NATIONAL BUREAU OF STANDARDS REPORT

2442

Semiannual Progress Report

of the

Office of Basic Instrumentation

For the Period Ending

December 31, 1952

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
U. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Aslin, Director THE NATIONAL BUREAU OF STANDARDS

The scope of activities of the National Bureau of Standards is suggested in the following listing of

the divisions and sections engagt i in technical work. In general, each section is engaged in specialized research, development, and engineering in the field indicated by its title. A brief description

of the activities, and of the resultant reports and publications, appears on the inside of the back

cover of this report.

Electricity. Resistance Measurements. Inductance and Capacitance. Electrical Instruments. Magnetic Measurements. Applied Electricity. Electrochemistry.

Optics and Metrology. Photometry and Colorimetry. Optical Instruments. Photographic

Technology. Length. Gage.

Heat and Power. Temperature Measurements. Thermodynamics. Cryogenics. Engines and

Lubrication. Engine Fuels. Cryogenic Engineering.

Atomic and Radiation Physics. Spectroscopy. Radiometry. Mass Spectrometry. Solid State

Physics. Electron Physics. Atomic Physics. Neutron Measurements. Infrared Spectroscopy.

Nuclear Physics. Radioactivity. X-Rays. Betatron. Nucleonic Instrumentation. Radiological Equipment. Atomic Energy Commission Instruments Branch.

Chemistry. Organic Coatings. Surface Cherpistry. Organic Chemistry. Analytical Chemistry.

Inorganic Chemistry. Electrodeposition. Gas Chemistry. Physical Chemistry. Thermochemistry. Spectrochemistry. Pure Substances.

Mechanics. Sound. Mechanical Instruments. Aerodynamics. Engineering Mechanics. Hydraulics. Mass. Capacity, Density, and Fluid Meters. Organic and Fibrous Materials. Rubber. Textiles. Paper. Leather. Testing and Specifications. Polymer Structure. Organic Plastics. Dental Research.

Metallurgy. Thermal Metallurgy. Chemical Metallurgy. Mechanical Metallurgy. Corrosion.

Mineral Products. Porcelain and Pottery. Glass. Refractories. Enameled Metals. Concreting Materials. Constitution and Microstructure. Chemistry of Mineral Products.

Building Technology. Structural Engineering. Fire Protection. Heating and Air Conditioning. Floor, Roof, and Wall Coverings. Codes and Specifications.

Applied Mathematics. Numerical Analysis. Computation. Statistical Engineering. Machine

Development.

Electronics. Engineering Electronics. Electron Tubes. Electronic Computers. Electronic

Instrumentation.

Radio Propagation. Upper Atmosphere Research. Ionospheric Research. Regular Propagation Services. Frequency Utilization Research. Tropospheric Propagation Research. High

Frequency Standards. Microwave Standards.

Ordnance Development. These three divisions are engaged in a broad program of research

Electromechanical Ordnance, and development in advanced ordnance. Activities include

Ordnance Electronics. basic and applied research, engineering, pilot production, field testing, and evaluation of a wide variety of ordnance materiel. Special skills and facilities of other

NBS divisions also contribute to this program. The activity is sponsored by the Department of

Defense.

Missile Development. Missile research and development: engineering, dynamics, intelligence,

instnimentation, evaluation. Combustion in jet engines. These activities are sponsored by the

Department of Defense. • Office of Basic Instrumentation • Office of Weights and Measures.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

OBI 2442

Semiannual Progress Report

of the

Office of Basic Instrumentation

For the Period Ending

December 31, 1952

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NATIONAL BIJmU OF STANDARDS

Office of Basic Instrumentation

SEMI-ANNUAL PROGRESS REPORT

July 1, 1952 to Dec. 31? 1952

The Basic Instrumentation Program at the National Bureau of

Standards is co-operatively sponsored try the Office of Naval

Research, Office of Air Research, and the Atomic Energy Commission,

and Is an extension and continuation of a limited program undertaken in 19^8, sponsored by the Office of Naval Research®

Trie Basic Instrumentation Program is a program designed to

realise the benefits in instrumentation research that accrue from

co-ordinated planning of such research from the standpoint of instrumentation as a science in itself, common to the "primary" technical

fields® The program is intended to help fulfill the needs of the

sponsoring agencies by providing a background common to the several

primary sciences from which problems in instrumentation may be more

effectively attacked®

This report contains progress reports on projects started during the present fiscal year as well, as reports on continuing projects®

For convenience, the project reports have been grouped according to

the technical division of the Bureau in which the work is conducted®

Wo A 0 Wildhack, Chief

Office of Basic Instrumentation

A® Vo Astin

Director
CONTENTS

ACTIVE PROJECTS PAGE

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Electricity Division

Survey of Millimicrosecond.

Oscillography© = . .

.

Heat and Power Division

Determination of Temperature

with the Noise Thermometer© © © . . . « .©...© o Atomic & Radiation Physics Division

Electron Interferometer© c©©©©©..©.©.©©©©©®

Mass Spectrometer for Study

of Solids 0 ©©a 000 © 9 e©©©©©© 00000 ©e©©©©© 0©0

Chemistry Division

Electronic Coating Thickness Gage© » . ®. ©»© © Mechanics Division

Carbon Dioxide Sypsometer o®®®®©©®©©©®©©.®

Absolute Measurement of Vibration

Amplitudes ©®oo© 9 ©o©©©oooo©©©©©©o®o«©oo©©

Ultrasonic Velocimeter

for IlLQUldS ©©0®©0«©0000©000©0©0»©©00©0©0

Acoustic Viscometer for Gases ©©©©©©©©.©©©e

Microwave Hygrometer© ©©o©©©©©©©®©©.©©.©©©©

Survey of Dynamic Pressure

Instrumenta lion® ©©©©©©©•©©©•©©•©©••© © © © © Vacuum Tube Accelerometer© ©©«.«.© © © » © . © ..

©

Survey of Strain Gage Recorders

Resistance Strain Gages

Electronics Division

Application of Feedback Around

Image Scanning Systems®

©

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Central Radio Propagation Laboratory

Precision Microwave Interferometer© ••©•©©»

Missile Development Division (Corona)

Survey of Analog-to “Digital Converters®® «®

Office of Basic Instrumentation

Research & Consultation on

Instrumentation Information© o©.,®©®.©©®®

Miscellaneous Investigation of Basic

Instrumentation®

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REPORTS AND PUBLICATIONS RELATED TO THIS PROGRAM© © ®© ®© © oooooooooeo 69
1 -

Surrey of Millimlcro second Oscillography - NBS Project 2018,

Electrical Instruments Section, J* Ho Park

Objective : To prepare a critical survey containing comprehensive

information on the present statue of oscillographic methods and instruments for the retarding of high-speed transient voltages in the

time intervals below one microsecond, and an evaluation of their

theoretical and practical capabilities*

Background : Recent developments in radar, television, atomic physics,

telemetering, etc., jriave greatly increased the need for oscillographic

measurements in the time range below one microseconds As a result,

new and faster oscillographs have been and are being developed® Such

instruments will also find applications in the study of electrical

breakdown under steeply rising voltage surges (a subj ect of growing

importance in the field of insulation testing), and in the general

development of high-voltage surge-testing techniques* Experiences

gained by work on the CRO-beam intensification project (2006) will be

helpful in evaluating the high-speed recording instruments available.

A survey in this field will be useful in the planning and conduct of

new research and development on high speed oscillography as well as in

guidance in instrumentation problems concerned with recording of highspeed transient voltages*

Progress : This project was started during the reporting period. Letters of inquiry were sent to manufacturers of high-speed oscillographs

and some replies have been received* A bibliography of pertinent technical articles and reports is being assembled and ^svitewad*-

Future Activity : The present bibliography is to be extended and individual articles reviewed and summarized* Summaries or tabulations will

be prepared containing data on mechanical and electrical characteristics of high-speed oscillographs, writing speeds obtainable under various

conditions, and accuracy of displayed wave foxms as affected by amplifier characteristics, electron beam transit time, and type and arrangement of deflecting systems. Work will be started on a portion of the

report on theoretical considerations concerned with design techniques

and operating Imitations of high-speed oscillographs*
- 2 -

Determination of Temperature With the Noise Thermometer

NBS Project 030i-31“263?5 Temperature Measurements Section*

E® Wo Hogue

General Objective. § To evaluate the capabilities of the noise thermometer as an instrument for measuring temperatures on the thermodynamic scale and to investigate the suitability of the device for

other temperature measurement and control applications®

Specific Objectives g To determine the principal limiting factors

on the sensitivity3 precision* and accuracy of temperature measurements made in this way®

Background g The limiting sensitivity of electrical measuring circuits

has been of interest to designers of equipment as -well as scientists

for maiy years® Even if no electric field is applied* electrons.,

moving in conductors as a result of thermal energy* may have at any

particular instant an unsymmetrical distribution along the conductor®

As a result* there is at that -feme a difference of potential between

the ends of the conductor® Over a long period of time* these differences in potential average to zero® The frequency distribution of

the fluctuations is given by the equation of Nyquist®

V" - ljk

/t'Re(Z)T Af

where ^ the mean-square fluctuation in voltage in a band of frequencies of width* f

k is Boltzmann 8 s constant

Re{Z) is the real part of the impedance of the passive network

T is the thermodynamic temperature of tie resistor®

The fluctuation in potential described by the above equation is commonly termed Johnson noise 0

Although this effect is generally considered harmful since it

limits the ultimate sensitivity of circuits* it does provide a method

for measuring the thermodynamic temperature® Kelvin* in 185U* first

proposed a method of defining a temperature scale which is independent of the properties of thermometric substances® Temperatures on

this scale are of primary importance to thermodynamic.is ts concerned

with the relation between properties of matter and temperature® In

the past* a gas thermometer has been used to determine temperatures

on this scale® Precise measurements require elaborate equipment*

available in only a very few research laboratories in the world* and

a large investment of time® The noise thermometer provides a possible substitute for a gas thermometer®

Recognizing this possibility* Drs® J® B® Garrison and A® W® Lawson

of the University of Chicago developed a noise thermometer with which
they measured ratios of temperatures© The equipment which they used

has been set up at the National Bureau of Standards where it has been

extensively modified, greatly increasing its sensitivity and stability© If an accuracy of 0©1$ can be obtained at temperatures above

the gold point (1063°C), the measurement of temperatures in this

range will be improved considerably and a deteimins.tion of the temperature of the gold point, which is one of the fundamental points on

this scale, could be madeP The value used for this temperature is

based on gas thermometer measurements -made approximately ij-0 years ago©

Preliminary results obtained in earlier work indicate that the

modified instrument can be balanced with a precision of approximately

0©1°C«, On this basis, it appears possible that temperature measurements equivalent to those made with a gas thermometer can be made*

Summary of Project Activitys Tiro experimental noise thermometers were

acquired from the University of Chicago Institute for the Study of

Metals where they were designed and built by J© B© Garrison and A* W*

Lawson®

One of these models had not been developed sufficiently for use

in. temperature measurements, but the other load been used by them to

make measurements at around 1000°K, and the results together with a description of the thermometer have been published in their article

"An Absolute Noise Thermometer for High Temperature and High Pressures

Rev© Sci® Instru© Voi© 20, No* 11, 785-79U, November 19k9* An accuracy of 0*1$ is claimed©

When the noise thermometer was received it was at first assembled

on the bench* Little test equipment was available at this stage for

work on it© No complete circuit diagram was available© Much of the

circuit was then traced© Preliminary attempts to mice a noise balance

showed some unbalance sensitivity, but very little© The thermometer

could just distinguish between an input resistance of 10,000 ohms and

short circuit© Further circuit tracing and adjustment of the synchronous switches increased the sensitivity, but nothing approximating a true balance could be obtained© Much of this trouble was finally

traced to interference from the signal of a television station about

a mile away®

Study and experimentation was carried out to dev: se a better way

to amplify and integrate the imbalance signal© Severed, schemes were

tried out in breadboard foim* The feedback integrating circuit used

in analogue computers seemed most promising, and several ways of constructing one were tried out© To get more sensitivity, more gain and

more bandwidth reduction (longer averaging or integrating tine) were

both necessary© The analogue integrator accomplishes both amplification and bandwidth reduction simultaneously®
- h

While the new circuit devised proved to be much more dependable

and convenient than the other, unbalance sensitivity remained far from

the theoretical* Further checks of the amplifiers in the thermometer

revealed noisy components in the electronic filter^ the high gain amplifier, and the preamplifier* High level electrical signals from an induction heating generator and from numerous but unlocatable machines in the

vicinity had been almost completely screened out by the newly acquired

screen room* Wien many of the internal sources of noise (faulty components) had finally been cleared up, balances were obtainable to a few

degrees, or about l%f as of January 1952

o

Using a calibrated mercury-in-glass thermometer to indicate the

temperature of the reference resistor of the noise thermometer, determinations of the ice point and steam point were made* The noise

thermometer element was placed in a steam hypsometer for the steam

point, and a noise balance was carefully made using both the low and

high frequency amplifiers*

A value of 99o8°C was obtained,. The actual, steam point, taking

into account the atmospheric pressure at the time, was between 99« 5°G

and 100°C.

When these measurements were made, the thermometer circuit was

up to full sensitivity* In subsequent checks the thermometer failed

to maintain this sensitivity consistently enough to make further temperature measurements* It is felt that the trouble is chiefly due

to faulty components in the preamplifier, and possibly in the electronic filter following it* As is well known, even though the noise level

of a sensitive amplifier may be calculated on the assumption of ideal

components, large departures from theory will occur in. actual amplifiers depending upon the choice of tubes and other components used* Time

existing noise-thermometer amplifier was not at all adapted to the easy

substitution of parts to allow a systematic search for quiet components,

so the design of a new preamplifier chassis has been started* This design, when completed, will allow quick interchange of components and

easy circuit re-design*

Progress ; At the beginning of this period 'the noise thermometer con- sisted of the original amplifier units (built at the University of

Chicago) to -which had been added the new high-gain integrator-detector

circuit* Although the old components had been ,? de-bugged" to a considerable extent, they failed to maintain high sensitivity at all consistently* Erratic disturbances (bursts of high level noise) and

microphonism were bad, and the electronic filter was found not to have

a sufficiently sharp cut-off*

During the last two quarters the old preamplifier unit has been

replaced by a much quieter, more stable and less microphonic one 3 and

a new filter-amplifier using a passive filter having a sharp upper
- 5 -

cut-off has been substituted for the original one® Unbalance sensitivity of the new circuit was then of the order of 0*b%» Unbalance

sensitivity measurements giving »0$% made earlier, on the old equipment have since been found to be in error® Because of the uncertain

behavior of the old equipment, good sensitivity measurements were

extremely difficult to get®

A serious source of interference and systematic error has been

traced to circuits carrying the electrical power used to drive the

synchronous switches. Small arcs in connections and switches in these

circuits greatly increased the overall noise level because they were

repetitive at the synchronous frequency. Also, a large and steady

error, or false balance, could be eliminated only by completely disconnecting the chassis carrying the preamplifier from all possible

connection with the synchronous power©

The resolving power of the first detector remained insufficient

to give 0,1$ detectability despite the fact that its dynamic range

had been increased by the use of a crystal rectifier and higher plate

voltages. It is felt that the chief limitation on unbalance sensitivity lies in the detector® Measurements on the other components

of the circuit indicate that they are capable of detecting sufficiently small differences in noise level to give 0,1$ detectability.

