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NBS TECHNICAL NOTE 905

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

A Test Method for Determining

the Effect of Thermal Transients on

Pressure-Transducer Response
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards 1 was established by an act of Congress March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and technology

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

research and provides: (1) a basis for the Nation's physical measurement system, (2) scientific and technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety. The Bureau consists of the Institute for Basic Standards, the Institute for Materials Research, the Institute for Applied Technology,

the Institute for Computer Sciences and Technology, and the Office for Information Programs.

THE INSTITUTE FOR BASIC STANDARDS provides the central basis within the United

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2 Located at Boulder, Colorado 80302.
OJP £TANDASD«

LIBRA BY JUN 2 1976

C^ £. 1 oo

A Test Method for Determining .uV-rs:?

the Effect of Thermal Transients on T^"

Pressure-Transducer Response - -

te» t 3 et>v^i.eftjL r\Mju, vu>i <i05>

John S. Hilten, Carol F. Vezzetti,

J. Franklin Mayo-Wells, and Paul S. Lederer

Electronic Technology Division

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

Sponsored by

Naval Air Systems Command

Washington, D.C. 20361

and

Transducer Committee TG/RCC

c/o Div. 9486 Sandia Laboratories Alburquerque, New Mexico 87115

°*EM of

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

James A. Baker, III, Under Secretary

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

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director

Issued March 1976
National Bureau of Standards Technical Note 905

Nat. Bur. Stand. (U.S.), Tech. Note 905, 52 pages (Mar. 1976) CODEN: NBTNAE

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1976

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 (Order by SD Catalog No. C13.46:905). Price $1.10 (Add 25 percent additional for other than U.S. mailing).
FOREWORD

The work described was performed as a task within the NBS Inter Agency

Transducer Project. This is a continuing project for the development

of calibration and evaluation techniques for electromechanical transducers which is currently supported by the Naval Air Systems Command,

the Transducer Committee of the Telemetry Group, Range Commanders

Council (TG/RCC) , and the National Bureau of Standards.

Paul S. Lederer, Acting Chief

Components and Applications Section

111

CONTENTS

A TEST METHOD FOR DETERMINING THE EFFECTS OF

THERMAL TRANSIENTS ON PRESSURE-TRANSDUCER RESPONSE

1 . Summary 1 2. Introduction 3

3- Development of Test Method 4

3.1 Background 4

3.2 Description of Experimental Arrangement ......... 4

3.3 Description of Apparatus 5 3-3-1 Energy Sources 5 3-3-2 Energy Meter 7

3-3-3 Transducer Mounting Fixture 8

3 • 3 - ^ Photodiode 8

3.4 Experiments to Determine Method Parameters 8

3.4.1 Investigation of Energy Available as a Function

of Distance 8

3.^.2 Investigation of Transducer Zero Shift as a Function of Distance 10

3.4.3 Investigation of Flash Source Duration and

Waveform 12

3.4.4 Investigation of Test-Method Repeatability .... 13

3-5 Other Experimental Investigations 16

3-5-1 Effect of Supply-Voltage Variation on ElectronicFlash Output 16

3.5-2 Effect of Various-Sized Apertures on Energy-Meter

Reading 17

3.5.3 Effect of Angle of Incidence on Transducer

Response 18

3.5.4 Effect of Reflectors on Transducer Response .... 18

3.5.5 Effect on Method of Energy Lost in Glass Window . . 19

3.5.6 Effect on Method of Increased Air Pressure

from Heating 19

3.5.7 Effect on Transducer of Exposure to Full-Scale

Pressure 20

3.6 Discussion of Uncertainties and Method 20

3.6.1 Method with Flashbulb Source 20

3.6.2 Method with Electronic-Flash Source 21

4. Results of Testing Transducers Using the Method 22

5. Conclusions and Results 23

5.1 Concerning the Test Method 23

5.2 Concerning the Transducer Tests 23

6. Recommendations 24

7. References 25

8. Acknowledgments 25

A TEST METHOD FOR DETERMINING THE EFFECTS OF

THERMAL TRANSIENTS ON PRESSURE-TRANSDUCER RESPONSE

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 the 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 6 ms, have been

generated using an electronic flash; pulses of up to 2.2 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 0.4%to about *+00% of the full-scale

output.

Key words: calibration; dynamic; photo flashbulb; pressure; pressure

measurement; pressure transducer; thermal transient; transducer; zero

shift.

1 . SUMMARY

In response to requests from the Naval Air Systems Command and the

Transducer Committee of the Telemetry Group, Range Commanders Council,

a test method has been developed to serve as an initial screening test

to identify pressure transducers that tend to give erroneous readings

when subjected to thermal radiant-energy transients.

The method consists of monitoring pressure-transducer output as the

test transducer is exposed to a transient thermal radiant-energy stimulus resulting from the ignition of a photographic flashbulb or from the

discharge of an electronic flash. The method also provides for monitoring energy and duration of the transient stimulus. The test transducer

is mounted in a fixture at one end of an optical bench so that the

transducer diaphragm faces toward the center of the bench. At the

other end of the bench is an energy meter positioned with its sensor

also facing toward the center of the bench. The flash source is

located midway between the transducer diaphragm and the sensor of the

energy meter. Transducer, flash source, and energy meter are all at

the same distance above the bench. The NBS embodiment of this apparatus

(shown in figure 1) incorporated a photodiode mounted at right angles to

the bench and aimed at the flash source. The photodiode was intended to

provide a check on the operation of the energy meter and information

about the waveshape of the stimulus.

In a test, the pressure transducer is mounted in the fixture and provided with the manufacturer's specified excitation, if any. Quantities

monitored are as follows: (l) the transducer output, displayed on an
oscilloscope; (2) the digital reading of the energy meter (which displays

pulse energy in joules, as intercepted by the 1 -cm area of the sensing

element); (3) the energy-meter output, displayed on an oscilloscope

(with peak amplitude proportional to the total pulse energy incident

on the sensing element); and (h) the photodiode output, also displayed

on an osci 1 loscope.

Of the various flash sources considered or evaluated during the development of the method, the commercial No. 22 photographic flashbulb and an electronic xenon flash operated at 150 J have proven most satisfactory.

The No. 22 flashbulb provides a test duration of approximately 37 ms with energy-density levels of up to 2.2 J/cm 2

. According to the manufacturer, the spectral distribution of energy curve for the No. 22 bulb

closely approximates that predicted by the Wien Law over the wavelength

range of about 350 to 650 nm. Above 650 nm, the flashbulb curve deviates

upward from the Wien-Law curve; information is not available for wavelengths shorter than 350 nm or longer than about 750 nm. With the No. 22

bulb used as source, the method provides knowledge of the transducer zero

shift as a function of measured energy level to within an estimated

±]h% of the true value. The electronic flash at 150 J provides a test

duration of approximately 6 ms with energy-density levels of 0.1 J/cm2

. The spectral distribution of energy for a flashtube depends on the

operating voltage, as well as on the fill gas and the envelope material.

Typical manufacturer's data show that the relative energy per wavelength

step of 100 nm is approximately constant over the range of 400 to 800 nm. Specific spectral information for the flashtube used is not available.

With the electronic flash used as a source, the method provides knowledge

of the transducer zero shift as a function of measured energy level to

within an estimated ±10% of the true value.

Twenty-five selected transducers were evaluated by the method, using

No. 22 flashbulbs. These represented seven models of strain-gage

types and three models of piezoelectric-crystal types. The center

plane of the bulb was 7 cm from the transducer diaphragm. Zero shifts

measured ranged from 0.4% to about 400% of the full-scale readings.

Tests on several transducers of the same model resulted in zero shifts

with maximum deviations from the average for that model within the

estimated ±]k% uncertainty. In general, semiconductor strain gage

transducers exhibited larger zero shifts than the other types of transducers tested. Within the semiconductor transducers, the largest zero

shift occurred in transducers with strain gages diffused into a silicon

diaphragm. Next come those transducers which had semiconductor strain

gages bonded to a metal diaphragm. Lesser zero shifts were measured for

transducers with semiconductor strain gages mounted on an auxiliary beam

connected to the diaphragm by means of a push rod.

Experimental work carried out in the development of the method other

than that concerned with evaluating sources included investigations of
energy available as a function of distance*, of transducer shift as

a function of distance, of flash source duration and waveform, and

of test-method repeatability. Also evaluated experimentally were

various aspects of the method, including the effect of introducing

apertures in front of the energy meter, the effect of supply-voltage

variation on electronic-flash output, the effect of misalignment of

the transducer on the measured zero shift (found not to be significant

for misalignment angles of up to six degrees), the use of reflectors,

and the amount of output shift resulting from exposure to the transient

with the transducer at full-scale pressure.

Recommendations include that pressure transducers being considered for use in environments in which thermal transients are likely to exist be

screened by the method to detect, prior to use, those vulnerable to

such transients. Also recommended is that the present method be

extended to provide thermal rad ient-energy transients with considerably greater energy content. This proposed extension of the method

would contribute to the evaluation of the effectiveness of techniques

for protecting a transducer from thermal transients, as well as provide

a better simulation of the transients encountered in some applications.

2. INTRODUCTION

In field use, pressure transducers are often required for measurements

under adverse experimental conditions. Among these conditions are

those in which the transducers are exposed to thermal transients, that

is, to rapidly changing temperature conditions which are found in

measurements of such quantities as nuclear or high-explosive blast

pressures, rocket- and jet-engine parameters, shock-tube phenomena,

and nuclear reactor performance parameters. NBS was asked by the

Naval Air Systems Command and the Transducer Committee TG/P.CCf to:

"Develop a test device and generate a test procedure to

impinge thermal -trans ient inputs on pressure transducers.

The requirements of the test device should include:

1. Inexpensive to build;

2. Simple to operate;

3. Easily reproducible by transducer manufacturers,

test ranges, or range users;

h. Capable of impinging thermal transients of any

duration greater than 1 millisecond;

5. Controlled heat flux inputs capable of being

quant ized."

* In general, over the range of distances investigated, deviations

from the inverse-square law of intensity as a function of distance

were within the estimated uncertainty of measurement of energydensity levels, including the effects of flash repeatability.

t Transducer Committee, Telemetry Group, Range Commanders Council.

