential pressure,

8-42
electro-magnetic, or heat transfer; ranges; Atm-IQU psi or 1U0 psi

and greater. Includes Qualified Products List, 26 September

19/b.

MIL-P-24212B, 22 October 1976

Pressure Transducer Equipment . ...covers electrical output

pressure transducer equipment for Naval ships - does not include

readout or display. ...Types: gage, vacuum, compound (gage,

vacuum), and water column. Sensing technique: Bourdon,

diaphragm, bellows, or straight tube. Transduction: strain gage,

variable reluctance, differential transformer. Fluids: steam,

oil, flue gas and ammonia, oxygen, other gases, fresh water, and

condensate.

MIL-F-24259, 17 October 1966

Fluid Flowmeter , Volume Velocity Type . ...covers fluid flowmeters

for use in fresh water, sea water, and fuels and oils as specified

herein and whose primary sensing element is driven by the

impinging flow of the fluid. For example, turbine,

vortex velocity, drag types are covered, while differential

pressure, mass anemometer, batch weighing, and so forth would be

excl uded.

MIL-F-24291B, 10 August 1971

Flowmeter , Fluid Electromagnetic Type . ...applies to

electromagnetic type fluid flowmeters for use in fresh or sea water, or any fluid having a conductivity as low as 10~4

mho/cm. ...sense and indicate rate of flow, total flow, and

direction of flow in either direction through sensor. Flow sensor

unit consists of metal tubing, with flanged ends and associated

electrical wiring, containing an insulating liner along the

complete length with insulated sensor electrodes penetrating

through the metal tube and liner 100 degrees apart in the center

of the flow sensor.

A water-tight housing around the outside of the sensor tube shall

enclose the excitation coils, sensor electrodes, and wiring.

MIL-D-24304A, 21 July 1969

Differential Pressure Transducer ( Electrical ) ( Naval Shipboard

Use ). ...covers the requirements for electrical output

differential pressure transducer equipment for Naval ships but

does not include readout or display. ...Sensing technique - diaphragm, bellows, straight tube; transduction - strain gage,

variable reluctance, differential transformer; application - steam, oil, seawater, flue gas, condensate, other gases. Includes

Qualified Products List, 23 April 1976.

8-43
MIL-T-24387, 1 June 19/3

Temperature Measurement Equipment Signal Conditioner and Power

Supply ( Electrical ) ( Naval Shipboard Use ). ...cover the

requirements for signal conditioners and power supplies

(electrical) used in conjunction with thermocouples and resistance

temperature element assemblies for Naval ships. ...does not

include the design of sensing elements and wells or the

requirements for readout or display. Type: resistance - platinum; or thermocouple, type K. Qualified Products List, 29

September 1978.

MIL-T-24388B, 26 Apri I 1979

Thermocouples and Resistance Temperature Elements . ...covers requirements for the design, manufacture, testing, and packaging

of thermocouple and resistance temperature element assemblies for

Naval ships and mounting hardware (but not thermowells).

Temperature element: resistance - nickel, platinum; thermocouple - type K. Includes Qualified Products List, 16 December 1975.

MIL-L-2440/, 22 December 1969

Liquid Level Transducer Equipment ( Electrical ) ( Naval Shipboard

Use). Cancelled 16 April 1979.

MIL-P-24423, 1 May 1970

Propul si on and Auxiliary Control Consoles and Associated Control

and Instrumentation Equipment , Naval Shipboard Use , Basic Design

Requirements . ...covers the basic general requirements applicable

to the design, materials, construction, inspection, and operating

conditions for automated or centralized propulsion and auxiliary

control consoles together with their associated control and

instrumentation equipment used for Naval shipboard service.

MIL-A-25719A, 8 July 1974

Accel erometer , Ai rcraft , Pilot's Warning , Type MA-1 . ...covers one type of 1 7/8 inch dial, -2 to +4 g range accel erometer designated

type MA-1. Includes Qualified Products List, 2 June 1978.

MIL-A-25915, 8 November 1967

Accel erometer , Aircraft , Pilot's Warning , Type MA- 2. ...covers one type of 1 7/8 inch dial, -2 to +8 g range accel erometer,

designated Type MA-2. Includes Qualified Products List, 2 June

19/8.

MIL-A-25933, 2U August 1964

Al ti meter , Pressurized Compartment , Integral ly Lighted , 0-50,000

feet , 1 7/8 inch Dial . ...covers the requirements for a single

8-44
pointer integrally lighted 0- to 50 000-foot range cabin

altimeter, designated as AAU-3A/A. Includes Qualified Products

List, 3 February 1976.

MIL-A-25949E, Z5 Apri I 19/8

Accel erometer , Aircraft Range -5 to + 10 g , Integral ly Lighted . ...covers integrally lighted -5 to +10 g range, aircraft

accel erometer. . . . (non-hermetical ly and hermetically sealed).

MIL-R-264/4, 10 June 1959

Reliability Requi rements for Production Ground Electronic

Equipment . Cancelled - Superseded by MIL-STD-785.

MIL-R-26484A, 18 April 1960

Reliability Requirements for Development of Electronic Subsystems

or Equipment. ...details the minimum requirements that must be

followed by a contractor to assure the design of reliable

equipment.

MIL-R-26667, 1 July 1963

Rel iabil ity and Longevity Requirements , Electronic Equipment , General Specifications . Superseded by MIL-STD-781.

MIL-R-2/0/0, Zb March 1960

Kel iabil ity Requirements for Development of Ground Electronic

Equipment . Superseded by MIL-STD-/85.

MIL-A-27195, 27 May 1961

Accel erometer , Aircraft ABU-6/A . ...covers one type of

integrally-lighted 1 7/8 inch dial, -2 to +8 g range

accel erometer.

MIL-A-2/261A, 8 November 1966

Accel erometer , Ai rcraft . ...covers integrally lighted 1 7/8 inch

dial aircraft accel erometers having a range of -2 to +4 g. ...purpose: to indicate acceleration during maneuvers and in

rough air ...Natural frequency 6 to 8 Hz and 0.5 to 0.7 critical

damping ...operating temperature -62 to +71 °C.

MIL-R-2/542A, Zl May 1963

Rel iabil ity Program for Systems , Subsystems , and Equipment . Superseded by MIL-STD-785.

MIL-T-28800B, 9 February 1976

8-45
lest Equipment for Use With Electrical and Electronic Equipment , General Specification for . ...describes the general requirements

for test equipment used in testing electric and electronic

equipment. The test equipment may be of military or commercial

design and includes general purpose, special purpose, peculiar,

console mounted, and automatic test equipment. This specification

should also be used for built-in-test equipment (BITE) when the

requirements for built-in-test are not included in the system

specification. Detail requirements for a particular test

equipment will be specified in a detail specification for that

equipment.

MIL-P-38027A, 12 November 1973

Pressure Indicating System , Hydraul ic A/A27J-1 . ...covers one type

of hydraulic pressure indicating system designated A/A2/J-1.

...Range 0-4000 psi . ...Use indicating aircraft hydraulic system

pressure.

MIL-A-38307, 31 July 1964

Accel erometer , Aircraft MX-6663/ATB-7 . ...covers the requirements

for one type of aircraft accel erometer design. ...is a component of

the AN/AJB-1 computer set (MIL-C-38295) designed to sense aircraft

acceleration normal to the longitudinal axis of the aircraft.

....consists of a spring supported mass and precision potentiometer

pickoff enclosed in a sealed container. Range: linear

acceleration 0 to 5 g; minimum natural frequency 8 Hz.

MIL-M-38510D, 31 August 1977

Microcircuits , General Specification for . ...establishes the

general requirements for monolithic, multichip, and hybrid

microcircuits and the quality and reliability assurance requirements which must be met in the procurement of

microcircuits. Detail requirements, specific characteristics of

microcircuits, and other provisions which are sensitive to the

particular use intended shall be specified in the applicable

device specification. Multiple levels of product assurance

requirements and control for monolithic and multichip

microcircuits and a single level for hybrid microcircuits are provided for in the specification.

MIL-T-38531, 15 March 1976

Transducer , Motional Pickup TR-299/G( ) . ...establishes

requirements for transducer motional pickup, TR-299/G( ), part of

Alarm Set, Anti -Intrusion Restricted Area AN/GSS-26A. The

transducer is a magnetic and seismic pressure sensitive cable

suitable for burial under the surface of the earth where it

detects magnetic and nonmagnetic disturbances caused by an intruder. Output = 1.00 +0.05 mV pk-pk at specified frequency and

8-46
magnetic fields. ...capable of withstanding 163 °C for 10 minutes

during installation.

MIL-I-45208, 16 December 1963

Inspection System Requirements . ...establishes requirements for

contractors inspection systems. These requirements pertain to

the inspections and tests necessary to substantiate product

conformance to drawings, specifications, and contract requirements

and to all inspections and tests required by the contract. These

requirements are in addition to those inspections and tests set

forth in applicable specifications and other contractual

documents.

MIL-C-45662, 18 March I960

Calibration of Standards . ...prescribes the minimum requirements

for the calibration of standards which control the accuracy of

inspection equipment used in contractor Inspection or Quality

Control Systems established under the terms of specifications

applicable to the contract.

MIL-G-45811B, 15 January 1974

Gage , Air , Low Presure , Pneumatic Floating Equipment . ...covers a direct reading gage calibrated to read air pressures up to 10 psi

(not electrical)

MIL-A-48515, 30 September 1974

Accel erometer , Integrating , Atomi c Weapon , Training ; M7. ...covers requirements, quality assurance provisions, and the preparation

for delivery criteria for one type of integrating accelerometer

assembly ...used with the Honest John warhead.

MIL-A-48734, 22 November 1974

Accelerometer , Integrating , Atomi c Weapon : XM12. ...covers requirements, quality assurance provisions, and the preparation

for delivery criteria for one type of accelerometer ...used with

the Honest John warhead.

MIL-A-487333, 22 November 1974

Switch , Accelerometer , Atomi c Weapon : XM49 . ...covers requirements, quality assurance provisions, and the preparation

for delivery criteria for one type of inertia-actuated,

integrating electromechanical switch device ...used with the

Honest John warhead.

MIL-A48799, 27 January 1975

8-47
Accel erometer , Integrating , M9. ...covers requirements, quality assurance provisions and the preparation for delivery criteria for

one type of accel erometer ...which is used in the Sergeant warhead.

MIL-S-52868A, 11 January 1977

Sensor , Capacitance Proximity , DT-548/FSS-9(V) . ...covers a capacitance proximity sensor designed to detect the presence of an intruder in close proximity to or in contact with protected metal

objects. It is a component of the Joint-Services Interior

intrusion Detection System.

MIL-S-52871A, 10 March 1977

Sensor Group , Vibration : Detection DT-546/FSS-9(V) and Processor

MX-9442/FS-9(v) . ...covers a vibration signal detector and

processor, which combine to form a vibration sensor designed to detect forcible entry through metal barriers placed over windows

and ventilators. The sensor group is a component of the

Joint-Services Interior Intrusion Detection System (J-S11DS).

Appendix contains test methods to determine whether vibration

sensors and major components procured under the specification

conform to the requirements set forth.

MIL-A-81621, 25 February 1969

Accel erometer , Electrical , Linear ABU-13/A . ...The equipment

covered by this specification shall operate as an acceleration

sensor and electronic voltage multiplier. ...Service conditions:

vibration - curves I & II of Mil-E-54U0; temperature - -54° to

+10U °C; shock - 25 g: acceleration (steady state) to 6 g.

MIL-P-8Z4b9, 28 July 1968

Pressure Transducer . ...covers requirements for the procurement of one type of pressure transducer. ...Range 0 to 500 psi ; fluid - hydraulic oil, sea water, dry nitrogen. ...uses a potentiometer.

MIL-A-82516, 17 November 1967

Accel erometer . ...establishes requirements of one type of

accel erometer. Range - 3 to 20 g; natural frequency 17 +2 Hz.

MIL-E-82590, 9 September 1970

Lnvi ronmental Requirements and Tests ( for Torpedo Mk37 Components

and Assemblies ) establishes the environmental requirements and

test procedures for all component parts and assemblies to be used

in the torpedo Mk37. ...Non-operating temperature range +160 to

-5 U F at 90-95 percent relative humidity; acceleration +3 g at 30

to 100 kHz.

8-48
MIL-T-83460, 4 February 1975

Transducer , Motional Pick-up . ...covers a differential (airspeed)

absolute (altitude) pressure transducer for aircraft application,

designated TRU-164/A. Components: impact pressure transducer

U-42.938" Hg differential; static pressure transducer 31.019" - 0.810" Hg absolute. Output 0-5 V dc. Input from pi tot tubes.

Application: with airborne recording system measuring flight

parameters relating to aircraft structural loads.

8-49

9. REFERENCES AND BIBLIOGRAPHY

9.1 References

Note: U. S. Government publications may be obtained from the National

Technical Information Service (NTIS), U. S. Department of Commerce,

5285 Port Royal Road, Springfield, Virginia 22151 (Tel. (703)

321-8507); or from the Superintendent of Documents, U. S. Government

Printing Office, Washington, D. C. 20402.

Military Standards and Specifications may be ordered from: Naval

Publications and Forms Center, 5801 Tabor Avenue, Philadelphia,

Pennsylvania 19120.

9.1.1 Cited References

[I] Lederer, P. S., NBS InterAgency Transducer Project, 1951-1979, An

Overview, Nat. Bur. Stand. (U.S.), Tech. Note 1110, August 1979.

[2] ANSI-MC 6.1-1975, Standard Electrical Transducer Nomenclature and

Terminology, Instrument Society of America, 1975.

[3] Anon, The Bell & Howell Pressure Transducer Handbook, Bell & Howell,

1974.

[4] Meindl, J. D. and Wise, K. 0., Editors, IEEE Transactions on Electron

Devices, Vol. ED-12, No. 12, pp. 1861-1977, December 1977.

[5] Middlehoek, S., Angel! , J. B. and Noolag, J. W. D., Microprocessors Get

Integrated Sensors, IEEE Spectrum, pp. 42-26, February 1980.

[6] ANSI Z210.1 (ASTM 380-76, IEEE Std. 268-1975), Standard for Metric

Practice, American National Standards Institute, 1976.

[7] Norton, H. N. , Handbook of Transducers for Electronic Systems,

Prentice-Hall , 1969.

[8] Harvey, G. F., ISA Transducer Compendium, Second Edition, IFI/Pioneer

Press, 1969.

[9] Oliver, F. J. , Practical Instrumentation Transducers, Hayden Book

Company, New York, 1971.

[10] Lomas, D. J., Selecting the Right Flow Meter, Parts I, II,

Instrumentation Technology, May 1977, pp. 55-62, June 1977,

pp. 71-77.

[II] 01 sen, L. 0., Introduction to Liquid Flow Metering and Calibration of

Liquid Flow Meters, Nat. Bur. Stand. (U.S.), Tech. Note 831, June

1974.

9-1
Freeze, P. D. and Thomas, D. B., Studies of Noble-Metal Thermocouple

Stability at High Temperatures, Nat. Bur. Stand. (U.S.), Interagency

Report 76-1026.

ANSI MC96. 1-1975, Temperature Measurement Thermocouple, available from

ISA, 67 Alexander Drive, Research Triangle Park, NC 27009.

Anon., 1979 Temperature Measurement Handbook, Omega Engineering Inc.,

Stamford, CT.

Considine, D. M. Editor, Handbook of Applied Instrumentation,

McGraw-Hill , 1964.

Smart, R. F. , Moore, J. C. , Materials Selection for Wear Resistance,

Wear, Vol. 56, No. 1, pp. 55-67, 1970.

Cashin, R. F. , Marine Turbine and Diesel Engine Oil Analysis,

Lubrication, Vol. 56, No. 3, pp. 37-48, 1970.

Cantley, R. E., An Examination of Rear Axle Wear Particulates,

Lubrication Engineering, Vol. 30, No. 10, pp. 498-503, October 1979.

Morgan, S. K., How to Configure a Data Acquisition System, EMR

Telemetry Division, Schl umberger , January 1977.

Natrella, M. E., Experimental Statistics, Nat. Bur. Stand. (U.S.),

Handbook 91, August 1963.

ANSI B88. 1-1972, A Guide for the Dynamic Calibration of Pressure

Transducers, American National Standards Institute, 1972.

Harris, C. M. and Crede, C. E., Shock and Vibration Handbook, Second

Edition, McGraw-Hill, 1976.

Hi 1 ten, J. S., et al .

, A Simple Hydraulic Sinusoidal Pressure

Calibrator, Nat. Bur. Stand. (U.S.), Tech. Note 720, April 1972.

Vezzetti , C. F., et al , A New Dynamic Pressure Source for the

Calibration of Pressure Transducers, Nat. Bur. Stand. (U.S.), Tech.

Note 914, June 1976.

Wool vet, G. A., Transducers in Digital Systems, Peter Peregrinus Ltd.,

Stevenage, England, 1977.

Hi 1 ten, J. S. , Accel erometer Calibration with the Earth's Field Dynamic

Calibrator, Nat. Bur. Stand. (U.S.), Tech. Note 517, March 1970.

Smith, R. 0., Willis, E. A., and Hilten, J. S., A Dual Centrifuge for

Generating Low-Frequency Sinusoidal Accelerations, Nat. Bur. Stand.

(U.S.), J. Res. 66C, No. 4, pp. 357-362, 1962.

9-2
[28] Lederer, P. S., Step Function Pressure Calibrator, U. S. Patent #3,034,332, May 15, 1962.

[29] Aronson, P. M., et al .

, Static and Dynamic Calibration Methods for

Pressure Gages, U. S. Patent #3,273,376, September 20, 1966.

[30] Smith, R. 0., A Liquid Medium Step Function Pressure Calibrator, J. of

Basic Eng., Trans. ASME 86D, No. 4, 723, December 1964.

[31] Bouche, R. R., Calibration of Shock and Vibration Measuring

Transducers, SMV-lls Shock and Vibration Information Center, Naval

Research Laboratory, Code 8404, Washington, D.C. 20375, 1979.

[32] ANSI S2. 2-1959, American Standard Methods for the Calibration of Shock

and Vibration Pickups, American National Standards Institute,

New York, NY.

[33] AMCP 706-198, Engineering Design Handbook, Development Guide for

Reliability, Part 4, Reliability Measurement, U. S. Army Material

Command, January 1976.

[34] Hilten, J. S., et al .

, A Test Method for Determining the Effect of

Thermal Transients on Pressure Transducer Response, Nat. Bur. Stand.

(U.S.), Tech. Note, 905, March 1976.

[35] Vezzetti, C. F. and Lederer, P. S., An Experimental Technique for the

Evaluation of Thermal Transient Effects on Piezoelectric

Accelerometers, Nat. Bur. Stand. (U.S.), Tech. Note 855, January 1975.

[36] Horn, L., Thermal Gradient Effects on Thirteen Flush Mounted Pressure

Transducers, Nat. Bur. Stand. (U.S.), Tech. Note 490, August 1969.

[37] Lederer, P. S. and Hilten, J. S., A Laser Technique for Investing the

Effects of Thermal Transients on Pressure Transducer Performance

Characteristics, Nat. Bur. Stand. (U.S.), Tech. Note 723, May 1972.

[38] Anon, Electromagnetic Susceptibility Procedures for Vehicles (Except

Aircraft), SAE J 1113a, Recommended Practice, Society for Automotive

Engineers, June 1978.

[39] Anon, Electromagnetic Susceptibility of Process Control

Instrumentation, SAMA Standard, PMC 33.1-1978, Scientific Apparatus

Makers Association, 1978.

[40] MIL-STD-810C, Environmental Test Methods, March 10, 1975.

[41] MIL-STD-202E, Test Methods for Electronic and Electrical Component

Parts, April 16, 1973.

9-3
[42J MIL-T-288800B, Test Equipment for Use with Electrical and Electronic

Equipment, General Specification for, July 20, 1977.

[43] Williams, R., The Effects of Extended High-Temperature Storage on the

Performance Characteristics of Several Strain Gage Pressure

Transducers, Nat. Bur. Stand. (U.S.), Tech. Note 497, October 1969.

[44] Lederer, P. S., Life Cycling Tests on Several Strain Gage Pressure

Transducers, Nat. Bur. Stand. (U.S.), Tech. Note 434, October 1967.

[4b] Lederer, P. S. and Hi 1 ten, J. S., Durability Investigation of a Group

of Strain Gage Pressure Transducers, NASA CR 120953 (NBSIR 10975),

December 1972.

[46] Test Methods for Telemetry Systems and Subsystems, Document 118-73,

Revised 197b, Range Commanders Council, White Sands Missile Range.

[47] Anon, Metrology Requirements List, (metrl), NavAir 17-35MTL-1,

Department of the Navy, July 19/9.

[48] Anon, Establishment and Adjustment of Calibration Intervals,

Recommended Practices #1, National Conference of Standards

Laboratories, August 1970.

[49] MIL-HDBK-217B, Reliability Predictions of Electronic Equipment,

September 1974.

[50] Anderson, R. T., Reliability Design Handbook, ROH-376, Reliability

Analysis Center, RADC, NY.

[bl] Eshback, 0., Editor, Handbook of Engineering Fundamentals, John Wiley,

Third Edition, 197b.

[b2] Rabinowicz, E., et al .

, A Technique for Accelerated Life Testing,

Transactions of ASME, Vol. 92(3), pp. 706, August 1970.

[53] Cohen, J., A Metrology for Testing Life-Cycle Performance of Consumer

Products, Nat. Bur. Stand. (U.S.), NBSIR 76-1167, August 1976.

[64] ANSI-MC 6.2-1975, Standard, Specifications and Tests for Strain Gage

Pressure Transducers, Instrument Society of America, 1976.

[55] DOD 4120. 3-M, Defense Standardization and Specification Program

Policies, Procedures and Instructions, August 1978.

[56] Anon, Directory of Transducer Users, Range Commanders Council,

May 1978.

[57] Leedy, K. 0., Catalog of Federal Metrology and Calibration

Capabilities, Nat. Bur. Stand. (U.S.), Spec. Publ . 546, June 1979.

9-4
Jutila, J. M, Electronic Pressure Transducers: A Status Report,

Instrumentation Technology, January 1980, pp 9-21.

Allan, R., New Applications Open Up for Silicon Sensors: A Special

Report, Electronics, November 6, 1980, pp 113-122.

Philips, G., Fiber Optics for Bearing Performance Monitoring,

Proceedings, 28th Meeting of Mechanical Failures Prevention

Group, November 1978, pp 191-199.

Garrett, J. D., Survey of Displacement Transducers Below 50 mm, Journal

of Physics E: Scientific Instruments (Great Britain), Vol. 12, 1979,

pp 563-573.

Verhoef, W. M., Measuring Torsional Vibration, Instrumentation

Technology, November 1977, pp 61-66.

Slomiana, M., Selecting Pressure and Velocity Mode Primary Elements for

Flow Measurement, Instrumentation Technology, November 1979, pp 40-53.

Coss, M. W. and Moore, J. H., Electronic Fuel Injection Systems

Utilizing Corona Discharge Air Mass Flow Transducers, SAE Paper 770402,

February 1977.

Anderson, R. L., Thermocouple Error Analysis in the Design of Large

Engineering Experiments, Proceedings, Tenth Transducer Workshop, Range

Commanders Council, White Sands Missile Range, June 1979.

Jutila, J. M., Temperature Instrumentation: Steady Growth, Steady

Gains, Instrumentation Technology, February 1980, pp 31-42.

Mendelsohn, A., Temperature Transducers: What's Cooking, Electronic

Products Magazine, May 1979, pp 51-58.

Powell, R., Burns, G., et al., Thermocouple Reference Tables Based on JPTS 68, Nat. Bur. Stand. (U.S.), Monograph 125, March 1974.

Doebelin, E. 0. ,. Measurement Systems, Application and Design,

McGraw-Hill Book Company, New York, 1975.

Bailey, S. J., Level Sensors '80: A Key Partner in Productivity,

Control Engineering, October 1980, pp 75-79.

Bailey, S. J., Moisture Sensors 1980; On-line Roles Increase, Control

Engineering, September 1980, pp 112-117.

DARCOM-P-706-410, Engineering Design Handbook: Electromagnetic

Compatibility, USA Darcom, March 1977.

9-5
[73J MIL-STD-461 A, Electromagnetic Interference Characteristics Requirements

for Equipment, August 1968.

[74] MIL-STD-462, Electromagnetic Interference Characteristics, Measurement

of, July 31, 1967.

L75] AD/A-0056S7, Non-Electronic Reliability Notebook, prepared for Rome Air

Development Center and Martin Marietta, Hughes Aircraft Company, 1976.

9-6
9.1.2 Non-Referenced Useful Sources

A number of sources were consulted in addition to those referenced in the Test

and listed in section 9.1.1. The following can provide additional useful

information and are recommended for further study. They are listed below.

A. Anon, Study Plan for JLC Panel on Automatic Testing, 5 October 1978, and

Subtask Descriptions, Department on the Air Force, Headquarters Air Force

Logistics Command, Wright-Patterson AFB, Ohio, 30 July 1979.

B. Creswick, F. A. and Wyler, E. N., Study of Advanced Automatic Diagnostic

Test Equipment for Maintenance of Military Automotive Vehicles, Battelle

Laboratories, Report A-4712, September 30, 1976.

C. Dominy, D., et al., Feasibility Study for a Diesel Engine Condition

Monitoring System for 1179 Class LDT's, Nat. Bur. Stand. (U.S.),

NBS-GCR-75-43, August 1975.

D. McWhirter, W. R. Jr., Basic Guidelines for Performance Monitoring of

Shipboard Machinery, David W. Taylor Naval Ship Research and Development

Center, Report 4560, November 1975.

E. Whitesel, H., Sensor Requirements and Availability for Shipboard Auxiliary

Machinery, Phase I-Range Accuracy, PAS-78-14, David W. Taylor Naval Ship

Research and Development Center, September 1978.

F. Lederer, P. S. , An Overview of the Performance Characteristics of Sensory

Transducers, Nat. Bur. Stand. (U.S.), Spec. Publ . 522, October 1978.

G. Norton, H. N., Error Band Concept Defines Transducer Performance, Ground

Support Equipment; see: Handbook of Transducers for Electronic Systems,

Prentice-Hall, Englewood Cliffs, New Jersey, 1969.

H. Belanger, B. C, Calibration and Related Measurement Services of the

National Bureau of Standards, Nat. Bur. Stand. (U.S.), Spec. Publ. 250,

April 1978.

I. Anon, Response Characteristics of a Simple Instrument, Statham Instruments

Note #2, Gould Measurement Systems, 2230 Statham Blvd., Ornard, Calif.

93030, April -May 1948.

J. Bouche, R. R., Calibration of Shock and Vibration Measuring Transducers,

SVM-11, Shock and Vibration Information Center, Naval Research Laboratory,

Washington, D.C. 20375, 1979.

9-7
K. Anon., Recommended Environmental Practices for Electronic Equipment

Design, Society of Automotive Engineers, 1211, Recommended Practice,

Society of Automotive Engineers, June 1978.

L. Stein, P. K., Spurious Signals Generated in Strain Gages, Thermocouples

and Leads, Ninth Transducer Workshop, April 1977. Available from Stein

Engineering Services, Inc., Phoenix, Arizona 85018.

M. Anon., Navy Manufacturing Screening Program, NAVMAT P-9492, Department of

the Navy, Headquarters, Naval Material Command, Washington, D. C,

May 1979.

9-8
9.2 Bibliography of Sensor-Related Books

A number of books dealing with sensor-related subjects exist and it seemed

worthwhile to attempt to review a number of them to provide information on their potential benefits and deficiencies to the user of the Sensor Handbook.

There are some books, particularly those intended as college texts of an introductory nature, which are somewhat similar and it would be difficult to

rank them qualitatively. The author feels that such an approach is not

desirable, since, first of all, ease of information transfer between book and

reader is quite subjective and, secondly, the incremental costs of additional

reference books on any given aspect of measurement engineering and systems are probably negligible compared to the costs of the systems to be designed or selected.

The books are reviewed in the following section:

Hix, F. F., Jr., and Alley, R. P., Physical Laws and Effects , New York,

John Wiley & Sons, Inc., 1958, 291 pages

This book is a compilation of some 300 physical effects and laws, where

effects are "observed reactions in nature to certain stimuli," and laws are the more formalized and generalized descriptions of such effects. All transduction

principles are based on such laws, and this listing may help stimulate possible

new approaches to the solution of difficult measurement problems. The effects

listed, while aimed at new applications, may also suggest positive pitfalls in

measurement situations. Each law or effect is treated briefly and succinctly,

usually with one or more references listed, from which additional details can

be obtained.

Although of little direct assistance to the planners or users of practical

ATE or measurement systems, it has good potential for the stimulation of

research beyond the present state-of-the-art of sensing or control.

Lion, Kurt, Instrumentation in Scientific Research , New York, McGraw-Hill Book

Company, Inc., 19b9, 324 pages.

This book attempts to offer a reasonably complete collection of the

existing basic methods and systems used as "input transducers" in electrical

instrumentation. In this case input transducer is defined as a device which

converts a non-electrical quantity into an electrical signal, e.g., a sensor. The book is intended to furnish a general coverage of the field with emphasis

on simple descriptions of the physical mechanisms and principles of the sensing

devices. Carefully selected references can give further detailed information.

The book is divided into chapters on: Mechanical Input Transducers (linear

dimensions, force, velocity, level, pressure, flow and humidity), Temperature

Transducers, Magnetic Transducers, Electrical Transducers, and Radiation

Transducers.

9-9
The emphasis in this reference, which represents the state-of-the-art of

instrumentation of about 1955 to 1957, is on the basic physics or mathematics

of metrology. Hence there is little detailed information on applications,

environment, calibration considerations, or ancillary equipment. The book is

thus primarily a good basic reference for students and designers and of less

help to the special application needs of systems procurement or testing.

Beckwith, T. G. and Buck, N. L., Mechanical Measurements , Reading, MA,

Addi son-Wesley , 1961, 316 pages

This book has two major parts: fundamentals of mechanical measurements and

applied mechanical measurements. The first part approaches measurements from a general standpoint dividing measuring systems into function groups. It

discusses possibilities and inherent limitations of each measuring system as well as standards and dynamic responses. The second part is devoted to a presentation of applications and techniques for special mechanical quantities.

Only such electrical matters as apply to the problem being considered are discussed.

The chapters include: The Significance of Mechanical Measurements, The

Generalized Measurement System, Basic Standards and Accuracy of Measurement,

Characteristics of Dynamic Signals, Basic Detector-Transducer Elements,

Intermediate Modifying Systems, Terminating Devices and Methods, Determination

of Count, Events per Unit of Time and Time Interval, Displacement and

Dimensional Measurement, Strain Measurement, Measurement of Force and Torque,

Measurement of Pressure and Flow, Temperature Measurement, Vibration and

Acceleration Measurement, Vibration and Shock Testing, and Application of

Radioactive Isotopes to Mechanical Measurements.

The book is intended as an introduction to measurement problems for

students and engineers and assumes a good general background in the elements of

mechanical engineering and mathematics. It is well written and illustrated.

Cook, N. H. and Rabinowicz, E., Physical Measurement and Analysis , Reading, MA,

Addi son-Wesley Publishing Co., 1963, 311 pages.

The aim of this book is to make mechanical engineering students aware of

the principles underlying physical measurements, stressing pitfalls and

limitations of such measurements. The dynamic and statistical points of view

are emphasized.

Chapters include: Experiments and Measurements, (Introduction),

Experimental Statistics, Dynamics of Measurement, Displacement Measurement,

Force and Torque Measurement, Temperature Measurement, Measurements on Fluids,

and Radiotracing Techniques.

The philosophy of measurement error assessment and considerations of the

dynamic nature of measurement are treated extensively and well. These two

9-10
chapters make this a useful reference for designers and users of sensor-based

measurement systems.

Neubert, H. K. P., Instrument Transducers, An Introduction to Their Performance

and Design , Oxford, Oxford University Press, 1963, 390 pages.

This book is devoted to the basic principles of performance and design of

instrument transducers with emphasis on the primary sensing element.

Chapters include: Classification of Instrument Transducers, Mechanical

Input Characteristics, Electrical Output Characteristics, and Force-Balance

Type Transducers. The author's introduction indicates that the coverage is

restricted to those transducer types for which a sufficiently advanced

technology had been developed by 1963, thus excluding pi ezo-resi stive devices.

Also excluded are thermocouples, microphones, and photocells, which are extensively covered in other publications.

The book specifically excludes chapters on calibration methods and

environmental testing with the statement that a single chapter cannot do

justice to those subjects.

Despite its stated limitations, this is also a fundamental and useful

reference on sensors in general.

Norton, H. N. , Handbook for Transducers for Electronic Measuring Systems , Englewood Cliffs, NJ, Prentice-Hall, 1969, 704 pages.

This book is intended not only for transducer designers and manufacturers

but also for those who select, purchase, test and use transducers. It can also

be used as a textbook. Chapters include: Electronic Measuring Systems,

Transducers, Transducer Performance Determination, Acceleration, Attitude,

Displacement, Flow, Force and Torque, Humidity and Moisture, Light, Liquid

Level, Nuclear Radiation, Pressure, Sound, Speed and Velocity, Strain and

Temperature.

The author in his preface makes a statement about this book which, in the

opinion of this reviewer, is so generally applicable to the entire field of sensors that it is quoted below in its entirely:

"Finally, a word of caution must be directed to the reader regarding the

use of transducers and their associated measuring systems. The prime

purpose of this book is to describe transducers, not measuring techniques.

Although a number of relatively straightforward measurement problems can

be solved solely on the basis of the material presented here, most

successful transducer applications require considerable additional

training and experience in measurement engineering, and a solid education

foundation in the physical sciences relating to the measurands. Practical

experience, often gained by discovering one's own mistakes, is probably

the best road towards obtaining valid data from transducer installations."

9-11
The book addresses calibration methods, error analysis, and environmental

considerations, although not with the detail which is required for a really

thorough understanding of sensor performance characteristics in actual

measurement systems. But then no such reference, as yet, has been found that

meets these needs adequately.

Oliver, Frank J., Practical Instrumentation Transducers , New York, Hay den Book

Company, Inc., 1971, 340 pages.

This is a guide to transducer selection and application with a comprehensive survey of physical -to-electrical transducers and their associated

signal conditioning circuits for use in measurement and control systems. It

describes and illustrates diagrammatically the basic operational principles,

practical manifestations, and units of measurements of transducers for

industrial and aerospace applications. Included are such topics as interference problems in hard wire telemetry systems, and transducers as feedback devices in solid-state systems. Chapter headings include: Transducer

Fundamentals and Physical Effects, Evaluation and Calibration of Transducers,

Measurement of Strain, Force, Load and Torque, Measurement of Linear

Displacement and Thickness, Angular Position, Shaft-angle Encoders, Measurement

of Rotary Speed, Measurement of Vibration and Shock, Measurement of Fluid

Pressure, Temperature Measurement, Radiation Detectors, Measurement of

Moisture, Humidity and Dewpoint, Measurement of Flow, Measurement of Liquid and

Dry Bulk Level, Low Level Transducer Signal-Conditioning Circuits, and

Interference in Transducer Signal Channels.

The treatment is quite thorough for physical quantities although

electrical and magnetic quantities are not included among the sensor principles

and types. Caution must be exercised as far as accepting statements of

achievable accuracy in application examples. The state-of-the-art changes

sufficiently rapidly that the most recent literature and manufacturers' data

should always be consulted prior to any final system design, application, or procurement decision.

The treatment of environmental effects on sensor performance and the

coverage of calibration considerations is not sufficiently adequate to be of

much use. Nevertheless, this book is a generally good and important reference

for those who design, specify, procure, test, or install sensor-based measuring

systems.

Harvey, G. F. , Editor, ISA Transducer Compendium, Parts 1, 2, 3 , New York,

IFI/Plenum Press, 1969, 212, 325, and 277 pages.

This publication was designed to be a centralized source of transducer

information, based on an extensive survey of manufacturers of sensors. It is

restricted to sensors with electrical output and presents extensive product

information classified by the measurand. For each sensor class or type,

information was sought on such characteristics as range, operating principle,

output, error, natural frequency, operative life, etc. Photos of most of the sensors appear as well as a listing of sensor manufacturers.

9-12
The publication is in three parts, and the information in each part is

arranged in tabular form by measurand and by range. Part 1 covers Pressure,

Flow and Level; Part 2 covers Motion, Dimension, Force and Torque, and Sound;

Part 3 covers Temperature, Chemical Composition, Physical Properties, Humidity

and Moisture, and Radiation. Each measurand section is preceded by an introductory text dealing with such topics as: Units, Ranges, Sensing

Techniques, Transducer Selection and Use, Evaluation and Consideration, Current

Problems and Future Trends, and References.

Its outstanding feature is the easy-to-use tabular array that enables the user to find quickly a commercial sensor to meet particular requirements. A

great deal of useful information is given for most sensors. The introductory

chapters in each section are fairly brief, providing a good overview for the

neophyte, but not giving enough application details for this compendium to serve as the sole sensor reference.

The principle limitation of the compendium is that most of the detailed

information on sensors listed is obsolete. This is inevitable with any

treatment of this type which attempts to survey the current state-of-the-art.

It nevertheless serves a very useful function by indicating the type of sensors available (at least in 1969) for most measurands, an indication of the

performance characteristics obtainable, and the listing of transducer

manufacturers. Consequently, consultation of the compendium should make it

relatively easy to take a fast cut at picking a likely sensor for most

applications, and then verifying its availability and characteristics from the

manufacturer. By necessity, certain more recent developments would not be

included, as might some manufacturers.

On balance, while it does not present today's state-of-the-art by giving a comprehensive coverage of the state-of-the-art of 1969, the ISA Compendium

serves as a very useful reference foundation.

O'Higgins, P. S., Basic Instrumentation-Industrial Measurement, New York,

McGraw-Hill Book Company, 1966, 495 pages.

This book is written primarily as a textbook for students of the

fundamentals of the theory and practices of industrial process control

instrumentation. It is divided into chapters on: Art and Science of

Measurements, Dimensional Analysis and Engineering Units, Measurement of

Weight, Density, and Specific Gravity, Basic Concepts of Pressure Measurements,

Fluid Pressure and Vacuum Measurements, Level Measurements of Liquids and

Solids, Viscosity Measurement, Fluid Flow Measurement, Temperature Measurement,

Art and Science of Instrumentation, Applied Electricity and Measuring Circuits,

Fundamental Electrical Measuring Instruments, Basic Electronics for

Instrumentation, Electrical Transducers, Humidity, Dew-Point and Moisture

Measurement, and Electrochemical Measurements.

There is almost nothing on calibration and operating environments in this

treatment, and its main usefulness is in introducing the concepts of industrial

process control measurements to technical people with a background knowledge of

basic physics and mathematics.

9-13
Wightman, E. J., Instrumentation in Process Control , Cleveland, The Chemical

Rubber Press, 1972, 367 pages.

