NBSIR 76-1 144

NBS InterAgency Transudcer

Project

Progress Report No. 5

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

Electronic Technology Division

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

November 1, 1976

Progress Report Covering Period January 1, 1976 to June 30, 1976

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 76-1144

NBS INTERAGENCY TRANSDUCER

PROJECT

PROGRESS REPORT NO. 5

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

Electronic Technology Division

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

November 1, 1976

Progress Report Covering Period January 1, 1976 to June 30, 1976

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

, /-V

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

Edward O. Vetter, Under Secretary

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

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director
'

I

'
NBS InterAgency Transducer Project

Progress Report No. 5, for the Period

From January 1 to June 30, 1976

to the

Naval Air Systems Command,

U.S. Navy and Transducer Committee,

Telemetry Group,

Range Commanders Council

NBS Cost Center 4253^3^

Prepared by

J. S. Hilten, C. F. Vezzetti,

J. F. Mayo-Wells, and P. S. Lederer

ABSTRACT

Experimental efforts are described in the development and evaluation of means to reduce the effects produced by thermal radiantenergy transients on pressure-transducer response. Both unbonded

strain-gage and piezoelectric pressure transducers were used in

this work with protective coatings applied directly to the diaphragms. The test method employed is to expose a pair of transducers —one protected and the other unprotected, but otherwise

nominally identical — to a known radiant-energy transient with

an energy density of approximately 20 mJ/mm2

. The resulting zero

shift is measured and taken as an index of coating effectiveness.

The effect of the presence of the coating on transducer dynamic

response was investigated by means of a shock tube, with a protected and an unprotected transducer pair exposed to the same pressure step of approximately 280 kPa (40 ps i ) . Each transducer

output was recorded as a function of time.

Test results with nine coatings and two transducer pairs are presented

.

Key words: coatings; dynamic; dynamic response; pressure transducer;

protective coatings; shock tube; tape; thermal radiantenergy response; thermal transient response; transducer;

zero shift.

1. INTRODUCTION

A brief background for the NBS InterAgency Transducer Project, its recent

history, and the current objectives were given in a previous report [1]*.

The task of developing a test method for evaluating the effects of shortduration, thermal radiant-energy transients on pressure-transducer response

Numbers in brackets indicate literature references, section 7.
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has been completed [2,3,^]. 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 [k] for evaluating protection from radiant-energy 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 protection

schemes for the use of existing pressure transducers in applications in which

thermal inputs are present and, for manufacturers, of recommendations relating

to pressure-transducer design and construction.

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 [A], 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 pressure steps generated in a shock tube.

Work on the first two elements of the plan was conducted in the previous reporting

period [5]. 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. Mounted thin metal disks were used to simulate transducer diaphragms, and the temperature histories of both bare and protected disks were

measured following exposure of the disks to thermal radiant-energy transients

generated by No. 22 flashbulbs. The protection provided by 16 different coatings

was thus evaluated.

2. EXPERIMENTAL DEVELOPMENT

Experimental work carried out during this reporting period was concerned with the

third and fourth elements of the plan outlined above.

2.1 Application of Protective Coatings

For all tests, the protective material is applied directly to the transducer diaphragm. The exposed diaphragm surface is first cleaned with acetone and allowed

to dry; then the transducer is installed in the mounting fixture with the diaphragm surface either flush or recessed, as noted below.

When the protective material is an adhesive tape, disks of tape are cut with a cork-boring tool and then pressed into place. The diameter of the disk is chosen

to be the same as, or slightly smaller than, the diameter of the diaphragm end of

the transducers. The transducer is mounted in the fixture so that the diaphragm

surface is flush with the face of the fixture.

When the protective material is a viscous grease (such as silicone dielectric

grease or silicone "heat-sink" compound), the transducer is mounted in the

**Transducer Committee, Telemetry Group, Range Commanders Council.
-3-

fixture so that the diaphragm surface is recessed from the face of the fixture

by 0.8 mm. The recess is filled to overflowing with the grease and the excess

removed by drawing a straight-edged knife blade across the face of the fixture

with the blade held at about 60° from the perpendicular and with the edge of

the blade in contact with the fixture at least for a few millimeters around the

periphery of the recess. If the knife is used carefully, the exposed surface

of the grease should be level with the face of the fixture and smooth in

appea ranee

.

When the protective material is a two-component room-temperatu re-vu 1 can i z i ng

(RTV) silicone rubber, the transducer is mounted recessed, the recess filled

with mixed but uncured rubber, and the excess removed as for the viscous greases,

except that the fixture must be supported so that the diaphragm is face up.

