NBS SPECIAL PUBLICATION

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

Detection, Diagnosis,

and Prognosis

MFPG

28th Meeting
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards1 was established by an act of Congress 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 performed by the National Measurement Laboratory, the National Engineering Laboratory,

and the Institute for Computer Sciences and Technology.

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The National Bureau of Standards was reorganized, effective April 9, 1978.
MFPG

Detection, Diagnosis, and Prognosis

Proceedings of the 28th Meeting of the

Mechanical Failures Prevention Group,

held at San Antonio, Texas

November 28-30, 1978

«ATlOWAt BUREAU

Of ffCAtfDASM

U8BABY

JUL 1 3 1981

Ocfoo

no. SV7

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c. >

Edited by

T.R. Shives and W.A. Willard

National Measurement Laboratory

National Bureau of Standards

Washington, D.C. 20234

The 28th meeting of the MFPG and these proceedings were sponsored by the Center for Materials Science of the National Bureau of Standards, Washington, DC 20234; the Office of Naval Research, Department of

the Navy, Arlington, VA 22217; the Naval Air Development Center, Department of the Navy, Warminster,

PA 1 8974; the Department of Energy -Fossil Energy, Washington, DC 20545; and the National Aeronautics and Space Administration, Goddard Space Flight Center, Greenbelt, MD 20771.

U.S. DEPARTMENT 0*F COMMERCE, Juanita M. Kreps, Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Issued July 1979
Library of Congress Catalog Card Number: 79-600078

National Bureau of Standards Special Publication 547

Nat. Bur. Stand. (U.S.), Spec. Publ. 547, 368 pages (July 1979) CODEN: XNBSAV

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1979

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

Stock No. 003-003-02083-4 Price $7.00

(Add 25 percent additional for other than U.S. mailing).
FOREWORD

The 28th meeting of the Mechanical Failures Prevention Group was held

November 28-30 at the Oak Hills Motor Inn in San Antonio, Texas. The

program was organized by the Detection, Diagnosis, and Prognosis Committee under the chairmanship of Henry R. Hegner of the ManTech of New

Jersey Corporation. The committee, the session chairmen, and especially the speakers are to be commended for the excellent program.

Most of the papers in these proceedings are presented as submitted by

the author on camera ready copy. Some moderate editorial changes were

required in a few instances.

The MFPG is grateful for the cooperation and assistance provided by the

Southwest Research Institute in hosting the meeting. Special thanks go

to Richard B. Curtin, Director, Data Systems Department of SwRI for

coordinating the meeting, and to David Black of the SwRI Special

Programs Office and Mrs. Thelma Greene for making the hotel and meeting

arrangements

.

Special appreciation is extended to Jerry Philips of the Naval Ship

Research and Development Center for his handling of the meeting

publicity and to Robert M. Whittier, Endevco Corporation, for assistance

in the mailing and distribution of the meeting announcements.

Appreciation also is extended to the following members of the NBS

Fracture and Deformation Division: T. Robert Shives and William A.

Willard for their editing, organization, and preparation of the

proceedings, and Leonard C. Smith and Joel C. Sauter for photographic

work. Gratitude is expressed to the following members of the NBS

Center for Materials Science. Larry W. Ketron for drafting work and

Marian L. Slusser for typing.

HARRY C. BURNETT

Executive Secretary, MFPG

Center for Materials Science

National Bureau of Standards

III
TABLE OF CONTENTS

Page

FOREWORD III

SESSION I: AEROSPACE APPLICATIONS

1. Space Shuttle Diagnostics. Dennis J. Webb 3

2. Multispectral Scanner on LANDSAT. Stephen M. Gritton 17

and A. Bernard Marchant*

3. Drivetrain Bearing Analysis. Thomas C. Belrose and 31

David Board*

4. Light Helicopter Detection, Diagnosis and Prognosis 36

Objectives and Applications. Henry G. Smith*

and Robert E. Rohtert

5. Gas Turbines and Millimeter-Wave Radar. N. Bruce Kramer 58

SESSION II: LAND BASED APPLICATIONS

1. Improving Vehicle Life-Cycle Reliability by Prognostic 65

Maintenance Management through Geriometry.

Richard G. Salter

2. Motor Vehicle Fault Detection and Diagnosis. 78

Joseph J. Innes

3. Diagnosis of Combat Vehicle Systems Using Simplified 98

Test Equipment. T. E. Fitzpatrick, R. E. Hanson,

and F. W. Hohn (paper was presented by Richard T. Cowley, RCA)

4. Automated Vehicular Test Equipment. L. Thomas Carter 111

SESSION III: MARINE APPLICATIONS

1. The Acoustic Valve Leak Detector - A New Tool for 129

Fluid Systems Maintenance. Joseph G. Dimmick*

and Joseph W. Dickey

2. Pielstick Engine Diagnostics. A. Genot 153

3. Machinery Condition Analysis for Maintenance Planning - 167

The Aircraft Carrier Experience. Michael D. Dougherty (paper was presented by Mark Libby,

U.S. Navy - PERA (CV)

)

IV
4. Diesel Engine Analysis: Past Experience and Future 176

Plans. Harold W. Rethmann

5. Fiber Optics for Bearing Performance Monitoring. 191

Gerald J. Philips

SESSION IV: INDUSTRIAL APPLICATIONS

1. Statistical Techniques for Automating the Detection 203

of Anomalous Performance in Rotating Machinery.

K. R. Piety* and T. E. Magette

2. Vibration Analysis Method for Detection of Abnormal 232

Movement of Material in a Rotary Dissolver.

C. M. Smith*, D. N. Fry, and W. T. King

3. Monitoring Inlet Steam Valves of PWR 900 MW Turbo- 250

generators. A. Jaudet and J. C. Sol*

4. An Approach to Monitoring Existing Utility Turbo- 280

generators . S . Doughty

5. Enhancing Machinery Protection through Automated 286

Diagnostics. J. L. Frarey

SESSION V: NEW TECHNOLOGY

1. Report on Industry/Joint Services Project Task 299

Group 1-d. J. P. Wright

2. A Polymer Sensor for Monitoring Bail-Bearing Condition. 303

Seymour Edelman, James M. Kenney, John F. Mayo-Wells,

and Steven C. Roth*

3. An Instrumentation Technique to Evaluate Spectra for 315

Engine Diagnostics. Tony Carolan

4. The Direct Reading Ferrograph. Daniel P. Anderson 323

5. An Advanced Real-Time Oil Debris Monitor. T. E. Tauber 330

6. A Practical Approach to Aircraft System Component 345

Malfunction Diagnosis. F. E. Bishop

APPENDIX

List of Registrants for the 28th MFPG Meeting. 361

MFPG Publications 368

*Indicates speaker when a paper had more than one author.

V
ABSTRACT

These proceedings consist of a group of twenty five submitted

papers from the 28th meeting of the Mechanical Failures Prevention

Group which was held in San Antonio, Texas, November 28-30, 1978. The

central theme of the proceedings deals with detection, diagnosis, and

prognosis as related to mechanical failure prevention. Special emphasis

is on aerospace applications, land based applications, marine applications and industrial applications.

Key Words : Bearing analysis; condition monitoring; engine diagnosis;

failure detection; failure diagnosis; failure prevention; maintenance;

performance monitoring.

UNITS AND SYMBOLS

Customary United States units and symbols appear in some of the

papers in these proceedings. The participants in the 28th meeting of

the Mechanical Failures Prevention Group have used the established

units and symbols commonly employed in their professional fields.

However, as an aid to the reader in increasing familiarity with and

usage of the metric system of units (SI) , the following references are given

:

NBS Special Publication, SP330, 1977 Edition, "The International System

of Units."

ISO International Standard 1000 (1973 Edition) , "SI Units and Recommendations for Use of Their Multiples."

E380-76 ASTM/IEEE Standard Metric Practice (Institute of Electrical and

Electronics Engineers, Inc ., Standard 268-1976).

Disclaimer

:

Certain trade names and company products are identified in order

to adequately specify the experimental procedure. In no case does such

identification imply recommendation or endorsement by the National

Bureau of Standards, nor does it imply that the products are necessarily

the best available for the purpose. Views expressed by the various

authors are their own and do not necessarily represent those of the

National Bureau of Standards.

VI
j

SESSION I

AEROSPACE APPLICATIONS

Chairman: Robert R. Holden

Hughes Aircraft Company

Co-Chairman: John George

Parks College of St. Louis University

SPACE SHUTTLE DIAGNOSTICS

Dennis J. Webb

NASA Johnson Space Center

Flight Operations Directorate

Houston, Texas 77058

Abstract : The Space Shuttle Orbiter employs an elaborate onboard failure diagnosis system. Failure detection, accomplished in a variety of

ways by the vehicle's data processing system, provides aural and visual

cues to the flight crew on vehicle anomalies. In some cases, redundancy

management is automatically performed to compensate for the failure.

The flight crew then refers to a comprehensive body of malfunction procedures, developed by mission control center personnel, to analyze the

detailed symptoms, identify the scope of the failure, and reconfigure

the vehicle for safe continuation of the mission. Operational verification of the diagnosis system and training in its use by the flight crew

and mission control center personnel is accomplished by classroom instruction and simulation experience. Examples and philosophy of the

diagnosis system design and the responsibilities of the flight crew and

mission control are discussed.

Key words : Manned spaceflight failures; automatic monitoring; failure

annunciation; redundancy management; malfunction procedures; training

for diagnosis.

Introduction

The Space Transportation System, with the reuseable Orbiter vehicle,

represents a significant challenge to existing procedures and philosophies of failure detection and diagnosis in manned spaceflight. The

Orbiter is one of the most complex space vehicles ever built, incorporating many systems new to manned spaceflight; e.g., hydraulic aerosurface actuation powered by hydrazine energized turbine, a flexible data

processing system of five computers capable of redundant program execution, and large reuseable rocket engines. The high volume of flights

with up to three vehicles in orbit simultaneously, indicates a more

limited ground support effort per vehicle and a more autonomous flight

crew and spacecraft. The Orbiter must be flexible enough to support

different payloads or payload combinations with only a seven-day ground

turnaround period for vehicle reconfiguration. Clearly the business of

operating the Orbiter is different from that of previous space programs

where unique, single use vehicles were managed with a large ground

support effort.

5
The consequences of failures in manned spaceflight range from minor

irritation to very serious circumstance. Often the required action is

merely the operation of a switch by the flight crew to engage a redundant system, but there are failures which require major reconfiguration

of the vehicle or significant change in the management plan.

In order to effectively cope with the serious implications of failure

in spaceflight, NASA has taken a number of significant steps. First,

although a description is beyond the scope of this paper, the Orbiter

has been designed and is being built and qualified by the exhaustive

processes which have become standard in the high technology aerospace

industry. A significant design feature is the implementation of an ex- tensive and flexible system of redundancy. Second, the Orbiter has

been endowed with a powerful onboard data processing system which is

tasked with a significant share of the monitoring and control activity.

Finally, the flight crew and ground support team prepare for the mission through participation in the Orbiter design process, development

of operational and malfunction procedures and guidelines, classroom

training, and a comprehensive sequence of flight simulations.

Failure Detection System

The central element in the failure detection system is the data processing system (DPS) which is composed of five unique computers interfaced

with a variety of input/output devices so that the computers can monitor vehicle status and send commands to the hardware subsystems which

include a cathode ray tube (CRT) display and keyboard system for crew

interaction. For the critical phases of ascent, on-orbit maneuvers,

and entry, the computers are run redundantly, synchronously executing

the same programs to protect against DPS failures. The flight software

utilization is divided between flight critical functions (guidance,

navigation, and flight control) and mission critical functions (electrical power, environmental control, communications, mechanical systems

and payload support). Included across all of these programs is a failure detection and identification system.

Fault Detection and Annunciation

To use the DPS resources and design effort most efficiently, automatic

monitoring is accomplished where possible by processors operating

repetitively on tabularly formatted data. One such processor is fault

detection and annunciation (FDA), a part of the mission critical systems management program. FDA processes approximately 450 measurements

including discretes, analogs (voltages, currents, pressures, temperatures, flow rates, etc.), and other more unique indicators.

FDA detects failures by comparing the current value of each measurement

to a specified set of high and low limits which bound an acceptable

range of system behavior. If the referenced value is outside of this

range for more than a specified number of samples, the out-of-1 imits

k
condition is annunciated. Orbiter standard annunciation (Table 1) is

composed of a scale of critical ity which maps to a priority scheme of

crew response. In case of a rapid sequence of annunciation, the crew must respond to the most critical failures first.

ALARM CLASS/TITLE IMPLICATION AURAL CUE VISUAL CUES

1 : EMERGENCY RAPID LOSS OF CABIN PRESS DETECTION OF SMOKE

KLAXON SIREN

RAPID AP LIGHT

SMOKE LIGHTS MASTER ALARM LIGHTS

2: CAUTION & WARNING

IMMEDIATE CREW SAFETY

EVENTUAL LOSS OF VEHICLE

DUAL TONE INDIVIDUAL C&W LIGHT

BACKUP C&W LIGHT

RED MASTER ALARM LIGHTS FAULT MESSAGE!

3: ALERT LOSS OF CAPABILITY SINGLE TONE

^.rlALLl UUI\nl lull j

BLUE ALERT LIGHT

rnUL 1 1 iLo jMul

4: (SPARE) NONE FAULT MESSAGE

5: OPERATOR

ERROR

ILLEGAL OPERATOR

COMMAND TO DATA PROCESSING SYSTEM

NONE FAULT MESSAGE ONLY ON CRT WHERE ERROR OCCURED

"ILLEGAL ENTRY"

Table 1 Orbiter Annunciation

Two classes of computer annunciation are of particular interest. Class

2 is a backup to the traditional caution and warning system which detects and annunciates failures which relate directly to crew safety.

Class 3 or "Alert" annunciation signifies the loss or impending loss of

a capability which by itself does not relate immediately to crew safety.

Each class provides unique aural and visual cues which include a fault

message which indicates the time of occurrence, the general area of

failure, and the number of the appropriate display format that can be

viewed by the crew on the CRT's. The fault message appears flashing at

the bottom of each of the four CRT units and remains until acknowledged

by the crew via the keyboard.

In many cases, systems and parameter behavior is a function of changing

vehicle or systems configuration as well as failure. To cope with this

problem, FDA allows a measurement to have multiple limit sets, each

equipped with a logical statement which defines the corresponding con- figuration. The logical statements are composed of a logical combination of one to four configuration measurements, usually discretes.

This process of automatic limit set selection is called preconditioning.

5
A useful example of the FDA process is the design for monitoring the

pressure across one of the water coolant loop pumps. As a critical com- ponent in the vehicle cooling system, the water pump must be monitored

to detect line blockage or leaks, pump degradation or failure, so that

the system may be reconfigured to compensate for or correct the problem.

Pump 2 (Figure 1) is controlled by a three-position switch which allows

ON, OFF, and GPC (general purpose computer) modes of operation. ON and

OFF are self-evident and GPC mode enables the DPS to periodically turn

on the pump. One water loop is circulating all the time, leaving the

redundant loop stagnated. To prevent the stagnated loop from freezing,

the computer automatically commands the pump on for four minutes every 6

hours. The computer subtracts the pump inlet pressure from the outlet

pressure to give a delta pressure value that indicates pump and loop

health as well as on/off status of the pump. Further, the position of

the switch is monitored via discrete indicators wired from the ON and

GPC positions.

The FDA process is illustrated in Figure 2. First, the configuration is

determined. The pump should be running if either the switch is in the

ON position, or if the switch is in the GPC position, and the computer

has commanded the pump ON. This logical statement, when true, will

select the "pump running" limit set. The pump will not be running if

H20 PUMP LOOP 2

V 30 AC

GPC

OFF

ON

V DC

WATER

PUMP 2

NOTE: CIRCUIT REDUNDANCY HAS BEEN ELIMINATED FOR CLARITY

GPC COMMAND:

PUMP ON SWITCH:

ON POSITION

SWITCH:

GPC POSITION

INLET PRESSURE OUTLET

PRESSURE

INPUT/ OUTPUT

SYSTEM

HARDWARE

SOFTWARE

WATER LOOP CONTROL SEQUENCER FDA

Figure 1 Water Pump 2 Control and Monitoring,

6
the switch is in the OFF position (not ON and not 6PC) or if the switch

is in the GPC position but the computer has not commanded the pump on. This logical statement, when true, will select the pump not-running

limit set. Should both statements be true or false due to failure of

the switch, power source, or data acquisition device, the "pump running"

limit set will be selected. FDA then compares the current sample of the

delta pressure across the pump to the selected limit set, and if the

value is greater than the high limit or less than the low limit, FDA

will initiate annunciation. As this is a class 3 alert parameter,

annunciation takes the form of the 4-second 500 Hz alert tone, illumination of the blue alert light at the front of the cockpit, which persists

until acknowledged by the crew via the keyboard, and the fault message

"S88 THERMAL H2O" flashing on the crew CRT which refers the crew to CRT

page 88 where they may view the delta pressure value and associated

measurements and proceed with the diagnosis.

REDUNDANCY MANAGEMENT

The Orbiter uses an extensive system of redundancy across all vehicle

systems. The flight critical systems which control the vehicle are re- quired to be tolerant to one failure with no loss of capability and a second failure leaving the vehicle in a safe configuration; this attribute is called fail -operational , fail-safe. Due to the complexity of

• PUMP RUNNING: (SWITCH=0N) OR [(SWITCH=GPC) AND (GPC C0MMAND=0N)]

ACCEPTABLE RANGE: 35 TO 50 PSID

• PUMP NOT RUNNING: [(SWITCH^ON) AND (SWITCH^GPC)] OR [(SWITCH=GPC) AND (GPC C0MMAND=0FF)]

ACCEPTABLE RANGE: 0 TO 5 PSID

Figure 2 Water Pump 2 Fault Detection and Annunciation

7
the redundancy scheme in these systems, the DPS often performs automatic

redundancy management (RM) to reconfigure around a failure. This processing is particularly beneficial because the crew is freed to make the

decisions which are beyond the capability of the simple logic and the

computer can respond faster than the crew could. In some cases, failures of redundant data or control items are annunciated either as information to the crew or as a request for a decision.

While RM is performed on a variety of devices (inertia! measurement

units, engine control systems, switches), the RM program which processes

the rotation hand controllers (RHC) is a useful illustration. The RHC,

loosely defined, is the "stick" which enables the crew to manually control the vehicle attitude as is occasionally required during on-orbit

maneuvers and the glide to the landing field as a conventional aircraft.

As a failure of the RHC capability could lead to loss of the crew and

vehicle, RM is performed on three redundant stick position channels for

each of the three degrees of freedom of pitch, roll, and yaw.

Figure 3 is a block diagram illustrating the hardware and associated RM

design for each of the three RHC's. Each degree of freedom (pitch ilr

lustrated) has three independent redundantly powered transducers which

i

PITCH CHANNEL

(SAME FOR YAW AND ROLL)

NOTE: TRANSDUCERS

ARE ACTUALLY

LINEAR VARIABLE DIFFERENTIAL TRANSFORMERS

DATA ACQUISITION

SYSTEM

COMMFAULTS

HARDWARE

DETECTION , MISCOMPARES

AB

BC

CA

IDENT

FAILS

SOFTWARE

SELECTION FILTER

VALUE SELECTION

SELECTED

VALUE

MODE SELECT

MODES

3 GOOD: MID VAL

2 GOOD: AVERAGE

1 GOOD: PASS

0 GOOD: INVAL DATA BAD

CLASS 2 OR 3 ANNUNCIATION:

"RHC L"

Figure 3 Rotation Hand Controller Redundancy Management (RHC RM)

8
put out a -5-volt to +5-volt signal which is a function of position of

the RHC. These measurements are made available to the software by the

data acquisition system; the signals are routed through redundant data

acquisition units and data buses to the computers which are also operating redundantly for failure tolerance. Should the failure of acquisition hardware or timing cause loss of current data to the computers, a "commfault" bit associated with each affected parameter is set so that

subsequent processing may be aware that the data should not be used.

Failures in the data acquisition system are annunciated by other programs as class 3 alerts.

RM first processes the values and their commfaults to determine if any

of the transducers have failed. This fault detection is accomplished by

comparing the position values (A, B, and C) and providing signals which

indicate which of the three comparisons (AB, BC, CA) indicate that two

signals disagree by more than a specified amount. A miscompare is not

declared if one of the two parameters is commfaulted because this does

not positively represent a transducer failure. The commfault is factored into the selection filter processing discussed later. The miscompares are evaluated to determine which of the transducers is failed; for

example, if AB and BC miscompares are flagged, transducer B is identified as failed. This information is passed on for annunciation as a class 3 alert with fault message "RHC X" where "X" is "A" for AFT, "L"

for left (commander), and "R" for right (pilot) indicating which RHC has

a single failure. On the second failure, class 2 caution and warning

annunciation (with the same fault message as the class 3) is issued

which would warn the crew that RHC is unuseable. The fail/not fail

states of the three transducers are passed, with the commfaults and

values, to the selection filter which ultimately determines the pitch

command value to be used by subsequent processing which rotates the ve- hicle to the desired attitude. The fail /not fail states and commfaults

are processed to determine the current level of redundancy. For a signal to be considered, it must not be failed and not be commfaulted. If

all signals are good, then the middle value of the three is sent out as the position of the RHC. If one of the signals is bad, the average of

the other two is sent out. If only one value is good, it is sent out.

If all are bad, no value is sent out and a data bad flag is set as an indication to the subsequent processing which subsequently ignores that

RHC.

This system of RM is representative of the generic capability. In more

complex systems, more failure indicators are available in the form of

built in test equipment (BITE) which is a part of many of the more complex devices. BITE indicators are usually formed from a group of bilevel indicators, each indicating the result of a particular self-test

operation within the device. A simpler form of RM processes redundant

switch contacts, where switch position is determined by two-out-ofthree voting, "or" operations or "and" operations depending on the circumstance and level of redundancy.

9
Other Failure Detection Methods

In many cases, failure detection cannot be accomplished by a standardized process such as FDA or RM, due to the complexity of subtlety of the

monitored hardware or transducers. Here, unique software accomplishes

the necessary monitoring. Where the subsystem hardware and software are closely bound in a closed-loop control system, the detection is often imbedded in this unique software as an integral part of the control process, in many cases, automatically safing the system until the crew can take corrective action. Some failures generate symptoms that are readily apparent to the flight crew and therefore require no software monitoring. Such symptoms include "cabin uncomfortably hot" or "loss of

communications with the ground."

Failure Diagnosis

Once a failure has been detected and recognized, the flight crew begins

the failure diagnosis. Having determined the general area of the anom- aly from the fault message, the crew refers to a malfunction procedure

associated with the symptom. The malfunction procedures form one volume

of the onboard library of documentation which also includes normal operating procedures, checklists, and reference data that the crew uses as r 2 0 1 1 / / 0 8 8 A P U / E N V I RON T H E R M 2 0 8 3 / 1 6 : 0 5 : 2 6

0 0 0 / 0 1 2 6 : 4 2

F R E 0 N LOOP 1 2 H 2 0 L OOP 1 2 A C C U M Q T Y 7 8 8 1 P U M P 0 U T P 7 0 1 5 +

F R E 0 N FLOW 1 5 0 0 0 0 U T T 6 0 7 6 + P L H X FLOW 5 0 0 0 + A P 5 5 0 A F T C P FLOW 5 5 0 0 +

I C H F L 0 W 5 0 5 5

R A D I N T 1 0 0 9 5 0 U T T 5 9 6 2

C N T L R OUT T 3 8 3 8 CAB H X I N T 5 6 7 6 +

E V A P OUT T 3 7 7 8 A C C U M Q T Y 8 7 8 8

D F I F LOW 4 6 0

E V A P TEMP D U C T N 0 Z A P U H I LOAD I N B D 9 0 2 6 0 F U E L T 1 2 3

0 U T B D 9 0 8 9 T K S U R F + 6 0 + 6 1 + 6 0 T 0 P P I N G F W D 2 6 0 T K H T R + 6 1 + 6 2 + 5 9 AFT 2 6 0 I S 0 L V L V + 6 0 + 6 3 + 5 8

L 1 5 5 5 0 T E S T L N + 5 9 + 5 9 + 5 8

R 1 5 5 5 0 FEE D L N + 6 1 + 6 0 + 6 3

E V A P F D L N T A B P U M P I N + 6 2 + 5 9 + 6 4

F W D 7 0 7 0 D R N L N + 6 1 + 6 0 + 6 1 MID 1 7 0 7 0 0 U T + 1 0 0 + 1 0 2 + 1 0 1 MID 2 7 0 7 0 B Y P L N + 1 0 0 + 1 0 1 + 1 0 2 AFT 7 0 7 0

S 8 8 THERMAL H 2 0 4 0 8 3 /0 9 1 !

+ Figure 4 - APU/ENVIRON THERM Typical Display

10
"paper memory" in their operation of the vehicle. A malfunction procedure is a flow diagram which guides the crew through a logical process

of anlaysis and decision to identify the cause of the anomaly and specify appropriate system reconfiguration to prevent further system damage

and to minimize the effect of the failure on the mission.

A failure of the previously discussed water pump is a convenient example

of this diagnosis process. The fault message "S88 THERMAL H2O" signals

an anomaly in the thermal control system water coolant loop. The crew

calls up display format 88 (Figure 4) on one of the computer-driven CRT's

by request through the keyboard. This display, titled APU/ENVIRON THERM

displays each current measurement value to the right of a descriptive

title. The H2O loop section is at the upper right of the display. In

this case, FDA has determined that the H2O loop 2 pump P has dropped

below the low limit and has flagged the anomaly with a "down-arrow"

character to the right of the displayed value. The crew then locates

the associated malfunction procedure (Figure 5) and proceeds with the

diagnosis.

The malfunction procedure starts with a statement of the symptom, indicated at the lower left of Figure 5. The crew refers to display 88

(Figure 4) as the procedure guides them through the analysis which, for

this example, is shown with darkened flow lines. Note that for efficiency, analysis which is common to more than one procedure appears only

once, in this case, on Figure 6. Throughout the analysis, other measurements, pump outlet pressure and accumulator quantity, are examined to

validate the out-of-1 imits condition and determine its precise cause. Figure 6, block 10, has the crew perform a test by manual operation of a switch with the system response making the next decision. In this case,

the diagnosis led to Figure 6, block 13, which identifies the failure as

a short in pump winding or loss of one phase of the three-phase AC power

supply and indicates that the effect is degraded thermal control. Other

failures that could have been diagnosed include failure or shift of one of the two pressure transducers, leakage at the interchanger or a blockage of the lines. Since the failure is a pump degradation, the pump is

shut down (block 16) and the water loops are reconfigured to minimize

the effect of the failure.

Several features of the malfunction procedure are apparent. First, the

language is very terse for maximum use of page space so that the crew

need not flip back and forth as they diagnose the symptom. Identification of switches or display nomenclature is in capitals to separate action from object of action. Also, the conclusion blocks, which complete

the diagnosis, are shown in bold outline. Clarifying remarks (see ex- planation of preconditioning, note 6, Figure 5) appear at the right to

explain system behavior or subtleties which may not be readily obvious

to the crew. This basic format has been used as far back as the Apollo

program and is the result of manned spaceflight experience.

11
SYMPTOM PROCEDURE REMARKS

ECLSS (ARS H20)

7 (Cont)

BLUE

Light on if: 7b _0

S88 H20 PUMP

P 1(2)

1 1 H20 LOOP 1(2) PUMP OUT P 1' ?

H20 LOOP 1(2) PUMP OUT P

< 50 psia

> 75 psia

7a

Ni YES

2 | H20 LOOP 1(2) NO*. POmp out P ? YES

7a 5

^TlTSTTaTaW

software fault or snsr failure

7c J0

S88 H20 PUMP

P 1(2) _J1 | H20 LOOP 1(2) PUMP OUT P 1

H20 LOOP 1(2) PUMP OUT P < 20 psia

YES

3 | H20 LOOP 1(2) ATCUM QTY ' + ' 7

NO,

NO.

2 | CLASS 3 ALARM SOFTWARE FAULT OR SNSRJFAILURE

YES

4 | FAILED OR SHIFTED H20 LOOP

1(2) PUMP OUT P TRANSDUCER R I EXTERNAL LEAK IDTPLETED ACCUM 7d

S88 THERMAL H20 1 | H20 LOOP 1(2) PUMP AP '+' ?

H20 LOOP 1(2) PUMP AP

< 35 ps1d

> 50 psid

(> 5 psid - dormant

I Htomp ap

H20 LOOP 1(2)

? YES YES

4 | H20 LOOP 1(2) PUMP OUT P ?

iliss 3 ALAftH SOFTWARE FAULT

OR SNSR FAILURE

7a

NO.

7a

YES

5 | H20 LOOP 1(2) Pump out p I

NO,

YES

6 | SHIFT OF H20

T7J0P 1(2) PUMP IN PRESS SENSOR

7a

To Figure 6

Preconditioning

will inhibit this check unless the

(LI) H20 PUMP LOOP

1(2) switch is in the GPC position

and 1A OR IB GPC ON signal is present. Preconditioning

will default to this set of limits

If the H20 PUMP

LOOP 1(2) switch 1s

In the ON position

(A) Preconditioning

will inhibit this check unless (LI) H20 PUMP LOOP 1(2) sw 1s in the OFF position or in the GPC position without the presence of

GPC ON signal (used

to check for static

loop leaks)

Preconditioning

will inhibit the limit range of 35-50 psid to an upper limit of 5 psid when the pump

switches are in the

OFF position or in the GPC position without presence of

GPC ON signal (used

to check for out of configuration or blockage)

0V102/ECLSS/7b-d

PRELIM PCN1

Figure 5 Water Pump 2 Malfunction Procedure

12
ECLSS (ARS H20)

7

H20 LOOP

YELLOW

Light on if: LOOP 1(2) H20 PUMP OUT P

< 45 psia

> 79.5(81.0) psia

RED 7a

S88 H20 PUMP

P K2)

Light on if: LOOP 1(2)H20 PUMP OUT P < 45 psia

> 79(80) psia

Nominal Configuration :

(L4:F) H20 LOOP PUMP

cb 1A/2 (three) - close

cb IB (three) - close

cb 2 (three) - close

(L4:K)

cb H20 CNTLR 1

- close

(L4:J)

cb H20 CNTLR 2

- close

(014:B)

cb H20 BYPASS LOOP

1 SNSR - close

(015:B) cb H20 BYPASS LOOP

2 SNSR - close

(LI) H20 PUMP

LOOP 2(1) - ON LOOP 1(2) - GPC LOOP 1 - B(A) LOOP 1,2 BYPASS

MODE - MAN

D• SM, SPEC 88 PRO (APU/ENVIRON

THERMAL)

H20 LOOP 1(2) PUMP OUT P ' ?

7b

NO 2 | H20 LOOP 1(2) PUMP OUT P '' ? no J5 I c7U FAILURE

YES

7d

ATJCUM QTY '' ?

7b

NO YES

5 | H20 ATCUM QTV

NOJ

YES

7d

LOOP 1(2)

7 | EXTERNAL IFAK DEPLETED

ACCUMULATOR

7d

16

YES,,

NO

1 1 rtmim

UAKAGE AT THE INTERCHANGER I16

8 1H20 flow check TUT)

• H20 LOOP 1(2) BYPASS MAN - INCR (obtain min

ICH Flow' H20 LOOP 1(2) ICH FLOW > 550 Ib/hr ? YES^

9 | SHIFT n m LOOP 1(2) PUMP OUT P SENSOR

NO

161 H20 flow check xa.

• H20 LOOP 1(2) BYPASS MAN - INCR (obtain min

ICH Flow) H20 LOOP 1(2) ICH FLOW >550 lb/hr ? !N0

111 m LMP 1(2) BTOCKAGE OR FLOW RESTRICTION

YES

TSf SHORT IN PUMP WINDING

OR LOSS OF ONE AC PHASE. DEGRADED

THERMAL

CONTROL

LOOP 1

LOOP 1

16

14|H20 Loop 1 Tump shutdown or reconfiguration TTTT

• H20 PUMP LOOP 1 A/B - A(B) H20 LOOP 1 ICH FLOW > 550 lb/hr ? I LOOP 2 NO

! Finn

!; . . IT1®

^^^^^^^^]16| H20 Loop 1(2) Pump shutdown

(LI)

12| H20 Loop 1(2) reconfiguration

HT

t H20 LOOP 1(2) BYPASS MAN - DECR

(CRT) t Verify H20 LOOP

1(2) ICH FLOW = 950 lb/hr

(R13)

• Reset C/W low limit on H20

PUMP OUT P based

on shift [item 105(115)]

YES.

11

H20 PUMP

• LOOP 1(2) - OFF

• LOOP 2(1) - ON

t H20 LOOP 2(1) BYPASS MAN - DECR (INCR) until H20 LOOP

2(1) ICH FLOW = 950 lb/hr

(R13) • Inhibit Loop 1 (2) C/W low limit on PUMP OUT P [Item 105

(115)1

15| Adjust H20 loop 1 ICH flow nn

• H20 LOOP 1 BY- PASS MAN - DECR

(INCR)

(CRT) • Verify H20 LOOP

1 ICH FLOW = 950 lb/hr

® Meter on Pnl 01

is an alternate readout source

© The upper B/U C/W FDA limits are slightly different from prime C/W (see SYMPTOM column).

The logic flow and subsequent actions/

failures are the same as for prime C/W

As pumps utilize H20 flow

for active cooling, extreme or total flow blockage will result in overheating and failure of pump in a matter of minutes.

OV102/ECLSS/7a

PRELIM PCN1

Figure 6 Water Pump 2 Malfunction Procedure (cont'd)

13
Detection and Diagnosis System Philosophy

The failure detection and diagnosis system has been designed using several ground rules for consistency to simplify training and to maximize

the design effectiveness within the DPS and flight crew capabilities.

First, although an apparently obvious consideration, is the exclusion of

those failures for which there is no corrective action or effect on the

continuation of the mission,, Second, is the exclusion of failures which

do not require corrective intervention within two hours, the longest ex- pected period without communication with the mission control center.

The Houston facility receives telemetered vehicle systems data at a greater level of detail than is displayed onboard the Orbiter, and is

therefore responsible for "catching" these failures. Also, while the

detection system will indicate any anomaly which occurs, the malfunction

procedures are designed for diagnosis of only single failures within a unit or subsystem. This rule is grounded in the fact that the probability of several independent failures occuring within a system is equal to

the product of their individual probabilities, a value which decreases

rapidly as the number of failures increases. Experience has shown that

the amount of analysis (or complexity of malfunction procedures) is

approximately proportional to the power of the number of failures. Multiple failures are therefore also the responsibility of the mission control center, thus simplifying the onboard malfunction procedures and crew training. Where the malfunction procedure cannot diagnose the

actual failure, it instructs the crew to invoke a redundant unit or to

safe the system. With these rules enforced, the detection and diagnosis

will yield a rapid and effective response to failure.

Training for Diagnosis

The flight crews and mission control center personnel follow an intensive program of training for each mission, the primary goal being an integrated common base of understanding of vehicle systems and onboard

and ground procedures among the personnel involved in actual mission

operations. This, of course, includes training in the detection and

diagnosis system described in this paper.

Training is composed of a sequence of classes produced within the mission control organizations for informal crosstraining among specialists

and formal classroom training by an independent training division for more general use. Detailed exercises in the interaction with the detection system and use of malfunction procedures first occur in the various

simulator facilities.

The first facility which exercises procedures is a low cost medium

fidelity simulator called the Single Systems Trainer (SST), which can model at a given time one of the major subsystems (electrical, environmental, navigation, etc.) with a computer modeling the subsystem hard- ware and software. The simulator is under the control of an instructor

who initiates simulated failures for the student to diagnose. This

Ik
facility has been instrumental in debugging not only malfunction procedures but normal systems operations as well. This provides early feedback to correct the procedures prior to their use in the actual vehicle.

The final stage of training is the integrated simulation which has the

flight crew stationed in the Shuttle Mission Simulator (SMS) and the

mission controllers at their consoles in the mission control center

(MCC). The SMS is a high fidelity flight deck simulator which features

computer generated visuals, a motion base to give the appropriate "feel"

of vehicle dynamics and Orbiter GPC's, processing flight software, interfaced with other computers simulating input/output devices which in turn

connect with software models of the vehicle subsystems. The SMS provides a two-way voice and data link with the MCC, just as the Orbiter

would during a mission. The MCC, configured as it would be for a mission, is staffed by the mission controllers who can view simulated systems data to perform the detailed analysis and management function. The

simulation is conducted by the training division personnel who create

failures for the crew and MCC to diagnose. Generally, over the course

of integrated simulations, all onboard and MCC procedures are exercised

as a final premission verification and test of compatibility among the

elements of the operational system.

Conclusion

The Orbiter failure detection and diagnosis system, composed of the data

processing system, the flight crew, the mission control center, and the

malfunction procedures, is responsible for reaction to failure occurrence during a Space Transportation System mission. Failure detection

is usually the responsibility of the data processing system, which provides, through a variety of programs, a standardized annunciation in

response to an anomaly. The crew, aided by the malfunction procedure,

performs the detailed diagnosis to identify the cause of the symptom.

The mission control center provides any monitoring and analysis which is

beyond the capability of the Orbiter and crew. The flight crew and mission control personnel follow a sequence of training activities which

provides commonality of knowledge and verification of the detection and

diagnosis system.

Currently, NASA is preparing for the first orbital test of the Space

Shuttle. Although the Approach and Landing Test flights, during the

fall of 1977, verified the airworthiness of the vehicle and its fly-bywire control system for landing, the program only began to scratch the

surface of automatic onboard failure detection. The design discussed

will be used for the first few orbital flights and therefore reflects a healthy caution that is due a test vehicle during shakedown trials. As

in past programs, these missions will be conducted with extensive realtime monitoring, management and troubleshooting by the Houston mission

control center. The present design is the response to this particular

challenge.

15
The mature Space Transportation System will rely heavily on the independence of the spacecraft and crew to accomplish the mission objectives

without exhaustive MCC support.. Coincident with the increasing confidence in the basic vehicle systems will be an increase in payload support

activities which include detection, diagnosis, and action for recovery.

The standards and methods discussed here will be applied to the design

of this Orbiter support of the payloads which, on examination of present

commitments, form a wide-ranging spectrum of unique mission requirements.

The standardization of the response to failure, with remote autonomy, are essential to the cost-effectiveness of a truly operational Space Transportation System. This is the challenge of the immediate future.

16
MULTI SPECTRAL SCANNER ON LANDSAT

Stephen M. Gritton

A. Bernard Marchant

Hughes Aircraft Company

Culver City, California 90230

Abstract: The multispectral scanner (MSS) is described; it is an instrument onboard the earth resources satellite that was formerly called

ERTS, but is now referred to as LANDSAT. Since July 1972, three scanners have been launched that have provided tens of thousands of pictures

of the earth. The scanning mechanism that produces these pictures has

proven to be extremely reliable and repeatable. After the first scanner

was turned off after five years of operation in orbit, the scan mirror

had accumulated 90 million cycles and was still performing flawlessly.

The design approach that was taken in order to achieve reliability is

discussed as well as the scan monitor that serves both to provide a cor- rection signal for data processing on the ground and as a diagnostic

device to detect impending trouble.

SCANNER OBJECTIVES

The four-band multispectral scanner (MSS) system is designed to provide

the capability for collecting earth imagery from the LANDSAT spacecraft.

The scanner portion of the system employs all reflective optics to

accommodate the four spectral bands, which occupy a broad spectral

range from visible to near infrared. Use of a single optical system for

all spectral bands ensures the excellent registration needed for signature analysis of agricultural scenes. Systematic coverage of the earth

with nearly uniform lighting is obtained via the near-polar sun synchronous orbit. The 496-nmi altitude permits the scanner to image the

entire earth every 18 days with a usable resolution of 225 ft.

SCANNER

The scanner is designed to scan a 100-nmi swath on the earth and to

record imagery in each of four spectral bands simultaneously. An

oscillating mirror provides the crosstrack scan, and the orbital progress of the spacecraft provides the scan along the track. The scan mirror, shown schematically in Figure 1, is at 45° with respect to the

earth and the double-reflector, Ritchey Cretien type telescope. The

±2.9° motion of the mirror scans a field of view of 11.6°.

IT
A four by six fiber optics array is placed in the focal plane of the

telescope: there are six fibers in a column and there is one column for

each of four colors. Each fiber defines an instantaneous field of view

(IFOV) of the earth. The image of the earth is swept across the fiber

array each mirror scan. Light impinging on the glass fiber is conducted

to an individual detector. An optical filter is combined with each

detector to determine the spectral band. By operating the mirror at a rate of 13.62 Hz, the orbital velocity is precisely such that the subspacecraft ground track advances six IFOVs , and the next line imaged by

the first detector in each band is contiguous to the sixth line of the

previous scan.

The 13.62-Hz mirror drive signal is derived by the multiplexer from its

master oscillator, which operates at approximately 30 MHz. Word and

bit rates are derived from internal division of the 13.62-Hz scan frequency and are maintained uniformly from scan to scan. Only the line

start synchronization pulse need be acquired in each scan. The line

start pulse, generated by the scan monitor, is used to reset and initiate

the multiplexer sampling sequence. Resetting the sampling frame with

the scan monitor makes the start of sampling completely angle dependent

and therefore immune to small timing variations that could arise from

the scan mechanism. The 24 channels are multiplexed into a 15-Mbps

stream, which is sent along with a bit clock to the spacecraft recorders

and transmitters.

SCAN MONITOR

Angle crossings of the scan mirror, which denote the west edge, center,

and east edge of the 100-nmi swath, are indicated by means of an optical

pickoff situated so as to view the scan mirror. The beginning pulse is

supplied to the multiplexer wherein it is used to initiate video

sampling. The center pulse can be transmitted upon command and is provided for checkout and troubleshooting. The end of line pulse is transmitted in the data to allow line-to-line corrections should the scanning

mirror show minor variations in time to scan a line.

The scan monitor system shown in Figure 2 consists of a gallium arsenide

laser diode emitter (operating in a sublasing mode) , an optical projection system, a series of reflectors, and a pair of detectors. The

system has a built-in redundancy in the form of two light sources in one package, only one of which will operate at any given time; one is

installed on-axis, while the backup must be offset by their minimum

center-to-center dimension. If one source fails, the redundant unit is

selectable by ground-originated commands.

Any malfunction of the scan mirror mechanism will show up as a sudden or erratic change in the time needed to scan a line. Except for temperature sensors, the scan monitor is the only diagnostic device on the scan mirror mechanism.

18
SCAN MIRROR MECHANISM AND OPERATION

The MSS scan mirror mechanism is shown schematically in Figure 3. It

consists of a lightweight beryllium mirror suspended on a pair of flex

pivots. There are bumpers, return springs and dampers, an electromagnetic torquer, and an optical switch. Figure 4 is a drawing of the

MSS scan mirror assembly.

The requirement for the scan mirror assembly is that it provide a constant-velocity scan that is repeatable from one scan to the next.

This ensures a ground picture free of distortion with the resolution

elements of one scan lined up with the appropriate resolution elements

of another scan. The design has the mirror rotate on a "f rictionless

bearing" with no drive forces acting on it during scan. A flexure

pivot is, for the accuracies required of this device, a f rictionless

bearing over the scan angles required. It has a small repeatable

torsional spring constant that results in a small but predictable picture distortion. For most user requirements the distortion is insignificant. For the most accurate mapping a correction can be made during

ground processing to remove this nonlinearity

.

At the end of scan the mirror impacts the bumpers and compresses the

turnaround springs. Most of the kinetic energy of the mirror is stored

in the springs and returned to the mirror in the retrace direction.

During retrace, an electromagnetic torquer adds the energy lost during

the turnarounds. During the forward scan the mirror coasts. Imagery is

produced only during this half of the cycle. The dampers eliminate any

residual motion in the bumper/spring assembly before the next impact in

order to ensure repeatable turnaround performance.

The mirror is controlled by a 13.62-Hz mirror drive signal that is

developed from a high-frequency clock aboard the spacecraft and by an optical switch. The optical switch consists of a light source with a slit that is imaged onto a photodiode. A reflective surface attached to

the scan mirror is part of the optical path. Motion of the scan mirror

causes the photodiode to see or not see the slit. The mirror position

at which the signal goes off is determined by the location of the

optical switch.

The relationship of mirror position to the mirror drive and optical

switch signals is shown in Figure 5. The torquer is turned on by the

mirror drive signal and turned off by the optical switch. The result is

a simple but stable control system. If the mirror scans too fast its

position advances relative to the mirror drive and the torquer turns

itself off sooner by means of the position-sensitive optical switch.

Less energy is added to the mirror, thus reducing its net velocity. The

opposite is true for a mirror that runs slow. The mirror position is

stable relative to the mirror drive to less than 3 yrad or 4% of a resolution element.

19
BUMPERS AND SPRINGS

A cross-sectional view of the bumper, spring, and damper assembly is

shown in Figure 6. The bumper impact interface consists of an impact

bar made of 17-4 stainless steel and a nylon bumper surface bonded in

the turnaround cups. Nylon was chosen because of its good wear and

impact resistance, suitability for adhesive bonding, and acceptable

properties in a space environment.

A reliability test was conducted by using a bumper/spring/damper unit

with a reduced travel bumper cup assembly driven against the impact bar.

The impact velocity and the force-time history of mirror turnaround were increased 20% over unit operation. A total of 142,000,000 cycles were run. The acceptable wear was 2.0 mils; the measured wear was only

0.2 mils. Besides indicating acceptable wear the test proved the

integrity of the bond between the nylon and aluminum bumper cup. As

part of the test, the turnaround springs were also tested at a deflection 20% above their normal deflection. In addition to these tests an intensive analysis of the spring was conducted to make sure that the

stress levels were well within values for indefinite life.

DAMPERS

Two elastomeric dampers operate with each bumper/spring unit. These

dampers dissipate energy via shear distortion as they are displaced

±0.019 inch during each scan cycle. A damping coefficient of 0.020 lb- i sec/in at a frequency of 125 Hz is specified to correspond with 4-msec

half sine wave turnaround. The dampers must have acceptable outgassing

characteristics for space environment, maintain an acceptable damping

coefficient, and show no failure in the elastomer-metal bond. A number

of materials and configurations were tested during the development phase

of the program.

Checks were made during the thermal vacuum test for condensable

materials after four days at the real-time temperature and in a vacuum

environment of 10~6 torr. For a silicone damper to pass this test, a postcure at elevated temperature was required. From the results of

tests on the Surveyor, it had been determined that silicone elastomers

postcured at 350°F showed the least change from the initial physical

properties while still reducing the outgassing to an acceptable level.

Tests made on dampers showed that after a 5-day bake at 350°F in air the

parts had less than a 0.1% weight loss when exposed to 4 days in hard

vacuum, and no oily deposits or condensables could be found.

Life tests were performed on an apparatus that was designed to

simultaneously flex six pairs of dampers. The life test was conducted

with a cyclic shear displacement amplitude of ±0.023 inch. This displacement is approximately 20% greater than that actually produced

during impact in the scan mirror mechanism. Three pairs of dampers

20
were tested in the condition in which they were received, and two

additional pairs were tested after an elevated temperature postcure.

Dampers were test cycled under the conditions of no prestress, a 0.030-

inch compression prestress, and a 0.046-inch shear offset prestress.

These mounting variations were evaluated to determine the effect they

would have on the damper fatigue life: no fatigue failures occurred and

the damping changes were comparable; therefore, no prestress was used

in the system. The postcure dampers were harder and had higher damping

constants. At equal displacements, the postcured dampers received a higher stress under the test conditions than the dampers in original

condition. The actual values of the damping constant are compared in

Figure 7 for two pairs of dampers from the commercial source that were

postcured. A damping value constant within 5% was maintained. As a result of the vacuum tests and life testing, the dampers produced by the

Lord Manufacturing Company of Erie, Pennsylvania, were selected for use

on the flight system.

Specifications were generated to provide the necessary controls and

screening procedures. The manufacturer is required to produce parts

from one controlled lot of materials. After receipt, the dampers are subjected to a postcure at 350°F. As a lot-acceptance test, ten % of

the lot is tested for condensables and outgassing. Each device that is

used in the system has the damping characteristics measured on a pair

basis.

FLEXURE PIVOTS

Two flexure pivots provide the suspension points for the scan mirror.

These pivots must withstand the launch environment and subsequently

operate at ±2.9° rotation for 150,000,000 cycles. These commercially

available devices are 90° symmetrical two-strip pivots; one of the

strips has been divided to ensure greater lateral rigidity. The

stationary portion of the pivot is brazed to a cylindrical barrel and

the rotating portion is brazed to another cylindrical barrel. The

flexing elements bend to allow rotation of one barrel with respect to

the other. The flexure elements are stamped from close tolerance, coldrolled spring stock of type 420 stainless steel. Flexure pivots do not

have a fixed center of rotation. The amount of the change of center of

rotation during rotational displacement of one sleeve with respect to

the other is called centershift. The flexure pivots being used are

5/8 inch in diameter and are designed for flexing up to ±15 . The

flexing strips are 0.0135 inch thick.

The two important tests that these parts must pass before being included

in any flight system are vibration and life testing. The pivots used

on MSS have successfully passed tests that simulate the launch environment. Vibration tests were conducted on an early engineering model and

later on the systems using the final design. There is negligible

inherent damping in flexural pivots, and this results in high

21
!

transmissibilities of input vibration levels. The pivots passed vibration levels in the qualification unit that were twice those expected

in the launch environment

.

To demonstrate compliance with the system life requirement, it was necessary to determine the fatigue-life characteristics of the flexure

pivots. A test program to produce a curve of stress as a function of

cycles to failure for the parts was performed. The results are shown in

Figure 8. The equivalent angle is included on the right of the figure

for the +15° pivot design, and the MSS operation required is also noted.

The expression used to calculate the stress for pure rotation is

where S = stress, E = modulus of elasticity (29 x 10 b psi for 420 CRES)

,

t = flexure thickness, 6 = angle through which pivot is rotated

(radians), and L = effective length of flexure.

The test grouping is typical of fatigue testing. Some scatter in

results is expected because of the inhomogeneous nature of metals and

tolerances used in manufacturing the parts. These particular pivots

closely follow the life curve that is predicted by the manufacturing

data.

In addition to meeting life and environmental requirements, the pivots

must meet critical parameters regarding mirror support. Two pivots

from each manufacturer lot are subjected to destructive static-load

test and to a metallurgical examination. Each pivot is visually

examined with both a conventional microscope and a small-diameter borescope for surface defects - it is examined for burrs, nicks, or scratches

that might reduce the strength or life of the part. Each pivot is subjected to a dye-penetrated inspection for evidence of surface and subsurface cracks. All flight pivots are subjected to a radial load of

220 pounds to test for defective braze joints.

To ensure minimum stress and satisfactory mirror alinement under scan conditions, each pivot is tested for center-shift and torsional spring

rate at ±3° rotation. Pivots are then paired to have closely matched

torsional spring rates so that when they are rotated the center shifts

are of the same magnitude and in the same direction. Only matched pairs

of pivots that pass all visual and physical tests were used in the

flight units.

LIFE TEST PROGRAM

A flight quality scan mirror assembly (as shown in Figure 2) was subjected to a life test program. The purpose of this test was to verify

that the scan mirror assembly would reliably support the mission

22
requirement of one year in space at a 20% operational duty cycle

(approximately 20 minutes on and 80 minutes off).

The unit was subjected to a complete acceptance program involving unit

test and vibration and thermal vacuum testing. Space operation was simulated by operating the unit at a pressure of less than 10 ~ 5 torr and

a base temperature of 90°F. To compress the test time, the operational

i duty cycle was raised to 50% (20 minutes on and 20 minutes off) . The

I unit was operated on a full-time basis with periodic performance checks

at approximately 4-week intervals with more frequent checks at the

beginning of the life test. During these performance checks eleven

parameters were measured and compared to specifications. Changes from

initially measured values were carefully monitored. At the conclusion

| of the test the scan assembly had been operated for 140% of the

required mission life without a failure or degraded performance. The

active scan time had decreased by less than 1%, which was within

' allowable limits.

LINE LENGTH MEASUREMENTS

Line length is defined as the time elapsed from the star t-of -scan pulse

! to the end-of-scan pulse. Line length measurements have been made

I for extended periods of operation for the engineering model during life

testing and for both LANDSAT I and II. LANDSAT III has been successfully operated in orbit but line length trends have not been established.

Table I lists the pertinent information.

TABLE I. LINE LENGTH VARIATIONS

Launch

Date

Data Span,

years

Number of

Scan Cycles

x 106

Line Length

Variation,

ysec

Life Test (1972) <1 120 -200

LANDSAT I 7/23/72 >5 90 -100

LANDSAT II 1/22/75 >2 52 -80

LANDSAT III 3/5/78 <1 3

The trend seems to be clearly established toward shorter line lengths

for longer periods of operation. Table II compares line lengths with

time for LANDSAT I and II.

i

i 23
TABLE II. LINE LENGTH IN ORBIT

Line Length, msec LANDSAT I LANDSAT II

At launch 32.21 32.50

First year 32.19 32.49

Second year 32.17 32.48

A more detailed description of line length variation as a function of

time can be seen in Figure 9, in which data for the first three years

on orbit for LANDSAT I is shown. The fluctuations are not understood.

The general trend towards shorter line lengths is attributed primarily

to changes in the elastomer damper. LANDSAT I was turned off in

January 1978 because of difficulties with the spacecraft control system.

The scan mirror mechanism was still performing as designed. The specified mission life was one year.

CONCLUSIONS

The long life of the scan mirror assemblies without failure or degradation may be attributed to the exhaustive .development program - con- sisting of analysis and test that preceded their construction. A key

factor was the design approach, wherein stress levels were kept well

below allowable limits. This was combined with a philosophy of testing

to levels above normal expected values and careful screening of manufactured parts.

ACKNOWLEDGEMENTS

We wish to thank J. Olson and W. Quinn for their descriptions of the

bumpers and dampers published in the article referenced, and to J. Balla

of NASA, Goddard, for supplying the on orbit data.

REFERENCE

Olson, J.L. and Quinn, W.S; "Mechanical Component Screening for Scanner."

7th Aerospace Mechanisms Symposium, NASA Manned Spacecraft Center,

Sept. 7 and 8, 1972.

2k
4 VIDEO

UTPUTS

11.6° VIEW TO

EARTH

Figure 1. Simplified schematic of scanner

Figure 2. MSS scan monitor optical system

25
FLEX PIVOT

OPTICAL SWITCH OPTICAL SWITCH DETECTOR LAMP Figure 3. Schematic of MSS scan mirror mechanism

Figure 4. MSS scan mirror assembly

26
TURNAROUND

MIRROR

—— SCAN —*> —— RETRACE —

POSITION

SCAN 1 1 1 1 MONITOR

r

MIRROR DRIVE CLOCK

TORQUER CURRENT

Figure 5. Timing diagram

27
r

DAMPER

SPRING

Figure 6. Sectional view of combined bumper, spring,

and damper

28
I oh\- ~ Z £C < UJ

h- « W 0) Z Q

O Z 0 0

o o

z w £ to

a.5<

Q

0.250

0.240

0.230

0.220

0.210

0.200

0.190

0.180

—

I I I I I I I

I I I

| I I I !