3
In addition, the precision of the method was required to be at least

adequate for the method to serve as an initial screening test, that

is, to provide information to the engineer permitting him to select a pressure transducer having minimal response to thermal radiant-energy

transients for use in measurement situations where such transients are expected or are known to exist.

The method consists of monitoring pressure-transducer output as the

test transducer is exposed to a transient thermal radiant-energy

stimulus resulting from the ignition of a photographic flashbulb or

from the discharge of an electronic flash. The method also provides

for monitoring the energy and duration of the transient stimulus.

The selected radiant-energy sources were chosen to satisfy the foregoing requirements, in particular the requirements concerning low

cost, simplicity of operation, and ready reproducibility.

3. DEVELOPMENT OF TEST METHOD

3.1 Background-'

Work had been done previously in the Components and Applications Section

of NBS on the effects of thermal gradients and transients on the perfor- mance of transducers. This work began with a method which generated

relatively slowly changing thermal gradients in pressure transducers by

partially immersing the test transducers in a hot bath [1]*. Subsequently,

a laser-source method was developed for applying thermal radiant-energy

transients to pressure transducers with an exposure time of about one minute [2]. Following this work, a thermal -transient testing method was developed for piezoelectric accelerometers , involving transients with

durations from 1 s to 1 5 s [3]. The experience gained from this earlier

work contributed to the development of the test method described here.

Experimental considerations, including selection of energy sources,

establishment of test parameters, evaluation of method accuracy and

repeatability, as well as the results of the experimental evaluation

of selected transducers, are presented in detail in the following

sect ions

.

3.2 Description of Experimental Arrangement

The experimental arrangement is shown in figure 1 and is as follows:

The flashbulb or flashtube is mounted in a vertical position at the

center of an optical bench. Mounted on the bench, on opposite sides

of the energy source, are an energy meter and the transducer mounting

fixture. The diaphragm of the mounted pressure transducer and the

sensing element of the energy meter are aligned with, and equidistant

from, the center of the flash unit. The energy meter and transducer

Figures in brackets indicate literature references listed in

Section 7.
may be moved along the bench to vary the respective distances between

them and the flash unit, which is held fixed. Also fixed in position

is a photodiode mounted at right angles 35 cm from the bench center

and used as a flash output monitor to check the operation of the energy

meter. All four elements are positioned to lie in the same horizontal

plane.

In a test, the quantities monitored are as follows: (1) the pressuretransducer output, displayed on an oscilloscope; (2) the digital reading of the energy meter (which displays pulse energy in joules, as intercepted by the 1-cm2 area of sensing element); (3) the energy-meter

output, displayed on an oscilloscope (with peak amplitude proportional

to the total pulse energy incident on the sensing element); and (k) the

photodiode output, also displayed on an oscilloscope. If the transducer

is at atmospheric ambient pressure at the beginning of the test, transducer output is identical to zero shift.

3.3 Description of Apparatus

Z.Z.I Energy Sources - Four sources were used in the investigations:

an electronic flash at an energy setting of 150 J, No. 5 flashbulbs,

No. 22 flashbulbs, and flood-flash FF-33 bulbs. The original plan of

experiment also included the electronic flash at 50 J; however, these

runs were dropped from the schedule because, even at the 1 50- J setting,

the zero shift in the selected test transducer output in response to

thermal radiant-energy transients from the electronic flash was small

compared to the zero shifts resulting from the flashbulb source.

Z.Z.1.1 The No. 5 and No. 22 flashbulbs are readily available from

photographic supply houses; the FF-33 bulb was designed for use in

automotive crash photography and can be purchased directly from the

manufacturer. According to the manufacturers, the amplitude-time

waveform of the radiation output from all three bulbs is roughly

triangular in shape. This waveshape was confirmed by trials with the

No. 5 and No. 22 flashbulbs, but not with the FF-33 (section 3. /+. lt.2).

Characteristics of the three flashbulbs are given in table 1, which

is derived from manufacturers 1 literature.

The manufacturers of the No. 5 and No. 22 flashbulbs provide the

following information concerning (l) light-output repeatability and

(2) spectral distribution of energy: (1) Assuming that the specified

excitation is supplied in each case, the population mean of measurements

of the light output (measured with an integrating sphere or equivalent

method) should fall within 10% of the manufacturer's published lightoutput value, with a confidence level of 95%. Experimental measurements

of repeatability tend to agree with this statement, but are themselves

subject to the variability in performance of the energy meter used to

make the measurements (section 3.^.^.1). (2) The spectral distribution

of energy closely approximates that predicted by the Wien Law over the

wavelength range of approximately 350 to 650 nm. At wavelengths longer

than about 650 nm, the spectral energy distribution curve for the flashbulbs diverges upward from the Wien-Law curve; information is not
available for wavelengths shorter than 350 nm or longer than about

750 nm. Note: The exact spectral energy distribution for flashbulb

sources depends on the combustible material, the oxygen fill pressure

(most modern flashbulbs burn aluminum in pure oxygen), and the absorption characteristics of the envelope. The flame emission lines of

aluminum are available in the literature; the other information is

proprietary.

Repeatability and spectral information were not sought for the FF-33

bulbs, as trials showed these bulbs to be unsatisfactory sources for

this application for a variety of reasons (section 3-4. 4.2).

3.3.S.2 The electronic flash system consists of a xenon-filled flash

tube, a capacitor bank, a power supply, and other associated electronic

components including a triggering circuit. In use, the capacitor bank

is charged by the power supply to approximately 450 V dc; the bank is

then discharged through the flash tube by applying a trigger pulse

to the gate of a silicon-controlled rectifier by means of a mechanical

switch.

The system used can operate at one of two energy levels, either 50 or

150 J. In the 1 50- J mode, the peak intensity of the light is only

slightly increased over the 50-J mode, but the capacitor discharge

time is extended. The rise time is about 0.3 ms for both the 50- and

1 50-J positions, but the fall time to about 10% of the peak value is

about 6 ms and 10 ms, respectively.

A repeatability figure is not available for the flashtube used in the

electronic flash or for the performance of the flash system as a whole.

Flashtube light output depends on physical dimensions, on energy input, on the operating voltage, and on xenon fill pressure. A representative

for the manufacturer of the system stated that variations in flash-toflash output under the operating conditions specified in the instruction

manual should be significantly smaller than those which would adversely

affect photographic results with available general -purpose films, including low-exposure-latitude color films. This statement is interpreted

to mean that the flash-to-flash variation is perhaps of the order of

ten percent, or possibly less. As with the No. 5 and No. 22 flashbulbs,

the experimental measurements tend to confirm this figure, but are subject to the variations in performance of the energy meter (section

3.4.4.1).

The manufacturer of the electronic flash system describes the color

content of the light as very closely resembling that of daylight. The

spectral distribution of energy for a flashtube depends on the operating

voltage, as well as on the fill gas and envelope material. Typical

manufacturer's data show that the relative energy per 100-nm step is

approximately constant from 400 to 800 nm. At wavelengths greater than

800 nm, the operating voltage has a large inverse effect, with a 500-V
tube producing on the order of half again as much energy as a 2000-V

tube. Specific spectral-energy-distribution data for the flashtube

used are not available from the manufacturer.

3.3.2 Energy Meter - The following information is abstracted from

the manufacturer's instruction manual: The energy meter consists of

a pyroelectric detector and associated signal-processing and display

electronics. The pyroelectric detector is a slice of ferroelectric

material which possesses a permanent electric polarization that is

highly temperature dependent. As radiant energy is absorbed by the

detector coating, a current is generated that is proportional to

the t ime-rate-of-change of the temperature of the ferroelectric

material. This current is integrated by a preamplifier and produces

an output that can be displayed on an oscilloscope. The peak amplitude of the preamplifier output waveform is proportional to the energy

content of the radiation pulse incident on the detector. The readout

circuitry measures the peak amplitude of the preamplifier output,

computes a scale factor, and displays the result digitally in the

proper units (joules).

The meter is provided with two modes of triggering. In the auto-trigger

mode, the instrument is triggered when the energy absorbed by the

detector is greater than 5% of full scale; in the external -trigger

mode, a positive-going trigger pulse ranging in amplitude from 5 V to

100 V must be supplied coincident with the radiation pulse to be

measured. The meter, with four-digit readout, is intended to measure

the total energy content of radiation pulses with durations ranging

from less than 1 ns to to a maximum of 50 ms . This range of pulse

durations represents a modification of the standard meter, which

covers a 1-ns to 1 -ms range.

Seven ranges are provided which are switch selectable, with full-scale

readings progressing in six decade steps from 2 uJ to 200 mJ , in addition to a 1-J position. In all cases, the reading represents the

energy absorbed by the 1 -cm

2 area of the detector.

The response of the pyroelectric detector is described as being flat

to within ±2% in the wavelength range of 400 nm to 20 urn. Manufacturer's

literature describes the overall system accuracy as ±k% of reading ±1%

of the full-scale reading when the sensing area is fully illuminated.

Least count is typically 0.05% of the full-scale reading. Maximum

noise level is given as 0.3 uJ

.

The meter was calibrated by C.A. Hamilton of the NBS Boulder Laboratories by comparing its measurements of laser pulse energy with those

of a calibrated pyroelectric radiometer. The overall result was that

the meter performed to specification. The calibration procedure

requires the use of a beam with a diameter much smaller than that of

the detection element of the meter; therefore, scars were made to

determine the degree of uniformity of response over the detector surface. The estimated uniformity error is ±1%, and is greatest with
short pulses. For the geometry used in the method, this error will

not affect repeatability of the energy measurement. Uniformity

error does contribute to the overall figures given by the manufacturer for the accuracy of the instrument for various ranges. A

test was also made to determine if the time delay between the trigger

and a short pulse (l ms) had an effect on meter reading, with negative results over a range of delays of to more than 50 ms.

3.3.3 Transducer Mounting Fixture - The transducer mounting fixture

used is a rectangular brass block approximately 10-cm high, 10-cm

wide, and 6-cm deep, and is purposely made massive to serve as a heat sink, with a mass of about 5 kg. A 3.8-cm bore extends through

the block, centered on the front face (the face towards the flash

unit). A round glass window with an aperture of 3 cm and a thickness

of approximately 0.6 cm is sealed into the bore at the front face.