This book deals specifically with the problems associated in the gathering

of data from physical processes. Methods are outlined by which it is possible

to relate transducers and their characteristics to digital data processing

techniques which utilize the measurements obtained in control applications for

industrial processes.

Chapters include: Transducer Performances, Temperature Measurement,

Pressure Measurement, Liquid Density Measurement, Displacement Measurement,

Application of A-D Conversion, Computing Corrections, Data Transmission, and

Digital Control Techniques.

Although the book is aimed at process control applications, its extensive

treatment of signal processing considerations makes it a useful reference for

other instrumentation systems as well. Calibration considerations are treated

separately; environmental effects not touched upon.

Soisson, H. E., Instrumentation in Industry , New York, John Wiley & Sons, 1975,

561 pages.

This book is intended to be a broad survey of industrial instrumentation,

including general principles of operation and a brief coverage of operational

characteristics. It provides a basic description of the theory and instrument

function, a discussion of measurement and response limitation calibrations of

the instruments, and an analysis of the success of the industrial process or operation in maintaining a quality product.

Chapters include: How Instruments are Used in Industry, Instrument

Standards and Calibrations, Pressure and Vacuum, Thermometers, Pyrometry,

Liquid and Dry Level Instrumentation, Flow Instrumentation and Measurement,

Automatic Measurement and Control Concepts and Systems, Analytical Industrial

Instrumentation, Radiation Measurement and Instrumentation, Nondestructive

Testing Equipment, and Environmental and Pollution Measurements.

Heavily oriented toward process industries, this book touches calibration

only lightly and operating environments not at all. It can serve as a moderately useful introduction to the field of instrumentation and sensors.

Doebelin, E. 0., Measurement Systems: Application and Design , McGraw-Hill Book

Company, Revised Edition, 1975, 772 pages.

Although this book is designed for use in connection with university

courses in mechanical engineering, it can serve as a useful reference to the

practicing engineer. The author, in his preface, describes the contents of the

text as follows:

9-14
"Consideration of measurement as applied to research and development

operations and also to monitoring and control of industrial and military

systems and processes.

"A generalized treatment of error-compensating techniques.

"Treatment of dynamic response for all types of inputs: periodic,

transient, and random, on a uniform basis, utilizing frequency response.

"Detailed consideration of problems involved in interconnecting

components

"Discussion, including numerical values, of standards for all important

quantities. These give the reader a feeling for the ultimate performance

currently achievable.

"Quotation of detailed numerical performance specification of actual

instruments.

"Inclusion of significant material on important specific areas such as sound measurement, heat-flux sensors, gyroscopic instruments, hot-wire

anemometers, digital methods, random signals, mass flowmeters, amplifiers and

the use of feedback principles."

Significantly, there is no consideration of operation in harsh

environments or durability and reliability aspects of sensor applications.

Despite this, the book is a fairly comprehensive reference on measurement.

Holman, J. P., Experimental Methods for Engineers , McGraw-Hill Company, Third

Edition, 1978, 490 pages.

This book is designed as a first survey of experimental methods for undergraduate students. The author recognizes that this book may be lacking in

depth in certain topics and includes references to more detailed coverages. It deals primarily with the theoretical basis of measurements and measurement

systems. Its chapters include: Basic Concepts, Analysis of Experimental Data,

Basic Electrical Measurements and Sensing Devices, Displacement and Area

Measurements, Pressure Measurement, Flow Measurement, The Measurement of

Temperature, Thermal- and Transport-Property Measurements, Force, Torque, and

Strain Measurements, Motion and Vibration Measurements, Thermal and

Nuclear-Radiation Measurements, Air-Pollution Sampling and Measurement, and

Data Acquisition and Processing.

It represents an average textbook-style treatment of the subject.

Harris, C. M. , and Crede, E. E., Shock and Vibration Handbook , McGraw-Hill Book

Company, Second Edition, 1976, 1322 pages.

This is undoubtedly the most comprehensive and authoritative reference on classical vibration theory and its modern applications. This one-volume

handbook covers fundamentals, instrumentation and measurements, data analysis

and testing, practical methods of control solutions to engineering problems,

equipment design and packaging, and the effects of vibration on people.

It contains 44 chapters written by 54 authorities from industry,

government, and universities. The second edition contains three totally new

9-15
chapters on vibration standards, environmental specifications and testing, and

applications of digital computers.

It is the outstanding coverage of the subject of shock and vibration.

Considine, D. M., Editor, Handbook of Applied Instrumentation , New York,

McGraw-Hill Book Company, 1964, 1167 pages.

This book, in conjunction with its companion, "Process Instruments and

Controls Handbook," was intended as a "complete compendium on the subject."

The book, as stated in the foreword, is directed to a variety of users: the

manufacturing, process, and instrumentation engineer who analyzes the needs and

benefits of instrumentation and selects or designs the equipment for the

particular application, the instrument and control user who desires knowledge

about these devices, the management person who desires to comprehend

instrumentation to take full advantage of its potentialities in achieving

management objectives, the student, the educator, and finally the instrument

technician.

The book is arranged into seventeen major sections covering general

principles of instrumentation, the measurement of a variety of measurands,

controls and their applications, and instrumentation practices in a variety of

industries. Sections include: Definition and Classification of Variables,

Measurement Errors, Factors in Selection of Measuring Methods, Temperature

Calorific Value, Radiation Fundamentals, Nuclear-Radiation Detectors,

Radioisotopes in Instrumentation, Photometric Variables, Acoustic Measurements,

Force Measurement, Pressure and Vacuum Measurement, Flow, Acceleration

Measurement, Speed Measurement, Weight and Weight Rate of Flow, Liquid Level,

Solids Level, Parts Dimension Measurement and Control, Thickness Measurement of

Sheet and Web Materials, Position Measurement and Control, Fluid-Density and

Specific-Gravity Measurement, Humidity and Dew Point, Moisture Control of

Materials, Viscosity and Consistency, Analysis Instruments, Electrical

Variables, Fundamentals of Automatic Control Engineering, Application of

Photoelectric Controllers, Controller Types and Final Control Elements,

Applications of Analog Computers, Application of Digital Computers,

Instrumentation Data Processing, Counters and Digital Indicating Devices, Steel

Production Instrumentation, Glass and Ceramics Industries Instrumentation,

Instrumentation Practices in the Process Industries, Instrumentation of Heat

Exchangers etc., Pulp and Paper Production Instrumentation, Food-Industry

Instrumentation, Automatic Combustion Control Systems for Boilers, Steam Power

Plant Instrumentation, Electric Power Generation and Distribution Control,

Nuclear Reactor Instrumentation, Process Laboratory Instrumentation,

Pilot-Plant Instrumentation, Environmental Test Instrumentation, Aircraft and

Aerospace Vehicle Instrumentation, Aircraft-Flight Simulation Instrumentation,

Basic Electricity and Electronics for Instrumentation Engineers, Preparation of

Wiring Diagrams for Instrumentation Applications, Instrument Panel Board Design

and Construction, and Instrument Air Supplies.

The individual sections of the book were written by experts in the

particular subjects and represent an earnest attempt to cover the field briefly

but with appropriate thoroughness.

9-16
Unfortunately, attempts to cover all of an enormous subject for a wide

range of interested readers and users rarely succeed. This book is no exception. It is also inherent to this type of treatment that it is always

out-of-date in an area of rapidly developing technology. This is not to

totally condemn this kind of book; it does present a fairly complete, though

dated, coverage of the field and thus provides a useful foundation and

background reference.

Woolvet, G. A., Transducers in Digital Systems , Stevenage, England,

Peter Peregrinus, Ltd., 1977.

This book presents a survey of transducers that give a digital output and

which are used mainly in computer-based systems for which a digital output is

required. The author points out that there appear to be no natural phenomena

that provide digitally coded outputs in response to variations of a physical

quantity. The possible exceptions are devices that produce a variable

frequency. The book describes the latter, as well as systems which convert

analog signals into digital ones.

There are chapters on: Digital Systems, Angular Digital Encoders,

Frequency Dependent Transducers, Digital Linear Transducers, Analog Conversion

Methods, Syncho-Resol ver Conversion, and other Techniques.

The usefulness of this book is in its coverage of digitizing sensors for

analog quantities. This information is most useful in supplementing earlier

treatments of transducers with analog outputs.

Liptak, Bel a G., Editor, Instrument Engineers Handbook , Volume 1, Process

Measurement, Chilton Book Company, Philadelphia, PA, 1969.

This handbook is intended as a reference for the broad field of process

instrumentation and aimed at process control loops specifically. The first

volume is concerned with the measuring element (sensor), the second volume

deals with other loop components (controllers, final control elements, and

supervisory hardware) as well as control systems. The purposes of the book are

to help the reader look for design features, make him aware of limitations, and

help him decide on the type of instrument for a specific application.

The process variables covered by this handbook include: Level, Pressure,

Density, Temperature, Flow, Viscosity and Weight. Analytical Sensors (such as for ph, Moisture Detection, Turbidity and Chromatography) are covered in a separate chapter. At the end of each chapter is a section titled

"Conclusions." It is designed to guide the reader in the selection of sensors.

The section on pressure states in the "Conclusions", "... care is to be taken

in considering vibration, freezing, corrosion, temperature and hard-to-handle

fluids." The introductory discussion on Measurement Accuracy and Sources of

Error is of the same unsatisfactory brevity.

The general subject of calibrations is not discussed at all, nor is the

measurement of motion (displacement, velocity, acceleration).

9-17
A large number of tables containing conversion factors, properties of

gases, steam, flowmeter parameters, and others would be of use for process

control system designers and users.

This is another of several references examined for the Sensor Handbook

bibliography section, which while possessing some useful information,

unfortunately lacks other equally needed information to serve as a comprehensive reference.

Moore, R. L., Basic Instrumentation Lecture Notes and Study Guide : Measurement

Fundamental

s

, Instrument Society of America, 67 Alexander Drive, Research

Triangle Park, NC 27709, Second Edition, 1976.

The guide contains descriptions of the working principles of measuring

instrument for a variety of parameters. After a brief introduction to measurement fundamentals, there are chapters on Measurements of: Pressure,

Level, Weight, Density, Flow, Temperature, Heat Flux, Humidity and Moisture,

ana Physical and Chemical Measurements. Some application information is

included as guidelines for application. The manufacturer's information on a given device is typical for that device; no attempt has been made to include

material from all manufacturers. The ISA Transducer Compendium is intended to serve as an adjunct to the guide.

The guide is intended for teaching purposes, to be supplemented by

additional texts suggested by the instructor. A large number of references is

given. The treatment, while intended to be general, appears aimed at process

industry applications. Significantly, vibration and force measurements are not

covered.

There is no discussion of calibration and evaluation methods,

environmental conditions, signal conditioning, or data reduction

considerations. The treatment is not complete enough to serve as sole source,

but does provide some information which may be useful.

Anon., Training Manual : Physical Measurements , Navy Metrology Calibration

Program, Pomona, CA 91766, Navair 17-35QAL-2, Revision 3, June 1979.

This is an illustrated, elementary treatment of physical measurement

principles. It includes a large number of sample numerical problems in all

chapters, as well as practice problems at the end of each chapter. Chapters

include: Introduction to Measurements, Physical Concepts, Electrical

Indicating Devices, Errors, Temperature, Humidity, Force, Torque, Rotational

Measurement, Mass, Weight and Balances, Pressure, Vacuum, Viscosity and

Specific Gravity, Fluid Flow, and a chapter on Pressure and Flow Fittings and

Tubing. Vibration has been omitted.

While principles of measurement are covered, sensors witti electrical

outputs are only sometimes discussed specifically. There is a table of

contents, but no index or list of references. The manual is presumably

intended for training purposes, but there is no foreword to indicate this.

9-18
Anon., Suggestions for Designers of Navy Electronic Equipment , NOSC TD 250,

1979 Edition, Naval Ocean Systems Center, San Diego, CA 92151, 147 pages.

This booklet is designed to serve as a checklist for engineers during the

development of naval electronic equipment. The objectives are to save engineering, development, and testing time and effort, and to increase

operational availability of better electronic equipment. The intent is to

alert the designer to possible trouble spots in his design, or to areas of

conflict outside his realm of expertise or specialization.

The booklet has chapters on: Physical Characteristics, Maintainability,

Environmental Conditions, Thermal Design, Materials, Processes and Parts,

Electromagnetic Compatioility, Safety, and Human Engineering.

While the material is intended for equipment developed for the Naval

Material Command, most of it applies to all types of military equipment.

Although sensors are not specifically monitored, many of the considerations

listed are applicable to sensors. Pertinent military standards and

specifications are referenced.

A very comprehensive and useful treatment, this booklet should be

consulted by all engineers concerned with ATE equipment design and

procurement.

Benedict, R. P., Fundamentals of Temperature, Pressure and Flow Measurements , Second Edition, New York, John Wiley & Sons, 1977, 517 pages.

This book is intended as a working reference for practicing engineers and

associated workers involved in the measurement of temperature, pressure, and

flow rate and as a text for engineering students. It provides a review of

measurement techniques and includes practical data. Applications are illustrated by practical, worked-out, numerical examples.

Chapters include: Early Attempts to Measure Degrees of Heat, The Air

Thermometer, Thermodynamic View Points of Temperature, The International

Practical Temperature Scale, Li qui d-i n-Glass Thermometers, Resistance

Thermometer, Thermoelectric Thermometry, Optical Pyrometry, Calibration of

Temperature Sensors, Uncertainties and Statistics, Temperature Measurement in

Moving Fluids, Installation Effects on Temperature Sensors, Transient

Temperature Measurements, The Concepts of Pressure, Pressure Standards,

Principles of Conventional Pressure Transducers, Pressure Measurement in Moving

Fluids, Transient Pressure Measurement, The Concept of Flow Rate, Open-Channel

Flow, Theoretical Rates in Closed-Channel Flow, the Discharge Coefficient, The

Expansion Factor, and Installations and Uncertainties.

This book covers the theoretical measurement considerations for

temperature, pressure, and flow extremely well. Other measurands are not

covered at al 1

There is also a good deal of practical application information. There is

little coverage of calibration and evaluation of sensors or environmental

9-19
effects. Despite this lack, it is one of the best treatments of the

measurements of the three parameters.

Ferson, L. M. , Standards and Practices for Instrumentation , Sixth Edition,

Instrument Society of America (ISA), Research Triangle Park, NC, 1980, 600 pp.

This book provides complete texts of all current ISA Standards and

recommended practices; titles ana abstracts for over 900

instrumentation-related standards published by other U.S. and international

organizations; and a subject index, cross-references to the over 900 titles and

abstracts.

This is an extremely useful comprehensive listing of existing civilian

standards documents in the general field of instrumentation. Existing sensor standards are included. ISA intends to up-date this volume at three or four-year intervals.

One of its good features is the listing of all (as far as known)

organizations and their addresses, enabling users of the handbook to easily

obtain up-to-date information on new standards or those under development. A

very valuable reference.

9-20
10. GLOSSARY

To facilitate understanding and the interchange of information, a glossary

of selected terms is included in this handbook. Most of the terms listed apply

to sensors, although other areas such as ATE systems and reliability are also

represented. The sensor terms are largely taken from ANSI and ISA Standards,

particularly ANSI MC6. 1-1975 (ISA S 37.1) "Electrical Transducer Nomenclature

and Terminology." Additional terms were taken from MIL-STD-1309C

(15 April 1980) "Definitions of Terms for Test, Measurement, and Diagnostic

Equipment."

A Note of Caution: The terminology of any specialized field should be used

with caution. Often terms may have a somewhat different meaning in a related field. In critical documents, it may be desirable to cite the

entire definition following the term itself, to preclude possible

misunderstandings.

-AAbsolute Pressure — Pressure referenced to a vacuum.

Acceleration Error -- The maximum difference, at any measurand value within

the specified range, between output readings taken with and without the

application of a specified constant acceleration along a specified axis.

Acceleration Function -- The relation between measured amplitude and frequency

normally encountered by a sensor and the corresponding values specified

in an accelerated life-test for the sensor.

Acceleration Limit — The maximum vibration and shock acceleration which an acceleration sensor can accept in either direction along its sensitive

axis without permanent damage, usually stated as + g's. The

acceleration limits are usually much wider than the acceleration range and

represent the overload capability of the sensor.

Acceptable Quality Level -- The quality standard associated with a given

producer's risk prescribed by the customer or quality engineer for the

products on order. It is usually expressed in terms of percent defective

per hundred units.

Accuracy — The ratio of the error to full-scale output or the ratio of the error to measurand output, as specified, expressed in percent. Accuracy

may also be expressed in units of the measurand. The term accuracy should

not be used in specifications; the tern error is preferred.

Acoustic Sensitivity — The output of a sensor in response to a specified

acoustical environment. This is sometimes expressed as that measurand

value sufficient to produce the same output as that induced by a specified

sound pressure level spectrum having an overall value of 140 dB referenced

to 0.0002 dyne per square centimeter rms.

10-1
ADC Abbreviation for analog- to-digital converter.

Algorithm -- A method of algebraic or numerical computation; in computer

terminology, a detailed, logical procedure for the solution of a particular problem.

Aliasing Error Errors caused in fast fourier transform analysis by

an insufficiently high rate of sampling of frequencies of interest.

Ambient Conditions -- The conditions (pressure, temperature, etc.) of the

medium surrounding the case of a sensor.

Ambient Pressure Error -- The maximum change in output, at any measurand value

within the specified range, when the ambient pressure is changed between

specified values.

Amplification Factor at Resonant Frequency — The ratio of the sensitivity of a sensor at its resonant frequency to its reference sensitivity.

Amplification factor at resonant frequency is sometimes referred to as "Q."

Analog Output — Sensor output which is a continuous function of the measurand,

except as modified by the resolution of the sensor.

AQL — Abbreviation for "acceptable quality level."

Arrhenius Law -- The table which relates the rate of a chemical reaction to

an exponential function of temperature.

ATE -- Abbreviation for "automatic test equipment."

Attitude Error -- The error due to the orientation of a sensor relative to the

direction in which gravity acts upon the sensor. (See acceleration

error)

Automatic System — A system in which the operations are performed by

electrically controlled devices without the intervention of operators.

Automatic Test Equipment -- An equipment that is designed to automatically

conduct analyses of functional or static parameters, evaluate the degree

of performance degradation, and isolate faults in malfunctioning units.

The decision making, control, and evaluative functions are conducted

without reliance on human intervention.

Automation — The investigation, design, development, and application of

methods of rendering processes automatic, self-acting, or

sel f -control 1 ing.

-BBack Pressure -- The absolute pressure level measured four pipe-diameters

downstream from a turbine flowmeter under operating conditions expressed

in Pa (or psi ).

10-2
Bellows -- A series of capsules used in pressure measurement.

Berkson's Premise -- The assumption that the independent variable in a planned

experiment is without error when it is carefully set to a preassigned

value.

Bernoulli's Theorem — Within an incompressible fluid under conditions of

steady flow, the sum of the energy of velocity, energy of pressure, and

potential energy of elevation remain constant; therefore, if the velocity

of a fluid in a horizontal tube increases, the pressure must decrease, and

vice versa.

Best Straight Line -- A line midway between the two parallel straight lines

closest together and enclosing an output vs measurand values on a calibration curve.

BITE -- Abbreviation for "built-in test equipment."

Bourdon Tube -- A curved or twisted tube whose end rotates when pressure is

applied to the inside of the tube.

Boxcar Filter -- Ideal electrical filter with flat amplitude and linear phase

response and with infinite attenuation at frequencies beyond design filter

limits.

Built-in Test Equipment — Any device which is functionally separate from, but

permanently connected to, the prime equipment and used for the express

purpose of testing the prime equipment. (See "BITE")

Burn In -- The operation of components or units prior to their ultimate

application intended to stabilize their characteristics and to identify

early failures.

-CCalibration -- A test during which known values of measurand are applied to a sensor under specified conditions and the corresponding output readings

recorded.

Calibration Curve -- A graphical representation of the calibration cycle.

Calibration Cycle -- The application of known values of measurand and the

recording of corresponding output readings over the full (or specified

portion) range of a sensor in an ascending and descending direction.

Calibration Interval -- The specified time interval between calibrations needed

to assure knowledge of effects of time and use on the performance

characteristics of the sensor.

10-3
Calibration Traceabil ity — The ability to compare a sensor calibration,

through a specified step-by-step process, with an instrument or group of

instruments calibrated by the National Bureau of Standards. The estimated

error incurred in each step must be known.

Calibration Uncertainty — The maximum calculated error in sensor output due to causes not attributable to the sensor.

Capsule -- An enclosure made up of two corrugated diaphragms used in pressure

measurement.

Center of Seismic Mass — The point within an acceleration sensor where

acceleration forces are considered to be summed.

Checkout Equipment — See test equipment.

Compensation — Provision of a supplemental device, circuit, or special

materials to counteract known sources of error.

Completion Network — Passive components, external to a sensor, which complete

the electrical network to form a complete bridge or similar array to

enhance signal conditioning.

Condition Monitoring -- Monitoring performed to assess the functional state of

equipment(s) by measurement of selected static and dynamic physical

characteristics.

Corrective Maintenance — Maintenance performed to restore a failed or degraded

equipment. Corrective maintenance includes fault isolation, repair or replacement of defective units, alignment, and checkout.

Creep -- Change in output occuring over a specified time period while the

measurand and all environmental conditions are held constant. (See also

"drift")

Critically Damped -- See damping.

-DDamping -- The energy-dissipating characteristic of a sensor which, together

with its natural frequency, determines the limit of frequency response and

the response time characteristics. In response to a step function of

measurand, an underdamped (periodic) system oscillates about its final

steady-state value before coming to rest at the value, an overdamped

(aperiodic) system comes to rest without overshoot, and a critically

damped system is at the point of change between the underdamped and

overdamped conditions.

Damping Ratio — The ratio of the actual damping to that required for critical

damping. (See "Damping")

10-4
DAS — Abbreviation for "data acquisition system."

Data Reduction -- The process of transforming masses of raw or experimentally

obtained data, usually gathered by instrumentation, into useful, ordered,

or simplified intelligence.

Dead Volume -- The total volume of the pressure port cavity of a pressure

sensor with room barometric pressure applied.

Defect — A characteristic which does not conform to applicable specification

requirements and which adversely affects or potentially affects the

quality of a device.

Degradation Gradual deterioration in performance as a function of time.

Derating The intentional reduction of stress/strength ratio in the

application of an item, usually for the purpose of reducing the occurrence

of stress-related failures.

Diagnostic Phenomenon -- A physical event or condition reflecting or relatable

to the functional condition of an equipment component.

Dielectric Withstand Voltage — The limiting voltage used to specify the

ability of insulated portions of a sensor to withstand a specified

overvoltage for a specified time without arcing or conduction above a specified current value across the insulation.

Diffuse-Field Response -- Frequency response of a piezoelectric sound-pressure

sensor with the sound incident from random directions.

Digital Output — Sensor output that represents the magnitude of the measurand

in the form of a series of discrete quantities or steps. (See analog

output)

Dither — The application of Intermittent or oscillatory forces just sufficient

to minimize static friction within a sensor.

Doppler Effect — The apparent change in frequency caused by relative motion

between the frequency source and the observer.

Downtime -- The period of time during which an item is not in a condition to

perform its intended function.

D/P — Abbreviation for "differential pressure."

Drift -- An undesired change in output over a period of time, which change is

not a function of the measurand. (See also "creep")

Durability -- The ability of a sensor to continue to perform its measurement

function in adverse environments and over an extended period of time.

(See "stability" for quantitative description of durability.)

10-5
Dynamic Calibration -- A calibration performed under room conditions and in the

absence of any vibration or shock, unless the latter is the measurand.

The applied measurand varies with time in a prescribed manner during the

cal i oration.

Dynamic Characteristics -- Those characteristics of a sensor which relate to its response to variations of the measurand with time.

-EEl ectromagnetic Field Sensitivity -- The maximum output of a sensor in response

to a magnetic field of specified amplitude and frequency; usually

expressed in gauss equivalent to a stated fraction of the measurand.

End Points -- Sensor outputs at the upper and lower limits of the specified

range.

End-Point Line — The straight line between the end points.

End-to-End Calibration -- A calibration during which a known actual or simulated measurand input is applied to a sensor and the corresponding

system output recorded.

Environmental Conditions — Specified external conditions (shock, vibration,

temperature, etc.) to which a sensor may be exposed during shipping,

storage, handling, and operation.

Environmental Conditions, Operating -- Environmental conditions during

operation during which the sensor must perform in some specified manner.

Error -- The algebraic difference between the indicated value and the true

value of a measurand, usually expressed in percent of full-scale output,

but some times expressed in percent of the output reading of the sensor.

Error Band -- The band of maximum deviations of output values from a specified

reference line or curve due to causes attributable to the sensor. The error oand should be specified, and verified, over at least two

calibration cycles so as to include repeatability. The band of allowable

deviations is usually expressed as + _ percent of full-scale output

UFSO), whereas in test and calibration reports the band of maximum actual

deviations is expressed as + _ percent, - _ percent of full-scale

output.

Excitation -- An external electrical voltage or current required for the proper

operation of a sensor, as distinguished from the measurand which is the

physical quantity to be measured.

10-6
-FFailure Termination of the ability of an item to perform its required

function.

Failure Analysis — The logical, systematic examination of an item or its

diagrams(s) to identify and analyze the probability, causes, and

consequences of potential or real failures.

Failure, Catastrophic -- Failures that are both sudden and complete.

Failure Mode -- The way in which a unit, equipment, or system deteriorates,

malfunctions, or fails.

Failure, Random -- Any failure whose cause and/or mechanism make its time of occurrence unpredictable, but which is predictable in a probabilistic or statistical sense.

Failure Rate -- The number of failures of an item per unit measure of life

(time, cycles, etc.). During the useful life period, the failure

rate is considered constant.

Failure, Wearout -- A failure that occurs as a result of deterioration

processes or mechanical wear and whose probability of occurrence increases

with time.

Fault — An attribute which adversely affects the reliability of a device.

FDM -- Abbreviation for "frequency division multiplex."

Floating Point ~ A method used by computers to preserve the significant

figures in a number by writing the numbers as a decimal fraction

multiplied by a power of ten.

FM — Abbreviation for "frequency modulation."

Free-Field Frequency Response -- The ratio, as a function of frequency of the

output of a sound-pressure sensor in a sound field to the sound pressure

existing at the sensor location in the absence of the sensor.

Frequency Division Multiplex -- A method of transmitting data from multiple

sources over the same link by assigning a different frequency to each source.

Frequency, Natural -- The frequency of free (not forced) oscillations of the

sensing element of a fully assembled sensor; also defined as the frequency

of a si nusoi dally applied measurand at which the sensor output lags the

measurand by 90 degrees.

Frequency Output Sensor output in the form of a frequency which varies as a function of the applied measurand (e.g. angular speed, flow rate).

10-7
Frequency Resonant — The measurand frequency at which a sensor responds with

maximum output amplitude; when major amplitude peaks occur at more than one frequency, the lowest of these frequencies is the resonant frequency.

A peak is considered major when it has an amplitude at least 1.3 times the

amplitude at the frequency to which the specified frequency response is

referred.

Frequency Response -- The change with frequency of the ratio of sensor output

amplitude to measurand amplitude (and of the phase difference between sensor output and measurand) for a si nusoi dally varying measurand applied

to a sensor within a stated range of measurand frequencies. Frequency

response should be referred to a frequency within the stated range and to

a specific measurand value.

Frequency Response, Calculated -- The frequency response of a sensor calculated

from its transient response, its mechanical properties, or its geometry,

and so identified.

Frequency, Ringing -- The frequency of the oscillatory transient occurring in a sensor output as a result of a step change in measurand.

Friction Error « The maximum change in output at any measurand value within a specified range before and after minimizing friction within the sensor by

dithering.

Friction-Free Error Band The error band applicable at room conditions with

friction within the sensor minimized by dithering.

FSO Abbreviation for "full-scale output."

Full -Scale — See "Range."

Full-Scale Output — The algebraic difference between end points.

-GGage Factor -- The ratio of the relative change of resistance to the relative

change in length of a resistive strain sensor (strain gage).

Gage, Nude -- A bul bless thermionic ionizing vacuum sensor for direct

installation in vacuum vessels.

Gage Pressure ~ Pressure referenced to atmospheric pressure.

Grounded, Ungrounded -- Refers to the presence or absence of an electrical

connection between the "low" side of a sensor element and the sensor case

or the portion of the sensor intended to be in contact with the test

structure. An ungrounded sensor should be further characterized by

stating "internally ungrounded" or "grounded by means of a separate

stud."

10-8
-HHall Effect -- The potential gradient across a conductor which experiences a magnetic field at right angles to the current in the conductor. The

potential gradient is perpendicular to both the current in the conductor

and the magnetic field.

Harmonic Content — Distortion in the form of harmonics in the sinusoidal

output of a sensor.

Hooke's Law — The deformation of a rigid body is proportional to the stress

applied to the body provided the elastic limit of the material is not

exceeded.

Hysteresis — The maximum difference in output, at any measurand value within

the specified range, when the value is approached first with increasing

and then with decreasing measurand. Friction error is included unless

dithering is specified. Hysteresis is expressed as percent of full-scale

output during any one calibration cycle.

-IIAT Abbreviation for "individual acceptance test."

Incipient Failure -- A condition wherein the first signs of failure become

apparent by an acceptable means of detection.

Infant Mortality — High failure rate during the early life of a new equipment

caused by faulty components or built-in flaws. This failure rate

decreased rapidly and stabilizes when the weak units have died out.

Input Impedance -- The impedance presented to the excitation source, measured

across the excitation terminals of a sensor. Unless otherwise specified,

input impedance is measured at room conditions, with no measurand applied,

and with the output terminals open-circuited.

Instrumentation -- Those devices (electrical, mechanical, magnetic, chemical,

optical) used to test, observe, measure, monitor, alter, generate, record,

calibrate, manage, or control physical or chemical properties, actions, or other characteristics.

Insulation Resistance -- The resistance measured between specified insulated

portions of a sensor when a specified dc voltage is applied at room conditions unless otherwise stated.

Isolating Element -- A movable membrane, usually of metal, that physically

separates the measurand fluid from the sensing element. Its purpose is to

provide material compatibility with the measured fluid while maintaining

the performance integrity of the sensing element. Usually this membrane

10-9
is considerably more flexible than the sensing element and is coupled to

the sensing element by a transfer fluid.

Interchangeable ity Error -- The error band defined by the maximum deviation

obtained when a sensor is replaced by another sensor of the same type with

equivalent measurand inputs and environmental conditions, usually

expressed in units of measurand.

-JJerk -- Time rate of change of acceleration; expressed in g per second, m per

second-^, or feet per second^.

-K-

-LLeast-Squares Line -- The straight line for which the sum of the squares of the

residuals (deviations) is minimized.

LED — Abbreviation for "light emitting diode."

Life, Cycling — The specified minimum number of full -range excursions or specified partial -range excursions over which a sensor will operate as specified without changing its performance beyond specified tolerances.

Life, Operating -- The specified minimum length of time over which the

specified continuous and intermittent rating of a sensor applies without

change in sensor performance beyond specified tolerances.

Life, Storage — The specified minimum length of time over which a sensor can

be exposed to specified storage conditions without changing its

performance beyond specified tolerances.

Linearity — The closeness of a calibration curve to a specified straight line,

expressed as a percentage of full-scale output. It is the maximum

deviation of any calibration point from the specified line during any one calibration cycle.

Linearity, End Point — Linearity referred to the end-point line.

Linearity, Least Squares -- Linearity referred to the least-squares line.

Load Impedance — The impedance presented to the output terminals of a sensor

by the associated external circuitry.

Loading Error -- Error due to the effect of the load impedance on sensor

output.

10-10
LSB -- Abbreviation for "least significant bit."

-MMagnetic Damping -- Damping accomplished by using the current induced in

electrical conductors by changes in a magnetic flux.

Maintainability -- The characteristic of design and installation which

expresses the probability that an item will be retained in, or restored

to, a specified condition within a given period of time when maintenance

is performed in accordance with prescribed procedures and resources.

Maintenance -- All actions required to keep equipment (hardware) or programs

(software) in satisfactory working condition, including tests,

measurements, replacements, adjustments, repairs, program copying, and

program improvement.

Maintenance, Corrective -- Maintenance performed to restore a system to operate

after a failure.

Maintenance Monitoring -- Monitoring performed to determine when corrective

maintenance actions are required.

Maintenance, Preventive -- Systematic maintenance performed in an attempt to

detect incipient failures.

Manual Test Equipment — Test equipment that requires separate manipulations

for each task (for example, connection to signal to be measured, selection

of suitable range, and insertion of stimuli).

Maximum (Minimum) Ambient Temperature -- The highest (lowest) ambient

temperature that a sensor can withstand, with or without excitation

applied, without being damaged, or subsequently showing a performance

degradation beyond specified tolerances.

Maximum Excitation -- The maximum value of excitation voltage or current that

can be applied to a sensor at room conditions without causing damage or performance degradation beyond specified tolerances.

Mean Time Between Failures -- For a particular interval, the total functioning

life of a population of an item divided by the total number of failures

within the population during the measurement interval -involved.

Mean Time Between Maintenance -- The mean of the distribution of the time

intervals between maintenance actions, either preventive, corrective, or

both.

Mean Time to Repair -- The mean of the distribution of time intervals between

failure of an item and its repair or replacement.

10-11
Measurand -- A physical quantity, property, or condition which is measured.

The term "measurand" is preferred to "input," "parameter to be measured,"

"physical phenomenon," "stimulus," and "variable."

Measured Fluid -- The fluid which comes in contact with the sensing element.

The chemical and/or physical properties of this fluid must be considered

in selecting a sensor.

Mechanical Isolation of Transduction Element -- The internal construction of a sensor which allows forces (particularly bending forces and external

pressures) to be applied to the sensor case whith negligible resulting

forces on the sensor element.

Median Time to Failure -- Time interval during which half of all identical

units will have failed.

Mission Time -- That element of uptime during which the item is performing its

designated mission.

Modem — Acronym for "modulator /demodulator."

Monitoring -- The continuous observation of diagnostic phenomena for an indication of a change reflecting a change in the performance of an equipment component.

Mounting Error — Error resulting from mechanical deformation of a sensor caused by mounting the sensor and making all electrical and measurand

connections.

MTBF -- Abbreviation for "mean time between failures."

MTBM -- Abbreviation for "mean time between maintenance."

MTTF -- Abbreviation for "median time to failure."

MTTR — Abbreviation for "mean time to repair."

-NNatural Frequency -- See frequency, natural

.

Noise Any spurious variation in electrical output not present in the input.

In a potentiometric sensor, noise is defined quantitatively in terms of an equivalent parasitic transient resistance appearing between the wiper and

the resistance element while the shaft is being moved.

Non-Volatile Memory -- A computer memory which retains stored information when

power to the system is turned off.

Nude Gage -- See gage, nude.

10-12
Null — A condition, such as of balance, which results in a minimum absolute

value of output.

-0-

On-Line Testing -- Any method of testing which allows the unit under test to be

tested in its operational environment.

Operating Temperature Range -- The range of ambient temperature within which a sensor must perform to the requirements of the "temperature error" or "temperature error band."

Output — The electrical quantity, produced by a sensor, which is a function of

the applied measurand.

Output Impedance -- The impedance across the output terminals of a sensor. Unless otherwise specified, output impedance is measured at room conditions, with no measurand applied, and with the input terminals either

open-circuited or short-circuited (to be specified).

Output Noise -- The rms, peak, or peak-to-peak (as specified) a-c component of

a sensor's d-c output in the absence of measurand variations.

Overdamped -- See "Damping."

Overload -- The maximum magnitude of measurand that can be applied to a sensor without causing a change in performance beyond specified tolerance.

Overshoot -- The amount by which the amplitude of the output of a sensor exceeds the final steady output value in response to a step change in the

measurand.

-PPassive Sensor -- A sensor requiring no source of power other than the signal

being measured.

PCM ~ Abbreviation for "pulse code modulation."

Performance Monitor -- A device which continuously or periodically scans a selected number of test points to determine if the uni t-under-test is

operating within specified limits. This device may include provisions for

the insertion of stimuli.

Performance Monitoring -- Monitoring performed to (1) detect performance

degradation, (2) predict failures, (3) isolate faults, and (4) predict

maintenance requirements by processing measurements of selected static and

dynamic characteristics of a prime equipment.

10-13
Periodic Check — A test or series of tests performed at designated intervals

to determine if all elements of the unit-under-test are operating within

their designated limits.

Phase Shift -- The amount of time by which the output of a sensor lags a si nusoi dally varying measurand, usually expressed in degrees or as a fraction of a cycle of the measurand frequency.

Pickup -- See "Sensor."

Pi rani Gage -- A compensated, thermoconducti ve vacuum sensor which measures low

gas pressures by measuring the resistance of a heated filament whose

temperature and, hence, resistance is a function of gas pressure.

Poisson's Ratio -- If a rod of elastic material is stretched, the ratio of the

contraction of the lateral dimension to the elongation of the length is a constant.

Polarity — The relationship between sensor output and the direction of the

applied measurand. Polarity is taken as "standard" when acceleration

directed from the mounting surface into the body of the accelerometer

produces a positive charge or voltage on the "high" side of the sensor. Also, a positive (increasing) pressure applied to the diaphragm of a pressure sensor produces as "standard" a positive-going output signal.

Similar considerations can be applied to other types of sensors.

Potentiometric Element — The resistance part of a transduction element upon

which the wiper (movable contact) slides and across which excitation is

applied. It may be constructed of a continuous resistance or of small

diameter wire wound on a form (mandrel ).

Pressure Connection (Pressure Port) — The opening and surrounding surface of a sensor used to permit access by the measured fluid to the sensing or isolating element. This can be a standard industrial or military fitting,

a tube hose fitting, or a hole (orifice) in a base plate. For

differential pressure sensors, there are two pressure connections: the

measurand and reference ports.

Prime Equipment -- An equipment or system that is to be monitored. (See also

"Unit-under-test.")

Prognosis — The art or act of predicting a future condition on the basis of

present signs and symptons.

PSF -- Abbreviation for "presampling filter."

Pulse Code Modulation -- A modulation method in which each element of

information is represented by the presence or absence of a pulse.

Pyrometer -- A device which measures temperatures, usually by means of

radiation or optical phenomena, without contacting the body or substance

to be measured.

10-14
-QQ -- Amplification factor at the resonant frequency; a measure of the sharpness

of resonance.

-RRandomness — The occurrence of an event in accordance with the laws of

chance.

Ramp Function -- A sensor input whose amplitude is a linear function of time.

Range -- The measurand values, specified by their upper and lower limits, over which a sensor is intended to measure.

Rangeability -- The ratio between the maximum upper and minimum lower range

values for a single sensor.

Recovery Time -- The time interval after a specified event (e.g., overload,

excitation transient, output short circuiting, etc.) before a sensor will

again perform within its specified tolerances.

Redundancy — Provision of more than one means of performing a function.

Redundancy, Standby -- Redundancy wherein the alternative means of performing a function is inoperative until needed, and is switched on by failure of the

primary means of performing the function.