• PAIR 1 PAIR 2 — •

• —

• • •

• • • — A_

i AA A A _

I I I I I I I I I I I 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 MILLIONS OF CYCLES

NOTE: DAMPING TEST FREQUENCY - 144Hz

Figure 7. Damping as a function of life

NUMBER OF CYCLES

Figure 8. Flexure pivot fatigue test results

29
II I I I I I I I

I

I I I I I I II II I

I

I I I I I I I I I I I

I 1I I I I I I I I I I I 1I I I I I I I I I I I

TIME, YEARS

Figure 9. Line length variation for LANDSAT I

30
DRIVETRAIN BEARING ANALYSIS

Thomas C. Belrose

US Array Aviation Research

and Development Command

St. Louis, MO 63166

DAVID BOARD

SKF Industries

King of Prussia, PA 19406

! Key Words: Aircraft Diagnostics, Diagnostic Equipment, Condition Monitoring, Bearing, Shock Pulse.

' Introduction: The US Army has recognized for some time the need for

improved condition monitoring and diagnostic equipment for helicopter

drivetrain systems. Recent studies-'- have confirmed that an unacceptably high false removal rate exists on many helicopter drivetrain components and that "phenomonal savings" would accrue to the Army by improving the diagnostic effectiveness. There have been several attempts

at developing cost effective, affordable and reliable equipment. It now appears that such a system exists. It is the Small Portable

Analyzer Diagnostic Equipment (SPADE). The equipment has been under

development for several years and is currently in a Development Test

at Ft. Rucker and an Operational Test at Ft. Hood. The purpose of this

paper is to briefly review the program, the equipment characteristics

and to review in detail the results of the Contractor Demonstration

Phase.

System Description: The SPADE is an item of ground support equipment

designed to semi-automatically inspect and diagnose bearing faults in

selected aircraft components. It functions on the principle of detecting and measuring shock pulses generated by the release of kinetic and

frictional energy within the monitored component. The history of the

shock pulse^ has been discussed in earlier MFPG proceedings as has its

j application to helicopter drivetrain diagnostics. Briefly the theory

j is that when the rolling elements in a bearing contact a surface discontinuity, repetitive impacts of short duration and very short rise

time are created, hence the shock pulse. This signal then propagates

through the mechanical structure. It decays as a function of the

distance it travels and is further attenuated at each mechanical interface. The signal is detected with an accelerometer and with appropriate processing is correlateable to mechanical condition.

The SPADE is a derivative of the commercial SKF MEPA-10A. It functions

on the shock pulse principle as does the MEPA-10A but it is implemented

in a slightly different fashion. Where the MEPA-10A requires manual

data collection and interpretation of data, the SPADE is automated.

Specifically, the MEPA-10A requires the interpretation of a plot of

51
the rate of the shocks vs. the amplitude of the shocks. The critical

factors are the area under the resultant curve and the shape of the curve. The SPADE measures the area by driving a voltage to frequency

converter with a demodulated signal and measuring the output directly

with a counter. This measurement is proportional to the level of the

defect and is compared to preset limits that are representative of

good, marginal and discrepant conditions. The status of the monitored

components is then displayed on the instrument control panel.

Contractor Demonstration Phase: This phase began with delivery of

first SPADE in February of 1978 and was concluded in September 1978.

During this time parts with known defects were implanted in various

UH-1 gearboxes. Baseline data was also taken on the UH-1, AH-1 and

OH-58. The purpose of this phase was to finalize the limits and to

demonstrate that the SPADE was ready for the Government testing phase.

The SPADE was operated without preprogrammed limits so that the maxi- mum amount of information would be available for correlating the

SPADE measurement with the actual part condition. Three different

accelerometers were also evaluated.

The following is a summary of the implant testing results on the UH-1H

drivetrain components:

Correct Incorrect Instantaneous Probability

Component Indication Indication of Detection (P^)

Main Trans 15 3 .83

42 Gearbox 10 0 1.00

90 Gearbox 9 1 .90

Hangar Bearings 0 0 0

TOTALS 34 4 .89

NOTE: The results of the hangar bearing test will not be proven until after the bearings are analyzed.

SPADE Fault Detection Capability: The implant approach is not a perfect test technique in that certain variables which are difficult to

quantify are introducted. Thus each case must be carefully evaluated

to eliminate as many of these as possible. The process of implanting

a discrepant component into an "alien" gearbox results in decreased

levels of kinetic energy due to misindexing of the defect relative to

its natural location in its "native" gearbox, removal of trapped debris generated by the defect, and various tolerance and clearance

changes which are a direct result of the component disassembly.

This above data was, for the most part, accumulated from bearings with

defects that were small relative to the levels of damage which would

result in loss of load carrying capability for a bearing. Since SPADE

readings are proportional to the level of damage within a bearing,

higher readings and higher detection rates would result if larger de32
fects were implanted or if implants when tested were allowed to progress to more significant levels of damage. Therefore, the actual

accuracy of naturally occuring defects may be different and would be

better determined by a different test technique.

Although these results approach the design requirements, another concept should be considered; that is the cumulative probability of detection. The detection probabilities listed are for each time that

a SPADE measurement is taken on a discrepant bearing. However, since

bearings do not fail instantaneously, the SPADE can be used several

times (on a regularly scheduled basis) between the time an intial

discrepancy appears and the time a bearing is so badly damaged that it

loses its load carrying capability. This period between initial

discrepancy and loss of function for a bearing is called the Failure

Progression Interval (1^). The number of aircraft operating hours

between scheduled SPADE inspections is known as the Utilization Interval (U). The cumulative detection probability (P^ ) for SPADE is

greater that its instantaneous value (P^.) because during the failure

progression interval there are several cnances (I^/U) for finding the

defect, and only one detection is required to remove the failing com- ponent from service. The mathematical relationship between the cumulative probability of detecting an ongoing failure and these other

diagnostic parameters is:

P, = 1- (1 -p, .) i./u

4c 4i f

Given this relationship and the experimental values for it re- mains to estimate the failure progression interval, 1^, for bearings,

and to select a SPADE Utilization Interval (U) that yields a satisfactory cumulative probability of fault detection. Of the twentyeight (28) bearings used for implant testing during this and preceding

Army diagnostic test programs, none have shown evidence of significant

failure progression. Of these same bearings, eleven have been operated

for times in excess of 100 hours and three in excess of 200 hours with

a maximum spalled bearing operating time of just over 290 hours.

Figure 1 shows SPADE' s cumulative probability of fault detection as a function of its utilization interval. The curves in this Figure re- present a range of instantaneous fault detection probabilities which

"bracket" the results of testing during the Contractor Evaluation of

SPADE. The important message from this Figure is that even for the

worst case estimate of SPADE accuracy, a high cumulative probability of

fault detection can be achieved with a 25 hour SPADE inspection interval. For example an accuracy of P^ = .45 would indicate a cumulative

probability of fault detection in excess of 99% at a 25 hour inspection

interval and better than 90% at a 50 hour interval. In addition, any

increase of the failure progression interval above 200 hours will result in an- increase in the cumulative probability of fault detection.

The other side of the coin, of course, is the false indication rate

that can be expected when employing the same limits that are associated

55
with the detection accuracy just discussed. The caution and remove indication limits in SPADE are set at the mean plus 2-sigma (m + Iff)

and mean plus 3-sigma (m + 3 if ) values respectively of all the con- firmed baseline data accumulated for four (4) UH-1H aircraft during

the Contractor Evaluation. Assuming a normal distribution of measurements, this should result in an instantaneous probability of false

removal indication (P^) °^ »0027. The cumulative probability of

false removal indication (P^ ) would then be the product of the number

of SPADE measurements times ^P„.). Over one hundred SPADE measurements

of baseline components were made during the Contractor Evaluation but no removal limit exceedances were observed. This record tends to confirm that P for SPADE is .0027 or less. The Mean Time Between Removals due to false indications or (MTBR^ . ) for each drivetrain com- ponent monitored by SPADE can be calculated from the equation:

SPADE UTILIZATION INTERVAL

MTBRf

. = No. of sensors on component X P 9.

Table I lists the MTBR and corresponding false removal rate for

each aircraft component at two SPADE Utilization Intervals (U=25 hr

& U=50 hr). This Table also summarizes false removal rates for the

total UH-1H drivetrain and the gearboxes vs. tail rotor driveshaft

hangar bearings as separate component classes. It is important to

note from this Table that even for a 25 flight hour SPADE Utilization

Interval, the false removal rate is only slightly over one removal

per thousand aircraft flight hours.

Conclusion: In summary then, even a pessimistic assessment of SPADE

Contractor Evaluation test results indicates a high fault detection

capability and a false removal rate of one per thousand flight hours.

This accuracy exceeds the design requirements of 90% fault detection

capability and 2 false removals per thousand flight hours.

REFERENCES

:

1. J.E. Marsh, "Evaluation of Aircraft Equipment Monitoring Devices,

Procedures, and Techniques". US Army Aviation Research and Development Command, Applied Technology Laboratory Technical Report

No. USARTL-TR-78-31, July 1978.

2. P.L. Howard, "Shock Pulse Instrumentation". Proceedings of the

14th Mechanical Failures Prevention Group Meeting, Los Angeles, CA,

Jan 1971.

3. J. A. George, T.C. Mayer, E.F. Covill, "Applications of the Shock

Pulse Techniques to Helicopter Diagnostics". Paper Presented at

the 22nd Mechanical Failures Prevention Group Meeting, Anaheim, CA,

April 1975.

3k
AIRCRAFT COMPONENT

Main Transmission

42 Gearbox

90 Gearbox

Hangar Bearings(4)

TOTAL DRIVETRAIN

MTBR _ . - Fit Hr False Removals/1000 Fit Hr

f i —

U = 25

3086

4630

9259

2315

U = 50

6173

9259

18519

4630

U = 25

.324

.216

.108

.432

926 1852 1.080

U - SPADE UTILIZATION INTERVAL

D - 50

.162

.108

.054

.216

.540

SPADE CAUSED FALSE REMOVAL RATES

TABLE I

• pao

pL, I 1 1 1 i f- 20 40 60 80 100

SPADE UTILIZATION INTERVAL

CUMULATIVE FAULT DETECTION CAPABILITY VERSUS SPADE

UTILIZATION INTERVAL

FIGURE I

35
I

LIGHT HELICOPTER DETECTION, DIAGNOSIS AND

PROGNOSIS OBJECTIVES AND APPLICATIONS

Henry G. Smith

Engineering Consultant

Redondo Beach, California 90277

Robert E. Rohtert

Hughes Helicopters

Culver City, California 90230

Abstract: The need for obtaining adequate diagnostic data on aircraft

and helicopters and the processing thereof for practical utilization has

long been recognized by both the airlines and the military. The implications in regard to flight safety, operational availability of the vehicle,

and maintenance and logistics economics are too tremendous to ignore.

The techniques for obtaining and processing such diagnostic information have been the subject of considerable experimental research and

development over the past several years. The advent of reliable miniaturized transducers as well as data processors /computers has now

made onboard diagnostics a current technical feasibility for even a light

helicopter such as the Hughes 500D.

Data projected to be measured and processed include engine condition,

gearbox condition, vibration levels, rotor hub and swashplate bearings

condition, and flight structural envelope exceedance.

Detection, diagnosis and prognosis (DD&P) applications that either have

been, or are being, considered by Hughes Helicopters in regard to its

500D light helicopter are:

1. Use of the recently developed and FAA certificated onboard computer system.

2. Installation of a system for providing a quantitative display in the

cockpit in the event of tail rotor imbalance.

3. Development of an engine data recording and analysis system with

the objective of establishing criteria and method for substantially

extending the time between overhaul (TBO) on all engine components.

36
k. Sampling and analysis of oil from main transmission and tail rotor

gearbox at regular intervals with the objective of developing

criteria and technique for extending the TBO.

Key words : Detection; diagnosis; prognosis.

j Introduction; For many years the military services and the airlines

have been testing and using DD&P systems on the larger, more

sophisticated aircraft and helicopters. Within the last few years

further technological advances in regard to both sensors and data

processors /computers have, through miniaturization, reduced the

j size, weight, and cost of such equipment to the point where it is now

' feasible and practical to apply it to a light helicopter such as the

' Hughes 500D (Figure 1). The type of data to be detected, diagnosed,

and prognosed ranges from engine condition and performance data to

tail rotor imbalance.

| Objectives for such a DD&P system for helicopters can be subdivided

' under three major headings: (1) in-flight, onboard DD&P; (2) testflight, onboard DD&P; and (3) on-ground-interrogative DD&P for

maintenance and record purposes. Because of the unusual extent of

rotating mechanical systems in a helicopter, as compared to a fixedwing aircraft, helicopter DD&P is much more concerned with rotor

imbalance, vibration levels, and gears and bearings deterioration.

Therefore, the greatest program effort at Hughes Helicopters has been

in these areas

.

This paper will consider, first, the needs /objectives for a light helicopter DD&P system, and second, the DD&P applications, either

existing or in work, at Hughes Helicopters for the 500D light helicopter.

Discussion : The need for obtaining adequate onboard diagnostics data

and the processing thereof for practical utilization has long been

recognized by both helicopter manufacturers and operators. Until

recently, this type of equipment was too large, too heavy, and too

costly to consider for installation in a light helicopter such as the

Hughes 500D. However, the advent of reliable miniaturized transducers, as well as miniaturized solid-state computer /data processing

technology, has now made onboard DD&P systems technically feasible,

and even practical, for light helicopters. The benefits to be derived

from such a system include: improved safety, improved operational

availability, reduced maintenance costs, etc.

37
As an example, miniature vibratory transducers are now available that

are roughly the size of a pencil eraser. Similarly improved sensors

are also available for pressure, temperature, noise, displacement and

the like. Even so, an onboard detection, processing, and display/

warning system should be held to the practical minimum consistent with

flight safety and operational needs. More detailed and more sophisticated DD&sP equipment could be installed or added to only as required

for occasional test flights or for specific problem analysis and correction. Also, additional data in unprocessed form could be simply

recorded for interrogation and analysis by ground based equipment at a later convenient time, or for occasional sampling and reporting on

the ground.

The three main categories of DD&P systems are shown in Figure 2.

The objectives for the overall DD&P system have been so categorized

in order to provide the most important in-flight information first, with

the test flight portion to be installed only as needed for more detailed

troubleshooting. The on-ground portion would be interrogated and

analyzed at a convenient time and location for routine maintenance and

operational purposes. These would include prediction of needed

replacements or overhauls. Economics, as well as safety, of operation would benefit significantly from greater reliance upon

"on- condition, " instead of arbitrary, replacements and overhauls.

Needs /Objectives of a Light Helicopter DDfaP System ; First, a list

of potentially critical helicopter mechanical and structural problem

areas was compiled and broken down into the three aforementioned

categories, as shown in Table I and diagramed in figure 3. These

potential problem areas were broken down by (1) system or major

component, (2) description of the potential problem in each case, and

(3) the type of information in need of detection by the DD&P system.

Then the type of sensor /transducer needed for measuring each type

of data was considered. The type of processing and presentation of

the DD&P results was then considered, including the display thereof.

Table II shows a summary of the DD&P objectives for a light helicopter.

It is evident that, in the area of structural information, we are most

concerned with the structural deterioration of the main and tail rotor

blades and with the vibratory loads imposed on the remainder of the

airframe structure by rotor imbalance, out of track, etc. In the area

of mechanical/propulsion systems, on the other hand, we are concerned with gears, bearings and engine deterioration. The methods of

38
sensing these items are also indicated in the table. Other factors;

such as, counting the number of engine/rotor stop/starts, and the

number of exceedances of design rpms, speeds, g-limits, yaw limits,

blade flapping limits, hard landings, etc, would also be very useful

both to the pilot and to the owner /operator. Once such information

has been detected and measured, it must be processed and compared

to some preestablished norm to determine whether it is of sufficient

magnitude for either display or warning to the pilot. The type of

display and/or warning is also a factor to be considered. Figure 4

diagrams a typical helicopter DD&P system from sensor to display

and/or warning.

DD&iP Applications : The remainder of this paper deals with various

DD&tP applications on the Hughes 500D light helicopter (Figure 5).

Onboard Computer : In mid- 1978, the FAA issued to Computer Avionics

Corporation of Santa Clara, California, a supplementary-type certificate for installation of its helicopter computer system (HCS) on the

Hughes Model 500 helicopters (Figure 6).

This small computer system starts with a basic manual mode configuration. It accepts inputs from the pilot which are the basis for feeding

back to the pilot flight status information. Safety of operation of the

helicopter is thus substantially enhanced. The pilot does not have to

depend on memory. He is not distracted by the necessity of thumbing

through pages of graphs or tables to obtain vital information regarding

the condition or performance capability of his helicopter in regard to

speed, power available, external load carrying capability, hover

capability in- or out-of-ground effect, fuel utilization, etc.

In the more sophisticated optional automatic mode, a sensor support

package is added to the basic system. This automatic mode system

accepts information not only from the pilot but also from a number of

sensors located throughout the helicopter, such as pressure altitude,

outside air temperature, engine torque, turbine outlet temperature,

fuel flow, airspeed, sling weight, etc. All these serve as the basis

for computing; data storage; supplying immediate flight information to

the pilot; and, subsequent to the flight, supplying information to the

maintenance crew when interrogated.

39
By a suitable choice of sensors and programming relative to the

typical flight scenarios of the operator, the display can bring to the

attention of the pilot conditions which warrant his immediate attention;

such as, overtemperature, overtorque, rotor overspeed, unusual

unbalance conditions, excessive sling load weight relative to hover

capability, etc. Moreover, the storage mode provides the capability

of accumulating these data for later retrieval on interrogation by the

maintenance personnel. These latter are thus informed as to the

magnitude, duration, and frequency of exceedance events. Appropriate inspections and corrective action can then be promptly initiated.

The weight of this complete onboard computer system is approximately

15 pounds, (0. 5 percent of the gross weight) including the various

sensors located throughout the helicopter. The basic manual mode

system is several pounds lighter. The display, located above the

cockpit instrument panel, is approximately 3 inches high by 9 inches

wide. Electrical power required is approximately 50 watts.

Tail Rotor Balance Indicator ; A system is currently under development by Chadwick-Helmuth, Inc. , which, when installed on the 500D

Helicopter, will provide quantitative indications in the cockpit of the

status of the tail rotor balance. This system consists of an accelerometer located at the tail rotor gearbox, suitable electronic circuitry

(black box), and a cockpit display (Figure 7). This display will provide

an indication of vibration velocity in inches per second.

A proper level of tail rotor balance is essential. The level represents

a compromise between practical production balancing techniques and

the adverse effects of unbalance on the fatiguing of blades, stabilizing

surfaces, and tail boom. Because of the tail rotor speed (normally

2933 rpm), the effect on vibration level due to small changes in the

blade mass, either in initial production or subsequent service, is

substantially magnified.

Limits of unbalance, format for the monitor display, and the circuitry

time delays will be finalized during the testing of the prototype installation. The production installation will enable the pilot to immediately

determine, by reference to his cockpit display, the status of tail rotor

balance. The monitor will indicate the vibration level normal for

cruise flight and provide a caution indication when it is approaching an

unsatisfactory level and a warning indication when corrective rebalancing

should be initiated. A more detailed presentation of the system capabilities is provided in the Appendix.
lEngine Condition Monitoring: Hughes Helicopters has under study the

development of an electronic data recording and analysis system to

monitor the gas turbine engine in its 500D helicopter. The objectives

of this system are the extension of time on components, the extension

.of TBO, and establishing "on-condition" maintenance. Such objectives

lappear attainable on completion of an initial data collecting and analysis

j phase in which the correlation is established between the cumulative

operating history of an engine and the state of its health at that time.

This would be in lieu of the current situation wherein the fixed TBO as

specified by the engine manufacturer requires overhaul no matter how

excellent the state of health of specific engine may be.

The favorable impact on operational costs is obvious. The type helicopter which delivers payload with less horsepower demands on the

engine, and the user, whose operational scenario does not cause a succession of exceedances, will be able to take advantage of these

factors in terms of a longer engine life and less maintenance costs.

Improved safety will also result because of an increased awareness of

engine condition at any point in time.

There are a number of detailed engine criteria which apply in establishing the TBO. Typical criteria are the limitations for the first- and

second-stage gas producer wheels; i.e. , 1775 maximum operating

hours or 3000 cycles, whichever first occurs. A cycle is defined as

a start or start attempt. It is recorded by means of an engine -furnished

counter which records the number of times the ignition exciter is

energized. It is reasonable to assume that a cold start is harder on

the engine than one starting from an elevated temperature, such as may

exist within a short period following a normal shutdown. The rationale

for such an assumption is that in the cold start the engine experiences

a much greater temperature gradient on each cycle. Similarly, an

engine whose history is one of operating through wide, rapid excursions

in (gas producer rpm), a large percentage of the time at or near the

limiting turbine outlet temperature (TOT), or with a number of or

temperature exceedances, will be degraded lifewise more rapidly than

one more conservatively operated.

Currently under study is the defining of a suitable data acquisition

system. Its "black box" will provide the capability of recording the

following data (Figure 8):

1 . Start cycles .

f'' (gas producer rpm) excursions.
3. Time at temperature (TAT).

4. Engine start temperature peak.

5. Engine start AT (incremental temperature).

Items 1 and 2 contribute to the low cycle fatigue failure mode due to

cyclic mechanical stresses imposed on the turbine wheels. Item 3

contributes to the stress rupture failure mode due to thermal stress

imposed on the turbine blades. Items 4 and 5 contribute to the thermal

mechanical fatigue (rim cracks) failure mode, a function of engine start

temperature gradients.

The next phase in the development of the system requires the collecting

of a substantial amount of data from a number of helicopter users for

operating hours over a time period of up to 2 years. Choice of these

users will be such as to provide a wide range of environmental conditions and operational scenarios. The analyses of the operational data

will be correlated with data collected during subsequent engine overhauls. Based on these correlations, criteria will be established

dealing with each of the detail specifications which currently define

the TBO for all engines. Once established, these criteria will permit

appropriate extension to the TBO of a specific engine based on its actual

operational history.

The end hardware (black box) system which will ultimately be used to

monitor the engine condition will be defined based on the data analysis,

correlations, and criteria established by the initial phases outlined

above. Such end hardware will also provide suitable cockpit displays.

Extension of Time Between Overhaul (TBO) : The long-term objective

is to increase the TBOs of the main rotor transmission (Figure 9) and

the tail rotor gear box (Figure 10) to on- condition overhaul. Currently

inspection and overhaul are at 1800 hours. Current oil changes are at

3 00-hour intervals. Extension of time between oil changes is a shortterm objective. A program has been established to document data

obtained from TBO transmissions returned from service to determine

problem areas. As such discrepant conditions are uncovered, corrective action will be incorporated. Extensions to the TBO will be

possible once an adequate data base from Field Service has been

compiled.

14-2
Implementation of this program has been initiated through a cooperative

plan between Hughes Helicopters and a fleet operator of the Model 500D.

This operator is achieving a utilization of approximately 1500 hours per

year per helicopter. The oil changes for the helicopters of this fleet

have been increased from the maintenance manual interval of 3 00 hours

to a 600-hour interval. Oil samples are taken from the main transmission (100 cc out of 6 quarts) and the tail rotor gearbox (100 cc out of

0. 4 pint) at 100-hour intervals. A single oil analysis firm has a contract to conduct a spectrochemical analysis of each of these samples

with reports being sent to Hughes Helicopters and to the appropriate

helicopter service center. On one helicopter the 600-hour spectrochemical analysis has already been completed. To date none of these

spectrochemical analyses have indicated any measurable wear.

When the main transmissions and tail rotor gearboxes of any of these

helicopters reach the present factory recommended overhaul (1800

hours), Hughes Helicopters will provide an exchange transmission for

use while the fleet operator's transmission or gearbox is at Hughes

Helicopters. Hughes Helicopters will tear down and examine the unit

and, upon reassembly without overhaul, return it to the same service

center for reinstallation and continued service in the same helicopter

from which it was removed. The accumulation of reports from the

oil samples in conjunction with inspections of TBO transmissions and

gearboxes will provide a basis for increasing the usable service time

on the helicopters of this specific operator. Instead of specific periodic

overhauls, maintenance will be a direct function of the actual condition

of the transmission.

A program has been established for systematically logging the results

obtained on inspection of each transmission returned for overhaul at

1800 hours. This covers the helicopters of all operators. Action will

be taken to initiate corrective action on all discrepant conditions

uncovered by these TBO inspections. Thus, a data bank will be

accumulated covering a very wide range of service environment for

the main rotor transmission and the tail rotor gearbox.

The criteria which must be met prior to an increase in TBO beyond

1800 hours or to "on-condition, " may be summarized as follows:

1. All discrepant conditions revealed by the fleet service experience

shall be corrected and incorporated into the fleet.

h3
2. Inspections of not less than 10 transmis sions / gearboxes at

1800 hours must prove that all components appear to be satisfactory for at least another 1800 hours of operation.

3. Analysis of results of abusive testing, i. e. , overload horsepower

runs in a test cell, must support such an extension.

Caution and Warning Indicators: A number of caution and warning

lights are located across the top of the cockpit instrument panel (Figure 11). These indicator light circuits are completed through their

respective fault sensors. They function as follows:

1. Engine out. The warning light flashes when engine speed decreases

to approximately 55 percent Np (gas producer rpm) or less, and/

or when the rotor speed (Nj^) decreases to approximately 98 percent or less

.

2. Main transmission oil temperature . If transmission oil temperature rises to 250°F, a temperature-sensing switch actuates to

energize the flashing warning light.

3. Main transmission oil pressure. In case of reduction or loss of

transmission oil pressure (below approximately 15 psi), a pressure

sensing sender energizes the warning light.

4. Battery temperature . The warning light illuminates at a battery

temperature of 160°F. The caution light illuminates at 140°F.

5. Chip detector caution lights. When sufficient loose ferrous

material is magnetically accumulated on the chip detectors, the

appropriate caution light illuminates. There are two detectors in

the engine oil system, two in the main transmission, and one in

the tail rotor gearbox.

6. Fuel low. When supply fuel weight decreases to 35 pounds, a spring wire contact is made by the tank unit float arm to complete

a ground circuit and illuminate the warning light.

7. Fuel filter . If the engine fuel pump filter becomes clogged, a warning light is illuminated by a case-grounded differential pressure switch.

kk
8. Generator out . If the generator output voltage falls below

battery voltage, a reverse current relay disconnects generator

from the 28-vdc bus and causes the light to illuminate.

Because of the obvious serious nature of "engine out, " an audible

warning horn is activated in conjunction with the panel warning light.

In addition, available as a separate kit, there is an engine automatic

reignition system. It provides a means to automatically reignite the

engine when either or both of the following conditions exist:

1. Engine N-^ (gas producer rpm) is less than 55 percent or

2. The N-^ (rotor rpm) is less than 98 percent (i. e. , less than

approximately 460 rpm).

Conclusions : DD&P applications are now feasible for a light helicopter

such as the Hughes 500D. This results from miniaturization and cost

reduction of the system components, all the way from the sensors to

the displays. Improved flight safety, improved operational availability,

and reduced maintenance costs are the significant benefits to be

expected.
APPENDIX

ON BOARD VIBRATION MONITOR SYSTEM

CHADWICK-HELMUTH COMPANY of Monrovia, California is actively

engaged in developing a miniaturized version of their VIBREX helicopter vibration measuring equipment. The new version is designed to

be used as a continuously operating "on-board" monitor to indicate

in-flight conditions and trending of from one to six vibration modes in

either or both the main and/or tail-rotor drive trains and mechanisms.

The approach taken consists of detecting of the vibration signals by one

or more accelerometers permanently mounted on the rotor mounts and

feeding these signals into a set of miniaturized active "band-pass"

filters and amplitude detectors. These filters are pre-set to respond

only to the pertinent frequencies at selected aircraft operating speeds.

The pass bank shaping of the filters is such that normal tolerance

variations of speed of the helicopter components will not affect the

output significantly.

Cockpit indication of vibration level is observed on a vertical set of

five Light Emitting Diode (L.E.D. ) indicators for each channel. The

threshold levels of the detectors are set such that the second light from

the bottom, a green indicator, will be lit in normal operation. The

bottom indicator will only be lit when the channel is not receiving any

signals, thus indicating a faulty channel or accelerometer. Third from

the bottom is a yellow L. E. D. to indicate "above normal" operation,

or caution. The fourth light is red to show excessive vibration. The

fifth, or top, L.E.D. is also red, but "latches on" to show that the

excessive level has been reached for a time considered to suggest a dangerous vibration/time level.

Only one light per channel is lit at any time except when the time limit

at excessive level has been passed. A reset switch is provided to

"unlatch" any exceedance indicator so that the pilot can restore normal

indication if vibration levels fall back to safe ranges as indicated by

the green indicator. The pilot might do this, for example, if the excessive vibration level were knowingly exceeded in a necessary violent

maneuver as would occur in an emergency or in violent weather conditions. The latched "danger" indicator would have shown the exceedance

k6
of maximum level/time conditions, after the event, even if the pilot

had not noticed the fourth level red light at the time of occurrence.

The instrument is packaged in two configurations at this time. The

first one is a single unit to be mounted in the instrument panel. This

unit is 2-1/2 inches high and its width is dependent upon the number

of channels desired. Each channel is a plug-in module, three quarters

of an inch wide, with one additional module for power and reset switches

in each frame. In this configuration a four channel, a vertical and a horizontal tail rotor, and a vertical and a horizontal main rotor indicator set for example, would require a panel space of 3-3/4 inches

wide by 2-1/2 inches high. Depth behind the panel is approximately

seven inches including relief for cables and connectors. Weight of

the four-channel indicator is slightly under 14 ounces. A six channel

unit would be 5-1/4 inches wide and weigh approximately 18 ounces.

The alternate model puts four channels in a one pound package placed

somewhere conveniently behind the instrument pod or elsewhere on the

aircraft with the indicator L. E. D. 's, all twenty of them, mounted in an

instrument indicator bracket, approximately 3/4 inch high by one and

1/4 inch wide, with the push button "Power On" and "Reset" switches

mounted nearby. The L.E.D.'s are 1/8 inch by 1/4 inch rectangular

units so that a normal flight indication would be an almost continuous

line of green horizontally, with yellow or red vertical excursions above

the normal position at the indicating channel position.

In both configurations, the instrument operates from the ship's 24-volt

d. c. power with a power consumption of less than 10 watts.

The band-pass filters in both configurations of the instrument are small

plug-in modules. Each module can be tuned to any frequency within a twenty-to-one range and the series of modules are available from

5 R. P. M. to 100, 000 R. P. M. , for measuring rotating mechanisms,

and from approximately 1 Hz to 1 0 KHz for other types of higher order

vibration.

The accelerometers are either Chadwick-Helmuth standard piezoelectric units for single axis monitoring or a new two-axis unit for

simultaneous vertical and horizontal channels from one mounting.

These same accelerometers and cables can then be used with the full

Vibrex equipment to correct an "out-of-balance" or "out-of-track"

condition when indicated by the in-flight monitor.
Preliminary flight tests of the prototype units have been performed and

further, more extensive "permanent" mountings and flight tests are

scheduled within the next two months. Release of the product is forecast to be early to mid 1979.

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TABLE II. SUMMARY - HELICOPTER DD&P OBJECTIVE

I. Fli^rht Operations Onboard DD&P

A. Vibration levels.

B. Structural deterioration.

C. Primary bearings deterioration.

D. Gearbox deterioration.

E. Engine deterioration.

F. Flight envelope exceedances.

II. Test Flight Onboard DD&P

A. Vibration analyzer.

B. Rotor track/pattern analyzer

C. Stres s / strain analyzer.

D. Performance analyzer.

E. Stability/control analyzer.

III. Ground Interrogative DD&P

A. Rotor balance analyzer.

B. Engine gearboxes oil analyzer.

C. Flight controls rigging and wear data.

D. Landing gear oleos condition.

E. Function and continuity of detection/warning system.

50
gure 1. Hughes 500D Light Turbine Helicopter

• FLIGHT OPERATIONS ONBOARD DD&P

•TEST FLIGHT ONBOARD DD&P

• GROUND INTERROGATIVE DD&P

Figure 2. Categories of Helicopter

Diagnostic Systems

51
I

I Figure 3. Hughes Model 500D Helicopter - Potential DD&P Items

52
Figure 4. Block Diagram of Typical DD&P System

• ONBOARD COMPUTER

• TAIL ROTOR IMBALANCE INDICATOR

• ENGINE CONDITION MONITORING

• TRANSMISSION TBO EXTENSION

• CAUTION AND WARNING INDICATORS

Figure 5. Hughes 500D Helicopter

DD&P Applications

53
Figure 6. Hughes 500D Helicopter — On Board Computer

ACCELEROMETER DISCRIMINATOR — PROCESSOR

COCKPIT

DISPLAY

Figure 7. Tail Rotor Imbalance System — Hughes 500D Helicopter

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Figure 10. Hughes Model 500D Helicopter —

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57
GAS TURBINES AND MILLIMETER-WAVE RADAR

N. Bruce Kramer

Hughes Aircraft Company

Electron Dynamics Division

Torrance, California 90509

Abstract: The Doppler Effect is widely used for detection and analysis

of remote moving objects via radar, sonar and beacon systems. Doppler

radar at millimeter wavelengths has been used to measure vibration

amplitude and frequency in physically confined systems at short ranges.

Methods for calibration of the radar for accurate vibration amplitude

and static displacements have been worked out in principle. Limited

testing has been done on an operating gas turbine proving the feasibility of the millimeter radar technique.

Some background to support the doppler radar technique is presented.

However, the principal point to be made is that in the last several years,

significant advances have been made in extending the frequency range of

practical millimeter hardware to 100 GHz and above and in building

extremely tiny and simple radar sensors to operate at these frequencies.

This means that sensors for a wide variety of applications can be

tailored to exact requirements and produced at low cost. Practical

considerations for gas turbine measurements include probe design and

transmission and absorption of millimeter radiation in various materials

and gases.

Key Words: Advanced sensors; gas turbine monitoring; vibration measurement; doppler millimeter radar; remote motion detection; static

displacement measurement.

The Doppler Effect is widely used for detection and analysis of remote

moving objects via radar, sonar and beacon systems. Doppler radar at

millimeter wavelengths can also be used to measure motion, including

vibration amplitude and frequency, of mechanical systems at short

ranges. Radial motion of the object (target) relative to the radar

results in frequency shift (doppler shift) of the reflected signal (echo)

that is proportional to the relative target velocity. No frequency

shift results from purely angular motion of the target relative to the

radar. A simple radar can be constructed (See Figure 1) that employs a non-linear element (mixer diode) as a detector. The transmitted signal

and the echo signal are combined and applied to the mixer diode. Sum

and difference frequencies of the two signals and their harmonics are produced by the non-linearity of the diode. Filtering can eliminate

all but the difference, Af, of the fundamental frequencies. This signal

at the frequency Af can then be amplified and analyzed. For purely

radial motion of the target at velocity v the doppler shift is

58
Af = 2f0 —— where f0 is the transmitted radar frequency, and c is the

velocity of light.

When the echo from a vibrating target is mixed with the transmitted

signal the filtered output of the diode can be expressed as a voltage,

V, with two components.

V = V0 + V

1

cos277 ft (1)

Both dc component, V0 , and ac component, V]_, depend on target size and

position, i.e., the amount of reflected RF power and its phase. For

target vibration amplitudes that are a small fraction of an FF wavelength it turns out that is directly proportional to the vibration

amplitude and vibration frequency is simply f. This provides a convenient and accurate way of measuring vibration waveforms remotely.

For example, if a doppler radar is pointed at a distant operating hi-fi

speaker and the mixer diode output is amplified and fed into an earphone

an excellent rendition of the music is heard.

A key feature of a radar system is directivity achieved by columnating

the electromagnetic energy into a confined beam. In this way reflection

from the desired target can be enhanced and reflections from nearby

unwanted reflectors near the target can be minimized. As the wavelength

of the radiated energy is decreased the size of the radiating probe or antenna can be made smaller (in direct proportion to the wavelength)

while preserving the same degree of beam confinement. Thus radar at

millimeter wavelengths (X = 1 to 10 mm) is convenient to use where small

size probes are desired ( See Figure 2) . This is an important advantage

for the utilization of radar probes on turbines or other rotating

machinery where introduction of large perturbing mechanical structures

could degrade turbine performance.

Practical millimeter-wave radar techniques for mechanical diagnostics

depend critically on the availability, cost and performance of semiconductor devices and RF components to perform the functions indicated

in the block diagram of Figure 1. All of the necessary components are now available from Hughes and from other manufacturers. Hughes has

also developed a simple, single-diode, self-mixing doppler sensor that

accomplishes all of the functions shown in Figure 1.

A prototype doppler radar operating at 50 GHz corresponding to Figure 1 has been built and tested. Initial experiments were conducted using

off-set round stock in a lathe with attachments to simulate rotor

blades. It was verified that the signal output from the mixer was proportional to the amount of off-set and the frequency was the rotation

frequency of the lathe. The rotor blades were apparent as a harmonic of

the rotation frequency.

59
A probe was constructed with an open ended waveguide antenna that could

be screwed into a gas turbine case. Experiments on an operating gas

turbine in an engine test stand showed that the radar output waveform

could be directly correlated with the output from magnetic probes that

had been previously installed in the turbine. Thus the feasibility of

millimeter-wave doppler radar for measuring vibration in operating gas

turbines has been demonstrated.

The questions remaining about the usefulness of this general technique

for the analysis of mechanical systems operating in adverse environments

can be listed as follows

:

1. Can an accurate method for in-situ calibration be implemented?

2. Can static displacements, e. g. , shaft expansion, be measured accurately?

3. Will reflections from surfaces other than the target surface cause errors or ambiguities in data interpretation?

4. Can a simple, accurate and reliable radar probe capable of withstanding the harsh environment of an operating turbine be manufactured at a reasonable cost?

All of these questions have already been examined in detail and techniques have been devised that give promise of providing all of the

desired features. What remains to be done is to couple a radar probe

design effort tightly with an engine test program so that these

problems can be worked out in an orderly and thorough manner.

Acknowledgements : The contributions of Harry Northern of DetroitDiesel Allison Division of General Motors in testing the prototype

radar are gratefully acknowledged.

6o
61
62
SESSION II

LAND BASED APPLICATIONS

Chairman: Richard G. Salter

Rand Corporation

Co-chairman: William J. Whelan

Rand Corporation

IMPROVING VEHICLE LIFE-CYCLE RELIABILITY

BY PROGNOSTIC MAINTENANCE MANAGEMENT

THROUGH GERIOMETRY

Richard G. Salter

The Rand Corporation

Santa Monica, California 90406

Abstract: Land vehicle life cycle reliability is a topical subject.

The military is recognizing the necessity to survive the peacetime

environment in order to improve combat readiness. Government intervention in the automotive world increases on behalf of energy, the

environment, and the consumer. This intervention forces the impleI mentation of revolutionary* designs and technology while insisting on concurrent reductions in consumer maintenance problems and costs.

Automobile first costs are showing the effects.

On-vehicle computing instrumentation technology now offers new

| capabilities to fight the battle through prognostic maintenance management (PMM) . Prognosis enables the selection of the best time for

maintenance while reducing inspection requirements, vehicle breakdowns

and secondary failures. A PMM program enables an improved user confidence while maximizing the productivity of scarce maintenance resources.

On-vehicle microdata systems enable two prognostic techniques: (1)

the automation of condition trend analysis, and (2) a new capability

geriometric accounting—the cumulative recording of stress energy and

cyclic stress functions which contribute to wear and fatigue damage.

Some homework is required, however—on-vehicle data acquisition

sufficient to identify the service parameters to monitor and the necessary maintenance criteria expressed in terms of these parameters. In

a practical sense, a bootstrap program is required in which an initial

system design will provide for both an operational PMM program as well

as the acquisition of data with which to improve both the hardware and

the software of the evolving system. We are now in a position to

design such an initial system.

The Problem Context

The problem is to reduce the cost of maintaining vehicles while

improving their reliability and availability for service. The difficulty is that maintenance systems are falling far short of the desired

*As opposed to evolutionary changes on a time scale consistent with good

automotive development practice

.

65
goals of vehicle users. New maintenance management techniques are now possible through the employment of on-vehicle microcomputers. This

paper describes an approach using condition trend analysis and geriometric accounting.-^ This approach is made possible by recent developments in LSI electronic technology.

A key part of the problem is the vehicle itself. Good vehicle development practice requires a deliberate evolution of the vehicle design so that new design concepts can be thoroughly tested in the hands of the

user. With this technique, each incremental change and its effect on

the entire vehicle system can be evaluated without potentially complex

interactions among a great many concurrent changes. This ideal concept

is currently practiced only in the commercial trucking industry. The

military produces vehicles that are designed for worst-case combat

conditions, which means they are not ideally suited to survive the peacetime environment. The combat vehicles are usually of revolutionary

design in order to benefit from the latest advances in technology and

doctrine. The tactical vehicles tend to be of traditional design, not

having benefited from even evolutionary trends. The automotive industry

is of course highly competitive and tends to introduce revolutionary

designs in order to beat the competition in styling, performance and

price. In recent years another influence, emissions and fuel consumption

regulations , has strongly forced the implementation of revolutionary

technology in new car designs.

The resources expended in maintaining vehicle fleets are significant,

but the results obtained are not satisfactory. The Army spends $1.3

billion each year below depot to maintain a $13 billion inventory. The

achieved availability is often quoted at the 90 percent level, however

most unit commanders would be happy to see 60 percent of their vehicles

rise to any given occasion. As for automobiles, the NHTSA has estimated^

that consumers spend $50 billion annually for maintenance on a $500

billion investment. They estimate that $20 billion of this maintenance

cost is improper or unnecessary. It is possible that even more of the

cost is avoidable; that increment that is due to the tendency of automobile owners to delay the maintenance of their cars and to drive them

until failure occurs. This delay is primarily due to a hesitancy to

commit themselves to the time, inconvenience, and expense of the process,

particularly when uncertainty surrounds these factors as well as the

necessity for the maintenance itself.

There is considerable interest and activity ongoing in the improvement

of the maintenance systems. The Defense Advanced Research Projects

Agency (DARPA) has been sponsoring the Vehicle Monitoring System (VMS)

project which is concerned with the on-vehicle acquisition of use pattern

condition and maintenance data on Army vehicles operating in the field.

This effort has been broadened to include geriometric data for use in

the development of prognostic maintenance management. The Army is

currently fielding the STE-ICE diagnostic test system for better offvehicle condition assessment and fault isolation of Army vehicles. The

66
i NHTSA is actively investigating the commercial maintenance system, and

in particular the potential for diagnostic inspection as a solution to

some of the problems. Both the automotive and test equipment industries

are implementing new equipment and techniques based on advanced technology and on evolving consumer requirements.

A Taxonomy

Vehicle maintenance^ is required to offset degradation which occurs as

the vehicle is employed. The causes of this degradation are components

of normal use, abnormal use or abuse, storage, neglect and the drive-tofailure ethic. Deterioration mechanisms include fractures, fatigue (due

to mechanical, electrical, chemical and thermal stresses), wear, age,

corrosion, etc. The effects of deterioration are manifested as noise,

low power, stalling, breakdown, and secondary failures.

Detection of degradation can be accomplished by visual, audio, or tactile observation by the people involved, employing in some cases an administrative record-keeping system; by testing the system for

emissions, function, or alignment with testers such as STE-ICE, Autosense, or built-in test equipment (BITE) ; or by monitoring the system

in-use for status, mileage, or cumulative stress by panel instruments

and on-vehicle systems such as VMS.

Maintenance can be categorized as corrective, preventive, or prognostic.

Corrective maintenance is the repair of obvious problems and failures.

It fixes the effects extant—the failure that has already occurred. It

is performed as necessary. Preventive maintenance is intended to slow

the deterioration mechanisms—changing the oil will reduce the wear

rates. It is usually performed on a time or mileage criteria. Prognostic maintenance is the interception of the deterioration mechanism

before the effect happens, thus forestalling the effect altogether.

Prognosis can be based on two criteria: condition trends, and cumulative

geriometric accounts.

Why Geriometry

Geriometry is the measurement of the causes of vehicle degradation,

whereas all other maintenance techniques measure effects. Geriometry

can provide prognostic criteria for vehicle subsystems with: unpredictable degradation trend patterns—the degradation curve for these

subsystems might, for example, drop so suddenly that anticipation is

not possible; wear or fatigue failure mechanisms which represent the

most significant failure mode; and inspection difficulties represented

by a requirement for significant dissassembly with risk of maintenanceinduced failure.

It is estimated that several vehicle subsystems are prime candidates

for prognosis based on Geriometry. Brake wearout has been determined

6?
to be a function of cumulative energy absorption.-' Electrical and

starting system life might be expected to correlate with their cumu- lative load-energy flux. Power plants might have several parameters

that would correlate with life. These may include a piston travel

function for upper cylinder life in reciprocating engines, and a thermal

cycle function for both reciprocating and gas turbine engines.

Why Prognosis

Even assuming that Geriometry is important to prognosis, why is

prognosis important to maintenance management? The answer, of course,

is that some technique is necessary to choose the time for maintenance

which will minimize maintenance costs while achieving a desired reliability and availability. The technique must be quantified in terms

of measurable parameters and the precision and variance with which these

parameters describe the subsystem life must yield decision criteria

with close confidence limits. The rationale for prognosis as an effective technique for vehicle maintenance is somewhat subjective since

data to prove the contention do not yet exist. It is anticipated by

many persons in the maintenance field, however, that a number of

benefits will accrue to the implementation of prognosis. Among these

benefits are the reduction of secondary failures—the anticipation of

the primary failure obviates the possibility of its causing the secondary failure; the reduction of physical inspection requirements—the

continuous measurement of the trends and geriometric accounts can be

thought of as continuous inspection; and the reduction of "unnecessary"

maintenance- -by definition, maintenance based on 'optimized' criteria

will eliminate premature actions and reduce the tendency to delayed

action. It is also anticipated that a proven prognosis technique will

improve vehicle owner confidence in the basis for maintenance decisions

and indeed allow the owner to concur in and even initiate the maintenance decision. Also, given a cost-benefit criteria, the owner can

choose to increase the reliability and availability of his vehicle (s).

And finally, these benefits would lead to a better productivity of the

maintenance resource system, which is currently highly overtaxed.

Instrumentation Attributes

It is appropriate to comment on the differing attributes of on-vehicle

and off-vehicle instrumentation systems. Obviously, on-vehicle systems can measure variables and compute parameters essentially continuously.

This capability allows for the automation of trend analysis and the

accumulation of geriometric accounts. On-vehicle systems can also

advise the operator of emergency situations and perform the functions

of the currently popular trip/fuel management computers . All monitoring

is accomplished during the normal vehicle use.

Negative attributes for on-vehicle systems include the fact that one system is required for each vehicle to be monitored and thus the cost

of the system must be low. Also, the sensors to which the system

68
connects must not only be of low cost, but must also be capable of

lliving continuously in a very difficult environment. The same can be

said, however, for the systems and sensors the industry is developing

for electronic engine controls and so we may anticipate early solutions.

- (Off-vehicle instrumentation systems, on the other hand, cannot monitor

'continuously, but rather must engage in periodic testing, which can

(support, along with a record keeping system, trend analyses of at least

certain variables. Although this capability is more limited, it may

still be useful in the overall scheme of maintenance management.

Another difficulty is that testing sessions must be scheduled outside

of the normal vehicle operating/use patterns. At these sessions, the

.vehicle must be warmed up and the sensor harness installed. The offvehicle system however has a number of positive attributes. Chief among

I these is the capability, through the use of more pervasive sensors, to

I perform more detailed fault isolation than on-vehicle systems. Thus,

off-vehicle systems can be thought of as competent to fault isolate at

the component level, whereas, on-vehicle systems are in a practical

sense limited to fault isolation at the subsystem level. A final

positive attribute of off-vehicle systems is the fact that they can be

j used across many vehicles and for this reason can contain more expensive

components with the attendant advantage of higher precision, etc.

In consideration of the relative attributes, it may be anticipated that

a rational maintenance system will contain both on-vehicle and offvehicle systems and facilities.

Implementation Problems

Primary to the difficulty of implementing prognostic maintenance

management is the complexity of existing vehicle systems and their

maintenance systems. Compounding the problem is the variability of the

use and maintenance patterns in which the vehicles are employed. And

fundamental to all of these is a lack of data with which to quantify

the system from a cost and performance standpoint. Without this

quantification, the benefits of improvements as compared to their cost

of implementation cannot be assessed.

Implementation Procedure

Given the frailty of existing data, an implementation program must be

designed to bootstrap, that is to take all possible advantage of existing

intuition, based on experience, to estimate the actual data requirements

and to perform the initial system designs. These designs must not only

serve the prime objective of providing owners with a meaningful

prognostic maintenance management capability but they must also help

to create a better data base with which to evolve and assess the hardware and software of better future systems.

69
Prognostic Data Development

The size of the "experiment" necessary to achieve a confident

characterization of the prognostic parameters for a given vehicle

model is determined by the maximum number of variables in any one parameter used to characterize any of the life/failure functions of the

vehicle system, and by the inherent variance of this characterization.

For most vehicles it is assumed that a maximum of one, two or three

variables will be required for any parameter, and that a factor of

three will handle the variance of the parameter. Thus, an experiment

comprised of ten life/failure cycles should suffice to prove the

parameter formulation hypotheses. It might also be assumed that the

experiment necessary to prove the generic character of these parameters

across various vehicle types would require the testing of ten vehicle

types for ten life/failure cycles each.

The engineering of prognostic parameters requires an understanding of

the physical degradation process and how the significant variables

enter into the motivation of the process. It is expected that this

understanding will derive from the experience gained from the many years

of vehicle development and use. As an example, we might define a parameter for upper cylinder wear in a reciprocating engine. Engine development lore suggests that the parameter will be a function of the

accumulation of engine revolutions, each weighted by its piston speed,

its Brake Mean Effective Pressure (BMEP) (a torque function) , and by

its clearance situation as characterized by its cooling temperature.

An expression for this parameter is defined as the product of these

factors summed over the engine running history. The formulation must,

of course, incorporate estimates of the coefficients and exponents to

be used. In this case, nominal values for RPM, EGT, and coolant

temperature (CT) (selected to represent the three factors) are estimated

at 1000 RPM, 200°F, and the thermostat control temperature. Exponents

are assumed to be square, linear and cube for the three factors respectively. The memory requirement needed to accumulate this parameter is

quite nominal—essentially just one register which is continually

updated so that it always represents the total sum to date..

In the early period of developing parameters to characterize significant

vehicle life/failure functions, multiple parameter formulations can be

recorded simultaneously—employing different variable sets, coefficients,

exponents and even basic formulations. This is possible because of the

aforementioned modest memory requirement for each parameter.

The purely statistical technique for developing a prognostic data base

requires the continuous time recording of a comprehensive set of

fundamental variables, so that they can be analyzed with a regression

model. This will allow the derivation by correlation techniques of the

significant parameters describing the various life/degradation/failure

functions. An alternative technique is to "engineer" these parameters

70
using intuitive engineering judgment. The benefits of using the latter

technique are compelling when considering that the memory requirements

of the former are over 100 times greater for a similar achievement.

Variables/Parameters

Chart 9 lists a set of variables/parameters, some of which are directly

sensed and some of which are computed from sensed variables and/or

time, which have been distilled from a much larger set of possibilities.

The current list, subject to change as time and experience are accumulated, requires 18 vehicle connections or transducers, most of which

will be common with those needed to provide data to engine, spark, and

fuel control systems . The prospects for concurrent use of sensors for

realtime control and for prognostics reduces considerably the number of

additional sensors dedicated only to prognostics.

A Preliminary System Specification

It is now possible to specify and design an initial system with which

to begin the implementation process. The system would need approximately

18 sensed inputs and would sense or compute on the order of 30 parameters,

incorporating approximately 10 formulations for each parameter. Facilities would include continuous display of critical variables, such as

oil pressure, demand display of all variables and parameter registers,

and would include the features of trip and fuel management computers.

(For rally buffs, it could also provide rally computations.) Other

features would include a short term high resolution realtime record,

similar to the airline flight recorder, in order to ascertain what

happened in the 30 minutes prior to and during a traumatic occurrence.

Also, long term trend and geriometric function registers would be

incorporated. Trends would be characterized by three values: a time

or distance parameter since initialization, a degradation since initialization, and the instantaneous slope or derivative of the degradation

curve

.

In order to support prognostic maintenance management, the system would

be programmed to annunciate the fact that a parameter has reached its

maintenance decision criteria level. The display would identify which

parameter (s) has reached its criteria. Reset of system oould be

relegated to an inspection system (or a motor sergeant) if appropriate.

The system would also be designed to enable a readout device to interrogate the memory and store useful data so that it can be incorporated

in a general data base for use in parameter development. This data

must be read out in computer-readable format and the readout device must

be capable of receiving input describing the maintenance actions that

were required. In the case of component overhaul or replacement, the

readout device must also be capable of initializing the necessary

parameters. Many of these features are now incorporated in the DARPA

Vehicle Monitoring System.

71
Based on the VMS experience and on that with the after-market trip

computer devices, it is estimated that the memory requirements for such

a system will be of the order of 8k BYTES. Early design might require

more memory in order to support program flexibility.

References

1. Salter, Richard G. , Geriometry: A Cumulative Stress/Damage Measurement of Useful Life, The Rand Corporation, P-5952, March 1978.

2. Claybrook, Joan B., (Administrator), Statement before the House

Committee on Interstate and Foreign Problems concerning Auto Repair

Problems and Titles II and III of the Motor Vehicle Information and

Cost Savings Act, NHTSA/DOT , September 14, 1978.

3. Salter, Richard G. , Maintenance Management Through Diagnosis , The

Rand Corporation, P-5867, June 1977.

