V
NBSIR 74-503 (R)

Development of a Dynamic

Pressure Calibration Technique

A Progress Report

Carol F. Vezzetti, Paul S. Lederer, & John S. Hilten

Electronic Technology Division

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

June 15, 1974

Progress Report Covering Period 9-15-73 to 2-15-74

Prepared for NASA Langley Research Center

Hampton, Virginia 23365
V
NBSIR 74-503 (R)

DEVELOPMENT OF A DYNAMIC

PRESSURE CALIBRATION TECHNIQUE

A PROGRESS REPORT

Carol F. Vezzetti, Paul S. Lederer, & John S. Hilten

Electronic Technology Division

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

June 15, 1974

Progress Report Covering Period 9-15-73 to 2-15-74

Prepared for NASA Langley Research Center

Hampton, Virginia 23365

I

U. S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts. Director
Development of a Dynamic Pressure Calibration Technique

A Progress Report

by: C. F. Vezzetti , P. S. Lederer, and J. S. Hilten

The objective of this task is to develop a dynamic pressure calibration

technique yielding a flat frequency response to 2000 Hz or greater and

amplitude capability of at least 3.4 x 10^ Pa (5.C psi) zero-to-peak.

Equipment was set up, a universal test fixture fabricated, and testing

was initiated of various liquids and damping schemes for a hydraulic

sinusoidal pressure generator consisting of a vibrating liquid column.

Two liquids of density greater than water, tetrabromoethane and fluorcarbon, were tested. As was expected from the densities and bulk

moduli, improved frequency response could be accomplished only with the

tetrabromoethane. Very little improvement of damping has been obtained

by using tubes with large wetting surface area. Although tests using

filters are only in early stages, indications are that the proper

combination of liquid viscosity and filter porosity may result in

improved damping.

Key Words: Calibration; dynamic; liquid column; pressure; sinusoidal.
DEVELOPMENT OF A DYNAMIC PRESSURE CALIBRATION TECHNIQUE

Progress Report for the Period

September 15, 1973 to February 15, 1974

to the

NASA Langley Research Center

NASA Order L-88319

NBS Project 4253456

Prepared by

C. F. Vezzetti, P. S. Lederer and J. S. Hi! ten

The objective of this task is to develop a dynamic pressure

calibration technique yielding a flat frequency response to

2000 Hz or greater and amplitude capability of at least

3.4 x 10 4 Pa (5.0 psi) zero-to-peak. Equipment was set up,

a universal test fixture fabricated, and testing was initiated of various liquids and damping schemes for a hydraulic

sinusoidal pressure generator consisting of a vibrating

liquid column. Two liquids of density greater than water,

tetrabromoethane and a fl uorocarbon , were tested. As was expected from the densities and bulk moduli, improved

frequency response could be accomplished only with the

tetrabromoethane. Very little improvement of damping has

been obtained by using tubes with large wetting surface

area. Although tests using filters are only in early stages,

indications are that the proper combination of liquid viscosity and filter porosity may result in improved damping.

1 . Introducti on

This is the second progress report (1) on a study to develop a source

of dynamic pressure signals constant in amplitude within ±5% to 2000 Hz or greater, and capable of amplitudes of at least 3.4 x 10 4 Pa (5.0 psi)

zero-to-peak. The approach being used is based on a hydraulic sinusoidal pressure generator developed by the National Bureau of Standards

Instrumentation Applications Section (2). The frequency range of this

system is 15 Hz to 2000 Hz with a maximum pressure amplitude of

6.7 x 10^ Pa (9.8 psi) zero-to-peak between about 100 Hz to 300 Hz and

pressure amplitudes constant within ±5% to about 1000 Hz. Means of

improving the frequency response characteristics of the pressure

generator are being investigated.

(1) First Progress Report: NBSIR 73-290, P. S. Lederer, Oct. 19, 1973.

(2) NBS Technical Note 720, "A Simple Hydraulic Sinusoidal Pressure

Calibrator", J. S. Hi 1 ten, P. S. Lederer, and J. Sethian, April 1972.

1
1.1. The Basic Technique

The transducer to be calibrated is mounted near the base of a liquidfilled tube. The tube is vibrated by an electrodynamic vibration exciter,

generating a sinusoidal pressure at the transducer. The natural frequency of the liquid-column-transducer structure determines the upper

frequency limit in this method.

