NBSIR 76-1060

NBS InterAgency Transducer

Project

Progress Report No. 4

P. S. Lederer, J. S. Hilten, C. F. Vezzetti, and J. F. Mayo-Wells

Electronic Technology Division

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

June 10, 1976

Progress Report Covering Period July 1, 1975 to December 31, 1975

This is a progress report. The work is incomplete and is continuing.

Results and conclusions are not necessarily those that will be included

in a final report.

Prepared for Naval Air Systems Command, U. S. Navy, and

Transducer Committee, Telemetry Group, Range Commanders Council

NBSIR 76-1060

NBS INTERAGENCY TRANSDUCER

PROJECT

PROGRESS REPORT NO. 4

P. S. Lederer, J. S. Hilten, C. F. Vezzetti, and J. F. Mayo-Wells

Electronic Technology Division

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

June 10, 1976

Progress Report Covering Period July 1, 1975 to December 31, 1975

This is a progress report. The work is incomplete and is continuing.

Results and conclusions are not necessarily those that will be included

in a final report.

Prepared for Naval Air Systems Command, U. S. Navy, and

Transducer Committee, Telemetry Group, Range Commanders Council

U.S. DEPARTMENT OF COMMERCE, Elliot L. Richardson, Secretary

James A. Baker. Ill, Under Secretary

Dr. Betsy Ancker-Johnson. Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS. Ernest Ambler. Acting Director

NBS InterAgency Transducer Project

Progress Report No. k, for the Period

July 1, 1975 to December 31, 1975

to the

Naval Air Systems Command,

U. S. Navy, and Transducer Committee,

Telemetry Group,

Range Commanders Council

NBS Cost Center

Prepared by

Paul S. Lederer, John S. Hilten

Carol F. Vezzetti, and J. Franklin Mayo-Wells

ABSTRACT

Initial experimental efforts are described relating to the

development and evaluation of means to reduce the effects

produced by thermal radiant-energy transients and other

thermal inputs on pressure-transducer response. Results

from earlier work suggest that a major source of the

thermally induced zero shifts observed in a number of

pressure transducer designs is thermal energy propagated

through the diaphragm to the sensing element. For many

transducer designs, the temperature at the back side of

the diaphragm provides a convenient measure of the energy

reaching the sensing element. Accordingly, a series of

tests was carried out to investigate the effects of a variety of protective coatings on the amount and rate of

energy transmission through the diaphragm as revealed by

measurements of the diaphragm back-side temperature. For

purposes of experimental simplicity, mounted thin metal

disks are used to simulate transducer diaphragms, and the

temperature histories of both bare and protected disks are measured with thermocouples following exposure of the disks

to thermal radiant-energy transients (of approximately

20 mJ/mm2 at the disk) generated by No. 22 photographic

flashbulbs. Protective means investigated include various

materials, such as tapes, greases, and room-temperaturevulcanizing rubbers (RTVs) , applied directly onto the disks

as coatings. Data are given for each protective material

tested

A description of other t ransducer- rel ated work and publications

is given in an appendix.
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Key words: Coatings; photoflash bulb; pressure transducer;

protective coatings; thermal radiant-energy

response; thermal transient response; transducer.

I. INTRODUCTION

A brief background for the NBS InterAgency Transducer Project, its

recent history, and current objectives were given in a previous

report [1]*. The task of developing a test method for evaluating the

effects of short-duration, thermal radiant-energy transients on pressure-transducer response has been completed [2,3,4] . The

Transducer Committee"" and NAVAIR as cosponsors have assigned as a follow-on task for the Project the evaluation of schemes in use or proposed to reduce such effects. The intent is to use the test

method described in [h] for evaluating protection from radiantenergy transients and to modify this method as required for generating

other thermal inputs to the test transducer and protection scheme.

The task assignment calls for schemes to protect pressure transducers

from "radiated and/or convected transients of various amplitudes and

durations." The main concept to be taken into account is the "effect

of any protection scheme on transducer performance, such as increased

acceleration sensitivity, degradation in dynamic performance, etc."

Goals of the work include development, for users, of guidelines and

protective schemes for the use of existing pressure transducers in

applications in which thermal inputs are present and, for manufacturers,

recommendations relating to pressure transducer design and construction.

