NBSIR 75-708

Development of a Dynamic

Pressure Calibration Technique

A Progress Report

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

Electronic Technology Division

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

June 5, 1975

Progress Report Covering Period 2-15-74 to 8-15-74

Prepared for NASA Langley Research Center

Hampton, Virginia 23365

NBSIR 75-708

DEVELOPMENT OF A DYNAMIC

PRESSURE CALIBRATION TECHNIQUE

A PROGRESS REPORT

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

Electronic Technology Division

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

June 5, 1975

Progress Report Covering Period 2-15-74 to 8-15-74

Prepared for NASA Langley Research Center

Hampton, Virginia 23365

U.S. DEPARTMENT OF COMMERCE, Rogers C.B. Morton. Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts. Director

Development of a DynaiTiic Pressure Calibration Technique

A Progress Report

by: C. F. Vezzetti , J. S. Hi 1 ten, and P. S. Lederer

Work continues on the development of a method of producing sinusoidal ly

varying pressures of at least 34 kPa zero-to-peak with amplitude variations within ±5/^ up to 2 kHz for the dynamic calibration of pressure

transducers

.

Sinusoidal ly varying pressures of 34 kPa zero-to-peak have been produced,

to date, between 40 Hz and 750 Hz by vibrating a 10-cm column of a dimethyl siloxane liquid at 36 zero-to-peak. Damping of the liquid

column was accomplished by packing the fixture tube with a number of

smaller diameter tubes.

Key Words: Calibration; dynamic; liquid column; pressure; sinusoidal

pressure; transducer.

DEVELOPMENT OF A DYNAf-lIC PRESSURE CALIBRATION TECHNIQUE

Progress Report for the Period

February 15, 1974 to August 15, 1974

to the

NASA Langley Research Center

NASA Order L-88319

NBS Project 4253456

Prepared by

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

Work continues on the development of a method of producing

sinusoidally varying pressures of at least 34 kPa zero-topeak with amplitude variations within ±5% up to 2 kHz for

the dynamic calibration of pressure transducers.

Sinusoidally varying pressures of 34 kPa zero-to-peak have

been produced, to date, between 40 Hz and 750 Hz by vibrating a 10-cm column of a dimethyl siloxane liquid at 36 g

zero-to-peak. Damping of the liquid column was accomplished

by packing the fixture tube with a number of smaller diameter

tubes

.

1. INTRODUCTION

This is the third progress report [1,2]* of an experimental investigation to develop a source of dynamic sinusoidal pressures of at least

34 kPa zero-to-peak, at frequencies of up to 2 kHz or greater, for

calibrating pressure transducers. Pressure amplitude variations

over this frequency range are not to exceed +5%.

The method selected is based on an extension of a method (previously

developed by the NBS Instrumentation Applications Section [3]) which

is capable of generating sinusoidally varying pressures of 10 kPa

zero-to-peak over the frequency range 15 Hz to about 1 kHz with a pressure amplitude variation of less than ±5%, and pressures of 67 kPa

zero-to-peak between 100 Hz and 300 Hz.

1.1 Basic Method

The transducer to be calibrated is mounted near the base of a liquidfilled tube; the tube is mounted on the armature of an electrodynamic

vibration exciter and vibrated so as to produce a sinusoidally varying

pressure at the transducer diaphragm. The amplitude of this pressure

^Figures in brackets indicate references, section 5.
-2-

is proportional to the product o£ the liquid head (above the center

of the transducer diaphragm) and the acceleration of the tube.

Various parameters limit the frequency range over which the method

is effective and the maximum pressure levels attainable.

Both the natural frequency and the degree of damping of the combined

liquid-column and transducer structure determine the useful upper

frequency limit. The natural frequency of a liquid column is directly

proportional to the speed of sound in the liquid and inversely proportional to the height of the column. An undamped system. is usable (i.e.,

capable of generating pressures with a variability in peak amplitude

of less than ±5%) over a range of frequencies up to about 20% of

the natural frequency; an optimally damped system is usable over

a frequency range with an upper limit of about 80% of the natural

frequency [3]

The factors that in combination determine the pressure levels attainable

over the frequency range of interest are (1) the force and displacement

capabilities of the vibration exciter, (2) the density of available

working fluids, and (3) the height of the liquid column. The range of

exciter capabilities is determined by the specific instrument available

and is therefore fixed; for a selected fluid density, the column height

required to generate a given pressure (at a given acceleration) is first

determined by calculation and then verified experimentally.