The window glass is of a 96%-silica composition with a low coefficient

of expansion. The effect on the test of this window is discussed in

3-5.5. The transducer to be tested is mounted in a brass flange; an air-tight seal to the bore is made by means of an ring between the

flange and the bjock. The flange is mounted to the block with six

bolts. This arrangement is similar to the way in which transducers

are mounted in typical applications.

A hole connecting with the bore permits pressure or vacuum to be

applied to the volume between the transducer and window. Thus,

the pressure the transducer sees during the test may be preselected.

3.3.4 Photodiode - The n-p-n planar silicon phototransi stor selected

may be used in either the phototrans i stor mode or the photodiode mode

of operation; in all tests described in this report, the photodiode

mode was used. The manufacturer gives the rise time and fall time as typically 350 ns and 500 ns, respectively. The output collector

current is linear with irradiance from to 80 mW • cm" 2

. The

spectral response is near zero at 0.5 ym, rises to a maximum at

about 0.9 ym, and returns to near zero at 1.1 ym. A supply voltage

of up to 50 V dc may be used in the photodiode circuit.

3.^ Experiments to Determine Method Parameters

3.4.1 Investigation of Energy Available as a Function of Distance - The change in measured intensity (amount of energy per unit area) as

a function of distance from the flash source was studied using the

epxerimental arrangement described in 2.1. Four sources were used

in the investigation: electronic flash at 1 50 J, No. 5 flashbulbs,

No. 22 flashbulbs, and flood-flash FF-33 bulbs. Since the flash

duration of the FF-33 bulb is much greater (by a factor between 60

and 300) than that of the other flash sources, tests with the FF-33

bulbs required modifications of the method and are described

separately in 3-^.1.2.
3.4.1.1 Distance from the center plane of the flashbulb source to

the energy-meter sensor (and consequently the distance from the source

to the test transducer diaphragm, for the investigation described in

3.^.2) was varied in 1 -cm steps over the range of 6 cm to 23 cm for

runs with both No. 5 and No. 22 flashbulbs. The dimensions of the

electronic-flash head and the relatively low energy levels available

even at the 1 50- J setting determined a smaller practical range of

distances for runs with this system. The minimum distance was limited

to 7.5 cm; at 15 cm the test transducer zero shift (which was also

measured, as described in 3.^.2) was about one-half of one percent of

the full-scale output, and accordingly 15 cm was chosen as the upper

limit for tests with the electronic flash. Steps of 0.5 cm were used

in order to provide approximately the same number of data points as

for tests with flashbulb sources.

The results from this series of tests are shown plotted as energymeter reading (mJ • cm" 2

) vs separation (cm) in figure 2. Energy-meter

reading is plotted on a logarithmic scale. Separation refers to the

distance from the center plane of the source to the energy-meter sensor. The data-point plots A, B, and D fall along curves whose form is similar

to that of an inverse-square relation; for comparison an arbitrary

inverse-square plot is given (dashed curve C) . The classical inversesquare relation of intensity vs distance for a point source of radiation does not strictly apply to the extended sources of these tests,

particularly at the relatively short distances between the source and

the sensor. Small deviations of experimental points from the smooth curves probably result from variations both in source energy and in

the performance of the energy meter. These deviations do not exceed

10% of the energy-meter reading.

The maximum intensity levels were measured at the minimum source- sensor distances, which, for both flashbulb sources and for electronic

flash, were limited by source and mounting-fixture dimensions. Maximum

levels of about 0.1, 0.8, and 2.2 J • cm

-2 were measured for the

electronic flash at 150 J, No. 5 flashbulbs, and No. 22 flashbulbs,

respectively.

3.4.1.2 Tests using the flood-flash FF-33 bulbs were carried out in a similar fashion to those described for the short-duration sources,

with the following exceptions: (1) a power meter, calibrated in watts,

was substituted for the energy meter, because the energy meter is not

capable of reading energy pulses with a duration greater than 50 ms

.

The maximum output of the power meter was read visually on a panel

meter "on the fly." That is, the operator was required to estimate

the maximum upward excursion of the (relatively slowly moving) meter

pointer. Output from the power meter was also displayed on an oscilloscope. (2) Tests were run In 1-cm increments from 8 cm to 15 cm; the size of the FF-33 bulbs prevented tests at source-sensor distances

less than 8 cm, and the low energy level (as determined by transducer
response) suggested 15 cm as a good termination point, as was the case

for measurements with the electronic flash at 150 J. The data from

these tests also follow an inverse-square relation.

3.4.2 Investigation of Transducer Zero Shift as a Function of distance -

In the measured intens i ty-vs-d istance tests described in 3.4.1.1, the zero shift of a pressure transducer located on the opposite side of the

radiation source from the energy meter was monitored with an oscilloscope,

For tests at ambient atmospheric pressure, any transducer output is

regarded as zero shift. The transducer used in these tests is a semiconductor strain-gage pressure type and is designated in this report as transducer Z*.

These measurements were made to assist the development of the method by

providing information on the zero shifts exhibited by a transducer

selected as being typical of a modern design in widespread use, and

were not made to characterize the particular transducer so chosen.

The results from this series of tests are shown plotted as transducer

zero shift {% of full scale) vs separation (cm) in figure 3. Transducer

zero shift is plotted on a logarithmic scale. Separation refers to the

distance from the center plane of the source to the transducer diaphragm.

The data-point plots A, B, and D fall along curves whose form is similar

to that of an inverse-square relation. An arbitrary inverse-square

relation is again plotted (dashed curve C) for comparison.

Table 2 shows test transducer zero shift (mV) and energy-meter reading

(mJ • cm" 2

) for three sources (No. 5 and No. 22 flashbulbs and electronic

flash at 150 J) at three selected distances: 8, 10, and 14 cm. The

table also includes the computed radiation sensitivity (defined as the

ratio of the transducer zero shift to the energy-meter reading, with

units of V • cm

2

• J" 1 ) for the three sources at the three distances,

for transducer Z.

Another measure, which permits direct comparison of zero shifts for

transducers with differing full-scale outputs, is percent full-scale

output radiation sensitivity (%FS • cm

2

• mJ" ). Using as a basis the

value of the radiation sensitivities for 8, 10, and 14 cm (0.12, 0.14,

and 0.15 V ' cm

2

• J" 1 for electronic flash at 150 J, for No. 5 flashbulbs, and for No. 22 flashbulbs, respectively) and transducer Z fullscale output of 500 mV, percent full-scale radiation sensitivities for

the three sources are 0.024, 0.028, and 0.030 %VS • cm

2

• mJ" 1

, for

transducer Z.

As may be seen by examination of the data just presented, radiation

sensitivity of transducer Z increases about 17% for the No. 5 flashbulb source as compared to the electronic flash; there is a further

In the progress report covering the period October 1, 1974 to

December 31, 1974 (NBSIR 75"732) this transducer was identified

as transducer D. 10
increase of about 1% for the No. 22 flashbulb source. An explanation

of this situation may lie in the relative sizes of the light-emitting

elements in each source. The diameter of the circular tube in which

the capacitive discharge takes place in the electronic flash is about

2 cm; the diameter of the combustible filler in the flashbulbs is

about 3.5 cm for the No. 5 flashbulbs and about 5 cm for the No. 22

flashbulbs. As the light-emitting element becomes large, an increasingly greater proportion of the energy radiating from the outer

portions of the element will not reach the energy-meter sensor but

will be intercepted by the 2.2-cm-long collimating shroud which shields

it; on the other hand, the transducer test fixture does not shield the

pressure-sensitive element except for very large angles of incidence.

Therefore, for sources with light-emitting elements greater than a few

millimeters, the transducer sees more than the sensor.

Figure k consists of three photographs of oscilloscope traces of

transducer zero shift in response to thermal radiant-energy transients

from the three sources. The source-to-transducer distance was 10 cm.

In all cases, the duration of the transducer zero-shift response is

much longer than that of the thermal -trans ient stimulus causing it.

The zero-shift for electronic flash rises to approximately half the

peak value in approximately 20 ms after the onset of the thermal

radiant-energy transient and reaches its maximum at approximately

50 ms. For the No. 5 and No. 22 flashbulbs, the transducer zero

shift peaks after about 115 ms and 130 ms, respectively. Comparison

of figures k and 6 shows that the shape of the zero-shift response of

transducer Z for the sources used is largely independent of the thermal

radiant-energy transient waveshape.

Measurements of transducer Z zero shift were also made during the tests

described in 3.^.1.2 with FF-33 bulbs as sources. The data are given

in table 3, and follow an inverse-square relation of zero shift with

source-transducer distance.

The bottom photograph of figure 5 shows an oscilloscope trace of transducer Z zero shift in response to a thermal radiant-energy transient

from an FF-33 bulb at 12 cm. The upper photograph of figure 5 shows

oscilloscope traces of the analog output from the power meter (thick

trace) and the photodiode output (thin trace) for the same conditions.

In contrast with transducer zero-shift behavior in response to shortduration transients, the duration of zero shift and thermal -transient

stimulus are approximately the same, and the waveshape of power- meter

output and transducer zero shift are similar, with a rise time to

maximum of approximately 1 s. The photodiode response is discussed

in 3. A. 3.

Although the data for transducer Z zero shift as a function of the

distance between the center plane of the FF~33 source and the transducer diaphragm follow an inverse-square relation, the calculated

11
rad iat fcon sen-si t ivi ties; exhibi ti erratic 'behavior. J "Ah' expl anat4dhhas been? proposed .to account ! for' the effect: Examination of figure k

shows that' the -time- from onset of the thermal transient until the zero shift reaches, »it'S rmaxi mum value Is on the order of 100 ms, 'that

is, transducer?!- has ahieffective thermal time constant of approximately

100 ms . The thermal energy from transients wi th durations considerably

shorter than 100 ms is absorbed by the transducer, and no significant

conductive heat' loss occurs unt 1 1 after the 100-ms 'per iod . This state- : ment is ' rn ipart conf i rmed<-experimentaTly by the results with the- No. 5 and No* 22 flashbulbs and the electronic flash at 150 J, all of which

produce ;trans ients with durations less than kO ms'. The duration of the

thermal transient resulting 'from ignition of the FF-33 bulb is greater

than : 2-sv This 'very long durat ion compared to the transducer thermal

time ^constant ,'permi t-s an appreciable amount of the absorbed energy to

be lost by conduction "to the massive brass block which forms the

mount ing flxtiiirev.