As noted in [3], a survey of transducer users at military test ranges

and at other agencies indicated that there exists a sufficiently wide

variety of applications, transducers, and measurement conditions to

prevent the selection of representative instruments or measurement

environments. With the concurrence of NAVAIR and the Transducer

Committee, the first phase of the work (1) uses the test method of

[4] with No. 22 flashbulbs as source, (2) is concerned with flushdiaphragm transducers with full-scale ranges of 0.35 and 6.9 MPa and

either strain-gage or piezoelectric sensing elements, and (3) evaluates

thermal protection either provided by diaphragm coatings applied inhouse or based on path geometry. Further work, covering a broader

range of transducers and conditions is to be proposed as indicated or justified by the results of the first-phase investigations. The plan

of work is first, to develop a method for evaluating coating performance; second, to test a number of coatings using this method; third,

using the test method of [4], to determine the zero shifts of pairs of

transducers —one with diaphragm protection and the other without; and

fourth, to compare the dynamic response of the two transducers in each

pair to a shock-excited pressure wave. Work with geometric protective

schemes is to follow a similar line of development.

-Figures in brackets indicate literature references, Section 5. "-Transducer Committee, Telemetry Group, Range Commanders Council.
-3-

2. EXPERIMENTAL DEVELOPMENT

Experimental work carried out during this reporting period was concerned

with the first and second elements of the plan of work given above.

2.1 Development of Method for Evaluating Coating Performance

Parameters of interest in characterizing coating performance include

the maximum rise in temperature measured at the back surface of a transducer diaphragm following a specified thermal input to the protected front surface and the time from the onset of the thermal transient to the peak back-side temperature. These parameters are of

interest because results from earlier work together with knowledge of

transducer design and construction suggest that a major source of the

thermally induced zero shifts observed in a number of pressuretransducer designs is thermal energy propagated through the diaphragm

to the sensing element. For transducer designs in which little thermal

energy is conducted through the housing from diaphragm to sensing

element, the temperature at the back side of the diaphragm provides a convenient measure of the energy reaching the sensing element. For

purposes of evaluating coating performance, it is not necessary to

accept the experimental complexity that would be involved in using an actual transducer diaphragm. A thin metal disk mounted in a relatively

massive housing simulates the thermal behavior of a diaphragm; virtually

identical disks may be fabricated for as many tests as are required.

2.1.1 Preliminary Work. In order to gain familiarity with making

thermocouple measurements of the temperature of thin disks, preliminary work was carried out with a number of thermocouple systems, wire

sizes, and mounting means. Thermocouples of the system copper versus copper-45% nickel were used initially because of their availability.

Thermocouples of the system nickel-10% chromium versus copper-^5%

nickel offer greater sensitivity and were used as soon as they became

ava i lable.

Thermocouples with wire sizes as small as 0.025 mm were tested, but were found to pose too many practical difficulties in handling;

thermocouples of wire of twice this diameter proved to be acceptable.

Several mounting schemes were tried including soldering and cementing.

The very small size of the measuring junction of a thermocouple made

with even 0 . 076-mm-d i ameter wire renders it nearly impossible to

determine if the junction is in good contact with the disk when these

techniques are employed. A system was devised in which the thermocouple is mounted at one end of a small ceramic rod with two axial

holes for the wires. Before the thermocouple is inserted, the junction end of the rod is tapered as shown in figure 1. The thermocouple is held in place with a small quantity of white glue packed

into the end of each hole. The thermocoupl e-and-rod assembly is

mounted in a swinging bracket in such a manner that a counterweight

forces the thermocouple against the disk with an adjustable force.

This arrangement is shown in the sketch of figure 1.
2.1.2 Description of Apparatus. The apparatus for the test method

for evaluating coating performance is based on that for evaluating

the effects of thermal radiant-energy transients on pressure-transducer

response. A source and the transducer mounting of the latter method

are mounted on an optical rail. The mounting fixture for the thin

metal disk, shown in figure 2, fits into the transducer mounting block.

The vertical position of the disk, the plane of which is perpendicular

to the long axis of the rail, is adjusted until the center of the disk

and the center of the source are in the same horizontal plane. The

mechanism for supporting the thermocouple is also mounted on the rail,

behind the transducer mounting block. The arrangement is shown in

figure 3- The vertical position of the thermocouple is adjusted so that the measuring junction is in contact with the approximate center

of the exposed portion of the disk.

The thermocouple cold junction is immersed in a flask of water at

nominal room temperature, the water being used as a heat sink to

eliminate small fluctuations to which the junction would be exposed

in room air. The thermocouple output is displayed on an oscilloscope

triggered by the same switch used to initiate the flash. The thermocouple manufacturer provides tables for converting thermal emf in

millivolts to temperature.