1.2 Summary of Progress in Previous Reporting Period

In the previous reporting period, a test fixture was fabricated for

preliminary testing of various liquids as working fluids and of various

means of damping the liquid column [2]. The fixture was designed to

accommodate different experimental tubes and transducers of different

sizes.

Liquids tested in the period were water, a fluorcarbon liquid of

specific gravity 1.88, te trabromoethane , and a light petroleum oil.

The effect on damping of increasing the wetted surface through the

use of tubes with various special internal configurations was evaluated.

Tube designs tested include tubes with smooth inside walls, with spiral

fins on the inside walls, with interlacing diagonal fins, and with

multiple separate channels. The use of a sintered-metal filter in the

tube was also tested.

Test results were given in the previous report.

2. EXPERIMENTAL DEVELOPMENT

2.1 Completion of Preliminary Experiments

At the start of the reporting period, the schedule of preliminary

work included several elements not then completed.
-3-

2.1.1 Experiments with Tvansducev Recessed. Measurements with the

same transducer mounted first in an earlier one-piece fixture and then

in the test fixture [2] showed a reduction in the resonance frequency

of about 40 Hz for a water column 35-cm high. The suggestion was made

that this reduction resulted from the geometry of the test fixture,

in which the transducer sensing head is recessed from the chamber.

Several tests were run at the 35-cm water-column height with spacer

rings inserted between the transducer mounting surface and the test

fixture. With various- rings in place, the transducer sensing head

was recessed by an additional distance of either 1.0 cm or 2.2 cm. The results did not show a significant variation in resonance frequency.

2.1.2 Magnetic Damping Experiment. The possibility of using magnetic

damping was investigated with a hydrocarbon -base magnetic fluid.

Because only a small amount of the magnetic fluid was available, a special fixture was fabricated for this experiment. A 34-cm-long

glass tube, 0.5-cm i.d., was epoxy bonded into a bore through a

2 . 5 -cm-diameter by 3.8-cm-long aluminum base block. The opposite

end of the bore was threaded to receive a pressure transducer, as shown in figure 1.

The tube was vacuum filled with magnetic fluid to a height of 35 cm. The fixture was then mounted on the vibration exciter armature, and

the frequency characteristics measured. The resonance frequency of this

system was determined to be 737 Hz with an amplitude ratio of 18. For

purposes of this report, amplitude ratio is defined as the ratio of the

measured maximum amplitude (at resonance) to the measured amplitude at

frequencies below the natural frequency over which the frequency- response

plot exhibits no significant departure from a straight line parallel to

the frequency axis. A magnet was first placed along the "side of the glass

tube near the top surface of the liquid column, then at the center, and

finally near the bottom. No changes in resonance frequency or in amplitude ratio were observed for any of the magnet positions. Next, a strip

of magnetic material was placed along the entire length of the column;

again, no changes in resonance frequency or in amplitude ratio were

detected. Finally, a solenoid was formed with approximately 800 turns

of 0 . 058 -cm-diameter (23 AWG) wire wound around the glass tube and

energized with 10 V dc (current of 4 A) . This attempt also resulted in

no observable changes in resonance frequency or in amplitude ratio.

2.1.2 Vacuum Chamber Modification. The presence of gas bubbles and

dissolved gases in the working fluid tends to lower the natural frequency

of the column. The liquid-filled test fixture was placed in a vacuum

chamber held at reduced pressure for at least 15 min. The pressure

in the chamber was intended to be above that at which the fluid boils

and low enough to degas the liquid in an open cylindrical tube.