Reference Port -- See "Pressure Connection."

Reference Pressure -- The pressure relative to which a differential pressure

sensor measures pressure.

Reference Pressure Error -- In a differential pressure sensor, the error

resulting from variations of the reference pressure within the applicable

reference pressure range.

Reliability — The characteristic of an item expressed by the probability that

it will perform a required function under stated conditions for a stated

period of time.

Reliability Engineering -- The science of designing systems by including those

factors which will assure the required degree of reliability.

Reliability, Inherent -- The potential reliability present in the design of an

i tern.

Reliability, Intrinsic — The probability that a device will perform its

specified function based on a statistical analysis of the failure rates

10-15
and other characteristics of the parts and components which comprise the

device.

Repeatability -- The ability of a sensor to reproduce output readings when the same measurand value is applied to it consecutively under the same conditions between output readings expressed as a percentage of full-scale

output. Two calibration cycles are used to determine repeatability unless

otherwise specified.

Resolution -- The magnitude of output step changes as the measurand is

continuously varied over the range. This term relates primarily to

potentiometric transducers.

Resonances -- Amplified vibrations within narrow frequency bands of sensor components observable in the output as vibration is applied along

specified sensor axes.

Resonant Frequency -- See "Frequency, Resonant."

Response Time — The length of time required for the output of a sensor to rise

between specified percentages of its final value as a result of a step

change of measurand. Unless otherwise stated, the specified percentages

are 10 and 90 percent of the final value.

RF — Abbreviation for "radio frequency."

Ringing Frequency -- See "Frequency, Ringing."

Ringing Period -- The period of time during which the amplitude of output

oscillations excited by a step change in measurand exceeds the steadystate output value by more than a specified amount.

Room Conditions -- Ambient environmental conditions under which sensors most

commonly operate:

a) Temperature: 25 +10 °C (77 +18 °F)

b) Relative humidity: 90 percent or less

c) Barometric pressure: 26 to 32 inches Hg

Tolerances closer than those shown are frequently specified for sensor calibration and test environments.

RTD -- Abbreviation for "resistance temperature detector," the temperatureresponsive element of a resistance thermometer.

-SScreening Test -- A test or combination of tests intended to remove unsatisfactory items or those likely to exhibit early failures.

10-16
Sealed Reference Differential Pressure Sensor -- Sensor which measures the

difference in pressure between an unknown pressure and the pressure of a fluid in an integral, sealed reference chamber.

Self Test A test or series of tests performed by a device upon itself to

determine whether or not it is operating within designed limits. This

includes test programs which check out the performance status and

readiness of computers and automatic test equipment.

Semiautomatic Test Equipment Any automatic testing device which requires

human participation in the decision-making, control, or evaluative

functions.

Sensing Element — That part of a sensor which responds directly to the

measurand. This term is preferred to "primary element," "primary

detector," and "primary detecting element."

Sensitivity -- The ratio of the change in sensor output to the corresponding

change in the value of the measurand. The slope of the straight line

representing the calibration curve.

Sensitivity Shift -- A change in the slope of the calibration curve.

Settling Time -- The time required after the application of a step change in

measurand for a sensor output to settle within a small percentage (usually

5 percent) of its final value.

Shock — A substantial disturbance characterized by an abrupt rise and decay of

acceleration from a constant value.

Shunt Calibration Resistor -- A shunt resistor which, when placed across a specified element of the electrical circuit of a sensor, will

electrically simulate a specified percentage of the sensor's full-scale

output at room temperature.

Shunting Resistance — The electrical resistance observed between the two

terminals of a piezoelectric sensor or its integral cable.

Signal -- A manifestation of an event containing information of interest.

Signature -- A characteristic of a waveform which is related to a known

condition of interest; a combination of signals characteristic of some known conditions of a device.

Software — Programs and documentation required for the operation or maintenance of a system.

Source Impedance -- The impedance which the excitation supply presents to the

excitation terminals of a sensor.

Span The algebraic difference between the limits of the range.

10-17
SPG — Abbreviation for "sinusoidal pressure generator."

SPS -- Abbreviation for "samples per second."

Stability — The ability of a sensor to retain its performance characteristics

for a relatively long period of time, expressed as a percentage of fullscale output for a stated period of time. Unless otherwise stated

specifically, stability is the ability of a sensor to reproduce the output

readings obtained during its original calibration at room conditions for a specified period of time. (See "durability")

Static Calibration — A calibration performed under room conditions and in the

absence of any vibration, shock, or acceleration unless the latter is the

measurand. The applied measurand is invariant with time during each step

of the calibration.

Step Function — An infinitely fast (rise time approaching zero) change in the

value of a measurand.

Step Stress Test — A test consisting of several stress levels applied

sequentially to a sample for periods of equal duration; during each period

a stated stress level is applied, and the stress level is increased from

one step to the next.

Stimulus -- See "Measurand."

Storage Life — See "Shelf life."

Strain Error — The error resulting from a strain imposed on a surface to which

a sensor, other than a strain sensor (strain gage), is mounted.

Strain Sensitivity — Sensitivity to strains applied to the base of a sensor by

bending, in the absence of any rigid-body motion of the sensor. It is

expressed as the equivalent measured level for a unit strain in the plane

of the base.

Stress, Component — The stresses on component parts during testing or usage

which affect the failure rate and hence the reliability of the parts.

Voltage, power, temperature, and thermal environments stress are included.

Survivability — A measure of the degree to which an item will withstand

hostile environments and not suffer abortive impairment of its ability to

accomplish its designated mission.

System Effectiveness -- A measure, which may be expressed as a function of

availability, dependability, and capability, of the degree to which an item can be expected to achieve a set of specific mission requirements.

10-18
-TTDM — Abbreviation for "time division multiplex."

TDME -- Abbreviation for "test, measurement, and diagnostic equipment."

Temperature Error -- The maximum change in sensor output, at any measurand

value within the specified range, when the sensor temperature is changed

from room temperature to specified temperature extremes.

Temperature Error Band — The error band applicable over stated environmental

temperature limits.

Temperature Gradient Error -- The transient deviation in the output of a sensor

at a given measurand value when the ambient temperature or the measured

fluid temperature changes at a specified rate between specified

magnitudes.

Temperature Range, Operating — See "Operating Temperature Range."

Terminal Line -- A theoretical line for which the end points are 0 and

100 percent of both measurand and output.

Test -- A procedure or action to determine under real or simulated conditions

the capabilities, limitations, characteristics, effectiveness, reliability,

or suitability of a material, device, system, or method.

Test Analysis — The examination of test results to determine whether the

device is in an operationally ready state, or to determine the reasons

for, or location of, a malfunction.

Test Equipment (Checkout Equipment) -- Electric, electronic, chemical, optical,

mechanical, hydraulic, or pneumatic equipment, either automatic,

semi-automatic, manual, or any combination thereof, which is required to

perform the test or checkout function.

Test Point -- A convenient safe access to an equipment, system, or circuit so that a significant quantity can be measured or introduced.

Test-to-Failure -- The practice of inducing increased electrical and mechanical

stresses in a device in order to determine its maximum capability so that

the derating required to extend the life of the device in subsequent

applications can be determined.

Theoretical Slope Line -- A line representing the calibration points with

theoretical end points at 0 percent and 100 percent of both measurand

and output.

Thermal Sensitivity Shift — Sensitivity shift due to changes of the ambient

temperature from room temperature to the specified limits of the operating

temperature range.

10-19
Thermal Zero Shift — Zero shift due to changes of the ambient temperature from room temperature to the specified limits of the operating temperature

range.

Thermometer -- A temperature-measuring device which is inserted into or attached to the body or substance that is to be measured.

Threshold -- The smallest change in a measurand that will result in a measurable change in sensor output. When the threshold is influenced by

the measurand values, these values must be specified.

Throughput Rate -- The total number of data points or measurands that a data

acquisition system or automatic test equipment can process in a given

period of time; a measure of the speed of the system.

Time Division Multiplex -- A method of transmitting data from multiple sources

over the same link by assigning a distinct time period to each source and

transmitting the data in time sequence.

Tolerance -- The total permissible variation of a quantity from a designed

val ue.

Transducer -- See "Sensor."

Transduction Element — The electrical portion of a sensor in which the output

originates.

Transfer Fluid -- A degassed liquid used to provide hydraulic coupling of the

pressure between the isolating and sensing elements of a pressure sensor.

Transfer Function -- The ratio of the output of a sensor to its input,

expressed in the frequency or time domain.

Transient Response -- The response of a sensor to a step change in measurand.

Transient Temperature Error -- The output of a sensor resulting from a specified transient temperature change within a specified operating

temperature range. The associated capacitance and load resistance, as

well as the time after the applied transient at which the amplitude peak

occurs, must be specified.

Transmitter — A term used synonymously with sensor in process - control

applications .

Transverse Sensitivity — The sensitivity of a sensor to transverse

acceleration or other transverse measurand, usually expressed in percent

of the sensitivity of the sensor along its sensitive axis.

Two Phase -- A fluid state consisting of a mixture of liquid with gas or vapors.

10-20
-uUnderdamped -- See "Damping."

Ungrounded — See "Grounded."

Unit-Under-Test -- The prime equipment or portion thereof whose proper

functions are to be monitored by automatic test equipment.

Uptime — The period of time during which an item is in condition to perform

its intended function. (See Mission Time)

UUT — Abbreviation for "unit-under-test."

-VVapor Pressure -- At a given temperature, the pressure of a vapor at which the

liquid and vapor are in equilibrium. Vapor pressure increases with

temperature.

Variable -- See "Measurand."

Venturi Meter — An instrument which measures the pressure difference created

by a constriction in a pipe to determine the rate of flow of a fluid.

Vibration Error -- The maximum change in output, at any measurand value within

the specified range, when vibration levels of specified amplitude and

range of frequencies are applied to the sensor along specified axes.

Viscosity -- The property of a liquid that presents a resistance to flow.

Viscosity, Kinematic -- The ratio of absolute viscosity to density: the SI

unit is the meter2 /s.

Viscous Damping -- Damping affected by the viscosity of fluids.

Volatile Memory -- A computer memory in which stored information is retained

only while power is applied to the system.

Voltage Ratio -- In a potentiometric sensor, the ratio of output voltage to

excitation voltage, usually expressed in percent.

-WWarm-Up Period -- The period of time, starting with the application of

excitation to the sensor, required to assure that a sensor will perform

within all specified tolerances.

10-21
Wearout — The process of attrition which results in an increase of failure

rate with increasing age (cycles, time, miles, events, etc., as applicable

for the item).

Wet-Dry — Configuration of differential pressure sensor in which a liquid

measurand is applied to one port, and a gaseous (dry) referenced to the

other port.

Wet-Wet — Configuration of differential pressure sensor in which liquid

measurands can be applied to both ports.

Wheatstone Bridge -- An electrical network in which the outputs of two

resistive dividers are compared by a sensitive galvanometer to obtain

accurate resistance measurements.

White Noise -- Signal with a mean square spectral density value constant at all

frequencies.

-YYield Margin -- The amount of an item of a particular quality level obtained by

selecting from the total production those items which fall within the

desired tolerance range, usually expressed as a percentage of total

productions.

-ZZero-Measurand Output -- The output of a sensor, under room conditions unless

otherwise specified, with normal excitation and zero measurand applied.

Zero Shift -- A change in the zero-measurand output at room conditions over a specified period of time, usually characterized by a parallel displacement

of the entire calibration curve.

10-22
11. RESOURCES

11.1 Manufacturers of Sensors and Related Items

In order to enhance the usefulness of the handbook, it was thought

desirable to append a listing of manufacturers of sensors and related items.

It should be clearly understood that this listing is, of necessity, incomplete.

Changes in the field are rapid and even with unlimited resources it would not

be possible for such a listing to be totally complete or up-to-date or correct.

The listing of, or exclusion of, any particular manufacturer does not

constitute an endorsement or condemnation of that manufacturer in any way,

shape, or form by the writer or publishers of this handbook. The information

was obtained from a variety of sources. Much of it was obtained, with

permission, from tables in "Measurement and Control" (the Journal of the

Measurement and Control Society) Pittsburgh, PA 15216, various volumes 1977 to

1979. Subsequent editions of the handbook will attempt to keep this section

updated.

Manufacturers are listed alphabetically within each class of device. The

devices are arranged by measurands and further by transduction principles

(class of device).

11-1
PRESSURE

Strain Gage Pressure Sensors

Action Instruments Co., Inc.

8601 Aero Drive

San Diego, CA 92123

(714) 279-5726

All tech, A Cutler Hammer Co.

19535 E. Walnut Drive

City of Industry, CA 91748

(213) 965-4911

B & F Instruments Division

FX Systems

CPO 1818

Kingston, NY 12401

(914) 338-0515

BLH Electronics

42 Fourth Avenue

Waltham, MA 02254

(617) 890-6700

barber-Colman Industrial

Instruments Div.

1700 Rock Street

Rockford, IL 61101

(815) 877-0241

Bell & Howell

CEC Division

360 Sierra Madre Villa

Pasadena, CA 91109

(213) 796-9381

Brewer Engineering Labs, Inc.

P.O. Box 288

Marion, MA 02738

(617) 748-0103

C. J. Enterprises

P.O. Box 834

Tarzana, CA 91356

(213) 966-4131

Celesco Transducer Products Inc.

P.O. Box 1457

7800 Deering Avenue

Canoga Park, CA 91304

(213) 884-6860

Cognition, Inc.

765 Ravendale Drive

Mountain View, CA 94043

(415) 969-8300

Conrac Corporation

Three Landmark Square

Stamford, CT 06901

(203) 348-2100

Consolidated Controls Corp.

15 Durant Avenue

Bethel, CT 06801

(203) 743-6721

Control Process, Inc.

201 Atwater Street

Plantsville, CT 06479

(203) 628-4721

D.J. Instruments Inc.

11 E. Esquoirm Road

N. Billerica, MA 01862

(617) 667-5301

Data Instruments

4 Hartwell Place

Lexington, MA 02173

(617) 861-7450

Degamo, Inc.

500 Ashland Avenue

Chicago Heights, IL 60411

(312) 754-3131

Digilin Inc. /Dynamic Sciences

(See: Dynamic Sciences)

11-2
Dynamic Sciences International Inc

16150 Stagg Street

Van Nuys, CA 91406

(213) 893-6341

Dynisdo, Inc.

20 Southwest Park

westwood, MA 02090

(617) 326-8210

El dec Corporation

16700 13th Ave., West

P.O. Box 100

Lynwood, WA 98036

(206) 743-1313

Electronic Flo-Meters, Inc.

P.O. Box 38269

Dallas, TX 75238

(214) 349-1982

Electrosyn Corporation

480 Neponset Street

Canton, MA 02021

(617) 828-2840

Encore Electronics, Inc.

RD 2, Route 50

Saratoga Springs, NY 12866

(518) 584-5354

Endevco

30700 Rancho Viejo Road

San Juan Capistrano, CA 92675

(714) 493-8181

Entran Devices, Inc.

145 Paterson Avenue

Little Falls, NJ 07424

(201) 785-4060

FX Systems

CPO 1818

Kingston, NY 12401

(914) 338-0515

Fatigue Dynamics Inc.

P.O. Box 2533

Dearborn, MI 48123

(313) 273-8270

Foxboro/I.C.T. Inc.

1750 Junction Avenue

San Jose, CA 95112

(408) 998-8720

GSE Inc.

23640 Research Drive

Farmington Hills, MI 48024

(313) 476-7875

Genisco Technical Corporation

18435 Susana Road

Compton, CA 90221

(213) 537-4570

Gentran, Inc.

1290 Hammerwood Avenue

Sunnyvale, CA 94086

(408) 734-5060

Gould, Inc.

Measurement Systems Division

2230 Statham Blvd.

Oxnard, CA 93030

(805) 487-8511

Harwood Engineering Co., Inc.

South Street

Walpole, MA 02081

(617) 668-3600

S. Hi mmel stein & Company

2500 Estes Avenue

Elk Grove Village, IL 60007

(312) 439-8181

Hottinger Baldwin Measurements, Inc.

10 Strathmore Road

Natick, MA 01760

(617) 655-0950

11-3
ICT Instruments, Inc.

5335 McDonnel Avenue

Los Angeles, CA 90066

(213) 390-4043

I.C. Transducers, Inc.

(See: Foxboro/I.C.T., Inc.)

ITT Barton

Box 1882

City of Industry, CA 91749

(213) 961-2547

Kaman Sciences Corporation

P.O. Box 7463

Colorado Springs, CO 80933

(303) 599-1500

Ki stler-Morse

13227 Northrup Way

Bellevue, WA 98005

(206) 641-4200

Konigsberg Instruments, Inc.

2000 E. Foothill Blvd.

Pasadena, CA 91107

(213) 449-0016

Kistler Instrument Corp.

75 John Glenn Drive

Amherst, NY 14120

(716) 691-5100

Kulite Semiconductor Products Co.

1039 G Hoyt Avenue

Ridgefield, NJ 07657

(201) 945-3000

LFE Corporation

Process Control Division

1601 Trapelo Road

Waltham, MA 02154

(617) 890-2000

Lake Shore Cryotronics, Inc.

64 E. Walnut Street

Westerville, OH 43081

(614) 891-2243

Lebow Associates

1728 Maplelawn Road

Troy, Mr 48099

(313) 643-0220

MBIS, Inc.

MB Products

25865 Richmond Road

Bedford Heights, OH 44146

(216) 292-5850

MKS Instruments, Inc.

22 Third Avenue

Burlington, MA 01803

(617) 272-9255

Measurements Group

P.O. Box 27777

Raleigh, NC 27611

(919) 365-3800

Micro-Strain, Inc.

Spring City, PA 19475

(215) 948-4550

Millar Instruments

P.O. Box 18227

Houston, TX 77023

(713) 923-9171

Moore Industries, Inc.

166650 Schoenborn Street

Sepulveda, CA 91343

(213) 897-7111

Narco Bio-Systems, Inc.

7651 Airport Blvd.

P.O. Box 12511

Houston, TX 77017

(713) 644-7521

Paine Instruments

2401 S. Bay view Street

Seattle, WA 98144

(800) 426-0366

(206) 723-1705

Precise Sensors Inc.

235 W. Chestnut Street

Monroevia, CA 91016

(213) 358-4578

11-4
Pressure Products Inc.

Duriron Company, Inc.

900 Louis Drive

Warminister, Pa 18974

(215) 675-1600

Pressure Systems Inc.

17 Research Drive

Hampton, VA 23666

(804) 838-1234

Schaevitz Engineering

P.O. Box 505

Camden, NJ 08101

(609) 662-8000

Senso-Metrics, Inc.

7775 Kester Avenue

Van Nuys, CA 91405

(213) 988-6070

Sensotec

1200 Chesapeak Avenue

Columbus, OH 43212

(614) 486-7723

Sigma Instruments, Ltd.

55 Six Point Road

Ontario, Canada M82 2X3

(416) 239-8161

Standard Controls, Inc.

(See: Paine Instrs.)

Strainsert Company

Union Hill Industrial Park

West Conshohocken, PA 19428

(215) 825-3310

Teledyne/Taber

455 Bryand Street

N. Tonawanda, NY 14120

(716) 694-4000

Trans Metrics Inc.

701 Beta Drive

Cleveland, OH 44143

(216) 461-0463

Tyco Instr. Division

(See: Data Instruments)

Uni measure Division

Konigsberg Instruments

(See: Konigsberg Instr. Inc.)

Viatran Corporation

300 Industrial Drive

Grand Island, NY 14072

(716) 773-1700

Vishay Instruments, Inc.

Photoelastic Division

63 Lincoln Highway

Malvern, PA 19355

(215) 647-5115

West Coast Research Corporation

P.O. Box 25061

2100 S. Sepulveda

Los Angeles, CA 90025

(213) 478-8833

11-5
Potenti ometric Pressure Sensors

AST Servo Systems, Inc.

930 Broadway

Newark, NJ 07104

(201) 484-4233

Ametek Controls Division

860 Pennsylvania Blvd.

Feasterville, PA 19047

(215) 355-6900

Bourns, Inc.

Adv. Department

1200 Columbia Avenue

Riverside, CA 92507

(714) 781-50/0

Bunker Ramo Instrs. Division

902 Wisconsin Street

Delavan, WI 53115

(414) 728-5531

Conrac Corporation

Three Landmark Square

Stamford, CT 06901

(203) 348-2100

Gulton Industries, Inc.

Piezo Products Division

212 Durham Avenue

Metuchen, NJ 08840

(201) 548-2800

Gulton Industries

S-C Division

1644 Whittier Avenue

P.O. Box 2176

Costa Mesa, CA 92627

(714) 642-2400

Konigsberg Instruments

(See: Uni measure)

Litton Industries

Potentiometer Division

226 3rd Street

Mt. Vernon, NY 10550

(914) 664-7733

Robinson-Hal pern

1 Apollo Road

Plymouth Meeting, PA 19462

(215) 825-9200

Sparton Southwest, Inc.

P.O. Box 1784

9621 Coors Road, NW

Albuquerque, NM 87103

(505) 898-1150

Systems Science and Software

P.O. Box 1620

LaJolla, CA 92038

(714) 453-0060

Unimeasure Division

Konigsberg Instruments

2000 E. Foothill Blvd.

Pasadena, CA 91107

(213) 449-0016

Vernitech Corporation

Division of Vernitron

300 Marcus Blvd.

Deer Park, LI, NY 11729

(516) 586-5100

11-6
Relucti ve and Linear Variable Differential Transducer Sensors

AST Servo Systems, Inc.

930 Broadway

Newark, NJ U7104

(201) 484-4233

Ametek

Controls Division

P.O. Box 152

Feasterville, PA 18960

(215) 355-6900

Automation Associates, Inc.

1339 Lawrence Drive

Newbury Park, CA 91320

(805) 498-6/87

Biotronex Lab. , Inc.

4225 Howard Avenue

Kensington, MD 20795

(301) 942-1800

C. J. Enterprises

P.O. Box 834

Tarzana, CA 91356

(213) 996-4131

Celesco Transducer Products Inc.

7800 Deering Avenue

P.O. Box 1457

Canoga Park, CA 91304

(213) 884-6860

Columbia Research Labs, Inc.

MacDade Blvd. & Bui lens Lane

Woodlyn, PA 19094

(215) 532-9464

Computer Instruments Corp.

100 Madison Avenue

Hempstead, LI, NY 11550

(516) 483-8200

Consolidated Controls Corp.

15 Durant Avenue

Bethel, CT 06801

(203) 743-6721

Electrosyn Corporation

480 Neponset Street

Canton, MA 02021

(617) 828-2840

Gulton Industries

S-C-D

1644 Whittier Avenue

Costa Mesa, CA 92627

(714) 642-2400

Kaman Sciences Corporation

P.O. Box 7463

Colorado Springs, CO 80933

(303) 599-1500

Kavlico Corporation, Inc.

20869 Plummer Street

Chatsworth, CA 91311

(213) 882-2400

The Lewis Engineering Company

Transducer Division

19-29 Sheldon Street

Norwich, NY 13815

(607) 334-3939

Robinson-Hal pern Company

One Apol lo Road

Plymouth Meeting, PA 19462

(215) 825-9200

Schaevitz Engineering

P.O. Box 505

Camden, NJ 08101

(609) 662-8000

Validyne Engineering Corporatio

19414 Londelius Street

Northridge, CA 91324

(213) 886-8488

11-7
Piezoelectric Pressure Sensors

BBN Instruments Company

Div. of Bolt, Beranek & Newman

50 Moulton Street

Cambridge, MA 02138

(617) 491-0091

Celesco Transducer Products, Inc.

P.O. Box 1457

Canoga Park, CA 91304

(213) 884-6860

Channel Industries

Box 3680

839 Ward Drive

Santa Barbara, CA 93111

(805) 967-07171

Columbia Research Labs, Inc.

McDade Blvd. & Bullens Lane

Woodlyn, PA 19094

(215) 532-9464

Degamo, Inc.

500 Ashland Avenue

P.O. BOx 653

Chicago Heights, IL 60411

(312) 754-3131

Dunegan/Endevco

30700 Rancho Viejo Road

San Juan Capistrano, CA 92675

(714) 831-9131

Gulton Industries, Inc.

Piezo Products Division

212 Durham Avenue

Metuchen, NJ 08840

(201) 548-2800

Kistler Instrument Corporation

75 John Glenn Drive

Amherst, NY 14120

(716) 691-5100

Massa Division

Dynamics Corp. America

280 Lincoln Street

Hingham, MA 02043

(617) 749-4800

Metrix Instrument Company

1711 Townhurst Drive

Houston, TX 77043

(713) 461-2131

National Controls, Inc.

1160 Hopper Lane

Santa Rose, CA 95401

(707) 527-5555

PCB Piezotronics

P.O. Box 33

Buffalo, NY 14225

(716) 684-0001

Quantum Dynamics

19458 Ventura Blvd.

P.O. Box 865

Tarzana, CA 91356

(213) 345-6828

Scientific-Atlanta Inc.

3845 Pleasantdale Road

Atlanta, GA 30340

(404) 449-2000

Gulton Industries, Inc.

S-C Division

1644 Whitter Avenue

Costa Mesa, CA 92627

(714) 642-2400

11-8
Sundstrand Data Control Inc.

Overlake Industrial Park

Redmond, WA 98052

(206) 885-3711

Transmed Scientific (formerly Biocom)

860-C Capitol io Way

San Luis Obispo, CA 934401

(805) 541-1103

Vibro-Meter Corporation

22109 South Vermont Avenue

Torrence, CA 90502

(213) 320-8410

11-9
Capacitive Pressure Sensors

Bell & Howell

360 Sierra Villa

Pasadena, CA 91109

(213) 796-9381

Computer Instruments Corp.

92 Madison Avenue

Hempstead, LI, NY 11550

(516) 483-8200

Datametrics

(See Gould Inc. Control & Systems Di v.

)

Disa Electronics

779 Susquehanna Avenue

Franklin Lakes, NJ 07417

(201) 891-9460

Engineering Dynamics Inc.

6651 S. Wellington

Littleton, CO 81020

(303) 798-3941

Gould Inc.

Control & Systems Div.

(formerly Data-metrics)

340 Fordham Road

Wilmington, MA 01887

(617) 658-5410

Hamilton Standard

Div. of United Aircraft Corp.

P.O. Box 300

Windsor Locks, CT 06096

(203) 623-1621

Hi tec Corporation

65 Power Road

Westford, MA 01886

(617) 692-4793

Kratos

403 South Raymond Ave, BIN 45

Pasadena, CA 91109

(213) 449-3090

Lion Precision Inc.

60 Bridge Street

Newton, MA 02195

(617) 969-4710

MKS Instruments Inc.

22 Third Avenue

Burlington, MA 01803

(617) 272-9255

Mechanical Technology, Inc.

MTI Instruments Division

968 Albany Shaker Road

Latham, NY 12110

(518) 785-2323 / (518) 456-4131

Parascientif ic Inc.

14827 N. E. 40th Street

Redmond, WA 98052

(206) 883-8700

Rosemount Inc.

12001 W. 78th Street

Minneapolis, MN 55435

(612) 941-5560

Ruska Instrument Corporation

6121 Hill croft

P.O. Box 36010

Houston, TX 77036

(713) 774-2533

Setra Systems

1 Strathmore Road

Natick, MA 01760

(617) 655-4645

Siltran Digital

P.O. Box 437

Silverado, CA 92676

(714) 649-2704

Sundstrand Data Control Inc.

Overlake Industrial Park

Redmond, WA 98052

(206) 885-3711

11-10
Digital Pressure Sensors

Bell & Howell

CEC Division

360 Sierra Madre Villa

Pasadena, CA 91109

(213) 796-9381

Foxboro/I.C.T., Inc.

1750 Junction Avenue

San Jose, CA 95112

(408) 998-8720

Hamilton Standard Div. of

United Aircraft Corp.

P.O. Box 300

(203) 623-1621

Ruska Instrument Corp.

Box 36010

6121 Hi 11 croft Avenue

Houston, TX 77036

(713) 774-2533

Scanivalve Inc.

P.O. Box 20005

San Diego, CA 92120

(714) 283-5851

Siltran Digital

P.O. Box 437

Silverado, CA 92676

(714) 649-2704

I. C. Transducers

(See: Foxboro/I.C.T., Inc.)

Kollsman Instrument Company

Daniel Webster Highway South

Merrimack, NH 03054

(603) 889-2500

Mensor Corporation

1055 Conrad Sauer Road

P.O. Box 55642

Houston, TX 77055

(714) 464-6228

Paroscientific Inc.

14827 N.E. 40th Street

Redmond, WA 98052

(206) 883-8700

Volumetrics

1025 W. Arbor Vitae Street

Inglewood, CA 90301

(213) 641-3747

Wallace & Tiernan Division

Pennwalt Corporation

25 Main Street

Belleville, NJ 07109

(201) 759-8000

Western Systems Inc.

P.O. Box 2133

Evergreen, CO 80439

Pneumatron

10459A Roselle Street

San Diego, CA 92121

(714) 453-4365

11-11
TEMPERATURE

Thermocouples

ARI Industries Inc.

9000 King Street

Franklin Park, IL 60131

(312) 671-0511

Acromag, Inc.

30765 Wixom Road

Wixom, MI 48096

(313) 624-1541

Action Instruments Co., Inc.

8601 Aero Drive

San Diego, CA 92123

(714) 279-5726

Acurex Corporation

485 Clyde Avenue

Mt. View, CA 94040

(415) 964-3200

All tech

A Cutler Hammer Company

19535 E. Walnut Drive

City of Industry, CA 91748

(213) 965-4911

Alberox Corporation

Industrial Park

New Bedford, MA 02745

(617) 995-1725

Alnor Instruments Company

7301 N. Caldwell Avenue

Niles, IL 60648

(312) 647-7866

Amperex Electronic Corporation

230 Duffy Avenue

Hicksville, NY 11802

(516) 931-6200

Amprobe Instrument

Div. of SOS Consolidated Inc.

630 Merrick Road

Lynbrook, NY 11563

(516) 593-5600

Atlas Wire & Cable Co., Inc.

72 N. Broadway

Yonkers, NY 10701

(914) 969-5158

B & F Instruments

Div. of FX Systems

P.O. Box 238

Cornwells Heights, PA 19020

(215) 639-7100

BLH Electronics

42 Fourth Avenue

Waltham, MA 02254

(617) 894-6700

Bailey Instruments, Inc.

P.O. Box 800

515 Victor Street

Saddle Brook, NJ 07662

(201) 845-7252

Bailey Meter Company

29801 Euclid Avenue

Wickliffe, OH 44092

(216) 943-5500

Barber-Colman Company

Industrial Instruments Div.

1706 Rock Street

Rockford, IL 61101

(815) 877-0241

11-12
Bristol Division, ACCO

929 Connecticut Ave.

Bridgeport, CT 06607

(203) 335-2511

Burns Engineering Inc.

10201 Bren Road East

Minnetonka, MN 55343

(612) 935-4400

CGS/Thermodynamics

Industrial Blvd.

Southhampton, PA 18966

(215) 355-9550

Calimatic Instruments Inc.

965 Richard Avenue

Santa Clara, CA 95050

(408) 247-1231

Cambridge Instrument Co., Inc.

73 Spring Street

Ossining, NY 10562

(914) 941-8100

Camille Bauer, Kimberly-James Inc.

P.O. Box D Newton Square, PA 190/3

(215) 353-2828

Canadian Research Institute

85 Curlew Drive

Don Mills, Ontario M3R 7R2,

Canada

(416) 445-6363

Celesco Transducer Products Inc

7800 Deering Avenue

Canoga Park, CA 91304

(213) 884-6860

Ceramaseal, Inc.

P.O. Box 25

New Lebanon Center

New York, NY 12116

(518) 794-6101

Cerro Wire & Cable Company

285 Nicoll Street

New Haven, CN 06504

(203) 772-2550

Conax Corporation

Esterline Corporation

2300 Walden Avenue

Buffalo, NY 14225

(716) 684-4500

Consolidated Controls Corp.

15 Durant Avenue

Bethel , CN 06801

(203) 743-6721

Control Process Inc.

201 Atwater Street

Plantsville, CN 06479

(203) 628-4721

Control Products Corporation

4431 W. Division

Chicago, IL 60651

(312) 235-1131

Cor-Tem Products, Inc.

(See ARI Industries)

Daburn Electronics & Cable Corp.

2359-B Hoffman Street

Bronx, NY 10458

(212) 295-0050

Degussa Inc.

Metals Division

Rt. 46 at Hoi lister Road

Teterboro, NJ 07608

(201) 288-6500

Devar Inc.

Control Products Division

706 Bostwick Avenue

Bridgeport, CT 06605

(203) 368-6751

Delta-T Company

P.O. Box 473

Santa Clara, CA 95052

(408) 243-0241

Dietert, H. W. Company

9330 Roselawn Avenue

Detroit, MI 48204

(313) 933-9790

11-13
Di getec

(See United Systems)

Digilin, Inc.

3521 W. Pacific Avenue

Burbank, CA 846-1800

(213) 846-1800

Doric Scientific Company

3883 Ruff in Road

San Diego, CA 92123

(714) 565-4415

Driver Harris Company

201 Middlesex Street

Harrison, NJ 07029

(201) 483-4800

Driver Wilbur B. Company

1875 McCarter Highway

Newark, NJ 07104

(201) 481-3100

Du-Co Ceramics

P.O. Box 278

Saxonburg, PA 16056

(412) 352-1511

Dynatech Medical Products

Dynatech R&D Company

99 Erie Street

Cambridge, MA 02139

(617) 868-8050

ECD Corporation

196 Broadway

Cambridge, MA 02139

(617) 661-4400

EDN Instrumentation, Inc.

15547 Cabrito Road

Van Nuys, CA 92111

(213) 781-2185

Ectron Corporation

8159 Engineer Road

San Diego, CA 92111

(714) 278-0600

Electro-Nite Company

10501 Decatur Road

Philadelphia, PA 19154

(215) 737-0600

Electro Optical Inc.

Transducer & Controls Division

255 N. Hal stead

Pasadena, CA 91107

(213) 449-1230

Electronic Dev. Labs, Inc.

19 Newton Road

Plainview, NY 11803

(516) 293-8997

Engelhard Industries Division

2655 U. S. 22

Union, NJ 07083

(201) 589-5000

Eppley Labs

Sheffield Avenue

Newport, RI 02840

(401) 847-1020

Extech International Corp.

177 State Street

Boston, MA 02109

(617) 227-7090

Fenwal Electronics Inc.

63 Fountain Street

P.O. Box 585

Framingham, MA 01701

(617) 822-8841

Fisher Controls Company

205 S. Center Street

Marshall town, IA 50158

(515) 754-3011

John Fluke Manufacturing Co., Inc

P.O. Box 43210

Mount! ake Terrace, WA 98043

(206) 774-2211

Foster Cambridge Limited

Howard Road, Eaton, Socon

Huntingdon, Cambridgeshire, Engla

PE 19 3EU

11-14
Foxboro Company

38 Neponset

Foxboro, MA 02035

(617) 543-8750

GIC Thermodynamics Division

George Instrument Company

4949 Delemere

Royal Oak, MI 48073

(313) 576-4700

Gay Engrg. & Sales Co., Inc.

P.O. Box 13232

5425 Blossom Street

Houston, TX 77019

(713) 869-3306

Gencom Division

Emitronics Inc.

80 Express Street

Plainview, NY 11803

(516) 433-5900

General Resistance, Inc.

75 Haven Avenue

Mt. Vernon, NY 10553

(212) 292-1500

Gordon, Claud S. Company

5710 Kenosha Street

Richmond, IL 60071

(815) 678-2211

Gulton Industries

Measurement & Control Systems Div.

Middle Road & Route 2 E. Greenwich, RI 02818

(401) 884-6800

Hades Manufacturing Corporation

151 A Verdi Street

Farmingdale, LI, NY 11735

(516) 249-4244

Harco Laboratories

186 Cedar Street

Brandord, CT 06405

(203) 488-8371

Harrop Laboratories

3470 E. Fifth Avenue

Columbus, OH 43219

(614) 231-3621

Hi tec Corporation

65 Power Road

Westford, MA 01886

(617) 692-4793

Honeywell, Inc.

Process Control Division

1100 Virginia Drive

Ft. Washington, PA 19034

(215) 643-1300

Hoskins Manufacturing Company

4445 Lawton Avenue

Detroit, MI 48208

Honeywell Instruments Inc.

3479 W. Vickery Blvd.

Ft. Worth, TX 76107

(817) ED6-7411

Hy-Cal Engineering

12105 Los Nietos Road

Santa Fe Springs, CA 90670

(213) 698-7785

Industrial Pyrometer

2107 Holland Street

Alton, IL 62002

(618) 465-7623

Industrial Temperature Control Co.

23419 Ford Road

Dearborn, MI 48128

(313) 278-2210

Instrulab

1205 Lamar Street

Dayton, OH 45404

(513) 223-2241

11-15
Instrumatics, Inc. Lewis Engineering Company

916 Boundary Street 238 Water Street

P.O. Box 8762 Naugatuck, CT 06770

Houston, TX 77009 (203) 729-5253

(713) 225-6626

Love Controls Corporation

K West 1714 S. Wolf Road

9371 Kramer Avenue Wheeling, IL 60090

Westminister, CA 92683 (312) 541-3232

(714) 893-6593

Marl in Mfg. Corporation

Karn Chemical Equipment Co. 12404 Triskett Road

815 Camp Home Road Cleveland, OH 44111

Pittsburgh, PA 15237 (216) 941-6200

(412) 931-2983

Matthew Bishop, Inc.

Kaye Instruments, Inc. Platinum Works

737 Concord Avenue Malvern, PA 19355

Cambridge, MA 02138 (215) 644-3100

(617) 868-7080

McDaniel Refractory Porcelain Co.

Kontes Glass Company 510 Ninth Avenue

Spruce Street Beaver Falls, PA 15010

Vineland, NJ 08360 (412) 843-8300

(609) 692-8500

Medtherm Corporation

LFE Corporation P.O. Box 412

API Instruments Hunts vi lie, AL 35804

1601 Trapelo Road (205) 534-7331

Waltham, MA 02154

(617) 890-2000 Minco Products, Inc.

7300 Commerce Lane

Land Instruments Inc. Minneapolis, MN 55432

P.O. Box 1623 (612) 786-3121

Tullytown, PA 19007

(215) 943-7882 Modutec Incorporated

18 Marshall Street

Leeds & Northrup Company Norwalk, CT 06854

Sumneytown Pike (203) 853-3636

N. Wales, PA 19454

(215) 643-2000 Molecu Wire Corporation

P.O. Box 495

Leico Industries, Inc. Farmingdale, NJ 07727

250 W. 57th Street (201) 922-9400

New York, NY 10019

(212) 765-5290

11-16
Moore Industries, Inc.