72
VEHICLE MAINTENANCE: THE PROBLEM CONTEXT

THE VEHICLES

• MILITARY (DESIGNED FOR WORST-CASE COMBAT): - COMBAT - REVOLUTIONARY DESIGNS - TACTICAL - TRADITIONAL DESIGNS • NON-MILITARY.- - AUTOMOBILES - REVOLUTIONARY DESIGNS - TRUCKS - EVOLUTIONARY DESIGNS THE MAINTENANCE SYSTEM

• MILITARY: - $1.3 B ANNUAL MAINTENANCE ON $13 B INVENTORY - LOW AVAILABILITY, SHORT VEHICLE LIFE • NON-MILITARY: - $50 B ANNUAL MAINTENANCE ON $500 B INVENTORY - $20 B (+) UNNECESSARY, MUCH CONSUMER FRUSTRATION ACT I V IT I ES • DARPA:- VMS PROGRAM - USE PATTERN AND PROGNOSTIC DATA • ARMY STE-ICE/ATEPS DEVELOPMENTS • NHTSA:- DIAGNOSTIC INSPECTION EFFORTS • AUTOMOTIVE /TEST EQUIPMENT INDUSTRIES: - MANY COMPUTERIZED TESTERS

CHART 1

VEHICLE DEGRADATION CAUSES

USE ABUSE

STORAGE

NEGLECT DRIVE-TO-FAILURE

A TAXONOMY

MECHANISMS

FRACTURE

FATIGUE WEAR

AGE CORROSION

EFFECTSNOISE LOW POWER

STALLING BREAKDOWN

SECONDARY FAILURE

DETECTION OBSERVATION

VISUAL AUDIO

TACTILE BY

PEOPLE ADM. RECORDS

TESTING

BY

EMISSIONS

FUNCTION ALIGNMENT

STE-ICE AUTO-SENSE

BITE

MONITORING

BY

STATUS MILEAGE CUMULATIVE STRESS

PANEL VMSINSTRUMENTS

MAINTENANCE

CORRECTIVE

FIXES EFFECTS CRITERIA

"AS NECESSARY'

PREVENTIVE SLOWS MECHANISMS

CRITERIA

TIME MILEAGE

PROGNOSTIC

FORESTALLS EFFECTS CRITERIA CONDITION /TREND GERIOMETRIC ACCOUNT

CHART 2

73
WHY GERIOMETRY

• MEASURE CAUSES AS WELL AS EFFECTS

• PROVIDE PROGNOSTIC CRITERIA FOR SUBSYSTEMS WITH: - UNPREDICTABLE TREND PATTERNS - WEAR OR FATIGUE FAILURE MECHANISMS - INSPECTION DIFFICULTIES (DISASSEMBLY)

• SUBSYSTEMS: - BRAKES - CUMULATIVE ABSORBED ENERGY - ELECTRICAL - CUMULATIVE LOAD ENERGY - STARTING - CUMULATIVE STARTING ENERGY - POWER - CUMULATIVE OPERATING STRESS AND /OR THERMAL CYCLES

CHART 3

WHY PROGNOSIS

• REDUCE: - BREAKDOWNS - SECONDARY FAILURES - INSPECTION REQUIREMENTS

-UNNECESSARY MAINTENANCE

• IMPROVE:- OWNER / OPERATOR CONFIDENCE

-VEHICLE AVAILABILITY / RELIABILITY -PRODUCTIVITY OF MAINTENANCE

RESOURCES

CHART k

1^
INSTRUMENT ATTRIBUTES

ON VEHICLE OFF VEHICLE

CONTINUOUS MONITORING PERIODIC TESTING • GERIOMETRIC ACCOUNTING • COMPONENT DIAGNOSIS

(FAULT ISOLATION) • SUBSYSTEM DIAGNOSIS • EMERGENCY WARNING • TREND TESTING WITH

ADMINISTRATIVE PROCEDURE • AUTOMATED TREND TESTING • ONE FOR MANY VEHICLES • OPERATING PARAMETER DISPLAY

(TRIP COMPUTER) • SPECIAL TEST SESSIONS -VEHICLE WARM-UP • ONE FOR EACH VEHICLE -HARNESS HOOK-UP • SENSORS MUST LIVE ON VEHICLE • TESTS WHILE OPERATING

IMPLEMENTATION PROBLEMS

• COMPLEX VEHICLE SYSTEMS

• COMPLEX MAINTENANCE SYSTEMS

• HIGHLY VARIABLE EMPLOYMENT - USE - ABUSE - ENVIRONMENT - NEGLECT

• DATA - EMPLOYMENT PATTERNS - DEGRADATION/ FAILURE MODELS

• PROGNOSTIC PARAMETERS /CRITERIA

CHART 5

• SENSORS

CHART 6

75
PROPOSED IMPLEMENTATION PROCEDURE

VEHICLE ENGINEERING

EXPERIENCE

ESTIMATED DATA REQUIREMENTS

INITIAL DESIGN PROGNOSTIC MAINTENANCE MONITOR

ON-VEHICLE MICROCOMPUTER

AND

SENSOR TECHNOLOGY

DEVELOPING PROGNOSTIC

DATA BASE

VEHICLE DESIGN AND PMM TECHNIQUES

PMM

DEVELOPMENT LOOP

ON-VEHICLE MAI NT. DATA SYSTEM DESIGN

COST-BENEFIT EVALUATIONS

CHART 7

PROGNOSTIC DATA DEVELOPMENT

• FOR EACH VEHICLE MODEL TEST FOR N FAILURE/LIFE CYCLES - N =MAX. NUMBER OF VARIABLES IN ANY PARAMETER TIMES f( VARIANCE) • ASSUME: N = 3 AND f = 3 OR 10 LIFE CYCLES REQUIRED • TO ESTABLISH GENERIC CHARACTER OF PARAMETERS • ASSUME: 10 VEHICLE MODELS • "ENGINEERING" A PROGNOSTIC PARAMETER - ENGINE CYCLE LIFE: i = n ^2 (REVOLUTION

)| (RPMJRPMq)3

< EGTj /EGT

Q

) b (CTq/CT-)'

i =0 • ASSUME: a ? 2, PISTON SPEED IS SQUARE FUNCTION, RPMo = 1000 b-1, BMEP IS LINEAR FUNCTION, EGTo = 200° F C = 3, CLEARANCE IS CUBE FUNCTION, CTo = THERMOSTAT TEMP. - USE MULTIPLE FORMULATIONS • DATA MEMORY

ENGINEERING PARAMETERS

(VARIANCE MODEL)

= 10-2 STATISTICAL PARAMETERS

(REGRESSION MODEL)

CHART 8

76
VARIABLES/PARAMETERS

SENSED COMPUTED

FUEL FLOW (C) DISTANCE (C) BRAKE SWITCH (C) REVOLUTIONS (C) EXHAUST GAS TEMPERATURE (2) (C/D) COOLANT TEMPERATURE (C/E) OIL PRESSURE (C/E) BEARING TEMPERATURE (S) (T, C/E) VERTICAL ACCELEROMETER (C) IGNITION SWITCH (C) STARTER SWITCH

BATTERY VOLTS (T) START CURRENT (T) CHARGING CURRENT (T) AIR FILTER AP (T)

MILES PER GALLON (T) BRAKING ENERGY (C) RPM (C/E) EGT MANIFOLD BALANCE (T) ENGINE WEAR FUNCTION (C) RUNNING TIME FRACTION (C) NO. COLD STARTS (NO. TRIPS) (C) TOTAL STARTS (C) STARTING SYSTEM POWER (T) STARTING SYSTEM ENERGY (C) COMPRESSION BALANCE (T) ENGINE POWER (T) COOL DOWN TIME (C/D) TRIP LENGTH (C/D) TRIP SPEED (C/D) OIL FILTER AP (T) COOLANT LEVEL (T) OIL LEVEL (T)

C - Cumulative T - Trend E - Excursions D - Distribution Moments

A PRELIMINARY DATA ACQUISITION SYSTEM

SPECIFICATION

• 18 SENSED VARIABLES • 30 SENSED OR COMPUTED PARAMETERS • TRIP /FUEL MANAGEMENT FUNCTIONS • CONTINUOUS OR DEMAND DISPLAY • SHORT TERM HIGH RESOLUTION TIME RECORDING • LONG TERM STORED DATA: - TREND FUNCTIONS - CUMULATIVE GERIOMETRIC ACCOUNTS • PROGRAMMED WARNING AT CRITERIA FOR TREND /CUM • COMPUTER READABLE OUTPUT • MEMORY - 8 K

CHART 9

CHART 10

77
MOTOR VEHICLE FAULT DETECTION AND DIAGNOSIS

Joseph J. Innes

National Highway Traffic Safety Administration

Washington, DC 20590

Abstract: Motor vehicle diagnostic inspection demonstration projects

conducted by the National Highway Traffic Safety Administration under

Title III of the Motor Vehicle Information and Cost Savings Act

indicate that high volume diagnostic inspections can result in greater

safety, improve fuel economy, and reduce the number of faulty and

unnecessary repairs and the amount of motor vehicle pollutants. The

projects conducted periodic safety and emissions inspections for a period of 15 months. They provided direct experience and documentation

of the benefits and costs of diagnostic motor vehicle inspection.

INTRODUCTION

The National Highway Traffic Safety Administration (NHTSA) , U.S. Depart

ment of Transportation, recently completed phase one of a multimillion dollar motor vehicle diagnostic inspection (MVDI) demonstration

program. The goal of the federally funded demonstration was to determine if a national system of diagnostic inspection centers would be

cost effective in the sense that the public benefits would exceed the

program costs. The specific objectives of the program were to provide

information and data on the following subjects:

1. The relative costs and benefits of the project.

2. The capability of the motor vehicle repair industry to correct

diagnosed deficiencies or malfunctions and the cost of such repairs

3. Vehicle-in-use standards and feasible reject levels.

4. The efficiency of facility designs employed.

5. The degree of standardization of diagnostic systems and test equipment . 6. The development of diagnostic equipment designed to maximize the

interchangeability and interface capability, and

7. Vehicle designs which facilitate or hinder inspection and repair.

To meet these objectives, NHTSA established a comprehensive program for

the acquisition, processing and analysis of information and data. At

the Federal level, NHTSA provided the basic support — It established

test criteria and diagnostic inspection procedures, designed the

experiment and provided the overall technical management to assure

timely and successful implementation of the projects. To satisfy the

provisions of the Motor Vehicle Information and Cost Savings Act, five

such demonstration sites were selected competitively; and through

cooperative agreements , Federal funds were awarded to the states in

the form of grants with matching state contributions. The five

78
I projects selected for the demonstration were located in the States of

Alabama, Arizona, Tennessee, the District of Columbia and the Commonwealth of Puerto Rico. Under the technical supervision of NHTSA's

staff the D.C. motor vehicle diagnostic inspection pilot lane was dedicated to the demonstration and six new facilities were constructed

I and equipped with modern diagnostic equipment to conduct safety and

emission inspections. While much of the diagnostic equipment employed

in this demonstration was of necessity off-the-shelf, some modifications

were encouraged to improve system performance.

Two contractors were engaged to provide essential support activities.

An engineering support contractor monitored the quality control and

reported on project operations and equipment calibration through

periodic on-site audits. The focal point for collecting, processing

and analyzing data was provided by a program evaluation support contractor. This source was responsible for the ADP activities including

periodic data evaluation reports as prescribed by NHTSA to aid overall

project management. Although these early data returns could not be

used to reach definite conclusions concerning diagnostic inspection,

the data were useful in identifying and explaining certain trends with

regard to vehicle failure rates, outages by system, subsystem and

components as well as the vehicle recruiting efforts. Thus, these early

trends facilitated corrective measures in vehicle recruiting activities

by identifying hard to fill cells and aided in the assessment of the

pass/fail criteria and repair cost information to assure statistical

validity of data.

MOTOR VEHICLE DIAGNOSTIC INSPECTION CONCEPT

Inspection/Maintenance Cycle

In order to make a meaningful evaluation of the relative costs and

benefits of the projects, two similar groups of vehicles were established at each site. One group was designated the diagnostic or "treatment" group, i.e., the group of vehicles which received specific

technical diagnostic information in order to facilitate correction of

any component failing inspection. The second group was designated the

"control" group, i.e., the group against which the costs and benefits

of diagnosis were measured. This group received only pass-fail information. Both groups received a periodic safety and emission inspection

in accordance with established criteria. However, only the vehicles in

the treatment group received the diagnostic information. A flow chart

of the inspection and repair cycle for vehicles enrolled in the demonstration is shown in Figure 1. In addition to the normal periodic

inspection, vehicles were inspected whenever the title was transferred

to another person, unless the transfer was for the purpose of resale,

or whenever the vehicle sustained substantial damage to any safety or emission-related system as prescribed by regulation.

79
Data Collection and Reporting

Inspection forms were designed to facilitate transfer of information to

80-column punch cards. Although the projects in areas with mandatory

periodic motor vehicle inspection (PMVI) were permitted to use their

normal (PMVI) inspection forms for the control group and compatible

forms for the diagnostic group, NHTSA had the final word on the design

to assure uniformity and to facilitate data processing and evaluation.

The flow of information is shown in Figure 2

.

In addition to the pass/fail and diagnostic information, it was extremely important that repair and maintenance costs were gathered over the

entire time span that a vehicle was in the program, not only for

inspection-related repairs , but repair costs for normal maintenance

between inspections were also reported. This was necessary for both

the control and diagnostic groups so that a comparison could be made

between the two to see if a reduction in overall repair costs is

achieved by the diagnostic group. To the extent possible, parts and

labor costs were listed separately for each operation so that inspectionrelated costs could be separated from owner-requested repairs not

associated with the inspection.

THE COMPUTERIZED DIAGNOSTIC INSPECTION LANE

Computer System

Although participating States were provided latitude in the design of

facilities and selection of diagnostic equipment, only the District of

Columbia engineering pilot lane was designed and equipped with a computerized AVCO 210 diagnostic inspection system (Figure 3)

.

The system was designed to provide on-line , real time computer control

over all inspection sequences. The AVCO System 210 was built around a Digital Equipment Corporation Minicomputer (PDP 11/05) with a 20,000

word memory and a (DEC RK05) disc system with unformatted capacity of

24.4 million bits which interfaces the computer with DEC RKll-DE/DJ

disc controller.

In addition to directing all inspection sequences, the computer system

acquired manually fed inspection data from visual observations and

direct outputs of major pieces of test equipment, and made pass-advise/

reject decisions against stored tables of limits. It also compiled

lane statistics, and transmitted data to a master computer bank on command

.

A motor vehicle to be inspected is first identified to the computer

system by entry of pertinent vehicle information via a cathode ray tube

(CRT) keyboard terminal at the entrance to the inspection lane (Figure

4) . The system then establishes a data file for the vehicle and

80
selects appropriate inspection standards to which vehicle data—derived

automatically from test machines or manually via remote entry and

display terminals (READIT's) is entered. All communication between the • inspectors at each test station and the computer is carried on via the

hand-held, overhead-supported READIT pendants. Five of these pendants

are suspended along the lane—one each at inspection stations 1, 3,

and 4, and two at inspection station 2. A close-up of a READIT pendant

is shown in Figure 5. The system file contains tables of specification

limits against which front end alignment and ball joint play measurements are compared to determine the acceptability or unacceptability

of the vehicle being tested. In addition to using data from these

tables, the system selects appropriate tests based upon the body style

and model year of each vehicle tested.

Each test station in the lane contains one or more items of motor

vehicle test equipment directly connected to the computer, and each is

also assigned a sequence of manual tests to be conducted in a prescribed order. The inspector need only determine that a specific test

is required or unacceptable. The computer makes all advise or reject

decisions on the basis of criteria entered in the system.

All direct interfaces between the computer and the test equipment

involve test equipment output data only and in no way influence the

normal operation of this equipment. In all instances, the test equipment is operated using the same procedures as would be used without the

direct computer tie. Thus this equipment may be operated manually at

any time without regard for the status of the computer. A description

of the major pieces of equipment shown in Figure 4 and the automatic

interface with the computer system follow:

Entrance Station

Contains a cathode ray tube (CRT) display and integral keyboard unit

used for entering vehicle identification information into the system

and for all communication with the computer system. The CRT also

provides means for editing test sequences, viewing lane statistics,

changing modes of operation, detecting and correcting anomalous

operation, and for all off-line communications with the computer.

This unit is an entirely self-contained alphanumeric video display unit

that can display up to 1440 characters large and legible enough to be

easily read under most ambient lighting conditions.

Station 1

Contains READIT pendant 1, a roller brake tester, an exhaust emission

tester, and a chassis dynamometer. The READIT provides a 15-character

alphanumeric display for presenting computer-generated instructions to

the inspector, and a compact keyboard containing 14 keys (10 numeric

81
and 4 special function) used by the inspector to enter judgments and

commands to the system. A code book affixed to the front of the READIT

(see Figure 5) provides a complete listing of all GENERAL, SPECIAL, and

TEST ID codes for convenient reference.

Roller Brake Tester . The system interfaces directly with the output of

the minicomputer-controller of the tester. All front panel MARGINAL

and FAIL light indicators of that equipment are monitored directly by

the AVCO System 210 computer upon command of the inspector via the

READIT. The system records all MARGINAL and FAIL lamps operated during

the brake test. In April 1975, this minicomputer-controller was shut

down and the brake analyzer was operated manually. The chassis dynamometer described next is integral with this brake analyzer.

Chassis Dynamometer . The system interfaces directly with the chassis

dynamometer, and both the ROADSPEED and HORSEPOWER analog meters of

that device are monitored by the computer. Upon command of the

inspector via the READIT, the system records the meter values and

stores them in the Vehicle Processing File for the vehicle under test.

These readings are taken simultaneously with the exhaust emission

readings in response to a single inspector command.

Exhaust Emissions Tester . The system interfaces directly with the

exhaust emissions analyzer, and both the Hydrocarbon (HC) and Carbon

Monoxide (CO) analog meters and their associated range switches are monitored by the computer. Upon command of the inspector via the

READIT, the system records the meter values and compares them to

standard values for the model year of the vehicle under test.

Station 2

Contains READIT pendants 2 and 3, and a scuff gauge. Since READITs 2 and 3 are used in the same station, they are so coupled into the system

that all testing assigned to each READIT at that station must be accom- panied before a vehicle can be logically cleared from this station.

They operate as independent READITs in all other respects.

Scuff Gauge . The system interfaces directly with the scuff gauge, and

both the scuff value and direction are monitored by the computer. Upon

command of the inspector via the READIT, the system records the peak

scuff value and direction of scuff and compares these values to the

standard value stored in the system.

Station 3

Contains READIT pendant 4 and a dynamic front end alignment tester.

Front-End Alignment Tester . The system interfaces directly with the

dynamic front-end alignment tester, and all CAMBER, CASTER, and TOE

82
analog meter outputs are monitored by the computer. Upon command of

the inspector via the KEADIT, the system records the meter values and

compares the caster, camber, and toe values to the specification values

for the make, model, and year of the vehicle under test.

Station 4

Contains READIT pendant 5 and a platform brake tester.

Platform Brake Tester . The system interfaces directly with the platform

brake tester, and the force levels on all four platforms are monitored

by the computer. Upon command of the inspector via the READIT, the

system records the peak platform force levels; computes the side-toside imbalance ratios of both axles, and the front to rear imbalance;

and compares these imbalance values with standard values. The system

also compares the imbalance values with those determined during the

roller brake test (conducted earlier in the lane)

.

Exit Station

Contains a line printer with an integral keyboard unit.

The printer generates a concise report (with a carbon copy) of inspection results at the lane exit. One copy is given to the vehicle owner

and the other is retained on file at the inspection facility. The

print-out is made automatically on special forms pre-printed with general information. The form used by the District of Columbia, Bureau of

Motor Vehicle Services is extremely functional in relaying diagnostic

information to owner and garage

.

This unit prints from a set of 64 characters at speeds of up to 30

characters per second. Data is entered from a 96-character keyboard.

It is also used in changing the number of sequence of the stickers

used to indicate that vehicles have satisfactorily completed inspection.

ASSESSMENT OF MOTOR VEHICLE DIAGNOSTIC INSPECTION

Impact on Safety

One of the objectives of the MDVI demonstration projects was to provide

a comprehensive analysis concerning vehicle-in-use (VIU) standards and

the sensitivity of rejection rates to changes in these standards.

Degradation data were analyzed at the system and component levels, and

related quantitative data were analyzed by site. Life-cycle data were

limited to the first, second and third periodic inspections of approximately six month duration for each cycle.

Although each project site was required to perform certain basic

diagnostic inspections, they were allowed to expand the list of criteria,

83
e.g., states or cities with PMVI programs were allowed to include

mandatory system or component inspections. All projects also performed

inspections of additional safety-related items not addressed by the

Federal VIU Standard. These varied somewhat among the projects, and

included headlamp function and aim, other lamps and reflectors, seatbelts, body condition, glazing condition, exhaust system, fuel system,

underhood and electrical items. The criteria common to all project

sites as promulgated by the NHTSA is expressed in Part 570, Vehicle In

Use Inspection Standards, of Chapter V, Title 49, Code of Federal

Regulations. The VIU Standards address the brakes, steering system,

suspension system, and tire and wheel components. These are the

systems and components which vehicle safety research has shown to be

safety critical.

An analysis of the data from over 125,000 in-depth inspections (including reinspections after repairs) covering a 15-month period yields some startling statistics. One the average, 74 percent of the vehicles in

the program failed the initial periodic inspection. In states without

a mandatory PMVI program, over 90 percent of the vehicles failed the

initial inspection (Table 1) . It is encouraging to note that the

safety and emissions systems of vehicles in the program show a 23 percent reduction in the reject rates for the relatively short period of

the demonstration. Furthermore, the reject rate decrease from the

initial inspection to the third cycle inspection is statistically

significant to a high level of confidence. The values shown in Table 2 reflect inspection failure rates for the Federal VIU safety and emission

systems criteria. Again, in all cases a significant improvement in the

mechanical condition of the systems and components was realized from

the initial (P 1) to the final (P 3) inspection. Analysis of the pass/

fail rate data from the first and third periodic diagnostic inspections

show 57 percent improvement in the condition of the vehicle safety and

emissions systems. In the safety critical brake system area alone, 35

percent of vehicles diagnosed had unacceptable system or component

degradation. This unusually high failure rate has substantial safety

implications, as brake problems account for nearly half of the vehicular

factors which caused accidents. However, it is noteworthy that the

reject rates were steadily decreasing over the life of the demonstration

A low reject rate is a measure of the roadworthiness of a vehicle from

the safety point of view. One final point that must be made is the

fact that advisories, which are an important part of the long-term

safety condition of vehicles, were not reflected in the above tables

but could enhance safety under extended life cycle test conditions.

Impact on Emissions

In addition to periodic safety inspections, the demonstration projects

were required to conduct emissions inspections pursuant to the criteria

promulgated by NHTSA in consultation with the Environmental Protection

Agency. The pass/fail levels for emissions were based on EPA

84
recommendations and on comments from the private sector. As such, the

criteria represent a fair balance between low and high rejection rates

to avert adverse public reaction to the demonstrations . The compromise

emissions criteria and test procedures provided for both the no-load

or idle test and the loaded-mode test conditions. In each case two

major air pollutants were measured — carbon monoxide (CO) and hydrocarbons (HC) . The relative HC and CO emission levels determined under

loaded mode inspection were also used in diagnosing engine malfunctions

Although NHTSA did not issue standards concerning specific emissionrelated components and systems, the Guidelines for State Proposals

suggested that the projects consider inspection of the PCV valve, air

filter, idle speed, sparkplug firing voltage, available coil voltage,

coil/condenser oscillations, ignition point operation and dwell,

ignition timing and variation, vacuum advance condition, mechanical

advance condition, dynamic cylinder balance, and manifold vacuum

condition.

No project inspected all items suggested, and there was some variation

among the projects. Most of the projects inspected the PCV valve, idle

speed, sparkplug firing voltage, available coil voltage, ignition point

dwell, ignition timing variation, and dynamic cylinder balance, inspections of the battery and charging system were also frequently

performed. Those projects which conducted loaded-mode emission inspections used the results in a "truth chart" matrix to further identify

carburetion or ignition problems as the probable source of the high

emissions

.

Table 3 shows the average emission levels reported for the loaded and

no-load modes for each of the inspection cycles. The combined average

HC and CO levels were down 22% and 12%, respectively, from the initial

to the final inspection. The composite failure rates for the emission

tests shown in Table 2 were also reduced significantly, from 22.8% to

9.9%, over the program duration. Results of loaded mode testing show

that :

• Idle test failures accounted for 60 to 80 percent of

all emissions outages

• CO failures accounted for 48 to 65 percent of all

emissions failures

• Idle CO accounted for 26.5 to 48.7 percent of all

emissions failures, and

• Idle CO and HC accounted for from 50 to 64 percent

of all emission failures.

85
Program results support the claim that specific diagnostic information on the condition of the engine help the industry to properly correct

emissions. The information provided apparently assisted the repair

industry in providing adequate repairs at reasonable cost. During the

first inspection cycle the rate of faulty emission repairs was about

25 percent for both the diagnostic and control groups. During the

second cycle, however, the diagnostic group had a faulty emissions

repair rate of only 11.5 percent, which was nearly 30 percent less than

the 16.3 percent rate experienced by the control group.

In addition to the clean air benefits resulting from the reduced pollution reported by the data evaluation contractor, fuel consumption data

under day-to-day driving conditions indicate a significant improvement

in fuel economy (Table 4) . The results are based on a representative

sample of all model years and vehicle weight classes. The before/

after tune-up analysis was conducted for all sites by model year, by

weight, class, and by diagnostic versus control groups. The major

findings were:

• All vehicles combined resulted in before/after

tune-up fuel economy of 4.7%.

• Diagnostic group generally exhibited a greater

improvement in fuel economy than the control group

(non-diagnostic)

.

The encouraging fuel economy results based on participant fuel con- sumption before-and-after tune-ups were substantiated by a joint EPA/

NHTSA audit of 57 vehicles enrolled in the Phoenix, Arizona project.

These vehicles were subjected to the standard EPA Federal Test

Procedures (FTP) urban and highway driving cycle tests. As in the case of the owner-submitted fuel consumption data, the EPA test results show

an improvement of 4.9% in fuel economy for compact cars and a FTP

composite of 5.3% for intermediate cars.

Conclusions drawn from these data are that periodic diagnosis followed

by corrective maintenance reduced exhaust pollution levels of HC and

CO, and significantly improved fuel economy for vehicles in the demonstration program.

Impact on Repairs

One measure of the impact on the repair process is an assessment of the

capability of the repair industry to repair diagnosed deficiencies and

the cost of such repairs. The capability of the repair industry to

repair specific outages was determined by reinspecting each item

initially rejected. The reinspection failure rate can be a direct

numerical measure of the industry's inability to perform adequate

repairs in response to inspection results. A vehicle is considered to

86
have failed reinspection of the repair of a defect was attempted

unsuccessfully or if no repair was performed on the vehicle. The

vehicle reinspection failure rates for the five diagnostic demonstration

projects are shown in Table 5. The rates are presented by project and

by periodic inspection cycle. The values range from a low of 1.1 per-

! cent for the first cycle D.C. control group, to a high of 50.0 percent

for the first cycle Alabama control group.

The objective of this task was to determine if detailed knowledge of

the specific problem can facilitate correction and impact repair costs.

The brake and emissions systems were particularly sensitive to the

effect of diagnosis. Analysis showed that approximately 6 percent

cost savings was realized from tune-ups and carburetor work for the

group with diagnostic information. In other areas, only a marginal

savings can be observed. Some of the true value of diagnostic inspecI tion appears to be lost, either as a result of the short duration of

the program or the dependence on the consumer and repair industry to

effectively use diagnostic information. However, in spite of the modest

cost benefits, the concept of an independent, objective diagnostic

inspection with no vested interest in the actual repair process was well

received by both the consumer and the repair industry. Program participants voluntarily spent approximately $2.4 million on vehicle

repairs, many of them spent money for repairs that were clearly discretionary. Furthermore, a closer examination of the results indicate

that a vehicle owner armed with diagnostic information has a greater

likelihood of receiving correct repairs, particularly for emissions

systems. The distribution of repair dollars by subsystems is shown in

Figure 6. Brakes, tires and wheels, emissions, and suspension systems

account for two-thirds of the repair cost dollars. The average expenditure for vehicle repaired in response to inspection during the program was 57 dollars.

CONCLUSION

The results of the demonstration show that the use of this technology

to determine the condition of vehicle safety and emissions systems is

viable and that it offers great promise to consumers and repair industry

alike. Diagnostic motor vehicle inspection will benefit consumers by

providing them information on the condition of vehicles, which if used

properly, can result in greater safety, lower pollution, improved gas

mileage and in the case of complex vehicle systems generally lower

overall repair and maintenance costs.

Perhaps the most gratifying aspect of the demonstration was the consumer

reaction to the diagnostic inspection program. A survey of consumer

demographic attitudes and experience conducted by a nationally prominent market research group shows that over 78 percent of a national

sample of vehicle owners agreed that vehicle inspection should be

required by law. When participants were asked if they would join a

8T
diagnostic inspection program again, 93 percent said they would. When

asked about the amount they would be willing to pay for a diagnostic

inspection, over 60 percent were willing to pay $10 or more. Obviously;

the concepts of an independent, objective diagnostic inspection with no vested interest in the actual repair process was well received by both

the consumer and the repair industry. Furthermore, the benefits of

diagnostic inspection can be considerably greater by improving com- munication between the inspection facility and the repair industry.

Since the consumer and the repair industry play key roles in the

effective use of diagnostic information, further improvement in this

critical communication link is highly desirable.

During 1979 NHTSA will continue its diagnostic inspection concept

program to compile , analyze , and document a practical set of alternatives by which States, local governments, or consumer groups could

make unbiased automotive diagnostic inspection more available to motorists. NHTSA' s planning for diagnostic inspection programs is especially

timely now because of related activities of the Environmental Protection

Agency (EPA) . Section 105 of the Clean Air Act authorizes the EPA to

make grants to the States to develop and maintain motor vehicle inspection and maintenance programs for vehicle emissions. To date, $5

million have been authorized for this effort and additional funds were appropriated should the need arise. The EPA's program must be con- sistent with the Periodic Motor Vehicle Inspection program under our Highway Safety Act. That Act authorizes the Secretary of Transportation

to make grants to the States to inspect vehicles for safety purposes,

and to set minimum Federal standards

.

88
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FASS

DIAGNOSIS FAIL OR

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PASS FAIL I

Figure 1. Vehicle Inspection and Repair Cycle Flow Chart

92
CONSUMER

PARTICIPATION

ANALYSIS

OF REPAIR ADEQUACY

REPAIR

IREINSPECTION CYCLE)

POST INSPECTION ACCIDENT A REPAIR DATA

CONSUMER REPORTS DMV FILES ON SITE ACCIDENT

INVESTIGATION

VEHICLE OATA

OUTAGE ft REJECT LEVELS

EMISSION LEVELS

REPAIR COST ft ADEQUACY

EASE OF DIAGNOSIS

INFO ON STANDARDS

PROJECT INFORMATION

OPERATING COSTS EQUIPMENT INFO. FACILITY DESIGNS MANPOWER REQUIREMENTS

COST IENEFIT ANALYSIS PROGRAM COSTS VI

•ENEFITS FROM

REOUCED REPAIR

COSTS, ACCIDENTS, ANO EMISSION

Figure 2. Motor Vehicle Diagnostic Inspection Data Flow Chart

93

95
Figure 5. Remote Entry and Display Inspection Terminal (READIT)

96
97
DIAGNOSIS OF COMBAT VEHICLE SYSTEMS USING SIMPLIFIED TEST EQUIPMENT

T.E. Fitzpatrick

R.E. Hanson

F.W. Hohn

RCA, Government Systems Division

Automated Systems

Burlington, Massachusetts

Abstract: In response to the current requirement to improve both the

efficiency and the effectiveness of U.S. Army vehicle maintenance, the

U.S. Army Tank-Automotive Research and Development Command has developed

Simplified Test Equipment for Internal Combustion Engines (STE/ICE)*.

Although the STE/ICE system has been developed for applicability across

the entire Army vehicle fleet, this paper describes the STE/ICE application to combat vehicles only. Because of the complexity of combat vehicle systems and attendant problems associated with test accessibility,

maintenance training and documentation, combat vehicle maintenance represents the most demanding challenge to the U.S. Army vehicle combat

service support mission.

This paper discusses the STE/ICE application to Combat Vehicle Hull sys- i terns. A specific vehicle application is described as an example of

STE/ICE test capability within the framework of the standard vehicle diagnostic connector interface definition.

A newly developed extension of STE/ICE test capability to Turret Systems

is also presented. This extension demonstrates that test of the entire

Combat Vehicle with a single test system is possible.

The STE/ICE System, capable of hull system test of the existing combat

vehicle fleet, and its demonstrated suitability for turret test extension provides a basis for conclusions relative to test system and vehicle design approaches for enhanced combat vehicle maintenance.

Key words: Combat vehicles; Diagnostic Connector Assembly; Fighting Vehicle Systems; generic DCA; Hull systems; Simplified Test Equipment for

Internal Combustion Engines; Turret Systems; vehicle maintenance.

*STE/ICE was developed for the U.S. Army Tank Automotive Research and

Development Command by RCA Government Systems Division, Automated

Systems

.
INTRODUCTION . Simplified Test Equipment for Internal Combustion Engines

(STE/ICE) has been described in detail at several points in its development process and it is not proposed to repeat that description herein.

Rather, the principal thrust of this paper is to report recent STE/ICE

developments which have verified and facilitated STE/ICE application to

the existing U.S. Army Combat vehicle fleet in the conventional STE/ICE

role of power pack diagnosis and to report on an extension of STE/ICE

1 application to the mission of total vehicle test support.

' Through recently completed Design/ Operational Testing, the STE/ICE System capability to test U.S. Army vehicles has been confirmed. The definition of a new and "adaptable" vehicle/ test system interface has facilitated vehicle design for "testability". Finally, an application of

STE/ICE to test a fighting vehicle system has demonstrated that the

STE/ICE system is capable of filling the mission need of a single test

system for organizational or "on-vehicle" support of the total combat

| vehicle system.

Given the STE/ICE test capability to support the power packs in the

present U.S. Army combat vehicle fleet and the system's ability to extend beyond the power pack into turret system test, a prospective exists

| from which to view a new and now viable possibility; organizational support of the total combat vehicle fleet via a single simplified test system. While this possibility is yet to be achieved, the progress reported here-in seems to bring this essential goal a significant step closer

to accomplishment.

Both the use of the "adaptable" vehicle - STE/ICE interface and the

extension of STE/ICE capability into turret system test have been demonstrated in the development of a new family of U.S. Army Fighting Vehicles o

Two of these vehicles are the XM2 Infantry Fighting Vehicle (IFV) and

the XM3 Cavalry Fighting Vehicle (CFV).

The IFV and CFV vehicles combine high mobility and fire-power. Mobility

is achieved by the combination of a 500 HP turbocharged diesel engine

and a hydro-mechanical transmission. Firepower is provided by the following vehicle subsystems:

o All electric stabilized turret

o 25 MM automatic cannon

o 7.62 MM machine gun

o Two turret mounted TOW anti-tank missiles

o A day/night integrated sighting system employing thermal imaging

techniques

o Six firing port weapons - 5.56 MM (IFV only)

99
An early focus of vehicle design addressed forward maintenance support

and the human factors considerations associated with both the vehicle's

operational crew and the vehicle mechanic. Consistent with the goal of

simplified, facile vehicle maintenance, a single test system STE/ICE, was designated for "on-vehicle" or organizational diagnosis of all hull

and turret equipment problems.

In the following sections, the application of STE/ICE to combat vehicle

hull systems and the FVS turret system is described. The concluding

section summarizes the benefits of the FVS test equipment approach, the

concepts validated in the course of test equipment implementation and

the future steps in the evolution of a user optimized test system for

organizational support of the combat vehicle fleet.

STE/ICE - COMBAT VEHICLE HULL SYSTEM TEST CAPABILITY . The Combat Vehicle Hull diagnostic problem is complicated by the restricted accessibility characteristic of armored combat vehicles. Figure 1 illustrates

the major systems and subsystems of the vehicle hull and indicates the

main areas of diagnostic significance and test equipment requirements

(faults in drive, suspension, and armor are more readily apparent and

diagnosable without aids). The STE/ICE system (Simplified Test Equipment/internal Combustion Engine) was developed by RCA to meet just those

requirements for the U.S. Army Tank-Automotive Research and Development

Command (TARADCOM)

.

AIR INDUCTION FUEL

COOLING ENGINE

STARTING

TRANSMISSION

CHARGING

DIAGNOSTIC

SIGNIFICANCE

Figure 1. Combat Vehicle

TRACK DRIVES

SUSPENSION

ARMOR

100
The heart of the STE/ICE system is the VTM (Vehicle Test Meter) shown in

Figure 2. It has been carefully designed to be simple to operate and

understand. The man-machine interface has been limited to a digital

readout for displaying measurement results, two ten digit indexing

switches used to select the desired test, a test initiation button and

an on-off switch. This microprocessor controlled device measures parameters and displays the results as either a pass /fail message or as digital values in appropriate units familiar to the mechanic (i.e. psi, rpm»

volts, ohms, amps, etc.).

Figure 2. STE/ICE VTM

The VTM interfaces to the vehicle in two modes: built in Diagnostic

Connector Assembly (DCA) and Transducer Kit (TK) . Although the DCA mode

is the mechanic optimized mode of operation, practical limitations preclude pre-wiring of all possible measurement parameters. Therefore, the

transducer kit (TK) has been included as a part of the STE/ICE Set to

supplement DCA measurements as well as to provide test capability for

the present vehicle fleet which is not yet equipped with DCAs.

The transducer kit consists of four sensors; two pressure transducers

(vacuum to 25 PSI, and 25 to 1,000 PSI), a Hall effect clamp-on current

probe (0 - 1500 amps) and a tachometer pick-up for diesel engine speed

measurement. Also provided as a part of the transducer kit are cables

and fittings required to connect the test system to the vehicle under

test.

While the transducer kit affords less than the optimum connection to the

vehicle under test, it remains both a simple and powerful test approach.

As an example of the effectiveness of the TK operating mode, with three

101
attachments to a diesel powered vehicle, it is possible to execute fourteen tests to assess the condition of the engine, starting and charging

systems. This simple hook-up and the attendant tests can be performed

in twenty minutes, even on a combat vehicle given test point accessibility complications.

The STE/ICE, in the Transducer Kit operating mode, is now applicable to

the following U.S. Army Combat Vehicles:

o M48 and M60 Series Tanks

o M551 Armored Reconnaissance Airborne Assault Vehicles

o M113 Armored Personnel Carrier

o M107 Gun Field Artillery, Self Propelled

o M109, Ml10 Howitzer, Self Propelled

o M579 Recovery Vehicle

The Diagnostic Connector Assembly operational mode has been developed

through evolution in parallel with STE/ICE Set development to facilitate the mechanic's task in test and diagnosis of vehicle systems. Prototype DCA's were developed to be vehicle specific, that is, each vehicle type was assigned a code resistor and had a defined complement of

sensors. By looking at the code resistor, the VTM would know what vehicle type was being tested and utilize Read Only Memory (ROM) tables to

identify the assigned transducer complement and appropriate scale factors. This concept would, however, necessitate updating all STE/ICE ROM

sets every time a new vehicle DCA is introduced. With STE/ICE sets issued to troops all over the world, the logistics burden of such change

programs would become impractical. A generic DCA concept was, therefore,

developed where fourteen general DCA types (Table 1), each with its own

code resistor, were defined by software tables programmed for each category. Each of these "DCAs" is really a "ceiling DCA" with a maximum

test complement defined for it. The vehicle developer then has the

flexibility to define the appropriate subset of measurements applicable

to his vehicle. Special wiring conventions allow the VTM to determine

unused test functions so that appropriate operator messages can be displayed when a non-instrumented DCA test function is called for.

Table 1. STE/ICE Generic DCA (Partial Listing)

DCA Type General Class

Number of Vehicles

1 Vehicles with medi- um sized diesel

engines

2 Vehicles with medium sized diesel

engines

Engine Types

Turbocharged and non-turbocharged en- gines with single plunger distributor

type funnel systems and turbocharged

engines with unit injector fuel systems

Non-turbocharged engines with unit injector fuel systems

102
Table 1. STE/ICE Generic DCA (Partial Listing) (Continued)

DCA Type General Class

Number of Vehicles

3 Vehicles with medium sized diesel

engines

4 Vehicles with medium sized diesel

engines

5 Vehicles with large

sized diesel

engines

Engine Types

Cummins engines with PT type of fuel

system (turbocharged or not)

Caterpillar and Mack engines with multiple plunger type fuel systems (turbocharged or not)

Turbocharged and non- turbocharged engines with single-plunger distributor

type fuel systems and multiple air.

cleaners and turbochargers

13

14

Optional Second

DCA connector

Special Purpose

DCA

Those vehicles with more test points

than can be handled with one DCA con- nector provide additional voltage

temperature, and pressure test points

Not defined at this time

The Fighting Vehicle Systems vehicle family was the first U.S. Army beneficiary of this generic DCA concept as well as the first vehicle to

test the validity and comprehensiveness of this approach.

The FVS vehicles have been outfitted with two DCAs in the vehicle hull

to maximize the benefit obtained through the use of STE/ICE for vehicle

support. Table 2 lists all the test functions available through the

two DCAs. The first DCA is the normal vehicle DCA (Generic DCA Number

3 from Table 1) and the second is an optional DCA (Number 13 from Table

1). Between the two connectors, the mechanic has extensive test capabilities in all the significant vehicle systems shown in Figure 1. In

many cases, he will be able to isolate system problems to an individual

component through the available DCA functions and avoid unnecessary re- moval of parts restricting access to test points.

Table 2. STE/ICE - FVS Hull DCA Test Functions

DCA #1 DCA #2

Function (Type 3) (Type 13)

Engine Tests

Speed X X

Power X X

Compression Balance X X

103
Table 2. STE/ICE - FVS Hull DCA Test Functions (Continued)

Function

Engine Tests (Continued)

Oil Pressure

Oil Temperature

Coolant Temperature

Air Cleaner Pressure (switch)

Fuel Filter Pressure (switch)

Fuel Rail Pressure

Turbocharger Outlet Pressure

Transmission Tests

Oil Pressure

Oil Temperature

Electrical Tests

Battery Voltage

Battery Current

Battery/Starter Resistances

Battery Electrolyte Level

Series Pair #1

Series Pair #2

Starter Voltage

Starter Solenoid Voltage

Starter Switch Voltage

Starter Switch Return Voltage

Alternator Output Voltage

Alternator Field Voltage

Alternator Field Control

Voltage

Fuel Pump Voltage

Fan Speed Solenoid Voltage

DCA #1

(Type 3)

X

X

X

X

X

X

X

DCA #2

(Type 13)

X

X

X

X

X

X

X

X

X

X

X

X

X

X

STE/FVS - TURRET TEST CAPABILITY . The FVS Turret presented the vehicle developer with a different and more complex diagnostic problem.

Figure 3 illustrates the complexity of the turret in terms of its electrical components. The initial parameter measurement requirements defined for maintenance support of this turret included 241 different

test signals. The rest of this section describes how the Simplified

Test Equipment concept was extended to include full turret test capabilities for this vehicle family.

10k
GUN/TOW

ROTOR

SWITCH

TURRET CONTROL

BACK-UP

BATTERY

TOW

CONTROL

GUN/

GRENADE CONTROL

MOTION

DETECT CKT

VEHICLE

BATTERY

DIGITAL ENCODER

SLIP RING

HATCH

SWITCHES

HULL GYRO

TURRET

DIST BOX

(HULL)

TURRET POS IND

(GNR)

25 MM

TURRET POS IND

(CMDR)

ANNUNC

PANEL

CGE

GUN

RX

TOW

RX

POWER

SUPPLY

INTEGRATED

SIGHT iRROR

DETECT

LIN ACT M

LX

LIFT ACT

ELECTRONIC CONTROL

ASSY

GNR

HAND

STATION

CMDR HAND

STATION

GUN

GYRO

TURRET GYRO

GUN ELEV SERVO

ELEV GEAR BOX

TRAVERSE SERVO

I

TRAVERSE GEAR BOX

TOW ELEV SERVO

TOW ELEV GEAR BOX

Figure 3. IFV Turret Components

The extension of the STE/ICE test and measurement capability to include

complete turret testing was effected through changes internal and ex- ternal to the standard STE/ICE set. Internal changes are primarily in

microprocessor program memory. External changes are concentrated m a Controllable Interface Box (CIB) that expands the normal STE/ICE measurement capability to 291 channels with full scale capabilities ranging from +5 to +187 volts, some single ended, some differential, some

shielded, and some with special overvoltage protection. The interface

between the turret and the test equipment is through 3 standardized 128

pin test connectors and a power connector as shown in Figure 4.

105
Figure 4. STE/FVS - Turret Test Configuration

The simplicity of the system is best illustrated by describing its operational characteristics. Recommended procedure for use of the system is

connect all cables (PI, CI, C2, C3, DCA) , turn system on with Vehicle

Test Meter power switch, select appropriate test numbers, and observe

displayed results. Once all cables have been connected, full turret

test capability is available at the standard soldier-tested (and accepted) VTM man-machine interface. The CIB has no control or display functions on it. Designing the system so that all test points can be con- nected simultaneously (3 cables) permits the mechanic to use the same

set up procedure for turret testing regardless of fault symptoms.

The operation of the VTM in its Turret Test mode makes use of 600, 700,

and 800 series test numbers. Normal vehicle testing uses test numbers

less than 100 (only two digiswitches available for input). To use the

systems for turret testing, the mechanic must first enter a "number series indicator" (06 for 600, 07 for 700, 08 for 800) and then enter

other test numbers within the series. The "number series indicator"

need be entered only once for a whole group of tests within a series.

Entering a "99" returns the VTM to its normal Vehicle Test Meter mode of

operation where it is possible to enter another number series. All 600

series test parameters come through a common test connector and the same

is true for 700 and 800 series parameters. Table 3 shows the distribution of turret system parameters within test and connector number series

Table 3. Turret Systems Test Points

Turret Systems

Number of Test Points per Test

and Connector Number Series

600 700 800

Turret Power Control, and Interlock

Distribution Systems 80 15

Turret Electric Drive and

Stabilization Systems 69

Integrated Sight and Fire Control

Electronic Systems 77

106
This distribution of systems within the number series permits much of the

testing to be confined to a single number series. Thus, the mechanic

is only required to make a single entry for most tests.

The types of measurements called for are DC voltage, AC/RMS voltage, peak

voltage, and peak-to-peak voltage. Table 4 shows the distribution of

these types of tests.

Table 4. STE/FVS Test Capability

Test Number Series

Measurement Type 600 700 800 Total

Volts DC 79 82 58 219

Volts AC/RMS 15 15

Volts Peak 1 2 1 4

Volts Peak-to-Peak 3 3

241

Standardization of the test connectors and their interface made several

desirable features possible including operational simplicity, redundant

parts, and a complete system self test. The turret test and self test

connectors are all coded; the three test cables and three CIB multiplexing interfaces are all identical. Thus, it was possible to include a connector search routine in the software so that it does not matter how

the using mechanic connects the cables. The microprocessor determines

which turret test connector is connected to which CIB connector and then

addresses the appropriate input channel. There is no wrong way to hook

up the three cables.

The CIB contains seven boards as shown in Figure 5. All six of the input multiplexer boards are identical and completely interchangeable. In

normal operation, there are three identical sets of hardware (cables,

connectors, boards, and wires) connecting the three turret test connectors to the CIB Receiver/ Interface Board. Given this redundancy, the

mechanic could have two faulty cables and four faulty Mux Boards but as long as one of the CIB Test Connectors was fully operational, he could

still perform all vehicle tests with the only penalty being the required

movement of the remaining cable each time the number series was switched.

Should he connect the one cable to the wrong connector, the VTM would so indicate by an error message.

The CIB self test is a full compensated system test which includes a test

of its own cables. Any one of the three test cables can be mated to the

self test connector. The self-test then checks out all input channels

and indicates either PASS or how many bad channels were found and which

ones they were. By simply interchanging cables, the support mechanic

can then fault isolate to a single board or cable. If necessary, the same information will often allow isolation of the fault to a single

chip or few chips. Thus, no new support equipment is required to support the test system itself.

107
TEST

1 TEST 5

TEST E

MUX

BOARD

1

MUX

BOARD

MUX

BOARD

/

MUX MUX MUX

BOARD BOARD BOARD

i1 c5

Figure 5. Simplified CIB Block Diagram

CONCLUSIONS . The progress in extending STE/ICE application and applicability as described here-in are most significant when viewed in conceptual terms. STE/ICE applications (TK mode) now encompass power pack support for virtually all of the U.S. Army Combat Vehicle Fleet. In addition this simplified test system has been demonstrated to be capable of

providing all required organizational or "on-vehicle" test capability

for a modern, sophisticated combat vehicle. Among the benefits expected

from the FVS test system approach are the following:

o Reduced vehicle logistics support costs from multiple use of a single organizational level test system.

o Hull systems mechanics will be trained in the use of STE/ICE in

the course of normal MOS training. The FVS will impose no additional test equipment interface training on the Army Mechanic.

o The interface between Simplified Test Equipment and the mechanic

initially designed for automotive mechanics will now be available to turret mechanics.

o The task of maintaining an inoperable vehicle in the field is

made manageable by the ability to bring only one test system to

the vehicle.

108
In the process of this demonstration, the STE/ICE application to FVS hull

systems has confirmed the validity of the STE/ICE Generic DCA concept.

It is possible to field STE/ICE in support of the existing Army vehicle

fleet while anticipating the future vehicle fleet in generic terms such

that future DCA equipped vehicles can be accommodated without change to

the test system.

From the perspective afforded by this demonstration, it is possible to

visualize additional characteristics of the test system that are desirable and achievable without significant additional test system complexity

„

The next desirable test system feature is selective automation of turret

diagnostics. The microprocessor resident in the STE/ICE VTM provides the

potential to automate turret test sequences to simplify the turret mechanic's task by making him significantly less dependent on technical

manuals. This automation should increase diagnostic accuracy while decreasing test time. The STE/ICE-CIB system now executes tests on a "oneat-a-time" basis 0 The turret mechanic depends on a technical manual

diagnostic procedure to link test results to form diagnostic conclusions.

One way to automate this diagnostic process is to validate the manual

diagnostics contained in technical manuals, await the "frozen" production

vehicle configurations and convert technical manual diagnostic procedures

to test system program memory 0 In this way, a well validated diagnostic

procedure can be obtained for the proper vehicle configuration while

minimizing the cost associated with software maintenance 0

It seems clear that the extended FVS test system approach described herein may have application to other combat vehicles; some of which are now

supported in part by STE/ICE. In the absence of direct applicability,

it may be concluded that two project concepts apply:

o It is possible for a single simplified test system to perform all

organizational level on-vehicle tests for a combat vehicle.

o It is possible for a test system to be developed, or applied, in

parallel with the development of the prime weapon system.

Given some standardization of diagnostic connector interfaces in turret

systems (perhaps employing a generic interface concept) it seems practical to configure a single simplified test system for on-vehicle test of

the entire combat vehicle fleet.

109
REFERENCES

1. Donald S. Sarna and Joseph W. Steyaert, "Diagnostic Equipment Develop'

ment for Military Vehicle Applications". Paper 780029 presented at

SAE Automatic Engineering Congress, Detroit, February 1978.

2. R.E. Hanson and H.L Q Fischer, "New Techniques for Automated Engine

Diagnostics" presented at AUTOTESTCON, Hyannis, November 1977.

3. HoL. Fischer/T.Eo Fitzpatrick, "Simplified Automatic Test Equipment".

Unpublished RCA paper presented at the Industry/ Joint Services Automatic Test Conference and Workshop, San Diego, April 1978.

4. Angelo Muzi, "Sensor Selection for Automatic Diagnosis of Vehicles".

Paper 770403 presented at SAE International Automotive Engineering

Congress, Detroit, March 1977.

5. H.E. Fineman, T Q E. Fitzpatrick, and A.H. Fortin, "Simplifying Automotive Test Equipment through use of Advanced Electronics" 0 Presented at IEEE NEREM, Boston, November 1974

„

110
AUTOMATED VEHICULAR TEST EQUIPMENT

L. Thomas Carter

National Account Manager

Hamilton Test Systems, Inc.

Windsor Locks, Connecticut

Abstract: Motor vehicles are becoming increasingly more complex as radically new vehicle systems are being incorporated as standard equipment

with each new model year. Government regulation of vehicle performance

is having a significant impact upon the design and maintenance of these

vehicles. Ever-increasing fuel costs are becoming a tremendous incentive to keep vehicles in an optimum state of tune to reduce fuel consumption and minimize pollution. These situations have combined to form a formidable challenge to the automotive repair industry. To meet this

challenge, the automotive repair industry will have to define a revised

approach to vehicle test and diagnostics. Any new approach must be cost

effective, minimize dependence on mechanic's skill and experience while

increasing the quality of diagnosis and subsequent repair; it must be

adaptable to new vehicle systems with minimum test equipment obsolescence; and it must be compatible with Government regulations and provide

acceptable service to the customer. One such approach to vehicle test

and diagnosis, which is described in this paper, involves one piece of

self-contained computerized test equipment - Autosense® - which performs

both the test and diagnosis.

Key Words: Automotive test and diagnostics; vehicle test and diagnostics; automated test and diagnostics.

INTRODUCTION

The present day automotive repair industry is faced with a number of

significant problems. Motor vehicles are becoming increasingly complex.

Radically new vehicle systems are being incorporated as standard equipment with each new model year. These new systems, such as HEI, LeanBurn, EFI, etc., accelerate test equipment obsolescence and worsen the

shortage of skilled mechanics. The availability of skilled mechanics is

also limited by promotion to levels of supervision and lack of adequate

training from the industry.

Government regulation of vehicle performance is also having an impact on

the repair industry. The Federal Government is involved in establishing fuel efficiency requirements for vehicles. When these requirements

are generated, they will require the industry to design and maintain

vehicles specified performance tolerances. Many state governments are already incorporating mandatory vehicle emission and safety inspections

ill
and require that vehicle test equipment itself be designed and certified

in accordance with state law. Some states have imposed requirements for

written records of work carried out during repair of vehicles as a further step to protect the public and improve the quality of vehicle

repair work. In addition, ever-increasing fuel cost is a tremendous

incentive to keep vehicles in an optimum state of tune to reduce fuel

consumption and minimize air pollution. Manufacturing problems, which

result in more recalls and subsequent apprehension by the public toward

vehicle safety and performance, also add to the repair problem.

The new vehicle systems and a trend toward increased maintenance to

obtain better fuel economy and to meet warranty obligations have forced

the repair industry to rely more heavily on the professional mechanic.

The repair industry, in turn, is short of the skilled personnel and

equipment necessary to maintain service quality on the ever-increasing

quantity of new and used vehicles,, The result is an increase in come- back problems and a reduction in vehicle availability.

A NEW APPROACH TO VEHICLE TEST & DIAGNOSIS

One solution to the problems faced by the automotive repair industry

is to define a revised approach to vehicle test and diagnosis. Any new approach must be cost effective (i.e., lower total time for vehicle

service), minimize dependence on mechanic's skill and experience while

increasing the quality of diagnosis and subsequent repair. It must be

adaptable to new vehicle systems with minimum test equipment obsolescence. It must be compatible with Government regulations and provide

acceptable service to the customer.

Conventional methods of vehicle problem diagnosis rely on the mechanic's

automotive experience and his skill to operate and interpret various

pieces of test equipment. The vehicle is tested by the equipment but

it is diagnosed by the mechanic

The new approach to vehicle test and diagnosis, which is described in

this paper, involves only one piece of self-contained computerized test

equipment^- Autosense - which performs both the test and diagnosis.