However, bubbles remained in the liquid in a rectangular-cross -section

tube with interlacing diagonal fins even after 30 min in the chamber.

Bubbles also were observed remaining in tubes in which the less porous

of the filter types tested were installed. Accordingly, the vacuum

chamber was modified to provide a means for vacuum filling the test

fixture
-4-

A short length of copper tubing was inserted through a hole drilled

in the removable cover of the vacuum chamber and an air-tight seal made

between tubing and cover. A vacuum valve and a stainless - steel beaker

with a hole drilled in the bottom were mounted on top of the tubing with

a liquid- and air-tight seal between tubing and beaker, and a short length

of rubber hose was attached to the vacuum side of the tubing.

For vacuum filling, the fixture is placed in the chamber. As the

cover of the chamber is being replaced, the free end of the rubber

hose is guided into the open end of the fixture. The vacuum valve

is then closed, and the chamber evacuated for about 15 min. Enough

liquid to fill the test fixture is poured into the beaker, and the

valve opened slowly to allow the liquid to flow into the fixture.

When the beaker is almost empty, the valve is closed. The fixture

is left in the chamber at the reduced pressure for an additional

15 min to complete the procedure.

2.1.4 Liquid-Tube Combination Expeviments . Tests were conducted to

evaluate the various liquid-tube combinations not yet studied, including tests with a heavy petroleum oil (of viscosity about 15 St).

Table 1 is a summary of the combinations tested, with resonant frequency

and amplitude ratio of each combination as experimentally determined.

Difficulty was again encountered in filling the rectangular crosssection tube and tubes equipped with low-porosity filters with either

water or tetrabromoethane as the working fluid. An explanation is

that at the lowered pressure of the chamber, irregularities and sharp

corners serve as bubble formation sites in an early stage of boiling.

The problems associated with filling, coupled with more promising

indications from other experiments, resulted in a decision to discontinue tests of low- viscos i ty working fluids with the rectangularcross - section tube (with internal diagonal fins) and with tubes

equipped with filters.

2.2 Experiments Using High-Viscosity Liquid Columns

A decision was made to concentrate on tests using high-viscosity

working fluids. The upper frequency capability specification of 2 kHz

requires either: (1) the use of an undamped column with a natural

frequency of at least 10 kHz, or (2) the use of a dam.ped column with

a natural frequency between 2.5 and 10 kHz, the specific natural

frequency depending on the degree of damping achieved. For all situations,

the liquid head must be large enough to produce 34 kPa zero-to-peak

pressures at an acceleration level within the capability of the vibration exciter. Low- viscos ity fluids have experimentally not been found

to provide the amount of damping required by a practical method.
-5-

2.2.1 Properties of Liquids. Table 2 lists pertinent properties of

liquids which were considered as working fluids for this method, and

figure 2 is a plot of the calculated acceleration levels required to

produce a sinusoidally varying pressure of 34 kPa zero-to-peak as a function of the liquid column height, for each liquid.

On the basis of its properties, glycerine appeared to be the most

suitable high-viscosity liquid. Dimethyl siloxane liquids also showed

promise. These liquids may be obtained in a large range of viscosities

(up to 1000 St) which are relatively constant over a wide temperature

range. Petroleum oils also showed promise but exhibit highly temperaturedependent viscosities.

Figure 2 also shows that a 2.5-cm column of mercury vibrated at 10

zero-to-peak should produce the desired pressure levels and flat

frequency response without any damping other than that of the mercury

itself; however, because of health hazards and other problems related

to the use of mercury, only a limited amount of experimentation is

planned with mercury as a working fluid.

2.2.2 Experiments Using Glycerine. Several attempts were made to

use glycerine as the working liquid. The glycerine contained many

small bubbles which could not be removed by heating, or even by maintaining the glycerine - filled tube at reduced pressure for several days.

The presence of bubbles reduced the natural frequency below the

minimum required frequency of 2.5 kHz.