16650 Schoeborn Street

Sepulveda, CA 91343

(213) 894-7111

Moore, Samuel & Company

Dekoron Division

Aurora, OH 44202

(216) 562-5151

Mykroy Ceramics Company

P.O. Box 496

Ledgewood, NJ 07852

(201) 398-7000

Nanmac Corporation

9-11 Mayhew Street

Framingham Centre, MA 01701

(617) 872-4811

Natel Engineering Co., Inc.

8954 Mason Avenue

Canoga Park, CA 91306

(213) 882-9620

Nationwide Electronic Systems

1536 Brandy Parkway

Streamwood, IL 60103

(312) 289-8820

Newport Labs, Inc.

630 E. Young Street

Santa Ana, CA 92705

(714) 540-4914

Noral, Inc.

23600 Mercantile Road

Cleveland, OH 44122

(216) 831-2345

Noronix Ltd.

8 Thomas Street

London SE18 6HR

England

Omega Engineering Inc.

P.O. Box 4047

27 Knapp Street

Stamford, CT 06907

(203) 359-1660

Pace Wiancko Division

Whittaker Corporation

12838 Saticoy Street

N. Hollywood, CA 91605

Pacific Transducer Corp.

2301 Federal Avenue

Los Angeles, CA 90064

(213) 478-1134

Pak-Tronics Inc.

Dept. ET

4044 N. Rockwell Avenue

Chicago, IL 60618

(312) 478-8282

Precision Digital

1329 Highland Avenue

P.O. Box 18

Needham, MA 02192

(617) 449-2265

Projects Inc.

38 Addison Road

Glastonbury, CT 06033

(203) 633-4615

Pyco, Inc.

600 E. Lincoln Highway

Penndel, PA 19047

(215) 757-3704

Pyro-Serve Instrument Inc.

348 River Road

N. Arlington, NJ 07032

(201) 991-8000

Pyrometer Instr. Co., Inc.

234 Industrial Parkway

Northvale, NJ 07647

(201) 768-2000

11-17
RDF Corporation

23 Elm Avenue

Hudson, NH 03051

(603) 882-5195

RFL Industries, Inc.

Powerville Road

Boonton, NJ 07005

(201) 334-3100

Raeco, Inc.

550 Armory Drive

South Holland, IL 60473

(312) 331-6001

Reacor, Inc.

740 S. Sherman Street

Richardson, TX 75080

(214) 235-1952

Revere Corp. of America

845 N. Colony Road

Wallingtford, CT 06492

(203) 269-7201

Richards, Arklay S. Company Inc.

72M Winchester Street

Newton Highlands, MA 02161

(617) 527-4385

The Riley Company

7401 N. Hamlin Avenue

Skokie, IL 60076

(312) 675-2500

Rochester Inst. Systems, Inc.

275 N. Union Street

Rochester, NY 14605

(716) 325-5120

Rosemount-Nashvil le, Inc.

100 Heil -Quaker Blvd.

Lavergne, TN 37086

(615) 793-7561

Scani valve, Inc.

10222 San Diego Mission Road

San Diego, CA 92120

(714) 283-0010

Science Products Corporation

U.S. Route 46

Dover, NJ 07801

(201) 366-0827

Scientific Eng. & Mfg. Co., Inc.

11505 Vanowen Street

N. Hollywood, CA 91605

(213) 982-1400

Sensor Corporation

303 Scottdale Avenue

P.O. Box 140

Scottdale, PA 15683

(412) 887-4080

Sentel Associates, Inc.

1125 C Stewart Drive

Sunnyvale, CA 94086

(408) 737-1400

Service Associated, Inc.

339 W. 112th Place

Chicago, IL 60628

(312) 568-4545

Sierracin Corporation

Harrison Division

3020 Empire Avenue

Burbank, CA 91504

(213) 849-6581

Sigma Insts. (Canada) Ltd.

P.O. Box 43

55 Sixpoint Road

Toronto 18, Ontario, Canada

(416) 239-8161

Simpson Electric Company

853 Dundee Avenue

Elgin, IL 60120

(312) 697-2260

11-18
Spectran Inst.

P.O. Box 891

La Habra, CA 90631

(213) 333-0666

Standard Wire & Cable Company

3440 Overland Avenue

Los Angeles, CA 90034

(213) 870-9231

Syscon International Inc.

1239 South Bend Avenue

South Bend, IN 46617

(219) 287-5916

Tem Tex Temp. Sys. & Components

5619 Dyer Street

Dallas, TX 75206

(214) 361-7100

Tempi ine

23555 Tel co Avenue

Torrance, CA 90505

(213) 539-2333

Temp-Pro Inc.

P.O. Box 265

Haydenville, MA 01039

(413) 268-7715

Tensolite Company

Div. Carlisle Corp.

198 W. Main Street

Tarrytown, NY 10591

(914) 631-2300

Theall Engineering Company

Box 362

Oxford, PA 19363

(215) 932-2488

Thermal ogic

Div. of Dytron Inc.

241 Crescent Street

Waltham, MA 02154

(617) 891-9496

Thermo-Couple Product Co.,

27 W. Beecher

Winfield, IL 60190

(312) 653-1400

Thermo Electric Co., Inc.

109 Fifth Street

Saddle Brook, NJ 07662

(201) 843-5800

Thermometries Corporation

8645 Yolanda Avenue

Northridge, CA 91324

(213) 886-3755

Thermonetics Corporation

1028 Garnet Avenue, #160

San Diego, CA 92109

(714) 453-2164

Thermotronic Devices Inc.

P.O. Box 184

Forrest & Hector Sts.

Conshohocken, PA 19428

(215) 828-4790

Thornthwaite, C.W. Assoc.

Route 1 Centerton

Elmer, NJ 08318

(609) 358-2350

Tracor Westronics Inc.

5050 Mark IV Parkway

P.O. Box 4619

Fort Worth, TX 76106

(817) 625-2311

Transmation Inc.

977 Mt. Read Blvd.

Rochester, NY 14606

(716) 254-9000

Trans-Met Eng. Inc.

601 S. Palm Street

La Hara, CA 90631

(213) 691-2266

11-19
Triplett Corporation

Dept. P-R

Bluffton, OH 45817

(419) 358-5015

Tudor Technology, Inc.

424 Caredean Drive

Horsham, PA 19094

(215) 674-4150

Tylok International

25700 Lakeland Blvd.

Euclid, OH 44132

(216) 361-0400

United Electric Controls Co.

85 School Street

Watertown, MA 02172

(617) 926-1000

United Systems Corporation

Di gitec

918 Woodley Road

Dayton, OH 45403

(513) 254-5251

Unitronix Corporation

1081 U.S. Hwy 22

P.O. Box 6515

Bridgewater, NJ 08807

(201) 725-2560

Validyne Engrg. Corporation

19414 Londelius Street

Northridge, CA 91324

(213) 886-8488

Virtis Company, Inc.

Route 208

Gardiner, NY 12525

(914) 255-5000

William Wahl Corporation

12908 Panama Street

Los Angeles, CA 90066

(213) 391-7234

Ward Leonard-Hagerstown Division

Angstrohm Precision Inc.

P.O. Box 1827

Hagerstown, MD 21740

(301) 739-9722

Watlow Electric Mfg. Company

12001 Lackland Road

St. Louis, MO 63141

(314) 878-4600

Weed Instruments Company Inc.

P.O. Box 549

109 W. 11th Street

Elgin, TX 78621

(512) 285-3411

West Coast Research Corporation

P.O. Box 25061

Los Angeles, CA 90025

(213) 478-8833

Wilcon Industries

9557 E. Rush Street

S. El Monte, CA 91733

(213) 579-0268

Yokogawa Corp. of America

5 Westchester Plaza

Elmsford, NY 10523

(914) 592-6767

11-20
Resistance Thermometers

ARI Industries, Inc.

9000 King Street

Franklin Park, IL 60131

(312) 671-0511

ARRGH Manufacturing Co., Inc.

P.O. Box S

San Rafael , CA 94903

(415) 479-0220

Abrams, A. J. Company

P.O. Box 571

Westport, CT 06880

(203) 226-3010

Action Instruments Co., Inc.

8601 Aero Drive

San Diego, CA 92123

(714) 279-5726

Airpax/North American Philips

Controls Corporation

Frederick Division

Husky Park, Frederick, MD 21701

(301) 663-5141

Amprobe Instrument Division

630 Merrick Road

Lynbrook, NY 11563

(516) 593-5600

Analog Devices

Rt. 1, Industrial Park

P.O. Box 280

Norwood, MA 02062

(617) 329-4700

Analogic Corporation

Audubon Road

Wakefield, MA 01880

(617) 246-0300

Ancom Ltd.

Denmark House

Devonshire Street

Cheltenham, Glos, GL50 3PR England

Andonian Cryogenics, Inc.

26 Farwell Street

Newtonville, MA 02160

(617) 484-0500

Artronix Inc.

18081 Chesterfield Airport Rd.

Chesterfield, MO 63017

(314) 532-8200

Athena Controls Inc.

20 Clipper Road

W. Conchohocken, PA 19428

(215) 828-2490

Atkins Technical

3401 S.W. 40th Blvd.

Gainesville, FL 32608

(904) 378-5555

B & F Instruments Division

FX Systems

(See: FX Systems)

BLH Electronics

42 Fourth Street

Waltham, MA 02154

(617) 890-6700

Barber-Colman Company

Industrial Instruments Division

1700 Rock Street

Rockford, IL 61101

(815) 877-0241

Bayley Instrument Company

Box 357

Kenwood, CA 95452

(707) '833-6014

Beacon Electronics Inc.

1800 Til ton Road

Pleasantville, NJ 08232

(609) 646-3770

11-21
Bristol Division

ACCO

929 Connecticut Avenue

Bridgeport, CT 06607

(203) 335-2511

Burns Engineering, Inc.

10201 Bren Road East

Minnetonka, NM 55343

(612) 935-4400

COS Thermodynamics

LaCrue Street

Concord Industrial Park

Concordville, PA 19331

(215) 358-1510

Cal-R Inc.

Thermonetics Division

1601 Olympic Blvd.

Santa Monica, CA 90404

(213) 450-1761

Canadian Research Institute

85 Curlew Drive

Don Mills, Ontario M3R 7R2 Canada

(416) 445-6363

Columbia Research

MacDade Blvd. & Bullens Lane

Woodlyn, PA 19094

(215) 532-9464

Conax Corporation

2300 Walden Avenue

Buffalo, NY 14225

(716) 684-4500

Daniel Industries Inc.

Flow Products Division

9720 Katy Road

P.O. Box 19097

Houston, TX 77024

(713) 467-6000

Da tametries

340 Fordham Road

Wilmington, MA 01887

(617) 729-9480

Degussa Corporation

Metals Division

Rte. 46 at Hoi lister Road

Teterboro, NJ 07608

(201) 288-6500

Canadian Thermostat & Control Devices Dentronics, Inc.

2255 Dandurand Street 60 Oak Street

Montreal, Quebec, Canada H2G 1Z6 Hackensack, NJ 07601

(514) 270-7135 (201) 343-9405

Carborundum Company

Graphite Products Division

P.O. Box 339

Niagara Falls, NY 14302

(716) 278-2521

Chemtrix, Inc.

135 North West Adams Street

Hillsboro, OR 91723

(503) 648-0762

Climatronics

1324-A Motor Pkwy.

Hauppauge, NY 11787

(516) 234-2772

Cole-Parmer Instrument Company

7425 N. Oak Avenue

Chicago, IL 60648

(312) 647-0272

Doric Scientific Company

3883 Ruffin Road

San Diego, CA 92123

ECD Corporation

196 Broadway

Cambridge, MA 02139

(617) 661-4400

ESE

142 Sierra Street

El Segundo, CA 90245

(213) 322-2136

Edison Electronics Division

McGraw-Edi son Company

Grenier Field

Municipal Airport

Manchester, NH 03103

(603) 669-0940

11-22
Electronic Control Systems, Inc.

P.O. Box 1232

Fairmont, WV 26554

(304) 363-8632

Electronic Development Labs, Inc.

19 Newtown Road

Plain view, NY 11803

(516) 293-8997

Electronic Research Company

(see: Industrial Timer Corp.)

Elnik Instruments, Inc.

410 Garibaldi Avenue

Lodi, NJ 07644

(201) 779-7388

Eltex Inc.

25165 Southport Street

Laguna Hills, CA 92653

(714) 770-9236

Engelhard Industries

2655 U.S. Rte. 22

Union, NJ 07083

(201) 589-5000

Extech International Corp.

114 State St.

Boston, MA 02109

(617) 227-7090

FX Systems

CPO 1818

77 Cornell Street

Kingston, NY 12401

(914) 338-0515

Fenwal Inc.

400 Main Street

Ashland, MA 01721

(617) 881-2000

Foster Cambridge Limited

Howard Road

Eaton, Socon, Huntingdon

Cambridgeshire, England PE19 3EU

Foxboro Company

38 Neponset Avenue

Foxboro, MA 02035

(617) 543-8750

Gencom Division

Emitronics, Inc.

80 Express Street

Plainview, NY 11803

(516) 433-5900

General Scientific Equipment Co.

Limekiln Pike & Williams

Avenue

Philadelphia, PA 19150

(215) 354-9677

Genisco Technology

Corporation

18435 Susana Road

Compton, CA 90221

(213) 537-4750

Gentran, Inc.

1290 Hammerwood Avenue

Sunnyvale, CA 94086

(408) 734-5060

Gordon, Claud S. Company

5710 Kenosha Street

Richmond, IL 60071

(817 ) 678-2211

Gould Control & Systems Division

(see: Datametrics)

Gulton Industries, Inc.

Measurement & Control Systems Div.

Middle Rd & Rt. 2

East Greenwich, RI 02818

(401 ) 884-6800

Gulton Industries, Inc.

Piezo Products Division

212 Durham Avenue

Metuchen, NJ 08840

(201) 548-2800

Harrel , Inc.

16 Fitch Street

E. Norwalk, CT 06855

(203) 866-2573

11-23
Heli trope General

3733 Kenora Drive

Spring Valley, CA 92077

Hewlett-Packard

Del con Division

1501 Pase Mill Road

(415) 969-088U

Honeywell, Inc.

Process Control Division

1100 Virginia Drive

Fort Washington, PA 19034

(215) 643-1300

Hy-Cal Engineering

12105 Los Nietos Road

Santa Fe Springs, CA 90670

(213) 698-7785

ITT Components Group Europe

Edinburgh Wah

Hawlow, Essex, England

Industrial Timer Corporation

An Esterline Company

U.S. Highway 287

Parsippany, NJ 07054

(201) 887-2200

Instrulab, Inc.

1205 Lamar Street

Dayton, OH 45404

(513) 223-2241

Julie Research Labs, Inc.

211 W. 61st Street

New York, NY 10023

(212) 245-2727

Keystone Carbon Company

Thermistor Division

1935 State Street

St. Marys, PA 15857

(814) 781-1591

Kulite Semiconductor Products, Inc.

1039 Hoyt Avenue

Ridgefield, NJ 07657

(201) 945-3000

Kurz Instruments

P.O. Box 849

20 Village Square

Carmel Valley, CA 93924

(408) 659-3421

LFE Corporation

Process Control Division

1601 Trapelo Road

Waltham, MA 02154

(617) 890-2000

Lake Shore Cryotronics, Inc.

64 E. Walnut Street

Westerville, OH 43081

(614) 891-2243

Leeds & Northrup Company

Sumneytown Pike

N. Wales, PA 19454

(215) 643-2000

Leico Industries Inc.

250 W. 57th Street

New York, NY 10019

(212) 765-5290

The Lewis Engineering Company

Transducer Division

19-29 Sheldon Street

Norwich, NY 13815

(607) 334-3939

Logical Technical Services Corp.

71 West 23rd Street

New York, NY 10010

(212) 741-8340

Love Controls Corporation

1475 S. Wheeling Road

Wheeling, IL 60090

(312) 541-3232

11-24
Mag-Con, Inc.

1626 Terrace Drive

St. Paul, MN 55113

(612) 633-8820

Matthey Bishop Inc.

4 Main Road

Malvern, PA 19355

(215) 648-8000

Measurement Science Corporation

P.O. Box 338

Brigham City, UT 84302

(801) 723-8541

Mensor Corporation

2230 IH-35 South

San Marcos, TX 78666

(512) 392-6091

Measurement Group

P.O. Box 27777

Raleigh, NC 27611

(919) 365-3800

Midwest Components, Inc.

P.O. Box 726

Muskegon, MI 49443

(616) 777-2602

Minco Products Inc.

7300 Commerce Lane

Minneapolis, MN 55432

(612) 786-3121

Mol ecu -Wire Corporation

P.O. Box 495

Farmingdale, NJ 07727

(201) 922-9400

Multi -State Devices Ltd.

(see Canadian Thermostat & Control Devices)

National Basic Sensor Corporation

Box 205

Feasterville, PA 19047

(215) 322-4700

Newport Laboratories, Inc.

630 E. Young Street

Santa Ana, CA 92705

(714) 540-4914

Noral , Inc.

23600 Mercantile Road

Commerce Park

Cleveland, OH 44122

(216) 841-2345

Noronix, Ltd.

8 Thomas Street

London, SE18 6HR, England

Oven Industries, Inc.

Hempt Road

P.O. Box 229

Silver Spring Industrial Park

Mechanicsburg, PA 17055

(717) 766-0721

Palmer Electronics, Inc.

156 Belmont Avenue

Garfield, NJ 07026

Pennsylvania Electronics Technology

Inc.

1397 Frey Road

Pittsburgh, PA 15235

(412) 243-3816

Phoenix Precision Instrument

Company

Division Virtis

Rte. 208

Gardiner, NY 12525

(914) 255-5000

Photofabrication Technology, Inc.

(PTI)

Century Building

Derry, NH 03038

(603) 434-4113

Prime Manufacturing Corporation

7730 South 6th Street

Oak Creek, WI 53154

(414) 764-1400

11-25
Protective Controls Inc.

(see Airpax/North American

Philips Controls Corp.)

Pyco, Inc.

6U0 E. Lincoln Highway

Penndel, PA 19047

(215) 757-3704

Quality Thermistor, Inc.

2096 South Cole Road

Suite 7 Boise, ID 83705

(208) 377-3373

RCD Corporation

8 Blueberry Lane

Bedford, NH 03102

(603) 669-0054

RDF Corporation

23 Elm Avenue

Hudson, NH 03051

(603) 882-5195

RFL Industries

Powerville Road

Boonton, NJ 07005

(201) 334-3100

R.T.D. Company

Box 7604

Colorado Springs, CO 80933

(303) 599-3700

Relco Products, Inc.

5594 E. Jefferson

Denver, CO 80237

(303) 756-1143

Reotemp Instrument Corporation

11568 Sorrento Valley Rd.

Suite 10

San Diego,, CA 92121

(714) 481-7737

The Riley Company

Panalarm Division

7401 N. Hamlin Avenue

Skokie, IL 60076

(312) 675-2500

Rochester Instrument Systems, Inc.

255 North Union Street

Rochester, NY 14605

(716) 325-5120

Rosemount Inc.

12001 W. 78th Street

Minneapolis, MN 55435

(612) 941-5560

Seci-Societa

Electtrotecnica Chimica Italiana

Via G. B. Grassi

97, 20157 Milano, Italy

Sensing Devices Limited

97 Tithebar Road

Southport PR8 6AG

Lancashire, England

Senso-Metrics Inc.

7775 Kester Avenue

Van Nuys, CA 91405

(213) 988-6070

Sentel Associates, Inc.

1125 C Stewart Drive

Sunnyvale, CA 94086

(408) 737-1400

Service Tectonics Instr. Div. of

Maskote Corporation

17168 E. Warren Avenue

Detroit, MI 48224

(313) 882-9100

Sierracin Corporation

Harrison Division

3020 Empire Avenue

Burbank, CA 91504

(213) 849-6581

11-26
Sigma Instruments Ltd.

P.O. Box 43

Toronto 18, Ontario, Canada

(416) 239-8161

Sigmund Cohn Corporation

121 S. Columbus Avenue

Mt. Vernon, NY 10553

(914) 664-5300

Simpson Electric Company

853 Dundee Avenue

Elgin, IL 60120

(312) 697-2260

Stow Laboratories, Inc.

Kane Industrial Drive

Hudson, MA 01749

(617) 562-9347

Syscon International Inc.

1239 South Bend Avenue

South Bend, IN 44617

(219) 287-5916

Sys-Tec, Inc.

877 Third Street, SW

New Brighton, NM 55112

(612) 636-6373

Technical Hardware, Inc.

P.O. Box 3609

Fullerton, CA 92634

(714) 870-1882

Temp, Inc.

407 Diamond Street

P.O. Box 929

Fairmont, WV 26554

Tempkey, Inc.

2155 Park Blvd.

Palo Alto, CA 94306

(415) 324-8798

Tempi i ne 23555 Telo Avenue

Torrance, CA 90505

(213) 539-2333

Temp-Pro Inc.

P.O. Box 265

35 Main Street

Haydenville, MA 01039

(413) 268-7263

Temtex

5619 Dyer Street

Dallas, TX 75206

(214) 361-7108

Texas Instruments

13500 N. Central Expressway

Dallas, TX 75231

(214) 238-03741

Thermal ogic

Division of DYTRON Inc.

241 Crescent Street

Waltham, MA 02154

(617) 891-9496

The rmoElec trie Co., Inc.

109 Fifth Street

Saddle Brook, NJ 07662

(201) 843-5800

Thermometries Inc.

808 U.S. Highway #1

Edison, NJ 08817

(201 ) 287-2870

Transmation Inc.

977 Mt. Read Blvd.

Rochester, NY 14605

(716) 254-9000

Tudor Technology, Inc.

424 Caredean Drive

Horsham, PA 19044

(215) 674-4150

11-27
Tylan Corporation

19220 S. Normandie

Torrance, CA 90502

(213) 532-3420

United Electric Controls

85 School Street

Watertown, MA 02172

(617) 926-1000

United Systems Corporation

Digitec

918 Woodley Road

Dayton, OH 45403

(513) 254-6251

Vaisala Oy (Industrial Sales)

PL 26, SF -00421

Helsinki 42, Finland

Validyne Engineering Corporation

19414 Londelius Street

Northridge, CA 91324

(213) 886-8488

Vertronix, Inc.

P.O. Box 907

Evergreen, CO 80439

Victory Engineering

Victory Road

Springfield, NJ 07081

(201) 379-5900

Virtis Company

(see: Phoenix Precision)

Vitec Incorporated

23645 Mercantile Road

Cleveland, OH 44122

(216) 464-4670

Wahl , William Corporation

12908 Panama Street

Los Angeles, CA 90066

(213) 391-7234

WeatherMeasure Corporation

P.O. Box 41257

Sacramento, CA 95841

Weed Instrument Company, Inc.

P.O. Box 549

109 W. Eleventh Street

Elgin, TX 78621

(512) 285-3411

West Coast Research Corporation

P.O. Box 25061

Los Angeles, CA 90025

(213) 478-8833

Western Thermistor Corporation

354 Via Del Monte

Oceanside, CA 92054

(714) 433-4484

Westinghouse Electric Corporation

95 Oragne Street

Newark, NJ 07102

(201) 465-0222

West Instruments

Gulton Measurement & Control

Systems

Gulton Industrial Park

East Greenwich, RI 02818

(401 ) 884-6800

Yellow Springs Instrument Company

P.O. Box 279

Yellow Springs, OH 45387

(513) 767-7242

Yokogawa Corp. of America

5 Westchester Plaza

Elmsford, NY 10523

(914) 592-6767

11-28
Thermal Radiation Sensors, Pyrometers, Heat Flow Sensors

Bailey Instruments, Inc.

515 Victor Street

P.O. Box 800

Saddle Brook, NJ 07662

(201) 845-7252

Barber-Colman Industrial Instruments

Div.

1700 Rock Street

Rockford, IL 61101

(815) 877-0241

Barnes Engineering Company

30 Commerce Road

Stamford, CT 06904

(203) 348-5381

Bristol Division

ACCO

929 Connecticut Avenue

Bridgeport, CT 06607

(203) 335-2511

CGS/Thermodynamics

LaCrue Street

Concord Industrial Park

Concordville, PA 19331

(215) 358-1510

Capintec Instruments Inc.

136 Summit Avenue

Montvale, NJ 07645

(201) 391-3930

Chi no Works Ltd.

1-22-8 Nishi-Ikebukuro

Toshima-Ku

Tokyo, Japan

Dynalco Corporation

5200 N.W. 37th Avenue

P.O. Box 8187

Ft. Lauderdale, FL 33310

(305) 739-4300

E T

P.O. Box 404

6315 Carpinteria Avenue

Carpinteria, CA 93013

(805) 684-5461

Electro Optical Industries Inc.

P.O. Box 3770

Santa Barbara, CA 93105

(805) 964-6701

Epic, Inc.

150 Nassau Street

New York, NY 10038

(212) 349-2470

Eppley Laboratory, Inc.

12 Sheffield Avenue

Newport, RI 02840

(401 ) 847-1020

Hamamatsu Corporation

120 Wood Avenue

Middlesex, NJ 08846

(201 ) 469-6640

Honeywel 1 , Inc

Process Control Division

1100 Virginia Drive

Ft. Washington, PA 19034

(215) 643-1300

International Thermal Instrs. Co.

P.O. Box 309

Del Mar, CA 92014

(714) 755-4436

Ircon, Inc.

7555 N. Linder Avenue

Skokie.'IL 60076

(312) 967-5151

11-29
Irtronics

Division of Mechtronics Corp.

57 Commerce Road

Stamford, CT 06902

(302) 348-2671

Kane-May Ltd.

for U.S. Freeman Associates

Burrowfield, Welwyn Garden City

Hertfordshire, England

Land Instruments, Inc.

P.O. Box 1623

Tullytown, PA 19007

(215) 943-7882

Laser Precision Corporation

1231 Hart Street

Utica, NY 13502

(315) 797-4449

Leeds & Northrup Company

Sumneytown Pike

North Wales, PA 19454

(215) 643-2000

Mikron Instrument Company

P.O. Box 211

Ridgewood, NJ 07451

(201 ) 891-7330

Molectron Corporation

177 N. Wolfe Road

Sunnyvale, CA 94086

(408) 738-2661

Newport Laboratories, Inc.

630 E. Young

Santa Ana, CA 92705

(714) 540-4914

Niagara Scientific Inc.

118 Boss Road

E. Syracuse, NY 13211

(315) 437-0821

Optronic Labs, Inc.

7676 Fenton Street

Silver Spring, MD 20910

(301) 587-2255

Pyrometer Instrument Co., Inc.

234 Industrial Parkway

Northvale, NJ 07647

(201) 768-2000

Raeco, Inc.

550 Armory Drive

S. Holland, IL 60473

(312) 33106001

Ratio Controls Corporation

260 Laura Drive

Addison, IL 60101

(312) 543-9330

Raytek, Inc.

325 E. Middlefield Road

Mountain View, CA 94043

(415) 961-1650

Sensors, Inc.

3908 Varsity Drive

Ann Arbor, MI 48104

(313) 973-1400

Sensor Technology

21012 Lassen Street

Chatsworth, CA 91311

(213) 882-4100

Sick Optik-Elektronik, Inc.

113 S. Main Street

Stillwater, NM 55082

(612) 439-6516

Syscon International , Inc.

1239 South Bend Avenue

South Bend, IN 46617

(219) 287-5916

11-30
Telatemp Corporation

P.O. Box 5160

Fullerton, CA 9263b

(714) 879-2901

Thermogage, Inc.

330 Allegany Street

Frostburg, MD 21532

(301) 689-6630)

Thermometries Inc.

808 U.S. Highway #1

Edison, NJ 08817

(201) 287-2870

UTI

325 N. Mathilda Avenue

Sunnyvale, CA 94086

(408) 738-3301

Victory Engr. Corporation

Victory Road

Springdfield, NJ 07081

(201) 379-5900

Wahl , William Corporation

12908 Panama Street

Los Angeles, CA 90066

(213) 391-7234

Wilco Inc.

(see: Sick Optik-Elektronik, Inc.)

Williamson Corporation

1152 Main Street

West Concord, MA 01742

(617) 369-9607

11-31
FLOW

Differential Pressure Flow Meters

Action Instruments Co., Inc.

8601 Aero Drive

San Diego, CA 92123

(714) 279-5726

Ametek, Inc.

Schutte & Koerting Div.

State Road

Cornwells Heights, PA 19020

(215) 639-0900

Asahi Instruments Co., Ltd.

Head Office

19-17 Tamachi , Kokuraki ta-Ku

Ki takyushu-Ci ty 803, Japan

BIF

General Signal

1600 Division Road

West Warwick, RI 02893

(401) 885-1000

Badger Meter Inc.

Instruments Division

4545 W. Brown Deer Road

Milwaukee, WI 53223

(414) 355-0400

Badger Meter Inc.

Precision Products Division

6116 E. 15th Street

Tulsa, OK 74112

(918) 836-4631

Bailey Controls Company

29801 Euclid Avenue

Wickliffe, OH 44092

(216) 943-5000

Bristol Division

ACCO

929 Connecticut Avenue

Bridgeport, CT 06607

(203) 335-2511

Beckman Instruments, Inc.

Technical Information Services

Cedar Grove Operation

89 Commerce Road

Cedar Grove, NJ 07009

(201 ) 239-6200

Bubble-O-Meter

Box 338

Temple City, CA 91780

Capital Controls Company

P.O. Box 211

Colmar, PA 18915

(215) 822-2901

Computer Instruments Corp.

100 Madison Avenue

Hempstead, NY 11550

(516) 483-8200

Conometer Corporation

Box 383

Haddonfield, NJ 08033

(609) 428-7776

Consolidated Controls Corp.

15 Durant Avenue

Bethel, CT 06801

(203) 743-6721

Datametrics

340 Fordham Road

Wilmington, MA 01887

Davis Instrument

513 E. 36th Street

Baltimore, MD 21218

(301 ) 243-4301

11-32
Dieterich Standard Corporation

Subsidiary of Dover Corp.

Box 9000

Boulder, CO 80306

(303) 449-9000

Henry G. Dietz Company, Inc.

14-26 28th Avenue

Long Island City, NY 11102

(212) 726-3347

Dwyer Instruments, Inc.

Box 373

Jet. Ind. 212 & US12

Michigan City, IN 46360

(219) 872-9141

Estech, Inc.

308 Talmadge Road

P.O. Box 594

Edison, NJ 00817

(201) 287-1111

Erdco Engineering Corporation

136 Official Road

Addison, IL 60101

(312) 543-6733

Fischer & Porter Company

775 Warminster Road

Warminster, PA 18974

(215) 674-6000

Flo-Tron, Inc.

495 E. 30th Street

Paterson, NJ 07504

(201) 279-6500

Flow-Dyne Engineering Inc.

P.O. Box 9034

Fort Worth, TX 76107

(817) 732-2858

Fluid Components Inc. (FCI)

870 Remmet Avenue

Canoga Park, CA 91304

(213) 883-0806

Flui dynamic Devices Ltd.

3216 Lenworth Drive

Mississauga, Ontario, Canada L4X, 2G1

(416) 625-9501

Flui dyne Instrumentation

2930 Lakeshore Avenue

Oakland, CA 94610

(415) 444-2376

The Foxboro Company

Dept. 120

38 Neponset Avenue

Foxboro, MA 02035

(617) 543-8750

Fox Valve Development Co., I 222 Great Meadow Lane

E. Hanover, NJ 07936

(201) 887-7474

Gould Inc.

Measurement Systems Div.

2230 Statham Blvd.

Oxnard, CA 93030

(805) 487-8511

Honeywell Inc.

Process Control Division

1100 Virginia Drive

Fort Washington, PA 19034

(215) 643-1300

ITT Barton

580 Monterey Pass Road

Box 2013

Monterey Park, CA 91754

(213) 289-3581

The W.A. Kates Company

P.O. Box 627

Deerfield, IL 60015

(312) 945-0950

Konigsberg Instruments

2000 E. Foothill Blvd.

Pasadena, CA 91107

(213) 795-9719

Kontes Manufacturing Company

Spruce Street

P.O. Box 729

Vineland, NJ 08360

(609) 692-8500

Leeds & Northrup Company

Sumneytown Pike

North Wales, PA 19454

(215) 643-2000

11-33
Leslie Company

399 Jefferson Road

Parsippany, NJ 07054

(201) 887-9000

Meriam Instrument

Div. of Scott & Fetzer Co.

10920 Madison

Cleveland, OH 44102

(216) 281-1100

Mid-West Instrument

P.O. Box 939

Troy, MI 48099

(313) 585-0900

Orange Research Inc.

404 Boston Post Road

Orange, CT 06477

(203) 795-6225

RCM Industries

P.O. Box 351

Orinda, CA 94563

(415) 687-8363

Ramapo Instr. Co., Inc.

2 Mars Court

P.O. Box 428

Montville, NJ 07045

(201) 263-8800

Robertshaw Controls Company

Industrial Instrumentation Div.

1809 Staples Mill Road

Richmond, VA 23230

(804) 358-2301

Ruska Instrument Corporation

6121 Hillcroft

P.O. Box 36010

Houston, TX 77036

(713) 774-2533

Scanivalve, Inc.

P.O. Box 20005

San Diego, CA 92120

(714) 283-5851

Setra Systems, Inc.

1 Strathmore Road

Natick, MA 01760

(617) 655-4645

The Singer Company

American Meter Division

13500 Philmont Avenue

Philadelphia, PA 19116

(215) 673-2100

J.W. Sweet Company

P.O. Box 6395

Columbia, SC 29260

(803) 754-7492

Taylor Instrument Company

Div. of Sybron Corporation

95 Ames Street

Rochester, NY 14601

(716) 235-5000

Teledyne Hastings-Raydist Co.

P.O. Box 1275

Newcomb Avenue

Hampton, VA 23361

(703) 723-6531

Tri mount Instrument Company

932 W. Wrightwood

Chicago, IL 60614

(312) 327-2288

UGC Industries, Inc.

P.O. Box 3736

Shreveport, LA 71103

(318) 631-0373

Unimeasure

(see: Konigsberg Instrs.)

United Sensor & Control Corp.

85 School Street

Watertown, MA 02172

(617) 926-1000

Validyne Engineering Corporation

19414 Londelius Street

Northridge, CA 91324

(213) 886-8488

11-34
Waugh Controls Corporation

9001 Full bright Avenue

Chatsworth, CA 91311

(213) 998-8281

West Coast Research Corporation

S. Sepulveda Boulevard

P.O. Box 25061

Los Angeles, CA 90025

(213) 8833

Westinghouse Electric Corporation

Computer & Instrumentation Div.

Box 402

Orrville, OH 44667

Turbine Flow Meters

American Meter Company

(see: Singer)

Autotronic Controls Corporation

6908 Commerce

El Paso, TX 79915

(915) 772-7431

Badger Metals Inc.

Instruments Division

4545 W. Brown Deer Road

Milwaukee, WI 53223

(414) 355-0400

Badger Meter Inc.

Precision Products Div.

6116 E. 15th Street

Tulsa, OK 74112

(918) 836-8411

Ball Manufacturing Inc.

903 W. Center Street, North

Salt Lake City, UT 84054

(801) 364-6451

Barton Instruments

900 S. Turnbull Canyon Road

Box 1882

City of Industry, CA 91749

Bearingless Flow Meter Co., Inc.

294 Beacon Street

Boston, MA 02116

(617) 262-4509

Brooks Instrument Division

Emerson Electric Company

P.O. Box 450

Statesboro, GA 30458

(912) 764-5471

C-E Invalco

P.O. Box 556

Tulsa, OK 94101

(918) 932-5671

Cameo Inc.

Energy Measurement & Control Group

7010 Ardmore

P.O. Box 14484

Houston, TX 77021

(713) 747-4000

Cox Instrument Division

Lynch Corporation

15300 Fullerton

Detroit, MI 48227

(313) 838-5780

11-35
Daniel Industries, Inc.

P.O. Box 19097

Houston, TX 77024

(713) 467-6000

Eastech Inc.

308 Talmadge Road

P.O. Box 594

Edison, NJ 08800

(201) 287-1111

Electrac, Inc.

1614 Orangethrope Way

Anaheim, CA 92801

(714) 879-6021

Electronic Flo-Meters Inc.

P.O. Box 38269

Dallas, TX 75238

(214) 359-1982

Engineering Measurements Co., Inc.

600 Diagonal Hwy.

Longmont, CO 80501

(303) 651-0550

Fischer & Porter

755 Warminster Road

Warminster, PA 18974

(215) 675-6000

Floscan Instrument Company

3016 N.E. Blakely Street

Seattle, WA 98105

(206) 524-6625

Flo-Tech, Inc.

403 S. Washington Street

Mundelein, IL 60060

(312) 566-9120

Flowcon System

Div. of Bower Industries

P.O. Box 1631

1601 West Orangewood Ave.

Orange, CA 92668

(714) 633-8334

Flow Technology Inc.

4250 E. Broadway Road

Phoenix, AZ 85040

(602) 268.-8776

Foxboro Company

38 Neponset Avenue

Foxboro, MA 02035

(617) 543-8650

Geosource, Inc.

Flow Measurement & Control Div.

1602 Wagner Avenue

P.O. Box 559

Erie, PA 16512

(814) 899-0661

Hal 1 i burton

Special Products Division

P.O. Drawer 1431

1015 Bois D'Arc

Duncan, OK 73533

(405) 255-3760

Hersey Products Inc.

Hersey Division

250 Elm Street

Dedham, MA 02026

(617) 326-9400

Hersey Products Inc.

Industrial Measurement Div.

Old Valley Falls Road

Spartanburg, SC 29303

(803) 578-3800

Hoffer Flow Controls Inc.

P.O. Box 745

149 Highway 36

Port Monmouth, NJ 07758

(201) 787-1998

ITT Barton

Box 1882

City of Industry, CA 91749

(213) 961-2547

11-36
Kent Meter Sales, Inc.

7 East Silver Springs Blvd.

Suite 400, Concord Square

Ocala, FL 32670

(904) 732-4670

Mead Instruments Corporation

One Dey Lane

Riverdale, NJ 07457

(201) 835-5988

Mergas Meters Inc.

Mercury Instruments Inc.

3940 Virginia Avenue

Cincinnati, OH 45227

(513) 272-1111

Moore Industries, Inc.

16650 Schoenborn Street

Sepulveda, CA 91343

(213) 894-7111

Olymic Control s Inc.

11246 South Post Oak

Houston, TX t77035

(713) 721-3431

Precision Flow Measurements

(see: Sponsler Co.)

Quantum Dynamics Inc.

19458 Ventura Blvd.

P.O. Box 865

Tarzana, CA 91365

(213) 345-6828

Richard Lee Company

12 Park Street

Canford, NJ 07016

(201) 276-0710

Simmonds Precision Products Inc.

Rockingham Road

Bellows Balls, VT 05101

(802) 463-4576

The Singer Company

American Meter Division

13500 Philmont Avenue

Philadelphia, PA 19116

(215) 673-2100

Smith Meter Systems Div.

Geosource Inc.

(see: Geosource, Inc.)

Sponsler Company, Inc.