The Autosense system is the first fully computerized digital automotive

test and diagnostic system. The interaction of mechanic and machine is

simply this:

* Hook Up - The mechanic makes the simple connections to the

vehicle.

* Test - The Autosense system guides the mechanic through a number

of tests and collects and prints the results of each test.

* Diagnosis - The Autosense system interprets the results and

recommends the necessary repairs.

112
* Repairs - The mechanic repairs the vehicle and uses the

Autosense system to help make any required adjustments.

* Quality Check - The mechanic uses the Autosense system to

test the quality of his work and the Autosense unit prints

the results of this check for vehicle records.

The vehicle user will then have a computer printout showing the actual

! test results and specification range for all the tests carried out on

! the vehicle, the recommended repair and the final test results following

repair.

The equipment can be readily adapted to interface with new car and truck

| systems at the user location. Most new vehicle systems and model year

changes can be accommodated by modifying the computer software. These

changes are accomplished by mailing a new cassette tape to the user

' location. This tape, when installed in the machine, will modify the

computer program to enable the Autosense system to test the new model

year vehicles. This ability to reprogram the Autosense computer by

simply inserting a new cassette allows the machine to be easily updated

to take advantage of new diagnostic methodology as it develops.

AUTOSENSE SYSTEM DESCRIPTION

The Hamilton Test System's Autosense system brings to the repair industry a new system designed for rapid and efficient testing of automotive

engine and vehicle systems. It provides for accurate test and diagnostic capability, thus resulting in an increase in customer satisfaction,

and fewer "come backs". The Autosense unit systematically evaluates

problems and identifies repair needs with minimum operator interpretation. The system offers the repairman an efficient, reliable tool, and

the vehicle owner an accurate, printed test report on the vehicle.

The Autosense system utilizes the latest in solid state electronics for

high reliability and it consists of the following subassemblies.

1. Vehicle Instrumentation Harness

2. Autosense Console

3. Hand Held Controller

4. HC/CO Infrared Emissions Analyzer

Vehicle Instrumentation Harness - The connections to the vehicle are

made via the Vehicle Instrumentation Harness. This harness consists of

the basic electrical harness which quickly attaches to 5 points in the

engine compartment and the 4 sensors used to measure current, secondary

voltages and timing. Additional connections and probes are available

113
FIGURE 1. VEHICLE HARNESS CONNECTIONS

111+
for specific tests or diagnostic purposes: e.g., Manifold vacuum, alternators, starters, emissions, etc. The Vehicle Harness Connections are

shown in Figure 1

.

The complete hook up is normally made only when a total vehicle health

check is being run. The basic hook up used for normal problem diagnosis

or post-tune up and quality checks can be made in 1 to 2 minutes.

One of the unique features of the Autosense unit is the current sensor.

It is an easy-to -connect "clamp-around" instrument which senses current

flowing through the wire to which it is attached. It has a computer

selectable range from 0 to 50 amps or 0 to 200 amps. It has a computer

used for measuring low current flows such as lamp circuits or to check

i for leakage current which can inadvertently drain the vehicle battery

I over a period of hours.

Autosense Console - The Autosense Console is a metal enclosure for the

printer, the integrated diagnostic computer unit and the Exhaust Gas

(HC/CO) infrared gas analyzer. It is depicted in Figure 2.

j The printer consists of a Teletype Model 33 typing unit and a call unit.

It receives communication signals from the diagnostic unit and prints the

identification codes and messages on a Vehicle Test Report as shown in

Figure 3. The printout shows the vehicle identification, the test number, the vehicle specifications and the actual test results. Repair

codes are referenced which indicate the necessary corrective action that

should be taken.

The integrated diagnostic unit is a three-bay chassis into which the

system power supply, automatic ignition defeat module, tape cassette

drive module, and printed circuit board assemblies are installed. An

eight thousand word random access memory provides the computer with the

necessary capacity to perform its tests, computation and diagnosis.

Analog signals are received by the integrated diagnostic unit from the

sensors and converted to digital signals prior to processing by the com- puter while the digital signals are processed directly. The signals are

compared with the vehicle's specifications, the results displayed on the

j operator's hand held control unit and printed upon request. All engine

data and vehicle specifications for the over 2000 domestic vehicles

manufactured in the U.S.A. in the last five years are stored on a single

tape cassette. Tape Cassettes are also available for domestic light

trucks and over 25 different makes of imported automobiles. Tape

cassettes are available for domestic vehicles dating back to 1966 and

for trucks and imported vehicles back to 1970. This data is available

to the operator from the computer's memory after he has entered the Autoj mobile Identification Number (AIDN). The AIDN is obtained from the

Hamilton Test Systems supplied AIDN manual which is categorized by

year, make and model of vehicle.

115
Printer

R033 Teletype

Power

Switch Service Light

Emissions

Analyzer

Dual Beam

Infrared

HC/CO

Computer

Control led

Paper

Storage

Computer,

Electronics, and

Tape Cassette

System for

Vehicle

Specification

Storage

FIGURE 2. AUTOSENSE® CONSOLE

116
cratosense

COMPUTER REPORT

TEST RUN ON YOUR VEHICLE

-ffl TEST NUMBER ACCEPTABLE LOW LIMIT YOUR

VEHICLE ACCEPTABLEHIGH LIMIT

AIDN-3010 CH 250A,S6

904 GENERAL HEALTH CHECK

1 12. 1 12.6

14 9. 0 10.5

31 75 74* 100 32 75 86 too

33 75 65* 130

34 75 78 100

35 75 100 130 36 75 86 100

40 540 610 660

51 7. 0 14. 2 16. 0 52 7. 0 17. 3* 16. 0 53 7. 0 15. 0 16. 0 54 7. 0 15.6 16. 0 55 7. 0 16. 7* 16. 0 56 7. 0 16. 8* 16. 0 67 780* 280

68 6. 45* 2.50

50 5. 0 11.0* 7. 0 90 40. 0 47. 5 48. 0 95 12.7 12. 6* 15. 0 7 1 3. 1 8. 0 72 4. 1 8. 0 73 3. 6 8. 0 74 4.5 8. 0 75 3.5 8. 0 76 3. 0 8. 0

0 R/C - BATTERY/ STARTER

114 R/C - TIMING

122 R/C - IGNITION

131 R/C - ENGINE

145 R/C - IGN ITION/CARB

155 R/C - CHARGING

TEST NUMBER

TEST DESCRIPTION

IGNITION OFF

1 Battery Voltage - Preconditioned (Volts) 2 Battery Current Leakage (Amps) KEY ON. ENGINE OFF POINTS CLOSED

3 Primary Ignition Current (Amps)

4 Battery to Ignition Switch - Voltage Drop (Volts)

5 Coil Primary Voltage (Volts) 6 Distributor Point Voltage Drop (Volts) (Electronic Ignition Coil Negative Voltage)

7 Ignition Switch Voltage Drop (Volts) ENGINE CRANKING OR ATTEMPT CRANKING

8 Starter Solenoid/Relay Current (Amps)

9 Starter Cranking Current (Low Limit) (Amps)

10 Starter Cranking Current (High Limit) (Amps)

11 Voltage Drop - Battery to Starter (Volts) 12 Voltage Drop - Battery to Starter Solenoid (Volts) 13 Starter Solenoid Voltage (Volts) 14 Battery Cranking Voltage (Volts) 15 Battery to Coil Voltage Drop (Volts 16 Cranking RPM (RPM)

17 Engine Rotation (RPM) STABILIZED ENGINE CRANKING

18 Coil Output Voitage at Coil (Kilovolts) 19 Coil Output Voltage at Distributor (Kilovolts) 20 Distributor Rotor to Cap Voltage Drop (Kilovolts) 21-28 Spark Plug Firing Voltage (Kilovolts) 29 Distributor Point Dwell (Degrees) 30 Basic Timing-Vacuum Disconnected (Degrees) 31-38 Relative Cylinder Compression (Percent) 39 Ignition Switch Voltage Drop (Volts) ENGINE AT IDLE ACCESSORIES OFF

40

41-48 Curb Idle (RPM)

Cylinder Power Contribution - Fast Idle (Percent) 49 Distributor Point Dwell (Degrees) 50 Basic Timing - Vacuum Disconnected (Degrees) 51-58 Spark Plug Firing Voltage (Kilovolts)

. 59 Coil Output Voltage at Coil (Kilovolts) 60 Coil Output Voltage at Distributor (Kilovolts) 61 Distributor Rotor to Cap Voltage Drop (Kilovolts) 62 Distributor Condenser Test (Counts) 63 Coil Test (Level) 64 Fast Idle (RPM)

65 Low Curb Idle (RPM)

66 Manilold Vacuum (IN HG ) 67 Hydrocarbon Content (PPM)

68 Carbon Monoxide Content (Percent) 69 Headlight Switch Voltage - Any RPM iVolts) 70 Battery to Coil Voltage Drop (Volts) SNAP ENGINE ACCELERATION

71-78 Spark Plug Load Test (Kilovolts) ENGINE AT 2500 RPM ACCESSORIES OFF

80 Timing - Any RPM (Degrees) 86 Hydrocarbon Content (PPM)

87 Carbon Monoxide Content (Percent) 88 Distributor Poml Dwell - Any RPM (Degrees) 89 Basic Timing with Mechanical Advance (Degrees) 90 Total Timing --Basic * Mech « Vacuum Adv (Degrees)

93 Coil Outpul Voltage (Kilovolts) ENGINE AT 2500 RPM ACCESSORIES ON

95 Battery Voltage (Volts) 96 Regulator Battery Voltage (Volts) 98 Alternator Oulput Voltage IVolts) 99 Alternator Output Current - Any RPM (Amps)

R0 «_

Mileage.

VIN »_ .Operator

» INDICATES OUT OF LIMIT CONDITION M INDICATES DATA ENTERED BY OPERATOR

'59465-iF Aulosense is a registered trademark ol United Technoldflies Co'poiatior HAMILTON TEST SYSTEMS

FIGURE 3. TEST REPORT PRINTOUT

117
Hand Held Controller - The hand held controller consists of a lightweight

plastic housing which contains the displays and keyboard. This controller is the means by which the operator and the system communicate with

each other. It is connected to the Autosense console by a 17-foot cable.

This arrangement makes it possible for the operator to conduct tests

from inside or outside the vehicle. The hand held control provides the

operator with a portable meter capable of reading all engine parameters.

The information is displayed in three, 4-digit alphanumeric displays.

Using the hand held controller, the operator is able to call up the

vehicle specification and compare these to the actual test results.. The

unit has 8 light emitting diode (LED) "Status Indicators" which are com- puter driven to automatically step the operator through a sequence of

tests. The Hand Held Controller is shown in Figure 4.

Exhaust Emissions Analyzer - The exhaust emissions analyzer is a nondispersive infrared gas analyzer that measures the hydrocarbon and carbon

monoxide content of the automobile's exhaust gases. The response time

of this analyzer is less than 10 seconds to 90$ of full scale (FS) reading. This response time provides rapid and accurate indication of overall power plant efficiency and makes this system ideal for a quick vehicle check to identify the need for further testing or adjustment and

service. The computer provides the analyzer with automatic zero and

span calibration as well as automatic temperature and pressure compensation. It ensures easier and more accurate operation by the mechanic

because the computer obviates the need for manual "span" and "zero"

adjustments.

AUTOSENSE SYSTEM OPERATION

The operation of the Autosense system is simple and is outlined as follows

:

1. Turn On Power - Initial power turn on causes the computer to

read its operating program from the cassette memory tape, and

carry out the internal self -checking routines to ensure the

Autosense unit is ready for operation. This cycle of tape

read, program load and check takes about 30 seconds and, when

completed, the computer lights the appropriate cue light on the hand held control.

2. Identify Vehicle - To ensure that the correct vehicle specifications are instantly available to the computer, a fourdigit AIDN is entered by the operator to tell the computer to

search the data stored on the cassette tape and load a specific group of specifications into memory. When the desired

specifications are in memory, the computer types out the

vehicle identification and signifies to the operator it is

ready to proceed by lighting the appropriate cue light on the hand held control.

118
Bracket on back for

hooking to steering

wheel , hood, etc

.

Operator instructions and

status indicators to guide

operator through test.

Re ference, test and limit

data displays.

When manual data

is entered, this key

is pressed first if

the data to be entered is negative.

AID, test number, and

manual data

entry key

board.

Pressing

"Start" key

clears all data;

system

requests

new AID

number

Pressing

key advances

printer paper

and al lows

manual data

entry.

Pressing

key clears

all displays;

system requests

new data.

Pressing key

displays high

and low 1 irni ts

.

Pressing key

again returns

data and refer- ence displays.

FIGURE 4. HAND HELD CONTROLLER

119
3. Vehicle Hook Up - The connections to the vehicle specified

in the manual for the particular test sequence are made.

The connections are typically clips to the vehicle coil and

battery, current probe, secondary voltage sensor, timing

sensor, and exhaust probe. The vehicle hook up takes

typically 1 to 2 minutes.

4. Test Sequence - The operator enters the test sequence appropriate to the problem to be diagnosed. The computer will

then sequence the individual tests which it requires the operator to carry out. As each test is completed, the operator

presses the "print" key on the hand held control unit. The

data is stored in the computer's memory and also printed

along with the high and low specification limits on the

Vehicle Test Report.

5. Diagnosis - Upon completion of the printing of the last test

results in the selected sequence, the computer lights the

appropriate cue light and displays the first repair code in

the center display of the hand held control. The operator

presses the "Print" key and prints out all the remaining

repair codes.

6. Repai

r

- The mechanic obtains the parts and carries out the

repairs to the vehicle recommended by the Autosense system.

He then uses the machine to set up the vehicle and make the

necessary post-repair adjustments.

7. Quality Check - After the repairs and adjustments have been

made, the mechanic re-enters the automatic sequence number

and the Autosense unit guides him through the appropriate

tests and prints out the results to verify that the repair

has indeed corrected the vehicle's problems. This automatic

sequence feature of the Autosense system ensures a uniform

high quality of testing and diagnosis and removes the variations that can occur with different operators. The Autosense

unit rapidly trains and improves the discipline of the mechanics. It increases the rate at which a skilled mechanic can diagnose and repair vehicles. It further has the advantage

of providing a hard copy of the result of the tests conducted

on the vehicle and evidence of it being within. recommended

performance levels after the repair work is completed. This

feature is significant in preparing shops to comply with

legislation which requires written evidence of work carried

out and improving their vehicle maintenance record keeping.

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TABLE 1

USES OF THE AUTOSENSE SYSTEM

TUNE UPS

PERIODIC ROUTINE MAINTENANCE

CUSTOMER COMPLAINTS

PRE-DELIVERY VEHICLE PREPARATION

USED CAR PRE-SALE PREPARATION

SELECTIVE MAINTENANCE

INVENTORY & COST CONTROL

FUEL ECONOMY ADJUSTMENTS

121
USES OF THE AUTOSENSE SYSTEM

The typical ways in which the Autosense system is being used are listed

in Table 1. The use of the Autosense system for tune up or regular

maintenance checks in a typical 2 or 3 bay garage or specialty shop ensures that rapid, accurate tune ups are completed and enables the

vehicle to be returned to the owner with the assurance that the work

has been correctly done. It further provides a printout of the data

which the owner can review.

When used as a troubleshooting device to attack specific complaints,

the Autosense unit ensures rapid identification of the vehicle problem

and the necessary repair, and can provide hard copy proof of the vehicle

condition after the repair has been carried out. This ensures fewer

comebacks for unsatisfactory service as it provides evidence at the

time of vehicle pick up of satisfactory completion of work.

The use of the Autosense system as a predelivery vehicle checking

system by both dealerships and fleet or rental companies to ensure

the satisfactory condition of a vehicle before the new owner or renter

picks it up is expected to increase sharply in the next year. Already

many Autosense users are taking advantage of the ability to completely

check out a used vehicle and provide hard copy evidence which is

displayed in the vehicle on the sales lot to show that it has been

properly serviced and meets recommended specifications. This gives

the prospective purchaser confidence that the vehicle he or she may be

considering buying is in satisfactory condition.

Because the Autosense system also indicates which parts are good, arbitrary parts replacement is eliminated. The use of the Autosense system

for selective maintenance, therefore, reduces parts usage and labor

hours because you replace only those parts that need to be replaced.

The Autosense printout becomes a valuable tool not only in quality control but also for the monitoring of parts and labor hours for maintenance managers.

In addition, many vehicle owners are losing money due to unnecessary,

poor fuel consumption. The Autosense system acts as a unique qualifier

in that its regimented nature allows for detection of problems normally

missed by mechanics using conventional equipment. Even as low as a 5%

fuel consumption improvement can mean savings of thousands of dollars

per year to fleet operators.

There are now many Autosense units in the field both in the United

States as well as many other parts of the world. Dealerships, Service

Stations, Repair Garages, Diagnostic Tune Up Centers, Specialty Shops

(tires, mufflers, etc.), National Corporations/Fleets, State/Municipalities, Federal /Mil itary, Universities and others are the categories of

users that have put the Autosense system to profitable use in their

operation.

122
AUTOS ENSE SYSTEM USERS

One of the major Autosense system users in the United States is Avis

Rent A Car. Since last June, Avis has been using 30 Autosense systems

at 21 of its service centers across the United States. As stated in an article which appeared in the June, 1978 edition of Automotive Fleet

Magazine, the results after less than a year point to substantial

j reductions in maintenance costs and customer complaints.

At the maintenance centers where Autosense units have been installed,

Avis uses them chiefly to_evaluate new cars being delivered by dealers

and manufacturers. From this experience, Avis has learned that no less

than 40-percent of its new cars fail to meet specified requirements.

The Autosense system allows Avis to get their new cars fixed before

they send them out on the road, and it also has given them leverage

in going back to the dealers to point out what's wrong with the cars.

Periodic maintenance is Avis' second priority in its use of the Autosense system. Using figures from the company's Chicago service center,

85-percent of the cars that received an Autosense evaluation when they

were new were able to pass a mandatory 7,000-mile maintenance check.

! Previously, only 30-percent of the Chicago Fleet could pass the test.

To the fleet owner this, quite simply, means more cars on the road generating more revenue.

Besides using Autosense units for periodic maintenance, Avis has also

instructed its mechanics to use the system as often as they can for un- scheduled curative maintenance.

Finally, Avis uses the Autosense system in evaluating vehicles being

sold to the general public under its "Young Used Car" program. Avis

currently sells about 50-percent of its domestic auto rental fleet a?

part of a fleet recycling program. On the cars being inspected, the

Autosense system helps them guarantee that the used cars they are

selling are in excellent mechanical condition.

j Initially, Avis field-tested five Autosense units at service centers in

i four cities: New York, Philadelphia, Chicago and San Francisco. The

j three-month evaluation was completed successfully, and the additional

units were delivered to maintenance centers throughout the country and

integrated into the Avis Car Care program.

In New York, Avis also has an Autosense unit in a small van that moves

among several area service centers that don't have Autosense units of

their own. In that way, service personnel aren't forced to waste time

i driving to Avis' main service center in Queens for a diagnostic test.

The van also exposes more mechanics to the Autosense system, which Avis

considers to be an effective training and motivational tool.

Cost-effectiveness and improved fleet utilization continue to be Avis'

prime considerations.

123
Figure 5 depicts a mechanic using an Autosense unit to check out a car

at one of Avis' fleet maintenance centers.

FIGURE 5. AVIS FLEET MAINTENANCE CENTER

Another major Autosense user is the Canadian Armed Forces (CAF). CAF

procured commercial 1-1/4 ton trucks for their fleet in late 1974.

These vehicles incorporated a High Energy Ignition (HEI) system as well

as some military options. Seyeral unforeseen maintenance problems oc- curred with these vehicles. An in-depth study of in-house CAF test equip-!

ment indicated that the CAF test equipment inventory was obsolete inso- 1 far as HEI systems were concerned. An evaluation of commercially

available test equipment was conducted and all except the Autosense

system fell short in the areas of prime importance to the CAF. A

field trial was authorized to determine the appl icabil ity of Autosense

to other vehicles in the CAF inventory and to determine the best method

of employing the Autosense unit in the field and base environment. As

a result of the favorable field evaluation, a contract was signed for

procurement of 58 Autosense systems in early 1978 with delivery of

systems to commence in March, 1978, training to commence in April 1978

and initiation of fielding the Autosense systems in May 1978.

At the time of this writing, the fielding of Autosense units is about

90% complete. The CAF, as stated in a technical paper entitled "Vehiculai

Automatic Test Equipment for the CAF" and presented at the AUT0TESTC0N

'78 meeting, believes that a comprehensive and valid assessment of the

introduction and employment of the Autosense system can be made only

after at least two years of use. However, some positive trends are already starting to develop and were reported in that paper as follows:

12k
a. Parts Savings - The time honored use of parts to diagnose

faults has been largely stopped where the Autosense system

is employed. Parts replacement is expected to rise initially

as the machine diagnosis identifies unsatisfactory parts

that could not otherwise be detected. However, after all

vehicles have been initially checked and brought back to

recommended specifications, the rate of parts replacement

is expected to drop and fuel consumption reduced.

b. Labor Saving - The accurate and very quick diagnostic action

of the Autosense system was immediately obvious to all who

saw and used it. The machine has yet to be proven wrong in

any of the operations witnessed by the fielding team or any

of the base maintenance supervisors with whom results have

been discussed. Each base had vehicles which did not run well or had a peculiar failure that defied diagnosis. Some of

these cases had been present for several years. In every

case, the machine diagnosed the problem within twenty

minutes of start and the problem was resolved by either

an adjustment or replacement of a small part.

c. New Tools - The Autosense system has an inherent ability

to correlate engine subassembly functions that cannot be

demonstrated by any other means. In particular, the relationship of carburetor balance, exhaust emissions and fuel

consumption cannot be grasped much less controlled without

this equipment. Mechanics have not had a tool that diagnosed

engine functions when the motor is running at high RPM or

the engine is hot. Senior technicians have come to realize

that they have a new tool for better performance, while it serves as a very useful training instrument for junior tradesmen.

d. Acceptance - The Autosense system has been received

very well in all but isolated instances. All service

personnel and civilians employed by the Department of

National Defense (DND) maintenance system who are forward thinking and confident about their trade are delighted to have a new and sophisticated piece of

equipment that moves auto mechanics into the "twentieth

century" as one senior foreman exclaimed. This attitude

runs right through the rank structure from Corporal to

Colonel and includes the conversion of many skeptics.

125
FUTURE DEVELOPMENTS

The basic design philosophy of the Autosense system was to construct a basic unit which is capable of being expanded by the addition of both

software and hardware packages to interface with new vehicle systems and

different types of vehicles. New software packages are available annu- ally to update the machine to interface with the new model year vehicles.

These packages are in the form of cassette tapes and amendments to the

Operator Manual. They are mailed to the user facility for the user to

install in the Autosense console. New hardware features are also being

made available to take advantage of improvements in diagnostic information available from on-board sensors. These features speed up the

operation of vehicle diagnosis and simplify the mechanic's task of

connecting to the vehicle.

With the ease of expansion provided by the basic Autosense system construction, we have also easily provided custom systems to meet particular

customer requirements. These custom systems have improved operational

characteristics which tend to maximize the economic return to their

users.

i

126
SESSION III

MARINE APPLICATIONS

Chairman: Raymond A. Coulombe

Naval Ship Engineering Center

Co-chairman: Rudie Hohenberg

Mechanical Technology, Inc.

THE ACOUSTIC VALVE LEAK DETECTOR

A NEW TOOL FOR FLUID SYSTEMS MAINTENANCE

Joseph G. Dimmick and Joseph W. Dickey

Propulsion and Auxiliary Systems Department

David W. Taylor Naval Ship R&D Center

Annapolis, Maryland 21402

Abstract: The operations, limitations and successful appli

cations of a portable, non- intrusive instrument currently

in use by the U.S. Navy to detect internal leakage through

shipboard steam, water, hydraulic and high-pressure air

valves are described. The Acoustic Valve Leak Detector

(AVLD), developed by the David W. Taylor Naval Ship R&D

Center, listens for the ultrasonic emissions characteristic

of internal valve leakage. The AVLD is being used for

troubleshooting, for overhaul planning, and in a systematic

preventive maintenance monitoring program.

Key words: Preventive maintenance, Failure detection,

Acoustic emission

Introduction: Work on the Acoustic Valve Leak Detector

(AVLD) began in November 1973* One year later, the first

prototype was delivered to a repair ship for field evaluation. Following the success of the first instrument,

several more were built and delivered to other repair ships

Later models incorporated evolutionary changes developed on

the basis of practical experience. Originally developed to

detect leakage through large seawater ball valves, the AVLD

has been successfully used to detect leakage through valves

in a variety of fluids in shipboard and shore installation

piping systems. Additional research and development are

being conducted to extend the concept to include measuring

as well as detecting internal valve leakage.

The Acoustic Valve Leak Detector is a portable, non intrusive instrument developed by the David W. Taylor Naval Ship

R&D Center in response to a requirement for an instrument

which would reduce the need for opening piping systems to

inspect valves. Applied in a systematic preventive mainten

ance program, the AVLD has begun to reduce the number of

costly and time-consuming inspections previously required.

Savings have also resulted from its ability to detect small

leaks before they become large enough to necessitate more

129
expensive repair procedures. The AVLD has proven effective

for troubleshooting by identifying the leaking valves in

parallel arrangements where it is not normally possible to \ determine which valve is leaking. It has also been used by

naval shipyards to identify ship valves requiring repair

during scheduled overhauls.

The AVLD listens for the ultrasonic acoustic emissions

characteristic of internal valve leakage. Transducers are

attached to the valve and connected to the AVLD. Types of

fluids to which the instrument has been successfully applied

include steam, water, hydraulic oil and high-pressure air.

Since the transducers are attached to the outside of the

valves, the time and expense of dismantling the valves or

removing them from the systems are eliminated.

The purpose of this paper is to introduce the Acoustic Valve

Leak Detector to potential industrial users. The underlying

theory, principles of operation and circuit design are

briefly described. Specific examples of some successful

applications of the instrument are described in detail,

including performance limitations. The preliminary results

of some current research and development are summarized.

Conclusions and recommendations with regard to performance

and industrial applications are presented.

Background: The U.S. Navy is attempting to extend the time

between major overhauls of ships, while simultaneously reducing repair costs and improving the material condition of

operating ships. To achieve this objective, there must be

instruments and procedures available which are able to

identify maintenance problems in their incipient stages and

to establish a record from which it may be concluded confidently that a ship should be continued in service beyond

its formerly scheduled overhaul date. By following a

similar program, aircraft industries have increased the

interval between scheduled disassembly, inspection and

remanufacture of commercial airline engines from a few

hundred to several thousand operating hours.

"Open-and- inspect" procedures are expensive and timeconsuming, especially if the equipment is complex or relatively inaccessible. There is also the risk of damage or of

introduction of contamination. Another disadvantage is the

fact that equipment or systems must be taken out of service

for the duration of the inspection. High standards of

quality assurance add to the cost and duration of such procedures. Opening and reclosing are often the major time

and cost factors, and these factors are wasted if it is

found that no repairs are required.

130
Ships operate at sea for several months, followed by an

upkeep period of a few weeks. During the upkeep period,

inspection, repair, reprovis ioning, and post-upkeep sea

trials take place, followed by another period at sea. Since • there is a limit to the amount of work that can be done

during the upkeep period, it is important to concentrate the

limited repair resources on those systems and equipment that

actually need repair. Equally important is the ability to

conclude that the other equipment is not in need of repair

before the ship returns to sea.

A typical ship has several hundred valves, holding various

fluids at pressures up to several thousand pounds per square

inch. Many are welded in place, and most are difficult to

remove because of the cramped quarters. There are many

valves for which the removal, inspection, replacement and

quality assurance costs exceed $50,000 per valve. Although

most valves are not in that category, large savings are

realized each time it is determined that a valve does not

require repair, or leakage is detected while it is still

possible to repair the valve in place.

Major shipyard overhauls present another opportunity for

savings. They are performed at intervals of several years

and require a year or more to accomplish. Shipboard surveys

that identify leaking and non-leaking valves prior to the

scheduled overhaul provide a rational basis for scheduling

and budgeting. The surveys also ensure that repair time,

labor and parts are not wasted on valves that are already

in working order.

Thus, the decision to develop the Acoustic Valve Leak

Detector was made on the basis of a need for a non-intrusive,

portable instrument to support a systematic preventive

maintenance monitoring program for fluid valves.

Sources and Distribution of Sound in a Piping System: Sound

source mechanisms in a leaking valve and piping system may

be classified as follows:

m Unsteady flow (turbulence)

„ Cavitation

m Flashing of liquid to vapor

« Mechanical movement of parts

Although each source mechanism is treated separately, it

must be understood that the generating mechanisms themselves

interact and that the total acoustic emission generated is

therefore a sum from all sources.

131
In addition to the noise source itself, the amplitude and

spectral distribution of the acoustic emission signal are

further influenced by: (1) the transducer's sensitivity and

spectral response; and by (2) cavity and mechanical resonances in the valve and its associated piping.

The various source mechanisms are not well covered in the

literature and there has been little reported work analyzing

the effects of temperature, vapor pressure or other physical

characteristics which have been found important to some

aspects of this work. Although the following discussion of

leakage sound sources are necessarily brief, the attention

of the interested reader is invited to reference [l] , wherein the theory is treated in greater detail.

Fluid Dynamic Sources: Sounds are end products of the decay

of turbulent eddies created just downstream from the orifice

which is causing the leak. The acoustic power generated by

turbulence in a fluid is given by the following equation. [2]

A2

Acoustic Power = p — (1)

where P is the fluid density, c the sound velocity in the

fluid and i is a characteristic length of the system bounded

by the orifice size and the downstream pipe diameter.

Since the extreme values for -l are unchanged with pressure,

a lower limit to the frequency spectrum expected from fluid

dynamic noise can be estimated by taking I to be the downstream pipe diameter and using the following values for the

frequency:

3 kHz for gas

frequency = -j 15 kHz for water (2)

12 kHz for oil

Cavitation Sources: Cavitation in a liquid will occur whenever the local pressure drops below the vapor pressure for

the liquid or for any dissolved gas in that liquid. The

degree to which cavitation occurs in leakage through an

orifice is directly proportional to the pressure across the

orifice and inversely proportional to the difference between

the local static pressure and the sum of the partial pressures of vapors and dissolved gases. The acoustic power

radiated by cavitation resulting from flow through orifices

is generally taken to be proportional to the square of the

pressure drop across the orifice. [3

J

132
(For both water and hydraulic fluid, there is experimental

[evidence [l] to show that cavitation often occurs under the

'fluid conditions found in many piping systems. There are

I very little data on the dissolved gas content or vapor pressure of water or hydraulic fluid at a valve. This, coupled

iwith the fact that the theory cannot handle real (impure)

i liquids such as tapwater, seawater and hydraulic fluid,

j suggests that the previously reported [lj observations be

I accepted. It was observed that cavitation occurs very

I irregularly in the seawater valves at 7 psi and leaking to

| atmosphere; and that cavitation usually does occur for

j hydraulic valves leaking to pressures which are lower than

j system backpressure (the pressure at which the fluid has

been stored in the sump, normally above atmospheric pressure).

However, it was observed that cavitation usually does not

occur for hydraulic valves leaking to pressures substantially

above the system backpressure. At system backpressure,

cavitation in hydraulic valves is very erratic.

Flashing Sources: The flashing of pressurized water to steam

as it leaks through a valve is known to be a very noisy process, but no information has been found regarding the

intensity or frequency distribution from this source, nor has

it been experimentally observed in this work. It is expected

to be broadband and very intense since the energy associated

with the phase transition is many (about eight) orders of

magnitude greater than that of turbulence under typical steam

plant conditions.

Mechanical Sources: Mechanical sources in leaking valves

arise from pressure fluctuations that pass from the fluid to

the valve, rattles of loose parts of the valve, and modification of the sound field due to cavity resonances. Valve

rattle has not been observed, but occasional inadvertent

metal-to-metal external contacts are easily identified,

indicating that rattles would be easily detected by the AVLD.

Equipment Description: The Acoustic Valve Leak Detector

monitors leak-associated acoustic energy in the frequency

range of 10 kHz to 100 kHz. This frequency range was chosen

because there is significant energy emitted by leaky valves

in this range and because acoustic energy in this range is

strongly attenuated with increasing distance from the source.

Therefore, background noise often can be electronically

separated from the signal. The detector permits the operator

to observe the acoustic energy density as an analog meter

reading or to listen to it on headphones. The audio output

is derived from the ultrasonic frequencies by beating the

input with a controlled frequency oscillator and amplifying

the resulting beat frequencies for the headphones. The

133
internal reference oscillator may be swept automatically or

held at a fixed center frequency of 25 kHz. Two outputs are

provided to permit recording the acoustic amplitude versus

frequency on a standard X-Y plotter.

The acoustic signals are obtained by temporarily attaching

commercially available piezoelectric transducers to the valv

or nearby piping. Since the transducers are attached to the

outside of the valves, the time and expense of dismantling

the valves or removing them from the systems are eliminated.

The detector unit is of all solid-state construction and fit

in a small case about 18 cm (7 inches) high by 2j5 cm (9

inches) wide by 25 cm (10 inches) long. The entire instrument, with all accessories stored in the case cover, weighs

less than 7 kg (15 lb). Two transducers, a set of headphones and a detector unit are shown in Figure 1. Other

accessories, which will be described separately, include

transducer holders, transducer standoffs, mounting discs, and

a hand-held probe. The case, when closed, is watertight and

buoyant. Power is supplied by rechargeable 6-volt batteries

Figure 1 - Acoustic Valve Leak Detector, Model C

Electronic Construction: The detector unit, which is mounted

in the bottom half of the case, is covered by the controls

and displays on the front panel. A functional block diagram

151+
of the detector unit is shown in Figure 2. Electrical

signals from each transducer are fed to preamplifiers

through coaxial cables. Signals from a local oscillator and

from one of the preamplifiers are then fed to a mixer stage

via a high-pass filter which eliminates low-frequency structureborne noise. The mixer stage outputs, which are the

differences between the amplified transducer signals and the

local oscillator signal, are in the audio spectrum. This

heterodyne technique allows the operator to hear a representation of the ultrasonic acoustic emissions on the earphones. The amplitude of the audio signal is also displayed

on the analog acoustic amplifier meter located on the front

panel.

TO PHONES

REFERENCE

VOLTAGE FIXED 1

RAMP SWEEP f

GENERATOR

OSCILLATOR

TRANSDUCER

B

METER

TO PHONES

Figure 2 - Acoustic Valve Leak

Detector Block Diagram

An amplitude output is provided to drive an X-Y plotter with

a d-c voltage proportional to the average rms value of the

input energy in a selectable bandwidth of ±J> kHz or ±10 kHz,

with a center frequency selectable from 10 kHz to 100 kHz

or from 20 kHz to 200 kHz. The frequency output provides a d-c voltage proportional to the center frequency of the

amplitude output. In the sweep mode, a voltage ramp drives

the variable control local oscillator over the required 10:1

range in approximately 30 seconds.

Power is supplied at ±12 volts from four series-connected,

sealed, 6-volt, lead-acid storage batteries. The detector

135
unit draws 60 ma and will operate continuously for 8 hours

on a 16-hour charge.

The electronics are mounted on two printed-circuit boards

located in the bottom half of the case along with the

batteries and charging transformer. Rectifiers and the

battery charging control circuits are mounted on the power

board. The preamplifiers, ramp circuit, local oscillator,

mixers and the audio amplifier are mounted on the main

printed circuit board.

Front Panel: All of the controls, connectors and displays

required to operate the detector unit are mounted on the

front panel. Two input attenuators, one for each channel,

each with 12 fixed steps of 5 ^B per step provide a maximum

of 60 dB attenuation to allow adjustment to the noise levels

present. The function selector is a rotary switch which

selects the input to the local oscillator. The sweep/reset

toggle switch starts and resets the voltage ramp to the local

oscillator when the sweep mode is selected. Either channel

may be monitored on the headphones. The volume control

adjusts the amplitude of the signal to the headphones. The

on/off power switch must be in the off position to allow

battery charging with the a-c power cord connected. The

battery test toggle switch allows the front panel meter to

momentarily monitor the battery condition. The test switch

applies power to an internal noise generator for a complete

system self-test without any additional test equipment.

Accessories: The transducer used with the AVLD is an Endevco

Model 2217E, and suitable headphones are available from

numerous manufacturers. Several unique accessories have been

designed to improve the means of acoustically coupling the

transducer to the pipes or valves. The devices include a

clamp for hands-free operation, a standoff for thermal protection of the transducer, and a hand-held probe. Basic to

all is a ball-and-socket connection which allows repeatable

acoustic coupling to be obtained reliably without requiring

accurate or even steady alignment.

Figure 3 shows a socket and a transducer attached to a standoff. The end of the standoff is a half-inch diameter ball

which fits the spherical indentation in the socket disc.

The standoff, which is a 3/8-inch drill rod with a 1/2-inch

ball bearing welded to one end, is attached to the transducer by a threaded mounting stud. The socket disc may be

epoxy-bonded to the valve to be tested, or it may be held

by a spring to the ball end of the standoff, forming a handheld probe, as shown in Figure 4. Note also the threaded

mounting stud for attaching the transducer.

136
Figure 3 - Mounting Disc, Standoff and Transducer

\J jtflTll - nn.il. r i ,

,

,

Figure 4 - Hand-Held Probe Parts

The circumferential groove around the socket disc is for

holding the disc to the standoff rod by means of the spring

shown in Figure 4, or for clamping the transducer to the

epoxy-bonded socket disc shown in Figure 5* The transducer

holder shown in Figure 5 uses a coil spring to clamp the

transducer to a socket disc which has been epoxy-bonded to

the test piece. When used as shown in Figure 5# a sector

of a 1/2-inch sphere is bolted into the face of the transducer to provide the ball portion of the connection. In all

cases, a small amount of acoustic coupling compound is

applied between mating metal surfaces.

137
Figure 5 ~ Transducer Clamped

to Mounting Disc

Operation: Due to the large variety of fluids, valves and

fluid conditions, it is considered important, at this point

in the program, to have trained operators conduct leak checks

In some Navy applications where a large number of identical

valves are to be checked, the breadth of experience required

to interpret properly the results is much less. Most of the

leakage detection programs are still in the stage where baseline data for specific valve and fluid types are still being

gathered and plots of acoustic amplitude versus frequency

are still being correlated with independent leakage rate

measurements where possible.

Basis for Detection: Useful frequency ranges for leakage

measurement were determined from measuring the acoustic

138
emissions of various valve and fluid combinations at ultrasonic frequencies up to 1 megahertz. It has been found that

leakage noise is generated from audio frequencies up to

I several hundred kilohertz. The signature depends on fluid

type and pressure, leakage rate, and valve type and condition.

The AVLD was designed to reject frequencies below 10 kHz

(because high levels of structureborne noise in most systems

' gave a poor signal-to-noise ratio there, and to reject

j signals above 200 kHz because in most systems the signal

levels in this range became quite small.

Normally, two transducers are employed for detection. One is

placed on the valve or adjacent piping to pick up leakageI generated noise which will be mixed with structureborne backI ground noise and the second is located either upstream or

! downstream of the valve to pick up structureborne noise only.

I This process is illustrated by Figure 6, which shows typical

signatures obtained from a leaking seawater ball valve. To

the extent that the leakage generated noise is attenuated by

the time it reaches the background transducer, and the

structureborne background noise is the same at the two transI ducer locations, the subtraction of the two signals will

j result in the leakage noise only.

LEAKAGE SIGNATURE BACKGROUND

Figure 6 - Basis for Detection

139
Attaching Transducers: The location and method of attachmen

of transducers depends on the nature of the application. if

the surface of the pipe or valve is hot (above 177° C), as

is the case with steam valves, the standoff must be used.

The hand-held probe with attached socket disc is especially

helpful for determining the most sensitive location for

attachment of epoxy-bonded discs. Its use is illustrated by

Figure J.

Figure 7

_ Use of HandHeld Probe

To detect leaks in a typical seawater ball valve, a mounting disc should be epoxy-bonded to the downstream side of

the valve to be checked. Additional discs should be

attached, one each, approximately 30 cm upstream and downstream of the respective flanges, as illustrated by Figure

8, when noise is present. As with any bonding process, it
is necessary to have the surfaces clean and free of anylagging, dirt or grease. The epoxy should be applied

smoothly and evenly to the disc to eliminate air gaps. The

epoxy should then be squeezed as thin as possible to assure

metal-to-metal contact at the center of the disc for good

acoustical coupling. Take care that the epoxy does not

enter the groove on the side of the disc.

_m_

TRANSDUCER "A" TRANSDUCER "13" \ABOUT TO BE PLACED IN THE DOWNSTREAM POSITION UPSTREAM POSITION FOR TRANSDUCER "8 7

30 cm OR MORE

FLOW

Figure 8 - Typical Transducer Locations

With the mounting discs in place, the transducers may be

clamped to the disc as shown in Figure 5/ or tne ball end of

the standoff shown in Figure 3 may t* e hand-held against the

socket in the mounting disc. The ball-and-socket connection

between the rod and the disc makes the acoustic measurement

independent of the angle between the rod and the disc. In

all cases, small amounts of coupling compound should be

applied to the transducer-rod, rod-disc, or transducer-disc

interfaces as appropriate to insure good acoustical coupling,

Interpreting Results: A complete system self-test, which

includes cables, transducers, detector unit and X-Y plotter

should be conducted at the beginning of each day's work,

using the internal noise source. Each test begins with a

determination of the transducer sensitivity (a partial selftest), followed by a measurement of the meter offset. The

transducer test uses the internal noise generator. Meter

offset at zero input attenuation with no signal present is

then recorded for comparison with later readings.

The next step is to determine if significant background

noise is present. This is done by attaching transducer A,

as shown in Figure 8, and decreasing the attenuation until

ikl
mid-scale meter deflection occurs with zero differential { pressure across the valve. The attenuation and meter readingl

are then recorded for comparison with readings to be taken i with normal differential pressure across the valve. If, with!

normal differential pressure across the valve, the meter

reading and attenuation setting indicate a signal above the

background noise level, it may be concluded that the valve

is leaking. If the results of the single-transducer procedure are inconclusive, both transducers and possibly the

j X-Y plotter will have to be used to determine if the valve

is leaking.

I The next step is to attempt to electronically separate the j background noise from the leakage signal, using the differ- f ential (A-B) function of the detector unit. Transducer B ) is first tested in the same manner as described for trans- I ducer A. Then, transducer A is moved to the upstream mount- 1 ing disc, and then to the downstream mounting disc, recording)

the signal levels observed, to determine which mounting disc

is nearest the dominant background noise source. Using the

attenuator controls and the panel meter, the signal levels

from both transducers successively placed at the mounting

disc nearest the dominant background noise source are matched

to compensate for differences in transducer sensitivity.

With the input selector in the "A-B" position, the A transducer is placed on the valve flange, and the panel meter

levels are recorded with the B transducer placed first upstream and then downstream. If a positive meter deflection

is observed at both the upstream and downstream locations

for the B transducer, or if there is a positive deflection

at one location and zero at the other, it may be concluded

that the valve is leaking. If zero deflection occurs at

both locations, it may be concluded that the valve is not I leaking. If a negative deflection (meter pegged below zero)

is observed at either location of the B transducer, the

situation is still ambiguous and a spectral plot must be made.

If, having recorded the amplitude versus frequency spectra

with the X-Y plotter, it is observed that the signals are

higher with normal differential pressure applied than with

zero differential pressure, it may be concluded that the

valve is leaking. If no differences are observed the results i remain inconclusive unless some way can be found to reduce

the background noise level to obtain a more positive indication. However, experience with shipboard systems indicates

that inconclusive results are rare.

I

I

lh2
Application Experience: U. S. Navy experience with the

Acoustic Valve Leak Detector has been of three distinct

types

:

m Monitoring programs for preventive maintenance

* Laboratory work

• Emergent applications

The AVLD is in general use by trained survey teams at several

shipyards and onboard submarine tenders, on both coasts and

at overseas bases. It is being used to detect leaky valves

as part of systematic preventive maintenance monitoring programs and for overhaul planning, scheduling and budgeting.

The survey teams are often called upon to determine which

of two or more parallel-connected valves are leaking, to

save the time and expense of removing or dismantling all of

the suspected valves. Although most experience in this

category has been limited to valves for water and steam, it

is planned to expand the systematic survey programs to

hydraulic and compressed gas valves also.

Experience has been gained under controlled laboratory conditions with water, steam, hydraulic and compressed air valves.

Most of the laboratory work has been done in connection with

a research and development program to extend existing detection technology to provide a leakage rate measurement capability. With a leakage rate measurement capability, it will

be possible to establish repair priorities and to support

long-term trend monitoring programs.

As a result of the increasing availability and acceptance of

the AVLD, several requests have been received to explore

other applications. Laboratory work has been found necessary

to confirm field results in some cases, but initial results

have often been good enough to support expansion of existing

systematic survey programs to include additional valves and

fluids

.

Water Valve Experience: The original purpose for the

Acoustic Valve Leak Detector was to detect leaks in seawater

ball valves of 4- to 12-inch diameters. In this application,

the differential pressures across the valves to be leakchecked are in the 5~7 Ps i range. Leaks are caused by marine

fouling on the ball, by wear of the resilient seats and by a

combination of corrosion and erosion between the seats and

the valve body. Small leaks tend to remain small for long

periods, but there is a threshold in the range of several

hundred milliliters per minute per inch of pipe size, beyond

which leakage rates tend to increase rapidly. The AVLD is

not normally capable of differentiating between ball-seal or

seal-body leaks.

Ik3
Since the AVLD can detect leaks of a few hundred milliliters

per minute consistently, periodic leak checks have made it

possible to identify leakers while it is still easy to repair

them by simple replacement of seats. Time and budget constraints make it impossible to repair all of the valves in a

ship at one time except during a regular shipyard overhaul.

Use of the AVLD makes it possible to maintain the piping

systems in a high state of readiness by concentrating the

limited repair resources on the few valves that actually

need repair at a given time. The systematic monitoring and

preventive maintenance program is resulting in a yearly

maintenance savings of tens of thousands of dollars per ship.

A typical troubleshooting application of the AVLD is illustra

ted by Figure 9* Without the AVLD, it might have been

necessary to dismantle and inspect nine large valves. In

the example shown, a few minutes work with the AVLD eliminated two-thirds of the time and labor which would otherwise

have been required.

Figure 9 - Example of Leak Detector

Application on Ship

Ikk
With the epoxy-bonded discs in place, it takes less than

2 minutes to determine if a valve is leaking, even if it is

necessary to make a spectral plot. In this application,

spectral plots are seldom required. A comparison of meter

readings at a center frequency of 25 kHz is usually sufficient for leak detection.

In the course of laboratory experiments [l] undertaken to

determine what characteristics of the acoustic emission were

related to leak rate, large variations were observed in the

amplitude of the acoustic emissions of leaking seawater ball

valves. No means were found to measure by acoustic emissions

the leakage rate through the seawater ball valves at constant

differential pressures in the 5~7 psi range because the variations in the acoustic amplitude were so large, but leakage

rates of a few hundred milliliters per minute were consistently detectable.

It was observed that the large variations in acoustic amplitude were caused by several phenomena loosely related to air

coming out of solution from water that had become supersaturated with dissolved air due to the pressure drop across

the leaking valve. It was concluded that means must be

found to predict, measure or control those phenomena before

leakage through seawater ball valves <. can be measured acoustically at differential pressures of 5

_7 psi. [ l]

On the basis of the experiments at low differential pressures,

it has been hypothesized that the 5~7 psi range is at or near

the lower limit of detectable differential pressures and that

higher differential pressures may produce acoustic emissions

more consistently related to leakage rates. Experiments to

test this hypothesis, using differential pressures up to 200

psi, are still in progress.

Shipboard surveys of water valves at even higher differential

pressures are also in progress. Although there is good confidence in the initial results, the valves suspected to be

leaking have not been examined internally and there are no

other means to detect leakage while the valves remain in

place.

Steam Valve Experience: Shipboard and laboratory experience

indicates that steam valve leaks are easier to detect than

water valve leaks. There are at least three factors which

contribute to the ease of detecting steam valve leaks:

• High pressures

• All-metal construction

• Low background noise

1U5
The relatively high differential pressures across a typical

leaking steam valve increases the acoustic power and frequency range of the noise source. The all-metal construction

(no resilient seats) results in low transmission losses

between the noise source and the point of transducer attachment on the valve body or valve stem. Background noise is

seldom a problem with steam piping systems. The signal-to-

(background) noise ratio for steam valves is further

increased by lagging which tends to damp structureborne noise

from other sources.

Another important consideration is that many shipboard steam

systems are at least doubly redundant. This means that in

case of doubt, it is often possible to compare the acoustic

signatures of two ostensibly identical valves in identical

service.

Because of redundancy requirements and other reasons, shipboard steam valves are often connected in parallel. Before

the introduction of the AVLD, steam leaks detected or suspected through other means were often impossible to attribute to a single valve. The AVLD is usually capable of

determining which valve is not leaking, thereby saving the

time and expense of removing or dismantling it. In the case , of large stop valves paralleled by much smaller warmup valves,

valve size must be considered in drawing conclusions. The

signatures of the large valves must be compared with the

signatures of the bypass valves and other large valves. If

the large valve signature is greater than the small valve

signature, it is reasonable to conclude that the large valve

is leaking. However, if the small valve is leaking also,

its signature will often be greater than the signature of

the large valve. In general, very large signatures from

large valves indicate large leaks, and very small signatures

from small valves indicate no leakage.

In attaching the transducer, it is sometimes necessary to

remove a small amount of lagging; however, in valves where

the stem connects directly with the noise source the exposed

valve stem is often a good point of attachment. Because

steam and piping temperatures exceed the temperature limits

of the transducer, it is necessary to use the standoff,

usually as a hand-held probe, as illustrated by Figure J.

Once the best locations for the transducers have been identified, it is possible to leak-check steam valves, including

poppet-type turbine throttles at the rate of about one valve

per minute.

The original purpose of systematic valve surveys was to

increase overall system operating life, reliability and

lk6
availability by determining where to concentrate limited

maintenance resources. Subsequently, requirements for

reduction of energy consumption have led to proposals to use.

the AVLD to minimize energy losses.

Laboratory experience with the AVLD indicates that it is

feasible to measure leakage rate through steam valves. However, since there is evidence that small steam leaks grow

! rapidly, a decision was made to abandon that effort in favor

of development of a simpler instrument capitalizing on the

high signal-to-noise ratios present in steam piping systems,

but capable of detection only. It is hoped that increased

use of the less expensive instrument will enable small leaks

j to be identified and repaired before they become so large as

to require more expensive repair procedures.

' A prototype of the simplified steam leak detector instrument

is currently being evaluated aboard ship. It is basically

an rms acoustic amplitude meter, operating in the 20 kHz to

80 kHz range and capable of an extremely large dynamic range.

In addition to the basic conclusion that steam valve leakage

rate measurement by analysis of ultrasonic emissions is

feasible, some other useful information was developed. With

a 3 1/2 inch globe valve mounted in a test stand and pressurized about 600 psi, it was possible to measure acoustically leakage rates as low as 0.2 ml/min of condensate, which

was collected at the valve discharge. Since a steam loss of

0.2 ml/min corresponds roughly to a fuel waste of about 0.002

pounds per hour, it is obvious that leaks causing significant

energy losses are easily detectable. Several spontaneous

changes in leakage rate were observed. It is suspected they

were caused by differential thermal expansion of the parts,

implying that acoustic measurements made for trend analyses

should be taken after the valve is thoroughly warmed up.

I Compressed Gas Valve Experience: Shipboard applications of

j the Acoustic Valve Leak Detector to 4000 psi compressed air

valves have been hindered by the high levels of background

noise typically present. The pipes and valves are so well

coupled acoustically that leakage noise and other noise

picked up from external sources tend to spread throughout

the system. The valves which have been of primary interest

in the program so far are 2- inch ball valves with resilient

seats, connected by steel pipe. No lagging is present.

I There is very little transmission loss of the ultrasonic

acoustic energy. The result is that with the presently

operational instrument, it is always difficult and sometimes

impossible to determine which of several valves is leaking.

1*4-7
Laboratory work is currently in progress to determine

which of several candidate signal processing schemes will

permit the AVLD or new techniques to work better in the high

noise environment.

Experience in the laboratory with the 2-inch ball valves

and aboard ship with smaller valves has been much more

successful. Leaks in smaller valves are more easily detected

For instance, the AVLD was recently used to locate a leak in

a shipboard oxygen generator system. A 1/2-inch valve pressurized at 1800 psi was cracked open to leak at a measured

rate of about 1 ml/min (at atmospheric pressure) . It was

also monitored by bleeding the leakage through a piece of

flexible tubing into a beaker of water. The leaking valve

was easily found by the AVLD from among several dozen other

valves in less than 2 minutes. Prior to the introduction of

the AVLD # troubleshooting the system for a leak of that size

took an average of 20 man-hours, and occasionally took 100

man-hours or more. Signfiicant leaks which are initially

detected by monitoring system pressure losses over time,

occur about four times a year per system.

Leaks smaller than the 1 ml/min rate were also detected.

There was an interesting phenomenon observed with very small

leakage rates. From monitoring the leakage noise on the

AVLD audio output, it was observed that the acoustic emission

was intermittent. This phenomenon had been observed previously in hydraulic and high-pressure water leaks. If the

leaks are as intermittent as their acoustic emission, that

could explain why some leaks in this system are very elusive

to traditional leak-finding procedures involving water and

soap.

Laboratory work with the 2-inch ball valve at 4000 psi has

shown that in the absence of high levels of background noise,

leakage rates as small as 100 ml/min can be detected reliably

on the basis of ultrasonic acoustic emissions, and that the

signals increase with increasing leakage rate. As a result

of this finding, work is in progress to develop an operational instrument capable of measuring high-pressure air

valve leakage rates by analysis of ultrasonic acoustic

emissions

.

Since the background noise levels in shipboard high-pressure

air systems are high, a successful instrument must incorpo-?.

rate noise rejection features. At least three techniques

to reduce the effects of background noise are being considered. Because detectable ultrasonic signals from leaking

high-pressure air valves have been observed at frequencies

as high as 400 kHz, and because there is a theoretical

ike
increase in transmission attenuation with increasing

frequency, surveys will be conducted to determine the extent

to which shipboard background noise is attenuated at higher

frequencies. A technique being investigated with some success in the laboratory is to damp the ultrasonic acoustic

emissions in the vicinity of a valve being leak-checked by

attaching sound-absorbing materials to nearby pipes.

A third approach being developed uses the cross-correlated

signal between two transducers mounted at different distances

along the pipe. The signal is different depending on the

direction of the noise and this difference is sensed to

indicate the direction from which the dominant noise is coming.