1.2. Methods of Obtaining Desired Frequency Response

Two approaches are available for extending the useful frequency range

of the pressure generating system. One is to optimize the damping of

the vibrating liquid column; the second is to increase the natural

frequency. Both are being investigated.

An undamped system has a useful frequency range, amplitude constant

within ±5%, up to about 20% of the natural frequency, while a suitably

damped system (damping ratio about 0.6) has a useful frequency range to

about 80% of the natural frequency. The methods for improving the

damping of the generator that have been or will be evaluated in this

study include: use of tubes with large wetting surface area to increase

friction; use of pressure snubbers as "filters" to impede the flow of

the liquid in the column; use of high viscosity liquid; adjustment of

viscosity by controlling the temperature of the liquid; and use of

magnetic fluids with electromagnetic control of damping.

The natural frequency of a liquid column open to air at one end is

given by the relation fn = v

s /(4h), where h is the height of the column

and v s is the velocity of sound in the liquid. Thus, the natural frequency can be raised by shortening the column height and also by using

a fluid in which the velocity of sound is greater. For a given acceleration, a shorter column produces a lower pressure; to compensate, a greater acceleration or use of a liquid of greater density is required.

Use of greater acceleration is limited by the output capabilities of

the vibration exciter and splashing of the liquid that occurs, especially

at low frequencies, when the pressure at the surface due to the acceleration exceeds the effects of surface tension of the liquid. Splashing

can be reduced by floating a thin disc of cork or other light material

on top of the liquid.

Greater acceleration without splashing and doubling of the natural

frequency can be accomplished by using a closed tube. However, the

pressure amplitude at a given acceleration of a closed tube system is

half that of one that is open at one end. Other disadvantages of the

closed tube system, such as increased temperature sensitivity, difficulty of filling and greater complexity, make this approach less

attractive.

The column height required to obtain a given pressure amplitude at a given acceleration is inversely proportional to the density of the

liquid. However the velocity of sound in a liquid, and therefore the

2
natural frequency, is proportional to (B/p) 1 / 2

, where B is the bulk

modulus and p the density. To obtain the desired pressure amplitude

and higher natural frequency at a given acceleration by using a shorter column of denser liquid, piB/p) 1 / 2 should be greater for the

denser liquid than for the original liquid (water). To verify this

analysis, two liquids of density greater than water, one for which

p(B/p) 1 / 2 is greater and one for which it is less than that of water, were tested: tetrabromoethane (density 2.95gm/cm3

, bulk modulus

2.99 x 10 9 Pa), and the fluorocarbon (density 1.88 gm/cm 3

, bulk modulus

1.00 x 10 9 Pa).

2. Progress During This Reporting Period

In the period covered by this report, the components and tubes for the

universal test fixture designed to facilitate testing of different types

of pressure transducers and damping schemes were fabricated and the

test equipment set up. The system was tested and the repeatability was found to be satisfactory for this phase of the study. Tests with the

two liquids of density greater than water were conducted. Tests evaluating the use of tubes with large wetting surface area are nearly complete, and tests using the filters (pressure snubbers) are in early

stages

.

2.1. The Vibration Exciter Equipment

Two vibration exciter facilities are available for this study. One,

a large electrodynamic vibration exciter used in a previous study (2),

is available part time and is used to check out the equipment, to

compare tube performance on the two vibration exciters, and for tests

where the larger force capability of this facility is required.

The other, a small electrodynamic vibration exciter purchased for this

study with NBS funds, is shown in Figure 1 with power supply and readout equipment. The vibration exciter (K) and trunnion (L) are securely

attached to a sturdy metal stand (a section of a shock tube) which is

fastened to the floor. The power supply (M), a variable oscillator (N),

charge amplifier (0) for the monitoring accelerometer, the various

amplifiers and power supplies (not shown) for the pressure transducers,

a frequency counter (P), and a digital voltmeter (S) are housed in a relay rack. An oscilloscope (T) is used tc monitor the signals. A

three-position selector switch (R) permits connecting the output of any

of three transducers to the voltmeter, frequency meter, and oscilloscope.

2.2. The Universal Test Fixture

A universal test fixture with provisions for changing liquid-column tubes

and mounting pressure transducers of various "sizes was fabricated. The

components of the test fixture are shown in Figures 2 and 3.