The fixture is left in this position until the rubber has cured. (It was found

convenient to prepare the transducer with RTV rubber coating near the close of

business and to permit the rubber to cure ovenight.)

2.2 Zero-Shift Measurements

The observed change (zero shift) in transducer output in response to thermal

radiant-energy transients with the transducers sensing atmospheric ambient

pressure is determined and recorded according to a modification of the method

of [4]*. In each test, a pair of transducers is used, one with a protective

coating applied to the sensing diaphragm and the other unprotected, but

otherwise nominally identical and, where applicable, supplied with nominally

identical excitation voltages. The thermal source for these tests is a No. 22

photo flashbulb with the center of the bulb 70 mm from the transducer diaphragm.

At this distance, the energy density (intensity) is approximately 20 mJ/mm2. To permit the simultaneous exposure of test and control transducers, the mounting fixture developed for the original method was modified to accommodate the

two transducers side by side.

As the dynamic performance of each pair of transducers is measured following

the zero-shift measurements, it was found convenient to mount the fixture onto

the hinged end plate of the shock tube used in the dynamic measurements (see

2.3) . The flashbulb source is mounted on a bracket designed to be clamped to

the end plate. This arrangement permits either dynamic or zero-shift measurements

to be carried out with a minimum of effort required to shift from one test to the

other.

The following procedure is used for each set of zero-shift measurements for a given coating:

1. Mount the transducer fixture (with test and control transducers installed)

onto the end plate of the shock tube.

2. Attach the mounting bracket for the flashbulb socket to the end plate.

*ln the method of [4], test transducer output is monitored and displayed on the screen of a storage oscilloscope or otherwise recorded as the transducer is

exposed to a thermal radiant-energy transient resulting from the ignition of a flashbulb or flashtube. As the transducer senses atmospheric ambient pressure,

that is, a gage pressure nominally of magnitude zero, any observed change in

output is taken as zero shift.
3. Adjust the distance from the center plane of the flashbulb to the plane of

the diaphragms to be 70 mm. Tighten clamps.

A. Screw a No. 22 flashbulb into the socket.

3- Examine the flashbulb to determine in which direction the ignition electrodes (each in the shape of an inverted "L") point.

6. Rotate the socket so that the direction in which the electrodes point is

approximately perpendicular to a line between the center of the flashbulb and

a point on the face of the fixture midway between the centers of the two diaphragms and on the line joining these centers.

NOTE: On ignition, a black spot commonly appears on the bulb in the direction

opposite to that in which the electrodes point. Step 6 prevents the spot from

reducing the intensity experienced by the transducers.

7- Make or check the required electrical connections, including the flashbulb

ignition-voltage source to the socket and to the trigger of storage oscilloscope, transducer outputs to storage oscilloscope, and, if required, transducer

excitation-voltage source to transducers. Turn on equipment.

8. Set the oscilloscope sweep rate to 10 ms/cm and adjust triggering controls

as required so that ignition of the flashbulb triggers the sweep. Adjust beam

intensity to a level that experience has shown will result in a well-exposed

photograph of the trace for a given film, shutter speed, and aperture.

9. Load the camera with film and adjust the camera shutter speed and aperture.

10. Fi re the flashbulb.

11. Observe the resulting traces on the oscilloscope screen. If they are satisfactory, proceed to step 12. If they are not satisfactory, determine

the cause. Make whatever adjustments may be necessary and remove the spent

flashbulb. Repeat steps A through 8 and fire the flashbulb. Repeat until

satisfactory traces are obtained.

12. Photograph the traces.

13. Remove the spent flashbulb and repeat steps k, 5, and 6. Set the

oscilloscope sweep rate to 100 ms/cm. Repeat steps 10, 11, and 12.

lA. Examine the photograph taken in step 13- If the traces show that both

t ransduce r outputs have started to decay, consider the set to be complete

with two photographs. If either transducer output has not started to decay, remove the spent flashbulb and repeat steps k, 5, and 6. Set the oscilloscope

sweep rate to 1 s/cm. Repeat steps 10, 11, and 12.

NOTE: The procedure given above results in a set of either two or three

photographs of the oscilloscope traces. The zero shift is determined by

scale measurement of the photographed traces. The measurements are made from

whichever photographs provide the greatest time resolution and incorporate

peak voltage values. The reference voltage levels are those levels, nominally

zero, corresponding to the output of each transducer before ignition of the
-5-

flashbulb. For each transducer, the zero shift is measured as the difference

between the peak voltage and the reference voltage level. The time of the peak

voltage is also determined. If positive- and negative-going peaks are present

in a single trace, both peak values (and times) are determined.