2.2.3 Experiments Using Dimethyl Siloxane Liquids. Samples of

dimethyl siloxane liquids of 10-, 12. 5-, 30-, and 60-St viscosities

were available. Experiments were conducted to determine which of these

liquids would be most useful, that is, which would be viscous enough to

provide sufficient internal damping but not so viscous as to cause

problems with the filling operation or the degassing process.

2.2.3.1 For the initial experiments with dimethyl siloxane liquids,

a test fixture of about 11-cm overall length was fabricated from 2.4-cmi.d. brass tubing as shown in figure 3. To fill the fixture, the

test liquid was poured into the fixture; then the fixture was placed in

a vacuum desiccator, and the pressure lowered. The fixture was maintained at reduced pressure until the liquid ceased to bubble. This

process required as long as four hours for some configurations.

After filling, the fixture was mounted on the vibration exciter

armature. Liquid was added or removed to bring the column height to

10 cm, and the frequency characteristics were measured. The natural

frequency of a 10-cm column of dimethyl siloxane liquid is computed

to be very close to the target frequency of 2.5 kHz, and the

acceleration necessary to produce the 34 kPa zero-to-peak pressure

level is computed to be 36 g^.

Measured amplitude ratios of these liquid-and-tube combinations ranged

from 33 for the 10-St liquid to 13 for the 30-St and 60-St liquids.

Results of measurements with dimethyl siloxane liquids are given in

table 3.
-6-

2.2.3.2 A series o£ experiments using both 10-St and 60-St liquids

was performed to determine tube diameter for optimum damping. Tubes

with diameters of 2.4, 1.1, 0.50, 0.28, 0.23, and 0.15 cm were tested.

The fixture used for the tests with the 2.4-cm column was that

illustrated in figure 3. The 1.1-cm column fixture was of similar

construction. The fixtures for the smaller-diameter columns were of

similar construction to that of the fixture used for the magnetic

damping experiments and illustrated in figure 1.

The two larger diameter fixtures were filled as described in

2.2.3.1. The four smaller-diameter fixtures were filled by submerging

them base-up in a beaker of the test liquid. The transducer was

suspended inside of the beaker with the liquid covering the

mounting threads. The beaker was placed in the vacuum desiccator,

and the pressure lowered as before. After the beaker was removed

from the desiccator, the transducer was screwed into the fixture base

while still immersed in the liquid. This procedure was intended to

prevent air bubbles from contaminating the system.

The fixture was mounted on the vibration exciter armature and the amplitude ratio measured. With 60-St liquid, amplitude ratios of 13, 8,

and 3.3 were obtained with tubes of 2.4-, 1.0-, and 0.5-cm-i.d.,

respectively. Tubes of smaller diameter could not be filled

successfully with 60-St liquid. With 10-St liquid, the measured amplitude ratios were 33 for a 2.4-cm tube, 26 for a 1.1-cm tube, 7.4 for a 0.50-cm tube, 2.7 for a 0.28-cm tube, and 1.4 for a 0.23-cm tube. With

10-St liquid the 0.15-cm tube was slightly overdamped, and no measurement was taken. Examination of the results of these experiments suggests

that the tube diameter for optimum damping (defined as amplitude ratio = 1.04) with 10-St liquid should lie between 0.15 and 0.23 cm.

2.2.4 Multi-Tube Fixture Experiments . A new fixture was constructed

based upon the results of the experiments described in 2.2.3. This

fixture was designed to be used with 10-St liquid and was of multi-tube

design; that is, a single large tube was packed with a number of smaller

tubes, and the voids between tubes filled so that the cross - sect ional

area of any liquid column would be no greater than that of a small

tube. As shown in figure 4, a number of 8-cm lengths of 0.16-cm-i.d.

brass tubing were soldered together and into a 2.4-cm-i.d. brass

tube about 11 -cm long, so that the bundle was 1 cm away from the intended

top end of the large tube. Solid copper rods were used to fill large

spaces between tubes. A plug was soldered into the other end of the

large tube, with a small space between the top of the plug and the

bottom of the bundle. A hole was drilled through the plug at its center,

and threaded to accept a transducer for test. This multi-tube design

permitted the use of small -diameter tubes for damping in a fixture large

enough to accept a pressure transducer for test. The clear space at the

top of the bundle permitted a more precise measurement of liquid level

than would have been possible if the level had to be determined inside

a 0.16-cm tube.
-7-

Filling this fixture with 10-St liquid required modification of the

vacuum- filling procedure previously described in 2.2.3.1. With a liquid

of this viscosity and with the given tube size, it proved necessary to

pour the liquid in a little at a time and to reduce the pressure around

the fixture after each addition of liquid.

