Method and apparatus for obtaining dynamic calibrations of pressure transducers. A calibration head (15), a flexible tubing (23) and a bellows (20) enclose a volume of air at atmospheric pressure with a transducer (11) to be calibrated subject to the pressure inside the volume. All of the other apparatus in the drawing apply oscillations to bellows (20) causing the volume to change thereby applying oscillating pressures to transducer (11) whereby transducer (11) can be calibrated

Davis, Pamela A.

Davis, William T.

Hess, Robert W.

NASA Technical Reports Server

United States Patent [191 [ i l l  Patent Number: 4,698,997 
Hess et al. [45] Date of Patent: Oct. 13, 1987 
1541 OSCILLATION PRESSURE DEVICE FOR 
DYNAMIC CALIBRATION OF PRESSURE 
TRANSDUCERS 
[75] Inventors: Robert W. Hem; William T. Davis, 
both of Yorktown; Pamela A. Davis, 
Newport News, all of Va. 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
1731 Assignee: The United States of America as 
[21] Appl. No.: 890,983 
1221 Filed: Jul. 30, 1986 
Related U.S. Application Data 
1631 Continuation-in-part of Ser. No. 711,551, Mar. 14, 
1511 Int. Cl.4 .............................................. GOlL 27/00 
1521 US.  Cl. ...................................................... 73/4 R 
1581 Field of Search ................ 73/4 R, 4 V, 4 D, 147, 
73/866.4, 865.6 
1985, abandoned. 
1561 References Cited 
U.S. PATENT DOCUMENTS 
2,976,715 3/1961 Roese et al. .......................... 73/4 R 
3,045,470 7/1962 Crandell et al. ...................... 73/4 R 
3,232,091 2/1966 Glassey ................................. 73/4R 
3,237,443 3/1966 Vinson .................................. 73/4R 
3,383,903 5/1968 Bogusz .................................. 73/4 R 
3,427,858 2/1969 Morrison .............................. 73/4 V 
3,590,626 7/1971 Hugli .................................... 73/4R 
3,777,546 12/1973 Rollins .................................. 73/4 R 
3,868,844 3/1975 Klein ..................................... 73/4 R 
4,051,712 10/1977 Zias et al. ............................. 73/4 R 
4,499,751 2/1985 Riggs .................................... 73/4R 
4,512,179 4/1985 Umble et al. ......................... 73/4 R 
4,515,012 5/1985 Jenkins et al. .................... 73/4 R X 
4,590,791 5/1986 Reed et al. ............................ 73/4 R 
FOREIGN PATENT DOCUMENTS 
267979 7/1970 U.S.S.R. ............................... 73/4R 
OTHER PUBLICATIONS 
“Primary Calibration of Pressure Transducers to 10,OOO 
H2”, Conference: Proceedings of the 15th International 
ISA Aerospace Instrument Symposium, Las Vegas, 
NV, USA, May 1960, John D. Favour et al., pp. 89-96. 
“Calibrator for Dynamic Pressure Transducers”, In- 
struments & Automation, vol. 27; pp. 1074-1075, Ray- 
mond C. Baird et al. Jul. 1954. 
“Basic Study into the Evaluation of Transducer-Type 
Pressure Gauges”, Instrument Practice, pp. 303-304, 
Mar. 1959. 
AIAA-87-0035, “Highlights of Unsteady Pressure 
Tests on a 14 Percent Supercritical Airfoil at High 
Reynolds Number, Transonic Condition”, 17 page 
paper presented at AIAA 25th Aerospace Sciences 
Meeting, Jan. 1987, Reno, Nevada, Robert W. Hess et 
al. & color photographic blowups of FIGS. 1 & 2 from 
p. 6 of above paper. 
Primary Examiner-Tom Noland 
Attorney, Agent, or Firm-George F. Helfrich; John R. 
Manning 
[571 ABSTRAa 
Method and apparatus for obtaining dynamic calibra- 
tions of pressure transducers. A calibration head (15), a 
flexible tubing (23) and a bellows (20) enclose a volume 
of air at atmospheric pressure with a transducer (11) to 
be calibrated subject to the pressure inside the volume. 
All of the other apparatus in the drawing apply oscilla- 
tions to bellows (20) causing the volume to change 
thereby applying oscillating pressures to transducer (11) 
whereby transducer (11) can be calibrated. 
10 Claims, 1 Drawing Figure 
241 25 20 
J -  ----- 26 ‘ 22 - 
.---I - - 
21’- 
30 
HYDRAULIC 
r 23 
https://ntrs.nasa.gov/search.jsp?R=20080007417 2019-08-30T03:20:35+00:00Z
U.S. Patent Oct 13,1987 
M cu 
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4,698,997 
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4,69 8,997 
1 2 
BRIEF DESCRIPTION OF THE DRAWINGS 
The sole FIGURE is a schematic block diagram of a 
OSCILLATION PRESSURE DEVICE FOR 
DYNAMIC CALIBRATION OF PRESSURE 
TRANSDUCERS 
ORIGIN OF THE INVENTION 
The invention described herein was made by employ- 
ees Of the United States Government and may be manu- 
factured and used by or for the Government for govern- 
mental purposes without the payment of any royalties 
thereon or therefor. 
This application is a continuation-in-part of applica- 