3
The 5.1 cm (2.0 in.) diameter by 7.5 cm (3.0 in.) aluminum chamber

section (A) has two flat surfaces for mounting the 4.8 cm (1.9 in.)

square transducer plates (B). These plates contain threaded holes

to receive the transducers (C) being tested and are attached to the

chamber section with four screws. Rubber 0-rings (D) seal the two

surfaces. 1.6 cm (0.6 in.) diameter ports (E) lead to the 2.2 cm

(0.9 in.) diameter chamber (F). The 30.5 cm (12.0 in.) long tubes (G)

(see also Figure 4) are connected to the top of the chamber with six screws. The seal is made with a paper gasket (H).

This assembly is mounted on the top of a 5.1 cm (2.0 in.) diameter by

3.3 cm (1.3 in.) aluminum cup-like component (I) containing the accelerometer (J). The accel erometer is mounted on the bottom of the cup

with a screw and the cup is connected to the vibration exciter table

with three screws.

The tubes (Figure 4) range from 1.3 cm (0.5 in.) inside diameter

(Tubes 1, 6, and 7) to 2.5 cm (1.0 in.) inside diameter (Tube 4). Some

have smooth inner walls (Tubes 5, 6, and 7); one has 51 separate

channels (Tube 3); one has spiral flutes (Tube 1); and one has a flat

cross section with intersecting diagonal flutes (Tube 2). Tubes 1-3

are copper; tubes 4-7 are brass. Tube 4 is a sol dered-together test

fixture that was used in comparing the performance stability of the

demountable test fixture with a one-piece fixture.

2.3. The Filters Used

The filters (Figure 4: 8-10) are commercially available porous-element

pressure snubbers. Filter "C" (8) is the most porous (recommended by

the manufacturer for use with highly viscous fluids) and is made of woven stainless steel strands. Filter "E" (9) is less porous (recommended for use with water and light oils). Filter "HX" (10) is the

type recommended for use with mercury. The filter discs of "E" and

"HX" are of sintered stainless steel. The housings of all the filters

are stainless steel

.

2.4. The Liquids Used

The liquids used in the test fixture during this period were water

(specific gravity 1.00, bulk modulus 2.14 x 10 9 Pa), a fluorocarbon

inert liquid (specific gravity 1.88, bulk modulus 1.00 x 10 9 Pa),

tetrabromoethane (specific gravity 2.95, bulk modulus 2.99 x 10 9 Pa),

and a light petroleum oil (specific gravity 0.86, bulk modulus

1.55 x 10 9 Pa) that was used in the tests with the filters.

2.5. System Performance Tests

Two pressure transducers, from our own stock, were selected for preliminary tests to check out the- system and determine the performance

of the system using the various liquids and damping methods. One

transducer (A) is a piezoelectric type with integral solid state

amplifier and the other (B) is a bonded straingage type with response to
The accelerometer to be used in the test fixture was calibrated using

the large vibration exciter. The test fixture accelerometer was attached directly to the vibration exciter table and known accelerations

were applied at frequencies from 10 Hz to 3000 Hz. Table 1 shows that

the acceleration indicated by the test fixture accelerometer agreed

with the acceleration indication of the vibration exciter accelerometer

within -3% to +6%. The calibration uncertainties (Table 2 -A) were estimated to be ±2.3%.

To ascertain the reliability of the demountable universal test fixture,

the fixture, with a 2.3 cm (0.9 in.) inside diameter tube (Tube 5 in

Figure 4) attached, was filled with water to a height of 33.3 cm (13.1

in.) above the center of the pressure transducer diaphragm. The maxi- mum pressure signal frequency and the transducer response at several

frequencies were determined. The fixture was emptied, refilled and

tested. This was done four times. The same test procedure also was performed on a one-piece fixture consisting of a 2.5 cm (1.0 in.)

inside diameter tube soldered into a brass block with a threaded hole

for attaching a pressure transducer (Tube 4 in Figure 4).

The data shown in Table 3 indicate that the universal test fixture

is sufficiently stable over the flat part of the frequency response

(up to roughly 100 Hz) to continue this phase of the testing program.

The repeatability of the transducer response was within 3.6% and that

of the maximum-pressure signal frequency was within 1.8%. The estimated uncertainty of the measurements was ±3.3 (Table 2-C).