Future Activityi It is hoped that a suitable set of mechanically

driven synchronous switches can be found to replace the electrically

driven ones,

A study will be made to try to find what the resolving power of

the present diode linear detector is, and what can be done to improve

it if it turns out to be the principal obstacle to the attainment of

greater unbalance sensitivity,

A final report on the work under OBI sponsorship will be prepared

during the coming quarter.
Electron Interferometer - NBS Project Olj.05-30-2929,

Electron Physics Section, Dr® L® Marton

General Objective s The experimental and theoretical investigation

of the design and performance of an electron interferometer*

Specific Objectives ? To design, construct and develop an interferometer using electron beams in place of light beams of the optical

interferometer and to use the instrument to demonstrate the formation of interference fringes* This requires the development of

electron beam splitters, the theoretical design of the interferometer

system, design and construction of the instrument mechanism, the as- sembly and fine adjustment to demonstrate interference, and the carising out of test measurements on the completed instrument©

Background: Ever' since the first experimental evidence of the wave

nature of the electron was reported in 1927, a large volume of work

with electron diffraction has confirmed the interference of electrons©

The gap between such naturally occurring interference phenomena in

crystals or electron microscope observations and controlled achievement of electron interference has not been bridged® Preliminary

calculations show that it should be perfectly feasible to bridge this

gap with an electron interferometer of a type reminiscent of the

•Mach-Zehnder * , but using diffraction from lamellar crystals as beam

splitters and deflectors® Such an instrument could be used to ex- tend the interferometric measurement of length and angle to new lower

limits now set by the wave length of visible light* It should also

be useful in the measurements of weak magnetic or electric fields in

a manner analogous to measurement of the refractive index in optical

interferometry® A number of important theoretical questions on the

nature of the electron would also be open to direct measurement*

Summary of Project Activity : During the previous year calculations

showed that it should indeed be possible to build such an interferometer* It was also sho^m experimentally that the necessary crystals

could be grown by evaporation on a suitable substrate, i*e* by the

process of epitaxy, and a light optical analogue was constructed and

tested* A design was prepared meeting all the required criteria and

a first model built* At the end of the last year the instrument was

installed on a modified electron microscope and the search for adjustment to give fringes was commenced*

Pro gress: The past six-month period has been spent in an attempt to

achieve the initial alignment of the instrument® It has been found

that with the thinnest crystals maintaining the necessary mechanical

strength (100 A annealed copper), contrary to our hopes the alignment must be done photographically for lack of sufficient intensity
- 7 -

for visual observations.* In a series of attempts to increase the

intensity the intercrystal distances were reduced from their initial

design values and the illuminating system of the microscope improved*

Although* the intensity is much better it has to date still proved

insufficient for visual observations with any beam density that avoids

immediate thermal destruction of the crystals *

In the alignment process therefore approximately one thousand

exposures were made and studied for fringes 0 The first of these

showed a lack of resolution which was progressively overcome by increasing the magnetic shielding® the mechanical rigidity of the

instrument* and by lowering the interferometer with respect to the

viewing system (to allow the use of short focus optics )o These improvements give a demonstrated least resolved distance in the region

of interest of less than 100 A®

To insure that the crystals were indeed as thin as the evaporation geometry implies, a Tolansky type optical interferometer was

set up to measure the crystal thickness « No significant deviation

from calculated thickness was found®

In view of the difficulty of alignment experienced* the optical

analogue* using diffraction grating replicas* was again set up and a series of experiments performed®. In the course of these experiments

it was found that this instrument belongs to a class of interferometer

partially studied by Carl Barus forty years ago and since almost forgotten® The instruments have the peculiar property that the number of

clear fringes is almost independent of the spectral purity of the source and in this sense the fringes are "achromatic "® However* since

the field of view is colored the fringes are not the achromatic fringes of Rayleigh but a form of "channeled spectrum" ®

As far as the main problem is concerned the results so far are inconclusive® The experiments were tried with a number of grating

replicas* with a number of intergrating spacings and a number of different light sources and conditions of iliumination0 In every case

it was possible to obtain fringes of varying contrasts and spacings*

A series of quantitative experiments was attempted to check the

alignment criteria developed in the early phases of the project* In

every case it was shown, that these criteria were not over-optimistic®

Some experiments using unmounted gratings were attempted but in this

case the fringes were inferior in contrast and stability® Some of

the difficulty was in the movement of the gratings in the air current

of the room and part to the wrinkled surface of the gratings® These

observations give a suggestion as to the cause of some of the difficulty experienced* since optical inspection of the crystals show that

they are not flat* It is difficult* however* to draw any valid conclusions due to the enormous difference in scale involved®
- 8

Future Activity: In the remaining half year the following activity

will be pursuedc Further attempts will be made to align the instrument with c:tystals of the present quality. Attempts will be made to

increase the perfection of the crystals and their mounting. Some

special cases of the theory of the instrument will be developed in a search for clues to the difficulty experienced. A full report will

be prepared of the status at the end of the project.
- 9

Mass Spectrometer for the Study of Solids - NBS Project

0k06 - 10 - 2930,5, Atomic Physics Section., Robert Lewis,,

Jo A. Hippie

General Objective ? Development of a magnetic type mass spectrometer

suitable for the analysis of solids*

Specific Objectives g To devise an analytical system which will com- bine the advantages of the spark source with the advantages of

electrometric detections The basic new idea to make this possible

is the incorporation of a monitor system at the first focus of a double focusing mass spectrometer to give continuous determination

of the ratio of any given mass to the whole samples

Successful development and test of this principle particularly

for those analyses not adequately treated by other methods are aims

of the projecto

Secondary objectives ares The investigation of the factors involved in the attainment of rapid analyses by presentation of the

data on a pen-and-ink recorder| the development of techniques for

different types of solids and the extension of the range to very

small concentration primarily through the use of electron multipliers*

Purely engineering refinements are left to subsequent commercial

development*

Background s The features which have led to the rapid acceptance of

the mass spectrometer during the past ten years as an essential

instrument in laboratories concerned with gas and vapor analysis indicate that it might be modified for rapid and accurate analysis of

solid samples

o

Highly developed spectro -chemical methods do already provide a means of solids analysis*, quite rapid compared to wet chemistry., ands for trace determination., considerably more accurate* However., this

same accuracy is sometimes not sufficient for the determination of

major constituents (i*e* chromium in the control of 18=8 stainless

steels) where the more tedious techniques of wet chemistry must be

employed* Often this is also necessary for even small concentrations of non-conductors such as phosphorus and sulphur* Moreover the

presence of certain elements sometimes interferes with an optical

analysis*

The more direct measurements possible with mass spectrometric

techniques may be able to supplement other methods in these regions

of difficulty and perhaps provide a simpler measurement for many

other problems* This application has been slow in developing* The
- 10 -

ion sources that are sufficiently stable to provide a source of con- stant intensity are very limited in their application,? On the other

hand* the high frequency spark would be applicable to a much wider

class of analyses* but its erratic nature makes it unsuitable for the

conventional mass spectrometers presently available commercially0 The

spark source has been used previously with photographic detection to

integrate the wild fluctuations 6 While the photographic method solves

the problem of the source fluctuations* problems of limited range*

non-linearity* calibration* speed and convenience limit its usefulness 0 Combination of the advantages of the spark source and electrometric

detection would form a useful analytical system*

Summary of Project Activity ; A monitoring system was developed to

permit measurement to be made in spite of the severe fluctuations of

the spark source* The monitor consists of an electrode placed at xhe

entrance to the magnetic field to sample the total ion beam* As the

various ions are scanned across the exit slit* the ratio of current

passing the exit slit to that received by the monitor is recorded,.

Since these two collectors receive current from the same source* the

fluctuations of this source are effectively nullified0 Calibration

was found to be linear over the range 1 % => 2$% in analyzing for nickel

and chromium in stainless steel*

A description of the successful analysis of six stainless steel

samples for nickel* chromium and iron appeared in Analytical Chemistry-^o Additional details of this work were reported at a Physical

Society meeting^* Application of this method to measurement of the

isotopic ratios for nickel* copper* and magnesium was reported at a

later meeting of the American Physical Society3®

Following these preliminary results studies were conducted to

improve and refine the operation of the system* Automatic recording

methods were introduced* Results wxxh automatic recording did not

match the results previously obtained with manual methods®

Preparation and tests have been made for using electron multipliers as sensitive ion detectors®

In order to improve the monitoring action* the performance of

the monitor was studied with a steady source of ions whose output

was subject to better control than the spark source* The output of

this "steady11 source could now be modulated to determine the effectiveness of the monitoring systan at various frequencies* This study

revealed several necessary modifications to the mass spectrometer and

amplifying system which were subsequently made* The monitor collector was split to assist in centering the beam on the magnet entry

slit (adjustment of the beam position axially in the direction of the

magnetic field)* Auxiliary deflectors were installed between the

electrostatic and magnetic fields for control of the ion beam in the

direction of the magnetic fieldo
11 -

Progress 3 Using the new auxiliary deflecting plates the beam distribution across the monitor was studied and adjusted for optimum performTM

anee® Ey sweeping the electrostatic analyzer voltage the beam distribution in the other direction was studied and found to be poorly defined

in the vicinity of the monitor® This was corrected by adding further

collunation above the magnet entry slit to suppress reflections® (Illustrations with the previous report. - June? 1952 - include a schematic

of the monitor system) ®

Other modifications in the ion optics brought the resolution to

the theoretical limits but3 although the stability was increased,,

further improvement was necessary® Centering the beam in the magnet

gap with the axial deflectors improves the operation and reduces the

noise on the mass peaks® The evidence was clear that the walls of

the magnetic analyzer were a contributing cause of the fluctuations!

because it is a major job to clean these surfaces,, the decision was made to tolerate this disturbance for the short time remaining on this

project®

Initial tests with the filament source following the above adjustments indicated that the ratios measured with the monitor method varied

less than 1 percent of the variation in the number of ions emitted by

the sources

A dummy circuit was constructed to simulate the action of the am= plifiers feeding their signals into the recorder® The time constants

of the circuits feeding the signals to the slide wire and chopper of

the recorder were made variable® It was thus possible to observe the

distortion in the recorded ratio as a function of mismatch of the two

input circuits® The square wave signal was obtained from a fast relay

driven by an audio oscillator® The frequency range was one to 130 c-ps e To balance out the fluctuations it was necessary to match the time con- stants within 10 percent at 0«1 second®

The time constants of the two amplifiers were studied by modulating the electrostatic analyzer voltage with the square wave generator mentioned above® This produced a 100 percent modulation in the

beam intensity at the monitor and collector® By varying the capacitances across the input resistors*, the time constants were adjusted to

balance out the variation produced in the ratio as a result of the

modulation® Difficulty was experienced in maintaining this balance

more than a few hours apparently because of varying characteristics

in the first stage of the amplifiers®

Experiments were conducted with the high frequency spark on ions

obtained from a finely powdered glass pressed into a matrix of silver®

The ions detected were those expected from the type of glass that was

used®

Electronic Coating Thickness Gage - NBS Project 050 6-31-3221*,

Electrodeposition Section, Abner Brenner,

General Objective s To develop a -thickness gage for measuring the

thickness of metallic coatings which differ from the basis metal in

electrical resistivity or in magnetic properties.

Specific Objectives

g

To develop an inexpensive, portable, direct^

reidlng'Tnstrument for nondestructively measuring the local thickness of those combinations of coatings and basis metal which are not susceptible to measurement by magnetic thickness gages.

Backgrounds Numerous magnetic devices are available for measuring

the thickness of metallic coatings which differ from the basis metal

in magnetic properties, but no convenient device is at present

available for nondestructively measuring the thickness of other com- binations of coatings and basis metals such as silver on brass, An

X-ray method has been developed for tin coatings on steel, but the

instrument is extremely expensive and not portable, A beta-ray back

scattering device has been developed for measuring the thickness of

films, but it requires an area about three inches in diameter and

therefore yields the average thickness rather than the local thickness of the coating. Devices based on inducing eddy currents in a metal surface are now available for measuring the thickness of nonconducting coatings upon metals, but they cannot be used for measuring the thickness of a metal coating upon a metallic base.

An exploratory study made several years ago in this laboratory

indicated that the thickness of a metal coating on another metal of

different electrical conductivity could be determined by using high

frequency current to induce an eddy current in the coating, Ey

virtue of the skin effect it was expected that the induced current

could be restricted mainly to the coating. Preliminary experiments

with a variable frequency oscillator and a primary and secondary

coil indicated that the current should have a frequency above 5>0 kilocycles. Experiments were subsequently made with a circuit similar to that used in the Naval Research Laboratory thickness gage

and evidence was obtained that the presence of a silver coating on

nickel brass could be detected.

Summary of Project Activity? Experiments with a simple resonantbridge circuit were made, in which the active test probe was a small coil of fine wire wrapped on a thin plastic rod. When operated at a frequency of about two megacycles the inductance of the

test probe when placed in contact with the plated surface was

sufficiently sensitive to variations in thickness of the plating,

when differing in conductivity with the basis metal, that fairly

accurate determinations of plating thickness could be made.
- Ik -

For localizing the area of measurement small probe coils were

made with diameter of ©05 to *01 inch* Sensitivity of the simple

bridge circuit was such that a change in reading of approximately

100 microamperes was obtained when the probe was placed on copper

and then on brass*,

Improvements were then made in the circuitry following a method

proposed ty Mr© Maurice L© Greenough of the Electronic Instrument

Section which approximately doubled the sensitivity of the instrumento

Further improvements were made by use of precision components and use

of germanium dials instead of vacuum tube dials©

Progress; The sensitivity has been further improved to 300 microamperes with a current of llj. milliamperes in the probe winding*

(Studies in calibrations have been made to determine the

effect of the thickness of the probe on the sensitivity) e A sharp

decrease in sensitivity occurred with increase in probe-tip thickness© For a tip thickness of 0 a 0l5 inch the sensitivity was 100

microamperes* but then this thickness was increased to 0©02i| inch

the sensitivity was decreased to 50 microamperes©

Experiments are now being conducted to observe the effects of

using various size coils on the operation of the instrument at

various frequencies* using appropriate values for resistance and

capacitance© The 1/16 inch probe has practically zero sensitivity

at all of the lower (5>0 KC - 1200 KC) frequencies* but the largest

probe (l/b inch) lias good sensitivity (l80y*-a) at 50 KC and very

good sensitivity (300/m. a) at 500 KC as compared to only 20 microamperes at 2 megacycles,.

The advantage in operating at lower frequencies is that the

depth of eddy current penetration is greater, therefore* enabling

the measurement of thicker platings# 3y using sheets of metal of

various thicknesses the approximate depth of penetration of the

eddy currents can be determined with this instrument©

A study is now being conducted to determine the effects of

geometry of the specimen on the sensitivity of the instrument® At

present it appears that the sensitivity doesn't change with shape

of specimen, but the actual meter readings are shifted©

Some experiments have been performed using mu metal and permalloy for the core (bobbin) of the probe© These probes* when

properly annealed* proved to be a great aid in increasing this

sensitivity of the instrument at lower frequencies ( 2-500 KC) S therefore permitting operation at lower frequencies than previously© The

sensitivity at 50 KC was i00/^a©
Future Activity g A final report on this project will be forthcoming

at a later date 0 The practical details of the instrument are now

being worked out on a grant from the Bureau of Engraving and Printings
- 16 -

Carbon Dioxide Ifyspometer - NBS Project 0602-3l|-352lj.s Mechanical Instruments Section, We G® Brombacher

General Objective ; To develop apparatus and technique for measuring

pressure-altitude at high altitudes by measuring the temperature of

subliming carbon dioxide snow®

Background ; There appears to be considerable promise in a "hypsometer” utilizing the temperature of subliming, solid carbon dioxide

in equilibrium with its vapor at ambient pressure as a measure of

pressure in upper air research,, An electrical output from the sensing

element is peculiarly desirable® The carbon dioxide hypsometer would

function similarly as a hypsometer using measurements of the boiling

point of water to determine ambient air pressure or pressure altitudes

The chief advantage of an instrument on this basis is the fact that

both the measured temperature and the pressure altitude vary approximately with the logarithm of the ambient pressure and thus the sen- sitivity on a pressure altitude basis is practically constant® A

change of 1°C is equivalent to a change in pressure altitude of

2172 feet from sea level to 60,000 feet and 5875 feet from 175,000 to

300,000 feet®

Previous work on hypsometers for this purpose included investigation of the utility of water and carbon disulphide® Pressure altitudes not over about 112, '000 feet can be obtained with water, and

carbon disulphide is unpleasant to work with®

The temperature to be measured is that of the solid carbon

dioxide which is formed by expanding liquid carbon dioxide through

a porous plug® The experiments are chiefly directed to obtaining a suitable porous plug, refinements to reduce the size of the instrument to a vacuum, and the development of suitable temperature probes®

Summary of Project Activity ; On the basis of theoretical studies and

preliminary experiments a variety of porous plugs was constructed

of fine copper powder compressed under high pressure which would

permit the flow of carbon dioxide from a 1000 psi tank at rates of

l/2 to 10 litres per minute, A standard size for the plugs was 2 inches in length by l/2 inch 0D by l/lj. inch ID® It was found that at

flows below 2 litres per minute carbon dioxide flow could not be

reliabily formed® The effect of the shape and length of the tube, in

which the thermocouple junction was placed for determining the temperature of the subliming carbon dioxide, was investigated to find an

arrangement which would reliably deposit solid CO2 on the thermocouple

junction,, In some arrangements it was found that the COg would form

a solid plug which would then be forcibly blown out, breaking the

thermocouple. It was found that flows of two to three litres per

minute appeared to give the best performance®
- 17 -

Progress i A number of hypsometer models were constructed and tested,

at reduced pressures in an altitude chamber © The most promising

models were tested to pressures corresponding to altitude of 105^000

feet©

Further theoretical study was made of the factors determining

the sensitivity of various possible vaporizing substances for use in

high altitude hypsometers and of the conditions required for initial

temperature of the expanded C02» A final report on the project is

being prepared©
- 18 -

Absolute Measurement of Vibration Amplitudes - NBS Project

0601-31-352 85

" Sound

General Objective s To develop and precisely calibrate a vibration

generator in the range from 100 to 10,000 cycles per secondj to

develop and calibrate a vibration detector on the basis of the known

motion of the vibration generator! to use the detector for vibration

measurements and for calibrating other vibration pickups®

Specific Objectives g (aj To develop a barium titanate shaker which will vibrate at

an approximately constant amplitude for a given input voltage in

the range from 100 to 10,000 cycles per second,,

(b) To calibrate the shaker over this mnge by an acoustic

method,

(c) To develop an electro static detector which can be c alibrated against the known, motion of the driver and which can be transferred to other vibration generators for detenriining their motion0

(d) To design one electrostatic pickup with high sensitivity

and another detector for practical applications®

(e) To devise and develop methods for calibrating the electronstatic detector independent of the acoustic method®

Backgrounds An important link between vibrations and acoustics is

provided'!^ the pistonphone, which is a device for developing an alternating pressure in a closed cavity by means of a vibrating

piston. This instrument was first built so that a known motion

could be imparted to the piston® By a simple expression which relates the motion and the pressure, the pressure in the cavity can be

calculated?