The objective of this development effort is to produce an

instrument which can detect a leak, isolate it to a single

source, and then measure the leakage rate; all by analysis

of ultrasonic acoustic emissions. The leakage rate information will then be used for trend analysis and for establishment of repair priorities and criteria.

Hydraulic Valve Experience: The Acoustic Valve Leak Detector

is currently being used to identify leaking hydraulic valves

on a troubleshooting basis if leakage is detected or suspected as a result of other evidence. Laboratory experiments

have determined that the minimum detectable leakage rate is

about 10 ml/min at 2800 psi, and have established the feasibility of measuring hydraulic valve leakage rates by analysis

of the ultrasonic acoustic emissions.

Laboratory work to date has the objective of developing an

operational instrument capable of measuring, as well as

detecting, internal leakage rates of hydraulic valves by

analysis of ultrasonic acoustic emissions. It has been

determined that there are detectable ultrasonic signals

associated with hydraulic valve leakage and that the signal

amplitudes increase with increasing leakage rate, [l] On the

basis of this finding, it was concluded that a quantitative

instrument is feasible. A capability to differentiate one

leaking manifold valve from the non-leaking valves was also

demonstrated. [1]

Despite the progress made in the laboratory and aboard ship,

some important aspects of the acoustic emissions of leaking

hydraulic valves remain incompletely understood and are

currently being investigated. In particular, signature

amplitude was observed to increase with decreasing valve

backpressure, [l] Another important factor is the sump pressure, usually above atmospheric pressure, at which the

lk9
hydraulic oil is stored for long periods in contact with air.

In some instances, large acoustic signature amplitude variations were observed at backpressures hear the sump pressure. [l]

Future Developments: Improvements to the existing Acoustic

Valve Leak Detector are being developed in four major areas:

. Leakage rate measurement (as opposed to

direction)

m Background noise rejection

m Accessories for ease of operation

m Design simplification

Leakage rate measurement as an extension of the existing

technology will permit a trend-monitoring program to be

established. This capability will be especially important

when applied to valves and fluids with a leakage rate

threshold, above which valve damage and leakage rates

increase rapidly. Experimental data reported elsewhere [l]

show that there are detectable ultrasonic acoustic signals

associated with hydraulic, steam and high-pressure air valve

leakage, and that the signals increase with increasing leakage rate. The known ranges of acoustically measurable leakage rates for the three fluids are tabulated in Table 1.

Note that the greater of the leakage rates listed are not

necessarily upper limits. They are simply the greatest leakage rates observed in the laboratory experiments which were

the basis for the data shown.

Table 1 - Known Range of Acoustically

Measurable Leakage Rates

Fluid Valve

Type

Valve

Size

Differential

Pressure

Acoustically

Measurable Leakage

Rate fml/min)

Hydraulic Spool 1/2-1 in. 2800 psi 10.0-1000

Steam Globe 3-1/2 in. 600 psi 0.2- 30 (condensate)

Air Ball 2 in. 4000 psi 100.0-3000 (measured

at atmospheric pressure)

Despite the progress reported, many factors affecting the

relationship of acoustic signatures to leakage rates remain

incompletely understood. These factors are related to valve

size, background noise, and fluid characteristics such as 1 pressure, temperature and dissolved gas content. Current

150
development work is directed toward obtaining a better underi standing of these factors and toward developing instruments

capable of measuring leakage through 2-inch ball valves for

high-pressure air and through hydraulic directional control

spool valves.

! Background noise rejection improvements are being developed

1 for shipboard high-pressure air systems. Methods being

| developed for rejection of excessive structureborne noise

include local damping, electronic signal processing and the

use of higher frequency signals.

Accessories which make the AVLD easier to operate have been

: developed as the need arose. A current example is a transducer clamp which will not require mounting discs to be

I epoxy-bonded to the pipe or valve surface, but will still

I permit hands-free operation.

Design simplification is a normal evolutionary process for

any new development. The existing AVLD is a very versatile

instrument which can be used for a variety of valves and

j fluids. By including only the features needed for a parti-

] cular application, it is possible to make a simpler, but less

versatile instrument. An example of this is the prototype

steam valve leak detector which was recently completed.

Summary: Detection and measurement of the internal leakage

of fluid valves by analysis of ultrasonic acoustic emissions

are rapidly expanding technologies within the U. S. Navy.

The Acoustic Valve Leak Detector, when applied in a

systematic program of preventive maintenance monitoring, can

eliminate most of the cost and downtime associated with

determining the internal condition of valves by traditional

methods of removal, disassembly and inspection. In troubleshooting applications, it enables repair efforts to be concentrated quickly on the actual cause of the problem, rather

than wasted in a long search for the leaking valves. In some

applications, the AVLD can be used to detect small leaks

| before they become too large to repair by simple methods.

The Acoustic Valve Leak Detector also has great potential for

energy savings when applied in a preventive maintenance program aimed at detecting and eliminating leakage losses,

particularly in steam systems and other piping systems which

use fluids to transport heat.

j Research and development efforts are continuing to expand the

capabilities of fluids, pressures, temperatures, valve types

and valve sizes. Since none of the fluids or valves are

particularly unique to the Navy, it is expected that the

151
instrument will find even wider commercial and industrial

applications

.

Technical References

:

1. Dickey, J. W. , et al , "Acoustic Measurement of Valve

Leakage Rates," Research Supplement, Materials Evaluation , Jan 1978

2. Morse, P. M. and K. U. Ingard, Theoretical Acoustics,

McGraw-Hill, I968

3. Boguslavski, Y. Y. , et al , "Sound Radiation by a

Cavitation Zone," Sci. Phy. Acoustics , Vol. 16, No. 1,

pp. 17-20, 1970

152
PIELSTICK ENGINE DIAGNOSTICS

A. Genot

S,E.M.T. - Pielstick

2 , quai de Seine

93202 Saint-Denis, France

Abstract: In order to improve engine reliability and reduce maintenance

expenses on ships, S.E.M.T. has developed a monitoring and diagnostic

system for medium speed diesel engines used in marine propulsion. The

system was designed to monitor ship's engines automatically, and without

manual intervention, while underway. The aim was both to prevent

failures and to perform maintenance only when necessary. The Pielstick

Engine Diagnostic system automatically monitors wear of the piston top

ring, main bearing alignment and shell wear, pressure charging circuit

fouling condition, and exhaust gas temperatures. The use of the system

will result in the extension of piston on-line time between inspections,

in the elimination of alongside monitoring of the shafting, and in the

improvement of the operating environment of the engine. The economical

justification will be extended engine life while eliminating unnecessary

labor and engine outages

.

This paper describes the monitoring arrangement, including data acquisition and processing, with results from both land tests and a sea- going vessel.

Key Words: Crankshaft displacement; medium speed diesel engine, piston

ring wear; turbocharging monitoring.

Introduction

The Pielstick Engine Diagnostic system (P.E.D.) monitors the on-line

condition of certain components of medium speed diesel engines with

outputs ranging from 480 to 1100 kw per cylinder. The system uses

pickups, "AND" circuits, and a data microprocessor to supply users with

information about piston ring wear, crankshaft bearing alignment and

wear, turbocharger fouling, and exhaust gas temperatures (fig. 1)

.

Some of the benefits of this system are: (1) automatic monitoring of

engine conditions which eliminates several hours of labor and engine

outages that are required for manual inspections; (2) helping to prevent

failures which would have serious consequences to ship operations; and

(3) permitting corrective actions to be taken only when actual wear

damage has occurred.

153
Research on the P.E.D. system started in May 1977 using a 12 cylinder

power station engine for the development of the system software. At

the end of December 1977 , a first prototype system was fitted onto an

18 cylinder propulsion engine of the container ship M/V "RENOIR" which

was commissioned in January 1978. A second prototype system has been

fitted onto a test engine in S.E.M.T.'s laboratory.

Piston Ring Wear Monitoring

Two cylinders from every Pielstick engine are inspected at 6000 hour

intervals for piston ring wear; all engine cylinders are inspected after j 12000 hours of operation. The main purpose of these inspections is to

check the amount of wear in the chromium layer covering the top ring

face . Chromium plating wear depends to a large extent on the engine

working conditions such as rotation speed, lube oil nature, cooling

water temperature, on/off cycles, etc.

The dismantling of a piston and con-rod assembly for checking piston

ring wear is a long and tiresome operation and therefore it is very

desirable to extend the inspection interval. In a great number of

cases, after dismantling, inspection shows that the interval could have

been extended without detrimental effects. But, once the top ring

protective chromium layer is worn, the cast iron ring rapidly deteriorates necessitating the replacement of the piston ring set. Therefore,

the intervals between inspections cannot be extended without some kind

of monitoring system such as the Pielstick Engine Diagnostic system.

This system continually measures the top ring chromium ring plating

thickness. The expected cost of the system will be recovered if the

piston ring service life can be increased by 1000 hours per set, based

on the smallest PC engine and monitoring one cylinder out of 3 or 4.

Inductive sensors are used in the P.E.D. system to measure the thickness

of the chromium plating on the piston rings. These sensors produce a signal whose amplitude varies with both the thickness and the magnetic

properties of the coating material (fig. 2)

.

These sensors are placed in the cylinder liner of the engine flush with ! the cylinder liner wall (fig. 3) . The sensor is placed in such a way

that all the piston rings pass successively in front of the sensor. This allows the sensor to scan each ring and generate an appropriate

output signal. If one of the piston rings is pure cast iron (no coating) , then it is possible to measure the thickness of the coatings by

comparing the amplitude of the signals given by the passage of each ring.

The accuracy of this technique is such that it has been possible to

compute a 0.044 mm reduction in coating thickness compared with an actual wear reduction measurement of 0.047 mm.

Figure 4 shows the signal from the piston rings transducer as displayed

by the data microprocessor. The computer is programmed to eliminate

15%
I

abnormal values resulting from the passage of ring gaps before the

sensor. The signal is analyzed vs time and the wear rate of the piston

ring is computed to help determine the next scheduled overhaul.

Measurements from the system installed on the M/V "RENOIR" reveal a

| slight chromium wear on the piston rings after 3400 operational hours,

i No dismantling has taken place since the installation of the P.E.D.

j system. Therefore, no direct measurements are available for comparison.

Crankshaft Monitoring

At the present time, crankshaft alignment and wear inspections are achieved by measuring crank deflections and under journal clearances.

! This inspection is performed after every 3000 operational hours, and

| while this is adequate for proper engine operation, it does not predict

I or prevent failures such as delamination of anti-friction metal, faulty

tightening, poor lubrication, faulty filtering, etc. Furthermore, these

I scheduled inspections require relatively long downtimes which often are unnecessary because no anomalies are found.

I From the economical standpoint, the new P.E.D. monitoring system

i eliminates time consuming inspection and reduces outages due to compoi nent failure. Its chief value may be its ability to detect imminent

failures because a shafting breakdown could stop the engine , and thereby

put the ship out of service for a long time.

Monitoring of the crankshaft is based on the analysis of the vertical

component of the crankshaft motion in the bearings. A contact free

displacement transducer is fitted in each main bearing on the engine vee

axis (fig. 5) . From the signals emitted by the transducers, the following parameters are computed: the total amplitude of the displacement

(a) from peak to peak during a cycle (two engine revolutions) ; the mean position of the crankshaft (b) during these same revolutions; and

the minimum lift (c) of the. crankshaft in the bearing. These three

parameters differ from one bearing to another and vary with the engine

speed (fig. 6)

.

Results from the M/V "RENOIR" show that for a given rotation speed,

amplitude "a" decreases slightly when the engine power demand increases;

this amplitude also decreases by 3/100 when the ship's displacement

increases from 16000 to 29600 tons. The ship's cargo seems to have no effect on "b" and "c" values.

In order to ascertain that the signal indicating crankshaft journal

movement in its bearing was affected by wear of the bearing anti-

! friction metal, we recorded the signals given by a transducer installed

on the bearings of a 12 cylinder engine operating under normal conditions

and after having removed the bearing shell of one of the bearings. It

! was observed that the signal amplitude doubled for the bearing with the

155
shell removed. Figure 6 shows that an increase in the rotation speed

results in an increase in the journal movement amplitude. As a result,

crankshaft monitoring is only done while the ship is at "full speed".

At "full speed", the engine rotates between 475 and 500 rpm depending

on the wind, the load, and hull fouling leading to a variation in

parameter "a" of about 0.03 mm or 10 percent.

Analyses of "b" and "c" values are used to monitor main bearing alignment by comparing the mean position "b" of a bearing with that of the

neighboring ones. The values of parameters "b" and "c" are not affected

by the roughness of the ocean over the range from a calm sea to a Beaufort number of 9. The value of "a" is not affected since it is

measured over two crankshaft revolutions which is a much shorter period

than one swell.

Exhaust Gas Temperatures I

Monitoring of exhaust gas temperature is an usual practice aboard ships.

We have found it to be practicable, both technically and economically, i to replace the analog equipment with a simple indicator and to perform

monitoring and analysis using the computer provided for the crankshaft

and piston ring monitoring. The exhaust gas temperature is measured at

each cylinder outlet. The readings are averaged and the individual

deviations with respect to the mean value are computed. The computer

verifies that each temperature does not deviate from the control values

established for a new engine, taking the control rack position into

consideration. The computing program also takes into account the sys-:

tematic deviation among the cylinders which is specific to each engine.

Practical experience indicates that with a fixed-pitch propeller the

rotation speed should also be taken into account in addition to the

control rack position.

The alarm threshold varies as the temperature average with the permissible deviation being larger for the low averages . Figure 7 shows the

influence of the after-cooler air temperature. Both experimental curves plotted for 31 and 39 °C air temperatures bracket the ideal curve.

Survey of the Supercharging System

The aim of this survey is to determine fouling of the supercharging

system and to predict the evolution of this fouling. The survey system

applies to the air-cooler, the turbine and the compressor. The econ- omical advantage of the system rests on the fact that any anomaly .in the j pressure charging entails a loss of engine efficiency and, in extreme

cases, damage to the valves.

The survey system measures the following parameters: $

• air temperature after cooler

156
• water temperature at cooler inlet

• air pressure after cooler

• difference in air pressure, before and after cooler

• fuel rack position

• revolutions of the turbo-blower.

Fouling of the air cooler will be determined by the difference between

the water temperature and the air temperature, and by pressure loss at

air side. These readings are subject to trend analysis in order to warn

the servicing staff that corrective measures must be undertaken.

Air filter or compressor fouling may be found by comparing the air

pressure value read before the compressor and that found by application

of the law giving that pressure in terms of turbocharger rotation speed.

Figure 8 shows the experimental results and also that the linear

function first adopted as the pressure - rotation speed relation was

over-simplified, as the difference between the measured and computed

pressures may exceed the alarm threshold fixed at 0.13 bar. The linear

function will be superseded by two straight line segments. The exhaust

gas side of the turbocharging system is monitored by comparing charge

air pressure at the compressor outlet with the theoretical pressure

given by the law relating the air pressure to the engine speed multiplied

by the control rack stroke. The product of the control rack stroke and

rotation speed is sufficiently accurate to be used for the power developed by the engine. Insofar as their installation has been anticipated by the builders, the system may be completed with accelerometers

to monitor turbocharger bearings. These accelerometers may either trip

an alarm for too severe vibrations or be used, with a particular routine,

to determine the time when the rolling bearing should be replaced.

Computation Means

The microprocessor is located in the control room a few meters distance

from the engine. It receives analog signals from the various sensors,

handles the data according to computation programs, compares the obtained

values with the reference values stored, commands sound and light alarms,

and prints instructions for the servicing staff. Computer storage

facilities are either unalterable ones or active ones fed by batteries

or the ship's electric circuit, depending on the importance of the data

to be stored and on the consequences of their being erased.

Hardware Problems

The first objection raised by the shipowners regarding monitoring

systems is the problem of the maintenance of these systems. It is

therefore necessary to search for sensors that are more rugged than

precise and to provide for easy access to the sensors. Wires should be

157
easily accessible and well protected against the shocks they might suffer

during dismantling of engine components. Since the system was put into

service, we have recorded the destruction of one air temperature sensor, i the drift of an "AND" circuit for a main bearing sensor, and the shut

off of the microprocessor electric supply due to vibrations. These

failures show that great care must be taken, especially from the vibration standpoint, when fitting electronic equipment into a medium

speed diesel engine machine room.

Conclusion

The results of the P.E.D. prototype system being tested aboard the M/V

"RENOIR" are promising. They show that the monitoring of a medium speed

diesel engine used for marine propulsion is possible. It was necessary

to try it at sea so that the system prototype would be subjected to a machine room environment. It is too soon to reach a conclusion about

piston ring wear reading accuracy and long term sensitivity of shafting

monitoring. The economical advantage of the P.E.D. system is not yet

established, but the system is a sound base for further research and

development.

158

INFLUENCE OF THE COATING THICKNESS ON THE

SIGNAL GIVEN BY THE PISTON RING

160
l6l
162
CRANKSHAFT SENSOR

Figure 5

163
DISPLACEMENT OF THE CRANKSHAFT

INFLUENCE OF ENGINE SPEED
Exhaust gas temperature

450

1 Average

Temp.

400

350

300

4

/Air temperature

after cooler 31°C

_Calculated low

.Individual limit

Experimental resiilt

250

Air temperature

after cooler 39°C

25 50 75 F.R.xrpm 100%

Figure 7.

I65
166
MACHINERY CONDITION ANALYSIS FOR MAINTENANCE PLANNING—THE

AIRCRAFT CARRIER EXPERIENCE

Michael D. Dougherty

Program Manager for Machinery Condition Analysis and

System Testing

PERA (CV), Code 1861

Naval Sea Systems Command

c/o Puget Sound Naval Shipyard

Bremerton, WA 98314

| Abstract: In 1970, Machinery Condition Analysis (MCA) began to

I replace the more traditional methods of planning the overhaul of

I aircraft carrier machinery. These traditional methods included

overhauling all machines, opening each machine up and inspecting to see what was wrong, or running until failure. None of these methods,

however, was particularly conservative in either money or time, and

MCA was intended to take a more objective look at high cost, mission

[ critical machines, and identify which ones were most in need of

overhaul

.

This paper addresses the evolution of MCA at PERA (CV), the process as it is conducted today, and the varied uses of its results. Particularly addressed are the benefits derived from the program and the

possible expansion of the program in the future.

Key words: Aircraft carrier; condition analysis; machinery; maintenance; monitoring; repairs; vibration.

WHY PLAN MAINTENANCE? The Navy, like every major firm that relies on machinery for production, processing or services, spends a considerable

amount of time, effort and money keeping them operational. From the

maintenance done by the operators on the ships, to the complete overhauls done in public and private shipyards, $2.5 billion will be spent

this year keeping the ships operational.

All of the planning that goes into the maintenance of ships is done

for one reason - neither the Navy nor the taxpayers can afford the

alternative of no planning. Ships have become too complex, materials

and parts take too long to buy, and the money is not available, for

ships to simply come into a shipyard without tremendous preparation,

and the Navy is the first to recognize this.

In 1967, the office for . Planning and Engineering for Repairs and

Alterations of Aircraft Carriers (PERA (CV)) was established at Puget

Sound Naval Shipyard in Bremerton, Washington. The purpose of this

167
I

organization was to do the advanced planning for all Aircraft Carrier

Industrial availabilities, both for maintenance of equipment and modernization.

EARLY MAINTENANCE PLANNING FOR AIRCRAFT CARRIERS.

Whether intuitively or analytically, it is fairly well known that

machine failures occur in a manner similar to the "bathtub" curve

(FIG. 1). Most failures occur when a machine is new or recently

worked on (break in), or when it has run for a considerable length of

time (wear out). The challenge of maintenance planning is to determine | when to overhaul a particular machine. Some give you clear signals,

such as poor performance, high vibration, or strange noises. But I others give no indication that is obvious or apparent prior to failure,

j Early maintenance planning at PERA (CV), and much of the present

planning also, took one of the following directions depending on the

criticality of the equipment, the length of overhaul, and the amount

of funds available.

2. Select a certain number of machines to be overhauled

(i.e., 4 of 12 Main Feed Pumps) and allow Shipyard

inspectors or Ship's Force to select the specific units.

3. Open and inspect machines when they arrived in the Shipyard.

4. Fix at failure.

With the exceptions of nos. 1 and 4, there was little objective

data on which to base the actions taken on a particular machine, and

often the complaint arose from the operator, "My machines were in

better shape before I came into the overhaul," and possibly he was correct. At a minimum, the failure rate of the machines overhauled

will be greater than upon arrival, and, until the breakin time is

over, the failure rate will not be at its previous level.

MACHINERY CONDITION ANALYSIS (MCA) BEGINS.

In 1970, it was proposed that Machinery Condition Analysis (MCA) be used

to determine which high-cost, miss ion -critical machines required overhaul. Vibration Analysis was chosen as the prime element in this program for several reasons.

T. Vibration Analysis had been used since 1939 for detecting

problems with rotating machinery in petrochemical plants. I

2. It had been very successful in the submarine noise

reduction program.

1 . Overhaul all machines of a certain type on a fixed

schedule (i.e., every major overhaul).

168
3. It could be done without taking the machine off the line

or interrupting ship's operation.

In January of 1971, the first MCA survey was conducted on 40 machines

in the USS FORRESTAL (CV 59) in support of its FY 1972 Regular Overhaul. The report was basically a priority listing of machines by need

for overhaul, and a simple OVERHAUL/DON'T OVERHAUL recommendation on each machine. Since 1971, 84 MCA surveys have been conducted on Aircraft Carriers - 72 prior to availabilities and 12 immediately

after availabilities.

MCA IN SUPPORT OF MAINTENANCE PLANNING TODAY.

To support Maintenance Planning today, two surveys are conducted

between each availability - one 30-60 days after the completion of an availability, and one five to six months before the next (FIG. 2).

This allows some trend analysis and provides quality assurance for

the past availability. During these surveys, between 150-250 machines

are tested. Accel erometers are attached to welded or glued blocks on each machine and vibration signatures are recorded on magnetic tape.

In conjunction with vibration, visual inspections and discussions

with the operators are held during the survey, and all the data

gathered goes on a single report. The survey itself takes from 4-8

days depending on the number of machines, the ship's operations, and

the number of compartments the machines are in.

The vibration data is then transferred to hard copy for analysis.

A typical survey will result in 2000-3000 vibration signatures (FIG.

3). Each signature is: (1) analyzed for high vibration, (2) com- pared to similar machines, and (3) compared to its previous signatures. Significant increases in vibration, or high peaks, are analyzed and recommendations are made for correction.

Within thirty days of the completion of a survey, a final report is

forwarded to PERA (CV). This report is then provided to the maintenance planner, the Navy customer and ship for use at the prearrival conference where machines are selected for overhaul.

The final report contains analyzed vibration information, visual

inspection and historical data, and detailed recommendations for

repair. This allows the flexibility to do selected repairs, such as changing bearings or aligning machines, rather than complete overhauls only. In many cases, overhauls have been deferred and minor

repairs have been assigned to Ship's Force.

WHAT BENEFITS HAVE BEEN SEEN? The primary benefits of MCA can be

best seen in conjunction with the rest of maintenance planning. A

repair profile is used to order material for machine overhauls 1^

years ahead of the availability. During the pre-arrival conference,

the customer decides the specific machines to repair, and MCA allows

the latitude to do less than the number scheduled by the profile, and

169
put the money and mandays where it can do the most good. Since MCA

began in 1970, the entire program has cost approximately $3.5 million.

This includes all development and the conduct of 84 surveys. However,

the funds reallocated thru the use of MCA for ]_4 avail abil i ties over

the past 4 years have totaled $10.3 million. This represents a return of $18.84 for every $1 spent on the 14 surveys.

In August of this year, the long range maintenance plans officer for

the Naval -Air Force, Atlantic (AIRLANT) stated that two years ago,

when he began to keep a list of the top 10 areas of casualties on- board AIRLANT ships, Main Feed Pumps and Forced Draft Blowers were

near the top. Since that time, they have disappeared from the list,

and he attributes this to the success of the MCA program for detecting

problems before casualties occur.

MCA IN THE FUTURE. MCA has become more accepted by the Navy cus- tomers in the past few years, as evidenced by the increase in the number

of machines requested for survey, the addition of post-overhaul

surveys to the program, and the increased use of the reports. MCA

identifies problems in machines, but, more importantly, it identifies

the cause of the problems, and this is the area to direct our attention. Ninety percent of the problems we see in rotating machinery

begins with either imbalance or misalignment, both of which can be

corrected if caught soon enough. Programs to improve the balance and

alignment of machinery immediately after overhaul are in the early

development stages.

Automatic processing of the enormous volume of vibration data gathered in each survey is also in the development stages. Up to this

point, every graph had to be physically screened by the analyst for

significant anomolies and obvious problems. These were then compared

to similar machines and previous survey of the machines in question.

At best, the task is formatible, at worst, impossible. By using a computer to do the initial screening and provide only the large deviations for analysis, the analyst is free to do more investigation.

This will also identify low level vibration problems that the analyst

cannot see under the present system.

CONCLUSIONS. Machinery Condition Analysis as used by PERA (CV), has

proven itself to be an extremely cost effective maintenance planning

tool over the past 8 years. With returns in excess of 18:1 the

program has been well accepted and used by both the Navy customers

and the carrier fleet. With modification, the program could easily

be adapted to any ship, manufacturing plant, or processing facility

with similar success.

170
171
o

CO

o

Q-O

CM

•H

172
173


DIESEL ENGINE ANALYZER: PAST EXPERIENCE AND FUTURE PLANS

Harold W. Rethmann

Southwest Research Institute

P.O. Drawer 28510, Div. 14

San Antonio, Texas 78284

Abstract: A computer-automated diesel engine analyzer system with four. \ test cells was developed in 1973-74 for use at the Long Beach Naval [ Shipyard. As originally designed, the system performed fully automatic i final testing of nine specific type diesel engines or manual testing of jj any diesel engines which could be fit into one of the four test cells.

The nearly four years of operation has proven many of the original de- jj sign concepts, as well as revealed some areas where changes were needed

if the full potential of the system was to be realized. Operation of i the automated diesel engine analyzer has also stirred the imaginations

of both the original designers and the test system operators as to how

the existing system might be augmented to perform final test after over- : haul on equipments other than diesel engines. This paper gives a brief j description of the system as originally constructed and implemented. It ij points out those facets of original design that have proven to be help- ; ful in updating and modifying the system to perform the task at hand.

It also points out areas where major changes will be made both in hard- [ ware and software to take advantage of the experience gained over the | several years of testing, as well as those required to cope with changing Navy test requirements. The final portion of the paper deals with

augmentations that will be made to the system to test shipboard air ] compressors. The description of a proposed fifth engine test cell for \ testing large diesel engine subsystems is also included. a

The Diesel Engine Analyzer (DEA) to be discussed in this paper was installed at the Long Beach Naval Shipyard in 1975 as part of the Navy's jj modernization program. The technical aspects of this system have been a covered in detail in other publications (references 1 and 2) and will not j be repeated here. A brief description of the system is included for

those who might not have had access to the earlier publications.

f The purpose of the DEA, as spelled out in the LBNSY Request for Techm- | cal Proposal, is to evaluate the quality of repair of diesel engines i under test in terms of (1) satisfactory performance within specifica- \ tions and (2) reliable operation with respect to run in test data. i Another feature of the DEA is to shut down an engine test when unreliable operation is detected prior to a catastrophic failure of the engine.

;

Key words: Automatic test system; Diesel Engine Analyzer.

176 1

i

1
The system was originally designed to conduct automatic tests on the following types of engines.

1. Cummins VT-12

2. Fairbanks Morse 38D8

3. GM 6-71

i 4. Packard V-12

I 5. Waukesha L1616

Figures 1-6 provide an overview of the system as installed.

Figure 1 is a diagram of the entire DEA area. The four test cells are

placed around the control area on three sides. Not shown are the cooling water towers and fuel storage facilities which are outside the

buildings near cell 2.

Figure 2 is a block diagram of the entire DEA system. The basic computer equipment is connected directly to the control consoles which are in

turn connected through the junction box to the engine/dynamometer com- bination for a particular cell.

Figure 3 shows the insides of the engine junction box. The large box at

the top is a 24-well , 150°F reference junction for the thermocouple

temperature probes. The smaller box and heat sink device are a 40 amp

solid state contactor and rectifier for providing pulsed DC to load the

eddy current dynamometer. The tank and piping at the bottom form a pneumatic shut down system that sequences the engine to a minimum throttle minimum load condition with timed cool down in case of electrical

power failure.

Figure No. 4 shows the test console arrangement in the control room

while Figure No. 5 is an enlarged view of one of the test consoles. The

test consoles are used primarily in the manual mode. The direct view

gauges across the top row display crankcase pressure, turbocharger pressure, exhaust back pressure, oil pressure, dyno water pressure, and

water pump pressure. Twenty-four separate temperatures can be read on

the digital read out at the left side of the console. Engine RPM is

shown both digitally and in analog form near the center of the console.

Exhaust smoke opacity is measured by the device at the lower left side

of the panel. The two large round controls are for manual adjustments

of speed and load. The remaining push button controls perform various

housekeeping functions.

Figure 6 is the associated computer equipment. Rack No. 1 at the left

contains the HP 2100S minicomputer, associated disc storage unit and

paper tape equipment. The rack at the right contains the calibration

relay/line driver/line receiver equipment, low level mul tiplexer/A-D

system and the mul ti programmer. All of this equipment, except the calibration relay section are standard off-the-shelf Hewlett-Packard items.

Interconnection of the three main equipment locations is by means of

177
multiple twisted shielded pair lines with hermaphrodite (Elco varicon)

multi -contact connectors. There are also some pressure tubes (PVC or nylon depending on pressures involved) which run from the Junction boxes

to their associated control console.

As originally configured, cells 1 and 2 were equipped with eddy current j dynamometers while water brake dynamometers were installed in cells 3

and 4.

Operation of the equipment is possible in either the full automatic mode

or in a manual mode. Each test cell function is entirely independent of

the other three cells with one minor exception. Test area barometric

pressure is provided for all cells by a pressure transducer in test cell

The preceding overview has, I hope, given you a small insight into the

DEA system as it was originally constructed.

Now, after several years of operation, what have we learned about automatic testing of diesel engines, and where do we go from here?

First, and I'm sure foremost, we have learned that automatic testing,

properly conducted, can be a cost effective way to test overhauled diesel engines. A study performed for the Long Beach Naval Shipyard in

October 1972 to determine the requirements for a diesel engine analysis

system reveals that during the years 1971 and 72, seven rebuilt engines

suffered catastrophic failure while on the shipyard engine test stands.

These were all engines of a type that are now tested on the DEA. It is

not possible to say positively that all of these failures would have

been detected and precluded by the DEA, but we do know that since the

DEA has been installed, there have been no cases of catastrophic failure while engines were being tested in the automatic mode. At least two

' engines have been saved from catastrophic failure. The total value of

saving thus realized from this one facet can only be estimated, but has

to be significant.

Now let me discuss some specific items that we think are significant.

Let me comment first about the automatic test scenario.

As originally designed, the system software program left little latitude

for the equipment operator to make decisions and minor modifications to

the test as it progressed. This type of program did not evolve by acci- \ dent. During the design stage, the LBNSY project technical monitor personnel were advised of the various scenarios that could be built into

the software. They preferred a system with only a minimum of operator

participation possible.

To complement this decision we chose a simple 8-hour test profile that we felt would provide an adequate test that could be easily completed by

an engine that met the overhaul specifications. If during this test,

178
I any of the approximately 40 parameters exceeded a specified bounds, the

test was automatically terminated and had to be restarted at the beginning after the indicated fix had been made.

In our test profile the engine was started and run at idle until certain

key temperatures had stabilized. The test then proceeded through a set

| number of phases of increased speed and load until the full load condii tion was reached. The full load condition was maintained for a specij fied time after which the load was slowly decreased to zero, then the

RPM was reduced to idle and the engine allowed to cool down. A "good"

engine could normally complete the test without exceeding any of the

established test parameters. This meant that the requirement to restart

a failed test did not result in excessive delays in completing the en- gines required tests.

I Subsequently a more detailed test procedure was superimposed by NAVSEC.

I This included a much longer test period (28 hours) with several cycles

of load and speed variations both up and down. This resulted in combinations of load and RPM that were not originally contemplated, as well

as excursions of temperatures and pressures that were not within the

previously established limits. As a result, we have encountered numerI ous test interruptions for seemingly inconsequential reasons.

Although it is a simple matter to change a particular limit in the com- puter program, it is not an easy matter to assure a completely adequate

test using a patched up program which has been modified to fit a different test profile. More about this later when we get around to future

plans.

Some of the diagnostic aids that we included in our original test sce- nario have failed to live up to our expectations.

Instantaneous crankshaft angular velocity (ICAV) is one of the areas

where we feel more work must be done. In this test we detect top dead

center, then measure variations in rotational speed of the crankshaft as the individual pistons progress through the various strokes. The test

can be performed either in the cranking mode or while the engine is

idling. Ideally the test can detect loss of compression in a particular

! piston/cylinder pair or faulty fuel delivery to a particular cylinder or group of cylinders. These measurements appear to have considerable

diagnostic potential but presently there are no set standards that can

be used to determine when an engine is "bad". We feel that this technique can and should be further developed.

Smoke measurements have been a disappointment. Consider steady state

smoke. We had hoped to be able to measure total energy into the engine

in the form of fuel and compare that with total energy out in the form

of torque, heat, and unburned fuel (black carbon smoke). So far we have

i been unable to do this because the installed opacity meter cannot tell

the difference between black carbon smoke and blue smoke caused by burn179
i

ing oil in the exhaust system. This further complicates the problem be- I cause oil smoke can show up at times that are not directly related to j the engine performance at that particular instance. The location and

complexity of the smoke meter stack unit makes it almost impossible to

keep the optical system free of the foreign matter. Naturally, this

creates errors in the readings. We feel that steady state black smoke

measurements can contain significant information but so far we feel

there is a way to go to before we can reliably get this information in an automatic test. Dynamic smoke measurements have also proven to be

disappointing. As stated before, oil deposits in the exhaust system

| tend to create smoke that is not directly related to the instantaneous

operating conditions within the engine.

A diagnostic phase was provided in the original test program. This procedure could be called for when an engine failed to achieve rated horsepower. The diagnostic phase included a post test idling ICAV, a dynamic

crankcase pressure measurement and a print-out of all those parameters

which were within 10% of their limits when the rated horsepower failure

occurred. Dissatisfaction with the current ICAV test seriously weakens

the diagnostic phase.

Other minor items such as an automated cooling system pressure test and

an automated rack and fuel cut off cylinder adjustment are in the pro- cess of being eliminated. It was found that it was much simpler to do

these items manually than try to include them in the automatic test.

Long pressure tubes from the engine into the test console have also re- sulted in some problems. Delays can be created in important parameters

like oil pressure. Low pressures such as crankcase pressure (1-2 inches

of water) can be completely negated by a drop of oil in the line. Plastic pressure tubes are also subject to breakage.

So far I have only mentioned those items that we have found to be in

need of change. Let me now tell you about some of the things that we found worked very successfully. The general manner in which the system

was constructed has, we think, served well in keeping the system not

only functioning, but developing as well. As you may know, the DEA, as ! developed at SwRI, is a one-of-a-kind item. This required . that the conj struction technique lend itself to ease of maintenance and expected

modification. To support this requirement we installed a large number

(20-25%) of spare cable runs between the three major locations (junction I box, console and computer) affecting each test cell. All interconnecting lines for a particular cell were passed through a cross connect

board in the console (see Figure 7) so that they were readily available, f To make maintenance of the system as simple as possible, we kept the

table of differences between the four cells at an absolute minimum. In essence all four cells were fabricated identically. Since there were

two types of dynamometers to operate (eddy current and water brake), all |; four cells were designed to be capable of operation with either type of

unit. We deviated from this practice only where unused high value items j would have been included, but even then the mechanical layouts were the

180 l
same with the unneeded parts merely left out.

The same techniques were used in the computer program. Look-up tables were used wherever possible to catalog test cell particulars. When a test is initiated, the engine type and cell number are both entered.

The engine type selects the proper test parameters and limits while the

j cell number selects the dynamometer type and establishes the correct

1 dynamometer constants so that load can be read properly. This procedure

| made it possible to test some engines in more than one particular cell.

This system of construction and programming greatly simplified the re- cent conversion of the two water brake test cells to eddy current dynamometers. The mechanical modification was limited to adding the few re- quired high value parts (D/A converter in multi programmer, rectifier and

contactor in J-box), modifying the control console to accommodate the

additional LOAD control and removing a few grounds in the console logic.

I Equally simple changes in software were required. The look-up table for

these cells now references the eddy current subroutines, and the new dynamometer factors replace the old water brake factors.

Successful operation in a heavy industrial area is another area where I

j feel we were successful. As everyone knows, in an industrial area you

must anticipate electrical noise problems. To counter this we used

twisted shielded pair wiring and filtered differential inputs for all

low level signals. We religiously kept track of our signal grounds, and

optically isolated our logic signals. To date we have had no problems

that we could trace to electromagnetic or conducted interference. The

system has continued to operate for approximately four years with a minimum of maintenance. Dirt, grease, diesel fuel, etc. are all items

that must continually be controlled though if successful operation is to

continue.

So much for past experiences, now to the "future plans" portion of the

presentation. This will be further subdivided into two portions: future plans that are directly related to the analyzing of diesel engines

and future plans that relate only to the utilization of the DEA hardware.

First, as applies to analyzing diesel engines.

i i

We are currently in the midst of a major rework of the entire computer

program. Under this program, which we refer to as "fast restart", we

plan to revise the software to simplify and speed up the completion of a given test. A major part of this rework involves the function of limit

setting. We currently have an upper and a lower limit on most parameters. If either of these are exceeded, the test is automatically

halted and must be started again from scratch. Under the new program

! we will still have an upper and a lower absolute limit, but within these

limits will be an upper and lower warning limit. When any parameter exceeds the warning limit, a flashing yellow light will be lighted on the

particular console and a flashing asterisk will identify the offending

181
limit on the CRT read out. The operator can then analyze the situation, i He will have the option of making running adjustments, taking other ac- tion that seems appropriate, or just watching the particular parameter. ! We feel that this warning will help us to counter those simple problems

which can be corrected before they can interrupt an otherwise satisfac- I tory test. Things such as loose thermocouples, leaky pressure fittings, | improperly set valves, etc.

The second major change in software will allow the immediate restart of

a test that has been halted for a non-debilitating reason. For example:

when changing from one test phase to another, we have occasionally ex- perienced conditions where the speed and load combination resulted in

horsepower, pressure or temperature readings that were momentarily out- i side the desired limits. Should a situation such as this occur in the

future, the operator will be able to immediately resume the test where

the interruption occurred and continue on through the run as soon as certain key temperatures stabilize. We feel that with the lengthy tests , specified by NAVSEC that a system such as this will greatly speed up

testing without endangering the engine or the quality of the test.

Another feature of our redesigned software will permit a more thorough

calibration of the DEA system. Calibration so far has been carried out

only on the console gauges which are used primarily in manual operation.

In the future a software change will allow calibration of the computer

read values to be conducted simultaneously with the console gauges.

A fifth engine test cell is also on the horizon. This cell will be de-

[ dicated exclusively to the testing of GM 149 series 16 cylinder engine j subsystems. The cell will be equipped with a complete GM Detroit Diesel

| 16V-149TI engine extensively modified by Stewart Stevenson to serve as a 1000 kw generator on the Navy FFG-7 series ships. The engine will be

used as a test bed for hot checking the various subsystems utilized on this series equipment. The hardware used in this cell will be much the

same as the other four cells with one major exception. In this cell we

| will be equipped to measure air intake volume on each of the four turbo- ; charger inputs. Also, on the Control Console we plan to read all pressures on remote digital panel meters when in manual mode. We will not

run pressure tubes into the control room for the reasons previously

stated.

i To handle the increase in memory requirements for this fifth cell (and

for some other requirements which I will mention in a minute) we are also changing out the HP 2100S computer and replacing it with an HP 21MX

with a much larger memory capacity. In this same modernization program

we are also replacing the 2.5 M byte disc recording system with 4.9 M

byte device.

I There are also future plans that apply to the DEA equipment but are not

concerned with testing diesel engines.

182
At the request of LBNSY a study was performed to see if it would be possible and economically feasible to use the DEA computer equipment to

conduct automated test after overhaul on devices other than diesel engines. Specifically, could the system be augmented to test multi-stage

air compressors, sealed hydraulic transmissions, and cryogenic generators. The study revealed that while testing all of these items was possible with certain hardware additions to the computer, only the air com- pressor and cryogenic generator testing appeared to be economically

I feasible. As a result of this study, the LBNSY has contracted to enlarge the system to encompass the air compressor testing.

The manner in which the software was originally written (with maximum

use of look-up tables) lends itself well to this addition. Although the

air compressor test will be different than a diesel engine test, the air

compressor cell will be generally treated as just another test cell with

periodic servicing by the computer. This cell will feature both manual

I and automatic operations just as the engine cells do. All parameters

will be available for display on digital meters on the console during

manual operation and additionally on an associated CRT read-out during

automatic operation.

I This concludes our look at where we are in the automatic testing of diesel engines and other pieces of Navy gear. Before closing though, I would be remiss if I did not say a few kind words about the people who

have operated the equipment over the past four years. Any system such

as this will not operate efficiently unless the people operating it believe in it and want it to work. We have been very fortunate in this

respect, and look forward to many more years of friendly cooperation.

ACKNOWLEDGEMENT

The author expresses his appreciation to Mr. R.B. Curtin and Mr. V.R.

Sturdivant of Southwest Research Institute for their contributions in

the preparation of this paper.

REFERENCES

1. Clark, John M., Jr., Hambright, Robert N., Curtin, Richard B., and

Sturdivant, Vernon R., "Marine Diesel Engine Analyzer (D.E.A.)". Proceedings of the International Symposium on Automotive Technology and

Automation, Rome, Italy, 27 September 1976.

2. "Computerized Evaluation of Engine Overhaul Operation", Diesel and

Gas Turbine Progress , January 1977, pp. 10-11.

3. Sturdivant, Vernon R., Curtin, Richard B., and Hambright, Robert N.,

"A Diesel Engine Analyzer", Instrumentation in Machinery Applications

Session, 23rd International Instrumentation Symposium, Las Vegas, Nevada,

3 May 1977.

183
UTILITY ROOM CELL 3, 4

JUNCTION

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TELETYPE

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UTILITY ROOM CELL

OIL RESERVOIR

(TYP 3 PLACES)

INERTIA BLOCK

(TYP 4 PLACES)

DYNAMOMETER

(TYP 4 PLACES)

JUNCTION

BOX

'JUNCTION

BOX

UTILITY

ROOM

CELL 2

TRENCH

(TYP 4 PLACES)

FIGURE 1 - THE DEA TEST FACILITY

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187

189

FIBER OPTICS FOR BEARING PERFORMANCE MONITORING

Gerald J. Philips

David W. Taylor Naval Ship Research and Development Center

Annapolis Laboratory

Annapolis, Maryland 21402

Rolling element bearings are used in rotating machinery to separate

stationary and rotating components. Commercial and military organizations have sought to improve the reliability of such machinery through

the detection and diagnosis of bearing problems and hopefully through

the prognosis of impending bearing failures. Traditional methods of

bearing performance monitoring employ accelerometers mounted somewhere

on the machine's external surface. The fiber optic method employs

proximity sensors that are mounted in the bearing housing, as shown in

figure 1. Data retrieved by such fiber optic sensors are not con- founded by the resonances and vibrations of the surrounding structure.

The signal obtained directly from the bearing is found to be relatively simple and easy to analyze. For example, an unfiltered bearing signal is shown in figure 2, wherein pattern recognition of the oscilloscope trace indicates the bearing contains a defective ball. Each wave

represents the deflection of the bearing outer race as a ball passed

by the fiber optic sensor. Discontinuities of the otherwise smooth

waveform are clustered about one wave or ball and repeat every eighth

wave (there are eight balls in the bearing) . The unfiltered signal of

an 11-ball bearing is shown in the top half of figure 3. Discontinuities were found at each eleventh wave, which again is indicative of a defective ball. When viewing the signal through a 1,000 - 10,000 Hz

window, the defect is more clearly discernible, as can be seen in the

bottom portion of the figure.

Through pattern recognition it is possible to identify the defect location, whether it be on a ball, the inner race, or the outer race. However, it is usually academic where a defect is and more important to

accurately detect the existence of the defect and predict its effect on

the remaining life of the bearing. Towards that end, the pk/rms ratio

of the filtered signal can be measured to indicate the relative magnitude of the defect. Figure 4 shows the signals from three bearings:

one good, one marginal, and one obviously bad. One problem currently

under study is the establishment of a fiber-optic pass/fail criteria

for bearings. That will be the pk/rms ratio at which a bearing should

be removed from service.

Obtaining a measure of the functional integrity of bearings (pk/rms)

is but one of the uses of the fiber optic sensors. Band-pass filtering

in the low frequency end provides important information regarding the

191
mechanical performance of the bearings and the machines in which they are installed. As applied to a typical electric motor, two proximity

probes are used to measure the vibration on the outer races of each of

the two ball bearings and another sensor is used to measure the rotational speed of the motor's shaft. Two of the principal components of

the signal produced by the bearing probes are the rate of rotation of

the shaft and the frequency at which balls in the bearing pass by the

probe. A measure of ball bearing operation is the bearing speed ratio

which is the ratio of the ball passing frequency to the shaft rotation

frequency. The value of the bearing speed ratio indicates the amount

of axial load on the bearing, the extent to which the bearing is installed too loosely or too tightly within the bearing housing, as well

as the condition of the lubricant. Speed ratio limits such as shown

in figure 5 based on normal variations of operating loads and clearances, can be calculated and used as an overhaul criteria. Too much

grease is just as bad as too little grease in a bearing. Figure 6

illustrates that extreme deviations from calculated speed ratio perfor- mance is encountered for improperly lubricated bearings.

When the rotor of a machine is not perfectly balanced, it will produce

vibrations at its frequency of rotation. These vibrations are detected

by the proximity sensors. The angular position of the unbalanced

weight on the rotor is determined by comparing the phase of the signal

with that from the shaft sensor. This can be done simply on an os- cilloscope screen as illustrated in figure 7. By setting the shaft

timing pulse to exactly six screen divisions, the peak amplitude of the

unbalance signal can be read directly from the oscilloscope. This

method has been found to be of value for in-place balancing of rotating

equipment. Compared to a standard method utilizing externally mounted

accelerometers , the fiber optic method is faster and can result in a lower residual unbalance level.

Traditional bearing performance monitoring methods normally employ ex- ternally mounted sensors. These sensors are fastened to the machine

in various ways such as with epoxy, dental cement, magnets, or hand

pressure. The fiber optic method sacrifices ease of installation but

delivers much more useful information to the bearing engineer. Some

applications of the fiber optic method are in new bearing inspection,

machinery balancing, the detection of ball skidding, bearing loads,

and shaft and housing fits. Therefore, with the fiber optic method it

is not only possible to determine the condition of bearing surfaces,

but also to determine if bearings have been properly installed in

machines and therefore given the best chance to survive to their

fatigue lives.

192 !
FIBER OPTIC PROBE NUT

Figure 1.

193

DC-10,000 Hz

1,000-10,000 Hz

Figure 3 - Effect of Filtering Illustrated

195
Good Bearing

Pk/rms =1.2

Rejected Bearing

Pk/rms =1.6

Rejected Bearing

Pk/rms =3.0

Figure 4 - Filtered Signals from Three Bearings

196
3.12

THRUST, LBS

Figure 5 - Speed Ratio Overhaul Criteria

197
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100 GRAMS (100%

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-400 -200 0 200 400 600 800 1000 1200 1400 1600

BEARING LOAD, LBS

Figure 6 - Bearing Speed Ratio Performance at

Three Levels of Grease Pack

198
199

SESSION IV

INDUSTRIAL APPLICATIONS

Chairman: Robert M. Whittier

Endevco Corporation

Co-Chairman: Robert Leon

Franklin Institute Research Labs
I

I

I

I
STATISTICAL TECHNIQUES FOR AUTOMATING THE DETECTION OF

ANOMALOUS PERFORMANCE IN ROTATING MACHINERY

K. R. Piety

Oak Ridge National Laboratory

Oak Ridge, Tennessee 37830

T. E. Magette

Nuclear Engineering Department

University of Tennessee

Knoxville, Tennessee 37919

Abstract

We have assessed the level of technology utilized in automated systems

that monitor industrial rotating equipment and the potential of alternative surveillance methods. We conclude that changes in surveillance

methodology would upgrade ongoing programs and yet still be practical

for implementation. We formulated an improved anomaly recognition

methodology and implemented these methods on a minicomputer system.

The effectiveness of our monitoring system was evaluated in laboratory

tests on a small rotor assembly, using vibrational signals from both

displacement probes and accelerometers. Time and frequency domain

descriptors are selected to compose an overall signature that characterizes the monitored equipment. Limits for normal operation of the

rotor assembly are established automatically during an initial learning

period. Thereafter, anomaly detection is accomplished by applying an approximate statistical test to each signature descriptor. As demonstrated over months of testing, this monitoring system is capable of

detecting anomalous conditions while exhibiting a false alarm rate below

0.5%.

Key words: Automated surveillance; rotating machinery monitoring;

statistical detection algorithm; vibrational signatures.

Introduction

Scope of the work : The purpose of this work is the demonstration of

surveillance techniques that can extend the performance capabilities of

automated systems for monitoring industrial rotating equipment. In

preparation for this work we have assessed the effectiveness of ongoing

monitoring programs and the potential improvements offered by alternative programs. Based on our evaluation of the merits and deficiencies

in existing and proposed surveillance systems, we formulated an improved

203
anomaly recognition methodology. The monitoring system implemented and

tested at ORNL offers improved monitoring performance, utilizing method

that are practical for even large industrial applications.

Background : The practice of monitoring gross vibrational levels as an indication of machinery health began more than 150 years ago. However,

it was not until 1939 that vibration sensors and rudimentary signal

analysis techniques enabled the compilation of empirical vibrational

severity criteria (1-3) . Only in the past 25 years have advancements

in data processing techniques and computer hardware allowed machinery

health to be evaluated using signatures derived from the detailed struc

ture of vibrational signals (4,5).

Although the advantages of signature analysis techniques are widely

acknowledged, the demands such analytical methods place on plant personnel limit the use of such techniques for general surveillance tasks

(5,6). Computer automation of these monitoring requirements alleviates

this drawback and allows maintenance personnel to direct their efforts

towards equipment most in need of attention. Additionally, a computerized surveillance system should provide sufficient sensitivity to give

early warning of incipient failures, thus enhancing diagnostic capabili

ties and allowing better scheduling of maintenance. However, while

monitoring of machinery to detect excessive vibration is a wellestablished practice, a best approach for automating such monitoring

activities has not gained general acceptance.

Limitations of monitoring systems : There are certain drawbacks associated with all systems presently used for on-line surveillance of rotating equipment. The most basic of such systems are those which derive a set of parameters characterizing the vibration signal (such as its peak

to-peak amplitude, RMS power, or power at the rotational frequency) for

comparison with absolute limits (7-9). To set such limits one must

resort to a vibration severity chart, perform analytical calculations

for the equipment to be monitored, or accumulate the necessary information from testing. Since fixed limits must encompass the "worst-case"

conditions over the entire range of normal operations, sensitivity to

anomalous performance at any given operational state is reduced (9,10).

Another disadvantage frequently associated with this approach is a lack

of information on which to base diagnostic decisions (9,11) once an anomaly has been detected.

To compensate for this deficiency some monitoring systems add trending

capabilities or utilize the detail available with complete spectral

analysis (12-16) . Unfortunately, due to the storage limitations which

exist in systems monitoring several hundred data channels, trending the

entire power spectrum is typically not practical. The storage problems

associated with maintaining full spectral detail are further compounded

if baseline signatures and limiting criteria are to be saved as a function of operational conditions. A common compromise is to trend only

20k
gross vibrational levels and to alarm if these parameters exceed acceptable limits. The complete power spectra of the vibrational signals are saved only at baseload conditions at the outset of monitoring, with

further spectral analysis performed only upon operator request, at

widely spaced intervals, or under alarm conditions. A decision to monitor only gross vibrational level sacrifices sensitivity (6,11,17).

1 However, the decision to monitor a larger set of detailed descriptors

J makes it difficult to establish meaningful detection criteria (particularly as a function of operational conditions) and has, in some cases,

exhausted the patience of operations personnel (7)

.

Another approach taken by some researchers is the implementation of

statistical algorithms as a basis for anomaly detection (17-19) . Both

the experience and success in applying these techniques have been

limited. Our own previous efforts with a strictly statistical approach

I revealed that the rotating equipment being monitored was nonstationary.

Even at fixed conditions, the equipment would operate for indefinite

periods described by one set of statistical parameters and then would

randomly change to other equally normal conditions with different statistics. Data taken under such conditions results in biased samples

of the statistical populations, thereby destroying the rigor of statistical tests (19) . Statistical techniques can also be data intensive

and thus become unmanageable with the added complication of varying

operational conditions.

The most mathematically complex techniques envisioned for automated

surveillance systems may be generally referred to as pattern recognition

methods (17, 20-22). Implementation of these methods typically requires

the accumulation of signatures for abnormal conditions in

addition to those for normal conditions. Such comprehensive data re- quirements cannot normally be satisfied, particularly at the onset of

surveillance activities. In addition, since pattern recognition methods

have characteristically been developed for other applications, they

rarely incorporate — and then only indirectly — engineering knowledge

pertinent to specific surveillance tasks. Nonetheless, it would appear

that some of these methods do show promise as diagnostic algorithms once

the required data is obtained.

The ORNL surveillance system

Overview : This monitoring system is the result of applying engineering

judgment to the specific task of automating machinery surveillance. To

maintain high sensitivity to anomalies, vibrational signatures are catalogued as a function of operational conditions, and detection decisions

are based on simple statistical tests. The determination of alarm criteria is accomplished automatically, based upon normal data obtained

during a learning period. Judicious feature selection is incorporated

205
to reduce storage requirements; however, data logging adequate for

diagnostic investigations is provided. False alarms are reduced by

implementing processing logic that compensates for normal data variations .

Feature selection : A vibration signature is obtained by selecting only

a subset of the various signal descriptors that might be derived from

the measured data. This selection process introduces available engineering knowledge related to individual equipment, critical fault events,

or the signal character into the monitoring system. For example, the

power in the fifth order (five times the rotational speed) would logically be included as a feature describing a fan with five blades. Obviously, the specific set of parameters comprising a signature will vary

for dissimilar applications. Discarding or combining redundant descriptors should result in a reduced set of descriptors which enhance the

information content of the measured data. For our test purposes we

chose 48 parameters per signal which define the phase, size, and shape

of the time-averaged waveform, the total power of the signal, the harmonic and nonharmonic power, the power and phase of the first three

orders of rotation, the spectrum-weighted order, and the average harmonic and nonharmonic order. A detailed explanation of these descriptors is given in the appendix. Although these features are not proposed

as an optimum set for other monitoring applications, many descriptors

in widespread use are included, and the ability to compare the performance of descriptors with different levels of detail is provided.