The transducer response measured with the universal test fixture agreed

very closely with the response measured with the one-piece fixture.

The maximum-pressure signal frequency of the universal test fixture

was about 40 Hz lower than that of the one-piece fixture, consistent

with the additional elastic surface (the second transducer) present

in the former. Some reduction in the maximum-pressure signal frequency

could also result from the fact that in the universal test fixture the

transducer diaphragms are recessed slightly from the main column chamber

(they are flush with the transducer plate surfaces). The effect of

this chamber geometry on the maximum pressure signal is being investigated.

2.6. Preliminary Test Procedure

The procedure followed was to assemble the fixture, attach the tube and

transducers to be used in the test, fill the tube and chamber with the

test liquid, evacuate the filled assembly for at least 15 minutes to remove entrapped and dissolved gas, and mount the assembly on the

vibration exciter table. The height of the liquid column was measured

with a depth micrometer and adjusted to the desired height by adding

or removing a few drops of liquid. Usually the top of the liquid

column was 1.3 cm (0.5 in.) from the top of the tube, producing a column height of 33.3 cm (13.1 in.) measured from the center of the

pressure transducer diaphragm, or 34.9 cm (13.7 in.) from the bottom of

the column to reduce splashing at low frequencies.

5
The frequency was then determined for the maximum pressure signal

observed on the oscilloscope while sweeping the frequency at which

the column was vibrated. The excitation power to the vibration exciter

was set at a very low level to prevent overranging the pressure transducers and was maintained at that setting. It should be noted that,

because the acceleration does not remain constant as the natural

frequency of the liquid column is approached, the frequency of the

maximum pressure signal is close to but not the same as the natural

frequency of the liquid column. However, the maximum pressure signal

frequency can be simply and rapidly determined in this way with sufficient repeatability (see Table 3) for the purposes of this phase of

the study. It is usually necessary to vibrate the column for about

15 minutes before the maximum pressure signal reaches a stable value

to remove any possible remaining adsorbed gas.

Readings of the output of the pressure transducers were taken at known

accelerations at 18 different frequencies, from 10 Hz to above the

maximum pressure signal frequency, and frequency response curves were

plotted from the data (See Figures 5-9). When the large vibration

exciter facility, which, has an accelerometer integral with the exciter

table, was used, readings of the output of the accelerometer in the

test fixture were taken as an additional check on system performance.

Static calibrations also were made on the DC responding pressure

transducer (B), by applying pneumatic pressures to the top of the

liquid-filled tube. Gage pressures of ±1.0 x 104 Pa (±40 in. of

water) were generated with a bellows and measured with a precision

gage. The static response was determined from the change in transducer output caused by the known pressure difference, 2.0 x 10 1* Pa

(80 in. of water). The calibration uncertainty as shown in Table 2-B was ±0.7%.

2.7. Test Results

A summary of the test results is given in Tables 4 and 5, and representative frequency response curves are given in Figures 5-9. The

maximum pressure signal frequency for the 34.9 cm (13.7 in.), total

height, column of water was around 950 Hz, which is consistent with

the approximately 1350 Hz resonance observed in the initial study

(2) with a 22.8 cm (9.0 in.) column of water. The static calibrations

of transducer response agreed within 3% with the dynamic transducer

response (Table 5).

Using the water, tubes with large surface area (compare Tests 3, 8,

9, and 10, Table 4) produced little improvement in the damping. Further

pursuit of this approach, at least with the less viscous liquids, will

be limited. One tube, Tube 2 in Figure 3, remains to be tested.

Attempts were made earlier to obtain useful data with this tube, but

the maximum pressure signal frequency was very low and unstable. It

is suspected that, because the complex structure of this tube, air

may have remained trapped in the many corners and pockets causing the

6
instability. Vacuum filling the test fixture would minimize the possibilities of trapping air in the tube. The vacuum chamber will be

modified to allow vacuum filling and Tube 2 will be retested.

Of the liquids of density greater than water (compare Tests 2, 5, 6,

and 7, Table 4), tetrabromoethane, based on the analysis in Section 2.2 was expected to, and showed, the most promising results. The maximum

signal frequency could be increased to 1650 Hz by using a 13.0 cm

(5.1 in.) column, while maintaining the same pressure amplitude as a 34.9 cm (13.7 in.) column of water. Also, confirming the analysis in

Section 2.2, the fluorocarbon proved unsatisfactory in that the maximum

pressure signal obtainable was less than half that for a column of

water of the same height.