A microphone acoustically coupled to the cavity can thus be calibrated® Development of this technique for use up to 200 cps, has been

accomplished® 1,2«

1® Wente, “Absolute Measurement of Sound Intensity", Phys® Rev® 10,

Po 48 (1917),

2® Ballantine, "Technique of Microphone Calibration", JASA 3-39

P* 338 (1932)o

p

3 Ap0dr

~T“

p

s peak pressure

A 3 Area of piston

Po® ambient pressure

d s peak amplitude of piston

motion

T s ratio of specific heats (loll)

V 3 volume of cavity
19 -

With the development of the reciprocity calibration of condenser

microphones 3 3 the use of the pistonphone for calibrating microphones

became somewhat outmoded a However9 it was suggested^ that the pistonphone procedure be reversed,, that is, to determine the amplitude

of motion of the piston on the basis of being able to accurately

measure the pressure in the cavity0 At the same time, the method

could be extended to include higher frequencies*

In this connection, the need arises for a method of transferring

the acoustic calibration to other vibration generators for purposes

of comparison or for calibration of vibration pickups* This can be

done by means of a capacitance pickup, whose sensitivity and frequency

response has been obtained b^ means of the acoustic calibration. Use

of a circuit after Van Zelstn was contemplated because of its simplicity and its adaptability as an electrostatic detector*

In. order to have a check on these measurements, it was planned to

investigate other methods of calibrating the electrostatic detector,

namely by electronic means and by direct microscope measurements*

Summary of Project Activities g The first instrument built makes use

of an electromagnetic driver arranged to vibrate a piston projecting

into a cavity* The diaphragm of a condenser microphone,, previously

calibrated by a reciprocity technique, is acoustically coupled to the

cavity* The pressure change in the cavity resulting from the motion

of the piston is detected by the microphone and the amplitude of

motion of the piston computed from hie observed sound pressures

The electrostatic pickup associated with this device is a parallel plate capacitor used as one componanf in the series resonant arm

of a low impedance bridge circuits A lc 6 me signal is injected,

which is modulated by the motion of the piston© The carrier is then

combined with the modulated signal to produce an amplitude modulated wave* The audo signal corresponding to the vibration of hie

piston is extracted by demodulation in an infinite impedance detector.

The best accuracy which could be obtained with this instrument

was about 10% up to a frequency of 2500 cps© The peak amplitude

range extended from 6 x 10“9 to 6 x 10“^ cm* After some experimentation, the reasons for the limitations in accuracy, frequency

response and amplitude became apparent and plans were made for developing a new instrument to overcome these difficulties©

3 «

' RV Ko Cook, ^AbsoTute°Tressura Calibration of Microphones®9 JASA 12=3* p* ia5 (1910.)

1*.© A* London, Discussion, J„ App© Mech© 1 p« 391 (191*8)©

5© Jo Jo Zaalberg van Zelst, "Circuit for Condenser Microphones

with Low Noise Level*1 Philips Tech* Rev* 9 S p®357 (191*7/8)©
20 -

The driver for the new device is a hollow, cylindrical barium

titanate crystal, designed to vibrate at approximately 10“5 cm peak

amplitude up to 10,000 cps for an input voltage of 5>0 volts 0 The

cavity is a reproduction of the 19*5 cc® cavity used in the Sound

Section of the Bureau of Standards for the reciprocity calibration of

condenser microphones 0 Measurements without theoretical corrections

are possible up to 3*000 cps using air in the cavity® Provision is

made for introducing hydrogen to eliminate the effects of standing

waves between 3*000 and 10,000 cps and permit calibration in this

range* A capacitance monitor pickup is included to yield an output

at the same time that the microphone is in use, so that the calibration of the shaker need not be depended upon*

Calibration of a capacitance probe vibration detector is accomplished adjacent to the same vibrating surface that is used to

generate the pressure in the cavity* The capacitance and its series

resonant inductance are arranged as a probe in a shielded enclosure

to eliminate possible effects of stray capacitances Thus, transfer

from the calibrating instrument to other shakers is made possible

without changing the sensitivity of the pickup* The design permits

measurement of the average amplitude of vibration of a flat surface,

3/h inch in diameter* For larger surfaces, the variations in surface

motion can be measured*

Two probes were built, one for high sensitivity, operating at a spacing of about 0*15 mm and one for practical use, operating at 0 c h5

mm® The former probe has approximately 10 times the sensitivity of

the latter®

A method for calibrating the electrostatic detector at low

frequencies independently of the acoustic calibration was also investigated® In this procedure, a known direct displacement is imparted

to the probe and the output of a null detector noted* After retuning

to a null, an alternating motion is given the piston, yielding an increase in the null reading* The two readings of the null detector

can be related mathematically and the morion of the piston calculated*

Use of this method has given results comparable with the accuracy of

the measurement of the direct displacement, xihich is at present the

limiting factor* The measurements generally agree within 10%9

A third method consists of illuminating a vibrating surface by

an alternating light source® Mien the frequency of this source is

slightly different from the vibration frequency, the vibration can be

observed in slow motion through a microscope and accurate measurements

made*

In the first attempts at an acoustic calibration, direct mechanical coupling between the driver and pickups presented the greatest

difficulty® It had been planned to mount the driver on vibration

mounts in order to minimize this effect*
- 21 -

However, another factor intervened. The rubbing of the piston

against the cavity walls is also a strong enough coupling element to

develop wave motion in the main structure of the instrument® Clearance

between the piston and the cavity enclosure is necessary to eliminate

this difficulty® With vibration mounts, the driver mechanism tilted

sufficiently to result in rubbing, despite a provision for clearance.

The mounts were therefore temporarily abandoned in favor of solid

clamping of the driver to the main structure* Although direct coupling still existed, the resistance factor was at least eliminated®

The clearance is about ®00li” and is sealed with vaseline to prevent

leakage of air* With this arrangement, acoustic calibrations were

obtained from 100 to 25>00 cps with an estimated accuracy of 3%* Above

2500 cps the results were too erratic to have any meaning®

It was found that the probe pickup can be tilted up to about 5

degrees compared to the flat vibrating surface without any noticeable

change in the outputs,

The output noise level of the detecting circuit in a 20 cps band

is 50 microvolts* This corresponds to a displacement of 10**^ cm peak

amplitude when referred to the calibration of the more sensitive probe*

The possibility of extending the frequency range was investigated

further and a method devised to support the driver mechanism by vibration mounts and still maintain the *00if clearance* With the mechanical coupling thus reduced, preliminary acoustic calibrations were

ma.de from 100 to 10,000 cps*

Progress ; The frequency response of the detecting circuit was measured

by disconnecting the bridge circuit and substituting an amplitude

modulated wave input* Close agreement with the response determined by

the acoustic calibrations was obtained from 100 to 10,000 cps*

On the basis of the electronically measured frequency response and

the microscope measurements at low frequencies, the accuracy of the

average of four acoustic calibrations performed is estimated as follows

Frequency Range, cps Accuracy

100 to 2,000

3.000 to 5,000

6.000 to 10,000

3%

h%
The general trend of the response curve of the capacitance vibration detector is regular except at 5*000 cps* where a 0®1 db dip

in sensitivity exists® This anomaly is attributed to the small

amount of mechanical coupling remaining between the driver and the

main structure® At 105 000 cps* the response falls off slightly

more than 1 db®

Several barium titanate accelerometers were calibrated up to

10*000 cps by comparison with the capacitance probe®

Future Activity; The objectives of this project having been

attained* a terminal report was prepared which is in the process

of approval,®
- 23 -

Ultrasonic Velocimeter for Liquids - NBS Project 0601-31-3531,

Sound Section, Martin G-reenspan

General Objective; To investigate the feasibility of applying the

"sing-around" and the 11 time -of-flight" pulse methods to a fixed

path acoustic delay line so as to provide a direct-reading 'instrument for measurement of the speed of sound in (and hence the compressibility of) liquids*

Specific Objectives : To determine which of the fixed path pulse

systems ( "sing-around" or "time -of-flight") is the more accurate

and reliable* To investigate the possibility of making an absolute indicating instrument, or if this is not possible, to deteimine the extent and nature of the corrections which must be

applied*

Background s The adiabatic compressibility is a quantity of fundamental importance in studies of the liquid state* Together with isothermal compressibility (from static measurements) it determines the

ratio of specific heats* This instrument would facilitate, for

example, the study of ionic equilibria in liquids* Sound-velocity

measurements could be used in the laboratory and in industry for

process control and for analysis much as index of refraction measurements are used* It may be possible to apply the results of this work

to the development of a device to measure continuously the velocity

of sound in sea water for sonar and other underwater sound applications®

Of the hitherto existing instruments for measurement of the

speed of sound in liquids the variable-path interferometer is the

most accurate and among the simplest® Operation of an interferometer is tedious and requires skilled personnel! further, a run

requires an hour or so, so that the instrument is not satisfactory

for use with liquids of which the temperature or composition is

changing, and very precise temperature and frequency control is required in any case 0 Most other methods, of which there are a great

many, are suitable for use in the laboratory only, and are less

accurate than the interferometer method* An instrument, even of

somewhat complex structure, but nevertheless reliable and capable

of operation by non-professional personnel, and approaching the

accuracy of the interferometer, would make it practicable to utilize

sound-velocity measurement in laboratories other than sound laboratories, and perhaps in industry and in the field*

Summary of Project Activity ; The apparatus is essentially an acoustic delay line® The line now in use is a tank about 10 cm long of

which the ends are quartz-crystal transducers® A high voltage pulse

is applied to the "sender" crystalj a corresponding pulse of sound

travels down the sample liquid and is received and converted ’to a voltage pulse by the "receiver" crystal®
- 2b -

The pulse is distorted by transmission through the liquid because the high-frequency components are attenuated more than the lowfrequency components® The sent and received pulses are thus of different shapes,, and precise specif ication of the location in time of

the pulse can be mads only by consideration of the instant at which

the signal begins to rise from the noise® Therefore a rapidly rising

pulse is essential and a pulse-modulated carrier lias no advantage

over a video pulse 0

Initially the s9 5ing-around,! system was investigated^ as it

appeared to be simpler® In this system the received pulse after suitable amplification and reshaping is again applied to the sender% thus

the device regenerates and the pulse repetition frequency depends

on the velocity of sound in the sample® In this “sing-around" system

considerable difficulty was encountered with multiple reflections®

Those echoes which arise from a single primary pulse are self-synchronous 5 but they are not synchronous with any other set because of time

delay in the amplifier and trigger circuits® Effort, was made to eliminate these troublesome reflections by putting absorbers in front of

the crystals ^ backing the crystals with tapered lead blocks,, reducing

cross-section of the path,, etc® All of these methods fend to obscure

the initial rise,, thus introducing an additional delay,, but what is

more important,, the proper adjustment and also the amount of delay

depend on the sound attenuating properties of the particular liquid®

The sound-attenuation coefficient varies enormously from liquid to

liquid® For these reasons the sing-around scheme was abondoned for

general use,, at least temporarily! nevertheless it is felt that it

holds great promise for the measurement of small variations in the

speed of sound among liquids of nearly the same attenuation! an Important example is sea-water in which it is important to detect the effects

of variations in temperatures pressure and salinity®

Experiments were conducted using many variations of the time-offlight method and finally a system was devised which reduces the

measurement to one of frequency and has great inherent precision®

Two fast pulses are produced,, the time interval being adjustable

and accurately known® The first is applied to the sending crystal

and the second is set in coincidence with the output of the acoustic

line® The repetition rate for this cycle is long enough for the

echoes to have died away before the next pulse is applied® The pulses

are derived from a variable-frequency,, sine-wave oscillator® Those

pulses other than the two desired are eliminated by means of two

series of binary dividers operated in parallel but one pulse apart- in

phase® Provision is made for equalizing the delays of the two pulses®

This system,, which is applicable to various time-measurement problems

in radar and elsewhere will be described in ft forthcoming issue of the

RSI under the title,, “An Accurate Time-Modulated Pulse Circuit11 5 by
Carroll Tschiegg and Martin Greenspan® This system (and any other)

requires an amplifier to restore to the received pulse the fast rise

lost in passage of the sound pulse through the tank® A fast amplifier

which saturates almost immediately after the signal rises from the

noise,, but not on the noise itself was developed and is in use® It

is important to note that the very beginning of the received signal

is obscured in the noise resulting, unavoidably* in a fictive delay

which must be held to a very small* or a known* value®

The coincidence measurement referred to above is ma.de on an

oscilloscope screen® For good resolution without excessive sweep

speed it is necessary to have markers of fast rise and short duration*

A pulse transformer based on a ferrite core was developed which makes

it possible to build a small blocking oscillator which delivers a pulse having a rise time of less than 0®Q2 microsecond and a duration

of about 0*1 microsecond* This development is described in the May*

1952 issue of the Technical News Bulletin (NBS) under the title* "New

Pulse Transformer Gives Faster Response"*

This fast blocking oscillator was found to be a more suitable

input pulse for the transmitting crystal® The fast pulse tends to

improve the initial signal intensity at the receiving crystal® More

important, it was found that this shorter pulse (about 0*1 microsecond)

does not excite the transmitting crystals radial mode of vibration

which is thought to send a small amount of sound through the walls of

the tank* With this improvement* it is not necessary to slot the

walls of the tank to produce an acoustic labyrinth as was previously

necessary®

A precision liquids interferometer of conventional type has been

constructed for use in calibration of the velocimeter© It was used

to measure the velocity of sound in six different liquids ( glycerine*

ethylene glycol* water* benzene* methanol* and carbon tetrachloride)®

These liquids vary greatly in attenuation and velocity® For comparison* those same liquids were checked in the velocimeter® A nearly

constant delay of 0 <,l& 'bo 0*50 microsecond was found for all liquids®

This suggests that a cycle of the crystal frequency (2Ke/s) is lost

in the noise® However* this error may have other causes as it does

not change with very large changes in attenuation® Crystals of twice

and half the frequency of the ones now in use are on order® With

these new crystals it should be Dossibie to pin down this source of

error* or determine if this delay is related to the crystal frequency®

A simple sing-around circuit was built consisting of a fast

blocking oscillator* delay tank* and a high gain* pulse shaping amplifier® The troublesome reflections were eliminated by tilting and

receiving crystal slightly* and also by increasing the attenuation by

using smaller diameter crystals® With proper adjustment it is possible to eliminate all reflections and still be left with enough
- 26 -

signal to saturate the amplifier for one pulse only© This procedure

results in the loss of several cycles at the beginning of the pulse? thus increasing the delay and apparent time of flight© It is felt

that tills loss is not important because Hie amplifier and trigger circult have delays that cannot be eliminated© If these overfall delays can be made constant over a narrow range5 such as encountered in sea water5 this instrument can be calibrated to give a direct reading of

the velocity© The breadboard model3 (still lacking many refinements)

is very stable and sensitive to changes in velocity© With proper

measuring devices a change in velocity of one part in 10° can be detecteda

Progress s

(a) Time-of"flight type© New delay tanks of fused quartz were

obtained© "TKeieTiave "optically flat open ends and it should be pos~

sible to assemble them with polished quartz transducers so that no cement is needed© Three sets of crystals of different thicknesses

are being polished© These will be used in an experiment to determine

the source of the 0ok$ - 0*5'0 microsecond delay©

(b) Sing-around type© The sing-around model velocimeter was calibrated~in artaXitcial sea water against a precision liquids inter"

ferometer over the temperature range 13© to li3PC s corresponding to a speed-of-sound range of about 1510 to 1570 meters/sec © Over this

range the electrical delay is constant at 1©55 microseconds except that

near the high end it gradually increases to 1©60 microseconds© The

calibration is reproducible®

The stability of the model was checked using a zero temperature

coefficient liquid© It was found that a stability of 1 part in 1CP

over a 2k hour period could be achieved if proper attention was paid

to the selection of stable components and to power supply voltage

regulation©

It is indicated that this device could be made to operate over

a 10$ range in any particular liquid except excessively attenuating

ones such as glycerine© The adjustments and calibration would need

to be made for each liquid independently©

An automatic recording model of this instrument for field use in

the sea is being constructed for the GNR© Work on this project will

be suspended until the sea-water model for the ONR is completed©

Future Activltyg

(a) Time -of"flight type© The direction of future activity

depends on^Ee^at^e~o^tdie 0©Ip - 0©50 microsecond delay© The determination of this is the next item on the program©
- 27 -