For each trace, amplitudes and times are measured at inflection points and at

a sufficient number of other points to enable a reasonable facsimile of the

oscilloscope trace to be reproduced, as shown in figures 1 and 2.

2.3 Dynamic Response Measurements

The effects of test coatings on the transducer dynamic performance are evaluated by comparing the simultaneous outputs of a pair of transducers —one

protected, the other not, but otherwise nominally identical — in response to

pressure steps generated in a shock tube. Transducer outputs are recorded and

analyzed to determine the effects of coatings on such parameters as ringing

frequency, rise time, and amplitude response.

The shock tube employed in this work has previously been used to evaluate the

dynamic performance of pressure transducers, as has been described [6]. The

shock tube is capable of providing a calculable pressure step with a rise time

on the order of 10 ns and a duration of approximately A ms. (The duration is

limited by a rarefaction which occurs at the end of the test section at approximately A ms.) Some variation in pressure-step amplitude as seen at the end of

the test section results from the method of generating the pressure wave, which

is the rupture of a cellulose-acetate diaphragm interposed between the highpressure and low-pressure sections. This variation may be as much as 5 percent

and may be accompanied by a variation in waveform, especially during the first

0.5 ms. This consideration led to a decision to expose test and control transducers to the same pressure step and therefore to record the outputs simultaneously. An incidental advantage of this procedure is that any error introduced

by the calibration of the recording means (estimated to be ±1 percent for the

oscilloscope, for example) may be ignored for the comparison measurement.

For these tests, the low-pressure section (i.e., the section downstream from

the diaphragm) is operated at atmospheric ambient pressure to simplify operation. With the gas fill used in the high-pressure section (upstream section),

the amplitude of the pressure step is approximately 280 kPa when the tube is run at the laboratory ambient temperature of 21°C.

A detailed procedure for the zero-shift method has been given in the preceding

section, as the information contained in that procedure may be used as a guide for the use of whatever apparatus is available to accomplish the same

purpose. This statement is not true for the operation of the shock tube, for

which the procedure is specific to the particular device employed, and therefore no procedure is given here. The methods used to determine rise time,

average amplitude, and ringing frequency depend on the transducers used in

the test.

For the unbonded strain-gage instruments, the outputs of the test and control

transducers exposed to the pressure step are both displayed on the screens of

two storage oscilloscopes, one operating at a sweep rate of 0.1 ms/cm and the

other at 1.0 ms/cm (total sweep times of 1 and 10 ms, respectively). The traces

are photographed. Information from the slow-sweep traces is used for monitoring
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the system behavior and for determining the duration of ringing and, therefore,

for providing an estimate of the degree of damping. Rise times are determined

from the photograph of the fast-sweep trace (see figure 3) as the difference

between the times at which the initial transducer pulse in response to the pressure step reached 10 percent and 90 percent of its peak value.

NOTE: It has been found convenient to simplify this measurement somewhat. For

a given transducer-coating combination, once the 10 percent and 90 percent amplitudes have been determined, the rise time may be estimated by calculating the

difference between the distances from any appropriate vertical graticule line

to the two points on the rising portion of the trace of the initial pulse at

which the amplitude of the trace is equal respectively to the 10 percent and

90 percent amplitudes.

Since the output signal exhibits ringing, an averaging calculation is used to

provide the average amplitude as follows: A value of average amplitude is

determined from scale measurement of (l) two consecutive minima at about 150 ys

and (2) the included maximum. The average value of the two minima is calculated.

The average of this average and the maximum is calculated to give the average

amp 1 i tude

.

The procedure is repeated at about 500 ys.

For determinations of ringing frequency, a two-channel transient recorder is used

to record the two transducer outputs resulting from exposure to the pressure step.

The recorded signals are then supplied sequentially to a frequency analyzeroscilloscope combination adjusted to operate over a frequency range of 0 to 40 kHz

and with a sensitivity of k kHz/cm of displayed trace. Each resulting trace of

the frequency spectrum is photographed. Ringing frequency is determined by

i nspect i on

.

For the quartz-crystal instruments, no measurement of ringing freqeuncy is possible as available equipment has an upper frequency limit of 100 kHz, while the

manufacturer reports a transducer natural frequency of kOO kHz.