The source used is the No. 22 photographic flashbulb. The performance

characteristics of these flashbulbs has been characterized and is

given in [k] . The source-to-disk distance selected is 70 mm, which

results in a transient of approximately 20 mJ/mm2 at the disk.

2.1.3 Procedure. In the following procedure, the word "disk" refers

to either a bare disk or a disk with protective material applied.

Preparation of the disks is described in section 3-

(1) Select a disk mounting fixture with the aperture desired for the

test. Clamp the disk between the body of the fixture and the clamping

plate. Be careful to center the disk on the aperture, so that the screw holes are unobstructed. Insert the screws and tighten them

evenly, in rotation.

(2) Insert the disk mounting fixture into the transducer mounting

block.

(3) Mount the thermocouple assembly onto its bracket. Adjust the

height of the bracket so that with the ceramic rod parallel to the

rail, the distance from the measuring junction to the rail is equal

to the distance from the center of the disk to the rail.

{k) Adjust the position of the counterweight so that with the

ceramic rod parallel to the rail, firm pressure is felt by the tip

of a finger held against the measuring junction in contact with

the back surface of the disk, the ceramic rod is parallel to the

rail. Be careful to prevent the measuring junction or ceramic rod

from striking the interior of the disk mounting fixture.
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(5) Move the thermocouple bracket assembly along the rail toward the

mounted disk until, with the measuring junction in contact with the

back surface of the disk, the ceramic rod is parallel to the rail.

Be careful to prevent the measuring junction or ceramic rod from

striking the interior of the disk mounting fixture.

(6) Immerse the thermocouple cold junction in a flask of water.

(7) Make all the electrical signal and power connections required.

(8) Adjust the oscilloscope controls as appropriate. Note — A total sweep time of 0.1 to 10 s is convenient. For the work described

in this report, vertical deflections of 0.05 to 0.5 mV per division

were adequate.

(9) Install a No. 22 flashbulb in the source position. Rotate the

bulb so that the supporting electrodes for the igniter element point

in a direction perpendicular to the long axis of the rail.

(10) Fire the flashbulb. Note -The No. 22 flashbulb constitutes a very bright source; it is recommended that the test operator not

look at the bulb during ignition.

(11) If desired, record photographically the resulting trace on the

oscilloscope screen.

(12) Asa minimum, measure and record the following data: (1) the

maximum thermocouple output and the output at 50, 100, 500, and 1000 ms after initiation of the flash and (2) the times required for the

thermocouple output to reach 10, 50, 90, and 100% of the maximum value

and to decay to 90 and 50%. If the sweep duration permits, measure

and record thermocouple output at 5 and 10 s.

(13) Retract the thermocouple bracket assembly until the ceramic rod

is clear of the transducer mounting block. Support the counterweight

to prevent the rod from striking the interior of the disk mounting

fixture or other parts of the apparatus.

{\k) Remove the disk mounting fixture from the transducer mounting

block and disassemble the fixture to remove the disk. Remove the

used flashbulb in preparation for another test.

2.1.4 Experiments with Various-Sized Apertures and Disk Thicknesses

To show the effect of aperture size, i.e., of the exposed area of the

disk, on the temperature history of the disk following exposure to a given thermal transient, disk mounting fixtures with three different

apertures were fabricated. The apertures are chosen to be representative of commercial pressure transducers and are 6.35, 9-53, and 12.7 mm

in diameter (with areas of 31-7, 71-3, and 127 mm 2

, respectively).

Experiments with three disk thicknesses — 0.080, 0.13, and 0.25 mm —

were also conducted. The intent of these tests was to determine if
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a thin, bare disk would experience a greater temperature rise following

exposure to a given thermal transient than would an otherwise similar

disk of greater thickness. A simple analysis suggests that this is

correct because, if the paths by which thermal energy may be removed

from the disk are approximately the same in both cases, a thin disk

will have to accommodate more energy per unit volume than a thicker

disk.

The results of these experiments are plotted in figures *t, 5, and 6.