(b) Sing-around type* The development of this model is complete except for construction details and adaptation to specific use*

A final report is in preparation*
- 28 -

Aeoustl© Viscometer for Gases - NBS Project 0601-31=3533

Sound Section* Martin Greenspan

General Objectives To develop an instrument based on acoustical

principles for measurement of the viscosity of gases and gas

mixtures over as wide a range of temperature and pressure as is

practicable®

Specific Objectives g Tc determine whether or not it is possible and

practicable to deduce ‘the viscosity coefficient of a gas from resonance measurements on a modified Helmholtz resonator® To study and

develop the necessary instrumentation* especially as regards suitable

transducers (microphones )

©

.An additional specific objective,, adopted since the last report*

is to determine the feasability of using a non-resonance technique

for the same purpose® The principle involved is the reduction of

phase velocity of a low-frequency sound wave by the high damping in

a small capillary tube®

Background g The absolute measurement of viscosity coefficient of

gases is of Importance in determining 'the physical properties of

sound-absorbent acoustical materials® Besides the application to

acoustics* viscosity coefficients are important in applying the principles of gas dynamics to combustion problems,, and to flow problems

encountered in wind tunnels and in flight of aircraft®

Nearly all of the available data on the viscosity coefficients

of gases were apparently obtained by static flow methods® In one of

these methods* a steady uni-directional flow of gas through a capillary is maintained, by a steady pressure difference between the two

ends of the capillary® The distribution of gas velocities within the

capillary tube is assumed to follow Hagen-Poiseuille 3 s Law®

We propose to deduce the viscosity coefficient through measurements of the 83 Q

83 and natural frequency of a Helmholtz resonator formed

by a capillary joining two volumes of gas® A preliminary analysis

reveals the remarkable fact that the measurement of vi.scosity coefficient can be made to depend only on measurements of the resonant

frequency* the “Q88 of the resonant frequency* the square of the diameter of the capillary* and the density of the gas® The static flow

method* however* gives a result which is dependent on the fourth

power of the diameter of the capillary* and in addition requires the

measurement of a pressure difference* length of the capillary* rate of

flow through the capillary* and the density of the ga.s 0
- 29 -

It is riot expected that an acoustic method will be as accurate

as the static flow methods, but it is felt that greater compactness

and greater speed and ease of operation will be achieved,. For ex- ample a capillary tube used in a static flow method may be more than

fifteen feet long and its associated equipment may fill a large

room* The acoustic resonator will be on the order of one foot long

and the associated electrical circuits will occupy a relatively small

space® Temperature and pressure regulating equipment also are expected to be less complicated,. Another advantage of the proposed acoustic technique is that flow measurements will be nude for extremely

small pressure gradients® Existing acoustic techniques are readily

available for measuring pressure differences as small as lO"? atmospheres®

The results of measurements thus far made on the resonators

are not very promising,. For this reason it may be desirable to concentrate for the time being on the other technique mentioned above,

which does not involve resonance methods,,

Summary of Project Activity’ s A typical resonator consists of two

equal volumes connected by a capillary tube, the whole filled with

the gas under investigation® Upon excitation the gas in the capillary may be thought of as a mass vibrating between the two springs

formed by the relatively large volumes of compressible gas® If all

of the dimensions are small compared to a wavelength of sound at the

frequencies of interest,, then practically, all of the pressure variation during an oscillation takes place in the volumes, and all of the

velocity variation in the capillary,, so that the gas in the capillary

acts as if it were incompressible® The walls of the resonator are very rigid so that no energy is lost by radiation® The gas in the

capillary remains practically at constant pressure and therefore at

constant temperature; thus there is negligible energy loss due to heat

conduction to the walls of the capillary® ^he temperature variations

occur in the volumes; however calculation shows that for the dimensions and frequencies involved, the heat conduction loss is negligible®

Thus the losses are determined principally by viscous effects in the

capillary and these are readily calculated on the assumption of Poiseuilie flow®

The techniques then, is to produce by means of a transducer a sound in one volume and measure either the sound pressure in the

other volume or the particle velocity in the capillary; from the response of the system as a function of frequency, the !! Q

5I! , and finally

the viscosity coefficient is calculated®

Five brass resonators were constructed® These were designed

to have the same natural frequency (about 150 cycles per second, for

air) and volumes (30 ml ea®), but the capillaries vary from 0o li cm in

diameter and 11 cm in. length to 0®1 cm in diameter and 0®6 cm in

length®
After preliminary experiments with various types of transducers

such as carbon,® crystal and condenser microphones 5 thermophones and

hot wire microphones^ it was decided to concentrate for the time being

on the hot wire instruments * These seem more applicable to use at

elevated temperatures and pressures than do the others0

The thermophones tentatively in use consist of about 20 inches

of OoOOl inch dias platinum wire wound in a spiral around insulated

posts o The hot wire microphone is similar to those used in wind

tunnel experiments and consists of a 0*0001 inch dia* platinum wire

stretched across the points of two ordinary sewing needles suitably

mounted* The frequency response characteristics of several thermophones were measured using a condenser microphone standard*

The electrical circuits for the biasing of the hot wire instruments were designed and built0 A suitable signal source for exciting

the thermophone and amplifiers for the hot wire microphone were

assembled© Circuits for shielding and filtering the output of the hot

wire microphone are being developeda It is to be noted that due to

the small signal developed by the microphone, the filtering and shielding requirements are quite exacting*

Preliminary results showed that it is difficult to realize Poiseuille flow in a resonator of convenient dimensions,, A more general

expression which gives the velocity distribution in terms of Bessel

functions^ with PoiseuiXle flow as a limiting case was calculated©

The is a complicated function of the parameter where

w Q

is angular resonant frequency

In the region of the parameter under investigation^ a first

approximation of the form Q

- 0 71 (CO r=><»56 can be used©

The experiments on air in brass resonators gave results for viscosity which are too high and therefore were repeated with the hot wire

transducers replaced by condenser microphoness whose properties are

better known® Indications are that excess loss amounting to about

15% is involved©

For use in experiments designed for tracking down the excess loss

a simpler^ although less accurate method of measuring the iC Q

89 of the

resonator was adopted© A transient is produced by firing a spark plug

in one volume and the response of the resonator is obtained by photographing an oscillogram of the output of a condenser microphone in the

other volume0 The decremerite, and hence the ,{ Q" of the response is obtained by measurement of the oscillogram using a travelling microscope©

These transient-response measurements are in essential agreorient with

the steady-state response measurements®

'r “ radius of the capillary©
- 31 -

The theory of alternating flow in a tube ms re-examined during

the quartern The general theory*, due to Kirehhoff*, shows that sound

propagation in a tube depends in a complicated not capable of

eaplicit expression*, on a parameter % s U)/Y' ^)l/2r where @0 is the

angular frequency*, r is the radius of the tube9 and T ^ is a constant of tie gas depending on the viscosity*, heat conductivitys ratio

of specific heats*, and density© For large values of % Kirchhoff

was able to find the form of T“ and obtain a solution which many investigators have verified experimentally within lS% and one (Lawley5 19.32) within $%& For “these large values of % the Q is too- great

to permit accurate measurement by the resonance technique and in any

case the losses depend as much on heat conductivity as on viscosity©

The equations for intermediate values of a have been hitherto

intractable unless the effect of heat conductivity is ignored*, in

which case there is a solution dne to Crandall (1926) adapted to com- putation by us during the proceeding quarter© ^he assumption that

the heat conductivity has a negligible effect was regarded as plausible on physical grounds and the resonators were designed around

values of % which give suitable values of Q© During the quarter

an approximation was developed which allows the Kirchhoff equations

to be solved with good accuracy for all except very small values of i©

.In the limiting case of small values of % Rayleigh showed that

the propagation of sound in the tube becomes diffusive in nature and

independent of heat conductivity*, and. that the velocity distribution

across the cross section becomes that of Poiseuille© These conditions correspond to small tube diameters and low frequencies*, that is

they approach static conditions for which the theory for low z is

accurate© During the quarter a study was made of the possibility of

doing experimental work in this range© The principle involved is the

reduction of pte.se velocity by high ‘damping© The measurement of pressure difference and flow velocity in the static method is replaced

by that of phase difference between the particle velocities between

the ends of the cap illary in. the present method® In principle this

measurement can be made to high accuracy© The result (for viscosity)

depends ©m a knowledge of the density and gas constant of the sample^

and om the first power (rather than the fourth*, as in the static method)

of the radius of the capillary^

Pro grsss g The theory was elaborated 'and instruments were designed

and built to measure the phase shift across a tube about Q©S m in

diameter and 83 cm long at 10 c/s® Under these conditions the pte.se

shift is about 29° for air if the tube is short-circuited at each

end© The tube was terminated at each end by a relatively large volume either of which can be driven by a loudspeaker© A hot-wir® microphone of diameter 2 ©3 microns ‘was used as a transducer at each end of

the capillary©
« 32 -

Another technique involves the measurement of the phase differ^

ence between the input impedance of the capillary open at the far end

and that for the closed condition (about 53° for air)® In both cases

preliminary measurements give the viscosity of air at room conditions

within about b%»

The phase shifts were measured using a phase shifter constructed

from a resolver with an oscilloscope as a null detectoro

Future Activity; More precise methods of measuring phase shift will

be tried® Precision-bore tubing of smaller diameter will be procured

and the frequency increased somewhat® ' Gases other than air will be

measured®
- 33 -

Microwave Hygrometer - MBS Project 0502-30»35>lt0, Mechanical

Instruments deletion, W* G, Bronibacher

General Objective; To investigate the possibilities of using the

microwave refractometer as a humidity standard#

Specific Objectives

?

To redesign the microwave refractometer of

Mrnbaum and to develop associated electronic equipment so that

the instrument may be used to continuously record the water vapor

content of air with high accuracy, low time lag and over a wide

ambient temperature range©

Background? Birnbaum of the Central Radio Propagation Laboratory

l

N

b£>

)

developed a recording microwave refractometer (Rev* Sci«

Inst* 21, 169, 1950) of high sensitivity that can continuously

sample and record the dielectric constant of a stream of air or

gas# Since the dielectric constant varies with the water-vapor

content, this instrument is inherently capable of being used as a recording hygrometer* The refractometer operates by comparing

two identical cavity resonators* Into one of these cavities, the

test sample is introduced# The resulting differences in resonance

frequency between the reference and test cavities is then a measure

of the dielectric constant of the test sample* The basic virtues

of this refractometer for use in measuring humidity are its high,

sensitivity, high speed of response and capacity for high accuracy*

In view of these considerations, it appears feasible to adapt the

microwave refractometer into a standard hygrometer for use over a wide moisture and ambient temperature range*

The relation between the

constant of air is given by

where n ®

'it- S O

and the relation between index of refraction and moisture content of

air is given by the empirical equation (Radiation Lab* Report No 0 95l5 dated April 6, !9b$)

li800e (n~l)lQ6 - -f- P +

where T E absolute temperature, °K

P ~ barometric pressure in millibars

e s partial pressure of the water vapor in the air

index of refraction and the dielectric

c ~ n

2 ^ n

index of refraction

dielectric constant
- 3h -

The refractometer determines index of refraction, n, which, when

inserted into the above formula with values of absolute temperature

and barometric pressure, yields the water vapor content in terms of

its vapor pressure* If N 3 (n-X)10 , then over a temperature range

of +50° to -4O

0

, the number of N units of saturated air is as follows

s

t, °G 50 hp 30 20 10 0 -10 -20 ”30 “Uo

N units 24-37 27? 172 102 58 30 15 6*1 2*37 *75

Summary of Project Activity; A critical review was made of the

factors affecting the performance of the refractometer when utilized

as a humidity measuring device* Ir. addition, a microwave refractometer was borrowed from the CRPL for laboratory study* As a result

of this, it was concluded that a refractometer could be constructed

with a sensitivity of 0*0,5 N units, but that in order to fully realize the potentialities of this sensitivity certain modifications and

new features would have to be incorporated into the basic design*

Some of these are as follows?

1) To operate the refractometer as a null-balancing instrument*

A servo system is required to drive a plunger into one of the test

cavities so as to bring it back to the resonant frequency of the reference cavity* This type of operation will aid in reducing instrument

dependence on klystron noise and frequency drift and possibly lead to

greater sensitivity*

2) To use two cavities, 'both operating at the same barometric

pressure, one containing dry air (the reference cavity) and the other

the test sample* Operating both cavities at the same barometric

pressure serves to cancel out this term from the equation and eliminates the necessity of making a precision pressure measurement*

3) To maintain the klystron, cavities and gas to be measured

at some fixed temperature* Fixed temperature operation will help

in reducing the noise level and per?:,lit ready control and precision

measurement of the temperature* Maintaining both cavities at the

same fixed temperature will eliminate the need for making the cavities from invar* Frequency drift of the klystron due to temperature fluctuations, will be reduced*

I4.) To develop pulsing circuitry for operating at the peak of

the resonance curve of the cavities* Again, this is desirable so as to reduce noise level* With the temperature fixed the number of

N units is proportional to the water vapor pressure*

5) To provide means for checking instrument drift at frequent

intervals® It is proposed to incorporate means for introducing

either dry air or the moist air sample into both cavities©
- 35 -

An initial model of a servo-system for balancing the two cavities by operating plunger was completed and tested® Satisfactory

performance was obtained although some improvements appear desirable

to obtain optimum performance® A preliminary model of a temperature

controller for maintaining and controlling the temperature of the

gas sample, cavities and klystron was completed*. This unit is based

on a modulated pulse width type heat input that is proportional to

the departure from the control temperature® Preliminary experiments

on a water bath operating at &hO°G indicated that the controller was

able to maintain a fixed temperature to better than 0 e 03°C for sev- eral hours duration® Design of other circuitry was started®

Several modifications have been made on the temperature controller in order to improve its performance® The basic principle has

been retained® On subsequent tests the controller was able to maintain the temperature of a varsol bath at •frJjOQC t ®01°C for a period

of 2 k hours®

Progress g A new method is being developed for measuring the frequency^HUFerence between the cavities which eliminates the need for

frequency modulating the klystron and the development of suitable

amplifiers and pulsing circuits as originally used in Bimbaum 3 s instrument® This proposed system reduces the complexities of the

development, construction, and maintenance of the equipment®

The method consists of using a carrier wave signal from the

klystron whose frequency is set at approximately the half power

point of the cavities*. The difference in d-c output of the crystals

will be zero if the cavities are at the same frequency® If the

resonant frequency of the measuring cavity changes, the output voltage win be either positive or negative, depending on the resonant

frequency shift, and will have a magnitude approximately proportional

to this shift® This d-c output is applied directly to a Brown con- verter-amplifier unit which drives a servo -motor® The servo-motor

drives the cavity micrometer plunger in such a direction as to

rebalance the frequency shift®

Preliminary experiments have indicated that this method is quite

feasible and that the sensitivity of the Brown converter amplifier

is sufficient to rebalance the system to within several hundred

cycles (approximately 0 o 02 N units)®

Future Activity’s One of the factors to be determined is the noise and

stability of the crystal rectifiers in the d-c range®

A preliminary model in which the microwave equipment will be

maintained at a fixed temperature is being constructed so that further

tests may be carried out to determine stability, sensitivity, and noise

level of the overall system®
- 36 -

Survey of Dynamic Pressure Instrumentation - NES Project

0602-j?0-3f>£5j Mechanical instruments Section,

W. Go Brombacher

General Objective: To make available in the form of a critical

survey, comprehensive information on the current status of development of instruments for measuring dynamic fluid pressures, including

an evaluation of their theoretical and practical limitations, useful

in the planning and conduct of research and development on such

devices and useful for provision of general guidance in instrumentation problems concerned with measurement of dynamic fluid pressures.

Background ; A critical, comprehensive survey on instrumentation for

measuring dynamic fluid pressures would be useful - a) in planning

research and development on such instrumentation and b) as a guide to

the selection of the most suitable type of instrument for particular

applications. Recent and fast growing needs, particularly in aeronautic and ordnance research, for making dynamic fluid pressure

measurements and relative inaccessibility and non-critical nature of

much of the technical information now available indicates that a sur- vey is a practical necessity both for those interested in application

and in development.