The rise time is determined in a manner similar to that described for the straingage transducers, except that the sweep rates are 0.01 and 1.0 ms/cm.

Average amplitudes are estimated by scale measurement of both the fast- and slowsweep traces between (1) the base level established by the transducer output

before the pressure step occurs and (2) points judged to be at mid-amplitude of

the ringing. These measurements are carried out at 15 and 50 ys on the fastsweep trace and at 12, 2, and 3 ms on the slow-sweep trace.

3. COATING EVALUATION

3. 1 Coat i ngs Used

Nine protective coatings were evaluated. The test coatings were selected from

those evaluated in the previous reporting period and represent various degrees

of thermal protection capability and several types of coating material. Included

as test coatings are a two-component RTV silicone rubber, a silicone "heat-sink"

compound, a silicone grease, one and three layers of black vinyl ("electrician's"

tape), one and three layers of white vinyl tape, and one and three layers of

thermal fiberglass tape.
-7-

The various tape coatings were chosen because (l) tape is commonly used as a protective coating by a number of transducer users (in particular, these users

report employing black vinyl tape), (2) tape is easy to apply and overall

thickness can be readily varied through the use of multiple layers, and

(3) tapes showed considerable variation in protective ability in the tests

performed earlier. One and three layers of vinyl tape represent thicknesses

of 0.15 and 0.A5 mm, respectively, which are typical thicknesses reported in use at several laboratories. A single layer of fiberglass tape is 0.23-mm

thick.

The silicone rubber was chosen because (l) silicone rubber is commonly used

by a number of transducer users, and (2) this particular red RTV silicone

rubber had performed relatively well in the earlier evaluation. Transducer

users cite applications for which thicknesses varying from 0.10 to 2.0 mm

are used. The 0.8 mm thickness used in these tests is considered reasonable

for initial testing purposes.

The "heat-sink" compound was chosen because it also performed relatively well

in the earlier evaluation. By contrast, silicone grease was chosen because,

although reported in use by a number of transducer users, it performed relatively poorly in the earlier evaluation.

After each set of tests with a given coating, the coatings were removed and

the transducers cleaned. The silicone materials were applied after the tapes,

with the RTV silicone rubber applied last.

3.2 Transducers Used

Two pairs of transducers were used in the coating evaluation tests. The two

types, unbonded strain-gage and quartz-crystal, are representative of those

reported in use.

The strain-gage model used has unbonded strain gages attached to a structure

composed of four support members; this assembly is attached to a push rod

that in turn is fastened to the transducer diaphragm. An analysis of this

geometry indicated that performance should not be appreciably affected by

thermal transients of short duration. The pressure range is 0 to 3^5 kPa.

The quartz-crystal model used incorporates an impedance-matching amplifier as part of the transducer. This model was also not expected to have its performance appreciably affected by thermal transients. The pressure range is 0 to

6.9 MPa.

3-3 Tests Conducted

3.3.1 Zero-Shift Measurements — Eleven sets of tests were carried out using

the pair of unbonded strain-gage transducers. Each set consisted of two tests

with the results displayed at two sweep rates, as described in 2.2. Two of

the sets were conducted with both test and control transducers unprotected;

each of the remaining sets was conducted with one of the nine selected coatings

applied to the test transducer. Ten sets of tests were carried out using the

pair of quartz-crystal transducers. Each set again consisted of two tests with

results displayed at two sweep rates. One set was conducted with both transducers
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unprotected; each of the remaining sets was conducted with one of the nine

coatings applied to the test transducer.

3.3.2 Dynamic Response Measurements — Twenty sets of tests were carried out in

all, ten sets with each transducer pair. These ten sets consisted of one test

with both control and test transducers unprotected and one or more tests each

with one of the nine selected coatings applied to the test transducer. Repetitive tests were conducted with the tape coatings in attempts to resolve discrepancies in the results.

3.4 Results

3.4.1 Zero-Shift Measurements — For the 11 tests with unbonded strain-gage

transducers, the control instrument had an average maximum zero shift of

approximately 7-3 percent of the full-scale reading (sample coefficient of

variation 7-3 percent) with an average time of occurrence of 60 ms (sample

coefficient of variation 8.2 percent). For the two tests in which the test

transducer was not protected, the average maximum zero shift was 7.6 percent

of the full-scale reading with an average time for the peak zero shifts of

65 ms. These values are considered to be in reasonable agreement.