1 Hendry Lane

Brick Town, NJ 08723

(201 ) 477-2095

Waugh Controls Corporatio

9001 Full bright Avenue

Chatsworth, CA 91311

(213) 998-8281

11-37
Mass Flow Sensors

Agar Instrumentation

2203 Blalock Road

Houston, TX 77U8U

(713) 461-2427

American Meter Division

Singer Company

(see: The Singer Co.,

American Meter Div.)

Bendix Corporation

Instrument & Life Support Div.

P.O. Box 4508

Davenport, IA 52808

Bristol Division (ACCO)

929 Connecticut Avenue

Bridgeport, CT 06607

(203) 335-2511

Brooks Instrument Div.

Emerson Electric Co.

407 W. Vine Street

Hatfield, PA 19440

(215) 368-2000

Datametrics

340 Fordham Road

Wilmington, MA 01887

(617) 658-5410

El dec Corporation

16700 13th Avenue, West

P.O. Box 100

Lynwood, WA 98036

(206) 743-1313

Electrac, Inc.

1614 Orangethorpe Way

Anaheim, CA 92801

(714) 879-6021

Electronic Flo-Meters, Inc.

P.O. Box 38269

Dallas, TX 75238

(214) 349-1982

Flo-Tron, Inc.

495 E. 30th Street

Paterson, NJ 07504

(201) 279-6500

The Foxboro Company

Dept 120, 38 Neponset Ave.

Foxboro, MA 02035

(617) 543-8750

ITT Barton

Box 2013

Monterey Park, CA 91754

(213) 289-3581

Jiskoot Autocontrol Ltd.

c/o A.W. Risser Company

64 Edgewood Drive

Grafton, OH 44044

(216) 458-5091

Kay -Ray, Inc.

516 W. Campus Drive

Arlington Heights, IL 60004

(312) 259-5600

Kurz Instruments

P.O. Box 849, 20 Village Square

Carmel Valley, CA 93924

(408) 659-3421

Leeds & Northrup Company

Sumneytown Pike

North Wales, PA 19454

(215) 643-2000

Matheson Gas Products

P.O. Box E 1275 Valley Brooke Ave.

Lyndhurst, NJ 07071

(201 ) 935-6 6 60

Micromotion Inc.

2700 29th Street

Boulder, CO 80301

(303) 442-5911

Milltronics, Inc.

2409 Avenue J Arlington, TX 76011

(817) 649-8540

Moore Industries Inc.

16650 Schoenborn Street

Sepulveda, CA 91343

(213) 894-7111

11-38
Precision Flow Devices Inc.

P.O. Box 2364

Santa Clara, CA 95051

Quantum Dynamics, Inc.

19458 Ventura Blvd.

Tarzana, CA 91356

(213) 345-6828

Ramapo Instruments Co., Inc.

P.O. Box 428

2 Mars Court

Montville, NJ 07045

(201) 263-8800

The Singer Company

American Meter Div.

13500 Philmont Avenue

Philadelphia, PA 19116

(215) 673-2100

TSI Inc.

500 Cardigan Road

P.O. Box 43394

St. Paul, MN 55164

(612) 483-0900

Technology Inc.

Instruments & Controls Div.

P.O. BOX 3036

Overlook Branch

Dayton, OH 45431

(513) 426-2405

Teledyne Hastings-Raydist

P.O. Box 1275

Hampton, VA 23361

(703) 723-6531

Thermal Instruments Co.

217 Sterner Mill Road

Trevose, PA 19047

(215) 355-8400

Tylan Corporation

19220 S. Normandie

Torrance, CA 90502

(213) 532-3420

UGC Industries Inc.

P.O. Box 3736

Shreveport, LA 71103

(318) 631-0373

Wallace & Tiernan Division

Penwalt Corporation

25 Main Street

Belleville, NJ 07109

(201) 759-8000

Westinghouse Electric Corp.

Computer & Instrumentation Div.

200 Beta Drive

Pittsburgh, PA 15238

(412) 782-1730

Westinghouse Electric Corp.

Computer & Instrumentation Div.

Box 402

Orrville, OH 44667

11-39
Ultrasonic Flow Sensors

Accusonic Division

O.R.E., Inc.

P.O. Box 709

Falmouth, MA 02541

(617) 548-5800

Badger Meter, Inc.

Instruments Div.

4545 W. Brown Deer Road

Milwaukee, WI 53223

(414) 355-0400

Badger Meter, Inc.

Precision Products Div.

6116 E. 15th Street

Tulsa, OK 74112

(918) 836-4631

Bailey Scientific

P.O. Box 1245

West Sacramento, CA 95691

(916) 371-1472

Baird Controls, Inc.

522 West 5th Avenue

Napierville, IL 60540

Brooks Instrument

Emerson Electric Canada

Box 150

Markham, Ontario, Canada L3P 3J6

(416) 297-2330

Columbia Controls

4545 Pine Timbers

Bldg. 300

Houston, TX 77041

(713) 462-7800

Control otron Corporation

155 Plant Avenue

Hauppauge, NY 11787

(516) 231-3600

DuPont Company

Instrument Products Div.

1007 Market Street

Wilmington, DE 19898

(302) 772-5500

Endress & Hauser Inc.

2350 Endress Place

Greenwood, IN 46142

(317) 535-7138

Hersey Products, Inc.

Industrial Measurement Div.

Old Valley Falls Road

Spartanburg, SC 29303

(803) 578-3800

Inventron Industries Inc.

4005 W. Jefferson Blvd.

Los Angeles, CA 90016

(213) 731-2507

Leeds & Northrup Company

Sumneytown Pike

North Wales, PA 19454

(215) 643-2000

Linden Laboratories, Inc.

P.O. Box 920

State College, PA 16801

(814) 355-5491

Manning Environment Corp.

120 Dubois Street

P.O. Box 1356

Santa Cruz, PA 95061

(408) 427-0230

Mapco Inc.

(Nusonics) Process & Pollution

Cont.

1800 S. Baltimore Avenue

Tulsa, OK 74119

(918) 488-1010

Milltronics Inc.

2409 Avenue J Arlington, TX 76011

(817) 649-8540

O.R.E.

(Ocean Research Equipment, Inc.)

(see: Accusonic)

11-40
Polysomes

3230 Mercer Street

P.O. Box 22488

Houston, TX 77027

(713) 623-2134

Siemans Corporation

Medical Systems Group

186 Wood Avenue, South

Iselin, NJ 08830

(201 ) 494-1000

Sirco Controls

2795 152nd Avenue, NE

Redmond, WA 98052

(206) 885-5303

Sparl ing

Div. Envirotech Corp.

4097 N. Temple City Blvd.

El Monte, CA 91731

(213) 444-0571

Stevens International Inc.

P.O. Box 619

Kennett Square, PA 19348

(215) 444-0616

Tech/Sonics

(see: Polysonics)

Texas Nuclear Division

Ramsey Engineering Company

Box 9267

Austin, TX 78766

Tri-Aid Sciences, Inc.

830 Linden Avenue

Rochester, NY 14625

(716) 381-1642

Wesmar

905 Dexter Avenue, N. Seattle, WA 98109

(206) 285-2420

Westinghouse Electric Corp.

Computer & Instrumentation Div.

Box 402

Orrville, OH 44667

Westinghouse Electric Corp.

Computer & Instrumentation Div.

200 Beta Drive

Pittsburgh, PA 15238

(412) 782-1730

11-41
Open Channel Flow Meters

American Meter Division

( see: The Singer Co.

)

BIF, A Unit of General Signal

1600 Division Road

West Warwick, RI 02893

(401) 885-1000

BIF, Sanitrol, A Unit of General

1800 12th Street, SE

P.O. Box 4

Largo, FL 33540

(813) 584-2157

Badger Meter, Inc.

Instruments Div.

4545 W. Brown Deer Road

Milwaukee, WI 53223

(414) 355-0400

Badger Meter, Inc.

Precision Products Div.

6116 E. 15th Street

Tulsa, OK 74112

(918) 836-8411

Cues, Inc.

P.O. Box 5516

3501 S. Fineland Road

Orlando, FL 32805

(305) 241-1671

Drexel brook Engineering Co.

205 Keith Valley Road

'

ignal Horsham, PA 19044

(215) 674-1234

Endress & Hauser Inc.

2350 Endress Place

Greenwood, IN 46142

(317) 535-7138

Fischer & Porter Company

775 Warminster Road

Warminster, PA 18974

(215) 674-6000

Flow Technology, Inc.

4250 E. Broadway Road

Phoenix, AZ 85040

(602) 268-8776

Bailey Scientific The Foxboro Company

P.O. Box 1245 Dept. 120, 38 Neponset Ave,

Sacramento, CA 95691 Foxboro, MA 02035

(916) 371-1472 (617) 543-8750

C-E Invalco Hersey Products Inc.

Div. of Combustion Engineering Inc. Industrial Measurement Div.

P.O. Box 556 Old Valley Falls Road

Tulsa, OK 74101 Spartanburg, SC 29303

(918) 932-5671 (803) 578-3800

Computer Instruments Corp.

100 Madison Avenue

Hempstead, LI, NY 11550

(516) 483-8200

Control otron Corporation

155 Plant Avenue

Hauppauge, NY 11787

(516) 231-3600

Cushing Engineering Inc.

(see: Monitek, Inc.)

Honeywell Inc.

Process Control Div.

1100 Virginia Drive

Fort Washington, PA 19034

(215) 643-1300

ISCO

4700 Superior Avenue

Lincoln, NE 68504

(402) 464-0231

11-42
Inventron Industries, Inc.

4005 W. Jefferson Blvd.

Los Angeles, CA 90016

(213) 731-2507

Kahl Scientific Instrument Corp.

P.O. Box 1166

El Cajon, CA 92022

(714) 444-2158

Leupold & Stevens, Inc.

P.O. Box 688

600 N.W. Meadow Drive

Beaverton, OR 97005

(503) 646-9171

Macrodyne Inc.

153 Princeton Road

Schenectady, NY 12306

(518) 356-3500

Manning Environmental Corporation

120 DuBois Street

P.O. Box 1356

Santa Cruz,CA 95061

(408) 427-0230

Marsh-McBirney Inc.

8595 Grovemont Circle

Gaithersburg, MD 20760

(301) 869-4700

Mead Instrument Corporation

One Day Lane

Riverdale, NJ 07457

(201) 835-5988

Milltronics Inc.

2409 Avenue J Arlington, TX 76011

(817) 649-8540

Monitek, Inc.

Monitor Technology Inc.

630 Price Avenue

Redwood City, CA 94063

(415) 365-6550

NB Instruments Inc.

935 Horsham Road

Horsham, PA 19044

(215) 674-8660

NP Industries, Inc.

P.O. Box 746

Niagara Falls, NY 14302

(716) 282-0022

Pro-Tech, Environmental Instr. Div.

Crane Company

1510 Russell Road

Paoli, PA 19301

(215) 644-4420

Raeco Inc.

550 Armory Drive

South Holland, IL 60473

(312) 331-6001

Ramapo Instrument Co., Inc.

P.O. Box 428

2 Mars Court

Montville, NJ 07045

(201) 263-8800

Robertshaw Controls Co.

Industrial Instrumentation Div.

333 N. Euclid Way

Anaheim, CA 92803

(714) 535-8151

Sierra Instruments Inc.

P.O. Box 909

Village Square Building

Carmel Valley, CA 93924

(408) 659-3177

Sigmamotor Incorporated

14 Elizabeth Street

Middleport, NY 14105

(7116) 735-3616

The Singer Company

American Meter Division

13500 Philmont Avenue

Philadelphia, PA 19116

(215) 673-2100

Sirco Controls Company

2795 - 152nd Avenue, NE

Redmond, WA 98052

(206) 885-5303

11-43
Sparling Division

Envirotech Corporation

4097 N. Temple City Blvd.

El Monte, CA 91731

(213) 444-0571

Stevens International, Inc.

P.O. Box 619

Kennett Square, PA 19348

(215) 444-0616

Tri-Aid Sciences, Inc.

830 Linden Avenue

Rochester, NY 14625

(716) 381-1642

Turner Designs

2247A Old Middlefield Way

Mountain View, CA 94043

(415) 965-9800

Universal Engineered Systems, Inc.

7071 Commerce Circle

Pleasanton, CA 94566

(415) 462-1543

Wesmar, Environmental Meas. Systems

905 Dexter Avenue, N Seattle, WA 98109

(206) 285-2420

Linear Displacement Sensors

ADE Corporation

127 Coolidge Hill Road

Watertown, MA 02172

(617) 923-2180

AS I 840 Del Rey Avenue

Sunnyvale, CA 94086

(408) 739-6700

Acme Cleveland Corporation

Box 91276

Cleveland, OH 44101

Alco Electronic Products Inc.

1551 Osgood Street

Andover, MA 01845

(617) 685-4371

Alina Corporation

175 Sunnyside Blvd.

Plainview, NY 11803

(615) 433-1000

Allen-Bradley Company

1201 S. Second Street

Milwaukee, WI 53204

(414) 671-2000

American Electronic Controls

Scientronics Division

25 Clark Drive

Barring ton, NJ 08007

(609) 546-5792

B. C. Ames Company

131 Lexington Street

Waltham, MA 02154

(617) 893-0095

11-44
Ametek Controls Division

860 Pennsylvania Blvd.

Feasterville, PA 18960

(215) 355-6900

Anorad Corporation

116 Plant Avenue

Smithtown, NY 11787

(516) 234-1824

Astrosystems Inc.

6 Nevada Drive

Lake Success, NY 11040

(516) 328-1600

Atmospheric Sciences Inc.

(see: ASI)

Autech Corporation

7020 Huntley Road

Columbus, OH 43229

(614) 888-9924

Automatic Switch Company

50-56 Hanover Road

Florham Pk, NJ 07932

(201) 966-2000

Automatic Timing & Controls Inc.

King of Prussia, PA 19406

(215) 265-0200

Automation Systems, Inc.

Del Mar Drive

Brookfield, CT 06804

(203) 775-2581

BIE Instruments Inc.

2100 West Loop South

Houston, TX 77027

(713) 961-1921

Banner Engineering

(see: Truck Mul tiprox Inc.)

Bentley Nevada Corporation

P.O. Box 157

Minden, NV 89423

(702) 782-3611

Burrell Corporation

2223 Fifth Avenue

Pittsburgh, PA 15219

(412) 471-2527

Columbia Research Laboratories

MacDade Blvd. and Bui lens Lane

Woodlyn, PA 19094

(215) 532-9464

Dearborn Gage Company

32330 Ford Road

Garden City, MI 48135

(313) 422-8300

Delavan Electronics Inc.

1441 North 73rd Street

Scottsdale, AZ 85260

(602) 948-6530

R.B. Denison Inc.

(see: Gould Inc Controls Div)

Disa Electronics

779 Susquehanna Avenue

Franklin Lakes, NJ 07417

(201 ) 891-9460

Dynapar Corporation

1675 Del any Road

Gurnee, IL 60031

(312) 662-2666

Edwards High Vacuum, Inc.

3279 Grand Island Blvd.

Grand Island, NY 14072

(716) 773-7552

El dec, formerly Electro Devel

Corp.

Box 100

16700 1.3th Avenue

W. Lynnwood, WA 98036

(206) 743-1313

Electro Corporation

1845 57th Street

Sarasota, FL 33580

(813) 355-8411

11-45
Electromatic Equipment Co., Inc.

6U0 Oakland Avenue

Cedarhurst, NY 11516

(516) 295-4300

Electronic Counters & Controls Inc.

1500 McCormick Blvd.

Mundelein, IL 60060

(312) 362-8910

Electro Sonic Control

(see: Key Electro Sonic)

Engery Inc.

Idaho Falls, ID 83401

(208) 524-1000

Gagne Associates Inc.

1080 Chenango & Hillcrest

Binghamton, NY 13901

(607) 723-9556

Gould Inc. Controls Div.

R.B. Dennison

103 Broadway

Bedford, OH 44146

(216) 232-8200

Gould Inc. Instruments Div.

3631 Perkins Avenue

Cleveland, OH 44114

(216) 361-3315

Hamlin Incorporated

Lake and Grove Streets

Lake Mills, WI 53551

(414) 648-2361

Hammond Industries, Inc.

155 Michael Drive

Syosset, NY 11791

(516) 364-1900

Helm Instrument Co., Inc.

4511 South Avenue

Toledo, OH 43615

(419) 531-0146

Hi tec Corporation

65 Power Road

Westford, MA 01886

(617) 692-4793

Hottinger Baldwin Measurements Inc.

1 7 Mercer Road

Natick, MA 01760

(617) 655-0950

IRD Mechanal ysis, Inc.

6150 Huntley Road

Columbus, OH 43229

(614) 885-5376

Ideal Aerosmith Inc.

1505 E. Fox Farm Road

Cheyenne, WY 82001

(307) 634-7714

Indikon Company, Inc.

71 Coolidge Hill Road

Watertown, MA 02172

(617) 926-2710

Industrial Solid State Controls

Inc.

435 West Philadelphia St.

P.O. Box 934

York, PA 17405

(717) 848-1151

Integrated Photomatrix Inc.

The Grove Trading Estate

Dorchester, Dorset, England

JMR Electronics Corporation

1525 Blondell Avenue

Bronx, NY 10461

(212) 792-9620

Kaman Sciences Corporation

P.O. Box 7463

Colorado Springs, CO 80933

(303) 599-1500

Kavlico Corporation

20869 Plummer Street

Chatsworth, CA 91311

(213) 882-2400

11-46
Key ElectroSonic

P.O. Box 6

Milton-Freewater, OR 97862

(503) 938-5556

Konigsberg Instruments

(see: Unimeasure Di v.

Krautkramer-Branson, Inc.

250 Long Beach Blvd.

Stratford, CT 06497

(203) 377-3900

LEL Company

5 Burns Place

Cresskill, NJ 07626

(201) 569-8641

Lion Precision Inc.

60 Bridge Street

Newton, MA 02195

(617) 9b9-4710

MTS Systems Corporation

Motion Products Div.

P.O. Box 24012

Minneapolis, MN 55424

(612) 944-4095

McFadden Electronics Co.

8953 Atlantic Blvd.

South Gate, CA 90280

(213) 564-5958

Mechanical Technology Inc.

MTI Instruments Division

968 Albany Shaker Road

Lathan, NY 12110

(518) 785-2211

Metrix Instrument Co.

1711 Townhurst Drive

Houston, TX 77043

(713) 461-2131

Micro Switch Div. of Honeywell Inc.

11 W. Spring Street

Freeport, IL 61032

(815) 235-5500

Namco Controls

(see: Acme Cleveland Corp.

New England Instrument Co.

14 Kendall Lane

Natick, MA 01760

(617) 873-9711

North American Philips Control Corp.

Cheshire Industrial Park

Cheshire, CT 06410

(203) 272-0301

The Ohmart Corporation

4241 Allendorf Drive

Cincinnati, OH 45209

(513) 272-0131 .

Omron Corp. of America

233 South Wacker Drive

Chicago, IL 60606

(312) 876-0800

Ono Sokki Co., Ltd.

22-16 Shimomaruko 2-Chome

Ohta-Ku, Tokyo, Japan

Optron Division, Universal Tech.

(see: Universal Tech. Inc.,

Optron Div.

Ortec Inc.

100 Midland Road

Oak Ridge, TN 37830

(615) 482-4411

PPR Electronics Co.

209 W. Church Street

P.O. Box 396

Centre Hall, PA 16828

(814) 364-9162

Panametrics Inc.

221 Crescent Street

Waltham, MA 02154

(617) 899-2719

Photomation Inc.

270 Polaris Avenue

P.O. Box 460

Mountain View, CA 94042

(415) 967-8992

11-47
Pickering and Co., Inc.

Measurement & Controls Div.

101 Sunnyside Blvd.

Plainview, NY 11803

(516) 681-0200

Post Electronic Products Inc.

P.O. Box 494

Beverly, MA 01905

(617) 922-5005

Sensor Corporation

303 Scottsdale Avenue

P.O. Box 140

Scottsdale, PA 15683

(412) 887-4080

Sick Optik-Elektronik, Inc

113 South Main Street

Stillwater, MN 55082

(612) 439-6516

Powell Magnetic Industries

Div. of Powell Electrical Mfg. Co

8550 Mosley Drive

Houston, TX 77034

Power/Mation Division

1441 Iglehart Ave.

St. Paul, MN 55104

(612) 645-0781

Research Inc.

Box 24064

Minneapolis, I 55424

Rechner Electronics

8661 Buffalo Avenue

Niagara Falls, NY 14304

(716) 283-8744

Robinson-Hal pern Company

One Apollo Road

Plymouth Meeting, PA 19462

(215) 825-9200

SIC Division

(see: Automatic Timing & Controls)

Schaevitz Engineering

U.S. Rte. 130 & Union Ave.

Pennsauken, NJ 08110

(609) 662-8000

Scientific Technology Inc.

1201 San Antonio Road

Mountain View, CA 94043

(415) 965-091U

Sigma Laboratories Inc.

88-11 31st Avenue

East Elmhurst, NY 11369

(212) 898-2427

Siltran Digital

P.O. Box 437

Silverado, CA 92676

(714) 649-2704

Sonic Instruments Inc.

1018 Whitehead Road Ext.

Trenton, NJ 08638

(609) 883-5030

Techmet Company

6060 Executive Blvd.

Dayton, OH 45424

(513) 233-9935

Temposonics Inc.

131 East Ames Ct.

Plainview, NY 11803

(516) 935-4100

Terra Technology Corporati

3018 Western Avenue

Seattle, WA 98121

(206) 682-9946

Testing Machines, Inc.

400 Bay view Avenue

Amity ville, NY 11/01

(516 ) 842-5400

Textron Inc.

Waterbury Farrel Division

Cheshire, CT 06410

11-48
Theta Instrument Corporation

24 Dwight Place

Fairfield, NJ 07006

(201 ) 22/-1 /OO

Warmer Electric Brake & Clutch Co.

449 Gardner Street

Beloit, WI 53511

(815) 389-3771

Turck Multiprox Inc.

9710 Tenth Avenue, N. Minneapolis, MN 55441

(612) 544-7977

Wilco Inc.

(see: Sick Optik-Elektronik, Inc

Wilson Instrument Company

587 South Hill Avenue

Pasadena, CA 91106

(213) 449-4858

UPA Technology Inc.

60 Oak Drive

Syosset, NY 11791

(516) 364-1080 Zygo Corporation

Laurel Brook Road

Middlefield, CT 06455

(203) 347-8506

Unimeasure Division

Konigsberg Instruments

2000 E. Foothill Blvd.

Pasadena, CA 91107

(213) 795-9719

United Detector Technology, Inc.

2644 30th Street

Santa Monica, CA 90405

(213) 396-31/5

Unit Process Assemblies, Inc.

(see: UPA Technology Inc.)

Universal Technology Inc.

Optron Division

30 Hazel Terrace

Woodbridge, CT 06525

(203) 389-5384

Valmet Inc.

100 Production Court

New Britain, CT 06051

(203) 223-6784

Vexilar, Inc.

9345 Penn Avenue, South

Minneapolis, MN 55431

11-49
Linear and Angular Position Encoders

Airflyte Electronics Company

Box 231, New Hook Road

Bayonne, NJ U7002

(201) 436-2230

Altek Corporation

2150 Industrial Parkway

Silver Spring, MD 20904

(301) 622-3907

Anadex Instruments, Inc.

9825 DeSota Avenue

Chatsworth, CA 91311

(213) 988-8010

Astrosystems Inc.

6 Nevada Drive

Lake Success, NY 11040

(516) 328-1600

Auto-Trol Corporation

5650 N. Pecos Street

Denver, CO 80221

(303) 458-5900

BEI Electronics, Inc.

1101 McAlmont Street

Little Rock, AR 72203

(501) 372-7351

Bendix Corporation

Environmental Science Div.

1400 Taylor Avenue

Baltimore, MD 21204

(301) 825-5200

Bendix Corporation

Industrial Tools Div.

1901 S. Rockwell Street

Chicago, IL 60608

(312) 24/-59U0

Clifton Precison

(see: Litton Encoder Div.)

Computer Conversions Corporation

6 Dunton Ct.

East Northport, NY 11731

(516) 261-3300

Datacap Inc.

732 S. Federal Street

Chicago, IL 60605

(312) 922-5366

Da tame tries

340 Fordham Road

Wilmington, MA 01887

(617) 658-5410

Data Technology, Inc.

4 Gill Street

Woburn, MA 01801

(617) 935-8820

Disc Instruments Inc.

102 E. Baker Street

Costa Mesa, CA 92626

(714) 979-5300

Dunlap Instrument Corp.

2254 Kingsway Drive

P.O. Box 521

Cape Girardeau, MO 63701

(314) 335-0522

Dynamics Research Corp.

Components Division

60 Concord Street

Wilmington, MA 01887

(617) 658-6100

Electronic Counters & Controls

1500 McCormick Blvd.

Mundelein, IL 60060

(312) 362-8910

Elographics, Inc.

19/6 Oak Ridge Turnpike

Oak Ridge, TN 37830

(615) 482-4038

Flight Research

Div. of Geotel , Inc.

Charles City & Lewis Roads

P.O. Box 1-F

Richmond, VA 23201

(804) 222-0163

11-50
Hutchinson Industrial Corp.

4U W. Highland Park

Hutchinson, MN 55350

(612) 8/9-2371

Hybrid Systems Corporation

Crosby Drive

Bedford, MA 01730

(617) 275-1570

ILC Data Device Corporation

105 Wilbur Place

Bohemia, NY 11716

(516) 56/-5600

Integrated Photomatrix Ltd.

The Grove Trading Estate

Dorchester, Dorset, England

Itek Measurement Systems Div.

Itek Corporation

27 Christina Street

Newton, MA 02161

(617) 969-7300

JMR Electronics Inc.

1525 Blondell Avenue

Bronx, NY 10461

(212) 792-9620

Key Electro Sonic

Box 6

Milton-Freewater, OR 97862

(503) 938-5556

LaBarge Inc.

Electronics Division

6540 E. Apache

P.O. Box 36

Tulsa, OK 74101

(918) 836-7611

Leupold & Stevens Inc.

P.O. Box 688

600 N.w. Meadow Drive

Beaverton, OR 97005

(503) 646-9171

Librascope Division

(see: Singer)

Litton Encoder Division

Marple at Broadway

Clifton Heights, PA 19018

(215) 622-1000

Litton Systems, Encoder Div.

20745 Nordhoff Street

Chatsworth, CA 91311

(213) 341-6161

Los Angeles Scientific Instrument Co.

Inc.

2451 Riverside Drive

Los Angeles, CA 90039

(213) 662-2128

North Atlantic Ind. Inc.

200 Terminal Drive

Plainview, NY 11803

(516) 681-8600

Northern Precision Laboratories

202 Fairfield Road

Fairfield, NJ 07006

(201) 227-4800

Perrine Inc.

Paraiso Hot Springs

Soledad, CA 93960

(408) 6/8-3502

Randall , Douglas

6 Pawcatuck Avenue

Pawcatuck, CT 02891

(203) 599-1/50

Renco Corporation

26 Coromar Drive

Goleta, CA 95017

(805) 968-1525

Sangamo Weston, Inc., EMR Teletry Div

Sarasota, FL 33578

(813) 371-0811

Science Accessories Corporation

970 Kings Highway West

Southport, CT 06490

(203) 255-1526

11-51
Sequential Information Sys. Inc.

249 N. Sawmill River Road

Elmsford, NY 10523

(914) 592-5930

Siltran Digital

P.O. Box 437

Silverado, CA 92676

(714) 649-2704

Singer Company, Librascope Div.

833 Sonora Avenue

Olendale, CA 91201

(213) 245-8711

Standard Microsystems Corp.

35 Marcus Blvd.

Hauppauge, NY 11787

(516) 273-8898

Teledyne Gurley

514 Fulton Street

Troy, NY 12181

(618) 272-6300

Transmagnetics Inc.

210 Adams Blvd.

Farmingdale, NY 11735

(516) 293-3100

Unidyne Inc.

Subsidiary of Tri-Tronics Co., Inc

619 Enterprise Drive

Oak Brook, IL 60511

Zeiss, Inc.

444 Fifth Avenue

New York, NY 10018

(212) 730-4400
Accel erometers and Vibration Equipment

Acurex Autodata Corporation

485 Clyde Avenue

Mountain View, CA 94043

(415) 964-3200

Airpot Corporation

Norwalk, CT 06852

(203) 846-2021

BBN Instruments Company

50 Moulton Street

Cambridge, MA 02138

(617) 491-0091

B&K Instruments Inc.

5111 W. 164th Street

Cleveland, OH 44142

(216) 267-4800

Bailey Scientific

P.O. Box 1245

West Sacramento, CA 95691

(916) 371-1472

Bell & Howell, CED Div.

360 Sierra Madre Villa

Pasadena, CA 91109

(213) 796-9381

Bently Nevada

P.O. Box 157

Minden, NV 89423

(702) 782-3611

Bouche Laboratories

11042 Olinda Street

Sun Valley, CA 91352

(213) 767-7273

Bourns Inc.

1200 Columbia Avenue

Riverside, CA 92507

(714) 781-5070

California Controls Company

2212 6th Street

Berkeley, CA 94710

(415) 549-1080

Columbia Research Lab, Inc.

McDade Blvd. & Bui lens Lane

Woodlyn, PA 19094

(215) 532-9464

Conrac Corporation, Instruments/

Control Div.

1600 S. Mountain Avenue

Duarte, CA 91010

(213) 359-9141

Dallas Instruments, Inc.

P.O. Box 38189

Dallas, TX 75238

(214) 341-2990

Degamo Inc.

500 Ashland Avenue

P.O. Box 653

Chicago Heights, IL 60411

(312) 754-3131

Disa Electronics

779 Susquehanna Avenue

Franklin Lakes, NJ 07417

(201 ) 891-9460

Ehrenreich Photo-Optical Ind., Inc.

Instrument Group

623 Stewart Avenue

Garden City, NY 11530

(516) 222-0200

Electrodyne Inc., Advanced Dynamics

Instrs. Div.

2316 Jefferson Davis Hwy.

P.O. Box 358

Alexandria, VA 22313

(703) 836-4641

Electro-Physics Company

9303 N. Major Avenue

Morton Grove, IL 60053

(312) 966-4/52

Endevco Dynamic Instruments Division

30700 Rancho Viejo Road

San Juan Capistrano, CA 92675

(714) 493-8181

11-53
Entran Devices Inc.

10 Washington Avenue

Fairfield, NJ 07006

(201) /85-4060

Epic Inc.

150 Nassau Street, Suite 1430

New York, NY 10038

(212) 349-24/0

General Axial Engine Company

38 Franklin Avenue

Lockport, NY 14094

GenRad Inc.

300 Baker Avenue

Concord, MA 01742

(617) 369-8/70

GenRad Inc., Time/Data Div.

2855 Bowers Avenue

Santa Clara, CA 95051

(408) 985-0/UO

Gould Inc., Measurement System Div.

2230 Statham Blvd.

Oxnard, CA 93030

(805) 487-8511

Gulton Industries S-C Division

1644 Whittier Avenue

Costa Mesa, CA 92627

(714) 642-2400

Helm Instrument Co., Inc.

4511 South Avenue

Toledo, OH 43615

(419) 531-0146

Hewlett Packard Santa Clara Div.

5301 Stevens Creek Blvd.

Santa Clara, CA 95050

(408) 246-4300

Hottinger Baldwin Measurement

17 Mercer Road

Natick, MA 01/60

(617) 655-0950

Humphrey Inc.

9212 Balboa Avenue

San Diego, CA 92123

(714) 565-6631

Inc.

IRD Mechanalysis Inc.

6150 Huntley Road

Columbus, OH 43229

(614) 885-5376

Impact-O-Graph Div. Torq Eng. Products

32 W. Monroe Street

Bedford, OH 44146

(216) 232-1880

Impact Register Inc.

W. Springfield Avenue

P.O. Box 3097

Champaign, IL 61820

(217) 352-4129

International Scientific

3255-6C Scott Blvd.

Santa Clara, CA 95050

(408) 249-9840

Ithaco, Inc.

Box 818

735 W. Clinton Street

Ithaca, NY 14850

(607) 272-7640

Instr. Inc. ( IS I

)

KDO Precision Products Inc.

3975 McMann Road

Cincinnati, OH 45245

(513) 943-2000

Kaman Sciences Corporation

P.O. Box 7463

Colorado Springs, CO 80933

(303) 599-1500

Kinetic Systems Inc.

70 Lincoln Street

Brighton, MA 02135

(617) 782-7800

Kistler-Morse Corporation

13277 Northrup Way

Bellevue, WA 98005

(206) 641-4200

Konigsberg Instruments Inc.

(see: Uni measure Div.,

Konigsberg Inst.)

11-54
Kistler Instrument Corporation

2475 Grand Island Blvd.

Grand Island, NY 14U72

(716) /73-3140

Kulite Semiconductor Products Inc.

1039 Hoyt Avenue

Ridgefield, NJ 07657

(201) 945-3000

L.A.B. Div., Mechanical Technology

Onondaga Street

Skaneateles, NY 13152

(315) 685-5781

Larson Aero Development

P.O. Box 135

Concord, CA 94522

(415) 228-/8/0

Ling Electronics Inc.

1515 S. Manchester Ave.

Anaheim, CA 92803

(714) 774-2000

Lion Precision Inc.

60 Bridge Street

Newton, MA 02195

(617) 969-4710

MBIS Inc.

25865 Richmond Road

Bedford Heights, OH 44146

(216) 282-5850

Mechanical Technology Inc.

MTI Instruments Division

968 Albany-Shaker Road

Latham, NY 12110

(518) 785-2211

Media Recovery Inc.

2550 Electronic Lane, Suite 205

Dallas, TX /5220

(214) 350-5725

Metrix Instrument Company

1711 Townhurst Drive

Houston, TX 77043

(713) 461-2131

Muirhead, Inc.

1101 Bristol Road

Mountainside, NJ 07092

(201 ) 233-6010

Nicolet Scientific Corporation

P.O. Box 159, 245 Livingston St.

Northvale, NJ 07647

(201 ) 767-7100

PCB Piezotronics, Inc.

P.O. Box 33

Buffalo, NY 14225

(716) 684-0001

Precision Filters Inc.

303 West Lincoln Street

Ithaca, NY 14850

(607) 277-3550

Production Measurement Corp.

(see: Scientific Energy Systems

Corp., PMC/Beta)

Robertshaw Controls Company

Industrial Instrumentation Div.

333 N. Euclid Way

Anaheim, CA 92803

(714) 535-8151

Robinson-Hal pern Company

One Apollo Road

Plymouth Meeting, PA 19462

(215) 825-9200

Rhode & Schwarz Sales Company

14 Gloria Lane

Fairfield, NJ 07006

(201) 575-0750

Schaevitz Engineering

P.O. Box 505

Camden, NJ 08101

(609) 662-8000

Scientific-Atlanta Inc.

New Jersey Div. (QuanTech)

Randolph Park West, Rt. 10

Randolph Twp., NJ 07801

(201 ) 361-3100

11-55
Scientific Energy Systems Corp.,

PMC/Beta

4 Tech Circle

Natick, MA 01/60

(617) 237-6920

Sensory Products Inc.

IKON Communications Consultants, Inc.

654 Washington St.

Wellesley, MA 02181

(617) 237-6060

Setra Systems Inc.

1 Strathmore Road

Natick, MA 01/60

(617) 655-4645

The Singer Company, Kearfoot Div.

1150 McBride Avenue

Little Falls, NJ 07424

(201) 256-4000

Spectral Dynamics Corporation

P.O. Box 671

San Diego, CA 92112

(714) 565-8211

Sprengnether, W.F. Instrument Co.

4567 Swan Avenue

St. Louis, MO 63110

(314) 535-1682

Sundstrand Data Control Inc.

Overlake Industrial Park

Redmond, WA 98052

(206) 885-3711

Systems Consultants Inc.

410 Jericho Turnpike

Jericho, NY 11753

(516) 822-5500

Systron-Donner Corporation

14844 Oxnard Street

Van Nuys, CA 91409

(213) 786-1760

Team Corporation

9949 Hayward Way

So. El Monte, CA 91733

(213) 442-3240

Terra Technology Corporation

3018 Western Avenue

Seattle, WA 98121

(206) 682-9946

Time/Data Corporation

(see: GenRad, Time Data Div.)

Trig-Tek, Inc.

423 S. Brookhurst St., Bldg. E Anaheim, CA 92804

(714) 956-3593

Unhol tz-Dickie Corporation

6 Brookside Dr /Barnes Industrial Park, N, Wallingford, CT 06492

(203) 265-3929

Unimeasure Div., Konigsberg-Instruments

2000 E. Foothill Blvd.

Pasadena, CA 91107

(213) 795-9719

Universal Technology Inc., Optron Div.

30 Hazel Terrace

Woodbridge, CT 06525

(203) 389-5384

Validyne Engineering Corporation

19414. Londelius Street

Northridge, CA 91324

(213) 886-8488

Vibra-Metrics/Kistler

385 Potnam Avenue

Hamden, CT 06517

(203) 288-6158

Vibration Control Company

(see: Bouche Laboratories)

Vibration Instruments Company

1614 Orangethorpe Way

Anaheim, CA 92801

(714) 879-6085

Vibration Sales & Service, Inc.

P.O. Box 3851

Amity Station, New Haven, CT 06525

(203) 389-1527

11-56
Vibration Test Systems

10246 Clipper Cove

Aurora, OH 44202

(216) 562-5729

Vibra-Meter Corporation

22109 S. Vermont Avenue

Torrance, CA 90502

(213) 320-8410

Vibroscope Company, Inc.

/0 Furnace Street

Kingston, NY 12401

(914) 331-4215

Vitec Incorporated

23645 Mercantile Road

Cleveland, OH 44122

(216) 464-4670

West Coast Research Corporati

P.O. Box 25061

Los Angeles, CA 90025

(213) 478-8833

Wilcoxcn Research

12156-B Parklawn Drive

Rockville, MD 20852

(301) 468-0055
FORCE/MASS

Force and Mass Sensors

A.L. Design & Development Co.

20/0 Niagara Falls Blvd.

lonawanda, NY 14150

(716) 692-5272

Acrison Inc.

2U Empire Blvd.

Moonachie, NJ U7U74

(201 ) 440-8300

Action Instruments Co., Inc.

8601 Aero Drive

San Diego, CA 92123

(714) 2/9-5726

Advance Weight System Inc.

715 West Smith

Medina, OH 44256

(216) 725-6409

Ail tech, A Cutler-Hammer Co.

19535 E. Walnut Drive

City of Industry, CA 91748

(213) 965-4911

Allegany Technology

143 Offutt Street

Cumberland, MD 21502

(301) 722-7330

American Scale Corporation

P.O. Box 299

Hartsdale, NY 10530

(914) 761-1745

Ametek, Controls Div.

P.O. Box 152

Feasterville, PA 1896U

(215) 355-6900

Ametek, Hunter Spring Div.

Hatfield, PA 19440

'

(215) 822-2971

Analogic Corporation

Audubon Road

Wakefield, MA 01880

(617) 246-0300

Automatic Control Systems, Inc.