Each of these figures shows curves of thermocouple output as a function

of time for the three disk thicknesses. The tests represented by

figure k used an aperture of 6.35 mm; those represented by figure 5,

9-53 mm; and those represented by figure 6, 12.7 mm. Comparison for

the same disk thickness of the curves of these figures shows that the

rates of temperature rise and decay are greatest for the smallest

aperture and least for the largest, with the differences in rate of

decay being the more pronounced. Again for the same disk thickness,

curves from the middle-sized aperture show the highest maximum

temperature rise, or, in the case of the thickest disk, a temperature

rise equal to the highest. Table 1 presents maximum temperature-rise

values for nine experiments, with value being an average from five

tests. The curves in each figure show that disk thickness is inversely

related to maximum temperature rise in a non-linear fashion and that

the rates of temperature rise and decay are similar for these three

th i cknesses

.

2.1.5 Experiments to Determine Method Repeatability . Twelve tests

were conducted, each on a new bare disk, to determine the repeatability

of the method. The results are given in table 2 and plotted as the

heavy curve in figures 7 and 8. The thermocouple used in these tests was fabricated from 0 .051 -mm-d i ameter wires of nickel-10% chromium

and copper-45% nickel and represents the "standard" thermocouple used

in all tests for which numerical results are reported. The disks were fabricated from 0 . 080-mm-th i ck stainless steel. The thermocouple

manufacturer indicates that the nickel-10% chromium versus copper-*»5%

nickel thermocouples supplied satisfy the ANSI Type E specifications.

The manufacturer cites a limit of error of ±1.7°C over the range of

0 to 315°C for this type of thermocouple. This is a systematic error,

however, and does not enter into the repeatability tests of concern

here. During these tests, the coefficient of variation was found to

be S.h% (as shown in table 2). This is only slightly greater than

the coefficient of variation of 8.7% found during repeatability tests

of the #22 flashbulbs. Earlier, preliminary, tests using thermocouples

soldered or glued (two sets of tests) to the back of the diaphragm

resulted in data with coefficients of variation of 28%, 33%, and 17%,

respectively. Hence the pivoting, mechanically held thermocouple is

considered quite adequate for these investigations.

The protection provided by 16 different coatings was evaluated using

the method. The coatings are identified in the column labeled
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"protection" in table 3- Included are 3 two-component room-temperaturevulcanizing rubbers (RTVs) , 5 single-component RTVs , 2 vinyl tapes, a "thermal" fiberglass tape, a silicone "heat-sink" compound, and a sili- cone dielectric grease. Five tests were made of each coating.

Each coating was applied to a stainless-steel disk 0.080 mm thick;

the aperture selected for all tests is 9-53 mm in diameter. These

dimensions are intended to provide the highest temperature rise as far as the disk by itself is concerned, and, consequently, the greatest sensitivity for the method. The RTVs were cast in place using a metal washer which was discarded after the material had set. The

thickness of the RTV layers is 0.8 mm. The tapes, in both single and

triple layers, were cut to fit the aperture by means of a cork-borerlike tool. The single-layer thickness is approximately 0.15 mm. The

two silicone greases require peripheral support in a vertical position.

The restraint is a washer similar to that used for casting the RTV

layers and is 0.8 mm thick. The restraint is left in place as part

of the coated disk. For these two coatings, clamping plates were

fabricated which are thinner than the "standard" plate by the thickness of the restraining washer. The mass of the metal in front of the

disk itself is thus the same for all tests.

The results of the coating-evaluation tests are given in table 3 and

plotted in figures 7 and 8. Each value or data point represents the

average of 5 tests. Inspection of the figures and the data shows

several interesting results. As examples, one commonly used material —

a single layer of black vinyl tape — increases the maximum temperature

rise by a factor of 1.4, while delaying the time of the peak by a factor of 2. One of the commonly used RTVs decreases the maximum

temperature rise by a factor of 5.3, while delaying the time of the

peak by a factor of 6.5- In general, except for the dielectric

silicone grease, all coatings tend to flatten the rate of temperature

rise. The "heat-sink" compound provides a very flat "peak" with one

of the longest delays and the smallest temperature rise. The information presented should be regarded as providing an indication of the

nature of the protection afforded by each coating, as evaluated by the

method. Further work is required to evaluate the effectiveness of

each coating in reducing or eliminating transducer zero shift following

exposure of the transducer to a thermal radiant-energy transient.

A selection of photographs of oscilloscope traces is given in figure 9.