Sinusoidally varying pressures of 34 kPa zero-to-peak, of constant amplitude to within ±5%, were produced in this fixture at an acceleration of

36 g zero-to-peak at frequencies between 40 Hz and 750 Hz. Displacement capability of the vibration exciter limited the maximum acceleration

to less than the 36-a level below 40 Hz. At the lower acceleration level

of 10 5' a sinusoidally varying pressure of 9.7 kPa zero-to-peak was

produceS between 20 Hz and 1250 Hz, of constant amplitude to within ±5%,

except for an anomaly in the region of 500 Hz observed in a number of

measurements. Detailed results for the multi-tube fixture are given • for measurements with transducer A-5 in table 4, with the measured

response expressed as a root-mean-square value in millivolts.

To provide an indication of the temperature stability of this liquidand-tube combination, the effect on the frequency characteristics of

temperatures 10°C above and below room temperature (25°C) was

investigated. The fixture was mounted on the vibration exciter armature, and an environmental chamber placed around it. The frequency

characteristics were measured at 15°C and at 35°C after a soak time

of 30 min to allow the liquid and fixture temperatures to stabilize.

The results of this experiment are given in table 5 with the measured

transducer response, corresponding to various test frequencies, expressed

as a root -mean- square value in millivolts for the three temperatures;

measurements of pressure amplitude at a given frequency agree to within

±6%. Transducer A-4 was used for these measurements, as A-5 was not

available. Both A-4 and A-5 have temperature coefficients of about

0.05% . °C-^ .

2.2. S Proposal for Balls as Tube Packing. At an early stage of the

work, the use of a material such as sea sand had been proposed as a means of increasing the column wetted surface, and hence the degree

of damping, by a very large factor. However, the results of a preliminary experiment discouraged further work along these lines.

The comparative success of the multi-tube fixture design suggests

that further investigations of the use of small particles is now

warranted. The suggestion has been made that small spheres, such

as balls used in instrument -grade ball bearings, be packed into a fixture tube. Because balls can be added incrementally, problems of

filling the column with the 10-St fluid may not be as great as with

the multi-tube fixture. Using balls of different sizes for different

packings of the tube should provide a wide range of wetted surface

areas. Accordingly, work with columns packed with balls will be

included in the next reporting period.

*As 36 g_^ was close to the upper capabilities of the vibration exciter

at low frequencies and operation at that level resulted in severe

shaking of the transducer leads, a majority of the tests were conducted

at 10 g . Reducing the acceleration level also reduced the risk of

of exciter thermal overload.
-8-

3. PLANS FOR THE REPORTING PERIOD AUGUST 15, 1974 TO DECEMBER 15, 1974

Work on this task is scheduled for completion in the next reporting

period.

3.1 Check-Out of Controller for Vibration Exciter

A programmable controller system for the vibration exciter, capable

of automatic frequency sweeping at constant armature acceleration,

amplitude, or velocity over the frequency range 5 Hz to 5000 Hz,

has been delivered to the laboratory but not yet tested. Advantages

provided by this system include the capability of measuring and recording transducer response over a continuous frequency sweep instead of at

a necessarily limited number of discrete frequencies. This controller

system will .be checked out and put into operation before further tests

are conducted.

3.2 Damping with Small Spheres

As discussed in 2.2.5, an evaluation of the use of balls as a packing

for the fixture tube will be carried out.

3.3 Tests Using Mercury

A brief series of experiments using mercury as the working fluid

may be conducted to determine if the advantages of the high density

of this material compensate for the hazards and difficulties associated with its use. These experiments will be dropped from the

program if other approaches are successful.