While an insufficient number of tests was run to draw any statistical conclusions, the data show that coatings of one layer of white tape, three layers

of white tape, one layer of thermal fiberglass tape, three layers of thermal

fiberglass tape, and silicone grease do not delay the time of occurrence of

the maximum zero shift. However, all but the silicone grease reduce the magnitude of the zero shift appreciably. The use of one layer of black tape, three

layers of black tape, "heat-sink" compound, and red RTV silicone rubber all

delay the time of occurrence of the maximum zero shift and reduce the magnitude

of the zero shift as well. Comparisons of the effectiveness of a single layer

of tape with the silicone materials should take into account the fact that the

tape has one-fourth the thickness of these materials.

The data are presented in detail in table 1 and in figures 1A and IB.

In all cases, zero-shift tests with quartz-crystal transducers resulted in the

production of a negative shift followed by a positive shift of comparable magnitude. For the ten tests, the control instrument had an average maximum negative

zero shift of 5-2 percent of the full-scale reading (sample coefficient of variation 7 .b percent) and an average maximum positive zero shift of 2.8 percent

(sample coefficient of variation 8.3 percent). The average time at which the

negative peak zero-shifts occurred was 36 ms (sample coefficient of variation

5-2 percent) and the average time at which the positive peak occurred was 112 ms (sample coefficient of variation 5-2%).

In the test in which the test transducer was uncoated, the negative zero shift was 5-3 percent of full scale at 36 ms, and the positive zero shift was 5.5

percent of full scale at 110 ms. While the positive zero shift for the test

transducer was significantly larger than that for the control transducer,

differences of this magnitude are not uncommon in transducers of the same model,

as shown in [A]

.
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As in the tests with the unbonded strain-gage transducers, one layer of white

tape, one layer of thermal tape, three layers of white tape, three layers of

thermal tape, and silicone grease do not delay apprectab-ly the time of occurrence of the maximum zero-shift; all but the silicone grease reduce the magnitude of the zero shift appreciably. The use of one layer of black tape,

three layers of black tape, "heat-sink" compound, and red RTV silicone rubber

delay the time of occurrence of the zero shift (both positive and negative

peaks) and the magnitude of the zero shift as well.

These data are presented in table 2 and in figures 2A and 2B.

3.4.2 Dynamic Response Measurements — Figure 3 shows the response behavior of

two unbonded strain-gage transducers to a pressure step of 280 kPa with both

test and control instruments unprotected. Comparison of the traces representing one instrument with the traces for the other shows slight variations in

degree of damping, ringing frequency, and sensitivity. (For example, the

control transducer exhibits a ringing frequency approximately 7 percent higher

than that of the test transducer; on the other hand, the sensitivity of the

control instrument is some 2 percent lower.) This degree of variation may be

expected with instruments of this type.

Figure 4 shows the same two transducers in a similar pressure-step test in

which the diaphragm of the test transducer is protected by three layers of

black vinyl tape; there is a slight reduction in the ringing frequency of the

test transducer and a noticeable increase in damping, but rise time and amplitude changes are too small to be detected. None of the nine different coating

materials is observed to produce a significant change in the dynamic character

istics of the protected transducer. Table 3 summarizes the data in detail.

In the series of pressure-step tests using the various tapes as protective

coatings, the dynamic responses of the quartz-crystal transducers show a wide

variation in rise time and amplitude. The observed amplitudes range from 20

percent above to on the order of 90 percent below that of the unprotected trans

ducer outputs. Figure 5 shows two examples of the variety of responses

recorded for the tape coatings. An explanation of these results may lie in

the design of this model of transducer and in the fact that tapes are applied

to the entire sensing face of the transducers. The instrument has a ridge

around the periphery of the diaphragm, as shown in figure 6. If the tape is

applied across the entire face of the diaphragm, i.e., over the ridge, there

may be a tendency for air to be trapped along the inner edge of the ridge.

Such trapped air would be expected to "cushion" the pressure step in an uncontrolled manner, causing variation in the pressure seen by the transducer

diaphragm (and hence by the transducer) compared to the pressure of the step.

Detailed information concerning the construction of these transducers was not

available at the time of the tests.

In the pressure-step tests with quartz-crystal transducers and using silicone

materials as protective coatings, there was not significant variation between

the outputs of protected and unprotected instruments. The data are given in

table U.
- 10 -

4. CONCLUSIONS

The observed performance of the nine coatings evaluated as protection for the

diaphragms of two different pressure-transducer types verified the results

obtained in the simulated diaphragm tests described in the previous report [ 5 ].