4. PLANS FOR THE REPORTING PERIOD JANUARY 1 TO JULY 1, 1976

Scheduled for the reporting period January 1 to July 1, 1976 are the

third and fourth elements of the plan of work given in section 1. Pairs of quartz-crystal and unbonded-strain-gage flush-diaphragm

transducers will be used. Data from shock-tube tests will be captured

in a transient recorder and analyzed to identify resonant frequencies.

Amplitude of selected frequencies will be measured. Evaluations of

the protection provided from a convective heat source will be carried

out for various coatings using a modification of the method described
-8-

in this report. Experimental work will begin on geometric protection

schemes

.

It should be noted that funding constraints may severely limit the

carrying out of some or all of these proposed tasks.

5. REFERENCES

[1] Lederer, P. S., and Hilten, J. S. , NBS InterAgency Transducer

Project — Progress Report Covering Period July 1, 197^ to September 30,

197^, NBS I R 75-65 z

* (February 1975).

[2] Lederer, P. S., Hilten, J. S., and Vezzetti, C. F. , NBS Inter

Agency Transducer Project — Progress Report Covering Period October 1,

1972

* to December 31, 1 97^ , NBS I R 75"732 (June 1975).

[3] Lederer, P. S., and Hilten, J. S. , NBS InterAgency Transducer

Project — Progress Report No. 3 Covering Period January 1, 1975 to

June 30, 1975, NBS I R 76-IO38 (March 1976).

[^] Hilten, J. S., Vezzetti, C. F. , Mayo-Wells, J. F. , and Lederer, P. S.,

Test Method for Determining the Effect of Thermal Transients on Pressure-Transducer Response, NBS Tech. Note 905 (March 1976).

6. APPENDIX: SELECTED TRANSDUCER-RELATED INFORMATION

6.1 NBS Inter Agency Project

The report A Test Method for Determining the Effect of Thermal

Transients on Pressure-Transducer Response3 by J. S. Hilten,

C. F. Vezzetti, J. F. Mayo-Wells and P. S. Lederer has been published as NBS Tech. Note 905- The abstract follows:

A test method for evaluating the effects of short-duration,

thermal radiant-energy transients on pressure-transducer

response is described. The method consists of monitoring

pressure-transducer output (zero shift with the transducer

at atmospheric pressure) as the transducer is exposed to

radiation resulting from ignition of a photographic flashbulb or from the discharge of an electronic flash. The

method is intended to serve as an initial screening test.

Thermal energy pulses as great as 0.1 J/cm2

, with durations of about 37 ms , have been generated using No. 22

flashbulbs. In tests with No. 22 bulbs, 25 commercial

pressure transducers have shown zero shifts ranging from

0.h% to about k00% of the full-scale output.

6.2 Publications Resulting from Other-Agency Work

6.2.1 Development of a Dynamic Pressure Calibration Technique

(For NASA Langley Research Center). Vezzetti, C. F. , Hilten, J. S.

,

and Lederer, P. S., "A Method for the Dynamic Calibration of Pressure

Transducers Using a Liquid Medium", NBS Technical Note 91^.
-9-

A method is described for producing sinusoidal ly varying

pressures up to 3^ kPa, 0-peak between 50 Hz and 2 KHz for

the dynamic calibration of pressure transducers. The method

uses a 10-cm column of dimethyl siloxane liquid vibrated on the armature of a vibration exciter. The high frequency

capability of the method is accomplished by damping the liquid

column with a section packed with steel balls. Calibration

results are included for transducers provided by the sponsor.

6.2.2 Dynamic Calibration Methods for Pogo Pressure Transducers

(For NASA G. C. Marshall Space Flight Center). Hi 1 ten, J. S.,

Lederer, P. S., Vezzetti, C. F. , and Mayo-Wells, J. F. , "Development

of Dynamic Calibration Methods for Pogo Pressure Transducers"

NBS Technical Note, to be published in 1976.

Two methods are described for the dynamic calibration of

pogo pressure transducers used to measure oscillatory

pressures generated in the propulsion system of the space

shuttle. Rotation of a mercury-filled tube in a vertical

plane at frequencies below 5 Hz generates sinusoidal pressures up to h8 KPa, peak-to-peak; vibrating the same mercury-filled tube sinusoidally in the vertical plane

extends the frequency response from 5 Hz to 100 Hz at

pressures up to 140 KPa, peak-to-peak. The sinusoidal

pressure fluctuations can be generated by both methods in

the presence of high pressures (bias) up to 55 MPa . The

results from the dynamic calibration of several transducers

are reported, using both methods.