Reference catalogue of baseline data : Baseline signatures are catalogued as a function of operational conditions. This procedure necessitates access to variables that define the operational state, for example,

speed, load, or flow. Discrete intervals are chosen to span the full

range available to controlling variables; once specified, the interval

structure determines the maximum number of entries required in the reference catalogue. Since it has been demonstrated that variations in

speed and load can introduce changes in vibration exceeding those associated with anomalies (10) , compensation for such changes stimulated by

control variables is necessary for maintaining sensitivity for anomaly

detection and for reducing false alarms. Although most investigations

support this conclusion (7-10), few monitoring systems implement capabilities for handling this complication. We chose the direct catalogue

ing approach after reviewing various mathematical alternatives and

experimenting with techniques based on principal components analysis and

regression analysis.

Establishing limiting criteria : Baseline signatures and their normal

interval of variation are established automatically by observing equipment operation during an initial learning period. During this period,

the equipment must be operated at or near all conditions for which

monitoring capability will be needed. The learning period should be of

sufficient duration to include a representative sample of normal variations. This period was 2-4 days in our investigations. The adequacy of

206
learning appears to be more closely related to elapsed clock time than

to the number of signatures measured, because of the biased sampling

previously cited (19). Several checks are available to ascertain if the

learning period has been adequate. These include counters which con- servatively estimate the proportion of the learning signatures considered

normal and the number of learning signatures since the last abnormal

classification, as well as the ability to switch to the monitoring mode

for a defined period during which a detailed monitoring summary is automatically obtained. If necessary, additional learning can be initiated

at any time. Since the system detects deviations from whatever baselines are established, sensitivity to further degradation is maintained

whether or not equipment was operating normally during the learning

period.

Detection logic : During monitoring, each vibration signature is

measured under steady operating conditions and tested to determine if

its deviations from the baseline signatures are statistically significant. While the application of classical statistics is invalidated by

biased sampling and by lumping differing operations into coarse intervals, the deviations calculated in approximate standard deviation units

do provide a quantitative measure of problem severity. Approximate

methods of calculating signature deviations, although lacking in mathematical elegance, are incorporated because they have proven to reduce

the incidence of false alarms.

During learning, the maximum and minimum values encountered for every

feature are stored for each operational interval. When a signature at

a given operational state is tested, the extreme values normal to that

operational interval and those values from its nearest neighbors are combined to obtain a smeared interval that encloses all extremes. From

this interval, a pseudo mean, m, and a pseudo standard deviation, a, are calculated as follows:

The absolute deviations calculated using these quantities are compared

against a confidence limit which decreases from C + 3 to C (an input

parameter) as the number of measurements, M, upon which m and a are

based, increases from 0 to 500:

m

Max + Min

2

a Max - Min

6

207
Statistical intuition and experience indicate that a value of 0^7 is

most appropriate. For industrial surveillance applications, testing the

gross vibration levels against established severity criteria (1-4) is al,

recommended. This additional detection capability would provide limited

protection during learning when no other performance monitoring is in

force and would inherently set an upper limit on the statistically

derived criteria.

Comprehensive data logging for diagnosis ; No automatic diagnostic logic

is implemented in this system. However, the detection of anomalous

events does automatically initiate procedures that log data to assist in

diagnosis. If a signature is encountered that exceeds normal bounds, an anomaly signature catalogue is begun for all signals from the suspect

machine. The anomaly catalogue allows detailed comparison between data

accumulated following the suspect event with that in the baseline reference catalogue obtained during learning. Additionally, a detection

summary which tallies suspect events for each signature component and

computes the average deviation is collected and available on request.

Also upon demand, a variety of visual displays from standard signal processing algorithms (orbits and detailed power spectra) can be obtained,

although data from these analysis capabilities are not automatically

retained. It is expected that the data collected for diagnostic purposes will allow the development of algorithms to diagnose the most

probable faults.

Results

Software implementation : The surveillance software has been implemented

on a Digital Equipment Corp., PDP 11/34 minicomputer with 28K words of

memory. Mass storage capability is provided by two disks, each with a 1.2M word capacity. All programs are written in FORTRAN except for the

peripheral handler routines that require assembly language.

A small portion of the disk storage is required for the software system;

the remaining portion, ^2M words, is available for data storage. The

burden of the data storage is associated with cataloguing baseline data.

The total storage requirement, R, for this reference catalogue is given

by

M

S i

R = 4 E °i £ % > 1=1 j=i j

where M is the number of machines to be monitored; 0-^, the number of

lumped operational states allowed for the ith machine; S-^, the number of sensors on the ith machine; and Djj , the number of descriptors used to

describe the information from the jth sensor on the ith machine.

208
I The mass storage requirements for the monitoring system are within

reason for even large-scale industrial applications. Assume, for

example, that one desired to monitor 100 machines, each equipped with

eight sensors. An analysis that assigns 20 lumped operational states

to each machine and characterizes each signal with 25 descriptors would

j require 1.6M words of storage. This allows one to describe each piece

1 of equipment with 200 descriptors and still reserve some storage area

j for logging diagnostic data.

Evaluation of monitoring system : A laboratory evaluation of the monitoring software has been accomplished using a small rotor assembly

driven by a fractional horsepower motor.* Three displacement probes

and two accelerometers are installed on the rotor as shown in Fig. 1.

One probe ("keyphasor") provides a tach signal and, through supplementary electronics, generates a rotationally synchronized sampling pulse

I to trigger the analog-to-digital converter. Two other probes, placed

at 90° to each other, measure the radial vibration of the shaft. In

addition, two accelerometers are installed on the inboard bearing

housing to measure the orthogonal components of radial vibration. In

our tests, two signatures describing rotor operation are actually cal-

| culated, one for the displacement probes and the other for the accelerometers. Each signature is composed from descriptors for both the

horizontal and vertical directions.

The rotor can attain speeds from 0 to 200 revolutions per second (rps)

;

this was the only control variable altered during our tests. Lumped

operational states were defined in 1-rps intervals. This speed resolution was a convenient choice which offered reasonable detail.

In our previous work (19) , the monitoring system was unable to maintain

a low false alarm rate over extended periods of testing using the limiting criteria which were automatically established. This difficulty was

overcome by modifying the detection logic and by extending the learning

period. We have, in fact, demonstrated that a learning file composed

in a few days can be used to monitor normal operation for periods of

several months without false alarms becoming a difficulty.

The detection capability of the monitoring system was investigated by

purposely introducing fault conditions into the test setup. The four

fault types chosen were shaft rub, imbalance, mechanical looseness, and

misalignments. Each anomaly type could be introduced in varying

degrees of severity. Some faults introduced no discernible perturbation

to the vibration signals; however, detection was always possible as the

severity level was increased. After the anomalous conditions associated

with fault testing were removed, the return to normal operation was

verified by the monitoring system. Examples of the type of diagnostic

Bently Nevada Corp., Minden, Nevada, Model RK-3.

209
data available from the system are presented as the individual tests

are described.

Imbalance test : The balance of the rotor was altered by the addition of

a 1.52-g mass 3.32 cm from the shaft centerline (translating to an imbalance force of 0.238 Nt m at 60 rps) . The change in the vibration

was readily detected by both horizontal and vertical displacement probes,

as illustrated by the detection summary shown in Table 1. Any signature

for which some descriptor was out of normal bounds is considered suspect. This was the case for all 1000 comparison signatures of each type

comprising this summary. An interesting detail in this test is that the

weight added actually improved the balance of the rotor. This can be seen in both Fig. 2, which shows the time-averaged orbit for both baseline and imbalance conditions, and in the detection summary, which shows

a reduction (negative deviation) in the signal descriptors associated

with the amplitude of the vibration. A change in vibrational amplitude

at the first order is well established as the primary indication of

changes in balance. However, as noted in Table 1, this descriptor was affected less dramatically than others. This results from the asymmetric domain (always positive) of power descriptors which reduces their

statistical sensitivity to reductions in their magnitude. This can be

corrected by using the log of their magnitudes. The phase of the first

order does show significant variations throughout the entire speed

range, as demonstrated in Fig. 3. The peak displacement was also significantly altered by the imbalance; Fig. 4 contrasts normal and anomalous variations for the peak displacement descriptor as a function of

speed.

Misalignment test : The alignment of the rotor can be altered by placing | shims under the bearing pedestals. The data shown resulted from raising j one side of the inboard bearing pedestal by 1.32 mm, thus offsetting the

center lines of the motor and rotor shafts. This misalignment was readily detected, as indicated by most of the descriptors shown in

Table 2. Unexpectedly, all descriptors except nonharmonic power showed

a decrease in their magnitudes. Figure 5 shows this effect in detail

for the power at the second order and is in contrast to Fig. 6 which

shows the increase in the nonharmonic power.

f

The decrease in overall and harmonic vibration levels was not, however,

an indication that the damage potential had been reduced, since the

coupling to the motor destructively failed within 12 hours. The prominent peak in the plot of nonharmonic power, Fig. 6, resulted from data

taken just prior to the destruction of the coupling. A reduction in

vibration levels was not common to all misalignment tests; nonetheless,

this case should serve to caution system designers that would ignore

the importance of such effects.

Mechanical looseness test : This test was accomplished by loosening the screws that fasten the inboard bearing pedestal to the base plate. In

210 I
this case, the accelerometers had a greater sensitivity to the abnormality than did the proximity probes. The rather pronounced effect on the • accelerometer signatures, tabulated in the detection summary given in

Table 3, most likely resulted from altering the mechanical impedance at

the bearing pedestal (23) . All descriptors influenced by the harmonic

content of the signal were strongly affected. A plot of the extreme

values experienced under both normal and loose conditions for the power

at the second order as a function of speed is shown in Fig. 7.

Partial shaft rub test : In our tests, the presence of shaft rubs was indicated most strongly by the accelerometer signals. The data shown

in Table 4 are from a partial shaft rub, where the rub screw (see

Fig. 1) was allowed to lightly bounce against the shaft. This anomaly

emphasizes again the importance of choosing descriptors which measure

nonharmonic signal power (11) . As seen from the detection summary

(Table 4) , the nonharmonic power is the only parameter which dependably

indicates the presence of the rub. Detailed power spectra for the

accelerometer under normal and rub conditions are shown in Figs. 8 and

9, respectively. The noise floor of the rub spectrum is raised over a rather broad order interval; this trait has been characteristic of rub

anomalies we tested.

Summary and recommendations

The monitoring system automatically established limiting criteria during

an initial learning period of a few days; subsequently, while monitoring

the test rotor during several months of normal operation, the system

experienced a false alarm rate of ^0.5%. At the same time, the monitoring system successfully detected all fault types introduced into the

test setup. Tests on "real-world" equipment are needed to provide final

verification of the monitoring techniques. The incremental expense

required to implement hardware for this purpose would be small in an industrial plant where sensors, electronics, and cabling already exist

for vibration monitoring. Furthermore, the data required to make this

monitoring approach effective would not hinder normal industrial operations.

There are areas that could benefit from additional investigation in the

laboratory environment. A comparison of the relative values of alternative descriptors under given fault conditions would be worthwhile.

This should be pursued in conjunction with extending the set of fault

types available, e.g., bearing problems. Other tests should examine

the effects of using fewer (more coarse) intervals to define the lumped

operational states. Finally, techniques to diagnose the most probable

fault should be developed by drawing upon the extensive data automatically logged by the monitoring system.

211
Appendix

In Table A-l is a list of the descriptors which we chose to include in our vibration signatures. Many of these descriptors are commonly used

and require no additional explanation. However, the following discussion and equations should serve to clarify the descriptors we used.

The waveform from a vibration sensor attached to a rotating machine has

a repetitive component. Regardless of magnitude of this component, its

presence can be enhanced by time-averaging the waveform. This process

requires that the raw signal be sampled at some integer multiple of the

frequency of rotation, fQ

. These sampled values, X(iAt) , are then

averaged using the following formula

NREV

X. = —~ £ X(iAt + nT) (i = 0, 1, 2, ... NPTS-1) (1)

n=l

where T is the period of rotation

T = NPTS • At = y~ (2) o

This time-averaging technique is equivalent to applying a comb filter to

the original signal which passes only the fundamental frequency and its

harmonics. The time averaged waveforms from two sensors at 90° to each

other can be used to obtain average orbital plots which describe the

motion of the shaft centerline at the monitored position. _ The "NPTS"

values (usually 30) that describe the averaged waveform, X., are correlated with the averaged waveform obtained initially as a baseline, XB_^,

to derive three additional quantities. The shape factor is the maximum

value obtained for the normalized correlation function, H(J) , which is

defined by

NPTS _

H(J) =

i—1 f T _ f\ 1 O \ fi\.

"NPTS 0 NPTS „ i/2

3^2 V x

2

_i=l e

i i=l \

(J = 0, 1, 2, NPTS-1) (3)

Values for Xi+j beyond XjjpTS are obtained by repeating the original

waveform. The point J = L where H(J) is a maximum also defines the lag

212
value, LAG, and the size factor, SZF, according to the following expressions:

/_360\ . \NPTSy LAG = L ' * —- ; (4)

NPTS

E X.

+L

• XB.

SZF —NPTs : • (5)

E TMl

i=l

When analyzing the vibrational signals from rotating machinery, orderdomain analysis (instead of the more familiar frequency-domain) simplifies interpretation of results, especially when variable speed operation

exists. The basic relationship that allows conversion between the two

domains is

f- , (6) o

where f is the fundamental rotational frequency.

Integral orders (Q = 1, 2, 3, etc.) occur at harmonics of the running

speed. If the vibrational signal is analyzed for NREV revolutions, the

minimum order resolution achievable is

The power at any order, Q^, will be denoted by G(Q^) , where Q. = iAQ,

i = 1, NOC (number of orders calculated).

Thus the total power in the vibrational signal up to some desired order,

Qp, is obtained by summing

K

TPOW = £ G(Q.s) » (8)

1=1

1

213
where

The harmonic power in the signal can be obtained by summing the power

spectrum estimates at integral orders:

N

HPOW = G ( m) » ( 10 ) m=l

where N is the largest integer for which < Q^.

The nonharmonic power is the difference of these two quantities

NHPOW = TPOW - HPOW (11)

When combining power estimates over an order interval, another parameter of interest is the power-weighted average order. This parameter

provides an indication of the order at which the power in the interval

is concentrated. This is given by

ATO =

-ll/2

E Q- G(Q.)

i=l

i=l

(12)

Similarly the average harmonic order is given by

N

,1/2

AHO = E m G(m)

m=l

N

E G(m)

m=l

(13)

21k
and the average nonharmonic order is given by

ANHO = i=i

N nl/2

E m G (m)

m=l

E 6(Q ) i=l

1

N

- £ G(m)

m=l

(14)

All of the parameters defined above can be calculated from the time

domain signal directly without the need for order domain transformations. The total power can be obtained by integrating the squared time

signal:

TPOW =

X CO dt ; (15)

NDAT _ k ^" NDAT .2 *i * £

G «i> • 1=1 1=1

(16)

The total harmonic power can be obtained by integrating the time

averaged waveform

NPTS _2

N

HP0W " npts £ *i "

1=1 1=1 £

G(m) (17)

The sums of the squared orders, weighted by their power in Eqs. (12)-

(14) , are equal to integrating the square of the derivative of the time

signal and the time-averaged signals, respectively:

Eq± G «y = I /

[ *' (t)]2 dt (18)

Eq? g(q.) NDAT

NDAT / X . - X. / E

1 ~ J (At) ; i=l

At

(19)

215
£m G(m) NPTS (At) (20)

References

1. M. P. Blake, "New Vibration Standards for Maintenance," Hydrocarbon

Processing and Petroleum Refiner, January 1964, pp. 111-114.

2. R. L. Baxter and D. L. Bernhard, "Vibration Tolerances for

Industry," ASME paper 67-PEM-14 for meeting April 10-12, 1967.

3. C. Jackson, "Vibration Measurement on Turbomachinery , " Chem. Engr.

Progress, V68, N3, March 1972, pp. 60-65.

4. C. Jackson, "A Practical Vibration Primer — Parts 1-8," Hydrocarbon Processing, April 1975-April 1978.

5. J. S. Mitchell, "Vibration Analysis — Its Evolution and Use in

Machinery Health Monitoring," Society of Environmental Engineers

Symposium on Machine Health Monitoring, Imperial College, London,

England, September 1975.

6. V. R. Dodd, "Spectral Applications for Petrochemical Plants,"

Engineering Foundation Conf. on Applications of New Signature

Analysis Technology, July 1977.

7. Performance Monitoring and AIDS Seminar /Workshop, AERO Data, Inc.

,

Washington, DC, September 20-24, 1976.

8. Bently-Nevada Machinery Protection Seminar, Cincinnati, Ohio,

May 17-18, 1978.

9. H. P. Koehler, "Vibration Monitoring: Pumpset Reliability at

Pickering GS," Ontario Hydro Report No. 574-11-K, February 1974.

10. M. M. Gupta and P. W. Davall, "Detection and Diagnosis of Incipient

Failures in Cyclic Machines," University of Saskatchewan,

Saskatoon, Canadian Defense Research Board Grant 9781-04, March 31,

11. E. Makay and 0. Szamody, "Summary of Feed Pump Outages," EPRI-FP754, April 1978.

12. R. James, B. Reber, B. Baird, and W. Neal, "Instrumentation for

Predictive Maintenance Monitoring," Mechanical Failure Prevention

Group Proceedings, 22nd meeting, April 23-25, 1975, pp. 114-127.

1976.

216
13. D. S. Wilson and J. L. Frarey, "Automated Machinery Surveillance

and Diagnostics," Progress in Nuclear Energy , VI, Pergamon Press,

pp. 723-733 (1977).

14. "The ICEMS Story — The U.S. Navy Inflight Engine Condition

Monitoring System as Applied to the A7E Aircraft and the TF41-A-2

Engine," Detroit Diesel Allison report EDR-8472, April 30, 1975.

15. J. R. Passalacqua, "Description of an Automatic Gas Turbine TRENDS

Diagnostic System," ASME Gas Turbine Conf., March 1975.

16. Spectral Dynamics Machinery Vibration Seminar and Course Notes.

17. D. R. Houser and M. Drosjack, "Vibration Signal Analysis

Techniques," USAAMRDL Technical Report No. 73-101, December 1973.

18. R. P. Wallace and W. L. McCarthy, "VIDEC Ship Propulsion System

Performance Monitor," Mechanical Failure Prevention Group

Proceedings, 22nd meeting, April 23-25, 1975, pp. 221-257.

19. K. R. Piety, "Statistical Algorithm for Automated Signature

Analysis of Power Spectral Density Data," Progress in Nuclear

Energy , V 1, Pergamon Press, pp. 781-802 (1977).

20. E. Cortine, H. L. Engel, and D. K. Scott, "Pattern Recognition

Techniques Applied to Diagnostics," Society of Automotive Engr.

,

Mid-Year Meeting, Detroit, Michigan, May 1970.

21. L. F. Pau, "Adaptive On-Line Failure Diagnosis and Predictive

Pattern Recognition," Second International J. Conf. Pattern

Recognition, February 1974.

22. H. E. Hunter, "Demonstration of the Use of ADAPT to Derive

Predictive Maintenance Algorithms for KSC Central Heat Plant,"

Report No. AVSD-0084-73-RR, AVC0 Systems Division for NASA,

Wilmington, Mass., 01887, November 1972.

! 23. Richard Woods, "An Investigation into Vibration Criteria for

Rotary Machinery," Ph.D. Thesis, University of Aston, Birmingham,

England, 1968.

Acknowledgment

Research sponsored by the Division of Reactor Research and

Technology, U.S. Department of Energy, under contract W-7405-eng-26 with

the Union Carbide Corporation.

217
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231
VIBRATION ANALYSIS METHOD FOR DETECTION OF ABNORMAL

MOVEMENT OF MATERIAL IN A ROTARY DISSOLVER

C. M. Smith and D. N. Fry

Oak Ridge National Laboratory

Oak Ridge, Tennessee 37830

W. T. King

Department of Nuclear Engineering

University of Tennessee

Knoxville, Tennessee 37916

Abstract: Vibration signals generated by the movement of simulated

nuclear fuel material through a three-stage, continuous, rotary dissolver were frequency analyzed to determine whether these signals

contained characteristic signal patterns that would identify each of

five phases of operation in the dissolver and, thus, would indicate

the proper movement of material through the dissolver. This characterization of the signals is the first step in the development of a system for monitoring the flow of material through a dissolver to be

developed for reprocessing spent nuclear fuel. Vibration signals from

accelerometers mounted on the dissolver roller supports were analyzed

in a bandwidth from 0 to 10 kHz. The analysis established that (1) all

five phases of dissolver operation can be characterized by vibration

signatures; (2) four of the five phases of operation can be readily

and directly identified by a characteristic vibration signature during

continuous, prototypic operation; (3) the transfer of material from

the inlet to the dissolution stage can be indirectly monitored by one

of the other four vibration signatures (the mixing signature) during

prototypic operation; (4) a simulated blockage between the dissolution

and exit stages can be detected by changes in one or more characteristic vibration signatures; and (5) a simulated blockage of the exit

chute can not be detected.

Key words: Monitor system; rotary dissolver; signature analysis;

vibration analysis.

Introduction: Vibration signals generated by the movement of simulated

nuclear fuel material through a three-stage, continuous, rotary dissolver were analyzed to determine whether these signals contained

characteristic signal patterns that would identify each of five phases

of operation in the dissolver and, thus, would indicate the proper

movement of material through the dissolver. This characterization of

the signals is the first step in the development of a system for monitoring the flow of material through a dissolver to be developed for

232
reprocessing spent nuclear fuel. Five phases of dissolver operation

are present during the movement of material through the three-stage

dissolver: (1) introduction of material into the inlet stage,

(2) transfer of material from the inlet stage to the dissolution stage,

(3) mixing of material in the dissolution stage, (4) transfer of material from the dissolution stage to the exit stage, and (5) discharge

of material from the exit stage.

Dissolver description: The dissolver is a three-stage, continuous,

rotary drum, 4 ft long and 4 ft in diameter. It rotates around a horizontal axis on two roller rings, one of which is V-shaped to provide

lateral stability. Each roller ring is supported on two rollers. The

dissolver is chain driven at the exit end. Figure 1 shows the internal

components of the dissolver.

The dissolver rotates cyclically at a speed of approximately 3 rpm, as follows: rotate in a "forward" (clockwise) direction for a predetermined time period (^20 min) , stop, make one revolution in the "reverse"

(counterclockwise) direction, and stop before repeating the cycle.

Discrete batches of material (^2 kg) are periodically (every 30 s)

introduced into the dissolver. During forward revolutions, baffles

in the inlet stage move the material into a wedge shaped chute (Fig. 1)

which transfers the material into the dissolution stage. The material

is mixed in the dissolution stage by a mixing-transfer baffle and

remains in this stage until the dissolver stops and makes a reverse

rotation. During this reverse movement, the mixing-transfer baffle in

the dissolution stage moves the material into a conical transfer chute

(Fig. 1) which transfers the material into the exit stage. Once the

material is in the exit stage, the dissolver again rotates forward and

repeats the cycle, and transfer baffles in the exit stage transfer the

material into the exit chute which discharges the material from the

dissolver.

The dissolver is a counterflow device; the fuel and the acid solution

move in opposite directions. When nuclear fuel is reprocessed, it

(cladding and oxide) will be chopped into pieces about 1 in. long. The

chopped fuel will be introduced into the inlet stage and moved to the

dissolution stage where an acid solution will leach the oxide from the

cladding. The empty cladding will be moved to the exit stage and discharged from the dissolver. The acid solution will be introduced in

the exit stage; it will flow to the dissolution stage where it will

leach the oxide from the cladding, and finally to the entrance stage

where it will be discharged for further processing.

In these experiments, simulated chopped fuel hulls consisting of stainless steel tubing packed with a mineral oxide were used instead of

cladded nuclear material, and water was present instead of acid. These

differences are insignificant to the results and conclusions of this

study because the important physical properties of the simulated fuel

233
and actual fuel are similar and the chemical reaction has a negligible

effect on vibration.

Instrumentation: The vibration instrumentation consisted of four,

Endevco, model 2233E accelerometers and a drum position and direction

indicator. The accelerometers, having a flat-frequency response of ±3

dB, between 4 and 6000 Hz, were located as shown in Fig. 2. (Four

accelerometers were installed to allow spatial analysis of the signals

if this were shown to be informative, but this has not been attempted.)

The signals from these sensors and indicator were conditioned and

recorded on a Bell and Howell, model 4010, 14-channel FM tape recorder

for off-line analysis.

The accelerometers were mounted with electrically isolated mounting

studs, using oil coupling to bolts which are part of the support roller

assemblies. Miniature coaxial cables, environmentally sealed at the

accelerometer connection, transmitted the vibration signals to voltage

preamplifiers. The single-ended signals were ac coupled with a 0.02-Hz

high-pass filter, amplified to a ±1 V level, and band-pass filtered

(3 Hz to 300 kHz) before being recorded.

The position of the dissolver was indicated by a 0- to 0.8-V signal

from electronic circuitry with proximity probes to detect the teeth on

the drive sprocket of the dissolver drum. The direction of dissolver

rotation was indicated by a 1. 25-V-forward, 1. 5-V-reverse, logic signal

from this same circuitry. The position and direction signals were

suitable for recording without further conditioning.

Experimental procedure: These studies were devised to accomplish three

goals, as follows: (1) to determine whether each of the five phases of

dissolver operation could be characterized by the vibration signal

associated with that phase of operation, (2) to determine whether the

characterization of each phase could be identified during continuous

operation when two or more phases might occur simultaneously, and

(3) to determine if improper movement of material through the dissolver

would result in significant changes in the characterization of the

phases of operation.

To achieve the first goal, several single, 20-kg batches of simulated

fuel material were processed individually through the dissolver. With

only one batch of material in the dissolver at a time, the signals

associated with each of the five phases of dissolver operation were separated and individually recorded and examined.

To achieve the second goal, several tests were conducted where 2-kg

batches of material were added at 30-s intervals (simulating continuous

operation) until 60-kg of material had been added. The dissolver was operated on approximately a 5-min cycle; thus, ^20-kg loads of material were collected in the dissolution stage before transfer.

23k
Two series of tests were conducted to achieve the third goal: in one,

an artificial blockage was installed in the transfer chute between the

dissolution and exit stages, and, in the second, an artificial blockage

was installed in the exit chute ^2 ft from the entrance. For both

series, tests were conducted with both single, 20-kg loads and individual 2-kg loads introduced at 30-s intervals.

Data analysis: The recorded vibration signals from the accelerometers

were frequency analyzed over a bandwidth from 0 to 10 kHz, using a fast

Fourier transform (FFT) algorithm. The position indicator was used to

arbitrarily divide each dissolver revolution into sixteen equal angular

segments, or orientations. To correlate the analysis with the dissolver

position, a separate FFT analysis was performed on the vibration signals

received during each orientation. Since the drum period was 20 s per

revolution, each orientation spanned ^1.25 s. A frequency analysis was performed during each orientation, with a maximum frequency of 10 kHz

(sampling rate of 20 kHz) and a resolution of ^40 Hz. Data from only

^0.8 s of each orientation were analyzed because of nonreal time processing which resulted because the computer was unable to finish processing one set of data before the next was ready to be processed.

For each orientation, the FFT analysis yielded a power spectral density

(PSD) , which is the amount of power in the signal at each frequency.

Preliminary analysis showed that there were no prominent, discrete frequency spectra features, but that each phase of dissolver operation

could be characterized by relatively broad-band (1-2 kHz) changes in

the spectra. Therefore, a method was determined for condensing and

extracting useful information from the numerous individual PSD spectra.

The individual spectra were subdivided into ten, 1-kHz bandwidths over

a range from 0 to 10 kHz, and the PSD values within each bandwidth were

used to form a single, root-mean-square (RMS) quantity for each bandwidth for each orientation of each revolution. This allowed the

orientation-dependent fluctuations in the bandwidth-limited RMS parameter to be studied. To simplify the analysis, a computer program was written which computed the bandwidth-limited RMS value without requiring an FFT analysis and plotted it versus dissolver orientation.

Results for single 20-kg charge: The results show that, although

vibrations were produced over all analyzed frequency ranges, there is a frequency range for each phase of operation in which the vibration

signals have a characteristic signature (or pattern) of RMS values when

these values are plotted versus dissolver revolutions (16 orientations

per revolution). Furthermore, one needs to observe only two frequency

ranges, 2 to 3 kHz and 5 to 6 kHz, to determine the characteristic signature for each phase of operation.

Figure 3, a plot of the 2- to 3- and 5- to 6-kHz RMS values versus

dissolver revolution, illustrates the characteristic signature for each

phase. The test was started with the dissolver empty. The material

235
was introduced into the inlet stage during revolution 5, transferred to

the dissolution stage during revolutions 6 to 8, and mixed during revolutions 9 to 29. The dissolver was stopped at the end of revolution 29,

and revolution 30 was a reverse revolution during which the material was transferred to the exit stage. Forward rotation of the dissolver was resumed to discharge the material during revolutions 31 to 38.

During revolution 5, the charging (entrance) of material produced

vibrations and corresponding RMS spikes in both the 2- to 3- and 5- to

6-kHz frequency ranges. This single, large spike is the characteristic

signature for material charging. This signature is identified in the

5- to 6-kHz range because of possible confusion with other spikes in

the 2- to 3-kHz range and the better signal-to-noise ratio in the 5- to

6-kHz range.

The transfer of material from the inlet to the dissolution stage also

produced spikes in both frequency ranges. The characteristic vibration

signature for this phase of operation consists of spikes during orientation 13 for several revolutions after the material is charged

(Fig. 3, revolutions 6, 7, and 8). This signature can be identified

in either frequency range since no other phase of operation produces a spike in orientation 13, and there is no significant difference in the

signal-to-noise ratio for the two frequency ranges.

Mixing in the dissolution stage produced spikes of significant amplitude only in the 2- to 3-kHz range, as seen in Fig. 3, revolutions 9

to 29. The signature for mixing is a relatively large spike during

the last orientation of each revolution (orientation 16). These mixing

spikes are periodic, are generated during forward revolutions, and are similar in amplitude.

The transfer of material from the dissolution stage to the exit stage

also produced spikes of significant amplitude only in the 2- to 3-kHz

range (Fig. 3, revolution 30). This signature is a relatively large

spike during orientation 3 of the reverse revolution. This spike is

similar to a mixing spike, but there are two important differences:

it is generated during a reverse revolution, instead of during a forward

revolution; and it is generated in orientation 3, rather than in orientation 16 (orientation numbers decrease with time during a reverse

cycle)

.

Figure 3 shows that for revolutions 31 to 38 the discharge of material

from the exit stage of the dissolver produced spikes in both frequency

ranges, but these spikes have a better signal-to-noise ratio in the

5- to 6-kHz range. The signature for the discharge phase is four

equally spaced spikes per revolution. These spikes are generated

during forward revolutions following a reverse, and their amplitude

tends to decrease as more material is discharged, leaving less material

in the exit stage. The signature for the discharge of material was chosen in the 5- to 6-kHz range because the spikes in the 2- to 3-kHz

236
range were similar to those for mixing. Since, in normal operation,

mixing and discharge would occur simultaneously, separation of these

two signatures in the 2- to 3-kHz range would be more difficult.

The vibration signatures in Fig. 3 were determined from the analysis

of only one of the four accelerometers , accelerometer A. The data

from all accelerometers were analyzed, and the results were similar.

However, in general, the amplitudes of vibrations were larger from

accelerometers located near the source than from those located farther

away; i.e., for charging, accelerometers A and B on the inlet side had

larger signals than accelerometers C and D on the exit side. Also,

vibrations not caused by material movements (i.e., vibrations from

individual rollers) could influence an adjacent accelerometer, but

being attenuated by distance, they had little effect on the other

accelerometers

.

J

" Results for 2-kg charges at 30-s intervals: The results in Fig. 4

(2 to 3 kHz) and Fig. 5 (5 to 6 kHz) show that a characteristic signature can be identified for each phase of dissolver operation except

one during normal, continuous feed operation. In Fig. 5, the single,

| large-amplitude charging spikes (i.e., the charging signature) are identifiable because their amplitudes exceed 3 x 10"^ V,* and their

occurrence is time dependent rather than revolution dependent, i.e.,

they do not occur at particular orientations of certain revolutions

(see Fig. 5, revolutions 2, 3, 5, 6, and 8). Once these spikes have

been identified in the 5- to 6-kHz range, their effect in the 2- to

3-kHz range can be inferred (i.e., a spike during revolution 2 of

Fig. 5 means that charging also caused the spike during revolution 2

of Fig. 4, and a spike during revolution 6 of Fig. 5 means that charging contributed to the spike during revolution 6 of Fig. 4).

It is difficult to identify a characteristic signature for transfer of

material from the inlet stage to the dissolution stage with a 20-kg

charging load, and such identification is unreliable with 2-kg charging

loads because the amount of material being transferred is less and the

associated signal is smaller. However, this transfer may be indirectly

monitored through the signature for mixing in the dissolution stage.

If the transfer from the inlet stage to the dissolution stage did not

occur, eventually (after the next reverse) there would be no material

j in the dissolution stage, and the mixing spikes would be absent.

In the analysis with 20-kg loads (Fig. 3) , the signature for mixing

in the dissolution stage is identified as a once-per-revolution spike

during orientation 16 in the 2- to 3-kHz range. In Fig. 4, this same signature is found, although additional spikes are present. The

! effects of charging and discharging also produced spikes in the 2- to

*The two charges immediately following a reverse have a smaller

amplitude because of analytical techniques.

237
3-kHz range, and these additional spikes must be considered (Fig. 4,

revolutions 17, 20, 23, and 26). As previously stated, the spikes

generated during the charging phase can be identified in the 5- to

6-kHz range, and similar effects can be found in the 2- to 3-kHz range.

Later, it will be shown that the spike generated during the discharging

phase can be handled in the same manner.

Thus, by using this method, one can determine the effects of charging

and discharging in the 2- to 3-kHz range; then, since mixing spikes are generated during orientation 16, the mixing signature can be determined

(Fig. 4, revolutions 17 to 26). However, possibly there is a problem:

if charging or discharging occurs simultaneously with mixing, this

analytical method is currently unable to separate the effects of each.

To determine the mixing signature, enough spikes caused only by mixing

must remain after the spikes caused by a simultaneous occurrence of

phases (mixing and charging or mixing and discharging) are discounted.

If a charging period is the same as a period of revolution, and if

mixing and charging occur simultaneously, there will be no spikes

caused only by mixing. Therefore, the analytical method is unable to

determine the mixing signature in this instance.

The simultaneous occurrence of mixing and discharging is different

because mixing and discharge can occur simultaneously only over a limited time period. Discharging occurs immediately following a reverse and lasts only several revolutions, with its effects diminishing in latter revolutions. Furthermore, during this same time period,

the mixing stage is being refilled, and mixing is producing only small

effects. Therefore, the simultaneous occurrence of mixing and discharging poses no significant problem in determining the mixing signature since the two phases cannot occur simultaneously over long periods

of time.

The signature for transfer of material from the dissolution stage to

the exit stage can also be identified in the 2- to 3-kHz range of

Fig. 4 (revolutions marked "REV") . This signature is relatively easy

to identify since it occurs only during a reverse and in orientation 3.

It is possible that charging may occur simultaneously, but this will be

indicated by a charging spike in the 5- to 6-kHz range. If this

happens, the effects are not separable by the analytical method, and

the transfer of material cannot be identified for this reverse revolution. However, there is an indirect indication of this transfer

because if it did not occur, there would be no material transferred to

the exit stage to be discharged during subsequent forward revolutions.

Thus, the signature for discharging would be absent.

The signature for discharging of material from the exit stage, which is

four equally spaced spikes per revolution, can be identified in the

5- to 6-kHz range of Fig. 5 (revolutions 13-17, 27-32, and 40-44).

Generally, the amplitude of these spikes is less than 3 x 10~^ V, and

it progressively decreases during the revolutions following a reverse.

238
It is possible for material to be charged simultaneously with the

observation of these discharging spikes, and when it is, the amplitude

of the resultant spike is greater than 3 x 10~3 V (Fig. 5, revolutions

14 and 16) . The simultaneous presence of a charging spike with a discharging spike has no significant effect on the identification of the

signature for discharging since there are four discharging spikes per

revolution. In Fig. 4, it can be seen that the discharging spikes also

produce effects in the 2- to 3-kHz range. By reasoning similar to that

previously used with charging spikes, the discharging spikes can be

identified in the 5- to 6-kHz range and the effects in the 2- to 3-kHz

range can be found.

Results for artificially induced blockages: The results show that

changes in the characteristic signatures for the phases of operation

can indicate some, but not all, types of blockages. A blockage in the

transfer chute between the dissolution and exit stages causes definite

changes in some of the characteristic signatures. These changes can

be seen in Figs. 6 and 7 which show the fluctuations in the RMS value

for the 2- to 3-kHz and 5- to 6-kHz frequency ranges, respectively, for

this blockage test.

Blockage of this transfer chute prevents material from passing to the

exit stage where it is discharged from the dissolver. With no material

being discharged, there can be no discharge signature in the 5- to

6-kHz range (four spikes per revolution), as indicated in Fig. 7, revo- lutions 13-17, 27-32, and 41-46. Furthermore, since all of the material collects and remains in the dissolution stage, mixing spikes of

large amplitude are present in the 2- to 3-kHz range in forward revolutions immediately following a reverse (Fig. 6, revolutions 14-16, 28-30,

and 42-43). Under normal operation, the dissolution stage should be

refilling at this time, and the mixing spikes should be small, if

present at all.

The characteristic signatures show no significant changes for a blockage

installed ^2 ft from the entrance of the exit chute in the exit stage.

Figures 8 and 9 show the fluctuations in the 2- to 3-kHz and 5- to 6-kHz

ranges, respectively, for this blockage test. Except for the presence

of a blockage, this test was similar to the test of Figs. 4 and 5. The

lack of significant differences in the data is best seen by comparing

Fig. 4 with Fig. 8, and Fig. 5 with Fig. 9. The discharge of material

is the only phase of operation which should have been affected by the

blockage. However, the discharge signature is not significantly different between the two tests (Figs. 5 and 9). Also, the effects of

discharging in the 2- to 3-kHz range (Figs. 4 and 8) show no major differences, and there are no unusual aspects of the data in Figs. 8 or 9

that would indicate abnormal operation of the dissolver. The reason

for the lack of significant differences in the discharge signatures

during this blockage test, we believe, is that the blockage is located

at some distance from the exit chute entrance. This allows the discharged material to provide a normal discharge signature because the

239
material moves into and down the chute in a normal manner before

encountering the blockage. Because of restrictions at the test facility, the blockage could not be moved to the exit chute entrance for

further testing.

Conclusions: A vibration monitoring system can be developed to detect

abnormal material movement in a rotary dissolver. It has been established that (1) all five phases of dissolver operation can be characterized by vibration signatures; (2) four of the five phases of

operation can be readily and directly identified by a characteristic

vibration signature during continuous, prototypic operation; (3) the

transfer of material from the inlet to dissolution stage can be indirectly monitored by one of the other four vibration signatures (the

mixing signature) during prototypic operation; (4) a simulated blockage

between dissolution and exit stages can be detected by changes in one

or more characteristic vibration signatures; and (5) a simulated

blockage of the exit chute can not be detected.

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MONITORING INLET STEAM VALVES OF PWR 900 MW TURBOGENERATORS

A. JAUDET

J.C. SOL

ELECTRICITE DE FRANCE

Direction des Etudes et Recherches

1 , avenue du General de Gaulle

B.P. 27 - 92141 CLAMART

FRANCE

Abstract :

A study of the reliability of overspeed protection systems for turbines

associated with nuclear reactors, confirms the essential role of steam

valves in the general reliability of these systems, and consequently in

the operational safety of the units.

Over and above the obvious reasons concerning operational safety, an improvement in investigation and diagnostic methods clearly provides

beneficial spin-off in terms of equipment availability.

Assessment of turbine operational safety, and more particularly evaluation of the risks generated by non-closure of steam-valves, has led to

a concentration of interest about three functional characteristics : - stem movement quality,

- seal-tightness,

- "general condition".

Each of these characteristics can be subject to specific mechanical

failures for which detection procedures exist, and which are described

in this paper.

In application of these principles, examples of the technological

solutions (including automatic surveillance system) adopted for monitoring the steam-valves of the units of the 900 MW standard are described,

together with the first operating results for these methods and this

equipment

.

250
1 - NEW SURVEILLANCE AND DIAGNOSIS METHODS [l]

1.1 - Principles

A study of the reliability of overspeed protection systems for turbines

associated with pressurized water reactors confirms the essential role

of inlet steam valves ( figure 1 ) in the general reliability of these

systems and consequently in the operational safety of the units.

Conventional operating tests (on-off type) are performed weekly [2] on

all the inlet steam valves of every E.D.F. turbine. These tests are now

completed by using endoscopes for inspections during stops (figures 2.3).

New surveillance and diagnosis methods were developed in order to

improve the quality of these classical tests. They are based upon two

types of complementary actions : a/ Permanent auscultation of simple parameters.

b/ Specific checking tests, deeper and finer but more complicated and

for that reason performed only periodically (or in case of abnormality

lity detection by the permanent auscultation system)

.

These methods obviously contribute to improve the reliability of the

valves by providing advanced warning in some cases of deterioration ; but they also improve their availability by providing information on their behaviour during operation and this information can be used to

optimize preventive maintenance and may even lead, in the future, to

predictive maintenance.

According to the evaluation of the risk generated by non-closure of

valves and to the statistical study of the most probable failures, we concentrated most of our interest on three fundamental functional

characteristics : - Stems' motion quality,

- Seal tightness,

- "General condition".

1.2 - Stems' motion quality

A statistical study of the fossil fuel thermal plants' incidents showed

that the main risks the stems' motion may be subjected to are incipient

seizures or stickings between the stem and its guides.

This type of degradation is one of the most important both for the

safety of the plant because of the possible consequences of a valve

non-closure and for the equipment availability for it is responsible

for 1/5 of the inlet steam valves' incidents.

251
Consequently, it is particularly interesting to detect such defects and

for this purpose we chose to record, as a permanent auscultation parameter, the closing time of every cutout valve (HP and LP) at every

closure

.

On the other hand, the conventional weekly performed checking test of

"closure or non-closure" was improved by systematically plotting the

stroke/hydraulic pressure curve during the motion.

At last, in case of abnormality detected through one of the two above

mentioned methods, more complete closure tests may be performed by

measuring : - The instantaneous stem speed with a laser velocimeter.

- The stem vibrations during the motion.

The measurement of the instantaneous stem speed with a laser velocimeter, by providing very rich information about the dynamics of the

valves' motion during the closure ( figure 4 ) has already led us to a better knowledge of this motion and allowed us to build up a computation model (figure 5) to explain the main characteristics of this movement. Unfortunately, this test needs a heavy equipment to be performed

and it will be used only in case of important abnormality.

The stem's vibrations measurement during its motion is, on the contrary,

very simple. The sensor is the accelerometer mounted on the stem for

the permanent monitoring (see below) . The signal processing device is

a mere oscilloscope (or a sonorisation) . In case of normal sliding

motion of the stem between its guides, the vibration level is low

except for the shocks produced by the normal movement ( figure 4 ) . In case of dry friction or sticking, high levels of stresses are generated

along the friction area in a very broad frequency band. Many resonances

are excited in the metal (particularly at high frequencies) and the

corresponding vibrations can be easily detected by the piezoelectric

accelerometer which is especially sensitive to high frequency

vibrations. Simulation laboratory tests showed ( figure 6 ) an increase

of the vibration level of more than + 46 dB in case of sticking for an area of only 0.8 cm2

.

1.3 - Seal tightness

Another common possible defect is a seal tightness defect following the

valve plug or seat erosion by the steam. This defect causes, when the valve

is supposed to be completely closed, a leak of steam into the inlet

pipes of the turbine with two important effects : a/ It brings some residual mechanical energy into the turbine.

b/ It emits a very broad band noise produced both by the jet itself

and by the collision of the jet inside the piping.

252
The first effect induces a motor torque on the turbine shaft and consequently modifies the rotor deceleration curve. It has been shown that

the K-coef f icient (coefficient of the tangent hyperbola) of this curve

is the most appropriate representation to detect such modifications. In

this case too, a computational model was built up with several coefficients adjusted on the experimental values. In this way, a leak constant

motor torque has been simulated (figure 7)

.

Consequently, we decided to record the rotor speed during every

deceleration and to compute and plot automatically the K-coef f icient

curve. Any modification of this curve may signify a global tightness

defect of the turbine.

Then, in order to localize and perhaps quantify the defect, we can perform the specific ckecking test based upon the second effect : the

measurement of the leak noise.

Many studies and tests have been previously performed to characterize

this noise and its transmission through the casing to the outside wall

of the valve. In fact the acoustic emission frequency range is very

broad : from a few hertz up to 1 MHz ; for the industrial mechanical

noise is mostly concentrated under about 100 kHz, the best signal/noise

ratio is obtained in the high frequency range and can be measured by a piezoelectric accelerometer working on its whole frequency range

including its resonance. Even better results can be obtained using an ultrasonic piezoelectric sensor (acoustic-emission type) with a higher

resonance frequency (figure 8)

.

1.4- "General condition"

Several other defects are liable to affect the steam valves as excessive clearances or disunions between parts (seal and casing for instance)

,

cracks (of the stem for instance) and so on.

Very generally, such defects induce modifications of the vibrational

characteristics and in most cases increase the energy dissipated by

vibrations

.

Consequently, we consider that measurement of the global (RMS) vibration

level is an accurate permanent auscultation parameter for the general

mechanical condition of the valve (see below the description of the

measurement)

.

In case of previously detected abnormality a deeper vibration signal

analysis may be performed by using directly the signal from the accelerometer .

253
Some laboratory tests showed that in case of excessive (abnormal)

clearances between parts, the vibratory excitation by the turbulent

steam flow induces incipient shocks inside the valve which may be easily

detected by the stem accelerometer using only the time representation

of the signal (display or sonorisation) (figure 9)

.

An experimental study of the evolution of the first bending mode

frequency of a cracked stem with the crack depth Efc-aws (figure 10)

that only major cracks can be detected by this way. ~~

2 - PERMANENT AUSCULTATION SYSTEM

Permanent auscultation is obviously the first stage of all the above

described surveillance methods. A specific automatic device was achieved

for this purpose ( figure 11 )

.

2.1 - Measurements

As said above three types of permanent auscultation parameters are considered : - closing times of cutout valves ( 1 2/ turbine)

,

- rotor speed (1 /turbine),

- overall vibration level of all the valves (24/turbine)

.

Closing times are elaborated from the position information of the

cutout valves. The vibration levels are elaborated by electronic signal

conditioners (amplifiers, low pass filter, RMS detector) from the

output signal of the accelerometer mounted on the stem of every valve.

At the same time, some other parameters have to be recorded both to

provide automatically statistical information on the valve operating

conditions and to help us to understand the auscultation parameters'

variations

.

These "statistical parameters" are : - the logical states (open or closed) of the cutout valves (12 binary

data/ turbine)

,

- the positions of the HP control valves (6/turbine),

- the electrical power output of the turbogenerator (1 /turbine).

2.2 - Data recording

All the above mentioned measurements sensors are connected with the

central data acquisition device (figure 12) and get in through appropriate electronic interfaces : - Closing time printed boards compute the closing times from the information about the position at every closure and record them in a buffer | memory.

2$k
- The rotor speed printed board computes the speed value (numerical

data) from the analog signal.

- The logical states of the valves board record in a buffer memory the new state in case of any change.

All the other analog measurements (overall vibration levels, position of the control valves, power output) are digitally converted

through two multiplexer levels.

The microprocessor monitors all these interfaces and scans all the

measurement inputs with a very short period cycle (a few seconds)

.

Some of them are systematically recorded i.e. everytime there is a value : the closing times and the logical states of the valves.

The others have continous variations (vibration levels, position of the

control valves, power output, rotor speed) and are recorded only when

the difference between the scanned value and the last recorded one is

larger than a certain previously defined threshold (relative or absolute) .

Every record contains the measured value and the instant of measurement

This method allows to record very few values in case of small variations and, on the contrary, a large number. of values in case of important variations (when it is interesting) ( figure 13 )

.

The record is performed on a magnetic tape cassette which is periodically (every week) sent to a computer system to be processed.

2.3 - Data processing :

During a first stage, simple computer programs were developed in order

to read back the cassette and plot the time-evolution of every parameter .

Then, from the study of the first results we began to define the princi

pies of the "automatic surveillance" programs. The idea is simple : first, we calculate, for every surveillance parameter, the "reference

state" from a statistical study (mean and standard deviation) of the

first results. Sometimes these characteristics are assumed to be dependent on another parameter and have to be represented as a function of

it, by a polynomial regression.

For the HP control valves' vibrations, the influent parameter is

obviously their own position.

As to the vibrations of the other valves and the closing times, it is

supposed to be a matter of the power output of the plant.

255
As for the K-coeff icient during rotor deceleration the most accurate

representation to detect the leak influences is to plot it as a function

of the inverse of the speed.

In each case, a confidence interval is plotted on each side of the mean

curve. It is defined from a compilation of the experimental data assu- ming that the statistical distribution of these data is, roughly, a Laplace-Gauss distribution.

Then, at the end of this first period, the automatic surveillance

programs compare the newly recorded values with the previously calculated "reference states" and any value outside its confidence interval

is supposed to be an "abnormal value" and consequently triggers an alarm message.

i Thus, normally, only a little information (alarm messages) has to be

considered each week during operation. This information is recorded

with some simple statistical characteristics of each parameter in order

to detect any time-modification in the statistical characteristics.

3 - FIRST RESULTS

The automatic surveillance system was first set up on the first six

PWR units. Now, more than one year of continuous monitoring has been

performed on the first two units.

3.1 - Closing times :

The closing times of the cutout valves appeared to be as good as an example of a surveillance parameter can be. Jndeed, the first results

show (figure 14) : - they depend very little on the power output,

- their standard deviation is very small.

Consequently, we may consider that any important modification of a closing time would be significant of a stem's motion quality defect

and in this case immediately perform the specific checking tests.

Defining the confidence interval at 95 % probability level, until now, we have had no significant alarm message.

3.2 - Rotor deceleration curves :

A compilation of the first experimental results shows that the

K-coef f icient curve is mainly dependant on the vacuum value inside the

256
turbine and, when this vacuum value is the normal one, roughly constant

(figure 15, figure 16) .

Thus boundary curves have been defined with their fitting theoretical

coefficients in the model. In case of normal vacuum, the experimental

curve must be between these boundaries.

A leak motor torque has been simulated and the model shows the fairly

good sensitivity of the method ( figures 17, 18 ) . Nevertheless the

relation between this theoretical leak torque and some real tightness

defect still has to be established by experimentation on an actual-size

turbine

.

If an experimental curve exceeds the boundary values, we have first to

look for a vacuum value modification before thinking of a leak defect.

3.3 - Vibration levels :

Here, the above statistical processing method was a little more difficult to perform because the number of recorded values is very much

larger (permanent scanning) and theirf a priori, standard deviation is

very important.

Under these conditions, the direct computation of the "reference states"

from all the experimental data gave very large confidence intervals and

thus the detection of an "abnormal value" was in most case impossible.

A closer study of these vibration levels showed that they are roughly

constant during the constant power operation and they are subject to

very large variations during the power variations.

These variations ( figures 19, 20 ) stay for a certain interval of time

(say 1 hour) after the power plant variations probably because of the

stabilisation (relaxation time) of some operating parameters.

Consequently we decide to consider as non significant and to eliminate

all the measurements recorded during the power plant variations.

Furthermore in order to avoid electrically or mechanically caused erratic

values, we also eliminate all the values, the duration of which is

shorter than a certain interval of time.

Finally, we obtained acceptable reference curves (figure 21) and we defined their confidence interval at 99 % probability level.

I In order to avoid too frequent "statistical" alarms it is necessary to

eliminate the same kind of measurements during the automatic surveillance phase. Nevertheless and to minimize the consequent information

loss we consider that these measurements are, in any case, significant

257
of a defect (and trigger an alarm message) when their values are up to

a certain critical level.

4 - CONCLUSIONS

The theoretical and experimental studies as well as the first Operating

results confirm the interest of the permanent auscultation and the

expected possibilities of the complementary specific checking tests.:

After one year operation, the methods and the important "reference

states" have been defined. We have now to : - confirm the detections capacity of the method on real defects (if

any ! )

,

- optimize the numerical criteria from a long period operation experiment (best probability law, appropriate alarm threshold)

.

In the future, we plan to complete the permanent auscultation system

including new operations parameters to improve the permanent auscultation parameters' analysis and otherwise the surveillance of the rotor

shaft vibrations (at nominal speed and during decelerations).

Anyway it is a new method applied on new equipment. We have finished

defining the first operating regulations and now, the method capabilities will be improved, following the better knowledge of the reliability of the equipment, of the main defects and their consequences for

the detection method provided by industrial operation.

REFERENCES

[1] G. SAPY - J. TESSIER. Surveillance des organes d' admission des

turbines associees a des reacteurs nucleaires. A.I.M. Liege 1978.

[2] R. BOUCHERAS, J. CAWART, J. KIESLING. Cycles d'entretien des

turbines a vapeur et moyens d'auscultation permettant de reduire la

frequence des visites. A.I.M. Liege 1974.