Progress s A bibliography of about 25>0 books, articles, and reports

of various government research laboratories, covering a period from

1920 to the present has been assembled. This mil be enlarged from

time to time* In addition, about h$ manufacturers in the U. S. and

Great Britain, listed as manufacturers of dynamic pressure gages,

were contacted, of idiom 28 supplied catalogs describing their products.

Twenty-six of the articles in the bibliography have been reviewed

and summaries prepared. These include information on the basic

pressure-pickup; the transducer, if any; the pressure and frequency

range; the sensitivity; and performance data, where available. A broad

outline has been prepared to guide the investigation of the literature.

Future Activity; The present bibliography is to be extended and individual articles reviewed and summarized. The manufacturers ! literature will be reviewed and some attempt made to evaluate the accuracy

where performance data are availableo The survey will be prepared

from the above data©
- 37

Vacuum Tube Accelerometer - NBS Project 060lH30-35£75 Engineering Mechanics Section^ S* Levy5 J* Bo Woodson

General Objective s To design and construct improved models of the

Ramberg Vacuum Tube Accelerometer*

Specific Objectives g To develop models of the Vacuum Tube Accelerometer covering a series of acceleration and natural frequency

ranges j to utilize high-strength steels in the plate support rods

so as to give increased performance j to improve the overload stops

j

and to develop a mechanical damper*

Backgroundg The Vacuum Tube Accelerometer invented by Dr*Ramberg

of the National Bureau of Standards is essentially a double diode

with elastically supported plates on either side of the common

cathode* Acceleration of the base in the sensitive direction causes

a relative displacement between the elastically supported plates and

the fixed cathode* The two diode plate-to-cathode resistances have

been reduced so that the relative change in resistance per unit deflection of the plate is quite large* For example3 the lOg capacity

tube having an undamped natural frequency of 160 cycles per second.,

when connected into the customary Wheatstone bridge,, gives an output

of the order of 3 milliamperes for an acceleration of lg*

Summary of Project Activity g Improved tubes of other acceleration

ranges have been designed and are being manufactured by Sylvania

Electric Productss Inc* The new tubes have high-speed steel platesupport rods,, Improved stops which will limit the plate motion.* and

a stiffened structure attaching the plates to the base* An improved

manufacturing technique using brazing instead of spot welding has

been perfected which permits more accurate adjustment of the plate

to cathode spacing* Two 10 g tubes,, six 100 g tubes^ and one 5>00 g

tube have been submitted by Sylvania and have been tested to determine the effectiveness of the improvements* A specially designed

Kelvin double bridge was used for testing these tubes,, in order to

minimize the effect of changes of contact resistance in the tube

socket* The 10 g and 100 g tubes were generally satisfactorys while

the $00 g tube was unsatisfactory because of having too limited a range of linear operation*

A part of the work during the past year has been toward the

development of a mechanical damper to reduce the natural frequency

response of the tube* Although electrical filters have been successfully used to suppress the natural-frequency output,, many advantages

would be gained by the use of a mechanical filter* The theoretical

work on the design of a mechanical damper indicated that a damper

having the desired characteristics is possible* Response and optimum

values of the parameters which control the characteristics were comi
38 -

puted using SEAC* The mechanical damper designed in accordance with

these calculations has been completed and tests to determine its

effectiveness have been made* To date the behavior of the damper has

not been entirely satisfactory*

Progress; The paper entitled "Damping of Elastically Supported

Element in a Vaccum Tube" was presented by Samuel Levy at the Eighth

International Congress of Theoretical and Applied Mechanics,, and has

been printed as NBS Report No* 1707* This report shows the method

of obtaining the optimum values of the damper parameters* It also

presents experimental evidence of the damper 9 s effectiveness in the

case of a suddenly applied acceleration®.

The following measurements were made on one 500 g accelerometerj

response to static acceleration, zero drift, zero shift following

high acceleration, natural frequency, and response to side acceleration0 The range of linear response was not satisfactory for this

tube®

Reduction of the data obtained previously on two 10 g and five

100 g accelerometers was completed, and a report presenting the

results was prepared in rough draft* The performance of these tubes

was generally satisfactory*

Sylvanla Electric Products, Inc*, reported that a good method

of centering the overload stops during assembly has been worked out

by the use of an improved type of jig* They also reported some progress toward developing a method for better control of plate to cathode

spacing*

In view of the fact that the first 50Q g tube received at NBS

had too low a range of linear operation, Sylvania has increased the

stop hole diameters of these tubes from *010" to o 01i;"o They also

reported making 100 g tube plate assemblies with a better controlled

siderod to crossbar joint, achieved by plating only the extreme ends

of the side rods, in order to bring about more nearly equal natural

frequencies for the two plates* A final shipment of twenty-eight

accelerometer tubes completing delivery of tubes on order from Sylvania Electric Products, Inc*, was received* Not all of these tubes

were operable* A Kelvin double bridge was constructed and used in

testing the vacuum-tube accelerometers, to render the accelerometer

output insensitive to contact resistance changes in the tube socket*

Future Activity ; The testing of the accelerometer tubes will be compie ted and the results will be included in the report, now in preparation*
FIGURE 1 ACCELEROMETER TUBE AND DAMPER (BOTH ENCLOSED

IN CASING) MOUNTED ON CANTILEVER BEAM PRIOR

TO RELEASE. (A SUDDEN ACCELERATION WAS

APPLIED TO THE TUBE IN THIS MANNER, WITH AND

WITHOUT THE DAMPER ACTING, TO EVALUATE THE

EFFECTIVENESS OF THE DAMPER.)

FIGURE 2

K

-J

\

.01 s

I\

ec.

* \/

/ /AAf\N\Jjvy\W

. \ Jf

r

Reference line /X

(b) Record, damper unlocked

co

a

i_Q)

0)O

o<

3 -

2 °

0

o Damper locked

+ Damper unlocked

o

‘®Oo009d!4 *j5a9

*

.1 .2 Time, sec.

.3 .4

(c) Accelerations obtained bq fairinq curve Throuqh

natural frequency response of above records.

RESPONSE OF VACUUM-TUBE ACCELEROMETER TO A SUDDEN ACCELERATION,

WITH AND WITHOUT THE DAMPER ACTING. (IT IS SEEN FROM (c) THAT

THE APPLIED ACCELERATION HAD APPROXIMATELY THE SAME TIME HISTORY

IN EACH CASE. )

- 39

Survey of Strain Recorders - NBS Project 060li»30“35585 Engineering Mechanics Section^, D® R® Tate., R® R® Bouche

General Objectives To survey and test equipment currently available

for producing autographic stress-strain records of tensile test

specimens

o

Specific Objectives g 1® To "write to manufacturers of recording equipment and testing

machines requesting information to ascertains (a) whether or not

they manufacture equipment capable of attachment to a standard testing

machine to record stress and strain simultaneously and3 (b) what the

operating principles3 accuracy^ and special features of such equipment

are®

2® To conduct tests on some of the basic stress-strain recording

instruments most commonly used in materials testing laboratories for

tensile testing® These tests will evaluate the accuracy of the devices

under calibration and will also exemplify diagrams obtainable under

service conditions©

3® To compile a report giving a brief history of the development

of stress-strain recording,, a summary of the survey of manufacturers^

a listing of the equipment available for stress-strain recording and

the results of actual tests of some of the most commonly used equipment®

Backgrounds The use of recorders for drawing autographic stress-strain

curves for tension specimens of metals and other structural materials

has become a standard practice in most materials testing laboratories

for acceptance as well as comparison tests® Recorders for this purpose

are supplied by manufacturers of testing equipment in a variety of

forms® There is,, however^ little in the open literature other than

advertising folders to guide the user in the selection of equipment®

There is even less information regarding the accuracy of recorders and

strain, gages® Recorders of two different makes were obtained during

fiscal year 1952 for the tests®

Progress g Plans were laid during the period for conducting the survey®

A systematic review was made of the files of the Engineering Mechanics

Section extending back over the past twenty years and conferences were

held with members of the Section whose experience in testing dates

back over approximately the same period® A complete review of the

Proceedings at the American Society for Testing Materials was conducted

and summarized®

Letters were written to thirty-five manufacturers of recording

instruments and testing equipment in an effort to obtain descriptive

literature on stress-strain recorders® The many replies received were
- ho -

processed and that material was selected which was pertinent to the

project* Principles of operation, etc* were discussed with represen”

tatives of the leading manufacturers of stress-strain recorders used

for metals testing®

A systematic search of the literature was launched by making use

of the facilities of the Library of Congress and the NBS Library®

Plans for conducting tests on the most common stress-strain recorders

used in metals testing were initiated®

Future Activity? The extensive review of the literature will be con- eluded with a careful coverage of the abstracting services relating

to materials testing® A better sampling of the foreign made recorders will be attempted by writing letters to some of the foreign manufacturers of testing equipment® Performance tests are expected to be

made on representative stress-strain recorders® The project will be

concluded by a report on the survey of stress-strain recorders®
la -

Resistanc e Strain Gages , - NBS Project 060^-30=355$^ Engineering

Mechanics Section,, fa© Re Campbell

General Objective

g

To determine fundamental performance characterise.

tics of two new types of resistance strain gages,, namely^the temperature compensated gage and the post yield gage©

Specific Objectives

8

X© Completion of report on the study of SR-lj. and G~H post yield

resistance strain gages 0 Laboratory work on this phase of the project

has been completed©

2 0 Development of a test procedure for calibrating resistance

strain gages at temperatures up to 300°Fo Tests will be made on

SR-i; gages temperature compensated for aluminum alloy and on gages

compensated for mild steel© Linearity of gage output with strain will

be determined for several temperatures in the range 75° to 300°Fo Calibrations will also be made under varying temperatures to determine

the effectiveness of gage compensations Temperature sensitivity of

representative gages will be studied to determine the degree of uniformity between gages© A report will be prepared*.

Background

g

The application of the resistance strain gage to the

measurement of large plastic strains,, such as those produced in

structures in underwater explosion studies^ and its application to

the measurement of strains in rockets and missiles which are subjected to rapid changes in temperature lias fostered the development

of post yield and temperature compensated gages for such measurements

©

Post yield strain gages are bonded resistance wire strain gages

intended for measurement of strains in the plastic region© Ordinary

bonded resistance wire gages are suitable for strains up to two or

three percent but by the use of special base papers 3 plasticized

bonding media and dual lead gage construction these special gages will

function at strains up to fifteen or twenty percent© Gages of this

type have been marketed in the United States by the Baldwin-LimaHamilton Corporation (SR-If. type PA°=3) and in Sweden by the GustafssonHuggenberger interests (G-H gages)©

Temperature compensated gages developed by the Baldwin-LimaHamilton Corporation are of considerable interest at this time as a single compensated gage can discriminate between the expansion of a structure caused by a temperature rise and actual strains in' the

structure caused by stresses « In the field tests of high speed aircraft or rocket missiles where telemetering methods must be used these

gages are a valuable addition to existing equipment©
The investigation of bonded wire strain gages requires special

techniques o Unlike mechanical and optical strain which may be calibrated by attaching one gage point to the frame of a comparator and

the other to a movable bit, these bonded resistance wire strain gages

must be calibrated by mounting them on a test specimen, straining it,

and measuring the strain with a specially designed, calibrated, mechanical strain gage®

During fiscal year 1952 G-H type A820S post yield resistance

strain gages were obtained from the Aeronautical Research Institute

of Sweden and a supply of SR-Ii. type PA-3 gages was obtained from the

Baldwin-Lama-Eamilton Corporation© A special lever transfer was

designed for use with a Tuckerman optical strain gage to measure

calibrating strains up to Xk percent© This device after calibration

on an interferometer comparator was used as an intermediary standard

to measure the actual strains in test bars to which the resistance

strain gages were attached© Laboratory tests were completed on the

post yield gages and the preparation of a report was sta.rt.edo

Summary of Project Activity

8

A procedure for calibrating post yield

res isbane e ~strain gages~was developed, and tensile calibrations of

SR“1; and G~H gages were completed© It was found that the error in

strains indicated by the SR-lj. type PA-3 gages did not exceed h percent of the applied strain for strains up to 0®lU© Similar results

were obtained with G-H type A820S gages except that numerous gage

failurecS were encountered at strains in the range 0 o G6 to 0©X2 e A

report describing this work was begun®

In preparation for tests of wire strain gages at elevated temperatures, calibrations of two special Tuckerman strain gages were

carried out at room temperature and also at approximately 370°F© The

results indicated that the calibration of the gages at high temperature is probably not affected by ary factors other than the expansion

of the stellite lozenge© This effect is compensated in part by ex- pansion of the gage body©

A transits oven was designed and constructed for use in maintaining calibration bars at temperatures ranging from room temperatore to 3O0°Fo Nichtome wire was used in the heating elements and

a Vyeor glass window was provided to facilitate reading Tuckerman

strain gages©

Progress g Laboratory tests were completed on gages compensated for

aiumnnum alloy© Stress-free gages bonded to aluminum plates were

subjected to temperatures ranging from 25° to 275°F© Changes in

gage resistance, which represented apparent strains, were recorded

for each often gages during the temperature cycle© Results indicated a high degree of uniformity between different gages, and apparent
b3

strains due to lack of perfect temperature compensation did not exceed

60x10“6* Calibration curves of resistance change vs® strain were determined for five gages at temperatures ranging from 125° to 25QOF® Results of these tests showed that calibration factors for the gages tested

were in excellent agreement with values given by the manufacturer, and

non-linearities in gage output were less than 2 percent® The performance

of these gages compared favorably with cellulose bonded gages which are usually used only at room temperature®

Work has continued on preparation of the report, on the post-yield

gages®

Future Activity; It is expected that laboratory tests will be completed®

Tests are to be conducted on gages compensated for mild steel, and a report describing the test and results on temperature compensated gages

is to be prepared®

The report on the post-yield gages will be completed®
Application of Feedback Around Image Scanning Systems - NBS Project 120ii-2

,

Electronic Instrumentation

Section, H® M® Joseph

General Objectives To investigate the application of two-dimensional, linear and non-linear feedback in optical-electronic

systems®

Specific Objectives

s

1« To assemble an optical-electronic apparatus useful for

studying the possible application of feedback around such a system®

(a) Build equipment incorporating feedback around a flying-spot scanning system similar to the one described in '’Background"®

(b) Build a constant-velocity scanning generator to obtain

a signal that can readily be modified©

2® Study the results obtainable with the system and determine

the techniques for applying the methods

(a) Operate upon the signal by incorporating differentiating and other networks in the feedback path and/or between the

system and the "slave" oscilloscope, and study the image outlining

and other effects that will occur©

(b) Explore the techniques necessary for using the system

as an analogue computer for partial differential equations©

(c) Manipulative techniques for determining the characteristics of patterns that may lead to methods of recognizing distorted

images.