Tests with the filters are not yet complete. Only one filter, "C," has

been tested and with only two liquids, water and light oil (Tests 11 and 12, Table 4; Also see Figure 9). Attempts were made to test the

other filters, "E" and "HZ", and to test filter "C" with tetrabromoethane, but the maximum-pressure signal frequency was not stable,

probably because of trapped air, as in the test with Tube 2. Plans

call for retesting when the test fixture can be vacuum filled. Some

improvement in the damping was accomplished when filter "C" was used

with the light oil (Tests 4 and 12, Table 4) and tests will be

continued with the filters.

Tests 1 and 2 were made with the one-piece test fixture and show

close agreement with Tests 3 and 5 made with the universal test

fixture.

3. Plans for the Next Reporting Period

Experiments will be conducted to check the effect of the transducers

being recessed from the main chamber on the maximum pressure signal

frequency.

The vacuum chamber will be modified to facilitate vacuum filling of the

test fixture. The tube and filters which did not have stable maximum

pressure signals will be tested after being vacuum filled.

Further tests will be conducted using tetrabromoethane. This will

probably necessitate a brass test fixture as the liquid is reported

to be corrosive to aluminum.

Additional methods of improving the damping will be tried, including

magnetic damping.

Tests with the pressure transducers supplied by NASA will be initiated.

7

TABLE 1 CALIBRATION OF TEST FIXTURE ACCELEROMETER

Frequency Applied Fixture Fixture Response

Acceleration Accel erometer Accelerometer Ratio

Output Equivalent

Acceleration

Hz g (0-to-peak) V (rms) g (0-to-peak)

10 1.00 0.69 0.97 0.97

15 2.00 1.39 1 .97 0.99

20 4.00 2.83 4.00 1.00

25 5.00 3.55 5.03 1.01

30 5.00 3.57 5.04 1.01

40 10.0 7.16 10.1 1.01

50 10.0 7.15 10.1 1.01

75 10.0 7.17 10.1 1.01

100 10.0 7.20 10.2 1.02

200 10.0 7.27 10.3 1.03

300 10.0 7.30 10.3 1.03

400 10.0 7.33 10.4 1.04

500 10.0 7.34 10.4 1.04

600 10.0 7.36 10.4 1.04

750 10.0 7.38 10.4 1.04

1000 10.0 7.41 10.5 1.05

1500 10.0 7.44 10.5 1.05

2000 10.0 7.46 10.6 1 .06 3000 10.0 7.47 10.6 1.06
TABLE 2 ESTIMATED MEASUREMENT UNCERTAINTIES

Source of Error' % of Reading

Systematic Random

A - Calibration of Accelerometer

Overall uncertainty of knowledge of acceleration applied ±C-.64 ±0.52

Charge amplifier noise: 1 pC rms/10,000 pf (Manuf. Lit.) ±0.10 source capacitance = 3250 pf Voltmeter calibration accuracy: ±(.05% Reading + .02% ±0.08

rieinge) («-ld.uuf. Lit.) signal = 7 V Repeatability and resolution of voltmeter reading ±0.07 (Estimate) ±5 mV Totals (root sum square) ±0.645 ±0.534 TOTAL ESTIMATED UNCERTAINTY (Systematic + 3 x Random) ±2.25%

B - Static Pressure Calibration

Voltmeter calibration accuracy: ±(.01% Reading + .01% ±0.03

Range) (Manuf. Lit.) signal = SO mV Repeatability and resolution of voltmeter reading ±0.10 (Estimate) ±0.05 mV

Static pressure dial gage accuracy (Manuf. Lit.) ±0.33

Static pressure dial gage sensitivity (Manuf. Lit.) ±0.20 Repeatability and resolution of gage reading (Estimate) ±0.02 Totals (root sum square) ±0.387 ±0.102 TOTAL ESTIMATED UNCERTAINTY (Systematic + 3 x Random) ±0.6 9%

C - Dynamic Pressure Response : Transducer (B)