851 5 Freeway Drive

Macedonia, OH 44056

(216) 467-2186

Automatic Packaging & Conveyor Co.

4010 Bluebonnet

Houston, TX 77025

Automatic Timing & Controls Co.

King of Prussia, PA 19406

(215) 265-0200

B&F Instruments Div., FX Systems

(see: FX Systems)

B&K Instruments Inc.

5111 W. 164th Street

Cleveland, OH 44142

(216) 267-4800

BLH Electronics

42 4th Street

Waltham, MA 02254

(617) 890-6700

Bay Labs, Inc.

20160 Center Ridge Road

Cleveland, OH 44116

(216) 333-3898

Bell & Howell , CEC Div.

360 Sierra Madre Villa

Pasadena, CA 91109

(213) 796-9381

Bitronics Inc.

732 Goepp Street

Bethlehem, PA 18018

(215) 866-U777

11-58
Borg-Erickson Corporation

1133 N. Kil bourn Avenue

Chicago, IL 60651

(312) 384-5600

Brewer Engineering Labs, Inc.

P.O. Box 288

Marion, MA 02738

(617) 748-0103

Brinkmann Instruments

Cantiague Road

Westbury, NY 11590

(516) 334-/500

CCS Systems, Inc.

15600 Megal Drive

Menomonee, WI 53051

(414) 255-5640

Cahn Instruments Div., Ventron Corp.

16207 S. Carmenita Road

Cerritos, CA 90701

(213) 926-33/8

The Carlson Company

P.O. Box 174, Hwy. 9 West

Clinton, AZ 72031

(501) 745-4811

Celesco Transducer Products Inc.

P.O. Box 1457, 7800 Deering Ave.

Canoga Park, CA 91304

(213) 884-6860

Chatillon, John & Sons

83-30 Kew Gardens Road

Kew Gardens, NY 11415

(212) 847-5000

Cleveland Machine Controls, Inc.

7550 Hub Parkway

Cleveland, OH 44125

(216) 524-8800

Comptrol Inc.

9505 Midwest Avenue

Cleveland, OH 44125

(216) 587-5212

Consolidated Controls Corporation

15 Durant Avenue

Bethel, CT 06801

(203) 743-6721

D.J. Instruments Inc.

11-E Esquire Road, N. Billerica, MA 01862

(617) 667-5301

Data Instruments

4 Hartwell Place

Lexington, MA 02173

(617) 861-7450

Data Scale Ltd.

4570 Enterprise Street

Fremont, CA 94538

(415) 651-7350

Detecto Scales, Inc.

103-00 Foster Avenue

Brooklyn, NY 11236

(212) 272-4500

Detroit Testing Machine Co.

9390 Grinnell

Detroit, MI 48213

Digi metric Co. /Div. of Sybron Corp.

(see: National Controls Inc.)

Dillon, W.C. & Co., Inc.

14620 Keswick Street

Van Nuys, CA 91407

(213) 786-8812

Doric Scientific Co.

3883 Ruffin Road

San Diego, CA 92123

(714) 565-4415

Dovey Mfg. Co., Inc.

P.O. Box 2249

Anderson, IN 46011

(317) 649-2576

11-59
Dynamic Measurements Corp.

6 Lowell Avenue

Winchester, MA 01890

(617) 729-/8/0

Electro-Numerics Inc.

1811 Reynolds Street

Irvine, CA 92714

(714) 549-8821

Electronic Scales International

P.O. Box 1087

San Gabriel, CA 91776

(800) 423-4384

Electronic Systems Design, Inc.

317 W. University Drive

Arlington Heights, IL 60004

(312) 398-0550

Electroscale Corporation

15 Third Street

Santa Rosa, CA 94501

(707) 546-6785

Emery, A. H. , Company

70 Pine Street

New Canaan, CT 06840

(203) 966-4551

Enerpac, Div. of Applied Power

Ind. Inc.

Butler, WI 53007

(414) 781-6600

Entran Devices, Inc.

1 0 Washington Ave.

Fairfield, NJ 07006

(201) 785-4060

FX Systems Corporation

CPO Box 818

77 Cornell Street

Kingston, NY 12401

(914) 338-0515

Fairbanks Weighing Div., Colt Industries

711 E. Street, Johnsbury Road

St. Johnsbury, VT 05819

(800) 451-4107

Fatigue Dynamics Inc.

P.O. Box 2533

Dearborn, MI 48123

(313) 273-8270

The Foxboro Company

Dept. 120, 38 Neponset Ave.

Foxboro, MA 02035

(617) 543-8750

GCA/Precision Scientific

3737 W. Cortland Street

Chicago, IL 60647

(312) 227-2660

GSE Inc.

23640 Research Drive

Farmington Hills, MI 48024

(313) 476-7875

Genisco Technology Corp.

18435 Susana Road

Compton, CA 90221

(213) 537-4750

Gentran Inc.

1290 Hammerwood Avenue

Sunnyvale, CA 94086

(408) 734-5060

Gould Inc., Measurement Systems Div.

2230 Statham Blvd.

Oxnard, CA 93030

(805) 487-8511

Guardian Electric Mfg. Co.

1550 W. Carroll Avenue

Chicago, IL 60607

(312) 243-1100

Hardy Scales Company

4075 Ruff in Road

San Diego, CA 92123

(714) 565-7701

S. Himmel stein & Company

2500 Estes Avenue

Elk Grove Village, IL 60007

(312) 439-8181

11-60
Hi -Speed Checkwei gher Company Inc.

P.O. Box 314

Ithaca, NY 14850

(607) 273-5121

Hi tec Corporation

Nardone Industrial Park

Westford, MA 01886

(617) 692-4/93

Honeywell Inc., Process Control Div.

1100 Virginia Drive

Fort Washington, PA 19034

(215) 643-1300

Hottinger Baldwin Measurements Inc.

17 Mercer Road

Natick, MA 01/60

(617) 655-0950

Houston Controls Packaging Inc.

P.O. Box 45873

Houston, TX 77045

Houston Instrument/Di v. Bausch & Lomb

One Houston Sq. at 850 Cameron Road

Austin, TX 78758

(512) 837-2820

Howe Richardson Scale Co.

680 Van Houten Avenue

Clifton, NJ 07015

(201 ) 471-3400

Industrial Nucleonics Corp.

650 Ackerman Road

Columbus, OH 43202

(614) 261-2000

Instron Corporation

100 Royal 1 Street

Canton, MA 02021

(617) 828-2500

Intech, Inc.

282 Brokaw Road

Santa Clara, CA 95050

(408) 244-0500

Intec Inc.

81 Chimney Road Rd.

Bridgewater, NJ 08807

(201 ) 356-8112

Interface Inc.

7401 E. Butherus Drive

Scottsdale, AZ 85260

(602) 948-5555

IRAD Gage, Inc.

14 Parkhurst Street

Lebanon, NH 03766

K-Tron Corporation

Warrick & Grill o Street

Glassboro, NJ 08028

(609) 881-6500

Kay -Ray Inc.

51 6 W. Campus Dri ve Arlington Heights, IL 60004

(312) 259-5600

Kelk, George Ltd.

48 Lesmill Road

Don Mills, Ontario M3R 7R2, Canada

(416) 445-5850

King, J .A. & Co. , Inc.

2620 High Point Road

P.O. Box 21225

Greensboro, NC 27420

(919) 292-0511

Kistler-Morse Corporation

13227 Northrup Way

Bellevue, WA 98005

(206) 641-4200

Konigsberg Instruments

(see: Unimeasure)

Kistler Instrument Corp.

75 John Glenn Drive

Amherst, NY 14126

(716) 691-5106

11-61
Kulite Semiconductor Products

1U39 Hoyt Avenue

Ridgefield, NJ 07657

(201) 945-3000

Lebow Associates Inc.

1728 Maplelawn Road

Troy, MI 48084

(313) 643-1220

Litton Industries Potentiometer Div.

226 E. 3rd Street

Mt. Vernon, NY 10550

(914) 664-7733

Magnaflux Corporation

Champion Spark Plug Co.

7328 W. Lawrence Avenue

Chicago, IL 60656

(312) 867-8000

Marshall Electronics Inc., Clayton Div.

7440 N. Long Avenue

Skokie, IL 60076

(312) 583-6060

Martin-Decker Corporation

1928 S. Grand

Santa Ana, CA 92/05

(714) 540-9220

Merrick Scale Mfg. Co.

180 Autumn Street

Passaic, NJ 07055

(201) 779-0697

Metron Corporation

928 W. Ninth Street

Upland, CA 91786

(714) 981-4981

Mettler Instrument Corp.

Box 100

Princeton, NJ 08540

(609) 448-3000

Micro-Measurements Div.

Vi shay Intertechnology Inc.

P.O. Box 306, 38905 Chase Rd.

Romulus, MI 48174

(313) 941-3900

Micro-Strain Inc.

Spring City, PA 19475

(215) 948-4550

Milltronics Inc.

2409 Avenue J Arlington, TX 76011

(817) 649-8540

Morehouse Instrument Co.

1742 Sixth Avenue

York, PA 17403

(717) 843-0081

National Controls Inc.

1160 Hopper Lane

Santa Rose, CA 94501

(707) 527-5555

Ohaus Scale Corporation

29 Hanover Road

Florham Park, NJ 07932

(201 ) 377-9000

Ohmart Corporation

4241 Allendorf Drive

Cincinnati, OH 45209

(513) 272-0131

Orbitran, Inc.

11487 Woods ide Ave.

Lakeside, CA 92040

(714 ) 448-5075

Ormond Inc.

11969 Rivera Road

Santa Fe Springs, CA 906/0

(213) 698-8358

PCB Piezotronics Inc.

P.O. Box 33

Buffalo, NY 14225

(716) 684-0001

Phoenix Precision Instr. Co.

Div. Virtis

Rte. 208

Gardiner, NY 12525

(914) 255-5000

11-62
Photobell Company, Inc.

12 E. 22nd Street

New York, NY 10010

(212) 674-2121

Pittsburgh Brass Mfg. Co.

Sandy Hill Road, R.D. 6

Irwin, PA 15642

(412) 863-0550

Powers Fiat Div. Powers Regulator Co.

3400 Oakton Street

Skokie, IL 60076

(312) 673-6/00

Princo Instruments

1020 Industrial Hwy.

Southampton, PA 18966

(215) 355-1 500

Process Analyzers Inc.

1101 State Road

Princeton, NJ 08540

(609) 921-7330

Process Systems Inc.

Subsidiary of Powell Industries, Inc.

8550 Mosley Dr., P.O. Box 12818

Houston, TX 77017

(713) 944-6900

Productronix Inc.

2409 West Bond St.

Park Forest South, IL 60466

(312) 563-1850

Proximity Controls Inc.

Box 50

Fergus Falls, MN 56537

(218) 736-6072

Ramsey Engineering Co.

1853 W. Country Rd. C. St. Paul, MN 55113

(612) 633-5150

Revere Corp. of America

845 N. Colony Road

Wallingford, CT 06492

(203) 269-7701

Rockwell Engineering Co.

2121 E. 45th St.

Indianapolis, IN 46205

(317) 251-9453

Ruska Instruments Corp.

6121 Hillcroft, P.O. Box 36010

Houston, TX 77036

(713) 774-2533

Schaevitz Engineering

P.O. Box 505

Camden, NJ 08101

(609) 662-8000

Scientech, Inc.

5649 Arapahoe Avenue

Boulder, CO 80303

(303) 444-1361

Sensotec Inc.

1200 Chesapeake Ave.

Columbus, OH 43212

(614) 486-7723

Soil test Inc., Cenco

2205 Lee Street

Evanston, IL 60202

(312) 869-5500

Space Electronics Inc.

P.O. Box 2166

Meriden, CT 06450

(203) 265-2945

Sterling Scale Co., Inc.

20950 Boening Dr.

Southfield, MI 480 75

(313) 358-0590

Straindyne Engineering Co.

P.O. Box 328

"

Los Altos, CA 94022

(415) 948-3227

Stra insert Co.

Union Hill Industrial Pk.

W. Conshohocken, PA 19428

(215) 825-3310

11-63
Streeter Amet, Div. Mangood Corp.

Dept. PBS, Slusser & Wickes Sts.

Grayslake, IL 60U3U

(312) 223-4801

Sundstrand Data Control Inc.

Overlake Industrial Pk.

Redmond, WA 98052

(206) 885-3711

Tensitron, Inc.

P.O. Box 185

Harvard Depot Rd.

Harvard, MA 01451

(617) 456-3511

Testing Machines Inc.

400 Bay view Avenue

Amity ville, NY 11701

(516) 842-5400

Thayer Scale Div.

Thayer Park

Pembroke, MA 02359

(617) 826-2371

Thor Power Tool Co. /Stewart-Warner Co

175 North State St.

Aurora, IL 60505

(312) 898-8000

Thurman Scale Company

1939 Regugee Road

Box 2179

Columbus, OH 43216

(614) 443-9/41

Toledo Scale Div. of Reliance

Electric Co.

Dept. 941, P.O. Box 1705

Columbus, OH 43216

Toroid Corporation

P.O. Box 1435

Huntsville, AL 35807

(205) 534-1687

Torsion Balance Co.

125 Ellsworth St.

Clifton, NJ 07012

(201) 473-6900

Transducer Products Inc.

95 Wolcott Ave.

Torrington, CT 06790

Transducers Inc./ELDEC

12140 E. Rivera Road

Whittier, CA 90606

(213) 945-3741

Tyco Instrument Div. Tyco

Laboratories

(see: Data Instruments)

Uni measure Div. Konigsberg Instr.

2000 E. Foothill Blvd.

Pasadena, CA 91107

(213) 795-9719

Vol and Corporation

27 Centre Avenue

New Rochelle, NY 10802

(914) 636-2014

Wallace & Tiernan Div. Pennwalt

Corp.

25 Main Street

. Belleville, NJ 07109

(201 ) 759-8000

Watson, 01 iver H.

232 Mi 11 bridge Road

Riverside, IL 60546

(312) 447-1024

Webster Instrument Inc.

1 1856 Mississippi Ave.

Los Angeles, CA 90025

(213) 479-6770

Weigh & Test Systems Inc.

8850 N.W. 22 Ave.

Miami, FL 33147

(305) 691-2561

Weight Systems Inc.

10210 N. Interregional

Austin, TX 78753

(512) 836-5513

West Coast Research

S. Sepulveda Blvd., P.O. Box 25061

Los Angeles, CA 90025

(213) 478-8833

11-64
Western Load Cell Co.

17929 Ventura Blvd.

Encino, CA 91316

(213) 996-2700

Wilcoxon Research

12156-B Park! awn Drive

Rockville, MD 20852

(301 ) 468-0055

Torque Sensors

AOK Tool Corp.

82-21 Sutter Ave.

Ozone Pk, NY 11417

(914) 835-2/40

AST Servo Systems Inc.

930 Broadway

Newark, NJ 07104

(201) 484-4233

A.V.D., B.V. of the Hague

c/o Netherlands Consulate General

Commercial Div. 571

One Rockefeller Plaza, NY 10020

Acurex Corp., Autodata Div.

485 Clyde Ave.

Mountain View, CA 94042

(415) 964-3200

Ametek/U.S. Gauge Div.

906 Clymer Ave.

Sellersville, PA 18960

(215) 248-3368

Apco Mossberg Co.

Lamb St.

Attleboro, MA 02703

(617) 222-U340

Asea Electric Inc.

4 New King St.

White Plains, NY 10604

(914) 428-600U

Brewer Engineering Labs, Inc.

P.O. Box 288

Marion, MA 02738

(617) 748-01 U3

The Carlson Co.

P.O. Box 174-Hwy 9 West

Clinton, AR 72031

(501 ) 745-4811

Chatillon & Sons, John

83-30 Kew Gardens Road

Kew Gardens, NY 11415

(212) 847-5000

Comstock & Wescott Inc.

765 Concord Avenue

Cambridge, MA 02138

(617) 547-2580

Data Instruments

4 Hartwell Place

Lexington, MA 02173

(617) 861-7450

Daytronic Corporation

2589 Corporate Place

Miamisburg, OH 45342

(513) 866-3300

Dillon & Company, W.C.

14620 Keswick Street

Van Nuys, CA 91407

(213) 786-8812

(212) 873-1354

Dynapar Corporation

1675 Del any Road

Gurnee, IL 60031

(312) 662-2666

Electronic Systems Design, Inc.

317 W. Washington Drive

Arlington Heights, IL 60004

(312) 398-0550

11-65
Fairlane Tool Company

31790 Groesbeck Hwy.

Fraser, MI 48026

(313) 293-0711

GSE Inc.

23640 Research Drive

Farmington Hills, MI 48024

(313) 476-7875

Kahn & Co., Inc.

885 Wells Road

Wetherfield, CN 06109

(203) 529-8643

Kavlico Electronics

20869 Plummer St.

Chatsworth, CA 91311

(213) 882-2400

General Thermodynamics Corp.

210 South Meadow Road

P.O. Box 1105

Plymouth, MA 02360

(617) 746-0200

Gentran Inc.

1290 Hammerwood Ave.

Sunnyvale, CA 94086

(408) 734-5060

Hi mmel stein & Co.

2500 Estes Avenue

Elk Grove Village,

(312) 439-8181

S.

IL 60007

Hottinger Baldwin Measurements

17 Mercer Road

Natick, MA 01760

(617) 655-0950

Inc.

Inductor Inc.

Union Grove, WI

(414) 878-3707

53182

Instron Corporation

100 Royal 1 St.

Canton, MA 02021

(617) 828-2500

Lebow Associates Inc.

1728 Maplelawn Road

Troy, MI 48084

(313) 643-0220

Link Engineering Co.

13840 Elmira

Detroit, MI 48227

(313) 933-4900

McFadden Electronics Co.

8953 Atlantic Blvd.

South Gate, CA 90280

(213) 564-5958

McNab Inc.

20 N. MacQuesten Parkway

Mt. Vernon, NY 10550

(914) 699-1616

Macotech Corporation

4104 W. Marginal Way S.W.

Seattle, WA 98106

(206) 932-4886

Magtrol

70 Gardenville Pkwy.,

Buffalo, NY 14224

(716) 675-3333

W.

James Gear Mfg. Co.

1140 W. Monroe St.

Chicago, IL 60607

(312) 226-1800

Jo-Line Tool s Inc.

P.O. Box 3186, 4225

Anaheim, CA 92806

(714) 524-3410

E. LaPalma

Meridian Laboratory Inc

Box 156

Middletown, WI 53562

(608) 238-3333

Morehouse Instruments

1742 Sixth Avenue

York, PA 17403

(717) 843-0081

11-66
Mountz Inc.

1080 N. 11th Street

San Jose, CA 95112

(408) 292-2214

Moxon, Inc.

222 Michel son Drive

Irvine, CA 92715

(714) 833-2000

Ono Sokki Co. , Ltd.

27-4 Yaguchi 1-Chome

Ohta-ku, Tokyo, Japan

Owatonna Tool Co., Tools & Equipment Div.

Eisenhower Drive

Owatonna, MN 55060

(507) 451-7163

Power Instruments Inc.

7352 N. Lawndale Avenue

Skokie, IL 600/6

(312) 676-2300

RFD Instrument Co., Inc.

404 N. Main Street, Box 548

Elgin, TX 78621

(512) 285-3385

Raymond Engineering Inc.,

Power-Dyne Torque Products Div.

217 Smith St.

Middletown, CT 06457

(203) 632-1000

Sensotec, Inc.

1200 Chesapeake Ave.

Columbus, OH 43212

(614) 486-7723

Snap-On-Tool Corp.

8028 28th Avenue

Kinosha, WI 33140

(414) 654-8681

Stewart Warner Corp.

(see: Thor Power Tool Co./

Stewart-Warner)

Sunshine Scientific Inst. Inc.

1810 Grant Ave.

Philadelphia, PA 19115

(215) 673-5600

Sweeney Mfg. Co. B.K.

6300 Stapleton S. Dr.

Denver, CO 80216

(303) 320-4800

Thor Power Tool Co./

Stewart Warner Corp.

175 N. State St.

Aurora, IL 60505

(312) 898-8000

Torquemeters America Inc.

P.O. Box 8

Allegany, NY 14076

(716) 373-2383

Torvaal

524 Washington St.

Chagrin Falls, OH 44022

(216) 247-6066

Transducers Inc.

Sub. ELDEC

12140 E. Rivera Rd.

Whittier, CA 90606

(213) 945-3741

Tyco

(see: Data Instruments)

Utica Tool Company, Inc.

Cameron Road

Orangeburg, SC 29115

(803) 534-7010

Vibrac Corporation

11 Alpha Dr. /Alpha Industrial Pk.

Chelmsford, MA 01824

(617) 256-6581

Waters Mfg. Inc.

Longfellow Center

Wayland, MA 01778

(617) 358-2777

West Coast Research

P.O. Box 25061 , S. Sepulveda Blvd.

Los Angeles, CA 90025

(213) 478-8833

11-67
Level Sensors

Abtec Ltd.

133 Rushey Green

London SE6 4AA, England

Action Instruments Co. Inc.

8601 Aero Dr.

San Diego, CA 92123

(714) 279-5726

Agitronics Manufacturing Co.

756-C Lakefield Rd.

Westlake Village, CA 91361

(805) 495-0874

Almac Cryogenics Inc.

1108-26th St.

Oakland, CA 94607

(415) 832-1505

Amprodux Inc.

150 W. 28th St.

New York, NY 10001

(212) 242-1636

B/W Controls Inc.

2200 E. Maple Rd.

Birmingham, MI 48012

(313) 643-8800

Bailey Controls Co.

29801 Euclid Ave.

Wickliffe, OH 44092

(216) 943-5500

Bailey Scientific

P.O. Box 1245

W. Sacramento, CA 95691

(916) 371-1472

Bill Manufacturing Inc.

903 W. Center Street N Salt Lake City, UT 84054

(801) 364-6451

Bell & Howell, CEC Div.

360 Sierra Madre Villa

Pasadena, CA 91109

(213) 796-9381

B indicator Company

1915 Dove St.

Port Huron, MI 48060

(313) 987-2700

Bristol Div.

929 Connecticut Ave.

Bridgeport, CT 06607

(203) 335-2511

Brooks Instruments

Div. Emerson Electric Co.

40/ W. Vine Street

Hatfield, PA 19440

(215) 368-2000

C-E Invalco Div. of Combustion

Engineering, Inc.

P.O. Box 556

Tulsa, OK 74101

(918) 932-5671

Chem-Tec Equipment Co., Inc.

Box 1030

Pompano Beach, FL 33061

(305) 946-6153

Coastal Data Service, Inc.

(see: Eppley Lab Inc.)

Columbia Controls

4545 Pine Timbers Bldg. 300

Houston, TX 77041

(713) 462-7800

Computer Inst. Corp.

100 Madison Ave.

Hempshead, LI, NY 11550

(516) 483-8200

Control otron Corp.

155 Plant Ave.

Hauppauge, NY 11787

(516) 231-3600

Cooke Vacuum Products Inc.

13 Merritt St., S

Norwalk, CT 06854

(203) 853-9500

11-68
Curtis Industries Inc.

8000 West Tower Ave.

Milwaukee, WI 53223

(414) 354-1500

Custom Controls Co. Inc.

1005 Sussex Blvd.

Lawrence Industrial Park

Broomall, PA 19008

(215) 543-5000

Delaval Turbine Inc.

Gems Sensors Div.

Farmington, CT 06032

(203) 677-1311

Delavan Electronics Inc.

1441 N. 73rd St.

Scottsdale, AZ 85260

(602) 948-6350

R.B. Denison Inc.

(see Gould Inc., Circuit

Protection & Controls Div.)

Desgranges & Huot, F.R. Industries Inc.

556 Long Road

Pittsburgh, PA 15235

(412) 242-5903

Digilin Inc. /Dynamic Sciences

(see: Dynamic Sciences Intl Inc/

Digilin)

Drexel brook Engineering Co.

205 Keith Valley Road

Horsham, PA 19044

(215) 674-1234

Dynamic Sciences International Inc.,

Di gil in

16150 Stagg St.

Van Nuys. CA 91406

(213) 893-6341

Electramtion

1099 Batavia

Orange, CA 92667

(714) 639-0832

Endress & Hauser Inc.

2350 Endress Place

Greenwood, IN 46142

(317) 535-7138

Epic Inc.

150 Nassau St.

New York, NY 10038

(212) 349-2470

Eppley Laboratory Inc.

12 Sheffield Ave.

Newport, RI 02840

(401 ) 847-1020

Ernst Gage Co.

250 S. Livingston Ave.

Livingston, NJ 07039

(201 ) 922-1400

Exactel Instr. Div.

(see: Technical Devices Co.)

F.R. Industries

(see: Desgranges & Huot)

Fluid Components Inc. (FCI)

870 Remmet Avenue

Canoga Park, CA 91304

(213) 341-7722

Fluid Products Co., Inc.

14740 Martin Dr.

Eden Prairie, NM 55343

(612) 941-8388

Foster Cambridge Ltd.

Howard Rd., Eaton, Socon,

Huntingdon, Cambridgeshire,

England

The Foxboro Co.

Dept. 120, 38 Neponset Avew.

Foxboro, MA 02035

(617) 543-8750

GPE Controls

6511 Oakton St.

Morton Grove, IL 60053

(312) 966-4000

11-69
Gagne Associates Inc.

1080 Chenango & Hi 11 crest St.

Binghamton, NY 13901

(607) 723-9556

Genelco Inc.

11649 Chairman Dr.

Dallas, TX 75243

(214) 341-8410

Gould Inc. Circuit Protection

& Control s Di v. 103 Broadway

Bedford, OH 44146

(216) 232-8200

Great Lakes Instruments Inc.

8855 N. 55th Street, P.O. Box 23056

Milwaukee, WI 54223

(414) 355-3601

Harwil Corporation

1548 17th St.

Santa Monica, CA 90404

(213) 829-2310

Hersey Products Inc.

Industrial Measurement Div.

Old Valley Falls Rd.

Spartansburg, SC 29303

(803) 578-3800

Hi -G Electronics

580 Spring St.

Windsor Locks, CT 06096

(203) 623-2481

Honeywell Inc. Process Control Div.

1100 Virginia Drive

Fort Washington, PA 19034

(215) 643-1300

ITT Barton

Box 1882

City of Industry, CA 91749

(213) 961-2547

Instrumentation & Control Systems Inc.

520 Interstate Road

Addison, IL 60101

(312) 543-6200

Inventory Sciences Inc.

17728 15th Avenue NE Seattle, WA 98155

(206) 363-0810

Inventron Industries Inc.

4005 W. Jefferson Blvd.

Los Angeles, CA 90016

(213) 731-2507

Jerguson Gage & Valve Co.

15 Adams St.

Burlington, MA 01803

(617) 272-3600

Jogler Inc.

2121 Governors Circle

P.O. Box 10899

Houston, TX 77018

(713) 681-4811

Kay -Ray Inc.

516 W. Campus Dr.

Arlington Heights, IL 60004

(312) 259-5600

Key Electro Sonic

Box 8

Milton-Freewater, OR 97862

(503) 938-5556

Knight Equipment Corp.

Box 1378

Costa Mesa, CA 92626

(714) 557-5400

Kodata Inc.

3621 McCart St.

Fort Worth, TX 76110

(817) 926-8483

Kolt Engineering Inc.

P.O. Box 1172

Los Gatos, CA 95030

(408) 356-7244

Konigsberg Instrument

(see: Unimeasure Div.,

Konigsberg Inst.)

11-70
LTI Corporation

P.O. Box 1828

Monterey, CA 93940

(408) 394-6775

Lake Shore Cryotronics Inc.

64 E. Walnut St.

Westerville, OH 43081

(614) 891-2243

Leeds & Northrup Company

Sumneytown Pike

North Wales, PA 19454

(215) 643-2000

Lenz Company

P.O. Box 1044, 3301 Klepinger Rd.

Dayton, OH 45401

(513) 277-9364

Liquid Level Lectronics Inc.

P.O. Box Drawer 788

Porter, TX 77365

(713) 354-2163

Liquidometer Corporation

19-29 Sheldon St.

Norwich, NY 13815

(607) 324-3939

Logicomp Electronics Inc.

895 Mamaroneck Avenue

Mamaroneck, NY 10543

(914) 698-9332

Lumenite Electronic Co.

2331 N. 17th Avenue

Franklin Park, IL 60131

(312) 455-1450

MSW Instruments Inc.

Bldg. Ill, 8750 Katy Freeway

Houston, TX 77024

(713) 468-6100

Madison Company

P.O. Box 608

Madison, CT 06443

(203) 245-4280

Magnetrol International

5300 Belmont Road

Downers Grove, IL 60515

(312) 969-4000

Manning Environmental Corp.

120 DuBois Street, P.O. Box 1356

Santa Cruz, CA 95061

(408) 427-0230

Masoneilan International Inc.

63 Nahatan Street

Norwood, MA 02062

(617) 762-4600

Meriam Instrument Div/

The Scott & Fetzer Co.

10920 Madison Avenue

Cleveland, OH 44102

(216) 281-1100

Metrig Engineering

10 Charles Street

Auburn, NY 13021

(315) 252-5657

Metritape, Inc.

33 Bradford Street

W. Concord, MA 01742

(617) 369-7500

Milltronics Inc.

2409 Avenue J Arlington, TX 76011

(817) 649-8540

Monitech, Inc. (Monitor Tech. Inc.)

630 Price Avenue

Redwood City, CA 94063

(415) 365-6550

Monitor Mfg. Inc.

Drawer AL

Elburn, IL 60119

(312) 365-9403

Monitor Technology Inc.

(see: Monitek, Inc., Monitor

Tech Inc.)

11-71
NP Industries Inc.

P.O. Box 746

Niagara Falls, NY 14302

(716) 282-0022

National Sonics Div., Envirotech Corp.

260 Marcus Blvd.

Hauppague, NY 11787

(516) 273-6600

The Ohmart Corporation

4241 Allendorf Drive

Cincinnati, OH 45209

(513) 272-0131

Oil -Rite Corporation

2318 Waldo Blvd.

Manitowoc, WI 54220

(414) 682-6173

Optek Inc.

127 Holmes Street

Galena, OH 43021

(614) 965-1819

Orion, Alpha Corporation

2974 Scott Blvd.

Santa Clara, CA 95050

(408) 247-4237

Peripheral Industries, Ltd.

439 Washington

Woodbury, CT 06798

(203) 263-3444

Petrometer Corporation

P.O. Box 245, 1807 Gilford Ave.

New Hyde Park, NY 11040

(516) 488-5777

Petur Instruments Co.

(formerly Thordason Inc)

11300 25th Ave., NE Seattle, WA 98125

(206) 365-0052

Princo Instruments Inc.

1020 Industrial Hwy.

South Hampton, PA 18966

(215) 355-1500

Qualitron Corporation

1385 Fairport Road

Fairport, NY 14450

(716) 586-1515

Rechner Electronics Industries Inc.

8651 Ave.

Niagara Falls, NY 14304

(716) 283-8744

Red Valve Co. , Inc.

500 North Bell Ave.

Carnegie, PA 15106

(412) 923-2677

Rexnord Instrument Products

30 Great Valley Pkwy.

Malvern, PA 19335

(215) 647-2400

Robertshaw Controls Co.

Industrial Instrumentation Div.

1809 Staples Mill Road

Richmond, VA 23230

(804) 358-2301

Sangamo Electric Company

Energy Management Div.

P.O. Box 75

West Union, SC 29696

(803) 638-3601

Schaevitz Engineering

P.O. Box 505

Camden, NJ 08101

(609) 662-8000

Sensor Technology

21012 Lassen Street

Chatsworth, CA 91311

(213) 882-4100

Sensotec Inc.

1200 Chesapeake Ave.

Columbus, OH 43212

(614) 486-7723

Sirco Controls

2795 152nd Ave., NE

Redmond, WA 98052

(206) 885-5303

11-72
Skan-A-Matic WeatherMeasure Corporation

Rte. 5 West P.O. Box 41257

El bridge, NY 13060 Sacramento, CA 95841

(315) 689-3961 (916) 481-7565

Stevens International Inc.

P.O. Box 619

Kennett Sq., PA 19348

(215) 444-0616

Taylor Instrument Company

Div. of Sybron Corp.

95 Ames St.

Rochester, NY 14601

(716) 235-5000

Technical Devices Company

11250 Playa Court

Culver City, CA 90230

(213) 870-3751

Temposonics Inc.

131 E. Ames Court

Plainview, NY 11803

(516) 935-4100

Texas Nuclear Div.. Ramsey Engr. Co.

Box 9267

Austin, TX 78766

(512) 836-0801

Thordarson Inc.

(see: Petur Instrs. Co.)

Uehling Instrument Co.

461 Getty Avenue

Paterson, NJ 07509

(201) 742-8710

Unimeasure Div., Konigsberg Instr.

2000 E. Foothill Blvd.

Pasadena, CA 91107

(213) 449-0016

Wesmar, Western Marine Electronics

Industrial Systems Division

905 Dexter Avenue North

Box CI 9074

Seattle, WA 98109

(206) 285-2420

Western Gauge Service Co.

921 A Mt. View Ave.

Oxnard, CA 93030

(805) 486-2358

Zi-Tech Div., Aikenwood Corp.

2151 Park Blvd.

P.O. Box 26

Palo Alto, CA 94302

(415) 326-2151

VEGA Controls US

P.O. Box 352

Wakefield, MA 01880

(617) 246-0026

W-K-M Valve Div., ACF Industries Inc.

P.O. Box 2117

Houston, TX 77001

(713) 499-1511

11-73
HUMIDITY

Humidity and Moisture Sensors

Abbeon Cal , Inc.

123 Gray Avenue

Santa Barbara, CA 93101

(805) 966-0810

Agridustrial Electronics Inc.

1827-C St.

Bettendorf, IA 52722

(319) 359-1691

Alnor Instruments Company

7301 N. Caldwell Avenue

Niles, IL 60648

(312) 647-7866

American Instrument Co.

Div. of Travenol Laboratories, Inc.

8030 Georgia Avenue

Silver Spring, MD 20910

(301 ) 589-1727

Anacon

30 Main Street

P.O. Box 267

Ashland, MA 01721

(617) 881-3000

Atkins Technical Inc.

3401 S.W. 40th Blvd.

Gainesville, FL 32608

(904) 378-5555

Bacharach Instrument Company

625 Alpha Drive

RIDC Industrial Park

Pittsburgh, PA 15238

(412) 782-3500

Bacharach Instrument Company

West Coast Operation

2300 Leghorn Street

Mountain View, CA 94043

Batson, Louis P. Company

Box 3978

Greenville, SC 29608

(803) 242-5262

Beckman Instruments Inc.

Technical Information Services

Cedar Grove Operations

89 Commerce Road

Cedar Grove, NJ 07009

(201 ) 239-6200

Bel fort Instrument Company

1600 S. Clinton Street

Baltimore, MD 21224

(301 ) 342-2626

Bendix Environmental & Process

Instr. Div.

1400 Taylor Avenue

Baltimore, MD 21204

(301 ) 835-5200

Blue M Electric Company

138th & Chatham

Blue Island, IL 60406

(312) 385-9000

C.W. Brabender Instruments Inc.

50 E. Wesley Street

South Hackensack, NJ 07606

(201 ) 343-8425

Breda Scientific Company

Suite 2225, One Sutter Street

San Francisco, CA 94104

(415) 788-4120

Bristol Div., ACCO

929 Connecticut Ave.

Bridgeport, CT 06607

(203) 335-2511

CTE Inc.

(see: Electromech Services)

Central Scientific Company

2600 S. Kostner Avenue

Chicago, IL 60623

(312) 277-8300

11-74
Chandler Engineering Co.

c/o John D. Mills & Associates

P.O. Box 45644

Tulsa, OK 7414b

Climatronics

1324-A Motor Pkwy.

Hauppage, NY 11787

(516) 234-2772

Climet Instruments Co.

1320 W. Col ton Ave., P.O. Box 151

Redlands, CA 92373

(714) 793-2788

Cosa Corp. (for Shaw Moisture Meters)

17 Philips Parkway

Montvale, NJ 07645

(201) 391-0200

Delmhorst Instrument Co.

P.O. Box 840

Boonton, NJ 07005

(201) 334-2557

H.W. Dietert Company

9330 Roselawn Ave.

Detroit, MI 48204

(313) 933-9790

Drexel brook Engineering Co.

205 Keith Valley Road

Horsham, PA 19044

(215) 674-1234

EG&G Environmental Equipment Div.

151 Bear Hill Road

Waltham, MA 02154

(617) 890-3710

Electromech Services

1240C Mt. View-Alviso Road

Sunnyvale, CA 94086

(408) 744-1870

Electronic Automation Inc.

732 Crofton, SE

Grand Rapids, MI 49507

(616) 949-0/79

Environmental Tectonics Corp.

Scott Environmental Systems Div.

County Line Ind. Pk.

Southhampton, PA 18966

(215) 322-5455

Epic Company

150 Nassau Street

New York, NY 10038

(212) 349-2470

Ernst Gage Company

250 S. Livingston Ave.

Livingston, NJ 07039

(201 ) 992-1400

Foster-Cambridge Ltd.

Howard Road

Eaton, Socon, Huntingdon,

Cambridgeshire, England PE193EU

The Foxboro Company

Neponset Avenue

Foxboro, MA 02035

(617) 543-8750

General Eastern Instrs. Corp.

50 Hunt Street

Watertown, MA 02172

(617) 2386

Gulton Industries Inc.

Measurement & Control Systems Div.

Middle Rd & Rte. 2

E. Greenwich, RI 02818

(401) 884-6800

H-B Instruments

4319 N. American St.

Philadelphia, PA 19140

(215) 329-9125

Haake, Inc.

244 Saddle River Road

Saddle Brook, NJ 07662

(201 ) 843-7070

Honeywell Inc., Process Control

Div.

1100 Virginia Drive

Ft. Washington, PA 19034

(215) 643-1300

11-75
Howard Engineering Company

P.O. Box 3164

Bethlehem, PA 18017

(215) 694-0939

Humidial Corporation

465 N. Mt. Vernon

Col ton, CA 92324

(714) 825-1793

Hy-Cal Engineering Co.

12105 Los Nietos Road

Santa Fe Springs, CA 90670

(213) 698-7785

Impact Register Inc.

W. Springdfield Ave., P.O. Box 3097

Champaign, IL 61820

(217) 352-4129

Industronics Inc.

489 Sullivan Avenue

S. Windsor, CT 06074

(203) 289-1594

Ionics Inc.

65 Grove Street

Watertown, MA 02172

(617) 926-2500

Kahn & Company Inc.

885 Wells Road

Wethersfield, CN 06109

(203) 529-8643

Kay-Ray Inc.

516 W. Campus Drive

Arlington Heights, IL 60004

(312) 259-5600

Lab-Line Instruments Inc.

15th & Bloomingdale Ave.

Melrose Park, IL 60160

(312) 345-7400

Land Instruments Inc.