Backgrounds This project was suggested by Dr® L® S® G® Kovasznay,

of Johns Hopkins University, who is now a part-time consultant on

this project® He formulated the basic method of this project when

considering a theory of the manner in which the human mind handles

visual information® The following paragraphs are taken from his

explanation of the development of the project®

A two -dimensional pattern can be handled by established techniques currently used in television© A known way of converting a stationary two-dimensional picture into an electrical signal makes

use of a flying-spot scanner® This consists of a cathode-ray tube,

a lens, a picture transparency, a light-collecting condenser, and a phototube, &s shown in Figure 1, without feedback® The luminous

spot scans an area on the face of the cathode ray tube® This in
turn is focused on the transparency« The light transmitted through

the transparency is collected by a condenser lens, and the light

intensity variations are converted into an electrical signal by the

phototube®

A basic modification of the usual flying-spot scanner is the

introduction of feedback by applying the phototube signal to the

intensity grid of the flying-spot cathode-ray tube®

If the feedback is strong, and is of a polarity that reduces

the spot intensity, the system tends to minimize the signal output

of the phototube, and therefore tends to produce a constant light

intensity reaching the phototube through each point on the transparency® The result is that, for each light or transparent portion

of the transparency, the face of the cathode-ray tube is darkened

and vice-versa® The picture reproduced on the cathode-ray tube is

therefore a negative, and because of the improvement due to negative feedback, the contrast range is the same as that of the original®

The finite response times of the various elements in the feedback loop are suppressed by this negative feedback, especially the

delay time of the phosphor, and the phototube amplifier®

The pattern can be viewed on a second cathode-ray tube run as

a “slave”, with or without modifying networks inserted in the circuit between the two systems®

The mathematical equation governing such a system depends both

on the circuits and on the method of scanning that convert the two

spatial co-ordinates into a single time variable® In conventional

television the two co-ordinate (horizontal and vertical) scanning

velocities are very different and effectively unidirectional®

Mathematical functions in two dimensions can be studied by

representing them on a transparency as an opaque wash so that the

transparency at a given point represents the value of the function

at that point® If a scanning method is used that is symmetrical

with respect to horizontal and vertical axes and the forward velocity has the seme magnitude as the return velocity (these conditions are met by triangular waves) the governing equations can be

transcribed in the form of a partial differential equation® The

boundary conditions can be introduced by superimposing an appropriate mask upon the original picture or pattern®

Another possibility of the feedback scanner is the study of

patterns modified by such operations as differentiation, integration, LaPlace operator, square detectors or others, with a view to

reducing the original pattern into some standard recognizable form®
- b6 -

Eventually this sort of approach may furnish a method for the ex- ploration of the whole problem of pattern recognition by automatic

means®

Dr» Kovasznay set up a system employing the sweep circuits and

cathode-ray tube of a Dumont 3 Q14-H oscilloscope to furnish the sweeps

and the flying spot* He utilized negative feedback with encouraging

results® A diagram of that system is shown in Figure 1®

He used conventional sawtooth sweeps in the system he set up,

but as mentioned above, a scan reversible in. time,, such as a triangular wave, was needed to produce a signal that can be more readily

modified by electrical networks® The scan can be produced by impressing a triangular wave on the horizontal deflection plates of a cathode-ray tube and another triangular wave differing slightly in

frequency applied to the vertical deflection plates® The scanning

pattern produced is a lissajous figure composed of rectangles instead

of the usual ellipses for sine waves® The pattern for a frequency

ratio of 3 to ii is shown in Figure 2 a In practice, a frequency ratio

of 256 to 257 would be suitable® Such a scan should produce a definition twice as good as high grade conventional television practice®

To sum up, the negative feedback is required to produce a video

signal that is accurately proportional to the variations of light

intensity' in the picture® The special scan is required to produce

a variety of signal that can be readily operated upon by simple computing networks®

A word on the applications s Important practical results may be

derived from the recognition of patterns such as matching of fingerprints, automatic reading of printed or written matter, or possible

weather prediction from synoptic maps® Significant contributions to

fundamental research may result from solutions of non-linear partial

differential equations® The equations in general cannot be solved by

mathematicians at this time® A property of such equations is that

integrals may contain discontinuities or ‘‘catastrophic 1 * solutions,

which either must be guessed, found experimentally, or as a result of

practical experience, as for example, in the flow fields around air

foils near sonic velocities®

Summary of Project Activity g Prior 'bo the beginning of this quarter,

it was decided that the first task would be the construction of a scanning generator for accomplishing Specific Objective 1 (b)*

The purpose of this generator was to furnish suitable deflection

voltage waves for the horizontal and vertical plates of the oscilloscope* Two waves were required, having frequencies of the order of

5000 cps, differing in frequency by about 10 cps® It was permissible

for the frequencies to vary slightly but essential that their ratio
“ hi -

remain constant at a value M where M is an integer„ This reauirement followed from the necessity for a stable pattern, so that the

output signal would be suitable for computing purposes, and so that

the illumination of the pattern would be uniform.

Discussing the above in greater detail, to attain stability the

elapsed time between successive patterns should equal an integral number M of wave periods of one frequency, and M * X wave periods of the

other frequency. That iss

M ej M 1

fl

' f2

(1)

Therefore

f9 M + 1

(2)

and f

2 " fl

“

(3)

M

or f

2 ” f

l

* fl 00

M

H

"2T

The elapsed time between successive repetitions of pattern is so that the frequency of repetition of pattern is f^/Mo That iss

F «

(5)

“ equation (3) (6)

For initial experiments, value of F«»1Q and M« 25>0 were selected as suitable. The corresponding frequencies would be f 2500

and f2^25lO<»

The simplest source of a frequency £2 having a proper relation

to f-]_ appeared to be a generator using subdivisions

M 3 An integer (see above) corresponding to l/2 the number of

discrete lines in the pattern,

fn « Lower of the two deflection frequencies

fj? e Higher of the two deflection frequencies

F * ‘'frame rate" (repetitions of the patterns each second.)

Then if a mechanism were provided which would divide a frequency

f-j_ by an integer M and add the result to the sum would be a frequency f2 conforming to equation ho
Obviously with this method f2 would hold a constant ratio to f^

regardless of gradual variations in f^o

This general method was first tried with a multivibrator chain

which turned out to be insufficiently stable® A chain of binary

dividers were then constructed which performed the division quite

accurately with no noticeable jitter 0

In addition (see Figure 3 ) a trigger circuit driven by an audio

oscillator was added to convert the oscillator sine wave to a pulse

train in order to furnish a suitable input to the chain* A filter

was provided at the binary chain output to change the (divided) lowfrequency square wave to a sine wave* This sine wave was applied to a synchronous motor which drives a sine-cosine resolver* The resolver has the property of adding its rotation frequency, F, to its

input frequency f resulting in an output frequency fg® The sinewave voltage at frequency is applied to an electronic switch and

integrator which produces a triangular wave that is applied to the

vertical deflection plates of a cathode-ray oscilloscope scanner®

Similarly f-. is converted to a triangular wave and applied to the

horizontal deflection plates of the oscilloscope®

The electro -optical system was set up according to the block

diagram of Figure 1, using the constant-velocity scan circuits®

These circuits drive the amplifiers of a commercial Dumont 2I4.8-A oscilloscope® The amplified voltages are applied (within the oscilloscope) to a high-intensity 5>RP-llA cathode-ray tube itfhich is used

as the feedback modulated light source® The expected negative picture appeared on the face of the cathode-ray tube®

In order to permit observation of the resulting picture without

disturbing the optical system, a

11 slave 81 scope was added by paralleling the elements of another identical type cathode-ray tube across those of the original tube* For convenience in viewing, a long-persistence phosphor was used for the second tube®

The results obtained with and without feedback for a constant

velocity scan are typified by the photographs, Figure I4.0 The results without feedback show the performance of the system as a flying-spot scanner o The increased range of contrast with feedback is

evident* As expected, the video gain control adjustment in the

feedback loop is not critical when feedback is used® The same control without feedback has to be carefully adjusted for optimum

results®

Progress ; The work was continued on the second specific objective

of studying the result obtainable by operating upon the video signal

with various networks, particularly differentiating types to study

outlining effects®
- h9 -

Figure 5 indicates the effect of differentiating the signal

resulting from scanning a portion of a picture that produces a signal shown as a solid line in Figure 5(a) o

The dotted line indicates the closer approach to an abrupt

rise and fall that may be achieved by subtracting the doubly differentiated signal in Figure 5(c) from the original signal (with

suitable amplitudes)©

In this manner an effect similar to the brightness contrast

visual illusion described by Byram$- which the reader may see in

Figure 6 is produced artificially© (The steps look as if each

varies across the step© The uniformity of each step may be

checked by looking at each step after concealing the adjacent

ones)© A similar accentuation or Eberhard effect is described in

swHardy and Perrin f s book©

In order to show how this effect is produced, it was necessary

to prove that differentiating the video signal in tame will produce

space derivatives when reproduced as a picture© The mathematical

analysis showed that a doubly (tame) differentiated signal is proportional to the space gradient of the picture density., Further

analysis showed that a picture detail slightly degraded by reason

of the finite scanning spot size can be restored by adding the

appropriate amount and polarity of those signals to the direct

signal as indicated in Figure 5®

Photographs showing the improvement resulting from adding the

negative of a doubly differentiated signal to the direct picture

signal are shown in Figure 7© Figure 7 shows some improvement re- sulting in pictures which were in good focus© Figure 8 shows

similar pictures taken with the scanning spot increased in size

(and thereby defocused or diffused) a sufficient anount to diminish

the differentiated signal by 50$© (The differentiated signal

amplitude is quite sensitive to deviations from good focus)© Similar

improvement is obtained when optical defocussing occurs*

Pictures taken with still greater spot defocussing show that

a limit has been reached© This is to be expected since the slopes

of a signal from a defocussed system are smaller, and some detail

has been lost© The net result of adding the differentiated signal

is to increase the apparent depth of focus© Similar effects are

produced by doubly differentiating signals resulting from a conventional type television scan© As will be noted in Figure 9 there is

enhancement of horizontal boundaries© There is however an improvement in the picture©

5 Journal

-05^©Ao,”lT31I7~^5l{i4.5 p 730 Physical and Photochemical

Basis of Visual Resolving Power, George M© Byram

w A. C. Hardy and F© H© Perrin, Principles of Optics
- 5o -

It will be noted that the density of increment of the fourth

or innermost square in Figures 7 and 8 is somewhat less than that

obtained in going from transparent region beyond the first boundary

to the first square* This is the result of the limitations of the

finite amount of feedback available* This effect was analyzed and

it was shown that the feedback is most effective for thin transparencies*

The analyses did not account for some complicating factors that

occur in practical equipments

1* The phosphor persistence of the cathode-ray tube light

source, a P-11 screen, is approximately 0*35 milliseconds for 70%

drop in brightness*

2® The low-frequency response of the feedback amplifier used

in the experimental work is insufficient to prevent the average

brightness changes which introduce shading*

This effect is most noticeable in the conventional sweep picture, Figure 9* The alternative of using faster sweeps is precluded

by the necessity for going slowly to reduce the effects of phosphor

delay* It should be noted that this delay is partly reduced by the

feedback* However the phase shift associated with the reduced lowfrequency response of the present feedback amplifier also prevents

the use of more feedback at the low sweep rates®

3© The analysis of feedback effects ignored the fact that the

d-c or cutoff level in the scanner and slave oscilloscope can be

set independently*

a* The cutoff level in the scanner source if set improperly

could produce oscillations since the phosphor delay would produce a

signal after the feedback voltage had driven the intensity grid below

cutoff, the result would be cumulative, etc* There are of course the

usual additional sources of instability in a feedback system*

b® A slave oscilloscope misadjustment of intensity has

two effects:

(1) Portions of the picture that are weak in intensity

(corresponding to thin portions of the transparency) may be suppressed*

(2) The contrast ratio between the brighter portions of

the slave oscilloscope pattern and the darker portion is artificially

enhanced*
TRANSPARENCY

LENSES

IMAGE

FEEDBACK

SYSTEM

PATTERN

VERTICAL

HORIZONTAL

SCAN: RATIO 3 TO 4

rig. 2

BLOCK

DIAGRAM

OF

SCANNING

GENERATOR

ORIGINAL NEGATIVE PRINT OF ORIGINAL

SLAVE SCOPE PICTURE SLAVE SCOPE PICTURE

WITHOUT FEEDBACK WITH FEEDBACK

FIG. 4 PICTURES OBTAINED WITH CONSTANT - VELOCITY SCAN

(a) Signal (dotted

lines show result

of substracting [c]

(b) First different!-

ation (sign depends

upon direction)

(c) Double differentiation (sign independent of direction)

Figure 5 Signal and Its Derivative

Figure 6 Illustration of Brightness-Contrast

Effect as Shown on a Step Wedge.

(a) POSITIVE (b) SECOND DERIVATIVE (c) COMBINED POSITIVE

AND SECOND DERIVATIVE

(d) POSITIVE (e) SECOND DERIVATIVE

Improvement in figure 7 (a) over figure 4 (d)

(f) COMBINED POSITIVE

AND SECOND DERIVATIVE

<J0T>

(slave oscilloscope with

feedback) due to improved technique.

Horizontal position interchange between figure 7 and figure 4 is due

to change in horizontal plates oscilloscope connections.

FIGURE 7 SLAVE OSCILLOSCOPE PICTURES WITH CONSTANT VELOCITY SCAN

(a) POSITIVE (b) POSITIVE PLUS

SECOND DERIVATIVE

(c) POSITIVE (d) POSITIVE PLUS

SECOND DERIVATIVE

FIGURE 8 SLAVE OSCILLOSCOPE PICTURES WITH CONSTANT

VELOCITY SCAN (WITH SCANNING SPOT DEFOCUSSED)

FIGURE 9

(a) POSITIVE (b) POSITIVE PLUS

SECOND DERIVATIVE

(c) POSITIVE (d) POSITIVE PLUS

SECOND DERIVATIVE

SLAVE OSCILLOSCOPE PICTURES WITH HORIZONTAL (TELEVISION TYPE) SCAN.

(VERTICAL DERIVATIVE IS NOT EFFECTIVE)

- 51 -

Future Activity: Some of the problems that will be investigated

ares

A* Those of apparatus

1* Hie specific requirements for scanning methods will be

studied in more detail*

2* Different methods of accomplishing the constant velocity

scan will be evaluated in view of (1) above*

3* Other methods of picking up the picture signal, particularly using camera tubes, such as the orthicon, vidicon, or image

dissector types * (This one may await further investigation of the

technique mentioned below)*

B* Further investigation of the technique*

1* Continued investigation of the contouring and picture

manipulation by circuit modifications discussed in this report*

2* Continuation of the pursuit of the Specific Objectives,

particularly the mathematical ones, since those are apparently essential to the recognition function*

As the investigation progresses, more uses for the signal derived from an electro-optical system may appear*
- 52 -

Precision Microwave Interferometer - NBS Project 1409-30-6817,

Microwave Standards Section, Edward S, Dayhoff

General Objective : To develop a design for microwave interferometer

of great absolute accuracy for measurement of wavelengths and for the

measurement of distances in terms of wavelengths of microwave radiation (3 mm region) , and suitable for measuring the dielectric properties of materials i to determine the capabilities of such a device in

those and other measurement problems*

Specific Objectives ? To construct a chain of frequency multipliers

which will produce power in the millimeter wavelength region of

sufficient strength and purity to be useful for illuminating a highaccuracy interferometer*

To construct a microwave Interferometer enabling measurements of

wavelength in the microwave region to a precision better than 1 part

in 106*

To perform the necessary theoretical analysis to enable corrections to be made to the readings of the above instrument so that the

result will have an absolute accuracy better than 1 part in 10

6

and

to evaluate possible different types of instruments to determine what

types are best suited to measurements of high accuracy*

Backgrounds

1* Millimeter wavelength work in general ; The region of wavelengths between 6 mm and 1 cm is a twilight region where the techniques and instruments quite successful at longer wavelengths become

very difficult to apply* Wavemeters, for example, must be made

extremely small, and are very delicate to manufacture and not very

accurate* The same applies to other items of microwave instrumentation* Even oscillators (reflec klystrons) which are available as signal sources in this region are weak, very unstable, and difficult

to operate* The region below 6 mm in wavelength is even more difficult* Wavemeters are quite impractical for measuring wavelengths,

standing wave machines and other items requiring complicated machining

are almost impossible to make because of their small size and there

are no oscillators for signal sources (except some special pulsed magnetrons, hardly useful for laboratory measurements)* Some laboratories

have used ciystal harmonic generators and even harmonics from pulsed

magnetrons as power sources but there appears to be still a good deal

of room for improvement of these devices* Indeed, recently several

laboratories have devoted a fair amount of effort to the problem

of discovering or developing some totally new source of energy in this

region of the spectrum* Such a totally new source of energy would be

widely useful but would not meet the needs of applications requiring

a precisely known frequency. It is clear that the situation in the

microwave spectrum below 6 mm wavelength is very unsatisfactory so far

as instrumentation is concerned*
2c Millimeter Microwave Interferometers; The desirability of an interferometer of some type for wavelength measurements has been recognized for some time* The cavity type wavemeter with its delicate

machining could be dispensed with if a laboratory-sized interferometer

of suitable accuracy could be developed* Several laboratories have

been conducting work along these lines, among which are the Columbia

Radiation Laboratory, where a convenient but not accurate laboratory

use instrument of the Fabry-Perot type has been developed for the region

from about 15 to 6 mm and the National Physical Laboratory where an

instrument requiring a monstrous vacant room and giving very high accuracy in the region around 1®3 cm has recently been reported® The Columbia instrument was intended from the beginning to be a general use

instrument of moderate accuracy for use to as short a wavelength as possible (l mm would be desirable) for measuring magnetron wavelengths®

Unfortunately its resolution becomes very poor below 6 mm and furthermore it gives an erroneous answer by several percent in this region*

It would seem, that a study of accuracy in interferometers for this

region of the spectrum is at present a pressing need.,

Summary of Project Activity! This project was started in April 1952*

fee first task was the writing of an informal survey which was completed by the end of June 1952 0

Progress g Interferometer Design® The chief problems have been proper

treatment of diffraction phenomena and of the microwave optics of the

illumination system® A suitable method, of treating the diffraction

phenomena has been decided upon and approximate formulae for design

purposes obtained® Experimental checking must wait until more stable

equipment is ready® The interferometer contemplated is to fellow as closely as possible the design of optical interferometers®

Test Bench Interferometer® A 5-inch aperture radius interferometer was set up for testing purposes using K-band radiation from a reflex klystron oscillator® Unfortunately instabilities of both electrical and mechanical nature prevented it from being used, for ary but

relatively rough measurements® It has, however, been useful for developing techniques of measurement and for setting up suitable auxiliary

instrumental ion0

Multiplier Chain® In order to obtain highly coherent radiation

of high stability for illuminating the interferometer, a chain, of

frequency multipliers starting at 100 kc and going to K-band with

considerable output power is under way® Currently it produces power

at 88 Me® The initial pair of multiplying stages (which multiply by

factors of 17 and 13, respectively) have attracted some interest,

however a final judgment must await the completion of the chain0
Millimeter-Band Harmonic Generator© It is intended to use

crystal rectifiers as harmonic generators to extend the output frequency of the multiplier chain to the neighborhood of 100^000 Me*

Several harmonic generator units and detector units for this frequency have been under construction for several months© There have

been delays due to difficulties in obtaining machine shop time©

These units are now very near completion© Several Hybrid tee waveguide junctions were completed©

Future Activity; Experimental verification of the diffraction es- timates will be made as soon as the apparatus permits© Construction of more refined apparatus capable of accurate comparisons with

'length standards will begin when it has been determined that suitable

designs and methods of use have been arrived at© Possible alternate

methods for accomplishing the same objectives will continue to re- ceive such consideration as is felt to be warranted in each case©
Survey of Analog-to "Digital Converters - NBS Project 8253;

Missile Instrumentation Section, M* G* Pawley

General Objective; To make available in the form of a critical sur- vey, comprehensive information on the current status of development

of instruments for analog-to-digital conversion, including an evaluation of their applications and of their theoretical and practical

limitations5 useful in the planning and conduct of research and

development on such devices and useful for general guidance in instrumentation problems concerned with analog-to -digital conversion.