Overall uncertainty of knowledge of acceleration applied ±0.64 ±0.52

Voltmeter calibration accuracy: ±(.05% Reading + .02% ±0.08

Range) (Manuf. Lit.) Signal = 800 mV Repeatability and resolution of voltmeter reading ±0.63 (Estimate) ±5 mV Height of liquid column (Estimate) ±0.30 in. ±0.30

Liqu'i density variation due to temperature variation ±0.10

(Estimate) ±2°C Totals (root sum square) ±0.645 ±0.875 TOTAL ESTIMATED UNCERTAINTY (Systematic + 3 x Random) ±3.27%

D - Dynamic Pressure Response: Transducer (A)

Overall uncertainty of knowledge of acceleration applied ±0.64 ±0.52 Voltmeter calibration accuracy: ±(.05% Reading + .02% ±0.07

Range) (Manuf. Lit.) signal = 100 mV Repeatability and resolution of voltmeter reading

(Estimate) ±0.5 mV ±0. 50

Height of liquid column (Estimate) ±0,03 in. ±0,30

Liquid density variation due to temperature variation

(Estimate) ±2°C ±0.10 Totals (root sum square) ±0,643 ±0.788

TOTAL ESTIMATED UNCERTAINTY (Systematic + 3,v. Random) ±3,01%
TABLE 3 COMPARISON OF REPEATABILITY OF DEMOUNTABLE TEST FIXTURE

VS. ONE-PIECE FIXTURE

Demountable One-piece

Frequency ^un Acceleration Transducer (B) Transducer (B) Number Applied Output Response Output Response

Hz g mV , mV mV/g mV mV mV/g

(O-to-Peak) (rms) (O-to-Peak) (rms) (O-to-Peak)

100 1 5 3 93 5 56 I 1

1

4 02 CD . , D o

ii

1 A

2 5 a n? c

, D o ii

1 A A

°t , . n?u z C

J . A ft

i Do ii

.

1 A

3 5 4.04 S .71 1 . 14 4..00 5 66 .1.,13

4 5 4.02 5 .68 1 .14 4 .04 5 .71 1 ,14

Average 1

.

.13 1

,

, 14 Repeatability 0 .03 (2,,6%) 0 ,01 Ratio: Demountable/One -piece 0, 99

50 1 5 3 , 95 5 59 . 12

2 5 3 . 96 5

,

60 1 .12 3

.

. 98 5

.

63 1 , 13

3 5 4.00 5 .66 1..13 3,.94 5. 57 1,,11 4 5 3.95 5 .59 1 .12 4,.00 5, 66 1

,

.13

Average 1 ,12 1

,

, 12 Repeatability 0..01 Co .9%) 0..02 Ratio: Demountable/One -piece 1,.00

25 1 4 3.06 4, 32 1. 08 3..92 54 1,,11

2 5 3.90 5,.51 1

,

10 3. 98 5. 63 1.,13

3 5 3.94 5, 57 1..12 3. 90 5

.

51 1

.

,10

4 5 3.92 5. 54 1. 11 3. 95 5. 59 1. 12

Average

t

1

,

10 1

.

,11 Repeatability 0,.04 (3. 6°6) 0. 03 Ratio: Demountable/One-piece 0.99 MAXIMUM PRESSURE SIGNAL FREQUENCY

Run Demountable One-piece

Number

1 N.A. 935 Hz 982 Hz

2 N.A. 940 Hz 982 Hz

3 N.A. 947 Hz 982 Hz

4 N.A. 952 Hz 980 Hz

Average

Repeatabil ity

Ratio : Demountable/One-piece

943.5

17.0 (1.8%) 0.96

981.5

2.0 (0.2%)
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TABLE 5

STATIC VS. DYNAMIC RESPONSE

Test Static Response Dynamic Response* Response Ratio

(see Table 4) mV/Pa mV/psi mV/Pa mV/psi Dynamic/ Static

-4 -4 x 10 x 10

2 3.25 2.24 3.29 2.27 1.01

3 3.31 2.28 3.34 2.30 1.01

5 3.26 2.25 3.34 2.30 1.02

7 3.28 2.26 3.35 2.31 1.02

8 3.26 2.25 3.32 2.29 1.02

11 3.22 2.22 3.32 2.29 1.03

12 3.26 2.25 3.29 2.27 1.01

Note: No static calibrations were made during tests 9 and 10 as the flutes and

chambers in the tubes made it impractical to insert a stopper in the top of the

tube. No static calibrations could be made during tests 4 and 6 as the leads to

transducer (B) had broken. (The test numbers are for identification only and do

not reflect the order in which the tests were performed.)