; <; • ,.;'HThe FF-33" bulbs did not prove to be a satisfactory source for the

method (section 3.^.^.2) and no experimental work was carried out

relating'to the behavior descri bed.

It has been shown at the beginning of this section that zero response

of transducer Zas a function of source-transducer distance follows an inverse-square relation and in 3.^.1 that energy-meter reading as a function of source-meter distance also has an inverse-square form.

Therefore, transducer Z zero shift varies as a linear function of the

energy impinging upon the transducer. To investigate the same function for other -transducers , tests were conducted using No. 22 flashbulbs as the source at source-transducer distances of 14, 9 • 9 , and 7 cm. These di stances were chosen to produce a 'doubling of energy with

each reduction of distance. Three transducers (B, M, and Q) of

different types were evaluated, along with transducer Z as a control.

Three tests' were run at each distance with each transducer.

The res-u-1 ts are given in table k. Transducers M, 0, and Z all exhibit ' the anticipated doubling of zero shift as the source-transducer distance is reduced from ]h to 9-9 cm and from S-3 to 7.0 cm, within

experimental error. Transducer B, however, does not exhibit doubling,

the factor being 1.6 for the first distance reduction and ] .k for thesecond. The explanation probably lies in the fact that M, 0_, and Z are flush-diaphragm transducers, whereas the diaphragm of transducer B' is recessed-2.2 cm from the front surface. The diaphragm is thus

shrouded by the transducer structure, and as the source-transducer

distance is reduced, an increasingly greater proportion of the source energy is blocked from reaching the diaphragm. The geometry of the

situation is akin to that discussed earlier in this section for the

energy meter when the source is close to the meter sensor.

3.4: 3- Investigation of Flash Source -Duration and Waveform - As described

in 3 - 3 > a photodiode was used in conjunction with the energy meter to

monitor the radiation emitted by the flash source. This photosensitive

12
semiconductor component was actually a silicon phototransts tor connected as a diode with a response time "better than I lis" over a wavelength range of 0.5 to 1.1 urn, according to the manufacturer.

The output from the diode displayed on an oscilloscope screen provided the approximate shape of the radiant thermal transient as well

as a measure of its amplitude.

Figure 6 consists of three photographs of osci 1 loscope traces of

photodiode output in response to thermal radiant -energy transients

from the electronic flash at 150 J, a No. 5 flashbulb, and a No, 22

flashbulb. The sweep time for each photograph was 50 ms, and the

amplitude scale 2 V per division. Comparison of the photographs shows

that the diode output waveform for the electronic-flash source has a sharp rise time (less than 0.2 ms measured with the oscilloscope set

to a fast sweep) and a slower decay of about 6 ms to drop to 10% of

its peak amplitude. The transients generated by the two flashbulb

types are more nearly symmetrical in rise and fall time. Rise times,

from 10% of the peak amplitude to the peak, are about 9 ms for No. 5

flashbulbs and about 13 ms for No. 22 flashbulbs. Decay times are respectively 20 ms and 2h ms. The total duration of the thermal

radiant-energy transients generated by these devices as measured by

the diode is therefore roughly 6 ms for the electronic flash at 150

J, 29 ms for No. 5 flashbulbs, and 37 ms for No. 22 flashbulbs.

The photodiode trace for an FF-33 bulb shown in the upper photograph

of figure 5 is characterized by a number of high-amplitude spikes, as

well as longer duration fluctuations of considerable amplitude (on

the order of 25% of the maximum). These phenomena are presumed to

result from erratic burning of the FF-33 bulb and were seen in all

photodiode traces for FF-33 bulbs. Their presence makes scaling

difficult.

3.4.4 Investigation of Test Method Repeatability - A series of tests was carried out to determine the repeatability of the test method with

transducer Z as the test transducer. Because of the modifications of

the method required for use of the FF-33 bulb as source, results of ,r tests with long-duration flash are reported separately in 3*4.4,2.

3.4.4.1 The results of tests with No. 5 and No. 22 flashbulbs and

electronic flash at 150 J are plotted in figures 7, 8, end ?, which

show the deviation in percent from a ten-shot average of transducer

zero shift, energy-meter response (digital reading), energy-sensor

output (analog signal available from the energy meter for which peak

amplitude is proportional to energy input), and photodiode output for

each of the three test sources.

As described in 3.2, the outputs of the photodiode, the energy sensor,

and the transducer under test were displayed on an oscilloscope and

measured; the digital output displayed by the energy meter was recorded.

The pressure seen by the pressure transducer at the beginning of each

run was atmospheric ambient.

13
The distance between the center plane of the flash source and the

transducer diaphragm was 7.5 cm for the electronic flash, 10 cm for

the No. 5 flashbulbs, and 12 cm for the No. 22 flashbulbs. These

distances were not arbitrarily selected. The minimum source-transducer

distance of 7.5 cm for the electronic flash was used because this source is relatively weak. The original intent was to use the same distance of 10 cm for the two flashbulb sources. However, the intensity of the No. 22 flashbulbs at 10 cm was at or above the energy

meter's upper limit of 1 J • cm" 2

, and the slightly greater distance

of 12 cm was therefore used for this source. (An attenuating screen

was available for use with the energy meter. Uncertainties of calibration associated with its use suggested that a direct measurement

should be employed for the repeatability study.)

Table 5 presents a summary of the data given in the figures. Sample

averages, maximum upper and lower percent deviations from the average,

and sample standard deviations are given for energy-meter readings,

photodiode output, and transducer Z zero shift.

Examination of the data presented in figures 8 and 9 for the flashbulb

sources shows that the maximum deviations for the four quantities

plotted fall within ±15% of the ten-shot average values. Examination

of the data presented in figure 7 for the single electronic-flash

source used shows that the maximum deviations for the four quantities

plotted fall within ±5% of the ten-shot average values. Coefficients

of variation" of the energy-meter readings based on ten shots are 2.3%

for electronic flash at 150 J, 3.6% for No. 5 flashbulbs, and 6.5% for

No. 22 flashbulbs. The corresponding coefficients of variation for

measured transducer zero shift are 1.1%, 6.6%, and 5.2%. The shot-toshot repeatability with a single electronic-flash system as the source

is thus seen to be greater than that for flashbulb sources. One

electronic-flash system with one flashlamp was used in the tests;

however, general experience with electronic flash for photography

suggests that shot-to-shot repeatability for a properly designed and

used (see 3-5.1) single unit can be superior to that for flashbulbs.

A detailed comparison of the plots A, B, and C in figures 8 and 9

provides the basis for some tentative conclusions; no such basis

results from examining figure 7, as the fluctuations do not correlate

(although the magnitude of the fluctuations is only a little greater

than that of the measurement errors expected). The same remark applies

to the plots of photodiode output, data points D. As expected, the

plots of the digital reading of the energy meter (data points B) and

the energy-meter output (data points C) are in reasonable agreement

in both magnitude and direction of change.

A comparison of B or C with A of figure 8 shows agreement in the

direction of change for test 2 to test 3, 3 to-"it, k to 5, 5 to 6,

The coefficient of variation is defined as the ratio of the

sample standard deviation to the sample mean, expressed as a percentage.

14
6 to 7, and 9 to 10. The same comparison with the plots of figure 9

shows similar agreement for 2 to 3, A to 5, 5 to 6, 6 to 7, 7 to 8,

8 to 9, and 9 to 10. A possible explanation for the discrepancies

lies in the fact that the energy output from the source may vary in

azimuth and hence the transducer under test and the energy meter may

"see" comparatively different energy levels for the same test run. The manufacturers have confirmed that a specific azimuthal variation

in flashbulb output is known to exist because of the orientation of

the igniter element.

Used flashbulbs were collected for safe disposal. Following the com- pletion of experimental work, dark spots were observed on a number of

No. 22 bulbs. Investigation showed that a blackened area was present

on most used No. 22 bulbs, and that a somewhat lighter darkened area

could be found on most used No. 5 bulbs. For both types, the darkened

areas always occur in the opposite direction from that in which the

ignition electrodes point. (The electrodes in the No. 22 bulb extend

side-by-side vertically upward from the base of the tube except for

the last half centimeter, which is bent to be at an angle of about

60° to the vertical portion; the construction of the No. 5 bulb is

similar.) The construction of flood-flash FF-33 bulbs is different

from that of the No. 5 and No. 22 flashbulbs; no patterns were found

on used bulbs of this type.

It is recommended that No. 5 and No. 22 flashbulbs be mounted so that

the area opposite to the direction in which the ignition electrodes

point does not face the transducer or any sensor.

A partial explanation for the lack of correlation of photodiode output

with the energy-meter outputs or with transducer zero shift may lie in

the spectral response characteristics. The energy-meter sensor is

described by the manufacturer as having flat response over the wavelength range 300 nm to 20 urn, whereas the photodiode range is quoted

as 500 nm to 1.1 ym. [Note: The percentage deviations in photodiode

output from a ten-shot average are smaller for the electronic flash

than for the flashbulbs; this aspect is in general agreement with the

behavior of the energy-meter outputs and the transducer zero shift

with respect to the two types of source. Coefficients of variation

based on ten shots for photodiode output are 0.8% for the electronic

flash at 150 J, 5-3% for No. 5 flashbulbs, and 3-8% for No. 22

flashbulbs.] Azimuthal variation of source output may also contribute to the lack of correlation, as may the fact that the photodiode

output as measured represents peak and not total energy.

Because there was some concern that the repeatability measurements

using No. 5 and No. 22 flashbulbs were made on bulbs from a single

lot for each bulb type, an extended series of measurements was made on both No. 5 and No. 22 flashbulbs taken from several lots. In these

tests, only the energy meter was used, and the source-sensor distance

was constant at 7 cm. The sample standard deviation for ^9 No. 5 bulbs

15
is kS mJ * cm

2

, with a sample mean of 60k mJ * cm" 2

. The coefficient

of variation is therefore 7-5%, or about twice that given above. The

tests with No. 22 bulbs at 7 cm required the use of a 16% screen to

reduce the energy impinging on the sensor to acceptable levels.