P.O. Box 1623

Tullytown, PA 19007

(215) 943-7882

Leone Engineering

117 Third Street

Newton, PA 15089

(412) 872-5189

Liebert Corporation

P.O. Box 29186

Colubmus, OH 43229

(614) 888-0246

Lockwood & McLorie, Inc.

P.O. Box 113

Horsham, PA 19044

(215) 675-8718

Luft Instruments

Old Winter Street

Lincoln, MA 01773

(617) 259-9215

Meteorology Research Inc.

Box 637

Altadena, CA 91001

(213) 791-1901

Moisture Register Co.

Div. of Berwind Corp.

6934 Tujunga Ave.

N. Hollywood, CA 91605

Moisture Systems Corp. (MSC)

P.O. Box 97

Hopkinton, MA 01748

(617) 435-6881

Monarch International Inc.

Columbia Drive

Amherst, NH 03031

(603) 883-3390

Motorola Inc., Semiconductor

Products Div.

P.O. Box 20912

Phoenix, AZ 85036

(602) 244-3464

Multiform Desiccant Products Inc.

1418 Niagara Street

Buffalo, NY 14213

11-76
Ohaus Scale Corporation

29 Hanover Road

Florham Park, NJ 07932

(201) 377-9000

The Ohmart Corporation

4241 Allendorf Drive

Cincinnati, OH 45209

(513) 272-0131

Omega Controls Corp.

1542 Moulton Parkway

Tustin, CA 92680

(714) 731-2233

Ondyne Inc.

P.O. Box 6302

Concord, CA 94524

(415) 825-8282

Panametrics Inc.

221 Crescent St.

Waltham, MA 02154

(617) 899-2719

Photovolt Corporation

1115 Broadway

New York, NY 10010

(212) 989-2900

Phys-Chemical Research Corp.

36 West 20th Street

New York, NY 10011

(212) 924-2070

Praxis Corporation

5420 Jackwood

San Antonio. TX 78238

(512) 684-3231

Princo Instruments Inc.

1020 Industrial Hwy.

Southampton, PA 18966

(215) 355-1500

Procema Ltd.

38 Hampton Road

Twickenham, Middlesex,

England TW2 5QB

Raeco, Inc.

550 Armory Drive

South Holland, IL 60473

(312) 331-6001

Refinery Supply Co., Div. of

Central Scientific

P.O. Box 15628, E. Twelfth St.

Tulsa, OK 74112

(918) 836-4681

Scientific Systems Corp.

9020 S. Choctaw

Baton Rouge, LA 70815

(504) 926-6950

Seaman Nuclear Corporation

3846 W. Wisconsin Avenue

Milwaukee, WI 53208

(414) 342-1030

Shaw Moisture Meters

Rawson Roads, Westgate

Bradford, England, BD135 Q

Sonic Development Corporation

3 Industrial Avenue

Upper Saddle River, NJ 07458

(201 ) 825-3030

Strandberg Engineering Labs, I Industrial Elec. Division

1001 S. Elm Street

Greensboro, NC 27406

(919) 274-3775

Taylor Instr. Co., Div. of

Sybron Corp.

95 Ames Street

Rochester, NY 14601

(716) 235-5000

Tenney Engineering Inc.

1104 Springfield Road

Union, NJ 07083

(201) 686-7870

Testing Machines Inc.

400 Bay view Avenue

Amityville, NY 11701

(516) 842-5400

11-77
Tewwipe Company

P.O. Box 2/8

Hillside, NJ 07642

(201) 664-0555

Thunder Scientific Corporation

623 Wyoming, SE

Albuquerque, NM 87108

(505) 265-8701

Totco Div., Baker International Corp.

506 Paula Ave., P.O. Box 3885

Glendale, CA 91201

(213) 245-7411

Tierice, H.O. Company

12950 Eight Mile Road

Detroit, MI 48237

(313) 399-8000

United Exporters Co.

World Trade Center

San Francisco, CA 94111

(415) 433-0771

Vaisala Oy (Industrial Sales)

PL 26, SF-00421

Helsinki 42, Finland

Volumetrics

1025 W. arbor Vitae

Inglewood, CA 90301

(213) 641-3747

Watlow Winona, Inc.

1265 E. Sanborn

Winona, MN 55987

(507) 454-5300

Watrous & Company, Inc.

110 East 23rd Street

New York, NY 10010

(212) 473-7789

Waynco Inc.

(see: Watlow-Winona , Inc.)

WeatherMeasure CorDoration

P.O. Box 41257

Sacramento, CA 94841

(916) 481-7565

Weathertronics, Inc.

2777 Del Monte Street

West Sacramento, CA 95691

(916) 371-2660

Weksler Instruments Corporation

80 Mill Rd., P.O. Box 3040

Freeport, NY 11520

(516) 623-0100

Wescor Inc.

459 South Main St.

Logan, UT 84321

(801 ) 752-6011

Yellow Springs Instr. Company

P.O. Box 279

Yellow Springs, OH 45387

(513) 767-7242

11-78
11.2 Sensor Calibration and Evaluation Resources

As far back as 1951, the Office of the Assistant Secretary of Defense,

recognizing the need for standardization of instrumentation systems and

activities, established the Range Commanders Council. This group, composed of

the commanders of the National Military Test Ranges, created a consulting

organization called the Inter-Range Instrumentation Group. The latter was to cover areas of range instrumentation through working groups which ultimately

produced a variety of standards documents. The Telemetry Working Group (IRTWG)

concerned with the uniform and accurate transmission and reception of

information (flight test data) from flight vehicles, in turn, established

several committees to cover sub-areas.

At the eleventh meeting of the Inter-Range Telemetry Working Group in

April 1958, a committee on transducers was established at the request of the

National Bureau of Standards. The purpose of this committee was to provide

effective feedback and guidance to the NBS Interagency Transducer Project [1]

by IRTWG, as well as to provide IRTWG with information of significant

developments in the field of telemetry sensors. Close liaison between the NBS

project and IRTWG was desirable to assure maximum usefulness to the sponsors

and to telemetry users generally.

Workshops sponsored by the Transducer Committee and characterized by a free exchange of information in an informal atmosphere have opened avenues of

communication among those having a direct interest in transducer developments.

These workshops have encouraged efforts to improve sensor performance, to

standardize telemetry transducer terminology, specifications, evaluation, and

calibration procedures, and to establish a clearinghouse for sensor calibration

and evaluation reports. Workshop proceedings were published after the meetings

held in 1967, 1969, 1972, 1975, 1977, and 1979. Those still in print may be

* obtained from the Secretariat, Range Commanders Council, White Sands Missile

Range, NM 88002. (Non-government agencies must obtain authorization from a sponsoring government agency.)

The Transducer Committee produces a "Directory of Transducer Users" [56]

which lists sensor resources (laboratories and experts) throughout the United

States. A summary of the Directory appears below, divided into government

installations and private industry facilities. The listing, based on voluntary

submission of information on sensor usage, expertise, and facilities is

probably not complete. The Directory was issued early in 1978 and may not be

totally up to date, but will be revised in the future. Nevertheless, it should

provide useful contacts for sensor experts.

Another source of information on federal metrology and calibration

facilities not specifically directed towards sensors , however, is the "Catalog

of Federal Metrology and Calibration Facilities," NBS SP 546 [57].

11-79
11.2.1 Government Sensor Laboratories, Contacts and Functions

The comments under each facility listing were furnished by

laboratory staff.

Air Force Flight Dynamics Laboratory

Charles E. Thomas

AFFDL/FBG

Wright-Patterson AFB, OH 45433

Richard Talmadge

AFFDL/FBG

Wright-Patterson AFB, OH 45433

Phone: (513) 255-2543

Autovon: 785-2543

Phone: (513) 255-4684

Autovon: 785-4684

Comments:

"Acoustic, pressure and vibration sensors are used extensively in

laboratory, ground and flight tests. We have a good calibration facility and

maintain a moderate inventory of acoustic and vibration sensors. Two

self-contained mobile laboratories are available for making on-site dynamics

measurements at remote test sites. In addition, we have a quick response data

acquisition system for ground and flight tests."

Air Force Weapons Laboratory

Terry Courthayn

Civil Eng. Research Div.

AFWL/DEO

Kirtland AFB, NM 87118

Phone: (505) 264-0358

Autovon: 964-0358

FTS: 475-0358

"Acceleration, motion, pressure and structural strain are measured in and

around high explosives tests. High level transient pressure and motion

measurements and related data recovery are achieved."

Armament Development and Test Center

Comments

Herbert W. Brown

Armament Dev. and Test Center

3246 Test W/TETT

Eglin AFB

FL 32569

Harold D. Nation

Armament Dev. and Test Center

3246 Test W/TETT

Eglin AFB

FL 32569

Phone: (904) 882-2785

Autovon: 872-2785

Phone: (904) 882-2785

Autovon: 872-2785

11-80
J.W. Kronmiller

Armament Dev. and Test Center

3246 Test W/TEEAS

Eglin AFB

FL 32542

Phone: (904) 882-2461

Autovon: 872-2461

Sid Shelley

Armament Dev. and Test Center

3246 Test W/TEERS

Eglin AFB

FL 32542

Phone: (904) 882-4461

Autovon: 872-4461

Comments:

"The 3246th Test Wing is the responsible agency at Eglin for all testing

and test facilities. An assortment of ground-based range instrumentation and

transducers are used to obtain performance profiles on conventional and

experimental munitions. Typical measurements include blast pressure,

acceleration, temperature, strain, fragment weight, fragment velocity and

dispersion. Air and ground tests can be performed. A sled track exists. The

ADTC maintains a complete sensor calibration and evaluation facility."

Army Aeromechanics Laboratory

Robert E. George

U.S. Army Aeromechanics Lab

NASA Ames Research Center

MS-N215-1

Moffett Field

CA 951 29

Phone: (415) 965-5835

Autovon: 586-5651

Comments

"The Army Aeromechanics Lab is a multi-test facility which uses a number

of transducers, including pressure (static and dynamic), temperature,

acceleration and position. The facilities include both wind and water tunnel

operations. Static and dynamic model rotor tests, plus some flight tests, are performed.

Army ballistic Research Laboratory

Arpad A. Juhasz

Ballistic Research Lab

DRDAR-BLP

Aberdeen Proving Ground

MD 21005

Charles D. Bullock

Ballistic Research Lab

DRDAR-BLP

Aberdeen Proving Ground

MD 21005

Phone: (301)278-4153 Phone: (301)278-3340

Autovon: 283-4153 Autovon: 283-3340

11-81
Willis F. Jackson

Ballistic Research Lab

DRDAR-BLT

Aberdeen Proving Ground

MD 21005

Phone: (301) 278-2040

Autovon: 283-2040

Comments

"Internal pressure measurements are made for large caliber weapons and

free-field overpressure measurements are taken during high explosives

detonations. Piezoelectric and strain gage type ballistic pressure gages are used for artillery, small arms and closed bomb applications. Primary standard

(deadweight) calibrations to 100 000 psi and secondary standard calibrations to

150 000 psi, plus development of capability for primary standard calibrations

to 150 000 psi are available.

Army Metrology and Calibration Center

J.R. Miller, III U.S. Army Metrology and Calibration Center

Bldg. 5435, DRSMI-MMP

Redstone Arsenal

AL 35802

Phone: (205) 876-2876

Autovon: 746-2876

Comments

"The U.S. Army Calibration Program managed by USAMCC, provides calibration

support for sensors throughout the Army. Three tiers of accuracy are available

in the various laboratories. Interest exists in the application of

microprocessors to sensor calibrations in order to develop automated transfer

standards."

NASA-Marshall Space Flight Center

W.T. Escue

EC-23

NASA-MShC

Huntsville

AL 35812

Phone: (205) 453-4627

FTS: 872-4627

Marian S. Harman

ES-23

NASA-MSFC

Hunts vil le

AL 3581

2

Phone: (205) 453-4627

FTS: 872-4627

11-82
Comments:

"Aerospace applications of sensors to Saturn, Space Shuttle, and similar

programs. Calibration and test capabilities exist to evaluate sensors in areas

of pressure, temperature, force, flow, liquid level, vacuum, remote sensing

vibration."

National Aviation Facilities Experimental Center

Jack J. Shrager, (ANA-410)

Airworthiness Branch

Aircraft & Airports Safety Division

National Aviation Facilities Experimental Center/FAA

Atlantic City

NJ 084U5

Phone: (609) 641-8200 Ext 2665/3718

FTS: 346-2665/3718

Comments

"Sensors are used in the development of aircraft and airport testing, and

test equipment. They are also used in the development of devices for both

airborne and ground-based operational equipments for aircraft navigation,

guidance and control."

National Bureau of Standards

Paul S. Lederer

El ectrosy stems Division

National Bureau of Standards

Washington

D.C. 20234

Phone: (301) 921-2727

John D. Ramboz

Electrosystems Division

National Bureau of Standards

Washington

D.C. 20234

Phone: (301 ) 921-3121

Comments

"NBS-Interagency Transducer Project from 1951 to 1979 developed

calibration and evaluation techniques with emphasis on dynamic calibration

methods for pressure sensors and accel erometers , durability and thermal

transient tests."

11-83
Charles R. Til ford

A149 Met.

Pressure and Vacuum Section

National Bureau of Standards

Washington

DC 20234

Phone: (301 ) 921-2121

Vern E. Bean

A149 Met.

Pressure and Vacuum Section

National Bureau of Standards

Washington

DC 20234

Phone (301 ) 921-2121

Comments:

"The Pressure and Vacuum Group of NBS provides calibration services for

pressure standards and sensors over the range of 1 Pa to 420 MPa. In the

pressure sensor characterization service, a battery of tests over a period of

several months are used to determine such parameters as zero drift, voltage

dependence, pressure and temperature hysteresis, relaxation, short- and

long-term stability, precision, temperature effects on zero and span, effects

of pressure cycling, attitude dependence, etc. Training courses in the use of

piston gages, piston gage data evaluation services and consultations are also

available."

National Parachute Test Range Test Facility

Lt. David G. Leupp

DORSI

6511th Test Squadron

National Parachute Test Range

El Centro

CA 92243

Phone: (714) 339-2474

Autovon: 958-8474

"We primarily utilize strain gages (foil), accelerometers and rate

transducers to determine parameters of parachute recovery systems. FM-FM and

PAM-FM telemetry systems provide information during test drops."

Naval Air Test Center

Comments

William D. Anderson

Head, Airborne Instr. Branch

Technical Support Directorate

Naval Air Test Center

Patuxent River

MD 206/0

Phone: (301) 863-4271

Autovon: 356-4271

Harry W. Clarke

Head, Aero Calibration Labs

Technical Support Directorate

Naval Air Test Center

Patuxent River

MD 20670

Phone: (301) 863-4557

Autovon: 356-4557

11-84
Comments:

"NATC utilizes sensors for the instrumentation of Navy aircraft. Tests

include: flying qualities, structural tests, engine performance, vibration

measurements, weapons release, avionics performance and temperature surveys.

Major types of sensors utilized are: pressure, strain gage, accelerometers,

vibration pickups, rate gyros, thermocouples and position sensors. NATC

maintains compelte sensor calibration facilities and is engaged in sensor

evaluations. NATC operates and maintains the NAVAIRSYSCOM Instrumentation Pool

which loans sensors to Navy activities and contractors holding NAVAIR

contracts."

Naval Ordnance Station

Eugene J. Stekfo

Ballistic Test Division

Code 3024, Bldg. 1576

Naval Ordnance Station

Indian Head

MD 20640

Phone: (301) 743-4387

Autovon: 364-4387

Ronald P. Denton

Ballistic Test Division

Code 3024A, Bldg. 759

Naval Ordnance Station

Indian Head

MD 20640

Phone: (301) 743-4477

Autovon: 364-4477

Comments

"The Division performs testing during the development, qualification,

pre-production and production phases of solid and liquid propulsion weapon

systems, components and devices. These tests subject the specimens to

conventional fleet/field use environments. Evaluation test equipment includes

shock machines, shakers, centrifuges, temperature/humidity/altitude chambers,

etc. Static test firings are conducted measuring strain, acceleration,

displacement, pressure, thrust and temperature. Pressure levels to 50 000 psi,

thrust levels to 200 000 lb., accelerations to 1000 g, and temperatures to

2500 °F are measured. Information is recorded by an automated data acquisition

system which provides on-line, real-time, data reduction."

Naval Ship Weapons System Engineering Station

Leroy Bates

NSWSES, Code

Port Hueneme

CA 93043

Phone: (805)

Autovon:

6340

982-4104

360-4104

Wes Paulson

NSWSES, Code 6310

Port Hueneme

CA 93043

Phone: (805) 982-4159

Autovon: 360-4159

11-85
Comments:

"A wide variety of accelerometers, pressure sensors, thermocouples,

microphones, etc., are used to support shipboard weapon (missile and gun)

system test and evaluation programs. NSWSES is responsible for engineering,

logistics and evaluation of operational weapon systems for surface ships.

Weapon systems include Tartar, Terrier, SM-1 , SM-2, Harpoon, Aegis, Point

Defense, CISW, 76mm gun and 5- and 8-inch guns. Specially tailored

instrumentation systems are temporarily installed for tests at sea."

Naval Surface Weapons Center

Dr. Philip M. Aronson

Naval Surface Weapons Center

Bldg. 427, Room 419

White Oak, Silver Spring

MD 20910

Phone: (202) 394-1920

Autovon: 290-1920

Comments

"NSWC, A prime Navy R&D laboratory, is heavily involved in the development

and testing of underwater and air ordnance. Measurements are made of pressure,

acceleration and temperature with emphasis on transient phenomena. Data

transmissions make use primarily of hard-wire telemetry systems.

The center has a wide variety of facilities and equipment including:

airblast facilities, hydroballistic tanks, wind tunnels, shock tubes, air guns,

shock tunnels, dynamic pressure and accelerometer calibrations, shockless

pressure-step generators, electrodynamic shakers and piezoelectric and strain

gage type pressure sensors."

Naval Weapons Center

Kenneth D. Cox William Francis

Code 6213 Code 6213

Naval Weapons Center Naval Weapons Center

China Lake China Lake

CA 93555 CA 93555

Phone: (714) 939-7427 Phone: (714) 939-7404

Autovon: 245-7427 Autovon: 245-7404

11-86
Franklin R. Hartzler

Instrumentation Division

Code 6243

Naval Weapons Center

China Lake

CA 93555

Phone: (714) 939-5551. 5554, 5586

Autovon: 245-5551, 5554, 5586

Jim Rieger

Instrumentation Division

Code 6243

Naval Weapons Center

China Lake

CA 93555

Phone: (714) 939-5551 , 5554, 5586

Autovon: 245-5551,5554,5586

Comments

"The Naval Weapons Center is the principal Navy RDT&E Center for air

warfare and missile weapon systems. To perform its mission, the Center

establishes and maintains the primary in-house research and development

capability and appropriate documentation for an important series of Navy and

Marine Corps aircraft weapons, tactical missiles, weapon subsystems, and

technologies.

The instrumentation branch designs or specifies sensors for airborne and

ground-based (wired and wireless) instrumentation systems for a variety of

customers.

Measurement experience exists in areas of free-flight, fires, explosions,

sled tracks and aircraft. Sensor types include infrared sensing, light

sensing, accelerometers, microphones, strain and displacement, electrometry and

non-contact motion sensing.

In-house facilities can design and produce signal -conditioning circuitry

for networking, including nonlinear processing and charge amplification.

The Transducer Calibration Laboratory in the Propulsion Development

Department has equipment to calibrate pressure sensors from 0.01 psi to

40 000 psi, load cells from 1 lb to 400 000 lb compression and 200 000 lb

tension. We make temperature measurements from -250 °F to approximately

3000 °F in various ranges using thermocouples."

Navy Metrology Engineering Center

Dale W. Rockwell

Metrology Engineering Center

Naval Plant Representative

P.O. Box 2505, MZ 3-18

Pomona

CA 91766

Phone: (714) 629-5111 Ext 3662

Autovon: 360-2811 Sta 6

11-87
Comments:

"The Metrology Engineering Center serves as technical director to the

Navy's Standards and Calibration Program. As such the Center writes

calibration procedures, develops/evaluates calibration techniques, and

develops/evaluates calibration systems and standards. It procures calibration

equipment required for use at Navy calibration and standards laboratories

supporting various test instruments (including transducers). The actual use of sensors by this Center is restricted to evaluation of calibration systems and

to evaluations of sensors for use as standards. The Metrology Engineering

Center does not perform evaluations or calibrations for other activities, but

Navy calibrations and standards are equipped to perform a wide range of

calibrations depending on the capability of each individual laboratory. They

are, typically, capable of calibrating sensors used in the measurement of

force, pressure, temperature, humidity, and vibration. In addition, several

laboratories are capable of providing calibration of gas and liquid flowmeters,

anemometers, dynamic pressure sensors, viscometers, densitometers, and shock

accelerometers."

Test Track Division

Joe A. Haden

6585th Test Group

Test Track Division (TKIA)

Hoi 1 oman AFB

NM 88330

Phone: (915) 679-2038

Autovon: 349-2038

Robert C. DeRoy

6585th Test Group

Test Track Division (TKIA)

Hoi 1 oman AFB

NM 88330

Phone: (915) 679-2611

Autovon: 349-2611

Comments:

"The Test Track Division instruments a wide variety of systems and

subsystems for sledborne testing. These include guidance systems, crew escape

systems, missile warheads, projectiles, parachute systems, airfoils, etc. The

test equipment is realized by utilization of rocket propelled test-bed vehicles

(sleds) with the sled and propulsion being designed to meet specific test

parameters. RF telemetry links are used for data transmission.

The Test Track Division makes a wide variety of measurements including

pressure, acceleration, vibration, stress and strain, velocity, temperature,

roll , pitch, and yaw.

11-88
Kenneth T. Smith

Commander

Tooele Army Depot

SDSTE-AEO

Tooele, UT 84074

Phone: (801) 833-2825

790-2825

Comments:

"Meaasurements are made of air blast pressures in the 1 to 100 psi range,

also of pneumatic and hydraulic pressures to 5000 psi g, and thermocouple

temperature measurements to 2000 °F. Strain gages are also used. This

facility has a 40-ft semi -trailer instrumentation van, 100-pound (maximum)

explosive test bays, an explosives test range, and high-speed (500 to

10 000 fps) movie cameras."

11.2.2 Private Industry Sensor Laboratories, Contacts and Functions

The comments under each listing were furnished by laboratory staff.

Boeing Aerospace Company

Norman G. Ray

Boeing Aerospace Company

P.O. Box 3999 M/S 86-12

Seattle

WA 981 24

Phone: (206) 773-8594

Comments

"The Engineering Labs within the Boeing Aerospace Company are involved in

the static and dynamic testing of aerospace systems and components, such as defense systems and components, commercial aircraft components, and various

commercial and civil oriented products and components. The wide range of

testing capability has led to a wide diversity of instrumentation requirements

necessitating "in-house" development of transducers and associated calibration

techniques. Primary parametric measurements are motion (X, X, X), force,

pressure, temperature, strain, and time. Areas of expertise are in the

development of strain gage instrumentation, high temperature strain measurement

techniques, structural modal analysis, the -S/N- Fatigue Life Gage, composite

instrumentation techniques, dynamic calibration of accelerometers,

vel ocimeters, and pressure transducers through transient excitations, wind

tunnel instrumentation techniques, and transient test and analysis

techniques."

Tooele Army Depot

Jerry R. Miller

Commander

Tooele Army Depot

SDSTE-AEO

Tooele, UT 84074

Phone: (801) 833-2825

790-2825

John D. Favour

Boeing Aerospace Company

P.O. Box 3999 M/S 86-14

Seattle

WA 98124

Phone: (206) 773-4802

11-89
Boeing Commercial Airplane Company

Albert E. Davis

Boeing Commercial Airplane Company

P.O. Box 3707 M/S 1W-04

Seattle

WA 981 24

Phone: (206) 655-1369

Comments:

"Pressure sensors and hot wire/hot film anemometer sensors are used for

test instrumentation. A variety of calibration and testing facilities

exists."

Boeing Vertol Company

A. Miller

Boeing Vertol Company

Flight Test Instrumentation

P.O. Box 16858 M/S P37-14

Philadel phi a PA 19142

Phone: (215) 522-7135

Comments:

Hans F. Pauls

Boeing Vertol Company

Flight Test Instrumentation

P.O. Box 16858 M/S P37-14

Philadelphia

PA 19142

Phone: (215) 522-7234

"We are concerned with all sensors utilized in the typical flight testing

of helicopters. The company maintains a calibration lab for flight-test

sensors. A real-time computer is available for on-line computing, plotting,

and hard copy of data from two aircraft simultaneously telemetering stress and

vibration measurements to a ground station."

Civil Engineering Research Facility, University of New Mexico

Stephen F. Pickett

University of New Mexico

CERF Campus, P.O. Box 25

Albuquerque

NM 87131

Phone: (505) 264-4644

Autovon: 964-4644

Neal P. Baum

University of New Mexico

CERF Campus, P.O. Box 25

Albuquerque

NM 87131

Phone: (505) 264-4644

964-4644

11-90
Comments:

"Pressure, tri axial stress, acceleration, velocity, displacement, strain

and angular motion instrumentation are used. Explosive-induced high pressures,

motion, and stress transients are measured."

EG&G, Incorporated, Las Vegas

Roger P. Noyes Lee E. Da vies

EG&G, Inc. EG&G, Inc.

P.O. Box 1912 M/S N-28 P.O. Box 1912 M/S N-28

Las Vegas Las Vegas

NV 89101 NV 89101

Phone: (702) 647-5340 Phone: (702) 647-5261

FTS: 545-5340 FTS: 545-5261

Comments:

"The EG&G Special Measurements Group calibrates and installs transducers

utilized in measuring pressure, temperature, acceleration and velocity in

support of the Lawerence Livermore Laboratory (LLL) Underground Nuclear Test

Program at the Nevada Test Site. A calibration laboratory exists for testing

pressure sensors, temperature sensors, variable reluctance velocity gages, and

accelerometers. This group has extensive field experience with both

dual -constant-current excitation and carrier-demodulation signal

conditioning."

EG&G, Incorporated, San Ramon

M.A. Hatch, Jr.

EG&G, Inc.

2801 Old Crow Canyon Road

San Ramon

CA 94583

Phone: (415) 837-5381

J. A. Kalinowski

EG&G, Inc.

2801 Old Crow Canyon Road

San Ramon

CA 94583

Phone: (415) 837-5381

Comments

"EG&G, San Ramon, in conjunction with the Lawrence Livermore Laboratory,

uses a variety of transducers to measure the dynamic and static behavior of

gases in line-of-sight pipes coupled to nuclear detonations. Measurements are

also made of the dynamic behavior of the pipe and other mechanical structures

during the detonation using transducers to sense temperature, pressure,

velocity, acceleration, strain, stress, ionization, and illuminosi ty."

11-91
"EG&G/San Ramon has a gas-gun shock-tube facility which is used for

evaluating pressure, temperature and acceleration sensors. It is capable of

producing planewave impact stresses in solids ranging from 0-100 k-bar. It is

capable of subjecting small structures, i.e., an accelerometer, to levels in excess of 50 000 g. The system can produce step pressure changes and rapidly

changing pressure impulses of several milliseconds duration in the 0-2000 psi

range."

Grumman Aerospace Corporation, Bethpage

Methody Sirkot

Grumman Aerospace Corporation

Department 802

Plant 12

Bethpage

NY 11714

Phone: (516) 575-5754

Comments:

"Grumman Aerospace Corporation makes extensive use of a large variety of sensors for both flight and ground test programs. These include angular and

linear accelerometers, acoustic, displacement, liquid and gaseous flow, force,

pressure and temperature sensors. A modern sophisticated calibration

laboratory exists to calibrate and maintain these instruments.

Familiarity with most of the pressure sensors presently being manufactured

has come through calibration of the same. Units calibrated vary from very low

differential pressure to those measuring 20 000 psi, inlet rake pressure

sensors, air data sensors and high frequency crystal types. Generally, units

are independently calibrated in the lab, but some system calibrations are performed, in situ."

Grumman Aerospace Corporation, Calverton

G. Rosen (Temperature)

Grumman Aerospace Corp.

Flight Test Dept.

M/S B28-07

Calverton

NY 11933

Phone: (516) 369-7471

H. Weiss (Flight Dynamics)

Grumman Aerospace Corp.

Flight Test Dept.

M/S B28-07

Calverton

NY 11933

Phone: (516) 369-7471

11-92
T. Harmon (Air Data & Dynamic P Grumman Aerospace Corp.

Flight Test Dept.

M/S B28-07

Cal verton

NY 11933

Phone: (516) 369-7472

s.) M. Keitel (General Pressure)

Grumman Aerospace Corp.

Flight Test Dept.

M/S B28-07

Cal verton

NY 11933

Phone: (516) 369-7472

Comments:

"Sensor usage at Cal verton chiefly involves the instrumentation of

aircraft for development flight testing. Sensors are utilized in the

acquisition of data relative to aerodynamic and power plant performance,

structural dynamics and thermodynamic surveys. Test requirements usually

dictate high accuracy sensors suited to hostile environments and compatible

with on-board tape recording systems and telemetry. Sensors typically used

include crystal accelerometers, strain gage accelerometers, all types of

pressure sensors, rate and attitude gyros, turbine flowmeters, thermocouples,

resistance thermocouples and thermometers, tach generators, and synchros.

A separate group, dedicated to sensor applications, exists in the Grumann

Flight Test Organization. This group specializes in the selection of sensors

and the development of probes, rakes and novel application techniques.

Substantial knowledge and experience has been accrued in the areas of air data sensors (air-speed/altitude) , dynamic pressure sensing (low range-high

frequency), general purpose sensing (absolute and differential, from fractions

to thousands of psi), flow measurements (liquid and gas) and flight dynamics

(rates, acceleration, etc.)."

Lawrence Livermore Laboratory, University of California

Henry S. Freynik

Lawrence Livermore Laboratory

Transducer Lab.

P.O. Box 808, L-342

Li vermore

CA 94550

Phone: (415) 422-6988

FTS: 532-6988

11-93
Comments:

"Measurements are made of strain and temperature, both static and dyanmic,

also of strain principally as stress, with some special sensor development.

Surface and gas temperature measurements cover a wide range and with very fast

rise times. Most applications are in conventional environmental tests and in

nuclear field tests. Other tests involve the long-term stability (2 years

plus) of installation, and special bonding techniques for gaging hostile

(radio-active) materials used in adverse environments."

Thomas B. Miller

Lawrence Livermore Laboratory

Transducer Lab.

P.O. Box 808, L-342

Livermore

CA 94550

Phone: (415) 422-7040

FTS: 532-7040

Comments

"Our principal use of transducers is in conventional environmental

testing, with some applications in tests using sheet explosives, flyer plates

and nuclear detonations.

Parameters measured and relative frequency range requirements are these:

acceleration, vibration, and shock (high), displacement, quasi-static (medium);

pressure, mostly static (medium); force, mostly static (low). Calibration

facilities exist for the sinusoidal calibration of accelerometers (20 Hz to

10 kHz; to 50 kHz for surveys), displacement sensors by the interferometric

method, pressure sensors (0.2 psia to 200 k psi), and force sensors

(to 60 1-lb)."

11-94
Bill Shay

Lawrence Livermore Laboratory

Materials Engineering Div.

P.O. Box 808, L-342

Li vermore

CA 94550

Phone: (415) 422-7044

532-7044

Ray Cornell

Lawrence Livermore Laboratory

Materials Engineering Div.

P.O. Box 808, L-342

'

Li vermore

CA 94550

Phone: (415) 422-6933

532-6933

Comments:

"We supply or use instruments for all types of testing on individual parts

to completed assemblies. The testing ranges from static to dynamic with the

test environments from ambient to high explosive and underground nuclear

detonations. The types of sensors used are: pressure sensors, accelerometers,

thermocouples, strain gages, and load cells.

We evaluate and calibrate pressure, load cell, displacement and

accelerometers used by the laboratory. Special areas of expertise are: gas

gun work, measurement of thermophysical properties, calorimetry, strain gaging

of special materials, strain, and temperature measurement for reactor

experiments and high explosive blast measurements."

David C. Hoi ten

Nuclear Explosives Eng. Div.

Lawrence Livermore Laboratory

P.O. Box 808, L-122

Li vermore CA 94550

Phone: (415) 422-8836

FTS: 532-8836

Arthur W. Hampton

Nuclear Explosives Eng. Div.

Lawrence Livermore Laboratory

P.O. Box 808, L-508

Li vermore

CA 94550

Phone: (415) 422-9596

FTS: 532-9596

11-95
Richard T. Hasbrouck

Field Test Systems Division

EE Department

Lawrence Livermore Laboratory

P.O. Box 808, L-218

Li vermore

CA 94550

Phone: (415) 422-3977

FTS: 532-3977

Comments

"We are principally a user of sensors in extensive field tests, laboratory

experiments and portable high pressure gas systems applications. Pressure

ranges from vacuum to 20 000 psi , in both absolute and differential pressures.

Heavy emphasis is placed on sensor mechanical integrity and signal conditioning

electronics reliability under difficult test conditions. Expertise exists in areas of mechanical quality control, specification, evaluation, certification,

and performance testing of absolute pressure sensors. There is an on-going

program to develop special sensor materials. Experience exists in high

reliability signal conditioning electronics, digital readout portable transfer

standards, and end-to-end static calibration via PCM/microwave telemetry

link."

Lockheed California Company

Ed Kaufman

Lockheed California Company

74/94 66-360

P.O. Box 551

Burbank

CA 91520

Phone: (213) 847-4092

Comments:

"The Lockheed Flight Test Laboratory uses sensors in its data acquisition

systems for flight and demonstration programs to measure pressure,

acceleration, flow, temperature, rpm, etc. Nearly all data is multiplexed on

1" magnetic tape reels.

The Flight Test Lab, in addition to providing, servicing and maintaining

the data acquisition systems for flight test aircraft, conducts numerous ground

tests in support of flight and demonstration programs. These involve all of

the sensors previously mentioned in such tests as ground vibration of

components and of the complete aircraft, engine tests, structural (strain gage)

calibrations, control surface response and free play, and other systems tests.

Digital sensors have been used for the measurement of air-speed, altitude, and

other critical parameters."

11-96
McDonnell -Douglas Corporation

D.D. Crompton

McDonnell -Douglas

M.S. 41-59

3855 Lakewood

Long Beach

CA 90846

Phone: (213) 593

Corporation

2482

P.M. Mumford

McDonnel 1 -Douglas Corporation

M.S. 41-59

3855 Lakewood

Long Beach

CA 90846

Phone: (213) 593-3268

J.H. Gault

McDonnel 1 -Douglas Corporation

M.S. 41-52

3855 Lakewood

Long Beach

CA 90846

Phone: (213) 593-8969

"DAC Flight Development uses large quantities of sensors for flight

testing of aircraft and for ground support equipment. They measure pressures

from 0.1 psi to 10 000 psi , accelerations from 0.1 g to 500 g (frequency

range 1 to 10 000 Hz), forces, temperature, position, airspeed, altitude,

proximity and frequency. Telemetry coverage via radio and microwave is from

Baja, California to Reno, Nevada.

Facilities include wind tunnels, fatigue and endurance testers, aircraft

simulators, seat ejection tests and flight testing of military and commercial

aircraft. Also there are facilities for pneumatic, hydraulic, acoustic, and

vibration measurements."

Pratt & Whitney Aircraft, East Hartford

Howard P. Grant

Pratt & Whitney Aircraft, CPD

XT 2 400 Main Street

E. Hartford

CT 06108

Phone: (203) 565-3355

Comments:

11-97
Comments:

"We are engaged in aircraft gas turbine engine development testing

(occasionally flight testing). There are instrumentation development

laboratories for strain gages, slip rings, near-field telemetry and optical

systems."

Pratt & Whitney Aircraft Group, West Palm Beach

James C. Birdsall

Pratt & Whitney Aircraft Group

P.O. Box 2691 M/S 3-87

West Palm Beach

FL 33402

Phone: (305) 844-7311

ext 2733

Peter V. Bechman

Pratt & Whitney Aircraft Group

P.O. Box 2691 M/S E-87

West Palm Beach

FL 33402

Phone: (305) 844-7311

ext 2733

Comments:

"Military jet engine (F100) pressures are monitored in the following

environment: -65° to 468 °F, up to 600 g at 20 kHz random vibration, and 20 g

to 2 kHz random vibration.

We have deadweight calibration facilities for pressure and force sensors. Development of silicon-on-sapphire solid-state pressure sensors in ranges from

25 to 1000 psia (in conjunction with Conrac Systems West Division) was

undertaken."

Sandia Laboratories, Albuquerque

P.L. Walter

Sandia Laboratories

Division 9486

Albuquerque

NM 87115

Phone: (505) 264-5226

Autovon: 964-5226

Frederick Schelby

Sandia Laboratories

Division 9486

Albuquerque

NM 87115

Phone: (505) 264-3907

Autovon: 964-3907

Comments:

"Sandia Laboratories, Albuquerque, instruments a variety of

components/assemblies for design verification testing. These include

electromechanical devices, mechanical structures, projectiles and parachutes.

Test environments utilized are vibration exciters, centrifuges, drop towers,

ballistics, rocket sleds, sheet explosives, flyer plates, shock tubes and

underground nuclear detonations. Both radio-link and hard-wire telemetry are employed.

11-98
We make a large quantity of acceleration measurements in impact-type

environments where levels in the tens of thousands of g are frequently

encountered. Expertise exists in measuring blast and ballistic type pressure

environments where very short pressure rise-times are encountered and pressure

levels from a few hundred to tens of thousands of psi are experienced."

Sandia Laboratories, Livermore

R.D. Culy

Sandia Laboratories

Division 8183-1

P.O. Box 969

Li vermore

CA 94550

Phone: (415) 422-2468

FTS: 532-2468

D.C. Stoner

Sandia Laboratories

Division 8183-1

P.O. Box 969

Li vermore

CA 94550

Phone: (415) 422-3119

FTS: 532-3119

Comments:

"Sandia Laboratories, Livermore, instruments a variety of

components/assemblies for design verification testing. These include

electromechanical devices, mechanical structures, projectiles, parachutes, etc.

Test environments utilized are vibration exciters, centrifuges, drop towers,

ballistics, rocket sleds, sheet explosives, flyer plates, shock tubes, and

underground nuclear detonations. Both radio-link and hard-wire telemetry are

employed.

We make acceleration, vibration, pressure, temperature and angular

velocity measurements on flight test vehicles, laboratory test assemblies, and

special test units. The latter two range from single components to full-scale

models."

Stein Engineering Services

Peter Stein

Stein Engineering Services, Inc.

5602 E. Monte Rosa

Phoenix

AZ 85018

Phone: (602) 945-4603

(602) 946-7333

Comments:

"Consultant collects, evaluates and organizes literature on transducer

performance and behavior, especially in hostile environments. He has an extensive library and develops educational programs specifically oriented to transducers construction, evaluation and application. Consultant on measurement problems."