3.4 Transducer Calibration

Transducers supplied by NASA Langley will be calibrated using the method

selected on the basis of the work of this project.

4. REFERENCES

[1] Lederer, P.S., Development of a Dynamic Pressure Calibration

Technique — Progress Report for the Period June 15, 1973 to

September 15, 1973, NBSIR 73-290 (October 1973).

[2] Vezzetti, C.F., Lederer, P.S., and Hilten, J.S., Development of

a Dynamic Pressure Calibration Technique — Progress Report for the

Period September 15, 1973 to February 15, 1974, NBSIR 74-503(R)

(June 1974) .

,

[3] Hilten, J.S., Lederer, P.S., and Sethian, J.D., A Simple

Hydraulic Sinusoidal Pressure Generator, NBS Tech Note 720 (April

1972) .
Table 1

Resonance Frequency and Amplitude Ratio of Liquid- and-Tube Combinations

Liquid

Water

Tetrabromo ethane

"Light" Petroleum

Oil

"Heavy" Petroleum

Oil

Fluorocarbon Liquid

Tube

2.2- cm Inside Diameter

Smooth Walls

1.3- cm Inside Diameter

Smooth Walls

1.3-cm Inside Diameter

Spiral Fins

1.3-cm Inside Diameter

Smooth Walls with Filter

1.3-cm Inside Diameter

Smooth Walls with Filter "HX'

51-Channel Tube

Rectangular Cross Section

with Interlacing Fins

2.2-cm Inside Diameter

Smooth Walls

l.'-cm Inside Diameter

Smooth Walls with Filter "C"

1.3-cm Inside Diameter

Smooth Walls with Filter

51-Channel Tube

2.2- cm Inside Diameter

Smooth Walls

1.3- cm Inside Diameter

Smooth Walls with Filter

51-Channel Tube

2.2-cm Inside Diameter

Smooth Walls

51-Channel Tube

2.2-cm Inside Diameter

Smooth Walls

'HX"

Resonance Amplitude

Frequency Ratio

(Hz)

944 14

732 12

639

702

713

*

642

466

918

918

706

926

'vSOO

425

9 . 5

8 . 0

9.0

5.0

3 . 7

16

3.8

4.5

12

1.1

9.0

*No data obtainable
Table 2 Characteristics of Working Liquids

Liquid Viscos ity

@25°C

(St)

Dens ity

(kg/m

Ve loc ity

of

Sound

(m/s)

Comments

Mercury •,

.

^ 0. 001 13. 6 X 10^ 1410 Health hazard; dissolves

most metals; low vapor

pres sure

Tetrabromoe thane

0.080 2. 95 X 10 ^ 1007 Corrosive to steel,

aluminum, and other

metals, and rubber;

unpleasant odor; nontoxic; high vapor

pressure

Fluorocarbon 0.026 1. 88 X 10 ^ 730 Non-toxic; non-flammable

Glycerine ' 7.500 1. 26 X 10^ 1904 Non-toxic; water soluble

Water 0.009 1

.

00x10^ 1460 High vapor pressure

Dimethyl

Siloxanes

* 0. 97 X 10^ 987 Low vapor pressure; nontoxic; little dependence

of viscosity on

temperature

Petroleum Oils * 0. 86 X 10^ 1340 Viscosity highly dependei

on temperature

*Available in large range of viscosities.

y

U I

11!
Table 3

oystem Resonance Frequency and Amplitude Ratio for 10-cm Columns

of Dimethyl Siloxane Liquids

Viscosity Resonance Amplitude

(St) _ Frequency Ratio

(Hz)

10 2000 33

12.5 2000 20

30 2100 13

60 1900 13

Tube diameter = 2.4 cm; acceleration = 10 g zero-to-peak.
" Table 4

Multi-Tube Fixture Frequency Response Characteristics

10- St Dimethyl Siloxane

Transducer A

Frequency Transducer Response Normalized

(Hz) (mV rms) Transducer Response*

run 1 run run 3 run 1 r un 2 run 3

40 94. 0 95. 1 94 . 5 0. 98 10 0 0.99

50 94. 4 95. 7 95 . J) 0 . 99 10 0 1 . 00

75 95 . 1 95

7 96

0 10 0 100 1.01

100 96. 1 96. 7 96. 9 101 1

01 1 . 01

150 96.4 97. 4 97. 7 101 102 1 . 02

200 97.1 97. 7 98. 0 102 1 . 02 1 . 03

300 98.3 98. 4 99. 3 1

03 1

03 1 . 04

400 • 101.3 100. 8 92. 9 1

06 ].