That is, some coating combinations appeared to be an order of magnitude more effective than others in delaying and reducing zero shift, at least as determined on the basis of a small number of trials.

"Heat-sink" compound, red RTV silicone rubber, and black vinyl tape (one

layer and three layers) were observed to be effective in delaying the time

at which the maximum shift occurred and, with the exception of one layer of

black vinyl tape, in reducing the magnitude of the zero shift with the transducers tested. Silicone grease, white vinyl tape (one layer and three layers),

and thermal fiberglass tape (one layer and three layers) were observed to have

little or no effect in delaying the time of the maximum shift but, with the

exception of silicone grease, were moderately effective in reducing the magnitude of the zero shift. Of the coatings tested, silicone grease and one layer

of black vinyl tape were least effective in reducing the magnitude of the zero

shift.

The nine coatings were not observed to downgrade the dynamic performance of the

unbonded strain-gage transducer as evaluated with a pressure step of 280 kPa

in the shock tube.

For the quartz-crystal pressure transducer, the ridge around the outer portion

of the diaphragm appeared to cause air entrapment at the time tapes were applied;

this entrapped air could account for the large variations observed. The three

coatings of silicone material was observed to have little effect on the rise

time and amplitude characteristics of the quartz-crystal transducers.

5. PLANS FOR THE REPORTING PERIOD JULY 1, 1 976 TO DECEMBER 31, 1976

(1) Additional replicate tests are planned to provide a more satisfactory

stat i st i ca 1 base

(2) The quartz-crystal pressure transducers will be exposed to pressure steps

of greater amplitude as a means of checking that response data taken with a pressure step equal to 4 percent of the full-scale reading are representative

of the transducers' dynamic performance.

(3) Pairs of transducers expected to have substantial response to thermal

transients will be used in the tests, as to date only pairs not expected to

exhibit such response have been tested.

(4) The position of the test and control transducers (with both unprotected)

will be interchanged 1 ef t- to- r i ght in the shock tube as a means of checking

that there is no side-to-side pressure gradient at the test end of the tube.

(5) The effect on the acceleration response of coating the diaphragm of the

transducer will be determined to check that acceleration sensitivity is not

significantly increased.
6. RECOMMENDATIONS

Recommendations for future work include the following:

(1) Tests to determine the significant effects of varying the protective

coating thickness, to provide information to permit an optimum choice of

thickness for a given coating;

(2) Tests using a convective heat source;

(3) Evaluation of the durability of the protective coatings; and

(4) Investigation of the use of path-geometry protective schemes (such as mechanical screens).

7. REFERENCES

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

Progress Report Covering Period July 1, 1974 to September 30, 1974, NBSIR

75-654 (February 1975).

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

Transducer Project — Progress Report Covering Period October 1, 1974 to

December 31, 1975, NBSIR 75-532 (June 1975).

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

Progress Report Number 3 Covering Period January 1, 1975 to June 30, 1975,

NBSIR 76-1038 (March 1976)

.

[4] Hilten, J. S., Vezzetti, C. F. , Mayo-Wells, J. F. , and Lederer, P. S. Test Method for Determining the Effect of Thermal Transients on PressureTransducer Response, NBS Tech. Note 905 (March 1976).

[5] Lederer, P. S., Hilten, J. S. , Vezzetti, C. F. , and Mayo-Wells, J. F. NBS InterAgency Transducer Project — Progress Report Number 4 Covering

Period July 1, 1975 to December 31, 1975, NBSIR 76-1060 (June 1976).

[6] Lederer, P. S., Methods for Performance-Testing of Electromechanical

Pressure Transducers, NBS Tech. Note 41 (February 1967).

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Figure 5" Response to a pressure step of 280 kPa by two quartz-crystal pressure

transducers. In the tests represented by photographs 1 and 3 the

test transducer had a protective coating of three layers of black

vinyl tape applied to the diaphragm; in the tests represented by 2 and k, the coating was three layers of white vinyl tape. The control

transducer received no protective coating in either set of tests.

The photographs are of oscilloscope traces displaying the outputs of

the test (upper trace) and control (lower trace) transducers. The

time scale for all traces is 1 ms/division; a vertical deflection of one division corresponds to 100 mV. It would be expected that the

four test transducer traces be in general agreement, as the color of

the tape should not affect the rate at which the energy in the pressure

step is transmitted through the tape to the diaphragm and as the

density and texture of the black tapes and the white tapes are similar.