258
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la tige

Sortie vapeur vers soupape HP

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Reglette pour velocimetre

laser

7/.">nh HP CUTOUT VALVE (VA)

ROBINET D'ADMISSION HP PRINCIPAL

260

Figure 2
HP CONTROL VALVE (SR)

SOUPAPE DE REGLAGE HP PRINCIPALE

Figure 3 26l
Instantaneous speed measured

with laser vetocimeter

Vitesse instantanee

( veloc/metre a laser)

500"- 4 Vibrational acceleration

measured with

piezoelectric accelerometer

Acceleration instantanee

( accelerometre piezoelectrique)

1 Choc d'ouverture Shock by pass clapper-head

2 Effet de l'a mortisseur viqueux Viscous damping

3 Choc de la tete sur le siege Shock head-seal

4 Choc de fermeture Shock by pass clapper -head

CLOSING OF A CUTOUT HP VALVE(VA)

VITESSE ET ACCELERATION INSTANTANEES RELEVEES

LORS DE LA FERMETURE D UN ORGANE EN BON ETAT

Figure A

262
M1

f0

,cc

-Tete Head

Siege Seal

Clapet pilote By pass clapper

Tige VA Valve stem

Tige servo-moteur Servo-motor stem

Servo-moteur Servo-motor

COMPUTER MECHANICAL MODEL OF A VALVE

MODELE MECANIQUE D'UNE VA

263

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f(KHz)

(0) Bruit de fond electronique Electronic noise (no teak)

(1) Bruit de fuite Leak noise

Pression amont: 6 bars Upstream pressure

Pression aval : 1 bar Downstream pressure

Section de fuite: 0.46mm2 Leak equivalent section RMS values ratio leak noise electronic noise

= 43dB

POWER SPECTRUM DENSITY OF A LEAK NOISE

MEASURED WITH A PIEZOELECTRIC ACCELEROMETER

DENSITE SPECTRALE DU BRUIT DE FUITE TRANSMIS PAR VOIE SOLIDE,

MESURE A L' AIDE D'UN ACCELEROMETRE PIEZO-ELECTRIQUE

SUR UN ROBINET D'AIR COMPRIME

Figure 8

266
TYPICAL SIGNAL SHAPE FROM A PIEZOELECTRIC ACCELEROMETER

IN CASE OF MECHANICAL SHOCKS ON THE STRUCTURE

ALLURE TYPIQUE DU SIGNAL DELIVRE PAR UN ACCELEROMETRE

FIXE SUR UNE STRUCTURE QUI EST LE SIEGE

DE CHOCS MECANIQUES REPETES

267

Figure 9
Friqutncy value

100 x initial value

(Encastrtment)

/ / / / /

Profondeur relative d< 1'cntaiU.c (P/D in %)

10 20 30 40 50 60 70 Relative depth of the crack (P/100 x D)

VARIATION OF THE FIRST BENDING MODE FREQUENCY

WITH THE CRACK DEPTH FOR A CANTILEVER BEAM

VARIATION DE LA PREMIERE FREQUENCE PROPRE EN FLEXION

D'UNE TI6E ENCASTREE LIBRE EN FONCTION DE LA PROFONDEUR

D'UNE ENTAILLE A L'ENCASTREMENT Figure 10 268
Enregistreur-lecteur de

cassette magnetique numenquc

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Rack d'alimentdtfon stobilisee;| basse tension : Low voltage DC power supply

Voyants et fusibles d'alimentation des boitiers electron iques —

locaux (accelerometres

)

Connection (with fuses and

sighting slits) to acceierometers

and associaied electronics

Panier central contenant

le microprocesseur et ses peripheriques

Main electronic rack

microprocessor and

peripherals boards

Venttlateurs Electric fans

Tirol" r Drawer

THE PERMANENT DATA ACQUIS/HON SYSTEM

PHOTO DE LA BAIE D' AUSCULTATION (FACE AVANT)

i

Figure 11

269
Enregistreur 6 cassette

I Cassette -recorder

Front panel

Face avant

Interface

Q

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12 "Logical st at es"(open closed)

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24 niveau* vibratoires

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lnterface(lB) a

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TF (18. TF ©

Auxiliary

6 temps de fermeiure VA MPX (13 TTT

6 temps de fermetureVI

6 Closing times VA \ Closing times VI

6 ouvertures des S.R. 6 Position of the HP control valves

Power output of the plant

H : Carte horloge Electronic clock board

SCAN: Multiplexeur 2' m< niveau convert isseur analogique dioital. Multiplexer + analog-digital converter board

MPX : Multiplexeur 1 er niveau Multiplexer board

MW : Carte puissance (amplif icatcur d'isolement) Power output board

TF : Carte temps de fermeture Closing time board

E.L : Carte etats logiques "Logical states" board

Vit : Carte vitesse Rotor speed board

PRINCIPLE OF THE DATA ACQUISITION SYSTEM

SCHEMA GENERAL DE PRINCIPE DU SYSTEME D'ACQUISITION

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CLOSING TIME REFERENCE CURVE

COURBE " POINT ZERO"D'UN TEMPS DE FERMETURE

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VIBRATION LEVELS FUNCTION OF POWER OUTPUT

POINT ZERO NIVEAUX VI BRATOIRES PUISSANCE

279
AN APPROACH TO MONITORING EXISTING

UTILITY TURBOGENERATORS

S. Doughty

Radian Corporation

Austin, Texas 78766

Abstract: A three stage program of minicomputer based, continuous monitoring development and application is currently in progress on several

large turbogenerators. The first stage is a period of planning the primary development effort in terms of review of existing vibration sensors selection of additional sensors, and identification of operating parameters which influence vibration. The second stage involves gathering

data in many different operating states in order to develop a vibration

comparison algorithm which removes the effects of the operating state.

In the final stage, the machine is monitored quasi-continuously with the

intent of detecting progression of failure modes as changes in the vibration response of the machine.

Key words: Vibration monitoring; vibration signal processing; rotating

equipment

INTRODUCTION

The sudden, unplanned outage of a utility turbogenerator resulting from

mechanical failure is, in the least severe case, a major hardship for

those served by the utility. In worse cases, castrophic failures can result in millions of dollars damage and even loss of life. Many equipment failure modes are progressive in nature, and thus lend themselves

to detection in a machinery monitoring program. With early detection,

only minor repair may be required while the load is shifted elsewhere at no inconvenience to the customer. The central goal of a machinery monitoring program is to anticipate failures before they actually occur, and

thus, to allow for a planned, orderly shutdown of the machine. Comparison of the costs and benefits makes proper monitoring mandatory at the

present time.

A turbogenerator monitoring program begins with assumptions about the

information available regarding the state of the machine. It is usually

assumed that a machine with no progressive failures occurring has minimal vibration during operation. Increasing vibration is presumed to be

associated with the progression of one or more failure modes. This suggests that the measurement, analysis and comparison of present vibration

with previous vibration will allow the prediction of approaching failures. Many vibration phenomena occur at the fundamental rotational

280
speed of the machine, which is 60 hz for a 3600 rpm machine. For some failure modes, high frequency spectral components are generated which

become apparent earlier than the fundamental components. Detection of

these high frequency components will give a greater lead time for cor- rective action. Other phenomena associated with turbine blading also

occur at relatively high frequencies. Comprehensive monitoring thus requires a broad spectrum approach. The Fast Fourier Transform algorithm,

along with signal processing techniques from the sonar, radar, and com- munications fields are the tools for extracting useful information from

the observed vibration data.

Radian Corporation has undertaken to monitor several large, existing

utility turbogenerators using both vibration and acoustic emission information. The vibration monitoring aspects are described below. This

work is presently in different stages at several sites.

MONITORING SYSTEM HARDWARE

Monitoring a large turbogenerator entails the rapid acquisition of large

amounts of data, the need for on-site reduction for data acceptance or rejection, and a need for versatility as the monitoring program develops,

i This all points to a minicomputer based monitoring system such as will

be described.

Vibration data is taken from the machine via vibration sensors installed

as part of the monitoring program and, in some cases, other pre-existing

vibration sensors as well. These sensors are accelerometers , velocimeters, and various types of displacement sensors as indicated for the

measurement situation. The resulting analog signals are the primary vibration data for the monitoring program. A multiplexer sequentially

samples the various sensors, either singly or in pairs, under computer

software control. These analog signals are digitized in a high speed

analog to digital converter. Computer selectable low pass filters are provided between the multiplexer and the computer input to remove the

high frequency components before the signal is digitized and thus avoid

aliasing. Switchable filters are required for compatibility with the

various sampling rates of the analog to digital converter. The computer

j system consists of a minicomputer with 64 K memory and also a disc unit.

A magnetic tape unit is provided to transfer information from the minicomputer monitoring system to a large, central site computer. A graphics terminal is included for spectra, orbits, and other displays of interest to an analyst at the monitoring site.

All primary vibration data is obtained through the multiplexer and high

! speed analog to digital converter acting directly under computer control.

I At the same time, a low speed, programmable data acquistion system gathers operating parameter values. This information is held in the low

speed system until requested by the computer. The application of this

equipment will be in three steps: an initial study period called Phase

I, a development period called Phase II, and an on-going program of continuous monitoring, Phase III.

281
MONITORING PROCEDURE

Initial Study - Phase I

The initial study, or Phase I, is a period of learning how to monitor a particular machine. While there are similarities among machines of a given class, the details of each machine must be considered for a suc- cessful monitoring program. Most utility turbogenerators of recent vintage are equipped with some monitoring equipment. In most cases, the

signal processing portion of the existing monitoring system is inadequate for the present monitoring program, however, the existing vibration sensors may be useful. Remembering that the existing vibration

sensors were, in most cases, designed for low frequency response and only simple signal processing, the initial study begins with an evaluation

of the existing vibration sensors in the light of the signal processing

to be performed here. This should be an evaluation of the actual transducers as they exist, not simply an evaluation of their specifications.

Anticipating the need for additional vibration sensors, a survey is also

made for supplemental sensor sites. The principal concerns of this sur- vey are access, environment at the sensor site, and value of data from

each site. On existing machines, access to the rotor is generally limited to areas adjacent to the bearings or at the couplings. High temperatures and oil mist are typical adverse sensor environments encountered.

A mathematical rotor dynamic analysis may be used to predict vibration

frequencies, amplitudes, and the location of nodal points. This analysis can be of limited value since the required detail design information

is generally considered proprietary. Much of the same information may

be obtained from the pre-existing vibration sensors, within the range of sensor credibility.

One of the major efforts of Phase II is the correlation of vibration

spectral components with the operating state of the machine. In order

to do this, it is necessary in Phase I to identify those operating parameters which may be expected to influence the vibration response. These

include the electrical load, various steam temperatures, stator and casing temperatures, and the exciter current. The experience of the operating personnel is valuable in identifying these operating parameters

which must be monitored in Phase II.

The full hardware complement described in section 2.0 is not required

for Phase I. The operating state parameters to be monitored are selected during Phase I, and only in later stages is the low speed data acquisition system required to record them. If the low pass vibration signal

input filters are not available, some aliasing will occur but will not

have a large effect on the results of Phase I. Since all necessary

analysis can be performed in the minicomputer, the tape system is not

needed to return data to a central site for processing. The required

components are the minicomputer with disc unit and the high speed analog

to digital converter with multiplexer.

282
Development - Phase II

The emphasis of Phase II is development of the means to extract useful

information from the raw vibration data. The full hardware complement

described in section 2.0 is required for this effort. The low speed

data acquisition system regularly samples and holds the list of operating

parameters that affect vibration. These are the operating state parameters associated with then current vibration spectra. Broadband vibration data is obtained from the vibration sensors that were supplemented

on the basis of Phase I results.

The intent of vibration monitoring is to detect failure modes in progress

by observing changes occurring in the vibration spectra. Yet, the operating parameter list developed in Phase I clearly recognizes the dependence of the spectra on the operating state of the machine. The direct

comparison of spectra from two different times will reflect both the difI ferent operating states (probably different electrical loads and associated steam flows) and possible failure mode progression, in an inseparaI ble fashion. In order to compare spectra obtained at different times and

correspondingly different operating conditions, it is useful to define a "Standard Operating State". The standard operating state is a machine

| condition defined by specified values for each of the monitored operating

parameters. Associated with the standard operating state are the vibration spectra that would be observed if the machine were actually operated at the standard operating state. These spectra vary only with the

status of the failure modes. An algorithm is required to translate the

spectra associated with an actual operating state to equivalent spectra

for the same machine condition at the standard operating state. There

is some statistical uncertainty associated with the equivalent spectra.

When spectra from different times have been reduced to equivalent spectra

in the standard operating state, any differences exceeding the uncertainty can properly be ascribed to physical changes in the machine, i.e., the

progression of a failure mode. The development of the necessary algorithms begins with the correlation of spectral components and the operating state parameters. The first approximation to the algorithm is a linear relation between spectral amplitudes and operating state parameters. This is extended as a power series expansion about the standard

; operating state with as many terms as required. For this reason, it is

best for the standard operating state to be chosen as a central, interior

point of the operating variable domain, rather than a boundary point of

that domain. The algorithm development requires acquisition of large

quantities of vibration data representing widely varied operating states

followed by a regression analysis. The necessary observed spectra are

recorded on tape and returned to a central site for the correlation and

algorithm development work.

! Early in Phase II, vibration measurements are made and processed into

i| the baseline spectra. It is not necessary to know if a progressive failj ure mode is present at the time the baseline data are taken. It is intended to use this data only for comparison, and not in an absolute

283
sense. When a satisfactory standard operating state reduction algorithm

is defined, the baseline spectra are transformed to the standard operating state and stored in the minicomputer to serve as a basis for comparison in Phase III.

When a particular spectral component or group of components has attracted attention, the question remains, "What does it mean?" One of the

most formidable tasks in any monitoring program is the identification of

spectral lines with physical phenomena existing within the machine. Experience is certainly a major tool in this effort. Much is also learned

from the manipulation of mathematical models to predict expected spectral components, in so far as the necessary physical data is available.

Determination of these physical parameters from machine drawings is a lengthy, expensive process even if the drawings are available. An attractive alternative is the determination of these parameters directly

from the physical part during an open case inspection modal analysis and

identification procedures.

The final step in the monitoring program development is the establishment of warning criteria and threshold values. Here again, experience

and mathematical models each play a roll in the definition of these parameters. The experience of power plant operating personnel may be con- sidered to define upper limits on many of these variables, but in many

respects, this judgement is too coarse to be employed with the spectral

information available. Comprehensive, well-verified mathematical models

provide a means to assess quantitatively the impact of proposed failure

mechanisms as they affect the vibration spectra. The threshold levels

representing significant deviations from the baseline spectra are set as fractions of the warning criteria which have been established.

Continuous Monitoring - Phase III

The final stage in the monitoring program is establishment of quasi-continuous monitoring under computer control to continue indefinitely in

the future. In Phase III, each of the vibration sensors is regularly

sampled at frequent intervals by the computer via the high speed analog

to digital converter. The low speed data acquisition system continues to

supply the operating variable values. The observed spectra are processed almost in real time, transformed to the standard operating state,

and compared to baseline spectra. Only spectra that deviate from the

baseline by more than a prescribed threshold are saved. These exceptional spectra and associated operating states are recorded on tape. If

the deviation exceeds the warning level, this information is relayed to

the operating personnel.

The tape with its record of exceptional spectra and their associated operating parameter values is periodically returned to the central site

for off-line analysis and interpretation. This includes possible recom- mendations for maintenance work, shut-down of the machine, or other operating changes. The tape also provides the basis for further refinements to the standard operating state reduction algorithm and improve281)-
ments to the threshold and warning criteria. The payoff for the entire

monitoring program is expected to occur during this Phase III activity,,

the on-going analysis and interpretation of the data generated leading

to the early detection of problems.

285
ENHANCING MACHINERY PROTECTION THROUGH AUTOMATED DIAGNOSTICS

J. L. Frarey

Shaker Research Corporation

Northway 10 Executive Park

Ballston Lake, NY 12019

Abstract: Shaker Research Corporation under contract to Electric Power

Research Institute, has installed an automated vibration monitor system

in Northeast Utilities Millstone II Nuclear Power Plant. The objective

of the program is to demonstrate that the system can provide insight

into the condition of critical pumps and thus guide the planned maintenance during scheduled shutdowns. To provide this insight, the system

must be capable of processing a large amount of vibration data and

based on the results, draw conclusions about the condition of the unit.

Both aspects of the system will be discussed.

Key Words: Automatic diagnostics; digitizes data; spectrum analyzers;

steady state mode; tolerance vibration levels.

It is becoming quite common for large rotating machinery to be equipped

with some type of vibration transducer along with their associated monitors and alarm systems. These systems may have been installed initially as alarm devices to warn of out of tolerance vibration levels or even

to automatically shutdown the machine if a given vibration level is

exceeded. It has become readily apparent to the maintenance engineer

that these transducer signals when analyzed periodically by modern

data processing equipment such as real time spectrum analyzers have

provided additional information on mechanical condition. Signal characteristics associated with certain defects may be recognized long before an alarm level. Trend information on the amplitude of vibration

components also provide an insight into the rate of machinery deterioration. All of these data allow better machinery protection and improved

maintenance efficiency during scheduled (or unscheduled) plant down

time.

Two problems are quickly encountered by one starting down this path to

improved maintenance. How does one attain the skill necessary to rec- ognize significant signal characteristics and even if it can be attained, how does one inspect, compare with the last inspection and trend the

data from a large number of rotating machines. Under the sponsorship

of the Electric Power Research Institute (EPRI) , Shaker Research Corp.

has installed an Automatic Vibration Monitor System at Northeast Utilities Millstone II Nuclear Power Plant. The objective of this program

is to demonstrate solutions to both these problems. This paper describes some of the aspects of the program and the monitor system.

286
System Requirements . Drawing on many years of experience in machinery

troubleshooting, it was concluded that a system could be built that

could automatically recognize some of the more common signal character- • istics that are related to machinery defects. In effect the system

would become an automatic diagnostic system. Additionally, for those

signals and defects not automatically diagnosed, data must be saved and

recalled in a format that allows a diagnosis to be made. Finally, it

should be easy to "teach" the system new symptoms so that the extent of

automatic diagnostics will continue to expand.

Clearly, if the automated diagnostics is going to be based on years of

human troubleshooting experience, then the system must be capable of

analyzing data during machinery operating conditons that have been

found to be productive in the past. These have included:

1. Normal analysis of vibration spectra for machinery steady state

operation

.

2. Analysis of transients such as start-stops, amplitude vs. speed

and waterfall data processing is included.

3. Demodulation of high frequency resonances to determine the source of excitation, i.e., rubs, ball bearing defects, etc.

4. Separation of mechanical and electrical runout from true vibration data for displacement probes.

This automated monitor system also includes the provision for continuous

on line monitoring of overall signals from each sensor. If the signal

level from any sensor exceeds the warning or alarm level, the computer

is automatically alerted and the system switches into the transient mode

to gather and analyze data from the distressed machine at this time.

System Description . The three modes of operation are shown in Fig. 1.

In start stop mode, the system digitizes data from all sensors on

the machine. After the start or stop the data is processed. Data presentation equivalent to tracking filter plots are calculated using a Discrete Fourier Transformer for the first three harmonics and are com- pared with the last start or stop. Another presentation known as a waterfall plot is also produced and stored for future reference. A

typical waterfall plot is shown in Fig. 2.

In the alarm mode, the computer is interrupted when either a warning or alarm level is exceeded on the continuous monitor panel. The system

digitizes data from the machine sensors, and checks to see if the signal

level is still increasing. When the signal level no longer increases,

the trend of the overall amplitude of each sensor is plotted.

The system operates in the steady state mode the overwhelming majority

of the time. In this mode, the system cycles through all sensors and

produces spectra from each sensor. These include low frequency spectra

as shown in Fig. 3 and also high frequency spectra as shown in Fig. 4.

Comparisons are made with the last spectrum and with original data. As new signals appear or signals always present vary in amplitude these

facts are printed out along with the source of the signal and its seriousness. Fig. 5 is a typical diagnostic printout. The signal ampli287
tude is also stored in a trend area. These data may be retrieved and

plotted as shown in Fig. 6.

The operator may take control of the system at any time and has several

options at his disposal to either change system constants, to extract

information or to run system diagnostics. A menu is presented to the

operator showing his choices and this is shown in Fig. 7. Using this

option, the operator may increase the diagnostic capability of the

system as new symptoms appear and are related to known mechanical degradation.

288
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SESSION V

NEW TECHNOLOGY

Chairman: William R. McWhirter, Jr.

Naval Ship Research and Development

Center

Co-Chairman: Henry R. Hegner

Mantech of New Jersey Corporation

REPORT ON INDUSTRY/JOINT SERVICES PROJECT

TASK GROUP 1-d

J* P. Wright

Hughes Aircraft CompanyLos Angeles, Ca. 90009

Abstract: Recognition by the armed services of a need for

definition in Automatic Test Arena led to the establishment

of first a Navy/Industry project and later to the establishment of a Tri Service/Industry project. The Tri Service

project, started in the last quarter of 1976, included

numerous committee meetings, a general meeting in January

of 1977 and a major working symposium in April of 1977. The

symposium attendance was 860 with an approximate 60/40 ratio

of industry/DOD attendance. The project included a specific

task group to deal with the application of Automatic Test

Techniques and Equipments to the testing of non-electronic

equipments.

The non-electronic testing group, chaired by Donald A. Prue

of Hamilton Standard, presented a series of findings regarding the application of automatic testing to non-electronic equipments. These findings include the recommendation

for:

• Equipment failure mode analysis

• Equipment designed for testability

• Standardization of test interfaces

The implications of these recommendations in terms of

acquisition costs were recognized by the group and the need

for an effective means of demonstrating cost effectivity

was established.

Key words: Military systems; non-electronic equipment;

testing.

In October of 1975, the Navy and Industry established an

Ad Hoc Automatic Test Equipment project under the joint

sponsorship of AIA, EIA, NSIA, SC/A, and WEMA. The efforts

of the participants in this project were directed towards

establishing communication between the Navy and the various

299
members of industry who are concerned with the utilization

and production of the automatic test equipments. The success of this project led to a tri-service/indus trybriefing in June of 1977 and the formation of the Industry/

Joint Service ATE project in the fall of 1977. This

project had expanded horizons in that the problems of all

three services were considered with a corresponding expansion of the industrial representation. It is apparent

that this project, like its predecessor, has been highly

productive and will lead to some major realignment in the

field of ATE.

The organizers of the Navy project, recognizing the need

for some degree of automatic testing or monitoring of

non-electronic equipments, established a specific task

group to collect and present data concerning this field.

This task group, designated A-4 Propulsion, Electrical,

and Auxiliary Systems Monitoring, concerned itself in

main with these elements as installed in ships. One of

the major findings of this group, which will come as no

surprise to the MFPG members, is that the need for improved

test techniques for non- electronic equipments is more

pressing than in the area of electronic equipment testing.

As a consequence of this finding, Task Group Id was formed

in the joint service project to carry on the work started

by the A-4 group. The Id group was chaired by Don Prue

of Hamilton Standard and ably supported by W. (Bill)

McWhirter, Jim Johnson, Barney Poppet and Hans Kohler from

the Navy and J. (Jeep) Hnatczak and R. (Bob) Watts of the

Army.

In the formative stages of Group Id, it was decided to

limit the scope of the task to a small class of complex

machines, rather than the more encompassing field covered

by the previous study. It was hoped that by limiting the

scope of the effort, a more in-depth analysis of the

requirements could be achieved. As you well know, the

family of complex machines which have been subject to

the most intensive study and for which the most extensive

set of field test data exists, is the internal combustion

engine, i.e. gas turbines, diesels, and spark ignition

engines. Accordingly, the project was limited to a study

of these devices and their associated auxiliaries. A

further limit introduced in the course of the study

reduced the scope to applications in which these devices

were used as propulsion units for ships or land vehicles.

This excludes, in the case of gas turbines, aircraft

300
applications. This latter restriction was imposed due to a

simultaneous study by SAE which provided more depth in the

area than could have been achieved within the framework

of this project.

The project effort included:

• Task group meetings.

• Individual data collection and analysis by

members

.

• A joint workshop in San Diego of all task groups.

• Preparation of the final report including

recommendations.

In addition to these activities which were directed to the

technical effort, there were numerous meetings between the

chairmen of the various task groups and an executive

steering committee. These meetings provide a forum at

which the general policy of the project and specific

direction of the activities of the task groups could be

discussed and developed.

The study showed that within the restricted field considered :

• There are numerous commercial applications in which cost

effect ivity has been adequately demonstrated.

• The methods used for proving cost effectivity in the

commercial world include setting values on availability.

A method of carrying this through to the military is

required.

• There are numerous military applications which have

been carried far enough to warrant implementation.

• As a minimum, one major military program must be fully

implemented - full production implementation. The need

for field data feedback from such a program is required

for the development of future programs.

In the more general area concerned with other types of nonelectronic equipments, the picture is not so well defined.

The major difference is related to the relative attention

which has been given to various types of machines. It is

apparent from available data that the following elements

require consideration:

• There is the same need for a method to assign a dollar

value to availability.

301
• There is a need for system by system failure mode

analysis

•

• There is a need for standarization of instrumentation

and test interfaces.

• There is an opportunity for the military to begin a

design for testability program on new equipment.

Task Group Id will meet in New Orleans in December of 1978

to review and approve the final report which will be one

section of the final report for the Industry/Joint Services

Project Report in 1979. The opportunity to exchange ideas

regarding an emerging technology has been a rewarding

experience for the participants and it is hoped that the

data provided to the joint services will aid in solving

some of the problems associated with the maintenance of

non- electronic equipment.

502
A POLYMER SENSOR FOR MONITORING

BALL-BEARING CONDITION

Seymour Edelman, James M. Kenney,

John F. Mayo-Wells and Steven C. Roth

National Bureau of Standards

Washington, DC 202 34

Abstract: Noise spectra have been used frequently in the past to detect

faulty bearings and to provide some indication of how the faults

worsened with time. Usually accelerometers or microphones were used

to detect the noise spectrum. This paper describes how the use of

piezoelectric polymer sensors coupled with spectrum analyzers now available make this technique more useful. Improvement in accuracy and

reproducibility, lower cost, greater convenience, and speed are potential benefits.

Key words: Bearing noise; failure prevention; machinery noise; noise

signature; non-destructive evaluation; piezoelectric polymer; spectrum

analysis; strain gage.

Introduction

Non-destructive evaluation of ball and roller bearings by detection and

analysis of their noise spectrum is a well-established procedure. It

has been shown that periodic monitoring of the noise spectrum of a bearing is a useful diagnostic tool.-^j^ Changes in the relative spectral power distribution, and especially an increasing proportion of highfrequency components, can give warning of deterioration long before

failure occurs. The provision of early failure warning has important

economic implications, as it permits an operator to replace damaged

bearings at a convenient time (e.g., during a scheduled maintenance

period) and may prevent consequent damage to expensive components such

as machine spindles or even to entire machines. All too common are examples of machine design in- which sudden failure of a bearing (for

example, a bearing supporting a massive rotating assembly or part of a pump for lubricating fluid) results in extensive damage.

The sensors used in most bearing studies have been either accelerometers

or microphones. There are, however, several deficiencies associated

with the use of these instruments for analyzing bearing condition. For

microphones, the presence of numerous sound sources in addition to the

specimen bearing itself makes analysis difficult, and requires inconvenient and expensive noise shielding which may not be fully effective.

Accelerometers having adequate high-frequency response are usually

expensive; more important concerns are that they conventionally require

a machined mounting flat, occupy a not negligible volume, and may have

sufficient mass to bring about significant changes in mechanical loading

303
in some applications. Also, it is usually impossible to mount an accelerometer close enough to the specimen bearing to avoid interfaces

in the path between bearing and accelerometer; such interfaces will

generally constitute discontinuities in acoustic impedance.

A few years ago, Jesse Stern of the NASA Goddard Space Flight Center

suggested that the use of piezoelectric polymer gages (responding to

quantities such as strain, force, acceleration) would avoid many of

the difficulties associated with conventional sensors. Staff of the

Polymer Science and Standards Division, NBS, have designed and con- structed a number of polymer sensors, both piezo- and pyroelectric for

a variety of applications, and developed means for evaluating their

performance. This report describes an experiment aimed at investigating

the usefulness of piezoelectric polymer gages as indicators of bearing

condition. The thesis offered is that polymer gages provide a practical

alternative to accelerometers with advantages of importance in some applications.

Construction of a Polymer Gage

The sensing element of a polymer gage is made from the poled portions of

a thin sheet of polymer material. "Poled" refers to the process by

which the material is made piezoelectrically active—in this case, by

the application of an electric field to metal electrodes in contact with

each side of the film while the material is at an elevated temperature

(above room ambient) . A simplified picture of the poling process is

that some of the electric dipoles present in the polymer structure tend

to become oriented with respect to the applied electric field (which is

of the order of 10^V/m) when the material is heated, and remain oriented

when the polymer is cooled and the field removed. The result is that

instead of a random distribution of dipoles pointing in all directions,

there is a preferred orientation in one direction, and the material

responds to strain with a change in its internal electric field and

hence with charge appearing at its surface.

Each gage was constructed with the following steps (some of these steps

are shown in figure 1)

:

(1) An aluminum electrode pattern is evaporated onto one surface of the

starting material, which in this case is polyvinylidene fluoride (PVDF)

in sheets 25 ym thick. The pattern for single gage element (each gage uses two elements) consists of a dot 2 mm in diameter with a 100 X 0.4

mm "tail", which will serve as connection to the dot for poling and in

the completed device.

(2) The reverse surface of the sheet immediately opposite the 2 mm

diameter dot is covered by a second metalization to form the ground

electrode. Care is taken to insure that the ground electrode is

opposite as little of the tail electrode as possible so that there is
minimal contribution from the tail to the signal from the completed

device (only polymer directly between energized electrodes becomes

poled)

.

(3) Electrical connections are made to the tail and shield electrodes,

the poling field applied, and the material heated to approximately

100°C. After 30 minutes, the material is cooled to room temperature

and the field then removed.

(4) Each gage is assembled as a sandwich of two elements bonded together

with flexible, insulating epoxy resin, with the dot-and-tail electrodes

in contact as the "filling" and the shield electrodes as the outer

surfaces. A short length of copper wire is inserted lengthwise between

the ends of the lead electrodes and bonded in place with conductive

epoxy resin.

(5) A single large aluminum electrode is evaporated onto each exterior

surface of the bonded gage. This electrode will serve as part of the

electrical shielding of the completed gage. The wire connecting to

the interior electrodes is masked (together with the end portion of the

bonded sandwich) so that no aluminum is evaporated onto it, which would

result in a short between the interior electrode and the shield.

(6) A miniature coaxial connector is made an integral part of the gage,

with its center conductor soldered to the wire and the body of the

connector and the ends of the PVDF strips potted together with insulating epoxy resin.

(7) Electrical connection between the shield of the connector and the

shield electrodes is made with conductive paint, which is applied to

the lead structure for half its length or more. When the paint has

cured, the gage is complete.

The finished gage is approximately 60 ym thick at the sensor. Gages as thin as 15 ym have been constructed from 6 ym PVDF sheet. Aluminum is

generally used as the electrode material because it is the easiest to

apply. However, for applications requiring submersion in water or for

biomedical applications gold electrodes are preferable. Other electrode

materials that are compatible with the fabrication process and with PVDF

are nickel and indium. Note that the gage construction places the

relatively heavy connector far enough away from the active element to

minimize mass loading.

Evaluation of Polymer Gage as Bearing Monitor

Figure 2 shows the apparatus used in this work: a motor-driven test

shaft supported by two specimen bearings mounted in pedestals. A

polymer gage is cemented in place directly on the stationary race of

each bearing, and an accelerometer is mounted above each bearing on an

305
aluminum cross piece that connects the bearing pedestals. Both the

method of mounting and the accelerometer locations are intended to

simulate field installation. The apparatus, with aluminum top and

bottom plates and a solid steel shaft between the bearings, constitutes

a closely coupled mechanical system. In order to reduce the effects of

variations in motor speed and torque and the transmission of mechanical

noise to the bearings, the driving electric motor is mounted on vibration isolators and coupled to the test shaft by a rubber belt.

For the experiments, both specimen bearings were degreased; one was relubricated to serve as the "quiet" bearing, while the other was run

dry as the "noisy" bearing.

Preliminary measurements indicated that for the purposes of this study,

the members of each pair of gages —accelerometers or polymer gages

could be considered identical.

A consideration in comparing the signals from a crystal accelerometer to

those from a polymer gage, is that both frequency response and directional response differ for the two types of instruments. The accelerometers used have, according to the manufacturer's characterization, a peak response at approximately 90 kHz, whereas the resonance corre- sponding to the thickness of the polymer sensor is considerably above

2 MHz, and any resonances at lower frequencies are well damped. For

the kind of measurements used in this study, the accelerometers respond

only to motion along the designed sensitive axis, for these experiments

in the plane of the speciman bearing; the polymer gage provides an approximately equal output in response to strain in any direction in

the plane of the sensor, which in these experiments includes the

sensitive axis of the appropriate accelerometer.

Figure 3 shows the output of one accelerometer and one polymer gage as

a function of frequency when, with the shaft stationary, the pedestal

supporting one bearing is excited by a PZT (lead zirconate titanate)

piezoelectric ceramic driver cemented to the vertical surface near the

bearing. The amplifier gain for the accelerometer signal had to be

reduced to the point that the signal below 30 kHz is in noise, in order

to avoid overloading the instrumentation at the 75 kHz resonance

frequency of the structure. (An indication of the true instrumentation

noise level can be obtained from the accelerometer trace as being less

than -52 dB referred to 0.1 V) . In contrast the output from the polymer

gage shows a significantly lower and broader peak to the 70 kHz region

and meaningful signal in the low-frequency range, with an average of

-35 dB over 10 to 40 kHz. It is conjectured that the peak at 70 kHz is

the result of a resonance from the PZT exciter and does not derive from

the polymer gage. (Other experiments have indicated that similar gages

produce nearly constant output over the range 100 kHz to 1 MHz in

response to a hydrostatic pressure pulse; this performance can be

interpreted as demonstrating no resonance behavior to the upper resonance.) This experiment demonstrates that the polymer gage does respond

306
to high-frequency signals while the accelerometer response falls off

rapidly above its resonance

.

The next several figures show output as a function of frequency from

both quiet and noisy running bearings . Figure 4 shows recorded polymer

gage signals from the quiet and noisy bearings over a frequency range

from 0 to 100 kHz. Examination of the two traces shows that there is a definite difference between them, with the level at a given frequency

in the trace from the noisy bearing greater than that from the quiet

bearing if the difference between the two traces is significant at that

frequency. It is obvious that the signal falls off rapidly with

increasing frequency. Note also the rather noticeable difference in

the 40-60 kHz region. Figure 5 shows a similar set of traces of the

accelerometer signals from the quiet and noisy bearings. Examination

of the two traces shows less marked differences between them, and at

some frequencies the higher level signal is associated with the quiet

bearing; there is no roll-off with frequency probably because the high

frequency components are amplified by the mechanical resonance of the

accelerometer. The behavior of the mechanical system which leads to

these four traces can be explained by considering the effect of the

interfaces between the steel stationary race of the bearing and the

aluminum pedestal. Unavoidable machining errors, differences in surface

finish, and difference in specific acoustic impedance cause most of the

sound generated in the bearing to be reflected at the interface and build

up a reverberant sound field in the races of the bearing. Little sound

is transmitted across the interface to the pedestal and the crosspiece

joining the pedestals. Very much less sound is transmitted across both

interfaces to the other bearing. Thus most of the sound generated in

each bearing stays in that bearing. Most of the small amount of sound

that gets into the aluminum structure stays there and builds up another

reverberant sound field which, above about 15 kHz, takes the form of a standing wave pattern. The signal from either accelerometer at a particular frequency depends on its location relative to the standing

wave pattern and has little relation to the nearer noise source. In

contrast, the polymer gage, in direct contact with its intended noise

source, sees negligible contribution from the second source, and internal

reflections of the intended source from the local interface serve to

augment the desired signal.

Discussion and Conclusions

Fundamental work predicting the frequencies to be observed, which result

from specific types of defects in specific locations for ball bearings

with given dimensions and numbers of balls, has been reported by a number of workers. ^ The purpose of our work has not been to carry

out any detailed analysis of frequency or mechanical bearing parameters.

It has rather been to investigate whether changes in the character of

the signals from an undamaged and from a damaged bearing can be detected

using polymer gages and if polymer gages show advantages compared to

307
crystal accelerometers in this application. We believe that the results

justify a positive conclusion.

It may be of interest to contrast some of the properties of polymer

gages with those of crystal accelerometers to see why polymer gages

should be particularly useful as indicators of bearing performance. The

gages are low in mass with flexible sensing elements that conform

readily to any curved surface; these properties, together with their

materials of construction, permit them to be bonded in place in close

contact with the bearing noise source so that sound energy from other

sources is attenuated relative to the desired signal. The fabrication

process lends itself to constructing gages of virtually any desired

shape and in a wide range of sensing areas. The gages tend to be free

from resonances below several hundred kilohertz (the range of interest)

and are in principle inexpensive to construct so that it becomes

practical to mount them in place permanently on every critical bearing

in a given piece of major equipment.

(A possible disadvantage of polymer gages relates to the temperature

response, both with respect to a pyroelectric contribution and to change

in gage sensitivity as a function of temperature. Future work may

determine if this is a problem in practice , as well as provide a more detailed analysis of gage performance.)

Conventional crystal accelerometers, on the other hand, have much

greater mass than polymer gages, even for relatively small high-frequency types. The accelerometer housing is usually designed to screw

into or be bolted to a flat machined surface, with a requirement for

good contact over the intended mounting surface. Accelerometer mass and

the relative rigidity of signal connections may preclude adhesive bonding. Accelerometers may have sensing crystals of different sizes, but

it is not usually feasible to tailor size to application, except

approximately. As has been noted, crystal accelerometers will have

resonances in their response substantially below 100 kHz.

Accelerometers vary widely in cost, but apart from calibration costs

(which, although by no means a small part of instrument cost, may be

assumed to be the same for polymer gages) , the high-frequency types

most suited for the bearing and other similar applications are relatively expensive.

Our overall conclusion is thus that polymer gages have a good potential

for monitoring bearing and other machinery noise, particularly with

respect to nondestructive evaluation of performance , and that for some applications the polymer gage has demonstrated distinct advantages over

the use of more conventional sensing instruments.

This work was supported by the Office of Nondestructive Evaluation.

308
References

1. A. S. Babkin and J. J. Anderson, "Mechanical Signature Analysis of

Ball Bearings Using Real Time Spectral Analysis", Application Note

3, Nicolet Scientific Corp., Northvale, N.J. (Sept. 1973).

2. George F. Lang, "Shake, Rattle, or Tap, or How to Conduct Vibration

Tests", Application Note 10, Nicolet Scientific Corp., Northvale,

N.J. (Oct. 1975)

.

3. J. J. Broderick, R. F. Burchall, and J. F. Clark, "Design and

Fabrication of Prototype System for Early Warning of Impending

Bearing Failure", MTI Tech. Report # MTI-71TR1, Prepared for NASAMarshall Space Flight Center, Huntsville, AL, Contract MA58-25706,

(Jan. 1972).

4. D. K. Snediker, L. F. Sturgeon, and S. M. Weinberger, "Characterization of Miniature Ball Bearings by Acoustic Signal Analysis",

Proceedings of the 17th Meeting, Mechanical Failure Prevention

Group, Tech. Report #10, (Mar. 1972).

309
310
311
•10 dB

£ -20 dB

-30 dB

5

-40 dB

-50 dB

20 40 60 80

FREQUENCY (kHz)

100

2

-10 dB

-20 dB

30 dB

40 dB -

-50 dB •

40 60 80

FREQUENCY (kHz)

100

FIGURE 3. OUTPUTS OF ACCELEROMETER AND POLYMER GAGE IN RESPONSE

TO EXCITATION BY PZT DRIVER, AS A FUNCTION OF FREQENCY.

312
3

10 dB '

-20 dB

•30 dB

-40 dB -

-50 dB -

40 60 80

FREQUENCY ( kHz )

5

-10 dB

20 dB

•30 dB

-40 dB

50 dB

40 60 80

FREQUENCY (kHz)

FIGURE k. POLYMER GAGE OUTPUTS IN RESPONSE TO SIGNALS

FROM BEARINGS AS A FUNCTION OF FREQUENCY.

313
-10 dB

20 dB

-30 dB

-40 dB -

-50 dB

40 60 '80 FREQUENCY (kHz;

-10 dB

-20 dB

-30 dB

40 dB -

-50 dR

40 60 80

FREQUENCY (kHz)

100

FIGURE 5. ACCELEROMETER OUTPUTS IN RESPONSE TO SIGNALS

FROM BEARINGS AS A FUNCTION OF FREQUENCY.

31k
AN INSTRUMENTATION TECHNIQUE TO

EVALUATE SPECTRA FOR ENGINE DIAGNOSTICS

Tony Cardan

B & K Instruments, Inc.

Cleveland, Ohio "44142

Abstract: This paper describes a method of using a digital

frequency analyzer as a "sliding time gate" when analyzing complex time signatures (e. g. as those produced by reciprocating

machines) . To isolate individual events such as valves opening

and closing, firing and exhaust pulses, rather than take a composite frequency analysis of the complete engine signature produced during one rotation, implies a triggered, movable, variable

width window which can be used to view each occurrence. Timing

can be with reference to any arbitrary occurrence during a cycle,

but a known reference such as Top Dead Center (TDC) is normally

used. An integral part of any flexible Digital Narrow Band

Analyzer should be the settable After Trigger Recording facility

allowing the memory contents to be locked at any time relative

to an incoming trigger pulse. If the incremental settings

available on the After Trigger Recording are sufficiently small,

this will enable the memory length to be used as a window to

look at any part of the incoming time signal. A triggerable

Gating System with variable delay and window length will also

be described. The results gathered from using the technique

on a marine diesel engine will be presented.

Key words: Gated frequency analysis; Gaussian window; Impulsive,

complex signals; Linear averaging; Reciprocating; Records after

trigger; Tape loop; Time signal; Time window.

Complex, impact-like time signatures are common occurrences in

nature. The pumping action of the human heart, the punch press

in a busy machine shop and, of course, the structural vibration

and cylinder pressure and temperature variations during the

operating cycle of reciprocating machines are typical examples.

The time signal for any one revolution is very complex in the

last instance because of the different exciting forces experienced. These are basically the primary force (the cylinder

gas force due to combustion or compression) , the secondary forces

(the crank mechanism, and piston, ring, bearing and timing gear

impacts) , and the forces generated in ancillary machinery

(generator, water pump, valve gear, etc.)

.

315
The impulsive signals produced by the combustion process are very

low in repetition rate compared to the natural frequencies of the

stiff engine structure. A four-stroke engine will have a firing

rate on one cylinder somewhere between 5 and 25 times per second

for a speed range of 600 to 3000 RPM. Engine block and structural resonant frequency components will be in the 800 to 2000

Hz region. Signal pickup can be by a variety of transducers,

but most commonly the acoustic signatures (using a good measuring

microphone) , cylinder head vibration signatures (using a high

quality accelerometer) , or cylinder pressure signatures are

taken. Each of these is normally related to a "once-per-rev

.

TT tachometer signal located at some convenient part of the mechanical cycle (e. g. TDC) , since each occurrence is uniquely time

related to the instantaneous flywheel position. Certain occurrences such as cooling fan noise, coolant cavitation, turbocharger noise are either non-integra lly related to the rotational

speed or entirely dependent on other phenomena (e. g. exhaust

gas velocity)

„

Noise due to Noise due to Noise due to Piston Impact K Piston Impact

Noise due to Pressure Rise

.004 in. Piston Clearance

60

Vibration Induced by Pressure

Fig. 1

.012 in. Piston Clearance

740440

316
To date, most diagnostic techniques are associated with relating

occurrences on the complex time history to engine timing marks

(Fig. 1) . Much experience has been gained in this way, but

techniques do now exist to further extend this valuable technique.

An example of the usefulness of the time-signal analysis technique is shown, relating tight and loose piston clearances. The

impact noise signal produced by the piston slap is easily identifiable. However, this type of analysis precludes the use of the

frequency domain. A doctor listening to a heartbeat with a stethoscope does not only hear a distinct level but does a running

series of Fourier analyses of the signal in his mind. He listens

for the low steady "thump- thump" but also for, say, higher frequency flutter noises associated with "leaky" valves; each noise

telling him a different story. This series of frequency responses

has up to now only been possible with the use of complex

electronics

.

Tape Recorder 7003 or 7004

plus Tape Loop Cassette UD0035

Oscilloscope for Monitoring Gated Signal

Gaussian Impulse

Multiplier 5623

Signal to be

analyzed

- * *

Gated

Signal

E * oT>'

4714

To Analyzer

Sinusoidal Trigger Burst Trigger Use of the Gauss Impulse Multiplier Type 5623 for gating

signals recorded with the 7003 or 7004 Tape Recorders

One of the recorder* fitted with car- rying case and shoulder strap Tape Loop Casette Type UD 0035

being fitted to one of the tape

recorders

Fig. 2

317
A system developed by B & K Instruments some years ago uses a Gaussian shaped "time window" to slide along a repeated time

signal. Each repetition was gated at a slightly different point

with respect to the previous point, and a frequency analysis was

made of the output of the gate.

The instrumentation required is shown in Fig. 2, and some typical outputs from the Gaussian Impulse Multiplier are shown in

Fig. 3.

Fig. 3

The Gaussian Impulse Multiplier pulls out individual portions of

the signal and allows each to be frequency analyzed separately.

Without this facility the spectrum obtained would be a smeared

amalgamation of all of the separate events occurring in the

signal.

The important factors to note are that 1.) the signal to be

analyzed must be repeated through the analyzer a number of times

(this can be by natural repetition if the signal is fully re- peatable or by use of a Cassette Tape Loop addition to an Instrumentation Tape Recorder, as shown in Fig. 2); 2.) the window

can be placed anywhere in the time history under review and

3.) the width of the gate is variable allowing greater or less

resolution of separately occurring events.

318
Updates of the technique first included replacing the Tape Recorder by a Digital Transient Recorder, but the most recent advance has been to use the Digital Narrow Band Spectrum Analyzer

Type 2031. This consists of a 1024- point digital memory to

store the sampled input analog signal and an FFT processor to

transform from the time to the frequency domain. The time

history length contained in the memory depends on the sampling

rate, which in turn defines the upper frequency of the analysis.

The memory length can be selected from 40 s to 20 ms, covering

a 0-10 Hz frequency range to a 0-20 kHz frequency range, in a 1-2-5 sequence. External sampling facility is also available

for other memory lengths. The change in memory length is

equivalent to varying gate widths.

Positioning of the ,r gate"relative to a known point on a flywheel is done using the Records After Trigger facility. If the

initiation of a frequency transformation is delayed with respect

to the trigger signal, the 2031 Spectrum Analyzer will continue

to input data during the delay. The Records After Trigger

(R.A.T.) can be varied in 0.1 increments from 0.1 to 9.9 times

memory length.

The window shape used is not Gaussian in this case but is a Harming window. The slight degradation of overall filter

selectivity is acceptable because of the simplification of

the hardware used.

The 2031 Spectrum Analyzer has a very significant advantage

over previously used techniques in that it has a Linear Averaging

mode allowing the Tape Loop to contain a number of firing pulses

and Tt once-per-rev. " trigger signals. Each firing pulse is

slightly different, but since they are analyzed at the same

instant relative to the trigger pulse, an averaging technique

can be applied to enhance the repetitive and remove the randomness.

A practical measurement was made of a marine diesel engine

i rotating at 60 RFM. Each cycle is approximately 1025 ms long

and using the 200 ms memory length with the Hanning weighting

gives an effective window width of 100 ms. The signal duration

was approximately 5.1 memory lengths and incremental steps of

0.3 memory lengths were chosen for the analysis. A Linear

Average of 16 spectra was made at each R.A.T. position. The

results are shown in Figures M~a and M— b. The signal can be

seen to be characterized by an initial high frequency component and later by a low frequency spike.

319

321
Conclusions

.

Use of modern Spectrum Analyzers with flexible Records After

Trigger control allows a new dimension in reciprocating machine analysis. Sophisticated and flexible analysis set-ups

can be made using the IEEE bus interfacing capacity of an

analyzer such as the 2031 Digital Spectrum Analyzer together

with a desk top calculator to control the analysis procedure c

322
THE DIRECT READING FERROGRAPH

Daniel P. Anderson

Foxboro Analytical

P.O. Box 435

Burlington, Massachusetts 01803

Abstract: The principle of operation, design, calibration, and a field

application are discussed for the direct reading ferrograph, a system

for rapid on-site monitoring of wear in oil-lubricated machinery. The

principle of operation is the magnetic precipitation of wear particles

from an oil sample within a glass tube. Light attenuation measurements at two cross sections of the glass tube provide a measure of large

and small wear particles present in the oil sample. Oil samples resulting in high severity of wear indices may be further scrutinized by analytical ferrography. Calibration of the direct reading ferrograph was performed with known weight concentration samples of ferrous wear particles generated in a gear box. Comparison of direct reading ferrograph

data to spectrometric data for the same oil samples is made. A typical

field application and results are discussed.

Key words: Ferrography; machine condition monitoring; oil analysis; oil

sampling; wear; wear particles.

Introduction: Ferrography (1), a technique to separate particles from

fluids for microscopic examination and subsequent analysis, was originally developed to magnetically precipitate ferrous wear particles from

lubricating oils, thus the name ferrography. The first application was

to condition monitor military aircraft engines, but now other applications have emerged, including modification of the method to precipitate

non-magnetic particles from both oil and other fluids. This is of interest for hydraulic systems where particles of non-magnetic material,

such as bits of seal material, found in the hydraulic fluid, may indicate impending failure. Recent research on particles found in the

synovial fluid, or lubricating fluid of human joints, offers new un- derstanding of joint diseases, such as degenerative arthritis, offers

the ability to monitor joint implantments and may result in bioengineering improvements. However, established applications are for failure

prevention in jet engines, diesel engines, transmissions, bearings, and

similar oil-lubricated machinery.

The Ferrograph: Two instruments are available for ferrographic analysis. The direct-reading (DR) ferrograph (2) provides information on the

concentration and size distribution of fluid borne wear particles. The

323
DR ferrograph is used for routine machine monitoring and for sample

screening prior to preparation of a ferrogram. The analytical ferrograph is used to prepare a ferrogram which is subsequently examined using a bichromatic microscope. A ferrogram, Figure l,is prepared by pumping

fluid through teflon tubing by means of a peristaltic pump onto specially prepared microscope glass which has a non-wetting barrier painted

on one surface to centrally channel the liquid. The ferrogram is

slightly tilted, with the entry end elevated, so that the fluid flows

downward within the oval ended barrier to a drain tube which delivers

the oil to a waste bottle. The ferrogram is mounted above two permanent

magnets which are separated by an aluminum sheet about 1/16" thick. The

ferrogram is positioned such that the separating aluminum sheet is under

the middle of the fluid channel of the Ferrogram. The magnets are separated with their magnetic poles counterposed; that is, where one magnet

pole is considered north, the other magnet across the aluminum strip is

south, such that a strong magnetic field gradient is created in the vertical direction above the aluminum strip. Magnetic particles in the

fluid experience a strong downward force. These particles migrate

through the fluid down to the glass surface where they are deposited in

strings perpendicular to the direction of fluid flow. The strings are

formed because particles align themselves with north to south pole, etc.

The strings are separated from each other by some distance because the

particles will be mutually repulsed if an aligned particle is pulled

down directly above another aligned particle. After all the fluid in a given sample has been run across the ferrogram, a fixer solution is run across the ferrogram to remove residual fluid. After the fixer dries,

which takes a few minutes, the ferrogram is ready for observation using

the microscope.

DISTANCE FROM EXIT END

IN MILLIMETERS

0 10 20 30 40 50 56

EXIT END

DRAIN TUBE

CZ

7

^ ENTRY REGIOI

WHERE FLUID

FIRST TOUCH

DOWN ON

FERROGRAM

<— 50 MM

POSITION

Figure 1. Particle Deposition on a Ferrogram

32U
The Microscope: A special microscope is used to examine ferrograms equipped with both reflected and transmitted light sources which may be

used simultaneously. This combines features of a biological microscope • with those of a metallurgical microscope. A recommended method for

sorting out metal particles from compounds, organic material, etc., is

to use red reflected and green transmitted light. This lighting scheme,

I called bichromatic illumination, will show metal as red and non-metal as

I green. Polarized light may be used for either light train as well.

Metallurgical (dry) objectives are used. The microscope is also equipped with camera attachments and a ferrogram reader, which provides a mechanically determined light extinction measurement which corresponds

to particle concentration at various locations on the ferrogram.

Particle Deposition: Ferrous particles are deposited on a ferrogram

I according to size because the force acting on a particle is proportional

to volume whereas the viscous resistance of the suspending fluid is proportional to surface area. Therefore, for spheres, force increases with

the cube of the diameter but resistance increases only with the square

of the diameter. The largest ferrous particles are therefore deposited

at the entry region of the ferrogram where the fluid, such as lubricating oil, first touches down on the glass surface. Figure 1 indicates a typical deposition pattern, although individual particles cannot be seen with the naked eye. At a position further along the ferrogram, all

ferrous particles larger than a characteristic size will have already

been precipitated. Near the exit end of the ferrogram, ferrous particles greater than about . 02um (20 nanometers) will have been precipitated. For non-ferrous particles, such as aluminum, brass, white metal,

etc., precipitation will occur because these materials are weakly magnetic. However, the deposition of these materials will be less size

selective. Consequently, large particles of non-ferrous metals may be

found anywhere along the length of the ferrogram.

The Particles of Wear: Examination of the ferrogram in the bichromatic

microscope reveals details of size, shape, and quantity of particles

from which the condition of oil-lubricated parts may be assessed (3)

.

Machines operating normally usually generate small flat particles at a slow steady rate. If the number of particles increases, and particularly the ratio of large or small particles, it is an indication that a more severe mode of wear has begun. The generation of large severe wear particles signals the imminent failure of the wearing surface. Abrasive

wear, which is analogous to a crude machining process, generates particles in the form of loops, spirals, and bent wires. Increase in the

number and size of these particles shows that an abrasive wear mechanism

is progressing rapidly.

Various mechanisms generate characteristic particles. Six regimes of wear have been identified with sliding wear (4) . Miscellaneous shaped

particles are associated with break-in wear. Small platelets are

325
associated with normal rubbing wear. As operating parameters become

more arduous, the metallic rubbing wear particles increase in size, become oxidized, and finally, just prior to failure, large metallic severe wear particles are produced.

Three types of particles are associated with rolling mechanisms. These

are spheres, fatigue chunks and laminar particles. Spheres are generated as microcracks open up on rolling surfaces. Fatigue chunks represent material removed as rolling elements spall. Laminar particles,

which are large, very thin platelets, result from material being passed

through the rolling contact.

Combined rolling and sliding, as in gears, produces scuffing particles

and fatigue chunks. Lubricant starvation will result in partially oxidized wear particles.

Elemental Identification of Particles: Determination of the composition

of particles can establish their origin. The site of deposition, re- flectivity, and color of particles aid their identification. If available, energy dispersive x-ray analysis in conjunction with a scanning

electron microscope can establish elemental composition. Otherwise, a simple heating of the ferrogram will allow categorization into broad

alloy classes by examination of oxide layer (temper) colors (5).

The Direct Reading Ferrograph: There is general agreement among re- searchers investigating wear that the particle concentration and size

distribution are critical indicators of machine condition. As a machine

runs, particle concentration in the oil increases until the loss rate

equals the generation rate. For many machines, the time for this to occur is relatively short. If the probability for any one particle

being lost or destroyed is independent of the presence of other particles, the loss rate is proportional to the concentration. It can be

mathematically demonstrated that the particle concentration in the oil

of any machine reaches an equilibrium concentration (6) if it is assumed

that particle removal mechanisms such as sedimentation, filtration, and

impaction are proportional to the number of particles present. For example, in certain jet engines, equilibrium takes about 20 minutes to

establish. If wear increases, the particle concentration during dynamic

equilibrium will be greater. The onset of severe wear is accompanied by

an increase in the number of large particles, which causes the ratio of

large to small particles to increase. The direct reading ferrograph

provides the necessary information about particle concentration and size

distribution to indicate a changing wear situation.