06 0.97

500 96. 2 95. 8 96. 9 1

01 100 1 . 01

750 104.102. 9 104. 2 1

09 1 . 08 1 . 09

1000 112.9 110. 6 113. 1 1. 18 116 1 .18

1250 106. 1 106. 4 111 1 . 11

3000 47. 7 0. 50

Acce 1 erat ion = 36 a zero -to -peak

^Average of transducer responses from 40 Hz to 100 Hz set equal

to 1.00.
Table S

Multi-Tube fixture Frequency Response

Characteristics at 15°C, 25°C, and 35°C

10-St Dimethyl Siloxane Liquid

Transducer A

Frequency Transducer Response Noriiialized

(Hz) (mV rms) Transducer Response

15° c 25''C 35° C 15 2 5°C 3S

20 2 4

g A A 25. 1 24. 5** 0. 96** 0 . 97 0. 9 5**

25 25. 2 * * 25. 2 24. g * * 0. gg * * 0 . 98 0. g 7 * ft 30 25. 5 25. 4 25. 1 0. 9 9 0 . 98 0. 97

40 25 . 1 25. 6 25. 3 1

00 0 . 99 0. 98

50 25. 8 25. 8 25. 4 1. 00 1 . 00 0. 98

75 26. 0 25 9 25. 7 101 1 .00 1. 00

100 26. 2 26. 1 25. 9 102 1 . 01 1, 00

150 26. 4 26. 3 26. 2 102 1 .02 1 . 02

200 26. 5 26. 5 26. 3 1

03 1 . 03 1

02

300 26. 6 26. 7 26. 8 1

03 1 .03 1 . 04

400 26. 6 27 . 0 27 . 3 1

03 1 . 05 1. 06

500 22. 7 24. 4 24. 2 0. 88 0 . 95 0. 94

750 26. 6 27. 7 28. 7 1

03 1 . 07 1. 11

1000 26. 7 28. 2 29. 7 1

03 1 . 09 1

15

1250 25. 4 27 1 28 . 0 0. 98 1 . 05 109

1500 25. 3 23. 8 24 . 3 0. 90 0 . 92 0. 94

1750 23. 3 22. 8 22 . 3 0. 90 0 . 88 0. 86

2000 25. 2 25 4 23. 4 0. 98 0 . 98 0. 91

2250 41

2 29. 7 28. 7 1. 60 1 .15 1. 11

2500 61. 2 55. 0 55. 2 2 . 37 7 .13 2. 06

2750 58. 5 1

47

3000 22. 6 0. 88

Accelerat ion = 10 zero--to -peak.

*Average of transducer responses from 40 Hz to 100 Hz set equal to 1.00

**Taken at less than 10 g because environmental chamber limited the

displacement of the vibrating column.

USCOMM-NBS-DC
, f-

'' ;

_1
TRANSDUCER

4

j—>

2.5 cm

GLASS TUBING

ALUMINUM BASE

Figure 1. Fixture for magnetic-damping experiments. The glass tubing

HAD A bore of 3.5 CM. FIXTURES OF SIMILAR CONSTRUCTION WERE

EMPLOYED FOR SOME OF THE EXPERIMElvTS USING DIMETHYL SILOXAriE

LIQUIDS. For this work, glass tubing with BORES OF 0.15,

0.2/ 0.3/ OR 0.5 CM WAS USED.
COLUMN HEIGHT, cm

Figure 2. Calculated levels of acceleration required to provide a pressure

AMPLITUDE OF 34 kPa AS A FUNCTION OF COLUMN HEIGHT FOR VARIOUS LIQUIDS;