6.3 Standards Activity

Four ISA Transducer Standards which had been submitted to ANSI were

approved by ANSI. These documents, after revision, will be reprinted

by ISA as ANSI Standards. They are:

ANSI MC6. 1 "Electrical Transducer Nomenclature and Terminology"

(ISA-S37. 1-1969) • Approved September 10, 1975.

ANSI MC6.2 "Strain Gage Pressure Transducers, Specifications and

Tests For" (ISA S37. 3-1970). Approved October 23, 1975.

ANSI MC6.3 "Strain Gage Li near Acceleration Transducers, Specifications and Tests For" (ISA S37 • 5~ 1 969) - Approved October 23, 1975.

ANSI MC6.4 "Piezoelectric Pressure and Sound-Pressure Transducers,

Specifications and Tests For" (ISA S 3 7 . 1 0- 1 969) . Approved

October 23, 1975.

6.4 Transducer-Related NBS Publications

A variety of activities at NBS related to transducers and to their

calibration results in publications. In order to enhance the
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cl i ssemi nat ion of this information, the following references and

abstracts are presented:

6.4.1 Piezoelectric Accelerometer Low-Frequency Response by

Signal Insertion Methods. Koyanagi, R. S., and Pollard, J. D.

,

NBSIR 7^-597 , May 1975.

The purpose of this study was to compare the frequency

response of selected piezoelectric accel erometers , using

a signal insertion method, to the response using a traditional mechanical vibration test. Signal insertion

methods included "voltage insertion" and "charge insertion"

techniques. The signal is inserted in series with the

electrical low-side of the acce 1 erometer by means of a suitable series resistance. Commercially available insertion devices were used. Confidence in the use of insertion

methods is increased where there is agreement between the

results from insertion tests and mechanically excited tests.

6.4.2 Piezoelectric Polymer Transducer for Impact Pressure

Measurements. DeReggi, A. S., NBSIR 75-7^0, July 1975.

Described are development efforts relating to the design,

construction, and calibration of a piezoelectric polymer

transducer for the recording of pressure transients

developed over the interface between two bodies as a result of impact. A bi laminate design was selected

which uses electrically poled sheets of 25~ym

poly(vinyl idene fluoride) as the active material. The

intended primary response of the transducer is to com- pression in the thickness direction, which is produced

by either hydrostatic or normal pressure; the transducer

was also found to respond to extension in the membrane

direction. I nd i v i dua 1 -sheet activity in the thicknesscompression mode is approximately 15 pC/N, resulting in a bi laminate transducer pressure response of k.S yV/Pa

(30 mV/psi). Instructions for poling sheets and for

constructing transducers are given in detail. Static and

dynamic methods for characterizing transducer output are described. In particular, in order to simulate field

conditions in which the transducer may bend or stretch,

or both, during impacts, a drop-test procedure with

curved impactors has been devised, and a theoretical analysis (simplified to the extent of considering the membranestress contribution negligible) has been developed to yield

the interface pressure.

6.4.3 A Guide to Methods and Standards for the Measurement of

Water Flow. Kulin, G. , and Compton, P. R. , NBS Special Publication

k2] , May 1975.

Selected information sources on methods and standards for

making measurements of water and wastewater flow in the
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field are listed and described. Both closed conduit and

free surface flows are treated, but emphasis is on open

channel flow measurements needed in water resource engineering and in water pollution control. Instruments and

methods covered include weirs, flumes, current meters

(and velocity traverse methods), dilution techniques, pipe

flow instruments, acoustic meters and others. In addition

to summarizing the basic properties of each instrument or method and referring users to the best available sources of

detailed information on performance and field application,

potential sources of error are described and quantified

where possible.

USCOMM-NBS-DC

TABLE 1

Maximum Temperature-Rise Values for Combinations

of Three Disk Thicknesses and Three AperturesDisk Thickness Aperture Diameter Maximum Temperature Rise*-

(mm) (mm) (Celsius 1

0.080 6.35 20.0

0.080 9.53 21 .3

0.080 12.7 19.2

0.13 6.35 13.7

0. 13 9.53 16.5

0.13 12.7 15.6

0.25 6.35 17.2

0.25 9.53 8.07

0.25 12.7 8.3**

"The disks were fabricated from stainless steel and were positioned

70 mm from the No. 22 flashbulb source, as described in the text.