Design: Experience with analytical ferrography, where optical densitometer readings of particle deposits are taken in conjunction with the

bichromatic microscope, indicated that the entry point of the oil

326
sample onto the ferrogram, where the largest particles are deposited,

and a position some 5 mm down from the entry, where 1 - 2 yM size particles are deposited, are the most sensitive locations for detecting a changing wear situation. Accordingly, the direct reading ferrograph was

designed to quantify particles in these two size ranges. The same criteria also apply to the on-line ferrograph, a compact, microprocessor

controlled instrument intended for airborne use, which is currently

under development.

As shown in figure 2, oil from a sample is siphoned through a precipitator tube, where a magnet assembly located beneath the tube precipitates the wear particles according to size. Virtually all unwanted carbon dirt particles are not precipitated, but are carried away by the

oil.

frI I

DBEDB

Figure 2. Schematic of a direct reading ferrograph optical system.

The large particles are deposited first and the smaller ones further

down the tube. Two light beams pass through the precipitator tube.

The first beam is located near the tube's entry where the larger (L)

particles (>5 yM) are deposited, and the second beam crosses the tube

where the smaller (S) particles (1 to 2 yM) are deposited. The

327
reduction in light intensity indicates the amount of wear particles deposited at each location. The level of light is sensed, amplified and

displayed in terms of units on a digital meter. The digital meter has a range of 0 to 190 units, where a reading of 100 units, which corresponds

to approximately one-half of the area covered, is the recommended upper

limit because, for readings greater than 100, the instrument response is

nonlinear due to coincidence effects; that is, particles pile on top of one another so that less light is attenuated. A switch allows selection

of either the L reading or the S reading.

So that variations in oil opacity will not affect the readings, the

sample oil is stopped just after it enters the glass precipitator tube

while two potentiometers are adjusted to bring the L and S readings to

zero. Two neutral density filters are included with the instrument to

allow periodic calibration checks. By inserting one of the filters in

the light path, without the precipitator tube in place, a reading within a certain range will result if the instrument is functioning properly.

Interpretation of Results: Recommended sample volume is 1 cm 3

. If too

many particles are deposited, the sample must be diluted so that the

ferrograph readings are within range. Occasionally, oil samples are en- countered which result in low readings, in which case the operator may

choose to run a greater sample volume than 1 cm3 so that enough particles are precipitated.

The readings obtained from the instrument are assigned the terms D^ and

Dg, for the large particles and small particles, respectively. The nor- mal wear process generates particles with a maximum size of 15 uM, the

majority of which are 2 uM or less. Any abnormal wear mode generates

particles larger than 15 uM.

In view of this, for normal wear processes, D^ would be similar to Dg.

In practice, D is slightly greater than Dg. However, for abnormal

wear, will fee significantly larger than Dg. Consequently, the parameter D - D may be used as an indicator of abnormality.

J-j O The onset of an abnormal wear mode results in a significant increase in

the quantity of wear debris. To indicate an increase in particle con- centration, the term D + DQ may be used.

Li O A single parameter, sensitive to the onset of severe wear, the product

of D^ - Dg (severity) and D + Dg (quantity) may be used. This quantity, termed the severity or wear index, I , is I = (DT - D ) (D + D_)

= D

2 +D 2

i Xj s

s sLbLb

Since different machine lubrication systems exhibit extreme variations

in both particle concentration and size distribution, it is impossible

to use I as an absolute quantity. Instead, the user must establish

what normal running values of I

g are for each machine he intends to

328
monitor. When comparing I between samples, it is important that ref- erence be made to the sampfe volume passed through the instrument.

From a practical standpoint, if the readings are reported as nD^ and

nD , where n is the dilution factor (it will be a fraction if more than

1 cm 3 of sample is used), then I - (nD^) 2 - (nD

g

) 2 = n

2 (D 2 - D

g

2 ),

and I will be comparable for samples run with different dilutions.

Instrument Calibration: Samples of known weight concentration of ferrous wear particles were prepared and subsequently analyzed by the direct reading ferrograph. These tests were run in order to obtain a calibration of the instrument in which the iron in the oil was weighed by

a balance. The data generated during these tests is available elsewhere (2) and will be provided by the author upon request. These tests

demonstrated that the direct reading ferrograph responded linearly to wear particle gravimetric concentration within the recommended operating

range and produced results consistent with spectrometric oil analysis.

Applications: Certain applications of ferrography have been discussed

in the literature such as gas turbines (7), (8), diesel engines (9),

and gear boxes (2) . Ferrographic analysis service is offered at several

commercial oil analysis labs including the author's lab. Certain other

applications such as oil additive optimization and military condition

monitoring have not been publicly discussed for obvious and justifiable

reasons

.

References

:

(1) E.R. Bowen, D. Scott, W.W. Seifert, and V.C. Westcott, "Ferrography", Tribology International, j?, (3), 1976, 109 - 115.

(2) D.P. Anderson and R.S. Silva, "The Direct Reading Ferrograph - Design, Calibration, and a Field Application" presented at the 33rd

Annual Meeting of the American Society of Lubrication Engineers,

April 17 - 20, 1978, Preprint No. 78-AM-1A-1.

(3) E.R. Bowen and V.C. Westcott, "Wear Particle Atlas", prepared for

the Naval Air Engineering Center, Lakehurst, New Jersey, under Contract

No. N00156-74-C01682, July, 1976.

(4) A. A. Reda, E.R. Bowen, and V.C. Westcott, "Characteristics of Particles Generated at the Interface between Sliding Steel Surfaces", Wear,

34, (1975) 261 - 273.

(5) F.T. Barwell, E.R. Bowen, J. P. Bowen, and V.C. Westcott, "The Use

of Temper Colors in Ferrography", Wear, 44 (1977), 163 - 171.

(6) D.P. Anderson and R.D. Driver, "Equilibrium Particle Concentration

in Engine Oil", submitted to Wear magazine for publication.

(7) D. Scott and V.C. Westcott, "Predictive Maintenance by Ferrography"

Wear, 44 (1977), 173 - 182.

(8) D. Scott, P.J. McCullagh, and G.W. Campbell, "Condition Monitoring

of Gas Turbines - An Exploratory Investigation of Ferrographic Trend

Analysis", Wear, 49, (1978), 373 - 389.

(9) M.V. Hofman and J.H. Johnson, "The Development of Ferrography as a Laboratory Wear Measurement Method for the Study of Engine Operating

Conditions on Diesel Engine Wear", Wear, 44 (1977), 183 - 199.

529
AN ADVANCED REAL-TIME OIL DEBRIS MONITOR

T. E. Tauber, Ph.D.

TEDECO

Technical Development Company

24 E. Glenolden Avenue

Glenolden, Pennsylvania 19036

Abstract: Diagnostic methods based on oil sampling tend to

disregard the fact that particles larger than 200 microns

are reliable indicators of incipient failure. This is confirmed by the success of diagnostic methods which utilize

visual inspection of lube system filters and of magnetic

chip collectors . Apart from the morphology of such particles, these methods rely on correlating the particle size

and quantity with data obtained from previous experience.

TEDECO has developed an in-line centrifugal oil monitor

which separates debris particles above 100 micron from the

oil stream and deposits them on a magnetic sensor. Each

particle is counted individually in accordance with its

mass, magnetic susceptibility and shape. Digital circuitry

registers and stores each event and permits calculation of

debris production rates. The debris is retained and easily

accessible for visual inspection.

A number of such systems are currently undergoing field

evaluation on an Air Force TF-39 engine, on a Navy LM-2500

engine and on a Westland Lynx helicopter transmission.

A similar system tested during the Army AIDAPS program on a

transmission implanted with defective parts confirmed the

soundness of this diagnostic approach.

Key words: Aircraft component failure; condition monitoring; failure detection; diagnostic techniques; debris monitoring; lubrication system monitoring.

The propulsion system of a helicopter is highly decentralized. It usually consists of one or two engines,- a main

rotor transmission, an intermediate and a tailrotor gear

box (Figure 1) . Larger helicopters have even more complex

and dispersed drive systems. Each component has its own,

self-contained lubrication system. The engine and transmission lubrication systems are of the circulating type and

330
have filters, coolers and pumps, while the intermediate and

tailrotor gear boxes are usually sump lubricated. Despite

these differences, an integrated helicopter lube debris

monitoring system should detect failures in each component

with equal reliability. In fact, a failure in the tail

rotor drive system is often more critical than a failure in

an engine or in the transmission, since it can cause loss

of control over the aircraft. An advanced helicopter condition monitoring system should therefore consist of relatively inexpensive peripheral sensors and a central signal

processing system.

By comparison, a gas turbine engine has a centralized

lubrication system (Figure 2) . The oil returning from the

individual shaft bearings and from the accessory drive

module combines on its way back to the reservoir. Since

each of these mechanical components is equally critical, a

modern gas turbine engine frequently has one full-flow

debris monitor in the main scavenge line. For failure isolation on the ground, magnetic chip collectors are installed in the individual bearing and gear box sumps or in their

scavenge return lines.

An additional challenge to the lube debris monitoring

system is the variety of materials and failure modes of oil

wetted drive system components. Each engine and transmission may behave differently with respect to its predominant

failure modes. This is especially true for immature

systems. They frequently have peculiar failure modes which

are not of the surface-fatigue or corrosive wear type but

involve cracking or abrasive wear. Since these failure

modes tend to reduce mean component life substantially,

efforts are generally made to eliminate them through design

changes during the development of the aircraft.

Surface-fatigue type failures, scuffing and corrosive wear

are the most frequent wear modes. Extensive experience

with many jet engines in service with certain European airlinesl) indicates that invariably such failures are characterized by particles of steadily increasing mean size

and by increasing debris production rates. Even

corrosive wear by itself may not produce large debris particles, the local loss of the oil film subsequently leads

to other wear modes which do

.

Figure 3 shows a model for development of the wear particle

spectrum with time during a surface-fatigue type failure.

Initially, while operating conditions are still normal, a

steady "background" of small to medium-sized wear particles

is produced. 2) Some isolated large particles may also be

331
generated from time to time, either as machining debris

left in the engine or from burrs and other macroscopic component flaws.

As a failure develops, the debris production rate and the

mean particle size increase. The European airline experience cited earlier relies completely on the appearance of

ferrous debris particles 1000 micron in size and larger

on magnetic chip collectors which are sampled at regular

intervals. At British Airways, this has been a completely

reliable, systematized and fully documented failure detection system for many years. 3) Further clues for failure

location and severity are obtained from particle morphology

by microscopic analysis and, sometimes, electromicroscopic

analysis. Similar data have been generated by the U.S.

Army Research and Development Laboratory Ft. Eustis.4)

The experience with the General Electric T-700 engine has

also demonstrated the soundness of this model. During the

recently completed development program of this engine,

every bearing failure was isolated in time (and not prematurely) through the appearance and detection of such large

particles in the oil stream.

An illustration of the rapid increase in debris particle

production rates during a failure is shown in Figure 4.

These data were developed on a large commercial turbofan

engine which, as sole debris monitoring device, has a

magnetic chip collector in the main scavenge line. The

normal debris deposit rate lies below .01 mg/hour, as evidenced by the decline of the curve after replacement of the

failed intermediate gear box. During the development of

the failure, the deposit rate increased by a factor of at

least 10 3 . Using this same technique, American Airlines

never removes this type of engine from the aircraft unless

SOAP data are confirmed by the appearance of large debris

on the chip collector. 5)

It must be emphasized that all condition monitoring techniques based on oil sampling, rather than debris sedimentation and collection, of necessity ignore these large

particles. As is well known, sedimentation rates in reservoirs are such that in real operating environments particles larger than 100 microns rarely appear in the samples.

More importantly, the production rate of large particles is,

of course, many orders of magnitude lower than that of

small ones and the probability of obtaining one of the

large particles in a sample is negligible . 6)

Recognizing the reliability of large debris particles as

532
failure indicators, a quantitative debris sensing system

was developed and has been evaluated in service. Figure 5

shows in cross section an oil debris monitor for a gas

turbine engine or a helicopter main transmission. The unit

has a cylindrical chamber, into which the oil enters

through a tangential inlet. The resulting vortex flow

separates the debris from the oil and deposits it on the

surface of a magnetic sensor. A quick-disconnect mechanism and an automatic shut-off valve permit simple removal

of the collected debris for visual or laboratory analysis.

The separation efficiency of this cyclonic debris separator,

at a flow rate of 16 GPM oil and 10 GPM air is indicated in

Figure 6. Figure 7 shows a photograph of the unit.

The sensor is also usable as a sump- type debris detector.

As magnetic debris particles are attracted, it generates a

pulse whose amplitude is a function of the particle mass,

magnetic susceptibility and its shape factor. With suitable electronic circuitry, as shown in Figure 8, this pulse

is amplified, converted to a digital count and stored in an

accumulation register. Real-time particle counts are

therefore available for direct read-out or, more usefully,

rate calculation by computer.

The system shown in Figure 8 was developed for participation in the Air Force Integrated Engine Condition Monitoring System (IECMS) Program. Two units are installed on a

General Electric TF-39 engine on an Air Force C-5A aircraft.

The preamplifier was required as a result of the 100 ft.

distance between engine and signal conditioning equipment.

The system is computer-interrogated and also must respond

correctly to a computer-generated test command which is

injected at the sensor level. System output is 0-5 VDC.

In addition, a "large chip" signal is generated if a single

particle larger than 500 microns in size is captured.

A second system is installed on a General Electric LM-2500

engine on the U.S. Navy's "Admiral Callaghan" . The ship

has concluded several voyages to Europe and, after calibration runs, the system is performing well.

Recently, a similar system has been supplied to Westland

for evaluation. The sensor will be installed in the oil

sump of a Lynx helicopter main transmission.

A somewhat less sophisticated system based on magnetic,

quantitative debris sensing was evaluated during the U.S.

Army AIDAPS program at Bell Helicopter Textron. Excessively worn gears and bearings were implanted into a UH-1 main

transmission and were correctly identified through persist333
ent, quantitative indications.

Currently, the resolution of the system is at the level of

particles of 200 x 200 x 50 microns (.008 x .008 x .002 in.)

This size corresponds to spall flakes typically generated

by bearings several tens of hours before secondary failure.

The resolution is expected to improve as the system is

further developed. However, it must be taken into consideration that resolution of a range of particles from, say,

100 x 100 x 20 to 1000 x 1000 x 200 involves a scale factor

of 1000 in mass. The limited dynamic range of electronic

equipment (digital or analog) of reasonable size, cost,

weight and complexity therefore requires a choice of a

certain optimum spectral range in which all particles are

to be reproduced in accordance with their actual magnetic

imprint. Particles above this range are recorded as if they

had the same size as those at its upper limit.

A simplified system with the capability to classify debris

particles in real time into three ranges has recently been

developed (Figure 9) . Owing to its simple circuitry, small

size and low cost, such a real-time particle counter

promises an entirely new approach to aircraft lube debris

monitoring

.

Footnotes

1) R. C. Hunter, "Engine Failure Prediction Techniques",

Aircraft Engineering, March 1975.

A similar method is used with excellent results by

CP Air, Vancouver.

2) This background of "normal wear fuzz" is responsible

for most nuisance indications of conventional electric

chip detectors which today are the most widely used

lube debris detection devices in helicopters.. The

recent development of the Pulsed Chip Detector successfully deals with this problem. This device is now going into production for the Sikorsky S-76, UH-60A Blackhawk, Hughes YAH- 64 and is under development for the

Bell 222 and 214ST.

3) A visit to the British Airways Condition Monitoring

Laboratory at Heathrow Airport, London, is highly

instructive (Chief: Gordon Grant, British Airways,

European Division)

.

4) D. Lubrano, USAMRDL; private communication.

33^
5) P. Roberts, American Airlines, Tulsa, Oklahoma;

private communication.

6) The average engine oil system has a capacity of

10 liters, while the average oil sample is 10 milliliters . Even without sedimentation problems , the probability of seeing a large particle in the sample is

therefore a factor of 10~3 smaller than its production

probability.

335
336
JET ENGINE LUBE DEBRIS MONITORING SYSTEM

ACQ

GEAR

BOX

N0.1

FILTER 0

TANK

.NO. 2 N0.3I NO. 4

MAIN BEARINGS

a-1

'MAGNETIC

CHIP COLLECTOR

COOLER

FULL-FLOW

DEBRIS MONITOR

LOGIC

FIGURE 2

337
538
DEBRIS DEPOSIT RATE

MAGNETIC CHIP COLLECTOR

100.0-

FIGURE 4

339
IRREGULAR I SECTION I

. OIL

OUTLET

TANGENTIAL

INLET PORT

IRREGULAR

SECTION

SELF-SEALING

VALVE

MAGNETIC DEBRIS—T^T^7>y

7

y/y^^j^ SENSING AREA ^ff'SSf'SS' (KV\1

HELILOK LOCKING

CAMS

DEBRIS SENSOR

CYCLONIC DEBRIS SEPARATOR

FIGURE 5

3^0


3^3

A PRACTICAL APPROACH TO

AIRCRAFT SYSTEM COMPONENT

MALFUNCTION DIAGNOSIS

F. E. Bishop

Aircraft Porous Media, Inc.

30 Sea Cliff Avenue, Glen Cove, N.Y. 11542

6301 49th Street North, Pinellas Park, Fla. 33565

ABSTRACT

Aircraft fluid system component failures and the

associated costs of unscheduled maintenance and loss of

operational readiness can be reduced significantly with

proper system monitoring. The author describes a multifunction monitoring system built into the aircraft that

will provide a signal at one central location when the

maximum allowable limit has been reached for the system

and/or component function being monitored. The appropriate

maintenance action can then be implemented or scheduled

for a convenient time without interrupting the operational

service of the aircraft. This concept would give a go-nogo signal and not require interpretation or special training. Another feature is that the monitoring is performed

by ground personnel at pre-flight or post-flight checkout.

The benefits of a system incorporating instant diagnosis

and analysis of fluid system component malfunctions are

increased system operating utility, reliability, andN safety

along with reduced logistic support and reduced maintenance

and operating costs.

Key Words: Accumulator; analog; centralized; check-out

system; desiccant; discrete; displacement; fiber optics;

filters; flight critical; flow; fluid; go-no-go; ground

readout; hydraulic; IMACS; instantaneous diagnosis and

analysis; level; maintenance oriented; malfunction

detection; monitoring; onboard; patented; pressure; pumps;

reservoirs; sensors; tailorable; temperature.

5^5
INTRODUCTION

:

Increasing costs associated with aircraft maintenance

and unscheduled downtime require a cost effective method

to deal with this problem. Current gas turbine powered

aircraft employ a variety of fluid systems, components,

and functions which are critical to the proper operation

of these sophisticated systems. Thus, the demand to

diagnose system and component critical operating functions

has been growing out of necessity.

Maximum cost effectiveness can be applied by optimizing the maintenance inspection 1

. Early identification

of component malfunction and incipient failure is the

basis for a reduction of unscheduled repairs. This type

of repair, in contrast to preventive repairs, is most

costly because of the secondary damage caused by premature

component failure. An example of this is abrasive particle

fluid contamination generated by a failing system component

which causes other system components to be damaged and

subsequently fail. However, even without an actual failure

of another system component, the overall system repair is

more costly and usually involves preventive component

repairs and extensive system decontamination.

Much of the aerospace industry effort to provide

system function information has been applied to the engine

fluid systems. For over a decade monitoring of the metal

wear debris particles taken from fluid samples of lubricating oil systems has been used to predict oil wetted component failure. But, this methodology is limited as a

future diagnostic tool. The reason for this is that there

is now a better understanding of the mechanisms of wear

and how they apply to system components 2

. These principles

were recognized some time ago with the application of 3

micrometre absolute lube oil filters for the Avco Lycoming 3

T-53 Engine and the application of 3 micrometre absolute

filters on G.E.'s T-700 Engine. However, the use of more

efficient fluid system filters to combat the most damaging

particles in film thicknesses of 0.1 micrometres (1000

Angstroms) to 1.0 micrometres (10,000 Angstroms) will

effectively remove those sizes of particles presently

monitored4

. This problem is presently being worked on by

various research institutes.

More elaborate aircraft engine monitoring systems are

evolving 5

. Some transmit information to the cockpit, and

some gather data in-flight and store it for extraction and

analysis by engine diagnostic equipment on the ground6 . These monitoring systems along with others in helicopter

transmissions and other fluid systems are testimony to

the increasing awareness and need for reduced costs,

increased safety, improved maintainability, reduced

3k6
logistic support and increased operational utility. The

desired benefits can be achieved through the application

of conditional monitoring of critical system component

parameters which provide diagnosis of a flyable system and

incipient failure analysis.

HYDRAULIC SYSTEMS:

Systems which can benefit greatly from a built-in

monitoring system are the aircraft's hydraulic systems.

They are composed of a large number of fluid components

which are subject to degradation and failure. Let us

review some of the background associated with hydraulic

system problems

:

It is well known that free and entrained air in

hydraulic systems has resulted in serious system malfunctions sometimes terminating in crashes and loss of

life.

Water in pneumatic bottles has frozen at discharge

during emergency procedures also with disastrous results.

Low fluid level in reservoirs has caused loss of

prime of pumps with the result of a loss of system pressure

and flight control.

Improperly performed maintenance has resulted in reversed control linkages, disconnected linkages and pulleys,

reversed installations of check valves, failure to reinstal

filter elements and many others which caused results

ranging from annoyance to catastrophic.

Servoactuators have suffered from loss of metering

edge, seal deterioration, and jamming causing hardover

signals

.

Hydraulic pumps wear out and fail in a variety of

failure modes.

Hydraulic fluid which can leak into emergency air

bottles during resetting of system, depleting the charge

of the bottles.

Accumulators are subject to blow by and internal

leakage

.

Filter elements are often left in the system too long

resulting in malfunctions of components such as, high backpressure on pump cases reducing cooling flow.

Contaminates in the fluid have been responsible for a

broad number of component malfunctions and failures such

as, malfunctions of electromechanical servovalves

.

The maintainability of the hydraulic systems contributes greatly to the operational utility, reliability,

and safety of the aircraft. Pre-flight and post-flight

checkout is an intrinsic part of maintaining these hydraulic systems, however, a large block of costly manhours

and materials are consumed in the process. Therefore,

3^7
let us examine an approach to providing a cost effective

built-in monitoring system for aircraft hydraulic systems.

THE SYSTEM CONCEPT:

Provide at one central location an onboard, lightweight, self-contained monitoring system to automatically

test the operability of the hydraulic system.

Provide in-system sensors that can measure component

functional parameters to give early warning of malfunction

and failure.

Provide an on-the-ground instantaneous go -no-go oncondition signal identifying what monitored component

and/or system parameter has reached the predetermined

functional limit. Let this signal be the basis for

planned maintenance action.

Provide a monitoring system utilizing flight tested

hardware which is not only applicable to new aircraft

designs, but one that is retrofittable into present aircraft to extend vehicle service life economically.

Provide a real time monitoring system with continuous

in-flight active sensors which will not affect the hydraulic system operation, even if a sensor fails.

Provide a programed microprocessor in a self-contained

monitoring system to increase reliability vs integrating

into existing aircraft computer system.

Provide a system which reduces skill level required

for routine maintenance and that is universally implementable in present maintenance systems, minimizing the use

of ground support equipment.

Provide a system to instantaneously diagnose and

analyze fluid system component malfunction to decrease

aircraft operating downtime, increase reliability and

safety

.

FLIGHT CRITICAL SYSTEM COMPONENTS:

Figure 1 lists the flight critical system components

and necessary functional parameters for system monitoring

and diagnosis by maintenance during ground checkout.

The different types of reservoirs used in aircraft

hydraulic systems are shown along with the critical parameters of level and temperature

.

Main system hydraulic filters in the pressure and

return lines are monitored for differential pressure, and

pump case drain lines are monitored for differential

pressure and temperature.

Accumulators are used for a variety of purposes in

hydraulic systems for stored energy devices and pump ripple

attenuators such as for brakes, ram air turbine, canopy

and main system. These are monitored for precharge

3U8
pressure

.

Likewise, pneumatic bottles used for emergency release

of canopy, landing gear, doors, and tail hooks are monitored for pressure, and the presence of moisture.

Shock struts critical to takeoff and landings are

monitored for precharge pressure and fluid level.

The heart of the hydraulic system is the pumps, and

these are monitored for maximum allowable case drain leakage and discharge pressure. The system leakage is monitored for maximum quiescent flow.

For the flight controls; components such as the rudder,

stabilizer and flaperon actuators are monitored for parameters of differential displacement and maximum allowable

quiescent flow. These aircraft controls are monitored for

differential displacement of the controls vs the controlled

surface

.

The utility system will, of course, contain some of

the same redundant flight control actuators along with

actuators for flaps, landing gear and other fluid power

functions. These actuators should also be monitored.

The desiccant for reservoir pressurization, window

defogging and other onboard uses is monitored for moisture

saturation

.

Hydraulic and spoiler type backup packages are monitored for over temperature

.

An elapse time meter records system operating hours

and flight duration.

Fluid system contamination monitoring provides for

quantity of particles or fluid cleanliness level, water

and chlorine.

System relief valves are monitored for leakage via

fluid temperature.

IN-SYSTEM SENSORS:

Let us now look at Figure 2 which describes a typical

monitoring system diagram used to determine acceptable

system operability. The proper reservoir fluid level is

checked automatically, along with external system leakage.

In addition, air in a boot strap reservoir is also indicated .Backup fluid power packages are checked for over

temperature operating conditions.

The systems filter elements are checked to determine

if they are plugged and should be changed. System fluid

samples can also be obtained to determine contamination

levels

.

If the system relief valve is leaking fluid, temperature will give the required indication.

Accumulator precharge pressure is determined instan3U9
taneously without manual system discharge and is automatically compensated for temperature.

Onboard emergency pneumatic bottles are checked for

acceptable charge pressure and the presence of moisture

is conveyed to the panel optically by the use of fiber

optics

.

Hydraulic pump discharge pressure, pump maximum

allowable case drain leakage, and maximum temperature are

monitored to indicate malfunction of each pump. In

addition, maximum allowable system discharge leakage is

also monitored by a quiescent flow sensor.

Rudder control pedal differential displacement and

rudder actuator differential displacement are checked to

ensure mechanical connections are correct prior to flight.

Other surfaces can be checked in a similar fashion.

Rudder actuator maximum permissible quiescent leakage is also indicated. The diagnosis of actuator maximum

quiescent flow requires a leakage sensor at each actuator.

Sub-systems can be checked for maintenance investigation

in the same manner.

Pneumatic desiccant condition is checked for saturation by employing fiber optics, to visually transmit

a color change at remote locations

.

External struts, precharge pressure and fluid level

are also provided for. These functions are particularly

critical for naval aircraft prior to launch.

SYSTEM SIGNAL TRANSMISSION AND INTEGRATION:

The signals from the in-system sensors, as shown in

Figure 3, are transmitted to a conveniently located

ground accessible display panel. All of the signals are

transmitted by a low power drain 5 Volt D.C. system

including the generation of the fiber optic signals.

The discrete and fiber optic signals monitoring the

components shown are received directly into the display

panel

.

The analog signals from sensors monitoring the components shown in Figure 3 are fed through analog digital

converters to a preprogramed microprocessor all contained

within the display panel.

Provision for tieing into the cockpit warning panel

can also be accomplished from the display panel.

DISPLAY PANEL:

Shown in Figure 4 is the diagnostic, analysis and

interrogation display panel installed at some convenient

point onboard the aircraft for use by ground maintenance.

The display and interrogation black box measures

350
approximately 12 x 6.5 x 4.5 inches and together with the

electronics and batteries weighs approximately 8 lbs.

Contained within the panel are:

° a microprocessor

° nickel cadmium batteries

0 battery heating and charging circuit

° analog to digital converters

° memory logic

° counters

° lamp drivers

0 display grain of wheat lamps

0 fiber optic interface outlets

° power interface (115V, 400 Hertz AC)

0 circuit and system test circuits

° shift registers

° elapse time meter

Grouped on the face of the panel are the flight

critical components and functions being monitored for

diagnosis of malfunction and out-of-limits performance.

Each function is represented by a red color grain of

wheat bulb which can be seen in direct sunlight as well

as in the dark.

There is also provided on the panel a spring-loaded

"center off" three position CIRCUIT TEST switch. In the

first position it tests all of the grain of wheat bulbs,

and in the second position it tests sequentially the

wiring to the in-system sensors for each group of monitored components

.

A spring-loaded "center off" three position SYSTEM

TEST switch is also provided. In the first position

before engine start, accumulator and pneumatic bottles

precharges are checked along with reservoir fluid level

before pressurization . Red lights would immediately

indicate maintenance action for the indicated condition.

The engines are then started and the second position

of the SYSTEM TEST switch is activated. Interrogation of

the operating hydraulic system then provides instantaneous

diagnosis and analysis of every function being monitored.

A red light will instantaneously pinpoint a maintenance

action

.

The entire maintenance check procedure can literally

be performed in a matter of seconds without the use of

any ground support equipment.

The discrete in-system sensors generate a simultaneous local visual signal of component malfunction which

must be cancelled manually. Therefore, the monitoring

system provides a quality assurance check that the

351
malfunction has been corrected, thus increasing reliability and safety of operation. Furthermore, the system

requires no special training or support.

ADVANTAGES OF SYSTEM:

This patented instantaneous maintenance analysis

check-out system can be tailored to any aircraft and

maintenance schedule.

The advantages of the instantaneous maintenance

analysis check-out system are:

0 reduces pre-flight hydraulic system check-out

time of flight critical components

° display panel identifies malfunctioned

components throughout the vehicle

0 reduces skill level required for routine

maintenance

° allows for component removal on "as required"

basis between major overhauls as scheduled, thus

reducing logistic support and costs

° maintains in-flight check of all critical

components

° identifies faulty components on post-flight check

° minimizes use of ground support equipment for

check-out

0 increases maintenance efficiency and operational

utility

0 proven and available hardware

° simple, reliable, practical and essentially

maintenance free

0 can be tailored to incorporate additional

design and maintenance requirements

SYSTEM FLEXIBILITY:

Additional benefits can be derived from the monitoring system by providing a two bulb display for each monitored system function. The red bulb would indicate as

before that the maximum allowable limit was reached

requiring an immediate maintenance action. However, an

amber warning bulb could also be provided to indicate

that an abnormal condition is being approached and

maintenance should plan to correct it at some convenient

time in the near future. This would further increase

operational readiness by not delaying the scheduled

flight because of a required maintenance action. It

would also reduce logistic support further.

352
SUMMARY

:

In summary, the instantaneous maintenance analysis

check-out system (IMACS) is a practical cost effective

and time saving means of attaining fleet operational

readiness and extending service life of aircraft through

increased maintainability.

REFERENCES

:

(1) Lieutenant Colonel Carlton L. Schelhorn

"Updating Aircraft Inspection"

U.S. Army Aviation Digest, May 1974

(2) F.E. Bishop and William Needelman

"The Effects Of Fluid Contamination On

Component Wear"

Field Service Report No. 56

Aircraft Porous Media, Inc., 1977

(3) C.W. Lynch and R.B. Cooper

"The Development of a Three-Micron Absolute

Main Filter for the T-53 Main Engine"

ASME Journal of Lubrication Tech. 93F,

430-436, 1971

(4) Richard S. Miller and W.K. Petrovic

"Wear Mode Identification and Particle

Removal in Oil Wetted Systems"

American Society of Materials Conference,

October 1976

(5) Barry Miller

"Inflight Engine Monitoring Use Expands"

Aviation Week, October 25, 1976

(6) J.W. Hollaway and Alan K. Olsen

"Engineering Methods In Engine Management"

Aviation - Engineering and Maintenance,

October 1977

353
TYPICAL FLIGHT CRITICAL SYSTEM COMPONENTS

FOR MONITORING

MONITORED

PARAMETER SYSTEM COMPONENT

o HYDRAULIC RESERVOIRS

L&T — Air oil L&T — Bootstrap

L — Backup System

o FILTERS

AP — Pressure AP — Return AP&T — Pump case drain o ACCUMULATORS

PC —Brake PC — Ram air turbine PC — Canopy

PC — Main system

o PNEUMATIC BOTTLES

PM — Canopy

PM — Landing gear PM — Door

P,M —Tail Hook (Dashpot) o SHOCK STRUTS

PC&L — Nose Gear PC&L — Main Gear

o HYDRAULIC PUMPS

F&T — Case drain (flow) QF — Pressure, flow (quiescent) P — Pressure

o FLIGHT CONTROLS

D.D.&QF — Rudder Actuator D.D.&QF — Stabilizer Actuator

D.D. —Control Column

no DMCI riNtUIVIAI IMATir* nCCCIPAMT UtoolOAIN 1 co. IVIlHolUlt? \OCllUI ailKJIIf o HYDRAULIC BACKUP PACKAGE

T — Over Temperature

o SPOILER SYSTEM & HIGHLIFT BACKUP PACKAGE

T — Over Temperature

0 ELAPSED TIME METER

H. —System operational hours — Flight duration o FLUID SAMPLING

FS — Particulate matter (cleanliness level) —Water — Chlorine content ° RELIEF VALVE

T — Over temperature

LEGEND

L Indicates level D.D. Indicates differential displacement P Indicates pressure S Indicates moisture saturation AP Indicates differential pressure T Indicates over temperature

PC Indicates precharge pressure H Indicates hours & tenths F Indicates flow M Indicates mixture hbO/oil in pneumatic bottles QF Indicates quiescent flow FS Indicates fluid sampling

Figure 1 35^
SIGNAL

TYPE

SWITCH

OPTICAL

COUPLER

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SWITCH

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COUPLER

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SYSTEM

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DESSICANT

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(RESERVOIR)

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ANALOG

SIGNAL

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ANALOG

SIGNAL

GEN

MECH/ELEC.

MONITORED PARAMETER

LEVEL AIR

TEMP

PRESS TEMP .IP .IP

TEMP

PRESS TEMP DISP

SYSTEM

COMPONENT

RESERVOIR

BACKUP

PACKAGE

FILTERS

PRESS

RETURN CASE

RELIEF

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356
TYPICAL ON-BOARD DIAGNOSTIC, ANALYSIS

AND INTERROGATION DISPLAY PANEL

Figure 4

s - C F B

Y 0 L A

s M 1 C

T B G K

E H U M T P

PRECHARGE Q O O O O BRAKE RAT CANOPY MAIN

DIFF DISP

o o o RUDDER STAB FLAP

STRUT

PRESS O O O — o o o

FILTER RELIEF VALVE o FLIGHT

COMB o

SYSTEM

OFF ON 2

OFF ON 2 ^ QUIESCENT FLOW ^ INSTRUCTIONS

1 SELECT CIRCUIT TEST 1 • LIGHTS ON

2 SELECT CIRCUIT TEST 2 • SEQUENCE ON

3 RELEASE CIRCUIT TEST

4. SELECT SYSTEM TEST 1

• RELEASE

5 PRESSURIZE HYDRAULIC SYSTEM

6 SELECT SYSTEM TEST 2 • FAULTY CONDITION WILL ILLUMINATE • RELEASE

7 TAKE APPROPRIATE CORRECTIVE ACTION

357
i

i

I

i
APPENDIX

MECHANICAL FAILURES PREVENTION GROUP

28th Meeting

Detection, Diagnosis and Prognosis

List of Registrants

Daniel P. Anderson

Foxboro Analytical

P. 0. Box 435

Burlington, MA 01803

Terrance E. Anderson

Boeing Military Airplane Dev.

15050 SE Fairwood Blvd.

Renton, WA 98055

William H. Austin

U. S. Navy Dept.

Naval Ship Engineering Center

Washington, DC 20362

Ron Bannister

Westinghouse Electric Corporation

MS-N205 Lester

P. 0. Box 9175

Philadelhpia, PA 19113

John R. Barton

Southwest Research Institute

8500 Culebra Road

San Antonio, TX 78284

John M. Beatty

Westinghouse Steam Turbine Div.

P. 0. Box 9175

Philadelphia, PA 19113

H. Belman

Technical Development Company

24 E. Glenolden Avenue

Glenolden, PA 19036

Baylus Bennett

Radian Corporation

8500 Shoal Creek Boulevard

Austin, TX 78758

F. E. Bishop

Aircraft Porous Media, Inc.

30 Sea Cliff Avenue

Glen Cove, NY 11542

David B. Board

SKF Industries

1100 First Avenue

King of Prussia, PA 19104

D. W. Botstiber

Technical Development Company

24 E. Glenolden Avenue

Glenolden, PA 19036

John E. Bower

U. S. Steel Research

125 Jamison Lane, M. S. 53

Monroeville, PA 15146

T. J. Bullock

Colt Industries

Fairbanks Morse Engine Division

701 Lawton Avenue

Beloit, WI 53511

Harry C. Burnett * National Bureau of Standards

Materials Bldg. , Room B-264

Washington, DC 20234

Ralph A. Burton

ONR

800 N. Quincy

Arlington, VA 22217

Andrew J. Callahan

ENDEVCO

Rancho Vie jo Road

San Juan Capistrano, CA 92675

56l
Richard J. Carleton

Naval Ship Engineering Center

1909 Foxhall Road

McLean, VA 22101

Tony Carolan

B&K Instruments, Inc.

5111 West 164th Street

Cleveland, OH 44142

John T. Carroll

Pratt & Whitney Aircraft

West Palm Beach, FL 33402

Tom Carter

Hamilton Test Systems, Inc.

Windsor Locks, CT 06096

Phillip W. Centers

U. S. Air Force

Air Force Aero-Propulsion Lab.

(AFAPL/SFL)

Wright-Patterson AFB, OH 45433

Rustam Chinoy

Mechanical Technology Inc.

968 Albany- Shaker Road

Latham, NY 12110

Raymond A. Coulombe

Naval Ship Engineering Center

Code 6146B, Room 368, NC-4

Washington, DC 20362

Richard T. Cowley

RCA «. P. 0. Box 588

Burlington, MA 01803

Richard B. Curtin

Southwest Research Institute

P. O. Drawer 28510

San Antonio, TX 78284

L. W. Deabler

Detroit Diesel Allison Div.

General Motors Corporation

1707 Beech Drive North

Plainfield, IN 46168

Harold 0. Demuren

Nigeria Civil Aviation Authority

122 Oyadiran Estate

Sabo-Yaba Lagos , Nigeria

J. G. Dimmick

Naval Ship R. & D. Center

Propulsion & Auxiliary Sys . Dept

Code 2732

Annapolis, MD 21402

Maxwell Dow

Cooper Airmotive

7555 Lemmon Avenue

Dallas, TX 75209

Yuri Esaki

Fugi Electric Co., Ltd.

30 E. 42nd Street, Room 927

New York, NY 10017

James J. Foti

U. S. Navy NAVSEC Phila.

733 Brooke Circle, N.

Morton, PA 19070

J. Frarey

Shaker Research Corporation

Northway 10

Ballston Lake, NY 12019

John A. George

Parks College of St. Louis Univ.

Cahokia, IL 62206

Alfred Genot

SEMT Pielstick

2 Ouai de Seine

93202 Saint-Denis, France

Norman Gleicher

Ocean Environmental Systems, Ltd

77 Quaker Ridge Road

New Rochelle, NY 10804

William A. Goldsworthy

Hughes Aircraft Company

P. 0. Box 3267

Terminal Island, CA 90731

362
Milton Gregory

Computer Avionics Corporation

398 Martin Avenue

Santa Clara, CA 95050

Robert Gullion

D-A Lubricant Company

1340 West 29th Street

Indianapolis, IN 46208

Larry Hargrove

Life Cycle Engineering, Inc.

145 King Street, Suite 309

Charleston, SC 29401

Robert H. Hawkins

Caterpillar Tractor Company

Technical Center, Bldg. A.

Peoria, IL 61629

Henry R. Hegner

ManTech of New Jersey Corp.

2341 Jefferson Davis Highway

Arlington, VA 22202

W. K. Herr

Colt Industries, Inc.

1901 L Street, NW - Suite 303

Washington, DC 20036

R. Hohenberg, Manager

Electrical Engineering Dept.

Mechanical Technology Inc.

968 Albany-Shaker Road

Latham, NY 12110

Robert R. Holden

Hughes Aircraft Company

Bldg. 117, Mail Station 1 P. 0. Box 90515

Los Angeles, CA 90009

Joe Innes

National Highway Traffic Safety

Administration

Washington, DC 20590

R. D. Jacobs

Colt Industries

Fairbanks Morse Engine Div.

701 Lawton Avenue

Beloit, WI 53511

P. George Jencek

Atomics International

8900 DeSoto Avenue

Canoga Park, CA 91304

S. E. J. Johnsen

Detroit Diesel Allison Division

General Motors Corporation

Plant 8, T9

Indianapolis, IN 46206

Robert L. Karlson

ENDEVCO

505 North Belt - Ste 305

Houston, TX 77060

Rudy 0. Karsch

Naval Ship Engineering Center

7426 Buffalo Avenue

Takoma Park, MD 20012

E. E. Klaus

The Pennsylvania State University

133 Chemical Engineering Bldg.

University Park, PA 16802

Bill Koelsch

Chadwick-Helmuth Company, Inc.

Ill East Railroad Avenue

Monrovia, CA 91016

Aaron R. Kramer

Thermo Engineering Inc.

338 Carlstadt

New Jersey 07072

Bruce N, Kramer

Hughes Aircraft Company

3100 West Lomita Boulevard

Torrance, CA 90509

363
Robert S. Kulp

Pratt & Whitney Aircraft Group

United Technologies Corporation

P. 0. Box 2691

West Palm Beach, FL 33402

William D Laingor

Bell Helicopter Textron

614 Arcadia, No. 1409

Hurst, TX 76053

Robert W. LeBlanc

General Electric Apparatus Service

Division, Measurement Services

3285 McGaw Drive

Chamblee, GA 30341

Richard Lee

U. S. Army—JOAP-TSC

JOAP-TSC, Pensacola NAS , Bldg. 780

Pensacola, FL 32508

Mark Libby

U.S. Navy—PERA (CV)

C 1861 P SNS

Bremerton, WA 98314

Daniel Lister

Princeton Gamma-Tech, Inc.

Box 641

Princeton, NJ 08540

Bryan Long

Beta Machinery Analysis Ltd.

6425 Bowness Road, N.W.

Calgary, Canada T3B 0E6

Thomas Magette

Oak Ridge National Laboratory

Box X, Bldg. 3500

Oak Ridge, TN 37830

A. Bernard Marchant

Hughes Aircraft Company

Strategic Systems Division

Bldg. 5, Mail Sta. B-146

Culver City, CA 90230

Joe A. Mclnturff

Lockheed Georgia Company

So. Cobb Drive

Marietta, GA 30062

William R. McWhirter, Jr.

David W. Taylor Naval Ship

Research & Development Center

Code 2731, Automation & Control Div.

Annapolis, MD 21402

J. H. Meyer

Aramco Overseas Co.

55 Laan Van Meerdervoort

The Hague, The Netherlands

Les Meyer

General Electric Co., Research Ctr.

1 River Road (37-680)

Schenectady, NY 12345

Louis Mileto

Engineering Services Group

Systems Engineering Test Directorate

Naval Air Test Center

Patuxent River, MD 20670

Raymond F. Misialek

NAVSECPHILADIV, Dept. of the Navy

Bldg. #633, 2nd Floor

Dynamic Instrumentation Branch

Philadelphia, PA 19112

Jacques Morel

Electricite de France

1 Place du General de Gaulle

92160-Clamart, France

Way Ion A. Neese

General Electric Company

1 Neumann Way, Mail Drop G-4

Cincinnati, OH 45215

Frank M, Newman

Southwest Research Institute

P. 0. Drawer 28510

San Antonio, TX 78284

361+
Philip Niosi

ManTech of New Jersey Corp.

2341 Jefferson Davis Highway

Suite 930

Arlington, VA 22202

Asao Nishimura

Mechanical Engineering Research

Laboratory, Hitachi Ltd.

502 Kandatsu-Machi

Tsuchiura, Ibaraki 300, Japan

H. O. Northern

Detroit Diesel Allison

P. 0. Box 894

Indianapolis, IN 46206

David H. Page

Engineer of Motive Power, CP Rail

Room 1000, Windsor Station

Montreal, Canada H3C 3E4

G. A. Peters

AT&SF Railway Company

1237 Navajo

Barstow, CA 92311

J. Philips

Naval Ship R. and D. Center

Annapolis, MD 21402

John A. Philosophos

Allis-Chalmers

P. 0. Box 512

Milwaukee, WI 53201

K. R. Piety

Oak Ridge National Laboratory

P. 0. Box X

Oak Ridge, TN 37830

C. Preston

Canadian Pacific Ltd.

Windsor Station, Res. Dept., Rm 369

Montreal, Quebec, Canada

Donald A. Prue

United Technologies

Bradley Field Road

Windsor Locks, CT 06096

Raul A. Raudales

SAHSA Airlines

Tegucigalpa, Honduras

SAHSA Pts Control de Calidad

Quality Control Dpto

Airport

H . Rethmann

Southwest Research Institute

6220 Culebra Road

San Antonio, TX 78284

W. W. Robinson

Pratt & Whitney Aircraft Group

Government Products Division

P. 0. Box 2691

West Palm Beach, FL 33402

Robert E. Rohtert

Hughes Helicopters

Mail Station 2 T11A

Centinela and Teale Streets

Culver City, CA 90230

Steven C. Roth

National Bureau of Standards

Polymers Building, Room B-324

Washington, DC 20234

Richard G. Salter

Rand Corporation

1700 Main Street

Santa Monica, CA 90406

Norm A. Samuels

Hughes Helicopters

2560 Walnut Street

Venice, CA 90291

George S. Schmidt

General Electric

Bldg. 2-440

Schenectady, NY 12309

T. Robert Shives

National Bureau of Standards

Materials Bldg., Room B-120

Washington, DC 20234

365
Donald Sidat

Pratt & Whitney Aircraft

EB3SW Main Street

E. Hartford, CT 06108

C. M. Smith

Oak Ridge National Laboratory

P. 0. Box X

Oak Ridge, TN 37830

George L. Smith

GENRAD, Inc.

Acoustics, Vibration & Analysis D

2855 Bowers Avenue

Santa Clara, CA 95051

Henry G. Smith

Engineering Consultant

201 S. Fronsica, Apt. 1

Redondo Beach, CA 90277

Kempton A. Smith

General Electric Co.

Bldg. 6, Room 328

1 River Road

Schenectady, NY 12345

R. T. Smith

Southwest Research Institute

P. 0. Drawer 28510

San Antonio, TX 78284

J. C. Sol

Electricite de France

1, Avenue du General de Gaulle

92141 Clamart, France

Roy W. Spacie

Harris Corp./PRD Electronics Div.

6801 Jericho Turnpike

Syosset, NY 11791

Leo L. Stavinoha

Southwest Research Institute

6220 Culebra Road

San Antonio, TX 78227

J. E. Stern

NASA/Goddard

Code 721

Greenbelt, MD 20771

Vernon Sturdivant

Southwest Research Institute

P. O. Drawer 28510

San Antonio, TX 78284

Richard W. Sweeney

Republic Steel Corporation

.Nassillon, OH 44646

Frank A. Tait

Royal Australian Air Force

Embassy of Australia

1601 Massachusetts Ave., N.W.

Washington, DC 20036

Wm. H. Tait

ASNT/CSNDT

Dom. Foundries

Hamilton, Ontario, Canada

Tadash Takigawa

Ishikawajima Harima Heavy

Industries Co. Ltd.

f-Mukohdai Cho

Tanashi City, Tokyo, Japan

Thomas Tauber

TEDECO

24 E. Glenolden Avenue

Glenolden, PA 19036

Tom Taylor

Russell Associates

8609 N.W. Plaza Drive

Dallas, TX 75080

Karl G. Tippets

E . I . DuPont

Louviers 13E30

Wilmington, DE 19898

366
Richard I. Trammell

IBM

Dept G62/142

5600 Cottle Road

San Jose, CA 95193

W. F. Wall

Lockheed Georgia Co.

South Cobb Drive

Marietta, GA 30063

Robert A. Walter

U. S. Dept. of Trans. —TSL

Kendall Sq.

Cambridge, MA 02142

George A. Warde

Air Bus Industries of North

America

630 5th Avenue

New York, NY 10020

Dennis J. Webb

Johnson Space Center (NASA)

Houston, TX 70058

Lavern D. Wedeven

NASA Lewis Research Center

21000 Brookpark Road

Cleveland, OH 44135

Herbert G. Wegner

Naval Ship Engineering Center

Philadelphia, PA 19112

Fred W. Weidner

U. S. Coast Guard G-DSA-3/TP44

400 7th Street, S. W.

Washington, DC 20590

R. L. Widner

The Timken Company

1835 Dueber Avenue, S. W.

Canton, OH 44706

Charles Witt

Endevco Corporation

San Juan Capistrano, CA 92675

James P. Wright

Hughes Aircraft Company

P. 0. Box 90515

Los Angeles, CA 90009

Lt. Col. Edward F. Young

JOAP-TSC

Bldg. 780 NAS

Pensacola, FL 32508

Henry K. Whitesel

David W. Taylor Naval Ship R&D Center

Code 2732

Annapolis, MD 21402

Robert M. Whittier

Endevco Corporation

Rancho Vie jo Road

San Juan Capistrano, CA 92675

367
MFPG PUBLICATIONS

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1. Glossary of Terms AD 721 354

2. Proceedings of Meetings 1-9 (set of 5) AD 721 359

Meeting Nos. 1-5 Papers and discussion on failure

analysis and control.

Meeting No. 6 "Detection, Diagnosis and Prognosis",

December 6, 1968.

Meeting No. 7 "Failure Mechanisms as Identified

with Helicopter Transmissions",

March 27, 1969.

Meeting No. 8 "Critical Failure Problem Areas in

the Aircraft Gas Turbine Engine",

June 25-26, 1969.

Meeting No. 9 "Potential for Reduction of Mechanical

Failure Through Design Methodology",

November 5-6, 1969.

3. Proceedings of Meeting No. 10 AD 721 912

"Vibration Analysis Systems"

January 21-22, 1970

4. Proceedings of Meeting No. 11 AD 724 475

"Failure Mechanisms: Fatigue"

April 7-8, 1970

5. Proceedings of Meeting No. 12 AD 721 913

"Identification and Prevention of Mechanical

Failures in Internal Combustion Engines"

July 8-9, 1970

368
6. Proceedings of Meeting No. 13 AD 724 637

"Standards as a Design Tool in Surface

Specification for Mechanical Components

and Structures"

October 19-20, 1970

7. Proceedings of Meeting No. 14 AD 721 355

"Advances in Decision-Making Processes

in Detection, Diagnosis and Prognosis"

January 25-26, 1971

8. Proceedings of Meeting No. 15 AD 725 200

"Failure Mechanisms : Corrosion"

April 14-15, 1971

9. Proceedings of Meeting No. 16 AD 738 855

"Mechanical Failure Prevention Through

Lubricating Oil Analysis"

November 2-4, 1971

10. Proceedings of Meeting No. 17 AD 750 411

"Effects of Environment Upon Mechanical

Failures, Mechanisms and Detection"

April 25-27, 1972

11. Proceedings of Meeting No. 18 AD 772 082

"Detection, Diagnosis and Prognosis"

November 8-10, 1972

12. Proceedings of Meeting No. 19 (NBS SP 394) COM-74-50523

"The Role of Cavitation in Mechanical Failures"

October 21 - November 2, 1973

Printed copies of the following MFPG publications (catalog numbers

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13. Proceedings of Meeting No. 20 (NBS SP 423)

"Mechanical Failure - Definition of the Problem"

May 8-10, 1974

Cost: Printed copy $6.10 SN003-003-01451-6

569
14. Proceedings of Meeting No. 21 CNBS SP 433)

"Success By Design: Progress Through

Failure Analysis"

November 7-8, 1974

Cost: Printed copy $3.50 SNQ03-003-01639-0

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15. Proceedings of Meeting No. 22 (NBS SP 436)

"Detection, Diagnosis and Prognosis"

April 23-25, 1975

Cost: Printed copy $4.25

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16. Proceedings of Meeting No. 23 (NBS SP 452)

"The Role of Coatings in the Prevention

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October 29-31, 1975

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17. Proceedings of Meeting No. 24 (NBS SP 468)

"Prevention of Failures in Coal

Conversion Systems"

April 21-23, 1976

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"Engineering Design"

November 3-5, 1976

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"Detection, Diagnosis and Prognosis"

May 17-19, 1977

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"Product Durability and Life"

November 1-3, 1977

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SN003-003-01556-3

NBS-SP-436

370
BS-114A (REV. B-78)

U.S. DEPT. OF COMM. 2.Gov»t Accession No BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. SP-547

. TITLE AND SUBTITLE

Detection, Diagnosis, and Prognosis. Proceedings of the 28th

meeting of the Mechanical Failures Prevention Group, held at

San Antonio, Texas, November 28-30, 1978.

3. Recipient's Accession No.lo.

5. Publication Date July 1979

$. PerfofisiRg Organization Code

>?HKra»X}SX EDITORS

T. Robert Shives and William A. Willard

8. Performing Organ. Report No.

PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

16, f^ect/task/Wor* Unit No.

11. Contract/Grant No.

!. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City, State, zip)

Center for Matls.Sci., NBS, Wash., DC 20234; ONR, Dept. of

Navy, Arlington, VA 22217; NADC, Dept of Navy, Warminster, PA

18974; DoE, Fossil Energy, Washington, DC 20545; NASA,

Space Flight Ctr., Greenbelt, MD 20771.

13. Type of Report & Period Covered

Goddar$i4, Spispsoricig Agency Code

). SUPPLEMENTARY NOTES

L0C 79-600078

I I Document describes a computer program; SF-185, FIPS Software Summary, is attached. ABSTRACT (A 200-word or leas (actual summary oi most significant information. If document includes a significant bibliography or

literature survey, mention it here.) These proceedings consist of a group of twenty five submitted papers from

the 28th meeting of the Mechanical Failures Prevention Group which was

held in San Antonio, Texas, November 28-30, 1978. The central theme of

the proceedings deals with detection, diagnosis, and prognosis as related

to mechanical failure prevention. Special emphasis is on aerospace

applications, land based applications, marine applications and industrial

application.

KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name

separated by semicolons)

tearing analysis; condition monitoring; engine diagnosis; failure detection;

ailure diagnosis; failure prevention; maintenance; performance monitoring

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toe following current-awareness and literature-survey bibli- ographies are issued periodically by the Bureau:

Cryogenic Data Center Current Awareness Service. A litera- ture survey issued biweekly. Annual subscription: Domestic, $25.00; Foreign, $30.00.

'iquified Natural Gas. A literature survey issued quarterly. Annual subscription: $20.00.

Superconducting Devices and Materials. A literature survey

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services to National Bureau of Standards, Cryogenic Data

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