*The average response for the frequency range 20 Hz to 50 Hz was used.

The pressure amplitude for the dynamic response is calculated from:

p = h p a ,

where h is the height of the liquid column above the transducer,

p is the density of the liquid, and

a is the acceleration amplitude

FIGURE 1: Overall view of small vibration exciter test set up.

K-Vibration Exciter with Universal Test Fixture;

L-Vibration Exciter Trunnion; M-Vibration Exciter

Power Supply; N-Variable Oscillator; O-Accelerometer

Charge Amplifier; P-Frequency Meter; R-Selector

Switch; S-Digital Voltmeter; T-Oscilloscope.

FIGURE 2: Assembled universal test fixture with 2,2 cm (0,9 in.)

inside diameter tube attached, a-chamber section;

B-Transducer Plates; C-Pressure Transducers; G-Interchangeable tube; h-paper gasket; i"acceler0meter section;

J-Lead from Accelerometer.

FIGURE 3: Components of the universal test fixture, A-Chamber

Section; B-Transducer Plates; C-Transducers; D-O-Ring;

E-Transducer Port; F-Chamber Cavity; 6-Interchangeable

Tube; H-Paper Gasket; I-Accelerometer Section;

J-Accelerometer.

1 2 3 4 5 6 7

FIGURE 4: Tubes and filters used in experiments with the universal

test fixture. 1-Spiral Fluted Tube; 2-Flat Tube; 3-51

Channel Tube; 4-0ne-Piece Test Fixture; 5-Smooth Tube,

2.2 cm (0.9 in.) inside diameter; 6-Smooth Tube, 1.3 cm

(0.5 in.) inside diameter; 7-Smooth Tube, 1.3 cm (0.5 in.)

inside diameter, with filter "c"; 9~fllter "e"; 10- fl lter

"HX".

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U.S. * PT. CF LC"M. BIBLIOGRAPHIC DATA

SHEET

1. I'l HI. I< A 1 ION OK RE Pi >R 1 NO. NBSIR 74-503 (R)

2. Gov't Accession

No.

3. Recipient'* Accession No.

a. riTi.i-: .and si m i iti.i; Development of a Dynamic Pressure Calibration Technique

A Propre?? Ronnrt

5. Publ ieat ion Date

6. Performing Organization Code

7. ALTIIOR(S)

C.F. Vezzetti, P.S. Lederer, 5 J.S. Hilten

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NA-ME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/ftorlc Unit No. 4253456

11. Contract /Grant No. L-88319

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

NASA Langley Research Center

Hampton, Virginia

23365

13. Type of Report & Period Covered

Interim

Q-lt;-7X tn ?_1t;_7/|

14. Sponsoring Agency Code

is. supplementary notes

16. ABSTRACT (A 2 00- word or less {actual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.) The objective of this task is to develop a dynamic pressure calibration technique

yielding a flat frequency response to 2000 Hz or greater and amplitude capability

of at least 3.4 x 1C* Pa (5.0 psi) zero-to-peak. Equipment was set up, a universal

test fixture fabricated, and testing was initiated of various liquids and damping

schemes for a hydraulic sinusoidal pressure generator consisting of a vibrating

liquid column. Two liquids of density greater than water, tetrabromoethane and a

f luorocarbon, were tested. As was expected from the densities and bulk moduli,

improved frequency response could be accomplished only with the tetrabromoethane.

Very little improvement of damping has been obtained by using tubes with large

wetting surface area. Although tests using filters are only in early stages,

indications are that the proper combination of liquid viscosity and filter porosity

may result in improved damping.

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; liquid column; pressure; sinusoidal.

18. AVAIl.Aim.ITY [^Unlimited

f\/r or Official Distribution. Do Not Release to NTIS

19. SECURITY CLASS

(THIS REPORT)

21. NO. OF PAGES

UNCLASSIFIED

L Order From Sup. of Doc, U.S. Government Printing Office Washington. D.C. 20 i02. SD Cat. No. < 1 * 20. SECURITY ( LASS

(THIS PAGE)

22. Price

1 Order From National Technical Information Service (NTIS)

Springfield, S'irginia 221M UNCLASSIFIED

USCOMM.OC