11-99
Systems, Science and Software

Russell Wilson

Systems, Science & Software

P.O. Box 1620

LaJolla

CA 92038

Phone: (174) 453-0060

ext 217

Comments:

"Personnel in the Shock Physics program at S6 use accelerometers , stress

gages, pressure sensors, and laser interferometer systems to study dynamic

environments produced by explosives (conventional and nuclear), light-gas guns

and flash x-ray tubes.

S** has the facilities and expertise to design, manufacture, calibrate,

and install quartz and ytterbium stress gages, particle velocity instruments,

and laser velocity interferometers usable at stresses of several k-bar,

accelerations above 10 000 g and velocities over 100 meters per second. Special

facilities at S^ include an explosive test site, a flash x-ray generator, a light-gas gun, and a dropbar stress and velocity calibrator."

TRW Systems

Ken Bushey

TRW Systems

P.O. Box 10

San Clemente

CA 92672

Phone: (714) 492-4157

ext 370

Comments:

"The Metrology Lab at TRW calibrates, evaluates and assists in design and

usage of a wide variety of pressure, force, flow, temperature, and vibration

sensors and their associated electronics. These sensors and associated

electronics are employed in tests ranging from rocket engine firings to

measurement of the pulsations of the human heart.

"Metrology at TRW is capable of special accuracies of low liquid flow and

accuracies in minipressures down to 1 to 2 inches of water within 0.01% of the

reading. Improvements in speed and accuracy of pressure sensor calibrations

through automation have been accomplished."

11-100
Vought Corporation

J.V. Kelly,, Jr.

Vought Corporation

Unit 2-59150

P.O. Box 5907

Dallas

TX 75222

Phone: (214) 266-3260

W.E. Dryer

Vought Corporation

Unit 2-59150

P.O. Box 5907

Dallas

TX 75222

Phone: (214) 266-3260

Comments:

"We use sensors in the ground and flight tests of missiles and aircraft."

11-101
11.2.3 Miscellaneous Sensor Information Resources

11. 2.3.1 Periodicals (The following periodicals present articles on sensors and related matters and advertise new sensors.

)

Instrumentation Technology (monthly)

Instrument Society of America

67 Alexander Drive

Research Triangle Park, NC 27709

ISA Transactions (quarterly)

Instrument Society of America

67 Alexander Drive

Research Triangle Park, NC 27709

Measurements and Control (bi-monthly)

Measurements and Data Corporation

2994 West Liberty Avenue

Pittsburgh, PA 15216

Instruments and Controls Systems (monthly)

Chilton Company

Radnor, PA 19089

Electronic Design (bi-weekly)

Hayden Publishing Comapny, Inc.

50 Essex Street

Rochelle Park, NJ 07662

Machine Design (bi-monthly)

Penton/IPC

Penton Plaza

Cleveland, OH 44114

Control Engineering (monthly)

666 Fifth Avenue

New York, NY 10109

Review of Scientific Instruments (monthly)

American Institute of Physics

345 East 45th Street

New York, NY 10017

IEEE Transactions on Instrumentation and Measurement

IEEE Service Company

445 Moes Lane

Piscataway, NJ 08854

11-102
11.2.3.2 Courses

Some universities and colleges at times offer courses related to sensors. Special inquiries should be made.

Short courses on measurements are currently being offered

as:

"Measurement Systems Engineering" and

"Measurement Systems Dynamics" by

Stein Engineering Services, Inc.

5602 East Monte Rosa

Phoenix, AZ 85018

11.2.3.3 Conferences

The Instrument Society of America sponsors a number of

meetings and conferences:

• Annual Conference and Exhibit, fall

• International Instrumentation Symposium, special

• Flow, Its Measurement and Control, every few years

• Temperature, Its Measurement and Control, every few years

The Range Commanders Council through the Transducer Committee

of the Telemetry Group sponsors a transducer workshop every

second year. Information may be obtained from Range Commanders

Council, White Sands Missile Range, NM 88002.

11-103

12. INDEX

Page

-Aabrasion 6-40

absolute pressure 4-2

accelerated life testing 6-70

acceleration function 6-71

constant severity level 6-71

cumulative damage 6-73

ideal characteristics 6-74

methods 6-70

model s 6-73

progressive stress 6-73

step stress 6-71

validity 6-75

acceleration 4-25,4-33

of gravity 4-34

sensors Tables A-7, A-8 ; see also acceleration sensors slowly changing 4-34

acceleration sensors Tables A-7, A-8 ; see also accelerometer

angular 4-36

damping of 4-35

force balance accelerometer 4-36

jerk 4-37

manufacturers 11-1

piezoelectric 4-27 servo accelerometer 4-36

transduction elements (table) 4-38

transverse sensitivity 6-8

accelerometers

dual centrifuge calibrator 6-28

earth's field dynamic calibrator 6-28

effect of thermal transients 6-49

acceptance testing 6-9

accuracy 3-6

acoustic level sensor 4-85

acoustic resonator 6-24

air bubble level sensor 4-83

aliasing error 5-6

Alphatron 4-16

American National Standards Institute 8-4

American Petroleum Institute 8-7

American Society for Testing and Materials 8-7

American Society of Heating, Refrigerating, and Air Conditioning

Engineers, Inc. 8-9

American Society of Mechanical Engineers 8-9

American Vacuum Society 8-11

amplitude response 6-18

analog-to-digital converter 5-7

bit rate 5-8

encoding resolution 5-8

angular velocity sensors 4-29

12-1
Page

aperiodic pressure generators 4-29 area meters 4-46

ATE systems 2-1 error assessment 7-1

fail safe considerations 6-76

fail safe design 6-76

part selection and control 6-77

redundancy 6-76

-BBasic Instrumentation - Industrial Measurement (book review) 9-13

Basic Instrumentation Lecture Notes and Study Guide - Measurement

Fundamentals (book review) 9-18

bearing performance 4-96

bellows 4-5

Berkson's premise 7-4

best straight line 7-2

bias 7-5

bibliography 9-1

bit rate 5-8

bonded strain gages 4-7

book reviews 9-9

Bourdon tube 4-5

boxcar filter 5-8

buffered data 5-12

burn-in 6-62

-Ccalibration 6-1

cycles 6-12

number of points 6-10

static ; see static calibration

dynamic ; see dynamic calibration

calibration data error analysis 7-1 error band concept 7-8

least squares straight line 7-2

polynomial fit 7-2

significant digits 7-3

uncertainty 7-4

capacitance in level measurements 4-85

capsule 4-5

Catalog of Federal Metrology and Calibration Facilities 11-80 common mode environment 5-6

completion network 5-5

conducted emission 6-53

confidence interval 7-4

controlled parts 6-76

creep,

test for 4-9

12-2
-D- Page

damping 4-34,6-19

factor 4-34,6-19

ratio 4-34,6-19

data acquisition system 5-1

accuracy 5-4

al iasing 5-6 common mode environment 5-6

computer interfacing 5-12

computer selection 5-12

data compression 5-11

data distribution 5-11

data transmission 5-9

dynamic range 5-4

general considerations 5-4

presampling filter 5-8

sample and hold 5-9

sample rate 5-7

selection of 5-3

system cal i oration 5-6

system parameters 5-4

time skew 5-9

data compression 5-10

data transmission 5-9

degrees of freedom 6-13

demultiplexing 5-10

diaphragm 4-5

differential pressure

in liquid level measurements 4-84

digital pressure sensors 4-13

digital transducers 4-13

Directory of Transducer Users 11-80

displacement sensors 4-26

absol ute 4-26

capacitive 4-27

encoders 4-27

in level measurements 4-83

integration of velocity 4-28

linear variable differential transformer 4-27

manufacturers 11-1

photoel ectric 4-27

piezoel ectric 4-27

potentiometric 4-26

resistive 4-26

strain gage 4-26

di ther 4-12

dual centrifuge 6-28

durabil i ty 6-54

dynamic calibration 6-1,6-16

frequency response 6-16

of accel erometers 6-35

of force sensors 6-36

of flowmeters 6-36

12-3
Page

of motion sensors 6-27

of pressure sensors 6-21

random stimuli 6-37

shock 6-36

vibration testing 6-35

-Eearly failures 6-62

earth's field dynamic calibrator 6-28

electrical connectors, effect of shock and vibration 6-68

electrodynamic vibration exciter 6-27

electromagnetic environment 6-53

standards 6-54

test methods 6-53

electromagnetic interference 6-53

electromagnetic radiation 6-53

Electronic Industries Association 8-11

EMI 6-53

encoders 4-27

encoding resolution 5-77

entrapped air diaphragm box 4-84

environmental effects 6-41

interacting 6-45

simulated 6-37

environmental testing 6-37

acceleration 6-50

combined environments 6-41

electromagnetic radiation 6-53

extreme steady-state temperatures 6-47

procedures 6-47

radiated emissions 6-53

shock 6-50

standards 6-47

test methods 6-47

thermal transients 6-49

vibration 6-50 error analysis 7-1 error band 7-8

exhaust gas temperature measurements 8-23

Experimental Methods for Engineers (book review) 9-15

-Ffailure mechanisms 6-67

changes in temperature 6-67

fatigue 6-67

high temperature 6-67

humidity 6-68

low temperature 6-67

other environmental effects 6-69

radiation 6-69

salt air 6-68

shock and vibration 6-68

12-4
Page

failure prediction C~7.9C fi-fil , O-Ol

failure rate D-Ot fi_fi4 f ati gue o—o / field strength 0-0 0

float devices for level measurements

A tt^

fl ow measurements /I "3Q 4-oy

comparison of sensors (table) 4-01 , 4-0£ mass flow rate H— tU

prouiems ana irenas

pulsating flow

A4-OUC fi ranges A4-4UAH

rate of f1 ow

A4— A1HI

sensing techniques

A4-41A1

si urry 4-OU

two-phase flow

A4-OU

units

A /in 4-4U

conversion table

a An

volumetric flow rate

A AH

flow rate

A4-4UAO

flow sensors Tables A-y, a-iu

acoustic

A Afi 4-4o

area meters

A4-40Aft axial flowmeters A4- A74 / comparison of (table) A4-01K1 critical flow nozzle 4—4 3

differential pressure A_A1 4—4 J. uoppier sniTt 4-4Q e i ec tromagne ti 

4-48

flow nozzle 4-40

gyroscopic

A A7

hot wire anemometer 4-4y

inferential

A4-40Aft linear resistance flowmeter A ac; manufacturers 1111-11 mass flowmeter /I4-4/A 7 obstruction meters A4-41Al

pi tot tube

A4-44AA

swirl 4-OU

thermal

A4-4y/I Q

thin plate orifice meter /I /ll 4-41

tracer 4-4y

turbine

A A~l 4-4/

vel oci ty

A4-41AlA Aft , 4-40

venturi

A4-41A1A A"} , 4-40

force 4—4-7?/ C Torce ana torque measurements iaDie m-io

defi ni ti ons 4-7?

materials compatibility 4-/o

range

A4-/47A sensor manufacturers 11-1 11-1

units

A4— 17. / 0

force balancing sensors 4-1 *+— x o1 force sensors 4-72

load cells ; see also load cells 4-74

12-5
Page

frequency discriminator 5-10

frequency division multiplex 5-10

frequency response 6-16

Fundamentals of Temperature, Pressure and Flow Measurements (book review) 9-19

-Ggage -- see under type of gage

gage factor 4-6

gage pressure 4-2

gas temperature measurements 4-67

conductivity effects 4-68

convection effects 4-68

exhaust gas temperature measurements 4-67

kinetic energy error 4-67

probes for 4-67

radiation effects 4-68

stagnation temperature 4-67

static temperature 4-68

stream temperature 4-67

thermal time constant 4-69

glossary 10-1

government sensor laboratories 2-2,11-80

government standards 8-31

-HHandbook of Applied Instrumentation (book review) 9-16

Handbook of Transducers for Electronic Measuring Systems (book review) 9-11

hot wire anemometer 4-49

humidity and moisture measurements 4-89

dew point hygrometer 4-91

electrical hygrometers 4-92

electrolytic 4-92

surface resistivity 4-92

volume resistivity 4-92

mechanical hygrometer 4-91

psychrometer 4-90

refractive hygrometer 4-94 sensor manufacturers 11-1

thermal conductivity bridge 4-93

hygrometer 4-92

hysteresis 6-15,7-2

-Iindustry sensor laboratories 11-89

infant mortality 6-62

Institute of Electrical and Electronics Engineers 8-12

Instrument Engineers Handbook (book review) 9-17

Instrument Society of America 3-1,8-15

Instrument Transducers (book review) 9-11

Instrumentation in Industry (book review) 9-14

12-6
Page

Instrumentation in Process Control (book review) 9-14

Instrumentation in Scientific Research (book review) 9-9

insulation breakdown 4-9

International Electrotechnical Commission 8-28

International Organization for Standardization 8-26

international system of units 4-3

Inter-Range Telemetry Working Group 8-20

ion gage 4-4

ISA Transducer Compendium (book review) 9-12

-Jjerk 4-37

-Kkinetic energy error 4-67

-Llife cycling 6-70

linear variable differential transformer

displacement sensor 4-27

pressure sensor 4-12

linear velocity sensors 4-28

linearity 6-15,7-2

liquid level measurements 4-81

direct method 4-82

displacement devices 4-83

electrical and electronic devices 4-85,4-88

float devices 4-83

head devices 4-84

in closed vessels 4-84

in open vessels 4-82

inferential method 4-82

materials compatibility 4-81

methods

acoustic 4-87

capacitance 4-86

optical 4-88

semiconductor 4-88

thermistor 4-87

ultrasonic 4-87 sensor manufacturers 11-1

state-of-the-art and future trends 4-89

units 4-81

visual devices 4-82

load cells 4-75

accuracy 4-78

dynamic behavior 4-79

hysteresis 4-78

load alignment 4-78

manufacturers 11-1

12-7
Page

nonl ineari ty 4-78

temperature effects 4-78

transverse sensitivity 4-78

lubricating oil analysis 4-96

-Mmaintainabil i ty 6-76

manufacturers of sensors ; see sensor manufacturers 11-1

materials compatibility 3-8

in flow measurements 4-39

in force and torque measurements 4-73

in level measurements 4-81

in motion sensors 4-26

in temperature measurements 4-54

mean time between failures 6-62

Measurement Systems (book review) 9-14

Mechanical Measurements (book review) 9-10

military standards 8-32

moisture and humidity measurements 4-89

motion measurements 4-23

motion sensors 4-24

displacement 4-26

dynamic calibration 4-28

materials compatibility 4-26

mounting force and torque 6-8

MTBF 6-65

multiplexing 5-7

_NMational Bureau of Standards 2-2,8-18

National Electrical Manufacturers Association 8-19

National Fluid Power Association 8-20

natural frequency 8-18

of liquid col umn 8-27

-0-

operating environment of sensors 6-2,6-37

operating signature 4-96

optical methods

in liquid level measurements 4-83

in torque measurements 4-74

overall system cal ibrati on 6-76

overload tests 6-15

overshoot 6-20

-Ppart selection and control 6-66

performance monitoring 2-2

periodic pressure generators 6-21

12-8
Page

phase response 6-19

photoelectric displacement sensors 4-26

Physical Laws and Effects (book review) 9-9

Physical Measurement and Analysis (book review) 9-10

piezoelectric crystals and ceramics 4-14

piezoelectric sensors accelerometers 4-35

effects of thermal transients 6-50

pressure 4-14

piezoelectric vibrators 6-28

Pi rani gage 4-15

pi tot tube 4-44

platinum resistance thermometers 4-61

position encoders 4-27

position sensitivity 6-4

potentiometer 4-11

contact noise 6-6

Practical Instrumentation Transducers (book review) 9-12

practical temperature scale 4-54

precision 7-4

pressure 4-1

absolute 4-2

conversion factors (table) 4-3

differential 4-2

gage 4-2

measurements 4-1,4-4

pulse generators 6-29

ranges 4-3

reference 4-2

sealed gage 4-2

sensing elements 4-5,4-19,4-20

sensing technologies 4-4 sensors ; see al so pressure sensors step 6-32

transducers ; see also pressure transduction elements

units 4-3

pressure sensors Tables A-l to A-3

digital 4-13

dynamic calibration 6-16

effect of life cycling 6-55

effect of thermal transients 6-49

force-summing elements 4-19

future trends 4-17

manufacturers 11-1

piezoelectric 4-14

strain gage ; see also strain gage sensors 4-6

transduction elements 4-5,4-21

linear variable differential transformer 4-12

piezoelectric 4-14

potentiometer 4-11

variable capacitance 4-12

variable reluctance 4-11

vibrating cylinder or wire 4-13

12-9
Page

proof tests 6-8

psychrometer 4-90

pulse code modulation 5-51

pyrometer 4-57

-Qqual ification testing 6-4

electrical tests 6-5

excitation variations 6-5

mechanical inspection 6-5

mounting force and torque 6-6

overload tests 6-8

position sensitivity 6-8

potentiometer contact noise 6-6

proof tests 6-8

transverse sensitivity 6-8

visual examination 6-5

warm-up effects 6-6

-R6-53

8-20

6-1,6-58

6-59

6-66

9-1

6-16

6-61

6-62

6-65

6-62

6-67

6-64

6-66

6-62

6-65

6-62

6-64

6-15,7-2

6-19

-S5-9

8-21

4-2

4-85

4-61

6-15

3-1,3-2

radiated emission

Range Commanders Council

re-cal ibration

intervals

redundancy

references

reference sensor

rel iabil ity

burn-in

degradation

early failures

failure mechanisms

failure rate

growth

infant mortality

mean time between failures

useful life

wearout

repeatabil ity

resonant frequency

sample and hold

Scientific Apparatus Makers Association

sealed gage pressure

semiconductor liquid level sensors semiconductor temperature sensors sensitivity sensoracceleration ; see also acceleration sensors

accel erometer ; see al so accel erometers

12-10
Page

accuracy 7-1

calibration laboratories 11-80,11-89

completion networks

corrosion 3-8

cost 3-7

defined 3-1,3-2

deformation sensitivity 3-4

displacement ; see also displacement sensors dynamic calibration ; see also dynamic calibration

dynamic nonlinearity 6-16 error analysis 7-1

evaluation laboratories 11-80,11-89

extended time operation 6-55

failure mechanisms 6-67

future trends 3-9

humidity 4-89

information sources ; see also sensor information sources isolating practices 3-9

level ; see also liquid level measurements

manufacturers ; see al so sensor manufacturers

materials compatibility 3-8

moisture 4-89

mounting 3-4

performance 2-2

position effects 3-4

pressure ; see also pressure sensors qualification testing 6-4

re-calibration 6-58

selection 2-3.3-3

self-calibrating 6-58 severe environments 6-47

signal conditioning 5-5

signal substitution 6-59

silicon integrated circuit 3-9

smart 3-10

standard documents ; see al so sensor standards

static calibration ; see also static calibration

strain gage ; see also strain gage sensors temperature ; see also temperature sensors temperature effects 3-4

torque ; see also torque sensors

use of microcomputers with 3-10 users government 11-80

industrial 11-89 vacuum ; see vacuum sensors velocity ; see velocity sensors, angular, and

velocity sensors, linear

sensor information sources bibliography 9-1

book reviews 9-9 courses 11-103

government laboratories 11-80

industry laboratories 11-89

12-11
Page

periodicals 11-102 sensor manufacturers 11-1

settling time 6-20

shock and vibration 6-50

Shock and Vibration Handbook (book review) 9-15

shock calibrators 6-35

shock tube 6-29

examples 6-30 sensor mounted on end plate 6-31 sensor mounted on side wall 6-30

vibration 6-31

shockless step pressure generators 6-32

examples 6-33

gaseous medium 6-34

liquid medium 6-34

Shulz-Phelps ion gage 4-16

shunt calibration 6-59

SI units 4-3

signature, operating 2-2

significant digits 7-3

sinusoidal pressure generators 6-21

Society of Automotive Engineers, Inc. 8-23

Society of Naval Architects and Marine Engineers 8-26

sonic measurement of liquid level 4-85

specifications 8-1

spring-mass system 4-29,4-33,6-17

stability 6-15,6-54

Standards and Practices for Instrumentation (book review) 9-20

standard error 7-4

standards 8-1

government 8-31

voluntary 8-3

standards documents 8-1

accuracy 8-8

dynamic calibration of pressure transducers 8-10 error analysis of data 8-21

flow measurements

fluid flowmeters

fl uid meters

fuel f1 owmeter

mass flow measurements

turbine flowmeters

motion sensor piezoelectric pressure transducers

potentiometric pressure transducers

pressure sensors dynamic calibration of pressure transducers 8-10

manometer tables 8-15

piezoelectric pressure transducers 8-17

potentiometric pressure transducers 8-16

pressure measurements 8-9

pressure ratio instruments 8-24

pressure transducers 8-43

strain gage pressure transducers 8-16

12-12

8-23

8-43

8-23

8-23

8-15

8-17

8-17

8-16
Page

radiation environment 8-34

reliability 8-34

shock and vibration measurements 8-6,8-7

strain gage

force transducers 8-16

linear acceleration transducers 8-16

pressure transducers 8-16

telemetry 8-10,8-20

temperature measurements

bushings and wells for temperature sensing elements 8-22

resistance thermometers 8-21

thermocouples 8-17

thermoelectric devices 8-8

transducers 8-16 vacuum gages 8-11

Standards Information Services 8-18

static calibration 6-1,6-9

basic calibration points 6-9

basic considerations 6-9

equipment 6-14

number of calibration cycles 6-12

procedures 6-13

recommended 6-12

3-point 6-10

11 - point 6-11

12-point 6-11

21 - point 6-11

22-point 6-12

statistical sampling

confidence levels 6-13

sample selection 6-13

sample size 6-13

step acceleration calibrators 6-35

ballistic pendulum 6-36

drop ball 6-36

dropping hammer 6-36

step function 6-29

storage life tests 6-55

strain gage sensors 4-6

bar gage 4-10

bonded 4-7

diffused 4-10

effect of extreme steady-state temperature 6-47

effect of life cycling 6-56

effect of storage at elevated temperatures 6-57

gage factor 4-7

manufacturers 11-1

pi ezoresi stive 4-10

pressure transducers 4-7

semiconductor 4-10

shunt calibration 6-59

thin film 4-8

unbonded 4-7

student's "t" 6-13

12-13
Page

Suggestions for Designers of Navy Electronic Equipment (book review) 9-19

systematic error 7-4

-Ttachometer 4-29

temperature measurements 4-53

gas temperature measurements 4-67

international practical temperature scale 4-56

materi al s compati bi 1 i ty 4-54

units 4-54

temperature sensors accuracy 4-60

bimetallic thermometers 4-57

bushings and wells 4-67

comparison (table) 4-71

installation effects 4-66

liquid in glass thermometers 4-57

manufacturers 11-1

platinum resistance thermometers 4-61

resistance thermometers 4-61

selection 4-65

semiconductor 4-63

thermistor 4-62

thermocouple 4-58

thermometer 4-57

thermal time constant 4-69

thermal transients 4-49

thermistor 4-62

thermocouples 4-58

thermometer 4-57

throughput rate 5-4

time division multiplex 5-1

torque 4-72

torque sensors 4-76,4-80

magnetically coupled 4-77

mechanical differential 4-76

optically coupled 4-77

telemetry 4-77

Training Manual : Physical Measurements (book review) 9-18

transducers 3-1

transducer workshops 11-103

Transducers in Digital Systems (book review) 9-17

transfer function 6-17

transmitter 3-1

-Uuncertainty 3-6

of a measured value 7-2

method of reporting 7-2

12-14
-V- Page

vacuum sensors 4-15

ion gage 4-16

ionizing 4-16

radioactive 4-16

thermoconductive 4-15

thermocouple 4-16

thermoelectric 4-16

velocity sensors, angular 4-29

analog 4-29

capacitive 4-31

di gi tal 4-29

eddy current 4-32

Hall effect 4-33

magnetic permeability 4-31

optical tachometer 4-32

permanent magnet al ternator 4-29

signal-to-noise ratio 4-31

tachometer 4-29

velocity sensors, linear 4-28

inductive 4-29

piezoelectric accelerometer 4-29,4-35

venturi meter 4-43

vibration and shock measurements 4-35

voluntary standards 8-3

-Wwarm up wear measurements 4-96 wear monitoring techniques 4-96

wearout 6-64

workshops, transducer 11-103

12-15

APPENDIX A

TABLES OF COMMERCIALLY AVAILABLE SENSORS

The following tables were compiled from current sensor manufacturers'

literature. This sampling of commercially available sensors is included to

indicate the types, ranges, characteristics, and operational environments that

such sensors encompass.

No conclusions should be drawn as to the quality of performance of any of

the listed devices. Listing of a particular sensor does not constitute

endorsement, nor does the absence of a device or manufacturer indicate

disapproval. The tables only serve to indicate approximately the scope of

commercial sensors.

Manufacturers of sensors should be contacted directly to get the most

up-to-date information on available sensors.

Key to Manufacturer's Codes

AKC Ametek Controls Division

ANL Analog Devices

AVL AVL Gesellschaft (Austria) - distributed by Degamo, Inc.

BAH Bell and Howell

BLE BLH Electronics

BBN Bolt, Beranek, and Newman, Inc.

BRN Bourns, Inc.

CCC Consolidated Controls Corp.

CEL Celesco Transducer Products, Inc.

COL Columbia Research Laboratories, Inc.

CNT Control otran Corporation

CXI Cox Instrument

DOS Degussa Inc., Metals Div.

DII Data Instruments Inc.

DM I Datametrics Inc.

DRC Dynamics Research Corp.

A-1
END Endevco, Dynamic Instruments Div.

EM" Entran Devices, Inc.

FAR Farrand Controls

FDN Fluidyne Instrumentation

FTI Flow Technology, 1 Inc.

FWL Fenwal Electronics

FXB Foxboro/I.C.T. Inc.

GLD Gould Inc.

GTN Gul ton

HBM Hottinger Baldwin Messtechnik

HFC Hoffer Flow Controls Inc.

HLS Haliburton Services

HMS Hamilton Standard

IGI IRAD Gage, Inc.

KAG Kistler Instrument Corporation - subsid. of Kistler Instrumente AG

KEY Keystone Carbon Company

KLT Kulite Semiconductor Products, Inc.

KMN Kaman Sciences Corporation

KSM Kistler-Morse

LBW Lebow Associates, Inc.

MRL Marl in Manufacturing Corp.

MNC Minco Products, Inc.

MSG Measurements Group, Vishay Intertechnology, Inc.

MTX Metrix Instrument Co.

OMG Omega Engineering Group

PCB PCB Piezotronics, Inc.

PSE Precise Sensors, Inc.

A-2
RES Research INv J V U 1 Wily Inc. AMv I

scv Sehaevitz Enaineerino

Oil 1 Sensotec Incorporated

OsssJJ Systems, Science, and Software

STN Strainsert Company

Setra Systems, Inc.

SUN ww I

Sunstrand Data Control, Inc.

SYC w 1 w Systems Corporation

TGY 1 w. 1 Teledyne Gurley

THR Teledyne Hastings -Ray dist

TMP Temposonics Incorporated

11 DT United Detector Technology, Inc.

will UNM1 Uni measure Div., Konigsberg Instruments

VLD Validyne Engineering Corp.

VNT Vernitech Division, Vernitron Corp.

VTN Viatran Corporation

WAT Waters Manufacturing, Inc.

WLX Wilcoxon Research

A-3

Bi-I I4A IREV. 2-bi;i U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO. MRC CD £1 E

INDo jr DID

2. Performing Organ. Report No. 3. Publication Date

UCT-ODcr 1 yo 1

i }. TITLE AND SUBTITLE

SENSOR HANDBOOK FOR AUTOMATIC TEST, MONITORING, DIAGNOSTIC, AND CONTROL SYSTEMS

APPLICATIONS TO MILITARY VEHICLES AND MACHINERY

5. AUTHOR(S)

Paul S. Lederer

1 i. PERFORMING ORGANIZATION (If joint or other than NBS, see instructions)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No.

8. Type of Report & Period Covered Final

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State, ZIP)

U.S. Army Material Command

C0RADC0M/DRDC0-TCS

Fort Monmouth, NJ 07703

10. SUPPLEMENTARY NOTES

The preparation of this document was one of the objectives of Subtask 20602 of the

Joint Logistics Commanders Panel on Automatic Testing (Department of Defense).

Library of Congress Catalog Card Number: 81-600127

J Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here) The Sensor Handbook is intended as a guide for those who design, specify,

use, and test military automatic test equipment containing -sensors. The

handbook addresses measurands and principles of measurement, data acquisition,

sensor calibration and testing, environmental considerations, stability,

durability, reliability, and error assessment. Sensor manufacturers and sensor

calibration and evaluation resources are included, as is an annotated bibliography.

The handbook is based largely on the present, proved state-of-the-art. Possible

future trends are briefly discussed. The handbook is addressed to the general

engineer, system designer, or manager with an engineering background. It does

not provide the highly detailed technical information needed by the measurement

engineer, although ample references are included for further study.

2. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

automatic test equipment; ATE; calibration; data acquisition; durability;

dynamic calibration; environmental testing; evaluation; measurand; reliability;

sensor; transducer. . 13. AVAILABILITY

[X~] Unlimited

|

| For Official Distribution. Do Not Release to NTIS

jX~] Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402.

~~2 Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

450

15. Price

$9.00

USCOMM-DC 6043-P80

fc U.S. GOVERNMENT PRINTING OFFICE : I9SI -354-868/9172





TABLE A-l COMMERCIALLY AVAILABLE PRESSURE SENSORS

i i i i - i

id' 10' n' 10' »' 10'

P1EZORESIST1VE (SEMICONDUCTOR nMll GAGE)

PIEZ0RESI5TIVE (SEMICONDUCTOR

STRAIN GAGE)

F1EI0RES1STIVE (SEMICONDUCTOR

STRAIN GAGE)

PIUORESIITIVE (SEMICONDUCTOR

STRAIN GACEI

OPERATING TEMP P



TABLE A-2 COMMERCIALLY AVAILABLE PRESSURE SENSORS

FULt SCALE RANGES FULL RANGE OUTPUT

OPERATING Tf MP RANGE |'C|

STRAIN G UN8GNDE

OIAPHRAC

STRAIN C( UNBONOED. OlAPHRAGM

STRAIN GAGE

BONDED; DIAPHRAGM

STRAIN GAGE

BONDED; OlAPHRAGM

STRAIN GAGE

BONDED; DIAPHRAGM

STRAIN GAGE

BONDED: DIAPHRAGM

STRAIN GAGE BONDED DIAPHRAGM

STRAIN GAGE

BONDED: OlAPHRAGM



TftBLE

A- 3 . COMMERCIALLY AVAILABLE PRESSURE SENSORS







TABLE A-5 COMMERCIALLY AVAILABLE DISPLACEMENT SENSORS

FULL SCALE RANGES

nm| IIT* 1DJitr

1 io° 10' io

1 io

1 io'L

NEARITY HYSTERESIS

FREQUENCY RANGE OPERATING TEMP RANGE fC)

J L

EDDY CURRENT

EODY CURRENT

(VARIABLE IMPEDANCE)

ANGULAR DISPLACEMENT

RVDT {ROTARY

VARIABLE

DIFFERENTIAL TRANSFORMER)

ACTIVE AREA

SOLID STATE- SEALED; STAINLESS STEEL WITHSTANDS 3000 PSI

NDN CONTACTING; MEASURES RADIAL

VIBRATION OR AXIA POSITION OF MOTOI

SHAFTS

NON< CONTACTING



TABLE A-6 COMMERCIALLY AVAILABLE DIGITAL ENCODERS (DISPLACEMENT SENSORS)

TRANSDUCTION

VARIABLE RELUCTANCE

3 0 0025 TO 0 005mm

800'C MAXIMUM

S, B, 12, OR 15 VOLTS

DIAMETER 3. 7. OR 1Z INCHES ROLLED STEEL OR ALUMINUM

MAXIMUM RADIATION DOSE -

3000 RPM - MAXIMUM CON- TINUOUS SHAFT SPEED. LED

LIGHT SOURCE; RUGCEO

REQUIRES ELABORATE SOURCE, WAVEGUIDE. AND OETECTOR

SYSTEM: MAXIMUM RADIATION

4 % t # n * n mjkX m

* H * M * $ m m m I M

« y y y wuQOCX#

n d M * jCjOi PQkXM

4 1 M #> Hit 4 * A A Mi

*> */ f> < W rf. j#>. 'tfk 1<' 'I ffl' T I

i k Pt

KnftKHlQySTM iff; tf * H- ll .* * ' - It #. f < '«',."* r i r*. iQOQOG

TABLE A-7 COMMERCIALLY AVAILABLE ACCELERATION SENSORS



TABLE A-8 COMMERCIALLY AVAILABLE ACCELERATION SENSORS

RANGES (g) 10- 10* 10' 10* 10' 10* 101 10*

I I I I I I I I

105 on

145 410 hO

LOA0)

I - IMPACT

t - SHOCK

V * VIBRATION

RESONANT

FREQUENCY

(tHi)

OPERATING TEMPERATURE RAHGE CO

0 + 200 +400

1 I I

ALUMINUM; VIBRATION; SHOCK;

IMPACT; INTERNAL CALIBRATION

SIGNAL; M75 10 SS75

STAINLESS STEEL. VIBRATION; SHOCK; IMPACT; EXTERNAL

CALIBRATION; $400

VIBRATION; DISPLACEMENT; C AVERAGE VELOCITY. FOR DYNAMIC

BALANCING; PIPELINES; AIRCRAFT

ENGINES

VIBRATION; BIS PLACEMENT; AVERAQE VELOCITY. REPAIRABLE;

AIRCRAFT; LONG LIFE

LINEAR; 1350 TO S365

ANGULAR; S3 SO TO MB

5



TABLE A- COMMERCIALLY AVAILABLE FLOW SENSORS (VOLUME)

RANGES (GAL/MINI

10"' 10"' 10-

MATERIAL MEASURED

LIQUID OAS SLURRY

OPERATING TEMPERATURE RANGE |'C|

I *J1 T

TOWEH REQUIRED

THERMOELECTRIC

PRESSURE

DIFFERENTIAL If SEMICONDUCTOR

RESISTANCE

CRYOGENIC {AVAILABLE!

MODEL) AVAILABLE FOR

CORROSIVE, CRYOGENIC. OH

VOLATILE FLUIDS

STAINLESS STEEL MINIATURE

S> REPLACEABLE ROTOR ASSEMBLY. LOW COST. ELEC- TRONIC PULSE OUTPUT

STAINLESS STEEL. COJm C 0 TUNBSTEN CARBIDE.

I- OR B I- DIRECTIONAL

IMOpllg POCKETLESS AND

LESS STEEL; BUILT CIRCUITRY TO DIGITAL UT EQUIP.



COMMERCIALLY AVAILABLE FLOW SENSORS (VELOCITY)

J I L

ItC 10" IP 10" 10* J I I I L

MATERIAL MEASURED

fov/eh neouiRGD

0 0 (H,0), (GASOLINE)

0.3 (OIL) 30.0 (AIR)

PflOBE FOR FERHAHEHT Ofl TEMPORARY INSERTION IN EXHAUST STACKS. ETC.

{FOR. EPA MEAS-)

RETRACTABLE PHOBE

IAL, CLAMP-OH TYPE • PORTABLE. WEATHER-PROOF;

ID EXPLOSION-PROOF

I DELS AVAILABLE

EXTERNAL, CLAMP-ON TYPE

0-300Q PSI. PRESSURE Si



TABLE A-ll COMMERCIALLY AVAILABLE TEMPERATURE SENSORS


\

I
TABLE A12 COMMERCIALLY AVAILABLE TEMPERATURE SENSORS

RANOE CC)

1

1 +4

|" + T

,

, *T T LiNUmrr ISEC.) (O'Cj (V) COMMENTS

FA*CIURER BBmT¥°rci

RESISTANCE * 10 OR SO STEEL SHEAT ^ENDaVe

0 03

10 ...... ..... . mar T ...

RESISTANCE ±0.11

O B OR

TS TO KM g u£S

FLEXIBLE RIBBON - PLAIN OR MNC

"FAST" mem.

GRID HIGH SENSITIVITY. SHUN

CALIBRATION, ttt TO S3? PEH mis

(CASE) RESISTANCE ±o.u .«„. ...

RESISTANCE CAS LIQUID 0.HK 1. OR U DC u

100 1 a oc

RESISTANCE 400 m. 1 TO 6.7

0 R 1 CAl PAC MGES

0R

i7 1' US30 ...

RESISTANCE » .M PROBES

M [WW I » 1ST0.I

»

LIQUID 0.. N„ ... H„ 4Hl) 3,000.000 1.5 1 SQUARE) CRTOGEHIC LIQUID LEVELS *,

TULFhPIISIUB *Ki" ,, U.U. CO.TMTM. .,..«..

((iA/-C|

1.0

RESISTANCE

THERMISTOR

|*/"Ef

BEAOj »

1000 CLASS BEAD OR PROBE FWL

-o.M gtoo-c

THERMISTOR -T OO TWC 10.000 IDC| 6.300 (AC)

SWnCHINS TEMPERATURE! (>C)

THERMISTOR

S TO 3,300

-

irf 1 I i » tf iH' tl • ft fll H M fti M P- } ty* *%VV% it* U OLA

i I | | "t '4. f|! fle ) *

) * <r e X * *• i? 4 *> *. H

JOt * Ol H * * AMi

ft W "» * * 4 4 mA)'M in hi % * *t % > 1.

4 • 4 4 £ * * * .* ,^ ft > v> « loot *ju*jC*XKM

gb «; *> «. i n, m, ,. *,? n

Jfc Jbjg. '<< flip! *GO ?1

TABLE A- 13 COMMERCIALLY AVAILABLE FORCE SENSORS

FULL SCALE RANGES

TRANSDUCTION LINEARITY HYSTERESIS

OPERATING Tf MP RANGE |"C)

J L

SEMICONDUCTOR

STRAIN GAGE

(CANTILEVER BEAM)

SEMICONDUCTOR

N GAGE

I CANTILEVER BEAMI

SEMICONDUCTOR

N GAGE

(CANTILEVER BEAM)

LINEAR VARIABLE

DIFFERENTIAL TRANSFORMER

PIEZOELECTRIC

OIRECTIONAl

STAINLESS STEEL

STAINLESS STEEL

DYNAMIC OR QUASI STATIC FORCES RES FREQ - 3D to 80 m

tlet for the foregoing data is

il Reference Data (JPCRD)

American Chemical Society

Physics (AIP). Subscriptions, om ACS, 1 155 Sixteenth St.,

ates technical information

ing materials, components,

ries presents research results,

i related to the structural and

urability and safety characitems.

which are complete in themnt of a subject. Analogous to

iive in scope or definitive in

i serve as a vehicle for final ider the sponsorship of other

^eloped under procedures merce in Part 10, Title 15, of

i. The standards establish
U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Washington. D.C. 20234

.-ICIAL BUSINESS

nalty for Private Use. $300

POSTAGE AND FEES PAID

U.S. DEPARTMENT OF COMMERCE

COM-215

SPECIAL FOURTH-CLASS RATE

BOOK