Backgrounds Although analog-to-digital converters are used in a number of different applications and new types are being developed

to meet new situations-, the use and. development of such devices has

been hampered by the lack of a comprehensive picture of the requirements to be met and the techniques presently used to meet them*

Most information exists in such widely scattered places as manufacturers catalogs., reports to government sponsors, and occasional

articles in technical journals® A need exists for a comprehensive

survey to bring this material together®

Progress ; Information has been collected on analog-to-digital converters manufactured by commercial companies and those being

developed by these companies and by governmental agencies® Most of

the information has been obtained by mail and some by personal

visits and review of published articles® Several schemes of organization of the material for the report are being considered©

Future Activity; Future activity will be similar to that mentioned

in the preceding paragraph® The final report on the survey is

scheduled for completion during Fiscal Year 1953®
Research and Consultation on Instrumentation Information -

'MBS' Project 3300-51-7505, Office of Basic Instrumentation,

Joshua Stem

General Objectives To provide access to existing instrumentation

Information, published and unpublished, towards solving instrumentation problems©

Specific Objectives; To improve accessibility of both published

anH~unpub1ished Instrument information by developing improved

systems for storage and retrieval of information, by fostering

developments elsewhere which will make more easily available information of instrumentation interest, by surveying specific developments in. instrumentation, by providing consultant services in

instrumentatione

Background s While good access to information is important in any

research endeavors, the rather recent emergence of the field of

Instrumentation as a new coordination of knowledge from a variety

of previously existing fields lias brought with it some particularly

severe problems© The major problems are the inadequate coverage of

instrument information by abstracting and indexing services whose

main interest is the information obtained by use of the instrument

and the non-existence of efficient classification systems for instrumentation© In common with all others concerned with access to information is shared the problem posed by the overwhelming rate at which

information is being generated© Development of mechanical aids

promises greatly improved information access© In order to make use

of the potentialities of these devices, it is necessary to have

information classifications specifically designed with mechanical

retrieval in mind© Such classifications do not exist for the field

of instrumentation©

Summary of Project Activity:

Task”Li Multidimensional Classification of Instrument Informaticn© Consideration of tKe various ways in which the problem of

~ classification has been approached in the past led to the recognition of the basic "multidimensional1 ® nature of human knowledge© The

concept that information might be located in a system of " coordinates"

by the interaction of a number of identifying terms was studied, and

discussed at a conference attended by a number of individuals interested in documentation problems® It was generally concluded that

this approach was a desirable one for this specific application® A

system based on eight dimensions has been evolved as follows i
- 57 -

"Dimensions"

Estimated

Breakdown

1.

2 . 3 . h.

5.

6. 7 . 8 *

Condition, quantity, or factor

to be measured 25 major headings 3,000 entries

Principle of measurement 5o ii ti 600 it Object being measured 100 it it 10,000 it Name of Instrument 5o n h, 000 ii Field of Application 300

Stages in Measurement Process 550 « States of Development 25 It Character of Document 25 11

The entries have been selected and their suitability studied*

A selection was made of a suitable system for experimental use

of the multidimensional classification* The "peek-a-boo" system was

selected as the most suitable for this purpose* The multidimensional

classification was brought to completion adequate for application to

the experimental use with the "peek-a-boo" system of information re- trieval* A number of conferences were held to achieve a suitable

rounding-off of the classification* Studies were initiated for the

establishment of guide lines for the selection of reference material

for storage in the experimental applications

Task lie Development of Mechanical Method for Information

Storage and RetHe'val*

" Investigations carried out on existing developments in "this "field have led us to the belief that mechanisms ar©

already far in advance of the other aspects of the information re- trieval problem* Our activities on this task liave been largely limited therefore to watching new developments in the field* Broad

aspects of some mechanical systems for information retrieval have been

worked out* These will remain of academic interest until the classification and coding problems have been solved sufficiently to permit

choice of the most suitable mechanization*

Task Vo Preparation of a Guide and Source List of the

Literature of IhstyumentatIon7 this taslF was^~un3nrd^ken~for O.B.Io

£>y hr. JiiIian~Tr~^aIth of"the’ Library of Congress. This work has

been completed and the resulting report entitled "Instrumentation

Literature and its Use*', is ready for limited distribution. It is

hoped that arrangements can be made with one of the professional

societies to reprint the report for wider dissemination.

Progress s Task I* Multidimensional Clas sification of Instrument Info rm- ation* A "peek-a-boo 19 card has been designed for use in~the experimentaf application of the multidimensional classification. The card

will be of a size suitable for storage in letter size file cabinets.
58

A field of 7” x 7” on the card is Imprinted with a 100 by 100 division grid which will accomodate 105 000 references <> Two holes punched

outside of the reference area will be used for positioning the superimposed cards for "punching in** operations and "reading out" operations* All cards pertaining to a particular reference are to be

punched simultaneously with the document identification hole* The

size of the reference hole is OaOlD8® and the hole locations are separated 0*070" on centers* Preliminary experimentation with holes of

the size chosen show that it is surprisingly easy to perform unambiguous coincidence determinations with only hand stacking* It is also

found to be unnecessary to view the cards against a lighted background*

Coincidence can easily be observed when the cards are merely laid on

a relatively dark background such as a desk top* The problem of printing registry however turned out to be a severe one* Ordinary printing

methods appear to be able to meet only the minimum requirements* Investigation has revealed the possibility of achieving far greater precision of registry by punching positioning holes and printing simultaneously* The precision promised by this technique together with

the gratifying experience with ease of comparing cards suggests that

even smaller holes and consequently greater card capacity are feasible*

While a capacity of 10,000 references per card was selected as adequate to the present application, the number of information fields for

which the peek-a-boo system is appropriate may be expected to increase

rapidly with increasing card capacity* It is of interest to compare

the storage efficiency which may be achieved from peek-a-boo cards

with magnetic storage* Using holes 0*015" in diameter and separated

0*025" on centers, 625 bits of information may be accomodated in one

square inch of card* This compares very favorably with the 1,000

bits which it is conservatively estimated can be accomodated by magnetic storage techniques* Against the smaller access time obtainable in magnetic storage may be balanced the superior mechanical

simplicity of the manual peek-a-boo system*

Plans for conducting the experimental application of the multidimensional classification have been refined and efforts made to

recruit additional personnel for the to rk« These efforts resulted

in the addition to the 0*B*I* staff of one person with wide experience

in documentation work who will devote a large fraction of time to the

experiment*

Task II* Development of Mechanical Method for Information

Storage and RetHival* No activity during this period*

Task V* Preparation of a Guide and Source List of the Literature of Ins trumentoETon* Data forlTse”:m

^

vement of

the guide is being accumir],ated«
59

Future Activity ; It is planned to vigorously pursue the experimental

application of the multidimensional classification by classifying

information and recording the classification on peek-a-boo cards® No

systematic attempt will be made to treat old information in this way®

The work will be started with abstracts published in 1953® The sources

to be covered are tentatively set as Science Abstracts, T 0 I 0 Po 5 and

Chemical Abstracts® The rate at which these can be processed can only be very roughly guessed at present® As soon as sufficient information has been processed,, experimentation with use of the classification as a search medium will commence,,
- 60 »

Miscellaneous Investigations in Basic Instrumentation - NBS

Project 3300-31”75>Q7/ Office of Ehsic Instrumentation,

We A* Wildhack

Objective: To carry out preliminary investigations of various

instrumentation problems and to carry these to a point where a report can be issued or where investigation is seen to be of

sufficient importance and complexity suggested by a separate project*

This project was established as a general project for preliminaiy investigations which might later develop into separate projects,

very short studies, etc® At the end of the reporting period, the

project comprised the following active tasks

s

A Diaphragm-Type, Capacitance-Type Micromanometer, Office of

"Basic instrumentation, T« A* Peris, W* H„ Kaechele,

D 0 S® Goalwin

Objective ? To investigate the pressure sensitivity attainable from

the combination of a very sensitive flexible diaphragm with an ex- tremely sensitive and stable electronic system for the measurement

of minute displacements, the resonant-bridge carrier system*

Background ; Details of the resonant-bridge carrier system have

been recently published by G* W® Cook of the David Taylor Model

Basin, in the January 1953 issue of “ELectronics", p* 105®

Summary of Project Activity? Details of the design and calibration

of t he cTiapEragrri-type , c apac itance-type micromanometer are con- tained in NBS report 2165, to be issued in January 1953® A calibration curve corresponding to the highest sensitivity obtained in

these tests is shown in Figure 1®

Progress ? The report was completed,,

Humidity Measurement by Spectroscopic Methods, Office of

Basic Instrumentation, W* A* Wildhack, J. Stem

Objective ; To investigate the possibility of utilizing the hydrogen exc itation spectrum for absolute humidity measurements at low

temperatures©

Background ; Most measurements of humidities with dew points below

0^0 are of low accuracy, and theoretical considerations indicate

that a substantial improvement in precision of humidity measurements
DdwH

W

S

o

o

Piu

w

Pi

ABOUT

0.

0035

inch.

- 6.1

in this range may be realized by measurement of the intensity of

lines of the hydrogen spectrum of air containing water vapor

The intensity of a spectral line is proportional to the amount

of material present,, The intensity depends also on other factors

such as the source intensity, but the ratio of the .intensity of two

spectral lines of two different substances in a sample depends only

on composition of the sample* The intensity of a line or band due

to pressure of water vapor to the intensity of a line or band from

gas present at constant concentration in air, such as argon or nitrogen, would be a measure of the quantity of water vapor* Thus it

should be possible to detect small amounts of water vapor and to

make quantitative determinations of humidity independent of temperature *

Summary of Project Activity? Spark excitation was used to produce

the air" spectrum* The hydrogen alpha line at 6563 A was chosen for

the experiments since it is the strongest line in the available

region of the spectrum* The nitrogen line at 6610 A was used as an

internal standard* The first approach involved photographing the

spectrum of air having different water vapor concentrations* The

humidity was controlled by passing the air through condenser coils

maintained at different temperatures* Line intensities were measured by the use of a microphotometer and indicated the possibility

of measurement of humidities with dew points lower than -20°G*

Apparatus to permit substituting photomultiplier tubes for

the photographic plate was then designed and constructed* A circuit was built to compensate for dark current* Improved apparatus

for laboratory control of humidity was assembled in which air was saturated at higher than a tmo spheric pressure and then expanded to

atmospheric pressure to obtain a known humidity* Experiments were carried out to determine the most effective method of excitation of

hydro gen*

Calibration experiments were performed to determine whether

the humidity of the air sample (known from its saturation temperature) correlated best with (1) the ratio of the output of the

photomultiplier tube when illuminated by the hydrogen line to its

output when illuminated by a nitrogen line or (2) the ratio of the

hydrogen line to the total illumination from the spark* In either

case the use of only one photomultiplier tube requires that the
- 62 -

intensity of the various lines be determined at different times#

This occasions no error if the average excitation is reasonably

steady over a number of seconds,, and if the observation on each

line gives a reading indicative of this average# These conditions

were investigated and found to be fairly well fulfilled by the

apparatus# The background illumination on the photomultiplier cell

(that is 5 the signal obtained between lines during the scanning) was found to be fairly constant but not entirely accounted for#

It was discovered that the compressed air from the high-pressure

tanks contained small amounts of hydrogen,, presumably due to rust

formation in the steel cylinders# A catalytic hydrogen remover

was procured and installed in the air line®

With these improvements,, it was found that a reliable measure

of humidities could be obtained doT.m to saturation temperatures of

about ~kQ°Cs where the saturation vapor pressure is 0#1 mm# Hg„ At

this temperature^ the uncertainty in the determination was about

±15#*

Progress g Favorable results obtained elsewhere in the Bureau on

excitation of hydrogen and deuterium spectra by use of radio frequency excitation at reduced pressure led to experiments using this

type of excitation for the measurement of humidity# Earlier work

on this project had been entirely devoted to exciting the spectrum

in air at atmospheric pressure with a spark discharge® The sensitivity of detection with low pressure discharge was found to be

somewhat greater than that obtained with spark excitation and it

appears that measurements of absolute humidity might be made to dewpoint as low as -5’Q° C or lower before the uncertainty becomes as great as 10# of the humidity measured® Both sensitivity and accuracy of the radio-frequency excitation method require more precise

measurement and control of the pressure and temperature^ and possibly flow of the low pressure gas in the excitation tube# The apparatus is being improved for this purpose# Experiments have been

made using two photomultiplier tubes,, with recording of ratio of

their signal,, to permit more nearly instantaneous measurement of

ratios of the hydrogen line to the total intensity of the spectrum

or to the intensity of a selected reference line#

Future Activityg The low-pressure gaseous discharge method will be

more adequately evaluated with the improved equipment and some further tests are contemplated of the spark excitation method using

ratio recording against a reference line® The report,, which has

been partially written,, will be completed®
— 63 —

Vibration Measurement by Interferometric Methods,

Corona laboratories,""^ Wo Smith

Objective ? To conduct a preliminary survey of interferometric

methods of measuring the amplitudes of mechanical vibrations over

a frequency range from 0 to 10,000 cycles per second and an am- plitude range from 10~6 to 10”2 inches* More specifically, to

evaluate the feasibility of adapting to vibration measurement the

instrumentation techniques employed by R* D 0 Huntoon in. his electronic fringe interpolator for an optical interferometer (MBS Report 1228 )« To consider other methods and equipment presently

available or adaptable to such measurements* To prepare an MBS

Report summarizing the results of the survey*

Background : This survey is part of a more comprehensive study of

methods of measuring vibrations and, in particular, of calibrating

vibration pickups* There is considerable need for a reliable

device to measure vibration amplitudes in the small-displacement

region where microscope methods become imprecise 0

Progress : Since, in measuring vibration with the aid of optical

interferometry, the characteristics of the light source will have

a crucial effect on the precision obtainable, some consideration

is being given to the suitability of various light sources, including the factors of spectral width and intensity fluctuation.

One simple scheme for pickup calibration has been thought of?

With a vibrator used as one plate of the interferometer, photomultiplier signals would be fed to the horizontal plates of an oscilloscope, and the output from a vibration pickup on the same vibrator

would be fed to the vertical plates* The resulting pattern would

then indicate the vibration amplitude*

Future Activity ? An analysis of the fringe system in the image

plane of an Interferometer under various conditions is planned*

Experimental and theoretical analysis will be continued, on the

simple calibration scheme with one vibrating plate as well as on

the scheme with both plates vibrating - one at a known amplitude

and frequency, the other with the amplitude to be measured® The

task should be completed with a report by June 30, 1953

Preparation of Final Report on Spring Transducer,

Office of Basic Instrumentation, A* WildEack,

T* A„ Peris, J„ H. Pinkard

The research on the Spring Transducer was carried out under

MBS Project 330Q-31~7500 and the Objectives, Background and Summary

of Project Activity for this work are discussed in the previous
6h

Progress Report of the Office of Basic Instrumentation (MBS Report

1923). During this period* experimental data were assembled from

all work done on Spring Transducers since 1958* and these data were

fitted into a detailed outline for the final report® Some sections

of the report have been written on a part-time basis®

Barium Titanate Accelerometers, Office of Basic Instrumentation*

T® A© Peris* C®~ W^ KisHn^r

Objectives To investigate design characteristics and calibration

methods for barium titanate accelerometers®

Summary of Project Activity t Only a small amount of preliminary work

was done on this project prior to this reporting period® This work

was primarily concerned with determining the causes of the relatively large transverse response (10-50$ or more) observed in most commercially available and laboratory made barium titanate accelerometers.