Because of their greater energy output, No. 22 bulbs are for most

purposes a better source for the method than No. 5, and more No. 22

bulbs were therefore used. The sample standard deviation for 80

No. 22 bulbs is 1 50 mJ • cm

-2

, with a sample mean of 1731 mJ • cm

-2

, and a corresponding coefficient of variation of 8.7%.

3.4.4.2 Repeatability tests with the flood-flash FF-33 bulbs as the

method source were carried out at a source-sensor and source-transducer

distance of 12 cm and consisted of 10 consecutive shots. Transducer Z was the test transducer. The effects of the long duration (about 2 s)

of the FF-33 flash, of the use of a power meter instead of an energy

meter, and especially of the observed erratic burning complicate the

reporting of results. Peak-power levels as determined from the analog

output of the power meter, displayed and photographed on an oscilloscope, show variations of up to 12% below and 18% above the ten-shot

average; the data are given in table 6. Peak-power levels determined

by reading the maximum excursion of the panel meter show variations

of similar magnitude. Peak transducer zero shifts, as determined from

a photographed oscilloscope display, show variations of up to 2k%

below and up to 21% above the ten-shot average. Comparison of transducer Z zero shift with the power-meter output from one shot to

another shows little or no correlation between the two quantities.

An explanation may be that the energy output from the FF-33 bulbs

varies greatly in azimuth, as is suggested by the erratic burning.

As was the case to a much lesser extent with the short-duration sources,

the transducer under test and the sensing meter would "see" different

power levels for the same test run. As described in 3.^.3, the photodiode response to FF-33 bulbs was characterized by the presence of

spikes and other fluctuations, and average levels could not be determined with any reasonable precision. Photodiode measurements were

therefore not useful in repeatability tests with FF-33 bulbs.

Following these tests no further work was carried out with FF-33 bulbs

as the method source. This type is not recommended for this application because It exhibits erratic burning and apparent large variations

in output from one bulb to another, and because it has lower output

and larger size relative to other sources available.

3.5 Other Experimental Investigations

3.5.1 Effect of Supply-Voltage Variation on Electronic-Flash Output - Evaluation of the electronic-flash system as a source for the method

included investigation of the dependence of flash-system performance

on supply voltage when the unit was operated from either the a-c line

or from a battery supply.

16
To measure the effect of a-c line voltage variations on electronicflash energy output, a variable transformer was inserted into the line

ahead of the internal flash power supply, and the radiant-energy output

was measured at selected a-c supply voltages ranging from 110 V to

120 V in 2-V steps. The a-c supply voltage was set with the variable

transformer and measured on a digital multimeter. The flash energy

output was measured with the energy meter and the photodiode; the

corresponding zero shift of transducer Z was also measured. Table 7 shows that the radiant energy available at an a-c supply voltage of

110 V is about 20% less than that at 120 V. The percentage change in

radiant energy is on the order of double the percentage change in

supply voltage causing it. This observation corroborates the recommen- dation that some type of voltage regulation be used in the supply line

to the flash system to ensure consistent flash performance.

The effect of battery voltage variations on electronic-flash energy

output was measured by monitoring the voltage drop across the battery

supply and the radiant-energy output of the flash system during a series of 15 consecutive shots. The voltage decreased from Al9 V to

397 V during the series. The resultant energy output as measured with

the energy meter decreased linearly by approximately 11%, as shown in

table 7- The percentage change in radiant energy is again on the order

of double the percentage change in voltage. The interval between

flashes was two minutes or longer to allow the flash unit to recharge.

Nevertheless, the battery voltage dropped gradually during the test,

indicating that the flash system performance would be more consistent

if the system were operated from a regulated a-c line. It whou 1 d be

noted that the batteries used in these tests had been used for several

hundred shots previously. New batteries would probably produce more

repe-3 table flash energies.

3.5.2 Effect of Various-Sized Apertures on Energy-Meter Reading - Geometrical relationships between the energy-meter sensor, the source,

and the paths followed by radiant energy from source to sensor vary

considerably for the various source-sensor distances and sources used

in the method. Extensions of the method have been proposed using

narrow-angle, high-energy sources. For these reasons, the response of

the energy meter was investigated with various-sized apertures placed

at the front end of the sensor collimating tube. Apertures with diameters of 0.38, 0.53, 0.75, 1.06, 1.50, 2.12, and 3-00 cm were used.

These diameters were chosen so that each aperture has twice the area of

of the next smaller aperture. Three tests with each aperture were

run with a No. 5 flashbulb as source 7 cm from the energy-meter

sensor. The data are plotted in figure 10, which shows energymeter reading as a function of aperture diameter, with energy-meter

reading on a logarithmic scale. The solid line represents a doubling of energy for a doubling of area. The plot shows that the

energy approximately doubles with doubling of the area until a diameter of 1 .06 cm is reached; since the diameter of the energy-meter

17
is 1.15 cm* (vertical dashed line), some roll off below the doubling curve at 1.50, 2.12, and 3.00 cm was to be expected.

3.5.3 Effect of Angle of Incidence on Transducer Besponse - The

response of transducer Z to thermal radiant-energy transients impinging on the diaphragm in directions 30, 60, and 99° from the normal to

the diaphragm was investigated.

It was necessary to remove the transducer mounting plug from the fixture

housing to perform these tests, as the housing would otherwise shield

the transducer from radiation entering the fixture at more than a few

degrees from the normal. A simple mounting pedestal was fabricated

on which the plug and transducer could be rotated about a vertical

axis through the center of the transducer diaphragm surface.

The tests were conducted with the center of the transducer diaphragm

7 cm from the center plane of the No. 5 flashbulb source. Five runs were made at normal incidence and three runs each at 30, 60, and 90°

from the normal. The results are given in table 8.

At 30° from the normal, the zero shift of test transducer Z was 80%

of the zero shift at normal incidence. At 60° from the normal, the zero shift was 56% of that at normal incidence, and at 90°, it was

k%. These figures correspond closely with the projected area of the

transducer diaphragm as seen by the beam of radiation at each angle.

The areas would be 87% of the normal area of 30°, 50% at 60°, and

at 90°.

Comparison of the data of table 8 with data given in tables 9 or 10

shows that the zero shift of transducer Z resulting from ignition of

a No. 5 flashbulb at a source-transducer distance of 7 cm is approximately 18% smaller when the transducer is mounted on the pedestal

described above than when it is mounted in the fixture used in the

method. A probable explanation is that internal reflections in the

mounting fixture increase the total amount of energy incident on the d iaphragm.

3.5.4 Effect of Reflectors on Transducer Response - A brief investigation to determine the gain in energy level that could be achieved

with the use of reflectors behind the energy source showed that by

using reflectors designed for photographic purposes, an increase of

about 18% was achieved with the No. 5 and No. 22 flashbulbs, and

about 3^0% with the electronic flash at 150 J, at a transducersource distance of 7 cm, as shown by the data in table 3.

Energy levels impinging upon transducer Z with and without the

reflectors behind the sources were compared by measuring the

The sensor diameter is also comparable to the diameter of the

diaphragm of the largest transducer tested.

18
resultant zero shift of the transducer. In the tests with No. 5 and

No. 22 flashbulbs mounted vertically as sources, a reflector from a photoflash gun was positioned behind the bulbs. This reflector has a mirror finish, a diameter of Yk.2 cm, and a depth of 3.4 cm. With

the reflector in place, the distance from the center of the bulb to

the reflector surface is approximately 3«7 cm.

The reflector supplied with the electronic flash unit was used with

the electronic flash. This reflector has a satin finish, a diameter

of 13.5 cm, and a depth of 6.8 cm. In use, the flashtube base passes

through the center of the reflector, and the center surface of the tube is

approximately 2.6 cm from the reflector surface.

The use of a reflector, while increasing the level of energy available,

renders energy monitoring difficult, since an energy sensor detector

cannot be located in the normal position on the optical bench. Therefore, the use of a reflector as part of the method is not recommended

unless the greater amount of energy available for a given test is an overriding consideration.

3.5.5 Effect on Method of Energy Lost in Glass Window - The transducer

mounting fixture was designed to permit the transducer to be subjected

to pressures above or below atmospheric pressure during exposure to

thermal radiant energy entering the fixture through a glass window.

The significance of the effect of this glass window on transducer

response was investigated by measuring the zero shift of transducer

Z with and without the window in place. No. 5 flashbulbs, 7 cm from

the transducer, were used in these tests. Table 10 shows that for the

ten shots without the window, the average transducer zero shift was

93.7 mV, and the average energy-meter reading 586.4 mJ • cm

-2

, corresponding to a radiation sensitivity of 0.160 V • cm

2

• J" 1

. With

the window in place in the transducer fixture, the average zero shift

was 89.8 mV and the average energy-meter reading 568.3 mJ • cm" 2

, corresponding to a radiation sensitivity of 0.158 V • cm

2

• J -1

. Adjusting the data for the differences in energy levels shows that the zero shift with the window is only 1.1% less than that without for

transducer Z. Unless a given transducer diaphragm material were

especially sensitive to the effects of radiation of wavelengths absorbed

by the window, this result may be taken to indicate that the presence

of the window will, in general, have no significant effect on the

results of the method.

3. 5. 6 Effect on Method of Increased Air Pressure from Heating - The

possibility existed that the air in the closed volume of the mounting

fixture would itself be heated by energy from the source to a significant degree. This heating would result in an instantaneous change in

air pressure which in turn would be sensed by the test transducer. To

investigate the significance of this effect, three tests were run with

transducers M and Z with the fixture at a vacuum pressure of 3.4 Pa

absolute (25 ym Hg absolute). The results were compared with results

from tests under the same conditions of distance and source, but with

19
the fixture at atmospheric ambient pressure. The data are given in

table 11. No significant difference between the results of the two

sets of tests Is seen. The conclusion may be drawn that any

"pressurizing" effect resulting from the heating of air in the

mounting fixture can be ignored for the purposes of the method.