A possible explanation for the variations shown here is advanced in

3.4.2.
Figure 6: Photographs of the faces forming part of the sensing assembly of a quartz-crystal (left) and an unbonded strain-gage (right) pressure

transducer. Part or all of these faces are the outer surfaces of

the respective instrument diaphragms. Note the presence of the

annular ridge (arrow) on the face of the quartz-crystal instrument

This ridge marks the periphery of the diaphragm; the significance

of the presence of the ridge is discussed in 3*^-2.
Zero

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TABLE 2

Zero Shift Resulting from Thermal Radiant-Energy Transient

Applied to Protected and Unprotected Quartz-Crystal Pressure Transducers

Test Transducer

Test No. Protective Coating Maximum Negative

on Diaphragm Zero Shift

% FS*

Maximum Positive

Zero Shift

% FS*

Time to Maximum

Negative Zero Shift, ms

Time to Maximum

Positive Zero

Shift, ms

12 None 5.3 5.5 36 110

13 One Layer Black Vinyl Tape 0.4 3.6 74 370

14 Three Layers Black Vinyl Tape 0.0 0.9 — 1100

15 One Layer White Vinyl Tape 1.8 2.4 34 120

16 Three Layers White Vinyl Tape 0.9 0.9 37 120

17 One Layer Thermal Fiberglass Tape 2.5 2.9 36 120

18 Three Layers Thermal Fiberglass

Tape

0.7 0.7 35 no

19 Silicone Grease 4.9 4.9 33 120

20 Silicone "Heat-Sink" Compound 0.2 0.2 36 1000

21 Two-Component Red RTV Silicone

Rubber

0.0 0.4 1500

Control Transducer

Test No. Protective Coating Maximum Negative

on Diaphragm Zero Shift

% FS*

Maximum Positive

Zero Shift

% FS*

Time to Maximum

Negative Zero Shift, ms

Time to Maximum

Positive Zero Shift, ms

12 None 4.7 2.7 38 105

13 None 5.8 3.1 39 120

14 None 5.5 2.9 38 120

15 None 4.5 2.4 35 105

16 None 5.1 2.5 36 no

17 None 5.1 2.7 38 120

18 None 5.3 2.9 35 no

19 None 5.1 2.5 34 no

20 None 5.3 2.9 34 no

21 None 5.5 2.9 35 no

Average 5.2 Coefficient of Variation,^ 7.4

2.8 8.3365.2112

5.2
TABLE 3

Response of Two Unbonded Strain-Gage

Pressure Transducers, One Protected and the Other Unprotected, to 280-kPa Pressure Step