Progress t Investigation was continued of means to remedy various defects of barium titanate accelerometers® New impetus was given to

this task by a request from personnel at the Aberdeen Proving Ground*

for an accelerometer suitable for recording extremely high accelerations* and having a natural frequency of about 100 Kc® Early tests*

as of the end of September* were very encouraging® Preliminary data

also pointed toward both an explanation for and a possible reduction

of* the observed transverse sensitivity of small barium titanate accelerometers® Experimental models of a total of 12 designs were built

and tested* with successive improvements with regard to shielding

natural frequency* sensitivity* transverse response* and spurius effects due to cable loading and mounting procedure® Methods were

developed to obtain accurate determinations of transverse response

(see figure )j and some preliminary work gave encouraging results in

calibrations up to accelerations of over 5*000 g

J s®

Future Activity; A report (NBS 2390) will be prepared covering this

work* Investigations will continue on several of the design features and

calibration methods for tnese accelerometers® Planning will continue

for a conference to be held* possibly in April or May* on the design*

calibration and performance of barium titanate accelerometers® Further

work on specific models for high frequency response* and for high

ranges* and on calibration methods* will be continued under a project

to be supported by the Aberdeen Proving Ground* (3305~50~75lQ)»

Preparation of Final Report on Pneumatic Instruments Based

on Critical Flow. Office of Basic Ins hruanentation*

ffl* A® Wildhack, " T * A 0 Peris* C® W® Kissinger

The research on Pneumatic Instruments Based on Critical Flow

was carried out under NBS Project 3300-31-7501 and the objectives*
CATHODE

FOLLOWER

SHAKER

POWER SUPPLY DUAL- BEAM

OSCILLOSCOPE

WAVE

ANALYZER

AMPLIFIER -

WMm.

DECADE

'» AMPLIFIER

VARIABLE

BAND-PASS

FILTER

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;

DRIVING

OSCILLATOR

SHAKER

i i

FIGURE 1 TEST SETUP FOR DETERMINATION OF TRANSVERSE RESPONSE

OF BARIUM -TITANATE ACCELEROMETERS

Background and Summary of Project Activity for this work are discussed in the previous Progress Report of the Office of Basic Instrumentation (BBS Report 1923)° During this period work was continued,

on a part-time basis, in preparing several sections of the final

report®

Survey of Thickness Measurements - George Keinath,, (Larchnont, N0 Y0 )

Objective s To make available comprehensive information on the current status of development of thickness measuring devices of all types,

and an evaluation of their applications and limitations useful in instrumentation problems concerned with thickness measurements*,

Pm gres s s This task was started during the reporting period,, Collection of pertinent literature and manufacturers 9 ‘data has been essentially completed and the material organized. Portions of the report

have been prepared, in draft form.

Survey of Variable Inductance Velocity Transducers -

R. Jo Jeffries, (Michigan State College) “

Objective i To make available in the form of a critical survey com- prehensive information on the current status of development of

variable inductance velocity transducers and an evaluation of their

theoretical and practical limitations useful in the planning and

conduct of research and development on such devices arid useful for

provision of general guides and instrumentation problems concerned

with velocity measurements*

Pro gres

s

g This task was started (hiring the reporting period, and

effort so far has been applied to the collection and organization of

pertinent literature and manufacturers 9 data®

Electrical Noise from Instrument Gables Subjected to Shock

and Office of Basic Instrumentation, T.A® Peris

Objectives To investigate, and find remedies for, the electrical

noise generated in instrument cables subjected to shock and ‘vibration®

Backgrounds Previous work on the reduction of cable noise ms carried out 'under NBS Project 3300-31-7502 (1), and is described in

MBS Report 1388 as well as in, an article in the June 1952 issue of

the Journal of Applied Physics®

Progress ; Work on noise-free cables was continued, including tests

on multiconductor cables, as shown in Fig® 3,, in which test results

are shown for four different constructions of double-conductorshielded cables® These cables differ only in the presence or absence
- 66

of the conductive coatings on the inside surface of the large dielectric tube and on the outside surfaces of the small dielectric

tubes o It is seen that conductive coatings on all contacting dielectric surfaces are required to reduce the noise from about 10 volts

to about 1 mv0 (The bond between the conductive coatings and the inside of the large dielectric tube was not as good in these tests a.s for the usual single-conductor-shielded cable,, and accounts for the

residual noise of about 1 mv» seen in the type-1* cable#

)

Noise-free cables were made in 3 feet lengths for use with

accelerometers developed and built 'under project ?50?-Task 22 a The

sensitivity of the test setup for cable noise was extended to 500

microvolts full scale., with an amplifier-noise level of 5 to 10

microvolts in a limited band of frequencies (19 to 1*0 «ps)o This

allowed intercomparison of various low-noise • cables f (see Fig® 2)*

It is seen that the cable with conductive coatings bonded to the

dielectric is the only one which retains its low-noise characteristics after repeated squeezing with pliers,, simulating rough field

conditions® The noise on the other test cables is increased by

about a factor of 10 after this rough treatment#

Underwater explosion tests were conducted with 10-foot lengths

of laboratory-made jacketed eable5 in an 11 foot water tank at the

David Taylor Model Basin# Liason was maintained with several manufacturers interested in, the commercial production of this cable#

Future Activity

8

Project considered completed#
10 V

FIGURE 1 NOISE TESTS ON 4 POSSIBLE CONSTRUCTIONS OF

DOUBLE -CONDUCTOR -SHIELDED CABLE.

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67

Stability of Feedback Systems - NBS Project 3300-31-7509 (Continuation of T5b7"(5)J7 Office of Basic Instrumentation,

H® L® Mason, J0 F® Koenig

General Objectives To study, compare, and evaluate various analytIcaX methods for predicting stability characteristics of feedback

systems

o

Specific Objectives! Develop analytical methods for the computation

orTZnear am non-linear feedback control systems, including systems

containing non-linearities such as contactors, coulomb friction and

backlash® Continue study of foreign literature on feedback control

systems, and prepare translations of selected articles®

Background s Servomechanisms and other automatic control systems are

widely used in. military and industrial applications® Often the

physical parameters of the device to be controlled are not known

exactly® Even when they are, the mathematical methods available for

predicting transient performance of linear systems are either laborious or approximate® Analog computers can solve rather complicated

problems quite rapidly, but generally require the preliminary guidance

of an analytical, solution® Further, there are many systems in which

the operation of one or more elements cannot be adequately represented by linear equations® The ranges and types of nonlinearity that

can be handled mathematically are quite limited, and one must usually

resort either to the analog computer or to linear approximations a There is therefore a need, for more convenient, more comprehensive, and

more comprehensible methods for analytical treatment of linear and of

non-linear problems

®

Summary of Project Activity ; A study of the literature in this field

was started aha a number of foreign articles were translated® Three

of these, describing the use of an amplitude-dependent transfer

function in. predicting stability of loops with non-linear elements,

were prepared in report form, NBS Report #1691®

A new method was developed for analyzing non-linear feedback

control systems containing non-linearities such as contactors,

coulomb friction, and backlash# This method involves approximation

by a special type of linearization® This permits the construction

of a stability diagram which shows how far a stable system is from

instability in terms of the amount by which three parameters may

change before the system becomes unstable® Another method was developed for obtaining the same type of stability diagram® In addition,

the absolute stability of the class of non-linear systems was ex- pressed in terms of a determinant criterion based on a characteristic

equation with complex coefficients, which relates stability to the

position of the roots in the complex plane® A paper describing both

methods was preparedc
- 68 no

A paper5

!} 0& the Zeros of Polynomials and the Degree of

Stability of Linear Systems** was partially completed* This research

paper presents a method,, called the "root trajectory" method* which

gives all the zeros of any n-th degree polynomial* and shows how

they change as physical parameters are simultaneously varied* The

paper presents new theorems and uses these in combination with known

theorems

o

Progress? Continued study of the literature of automatic control

indicates that existing indexes are insufficiently detailed to

provide a satisfactory classification for the specialist's reference files* Preparation of a new list of subject headings* extending and supplementing selected items from the TID list of June 1952*

has been begun* It is also evident that there are gaps in. the listing and translation of foreign articles and. effort has been made to

fill some of these*

A paper has been written, and is now under review* describing

the two methods mentioned above* for analyzing the stability of

feedback systems whose linear elements provide adequate low-pass

filter action for linearizing nonlinear effects* The final draft

of the paper "On. the Zeros of Polynomials and the Degree of Stability of Linear Systems'* lias been submitted for publication.

An analytical method for meeting relative stability criteria

has been developed© This is covered by a paper "A Relative Damping

Criterion for Linear Systems'* which is presently being reviewed®

In the first semester of the NBS in-hours graduate course

"Instrumentation", organized and presented this fall for the first

time, a major fraction of the time has been devoted to the theory

of automatic control systems* Beginning with measurands and the

statistical interpretation of experimental data, 'die syllabus proceeds to the study of components of the control loop, typical foxms

and functions, their combination, end finally to the transient-state

and frequency-dependent responses of open and closed loops*

Future Activity? It is expected that reviewing of the last two

papers mentioned, above will be completed* Study of the literature

will be continued, with special attention to theory and to aircraft

control systems o As work progresses on the list of subject headings, topical classification will be made of recent material in

these two fields, and it will be tied in with the OBI multidimensional system*
- 69 -

REPORTS AND PUBLICATIONS RELATED TO THIS PROGRAM

lo Is There a Science of Instrumentation?

E« U* Condon, Science, 0cto 7, 1949, vol, 110 #2858,

pp. 339-342

'

2, Instrumentation in Perspective

W, A, Wildhack, Science, Nov® 3, 1950, vole 112, #2911;,

PP « 515-519

3 , A Versatile Pneumatic Instrument Based on Critical Flow

W0 Ao Wildhack, RSI, vol. 21, #1, Jan* 1950, pp® 25-30

4, An Externally Excited Electronic Power Switch for Producing

Variable Width, Variable Repetition Rate Rectangular Pulses

Jack Sargent, NBS Report, July 29, 1949

5« Attenuation of Oscillatory Pressures in Instrument Lines

A* S» Iberall, NBS Journal of Research, vol* 45,

July 1950, RP 2115

6. Permeability of Glass Wool and Other Highly Permeable Media

A® S® Iberall, NBS Journal of Research, 1;5, No 0 5, Nov* 1950, RP 2150

7* The Effective Gamma for Isentropic Expansions of Real Gases

Ac S® Iberall, Journal of Applied Physics, vol, 19,

No® 11, Nov, 1948, pp* 997-999

8* Evaluation Report on German Subcutaneous Metal Indicator

S. R. Gilford, Nbs Report 1-123

9a Analysis of Solids with the Mass Spectrometer

Jo G a Gorman, E, Jc Jones, J. A, Hippie, Analytical

Chemistry, vol, 23, March 1951, pp* 438

10, Status Report on Spring Transducer

W® A, Wildhack, To A, Peris, Feb, 28, 1951, OBI Status

Report

11* A Fifty-Fold Momentary Beam Intensification for a High-Voltage

Cold-Cathode Oscillograph

John H, Park, Jnl, Research, NBS, Aug, 1951, p*87 RP 2231

12. Method and Instrument for the Measurement of Microphonic

Effects in Microwave Tubes

Guy F® Barnett, NBS Report 1076, April 2, 1951
- 70

13a A Bar Magnet Velocity Meter

Thomas A<> Peris and Erich Buehraann# Rev® of Sci® Inst.,

volo 22c, No« 7# July 1931

liie A Simple Type X(t) « X Recorder

Thomas A® Peris and Wc A® Wildhack# Rev* of Sci® Inst®#

vole 2.2

s No* 7# July 19.31

15® New Tools for Research

W* A® Wildhackc, Science# Oot0 5# 1951# vol® Hit, No* 2962

16® A Ceramic Accelerometer of Wide Frequency Range

Lawrence T0 Fleming# Instruments# August 1951# vol* 2

No® 8# p 0 105

17a Operational Aspects of Instrument Design

Churchill Eisenhart# Science# October 7# 19h9s vol* 110#

No 0 2858, pp® 31*3-346

18 « Electrical Noise from Instrument Cables

Subjected to Shock and Vibration

Thomas A* Peris# UBS Report 13 88, January 1952

19 0 A Miniature Barium Titanate Accelerometer

Lawrence Fleming# NBS Report 109It, November 28, 1951

20® Electron Interferometer

I.® Mar-ton# The Physical Review# March 15# 1952# vol0 85#

No® 6, 1057-1058

21« A Program of Research and Development in Basic Instrumentation

LCDR Frank L„ Thomas# USNR# Monthly Research Report of the

Office of Naval Research# January 1952

22* Translation of Papers on Stability of Non-Linear Feedback

Control Systems

Office of Basic Instrumentation, NBS Report 1691,

May 29# 1952

23® Fifth Conference on Basic .Instrumentation# April 29-30# 1952

Sponsored by Office of Basic Instrumentation

NBS Report 1693

2k. New Pulse Transformer Calves Faster Response

NBS Technical News Bulletin# May 1952
71

25o Damping of Elastically Supported Element in a Vacuum Tube

Samuel Levy, Edward V® Hobbs, Wilhelmina D e Kroll,

Leonard Mordf.in, NBS Report 1.707, June 1952

26* Office of Basic Instrumentation Quarterly Progress Reports,

1, 2 3 3, 1010, 1080, 1U67, 1753, & 1923* (These

reports are superseded by the current report, since

most background information is repeated®

)

27® Thermally Opera,ted Glass Valve to Provide Very Small

Controlled Gas Flow Rates

Ralph Forman, NBS Report 1762, June 1952

28* A Magnetostriction Magnetometer

Thomas A® Peris, NBS Report 1632, May 1952

29* Methods of Respiratory Gas Analysis

Harold Morowitz, NES Report 2167, June 1952

30* RDB-NE8 Symposium on Infrared Instrumentation

NBS Report- 1QA107 (Confidential) July 1952

31® Suggestions on Literature Survey

To Wo Lashoff, NBS Report 1898, Sept® 1952

32 e A Phase-Sampling Telemeter

M« Go Pawley and J* 0® Dick, NBS Report 2020, Sept* 1952

33® Instrumentation Literature and Its Use

Julian Smith, 0ct o 1952

3h» An Evaluation Study of a Fast-Neutron Spectrometer Based

on the Total Absorption Principle

Marshall Rc Cleland, NBS Report- 2036, Oct® 1952

35® Study of Performance of Photomultipliers Operated at

High Voltage

Ben Petree and Frank Viers, Jr® NBS Report 2065', Nov® 1952

THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The functions of the National Bureau of Standards are set forth in the Act of Congress, March

3, 1901, as amended by Congress in Public Law 619, 1950. These include the development and

maintenance of the national standards of measurement and the provision of means and methods

for making measurements consistent with these standards; the determination of physical constants and properties of materials; the development of methods and instruments for testing materials,

devices, and structures; advisory services to Government Agencies on scientific and technical

problems; invention and development of devices to serve special needs of the Government; and the

development of standard practices, codes, and specifications. The work includes basic and applied

research, development, engineering, instrumentation, testing, evaluation, calibration services, and

various consultation and information services. A major portion of the Bureau’s work is performed

for other Government Agencies, particularly the Department of Defense and the Atomic Energy

Commission. The scope of activities is suggested by the listing of divisions and sections on the

inside of the front cover.

Reports and Publications

The results of the Bureau’s work take the form of either actual equipment and devices or published papers and reports. Reports are issued to the sponsoring agency of a particular project or program. Published papers appear either in the Bureau’s own series of publications or in the

journals of professional and scientific societies. The Bureau itself publishes three monthly periodicals, available from the Government Printing Office: The Journal of Research, which presents

complete papers reporting technical investigations; the Technical News Bulletin, which presents

summary and preliminary reports on work in progress; and Basic Radio Propagation Predictions,

which provides data for determining the best frequencies to use for radio communications throughout

the world. There are also five series of nonperiodical publications: The Applied Mathematics

Series, Circulars, Handbooks, Building Materials and Structures Reports, and Miscellaneous

Publications.

Information on the Bureau’s publications can be found in NBS Circular 460, Publications of

the National Bureau of Standards ($1.00). Information on calibration services and fees can be

found in NBS Circular 483, Testing by the National Bureau of Standards (25 cents). Both are

available from the Government Printing Office. Inquiries regarding the Bureau’s reports and

publications should be addressed to the Office of Scientific Publications, National Bureau of Standards, Washington 25, D. C.
NBS