5.5.7 Effect on Transducer of Exposure to Full-Soale Pressure - A series of 9 tests was run to investigate how transducer output

In response to a thermal transient was affected when the transducer was exposed to pressure above ambient atmospheric in the mounting

fixture. The pressure chosen was the full-scale pressure for the

two transducers used (M and Z) , 3*»5 kPa.

Transducer 2 has been described (3.4.2); it is a semiconductor straingage type and was chosen for this investigation because its zero shift

for the test conditions, other than with the fixture at 3^5 kPa, was

well characterized and positive in direction. Transducer M is a semiconductor st rain-gage type with a metal diaphragm and was also

known to have a positive zero shift. Three tests were made with each

transducer at atmospheric ambient and at 3*»5 kPa, with the tests at

3*»5 kPa first. Tests were run with the transducer diaphragm 7 cm from the center plane of the No. 5 flashbulb source. The data are given In table 11.

As might be expected, the results show that the shift in the response

measured when the transducer is exposed to full-scale pressure is

larger than the zero shift. The differences, however, are small.

For transducer M, the shift at 3^5 kPa is approximately 38% of the

full-scale output (38% FS) , and the zero shift measured immediately

following the test at full-scale pressure is approximately lk% FS.

The corresponding figures for transducer Z are 19% FS and 16% FS,

respectively. These results suggest that for the intended screening

purposes, ambient atmospheric pressure may be specified for the method

at no significant loss in discriminating power compared to tests run at pressures higher than ambient. Special circumstances, such as application of the method to transducers known to have a strongly

enhanced, non-linear pressure response over some part of their rated

range, may require ad hoc treatment.

3.6 Discussion of Uncertainties and Method

3.6,1 Method with Flashbulb Source - The experimental results show

that the No. 22 flashbulb without reflector produces energy levels

of about 2.2 J cm" 2 at the minimum distance of 6 cm between energy

source and test transducer diaphragm and about 1.7 J * cm

-2

at the

recommended distance of 7 cm. The total duration of the thermal

stimulus generated by this bulb is about 37 ms, roughly 30% longer

than that of the No. 5 bulb. The energy level of the No. 22 bulb

is almost three times that of the No. 5 bulb. Repeatability of the

No. 22 bulb is somewhat poorer (coefficient of variation 8.7%) than

that of the No. 5 bulb (coefficient of variation 7.5%).

20
The userof a glass-window in front .of .the :test <tr;a,nsd'tf<3ef?i.deo reaped j ry

the transducer zeroshi.ft by? little .more' than !$&»'! 'TheHQffects J df 5 .U;t: transducer diaphragm ,misalignments "wi tb the ridrmalvaxi a *of 3 Incident! %<

radiat ion fol low the cosine law and thus produce aQ-tierrjor^of xle&s s^it* 1 than 1% with misal ignments .of uprto ii6°i -

- xn ...»

' $>s ?-&£ !*"* ..s^n §fil;?frsra*fc

The manufacturer's statement of the energy-meter accuracy allows a maximum error of ±5% of full-scale, reading at full-scale (less at a less than ful 1 -scale readings) plus an additional error of ±2% of :< ft? reading over the wavelength range of the sensor; O^^to 2*0 ym. fym

Over the wavelength region of interest*, approximately 0:35 : to . s .o

-

0.8 vim, this error will be proportionately less. An -estivmate of,M ..- the overall uncertainty in the energy-meter reading for the purposes

of the method may be taken to be ±5% of the reading.; It .lis likely". • that variations in flashbulb energy output as a function of azimuth,-

angle (angular orientation) are in part the source of, the discrepant"

cies found between photocell output readings and energy-meter readings.

A measure of the limit of the instrumental error involved may be com-- > puted from the square root of the sum of the squares (the root-sum ,, square, or RSS) of the maximum uncertainties observed- for photodiode

and energy-meter readings: ±12% and ±5%, respectively, for measure-^?

ments on the No. 22 flashbulb, yielding a limit of ±13% of the reading,

For the No. 5 flashbulb, the corresponding figures are '±8% ^and ±5&, • i yielding a limit of ±3.h% of the reading. Finally, it is estimated

that the maximum transducer output can be determined to -within ±3%

using the oscilloscope. - .•-,• ns

In summary, it is estimated that with the use of the No. 22. flashbulb'

without reflector, 7 cm from the diaphragm of the test transducer ,, and the sensor of the energy meter, transducer zero shift as a func- . tion of energy level for a flash duration of 37 ms can be determined;

within approximately ±14%.

. v .

3.6.2 Method with Electronic-Flash Source - The experimental results

show that the electronic-flash system at the 1 50- J setting produces

energy levels of 0.1 J -cm"" 2 at a minimum distance of 7-5 cm. The

total duration of the flash from this source is about 6 ms, about, v one-sixth that of the No. 22 bulb; the energy level, correspondingly,

is about 5% that of the No. 22 bulb. The degree of repeatability of

the electronic flash can be better (within ±5% of the average energy

level) than that of the flashbulbs if appropriate precautions in use

are fol lowed.

A disadvantage of electronic-flash systems employing flashtubes such

as the xenon tube is that the energy output is highly dependent on the voltage supply. Variations in line voltage or battery voltage

The introduction of the neutral-density screen was found to introduce no experimentally detectable error.

21
produce a change in energy output proportional for small voltage changes

to double the percentage change in voltage. A voltage regulator is

therefore highly desirable for an a-c line operated electronic-flash

system and is recommended. Other test considerations are the same as those 1 isted in 3.6.1.

In summary, use of the electronic-flash system at 150 J is recommended

only if a shorter-duration transient than that provided by No. 22

flashbulbs is required, or if repeatability requirements are an overriding consideration. For the electronic flash used in this work, it

is estimated that with the flash at 150 J without reflector, 7-5 cm from the diaphragm of the test transducer and the sensor of the energy

meter, transducer zero shift as a function of energy level for a flash

duration of 6 ms can be determined within approximately ±10%. Other

electronic-flash units with significantly greater output are produced

commercially, especially to order, but their usefulness for the purpose

of the method is limited by considerations of size, availability, and

cost.

k. RESULTS OF TESTING TRANSDUCERS USING THE METHOD

The work and results described and discussed in previous sections

have been primarily concerned with the development of the method. In the course of this work, the zero shift of transducer Z as determined

by the method has been well characterized. It is of interest to

investigate by the method the zero shifts of other models of the same

type as that of transducer Z and of other transducer types and to

compare these results.

Accordingly, 25 transducers, including Z as a control, were selected

and tested by the method with a distance of 7 cm" between the transducer diaphragm and the center plane of the No. 22 flashbulb source.

All measurements were made with the transducer exposed to ambient

atmospheric pressure. Each transducer was tested three times, and

an average zero shift computed. These average zero shifts were expressed as a percentage of the transducer full-scale output and are given in table 12, along with a brief indication of transducer

type, range, pressure equivalent to the zero shift, and percent fullscale radiation sensitivity. The average zero shifts ranged from

about 0.h% of full-scale output for transducer S to 430% of full-scale

output for transducer N. The semiconductor strain-gage transducers as

a class exhibited the greatest vulnerability of any transducer type

to the thermal radiant-energy transients produced in the method.

This distance is convenient for the No. 22 flashbulb. The energy

levels available at the transducer diaphragm are considerable

(approximately 1 .7 J • cm

-2

) and there is good access to flashbulb

and mounting fixture.

22
5. CONCLUSIONS AND RESULTS

5.1 Concerning the Test Method

The experimental work has resulted in a simple, practical method for

evaluating the effect of thermal radiant-energy transients on pressure

transducer performance. The method is most suitable for flushdiaphragm transducers. The use of commercial flashbulbs as the energy

source provides a short-duration test (about 37 ms for the No. 22 bulb)

at moderate energy-density levels (up to 2.2 J • cm

-2

). Use of an electronic-flash source results in a test of considerably shorter

duration (about 7 ms) at somewhat lower energy-density levels (up to

0.1 J • cm

-2

). The estimated repeatability of the method, within

±\k% with the flashbulb source and within ±10% with the electronicflash source, appears to be adequate for the intended initial screening purposes and may be suitable for certain data-correction purposes

as wel 1 .

The method is easy to implement, requires only a moderate amount of

equipment, and produces data quickly. The energy levels generated are

large enough to produce significant zero shifts in a selection of transducers, as shown in table 12. The magnitudes of the transients produced

in the method are large enough to be comparable to the short-term thermal

environments of some applications, as the following example shows: The

time average of the energy levels generated during a run with a No. 22

bulb at a source-sensor distance of 7 cm yields a power level of approximately 1.2 x 10

6 W • m~2

, if the waveshape is assumed to be triangular

over the 37~ms duration. A corresponding figure for the electronic

flash is 0.3 x 10 W • m~

2

. Heat transfer rates in common types of

rocket engine are reported to range from 3 x 1 6 to k x 1 7 W • m~

2

. [The laser-source method mentioned in 3-1 produced a heat transfer

rate of about 1 x 10 6 W • m~

2 .]

5.2 Concerning the Transducer Tests

The transducers tested were composed of strain-gage types (7 models)

and piezoelectric crystal types (3 models). Each strain-gage transducer had the same full-scale range of to 3^5 kPa (o to 50 psig).

All transducers had been calibrated prior to this program to assure

that they were functioning according to specification. Of the straingage types, two models had metallic strain gages; the other five used

semiconductor strain gages. The intent of the test program was to

test several samples of each model; cost and procurement time precluded

this for the transducer types represented by transducers I, M, and Z.

The main purpose of the transducer testing program was to demonstrate

the thermal transient test method by applying it to a variety of types

of pressure transducer. No attempt was made to sample the entire field

of pressure transducers, nor was a statistically thorough sampling of

each type contemplated. A secondary purpose of the transducer testing

23
program was to obtain a rough survey of the magnitudes of zero shift

likely to be encountered with commonly used transducers in measurement environments with thermal transients present. This information

is reported in section k.

Examination of the data given in table 12 shows that for some transducer models, there is good agreement between the average zero shifts.

This statement particularly applies to transducers A, B, C, and D,

with a maximum deviation from the average zero shift for that model

(expressed as percent of the full-scale output) of \k% and to transducers E, F, G, and H, with a maximum deviation of 11.9%- These

results also appear to validate the capability of the test method to

produce meaningful results.