The thermocouple is of the system nickel-10% chromium versus copperk$% nickel

-'-'Each value represents the average from five tests.
TABLE 2

Repeatability Tests

Run No. Maximum Thermocouple Output Time of Maximum Output

(mV) (ms)

1 1.12 500

2 1.12 510

3 1.26 380

k O.96 450

5 1.16 300

6 1.18 300

7 1.16 320

8 1.16 270

9 1.06 320

10 0.9^ 3^0

11 0.9** 350

12 1.08 280

sample mean = 1.095 mV sample mean = 360 ms sample standard sample standard

deviation = 0.103 mV deviation = 83. 1 ms coefficient of coefficient of

variation = 3.k% variation = 23%
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Figure 1: Sketch of thermocouple fixture with cross-section detail

of thermocouple mounted in ceramic rod (A). The thermocouple MEASURING JUNCTION IS IDENTIFIED BY (B) , THE

THERMOCOUPLE WIRES PROJECT BACK THROUGH TWO AXIAL BORES

in the rod. White glue (C) holds the thermocouple in

place. The thermocouple-and-rod assembly is clamped in

arm (d) pivotally mounted at (e) . the position of the

counter weight (f) may be adjusted to control the force

exerted by the junction against the disk (g).
Figure 2: Sketch of disk mounting fixture, The side view at the

left shows the fixture disassembled with the disk (a) in

position ready to be clamped to the body (b) by clamping

plate (c). as explained in the text, the diameter of the

bore determines the aperture, that is the area of disk

exposed to thermal radiant energy. the outer diameter of

the fixture is set by the requirements of the transducer

mounting block,
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Figure 9: Photographs of oscilloscope traces of thermocouple

output as a function of time for four tests using the

method. the total sweep time in each photograph is

Is, The upper left photograph is for an unprotected

DISK (CODE LETTER Q)j AND THE UPPER RIGHT, FOR ONE LAYER

OF BLACK VINYL TAPE (K) . THE VERTICAL SCALE FOR BOTH

PHOTOGRAPHS IS 0,2 MV/DIVISION, THE BOTTOM LEFT PHOTOGRAPH IS FOR A TWO-COMPONENT RED RTV (A); AND THE BOTTOM

RIGHT, FOR "HEAT-SINK" SILICON COMPOUND (0), THE VERTICAL SCALE FOR BOTH PHOTOGRAPHS IS 0,05 MV/DIVISION,
NBS-1 14A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT No. NBSIR 76-10602. Gov't Accession

No.

3. Recipient's Accession No.

4 I I 1 1 F AND SUBTITl E

NBS InterAgency Transducer Project

Progress Report No. k

5. Publication Date April 10, 1976

6. Performing Organization Code

7. auihor(s) p au j s . Lederer, John S. Hilten, Carol F. Vezzetti , and John F. Mayo-Wells

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 4253 /t3 i

r 11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Naval Air Systems Command Transducer Committee TG/RCC

Washington, DC 20361 c/o Div. 9486

Sandia Laboratories

Albuquerque, NM 871 15

13. Type of Report & Period Covered •

1 nter 1

m

7/1/75 to 12/31/75

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less (actual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.) Initial experimental efforts are described relating to the development and

evaluation of means to reduce the effects produced by thermal radiant-energy transients and other thermal inputs on pressure-transducer response. Results from earlier

work suggest that a major source of the thermally induced zero shifts observed in a number of pressure transducer designs is thermal energy propagated through the diaphragm to the sensing element. For many transducer designs, the temperature at the

back side of the diaphragm provides a convenient measure of the energy reaching the

sensing element. Accordingly, a series of tests was carried out to investigate the

effects of a variety of protective coatings on the amount and rate of energy transmission through the diaphragm as revealed by measurements of the diaphragm back-side

temperature. For purposes of experimental simplicity, mounted thin metal disks are

used to simulate transducer diaphragms, and the temperature histories of both bare and

protected disks are measured with thermocouples following exposure of the disks to

thermal radiant-energy transients (of approximately 20 mJ/mm 2 at the disk) generated

by No. 22 photographic flashbulbs. Protective means investigated include various

materials, such as tapes, greases, and room-temperature-vulcanizing rubbers (RTVs)

,

applied directly onto the disks as coatings. Data are given for each protective

material tested.

A description of other t ransducer- re 1 ated work and publications is given in an appendix.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons)

Coatings; photoflash bulb; pressure transducer; protective coatings;

thermal radiant-energy response; thermal transient response; transducer.

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