.: . . A/ MERCURY; B/ TETRABROMOETHANE; C, FLUOROCARBON; D, GLYCERINE; E, WATER;

F, DIMETHYL SILOXANE; AND G, PETROLEUM OILS. ThE SYMBOL A IDENTIFIES

THE POINT ON EACH CURVE CORRESPONDING TO A CALCULATED NATURAL FREQUEhCY

OF 2.5 kHZ/ and THE SYMBOL # IDENTIFIES POINTS CORRESPONDING TO A

CALCULATED NATURAL FREQUENCY OF 10 KilZ.
'11 cm

BRASS TUBING

Figure 3, Fixture for experiments using dimethyl siloxane liquids.

This design of fixture was used v^hen the design of figure

1 was not suitable. The' brass tubing had bores of 1.1 or

2.^ CM.
SIDE

10 cm

LIQUID SURFACE

L

1cm

0.32-cm O.D., 0.16-cml.D. TUBES

BRASS T4JBING

BRASS PLUG

TRANSDUCER

TOP

0.32-cm O.D., 0.16-cm I.D. TUBES

SOLID RODS

FiGURt 4. riULTI-TUBE FIXTURE.
NBS-1 14A (REV. -7 J)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET NBSIR 75-708

2 . ( > 0 V

' I A (.(( .s .s 1 1 1 1

N„.

J. i\c( ipictii ^. -Ti. ( '. .sion i\'>.

A ri TI 1.' AMIA <I U I t 11 1 4. 1 I I I - 1 . .T l\ I ' >l 1 ' I 1 1 1 . 1 DEVELOPMENT OF A DYNAMIC PRESSURE CALIBRATION

lELHNiQuL — A rKOuRLSo KEFUKl

5. Dul.lu .111011 D.it.

6» i 't r i or ni 1 n g OrgtUi i /tit ion ^ oili'

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

8. I'l rlorniing Organ. Kopori No.

v. l-'l'. K 1- OKMINCi OKCiANl/.AI ION NAMr. AND ADDKIiSN

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Dro)ori/ l a.sk/Work Dim No. 4 2 53456

1 1 . < ontraoi 'drant No. L-88319

12. Sp (.in s c)r 1 Or^ .m i / a 1 1 (,in N .1 m t uiti l1 ^ c mp 1 c t c A J J re s s (S tree t , Ci ty , State, ^ IP) NASA Langley Research Center

Hampton, Virginia 23365

13. Type- of Rcpori & l'( rloii

( ovcroj Interim

2/15/74 to 8/15/74

14. Spi)nsoring Agi n. y ' oil(

15. SDl^Fl.HMHNTAK'*- NOI i:S

16. ABSTRAC T (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.) Work continues on the development of a method of producing sinusoidally

varying pressures of at least 34 kPa zero-to-peak with amplitude variations within ±5% up to 2 kHz for the dynamic calibration of pressure

transducers.

Sinusoidally varying pressures of 34 kPa zero-to-peak have been produced,

to date, between 40 Hz and 750 Hz by vibrating a 10-cm column of a dimethyl siloxane liquid at 36 g^^ zero-to-peak. Damping of the liquid

column was accomplished by packing the fixture tube with a number of

smaller diameter tubes.

17. KEY Vt'ORDS (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 pressure;

transducer

18. AVAILABILITY \W_ Unlimited 19. SECURITY CLASS

(THIS REPORT)

21. NO. OF PAGES

r For Official Distribution. Do Not Release to NTIS

UNCL ASSIFIED 19

1

' Order From Sup. of Doc, U.S. Government Printing

Washington, D.C. 20402. SD Cat. No. C13

Office 20. SEC:URITY CLASS

(THIS PAGE)

22. Price

1 X Order From National Technical Information Service

Springfield, Virginia 22151

(NTIS)

UNCLASSIFIED $3.25

USCOMM-DC 29042-P74