There was less consistency in the results for other types between

transducers of the same model; in addition, the zero shift in some cases showed two peaks; a positive peak followed by a negative one.

In the case of transducers N, 0, and P, and S, T, and U, this doublepeak response may result from the multiple-layer construction of the

sensor. This type of construction could be expected to undergo a complex series of differential thermal expansions and other related

changes in response to thermal transients.

In general, semiconductor strain-gage pressure transducers exhibited

larger zero shifts than the other types of transducers tested. Within

the semiconductor transducers, the largest zero shift occurred in

transducers with strain gages diffused into a silicon diaphragm (such

as transducers M, N, 0, and P) . Transducers which had semiconductor

strain gages bonded to a metal diaphragm (such as transducers A, B, C,

D, and Z) exhibited smaller zero shifts than did the diffused straingage transducers. The smallest zero shifts were measured for transducers with semiconductor strain gages mounted on an auxiliary beam

connected to the diaphragm by means of a push rod (such as transducers

E, F, G, and H) .

In the group of 25 transducers tested, zero shifts ranged from 0.k% to

about h30% of the full-scale output, a substantial spread that demonstrates the need for a screening method of this type.

6. RECOMMENDATIONS

Many transducers are currently used in thermal -trans ient environments

with little user awareness of the resultant potentially large measurement errors. The test method developed and described here is strongly

recommended for the screening of all pressure transducers that are to

be used in such environments.

Tests of various schemes and techniques for mitigating the effects of

thermal transients, such as protective baffles and coatings, can in

principle be carried out with the aid of this test method. It is

24
likely, however, that the evaluation of effective protection schemes

will require thermal -trans ient inputs of greater energy than are presently available. An extension of this work with the aim of

investigating potential sources of such inputs is recommended.

7. REFERENCES

[1] Horn, L., Thermal Gradient Effects on Thirteen Flush Mounted

Pressure Transducers, NBS Tech. Note *»90 (August 1969).

[2] Lederer, P. S., and Hilten, J. S., A Laser Technique for

Investigating the Effects of Thermal Transients on Pressure

Transducer Performance Characteristics, NBS Tech. Note 723 (May

1972).

[3] Vezzetti, C. F., and Lederer, P. S. , An Experimental Technique

for the Evaluation of Thermal Transient Effects of Piezoelectric

Accel erometers, NBS Tech. Note 855 (January, 1975).

8. ACKNOWLEDGEMENTS

Kurt Muhlberg designed and constructed most of the mechanical portions

of the test set-up. Clark Hamilton provided a calibration check of

the energy meter.

25
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I"1000

cs

uj 100—

cs

10 12 14 16 18 20 22

SEPARATION (cm)

Figure 2, Energy-meter reading as a function of separation, i.e.,

distance from the center plane of the source to the

energy meter sensor, tnergy-meter reading is plotted

on a logarithmic scale. data points a refer to ijo. 22

flashbulbs, data points b refer to no, 5 flashbulbs,

and data points d refer to the electronic flash at

150 J. Curve C is a plot of an arbitrary inverse-square

RELATION FOR COMPARISON.

27
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SEPARATION (cm)

Figure 3: Transducer Z zero shift expressed as percent of

THE FULL-SCALE READING AS A FUNCTION OF SEPARATION, I.E./ DISTANCE FROM THE CENTER PLANE OF

THE SOURCE TO THE ENERGY-METER SENSOR, TRANSDUCER

ZERO SHIFT IS PLOTTED ON A LOGARITHMIC SCALE.

Data points A refer to No. 22 flashbulbs, data

points B refer to No, 5 flashbulbs, and data points

D refer to the electronic flash at 150 J, Curve C

IS A PLOT OF AN ARBITRARY INVERSE-SQUARE RELATION

FOR COMPARISON.

28
• - / N

+4+4- +444- 4+44- 4+44- 4+4+ 4+44- +444- +444- +444- •44+4"

f= T |

- -•—h^

Figure 4: Oscilloscope traces showing transducer Z zero SHIFT IN RESPONSE TO THERMAL RADIANT-ENERGY

TRANSIENTS FROM (TOP) THE ELECTRONIC FLASH AT

150 J, (center) a No, 5 flashbulb, and (bottom)

A No. 22 FLASHBULB, THE SOURCE-TO-TRANSDUCER

DISTANCE WAS 10 CM, THE SWEEP TIME FOR EACH

PHOTOGRAPH WAS 200 MS, AND THE AMPLITUDE SCALE,

25 MV PER DIVISION (CORRESPONDING TO 5% OF THE

FULL-SCALE OUTPUT PER DIVISION).

29
Figure 5. Response of power meter, photodiode, and transducer Z TO RADIATION FROM FF~33 FLASHBULBS, THE

DISTANCE from the center plane of the flashbulb

to the power-meter sensor and to the transducer

DIAPHRAGM WAS 12 CM, In BOTH OSCILLOSCOPE-TRACE

PHOTOGRAPHS, THE TIME SCALE IS 500 MS PER HORIZONTAL division, The top photograph shows analog

OUTPUT OF THE POWER METER (THICK TRACE) AND OUTPUT OF THE PHOTODIODE (THIN TRACE) . , THE BOTTOM

PHOTOGRAPH SHOWS TRANSDUCER Z ZERO SHIFT. THE

MAXIMUM SHIFT SHOWN CORRESPONDS TO 9,7% OF THE

FULL-SCALE OUTPUT,

30
Figure 6: Oscilloscope traces showing photodiode output in

response to thermal radiant-energy transients

from (top) the electronic flash at 150 j/ (center)

a no. 5 flashbulb/ and (bottom) a no . 22 flashBULB. The sweep time for each photograph was

50 MS/ AND THE AMPLITUDE SCALE/ 2 V PER DIVISION.

31
10 _ I I I I I A

I I I

I l_ _

— -10J

__ O—

^^^

+1 1 _

i- "10

1/5 +10

i "

-101—

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-10 I

J

I I I I

1 234 56789 10

TEST NUMBER

Figure 7: Repeatability of test method using electronic flash

at 150 J as source. Shown is percent deviation

FROM A TEN-SHOT AVERAGE FOR THE QUANTITIES (A)

TRANSDUCER Z ZERO SHIFT, (B) ENERGY-METER RESPONSE/

(C) ENERGY-SENSOR OUTPUT, AND (D) PHOTODIODE OUTPUT, THE DISTANCE BETWEEN THE CENTER PLANE OF THE

FLASH SOURCE AND THE TRANSDUCER DIAPHRAGM WAS 7,5 CM.

32
3 4 5 6 7

TEST NUMBER

8 9 10

Figure 8: Repeatability of test method using No, 5 flashbulbs

as source. Shown is percent deviation from a tenshot average for the quantities (A) transducer Z ZERO SHIFT/ (B) ENERGY-METER RESPONSE, (C) ENERGYSENSOR OUTPUT, AND (D) PHOTODIODE OUTPUT, THE DISTANCE BETWEEN THE CENTER PLANE OF THE FLASH SOURCE

AND THE TRANSDUCER DIAPHRAGM WAS 10 CM,

33
— -IOJt

< +10

o:

LU>

^

|_ -10

61 J IE f GO + 10

UJ

-10Jb

1 23456789 10

TEST NUMBER

Figure 9: Repeatability of test method using Ho. 22 flashbulbs

as source. Shown is percent deviation from a tenshot AVERAGE FOR THE QUANTITIES (A) TRANSDUCER Z ZERO SHIFT, (B) ENERGY-METER RESPONSE, (C) ENERGYSENSOR OUTPUT, AND (D) PHOTODIODE OUTPUT. THE DISTANCE BETWEEN THE CENTER PLANE OF THE FLASH SOURCE

AND THE TRANSDUCER DIAPHRAGM WAS 12 CM.

34
0.53 0.75 106 1.50

APERTURE DIAMETER, cm

Figure 10: Plot of energy-meter readings (mJ cm -)

corresponding to apertures of fixed diameter (cm.) . Each measurement was taken with the energy-meter

sensor 7 cm from the no. 5 flashbulb source, with

the aperture mounted in front of the energy meter'

s

collimating shroud, energy-meter readings are plotted on a logarithmic scale, the straight line

represents a doubling of energy for a doubling of area and passes through a point with coordinates of

(1) the energy level measured with the smallest

aperture and (2) the diameter of that aperture.

The sensor diameter is indicated by the vertical

dashed line,

35

3.00
TABLE 1

FLASHBULB CHARACTERISTICS*

Bulb

Designation

Flashbulb

Output

(klm • s)

Peak Luminous

Flux (klm)

Approximate

Time to Peak

(s)

Approximate

Duration of

Flash (s)**

# 5 clear 20 1450 0.020 0.033

# 22 clear 70 4200 0.020 0.030

FF-33 140 120 0.640 2.3

*From manufacturers ' literature.

**Time measured from instant when falsh reaches 10% of its maximum

value until it falls to 10% of its maximum value.

36
TABLE 2

TRANSDUCER Z ZERO SHIFTS IN RESPONSE

TO THERMAL RADIANT-ENERGY TRANSIENTS

Distance from

Line of Energy

to Transducer D (cm)

Center

Source

iaphragm

Transducer

Zero Shift*

(mV)

Energy

Meter

Reading

(mJ.cm- 2

)

Radiation

Sensitivity

(V-cm^J- 1 )

Source: Electronic Flash at 150 J

8 11.3 91 0.12

10 7.2 59 0.12

14 3.5 28 0.12

Source: No. 5 Flashbulb

8 63 440 0.14

10 41 290 0.14

14 19 140 0.14

Source: No. 22 Flashbulb

8 240 1630 0.15

10 140 930 0.15

14 76 520 0.15

*Full-scale output for transducer Z is 500 mV, corresponding to 340 kPa (50 psig)

All measurements were taken with transducer at ambient atmospheric pressure and

with constant electrical excitation.