Test Transducer

Test No. Protective Coating

on Diaphragm

Rise Time

10-90%

m sec

Amplitude* at 150 us, 500 us, 1 ms, 2 ms, 3 ms Major Resonant

Frequencies

kHz

1 None 14 37.1, 38.6, 38.0, 38.5, 39.0 9.8, 20.4, 31.0

2 One Layer Black Vinyl Tape 14 35.3, 36.7, 39.0, 30.0, 40.0 10.0, 20.8, 31.8

3 Three Layers Black Vinyl Tape 16 32.9, 36.3, 36.0, 37.0, 37.0 10.0, 21.8, —

4 One Layer White Vinyl Tape 16 34.3, 37.3, 37.5, 38.0, 38.0 9.8, 10.4, 31.2

5 Three Layers White Vinyl Tape 16 32.5, 36.5, 38.0, 38.3, 38.5 9.8, 20.8, —

6 One Layer Thermal Fiberglass Tape 16 35.0, 37.9, 38.0, 38.0, 39.0 9.6, 10.2, 30.6

7 Three Layers Thermal Fiberglass Tape 14 32.3, 36.8, 36.5, 37.5, 37.5 9.2, 19.6, 29.4

8 None 16 34.4, 37.0, 38.0, 38.0, 38.0 9.6, 20.2, 31.0

9 Silicone Grease 16 32.9, 34.8, 35.5, 35.5, 36.0 9.9, 19.6, 29.4

10 Silicone "Heat-Sink" Compound 14 33.3, 36.1, 37.5, 37.5, 38.5 8.8, 18.4, 28.0

11 Two-Component Red RTV Silicone Rubber 14 33.3, 34.3, 36.0, 36.0, 37.3 9.2, 19.4, 29.2

Control Transducer

1 None 9 35.3, 38.0, 39.1, 39.8, 39.1 10.6, 21.6, 33.2

2 None 14 34.5, 37.7, 39.1, 40.1, 40.9 10.6, 21.8, 33.2

3 None 11 33.4, 37.4, 37.7, 38.2, 37.7 10.6, 21.8, 33.2

4 None 14 33.7, 36.6, 37.7, 38.7, 38.7 10.4, 21.8, 33.2

5 None 11 32.2, 36.7, 38.0, 37.7, 37.7 10.6, 21.8, 33.2

6 None 14 33.1, 37.0, 39.1, 38.7, 38.7 10.6, 21.6, 33.0

7 None 11 33.1, 35.5, 36.9, 37.7, 37.7 10.6, 21.8, 33.0

8 None 14 33.1, 36.0, 38.7, 38.7, 38.7 10.0, 21.6, 32.6

9 None 11 33.2, 34.8, 37.1, 37.1, 37.1 10.6, 21.8, 33.2

10 None 16 32.1, 35.6, 36.6, 36.6, 37.7 10.6, 21.8, 33.2

11 None 11 32.8, 35.6, 36.6, 36.6, 37.1 10.6, 21.8, 33.2

Average 12 33.3, 36.5, 37.9, 38.2, 38.3 10.6, 21.8, 33.1

Coefficient of Variation, % 17 3.8, 2.8, 2.6, 3.1, 2.8 1.8, 0.6, 0.6

*Recorded trace deflection in units of 0.02 in (0.05 cm).
TABLE 4

Response of Two Quartz Pressure Transducers,

One Protected and the Other Unprotected,

To 280-kPa Pressure Step

Test Transducer

Test No. Protective Coating

on Diaphragm

Rise Time

10-90%

w sec

Amplitude* at 15 us, 50 us,

1 ms, 2 ms, 3 ms

1 Silicone Grease 1 54, 52, 52, 53, 54

2 Silicone "Heat-Sink" Compound 1 49, 49, 52, 53, 53

3 Two-Component Red RTV Silicone Rubber 4 51 , 52, 52, 53, 53

Control Transducer

1 None 1 53, 50, 53, 53, 53

2 None 1 49, 48, 53, 53, 54

3 None 1 52, 52, 52, 53, 54

Coefficient of

Average 1.3

Variation, % 43

51, 50, 53, 53, 54

4.1, 4.0, 1.1, 0, 1.1

Recorded trace deflection in units of 0.02 in (0.05 cm).
NBS-1 1 4A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBS 1 R 76-1 1 44

2. Gov’t Accession

No.

3. Recipient’s Accession No.

4. TITLE AND SUBTITLE

NBS InterAgency Transducer Project

Progress Report No. 5

5. Publication Date October 1976

6. Performing Organization Code

7. author(S) Paul S. Lederer, John S. H i 1 ten , 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. 4253434

11. Contract/Grant No.

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

Naval Air Systems Command Transducer Committee TG/RCC

Washington, D.C. 20361 c/o Div. 9486

Sandia Laboratories

Albuquerque, NM 87115

13. Type of Report & Period Covered Interim

1-1-76 to 6-30-76

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.) Experimental efforts are described in the development and evaluation of means to

reduce the effects produced by thermal rad i ant-energy transients on pressuretransducer response. Both unbonded strain-gage and piezoelectric pressure transducers were used in this work with protective coatings applied directly to the

diaphragms. The test method employed is to expose a pair of transducers —one

protected and the other unprotected, but otherwise nominally identical — to a known radiant-energy transient with an energy density of approximately 20 mJ/mm2

. The resulting zero shift is measured and taken as an index of coating effectiveness.

The effect of the presence of the coating on transducer dynamic response was investigated by means of a shock tube, with a protected and an unprotected

transducer pair exposed to the same pressure step of approximately 280 kPa

(^0 psi). Each transducer output was recorded as a function of time.

Test results with nine coatings and two transducer pairs are presented.

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; dynamic; dynamic response; pressure transducer;

protective coatings; shock tube; tape; thermal radiant-energy response; thermal

transient response; transducers; zero shif

18. AVAILABILITY fX~| Unlimited

For Official Distribution. Do Not Release to NTIS

Order From Sup. of Doc., U.S. Government Printing Office Washington, D.C. 20402, SD Cat. No. Cl 3

be ! Order From National Technical Information Service (NTIS)

Springfield, Virginia 22151

19. SECURITY CLASS 21. NO. OF PAGES

(THIS REPORT)

UNCL ASSIFIED 25

20. SECURITY CLASS 22. Price (THIS PAGE)

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