37
TABLE 3

TRANSDUCER Z ZERO SHIFT IN RESPONSE TO THERMAL RADIANT-ENERGY

TRANSIENTS FROM FF-33 FLASHBULB SOURCE

AS A FUNCTION OF SOURCE-TRANSDUCER DISTANCE

Distance from-Ene?rgy Transducer Z Source to Transducer Zero Shift

Diaphragm (% of full scale)

(cm)

8 23.2

9 20.0

10 15.2

11 14.4

12 9.7

13 8.5

14 8.2

15 6.9

(W) **

30.3

27.9

18.6

18.3

12.2

8.4

8.0

6.8

Power Meter

Reading

Corrected*

to 1 cm2 (W)

10.7

9.8

6.5

6.4

4.3

3.0

2.8

2.4

*A11 measurements were taken with constant electrical excitation supplied to

the transducer and at ambient atmospheric pressure.

**Power meter sensor has an area of 2.84 cm2

; for comparison, calculated values are also shown for 1 cm2

, the area of the energy-meter sensor.

38
TABLE 4

ZERO SHIFT OF FOUR DIFFERENT TRANSDUCERS IN RESPONSE

TO THERMAL RADIANT-ENERGY TRANSIENTS AS A FUNCTION

OF SOURCE-TRANSDUCER DISTANCE*

Transducer Dista

Energy

To Tra

Diaphra

riceSource

nsducer

gm (cm)

9.2 (7.0)**

12.1 (9.9)

16.0 (14)

7.0

9.9

14.0

7.0

9.9

14.0

7.0

9.9

14.0

Transducer

Zero Shift

(%FS)

18 (22)**

12 (16)

8 (10)

115

59

28

2.2

1.1

0.54

60

32

15

*A11 measurements were taken at ambient atmospheric pressure.

**The distances 7, 9.9 and 14 cm were measured to the front edge of

transducer B; its diaphragm is recessed 2.2 cm. Equivalent values

for zero shift have been calculated for comparison and are given

in parentheses in the third column.

39
TABLE 5

TEN-SHOT REPEATABILITY OF THERMAL-TRANSIENT SOURCE

AND TRANSDUCER Z ZERO SHIFT*

Electronic Flash No. 5 Flashbulb No. 22 Flashbulb

at 150 J Energy-Meter Readings

Sample_Average 101.0 297.0 763.6

(mJ-cm~ 2

)

Maximum Deviation -4.0, +3.4 -5.1, +4.7 -10, +12

from Average (%)

Sample Standard _ 2.3 [2.3] 10.8 [3.6] 49.8[6.5]

Deviation (mJ-cm~ 2

) [1S%] Photodiode Output1

-5. 1, +4.7

10

pu1

8

-**

[3.6]

4 .36

-7 » +10

0. 23 [5.3]

Sample Average (V) ^ 8.02 4.36 12.78

Maximum Deviation -1.5, +1.0 -7, +10 -6, +4

from Average (%)

Sample Standard 0.6 [0.8] 0.23 [5.3] 0.48[3.8]

Deviation (v)[lS%]

Transducer Z Zero Shift

Sample Average (mV) 12.81 38.56 98.59

Maximum Deviation -2.0, +1.1 -11.1, +10.5 -10. 3, +6.

9

from Average {%)

Sample Standard 0.14 [1.1] 2.54 [6.6] 5.17 [5.2]

Deviation (mV)[lS%]

*A11 measurements were taken at ambient atmospheric pressure; the transducer

diaphragm was 7.5 cm, 10 cm, and 12 cm from the center plane of the electronic

flashtube, the No. 5 flashbulb source, and the No. 22 flashbulb source,

respectively.

**The photodiode output is given in peak volts and, unlike the energy-meter

readings, does not represent a measure of the total energy available in the

transient.

40
TABLE 6

TRANSDUCER Z ZERO SHIFT IN RESPONSE TO

THERMAL RADIANT-ENERGY TRANSIENTS FROM FF-33 FLASHBULB SOURCE

Run Transducer Zero Shift Power Meter Output

as Percentage of as Percentage of

10-Run Average* 10-Run Average

1 96.6 87.9

2 96.6 101.1

3 92.5 102.7

4 103.8 93.7

5 107.9 105.2

6 103.8 95.3

7 102.8 93.7

8 76.1 98.6

9 121.3 103.5

10 98.7 118.3

*A11 measurements were taken with constant electrical excitation supplied

to the transducer and at ambient atmospheric pressure.

41
TABLE 7

EFFECT OF SUPPLY-VOLTAGE VARIATION ON PERFORMANCE

OF THE ELECTRONIC FLASH*

Tests with Line Power Supply Tests with Battery Power Supply

Supply Voltage

(a-c V)

Run Energy Meter

Reading

(mJ-cnr*)

no 12

3

81.9

80.4

83.9

av 81.8

112 12

3

91.1

84.7

92.9

av 89.6

114 12

3

92.6

90.0

95.3

av 92.6

116 12

3

98.8

92.7

96.5

av 96.0

118 12

3

97.0

94.2

102.4

av 97.9

120 12

3

100.5

104.8

103.5

Supply Voltage

(d-c V)

Energy Meter

Reading

(mJ-cm-2)

419 73.7

414 71.9

411 70.7

409 70.0

408 69.4

406 68.5

404 67.6

403 67.2

402 66.8

401 66.3

400 66.2

399 65.9

398 65.6

398 65.4

397 64.7

av 102.9

*The electronic flash was operated at a setting of 150 J; the energy meter

was 7.5 cm from the center of the flashtube.

42
3H

3H

3

JL2

JL2

ir2

TABLE 8

TRANSDUCER Z ZERO SHIFT IN RESPONSE TO

THERMAL RADIANT-ENERGY TRANSIENTS

INCIDENT AT SELECTED ANGLES

Angle of

Incidence

(rad) [deg]

Rur

1

2

3

4

5

Zero

Shift*

(mV)

Ratio of Zero Shift

at Test Angle to Zero

Shift at Normal Incidence

72 1.00

81 1.00

69 1.00

69 1.00

74 1.00

av 73.0

[30] l 59

[30] 2 68

[30] 3 av

67

64.7

[60] l 40

[60] 2 37

[60] 3 av

46

41.0

[90] 1 2.5

[90] 2 2.5

rgol 3 4.5

av 3.2

0. 81

0. 93

0. 92

0. 89

0. 55

0. 51

63

.56

.03

.03

.06

.04

*A11 measurements were taken with constant electrical excitation supplied

to the transducer and at ambient atmospheric pressure.

43
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r- £

co to >* +-> CU

re

u

s- T3 3 e o

<o 10

s- -C

cu to o to 3 r—

T3 qL0C CU

fO -C

s_ +->

+-> qCU o

-E

+J cuE o fO

4-> "o. "O

CU 1-

•i— cu ^— 4J Q. E

O- CU 3 o

</) cu CO e J= >— o 4-> • »r— i— 4-> E

03 o +J s-

•c— q- OX E

CU o

r— r-. <0o to

!-» to s- 2 +Jo E

CU a>

^~ to

CU s- ^z

4-> Q- E to to •r- +J -o

10E s_ O cu o o3

^:

x 4-> to •^ E 2 10

i- E -•-> CU _^ cu CO to J=

I— +J +J i—' CU . r, s- CU

CU i~ 2 3

to

to to

H-> cu E i- CU a. E

CU o

s- p" 3 sto ai fO J=

CU O- E too

r— E

r— +J <c to *

44
TABLE 10

GLASS WINDOW ENERGY TRANSMISSION LOSS

AS SEEN IN TRANSDUCER Z ZERO SHIFT

Run Transducer Zero Shi ft* Energy Meter Reading

(mV) (mJ.cm-2)

with window without window

1 78 665

2 95 660

3 94 579

4 104 561

5 94 551

6 94 592

7 91 519

8 96 569

9 91 581

10 100 587

av 93.7 av 586.4

sample SD 6.8 sample SD 45.3

11 84 600

12 90 576

13 95 557

14 97 560

15 98 549

16 90 589

17 80 580

18 82 524

19 88 582

20 94 566 av 89.8 av 568.3

sample SD 6.3 sample SD 22.0

*A11 measurements were taken with constant electrical excitation supplied

to the transducer and at ambient atmospheric pressure; the transducer

diaphragm was 7 cm from the center plane of the No. 5 flashbulb source.

45

Muua
TABLE 11

SHIFT IN TRANSDUCER OUTPUT FROM INCIDENT THERMAL RADIANT-ENERGY

TRANSIENTS WITH TRANSDUCER MEASURING ELEVATED, AMBIENT,

AND VACUUM PRESSURE, FOR SELECTED TRANSDUCERS

Test Fixture

Pressure

345 kPa

[50 psi]

Output Shift*(mV)

Transducer Z Transducer M

97 28

95 30

96 28

av 96 av 29

Ambient 82 25

Atmospheric

78 26

80 25 av 80 av 25

Vacuum 78 22

(3.4 Pa absolute)

[25 urn Hg absolute] 92 26

85 25 av 85 av 24

*A11 Measurements were taken with the transducer diaphragm 7 cm from

the center plane of the No. 5 flashbulb source.

46
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47

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NBS-114A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBS TN-9052. Gov't Accessic

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE A TEST METHOD FOR DETERMINING THE EFFECT OF THERMAL

TRANSIENTS ON PRESSURE-TRANSDUCER RESPONSE

5. Publication Date March 1976

6. Performing Organization Code

7. author(S) John S. H i 1 ten , Carol F. Vezzetti, J. Franklin

Mayo-Wells, and Paul S. Lederer

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. ^253^34

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 87115

13. Type of Report & Period Covered p f na ] 7/1/7*1 to 3/31/75

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant bibliography or literature survey, mention it here.) A test method for evaluating the effects of short-duration, thermal radiant-enerqy 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 the 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/cm , with durations of about 6 ms , have been generated using an electronic

uIinn

; No

Ul ^%?f h£ X

2 ' 2 VTM> with durations of about 37 ms , have been generated using No. 22 flashbulbs. In tests with No. 22 bulbs, 25 commercial pressure trans- ducers have shown zero shifts ranging from 0.k% to about 400% of the full-scale

output.

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) Calibration; dynamic; electronic flash; photographic flash- bulb; pressure; pressure measurement; pressure transducer; thermal transient- transducer; zero shift. '

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:r rrom imp. or Doc, U.S. Government Printing Utti hington, D.C. 20402, SD Cat. No. C13 . 46:905

_] Order From National Technical Information Service (NTIS)

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52

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