preferred embodiment of the invention. 
DESCRIPTION OF THE PREFERRED 
EMBODIMENT 
Turning now to the embodiment of the invention 
selected for illustration in the drawing, the number 11 
10 designates a transducer that is to be calibrated. Trans- 
ducer 11 is located below a surface 12 and has a hole 13 
leading to it through which pressure measurements are 
made by the transducer. The output of transducer 11 is 
15 chamber 16 and is designed so that the calibration head 
will set flat on surface 12 and subject the pressure inside 
chamber 16 to transducer 11 through hole 13. A short 
length of tubing 19 extends from the calibration head 15 
20 short length of tubing (not shown) could extend from the dynamic calibraion of pressure transducers. 
Prior dynamic transducer calibrations were made the bottom of the calibration head 15 into hole 13 to 
using a static calibration device to determine the sensi- provide a seal around transducer ll. Calibration head 
calibration could be made at only one frequency in the be fitted pressure tight into the hole by any conven- 
using an acoustic calibrator with the transducer sure in chamber 16. in another hole in calibration head 
tor. The range of pressure and frequencies of interest in that it produce an output proportional to the pres- 
unsteady aerodynamic pressure m m ~ ~ m e n t s  is from sure inside chamber'l6. A bellows 20 including a Teflon 
Os1 to HZ to 200 Hz* The previous 30 shaft 21 has a chamber 22. Teflon shaft 21 is connected 
techniques do not satisfy the requirements outlined to the free end of bellows 20 and keeps the bellows 
above because the dynamic calibration cannot be Per- axially aligned during compression and also reduces the 
formed in situ at representative frequencies and oscillat- inactive volume of the bellows. Chamber 16 of the 
ing pressures. calibration head 15 is connected to chamber 22 at the 
An object of the present invention is a method and 35 fixed end of bellows 20 by means of a flexible tubing 23. 
apparatus to accurately measure the dynamic character- Consequently, calibration head 15 is easily movable 
istics of pressure transducers installed in models and relative to bellows 20. 
flight vehicles at the frequency and oscillating pressure A hydraulic actuator 24 including a piston 25 and a 
ranges ~nCountered during an Pressure mea- shaft 26 has its shaft attached to Teflon shaft 21. When- 
surement test to establish that static and dynamic sensi- 40 ever piston 25 is moved in either direction shaft 26 
tivities are the same. collapses or expands bellows 21 thereby changing the 
Another object ofthe invention is a method and aPPa- volume of chamber 22. Shaft 26 is also attached to the 
ratus to accurately measure the dynamic characteristics probe of a linear-variable-differential-transformer 
Of pressure transducers in their installation Configura- (LVDT) 27 which produces a signal indicating the 
tions to determine if the installation configuration ef- 45 position of piston 25. Piston 25 is positioned by a hy- 
fects the amplitude and phase response as related to draulic pressure supply 28 and a hydraulic valve 29 by 
conditions on the surface of the model. controlling the pressure through tubings 30 and 31 to 
A further object of the invention is an apparatus that hydraulic actuator 24. 
is portable and can accurately measure the dynamic Hydraulic valve 29 is controlled by a low frequency 
characteristics of pressure transducers in situ. 50 signal from a signal generator 32 which is applied 
Other objects and advantages of the present invention through a difference circuit 33 to the valve. The output 
will be readily apparent from the following description of signal generator 32 can be varied in frequency and 
and drawing which illustrates a preferred embodiment amplitude. Signal generator 32 should be of the type 
of the present invention. capable of generating various waveforms across the 
tion Ser. No. 711,551, filed Mar. 14, 1985, now &an- through electrical leads 14. A calibration head 15 has a doned. 
BACKGROUND OF THE INVENTION 
This invention relates generally to calibrators and in 
particular to a portable pressure device for and covers hole 13 to provide a sea] around the hole. A 
tivity of the pressure transducer* Dynamic transducer 
kilo hertz range at 
nlounted in an adapting fixture accepted by the calibra- 
15 has a hole in it so that a standard transducer 17 can 
On the Order Of O.O1 Psi 25 tional means such as threads and be subjected to pres- 
. 15 a pressure transducer 18 is pressure tight fitted SO 
Psi and from 
55 desired spectrum of frequencies and amplitudes. Gener- 
ator 32 should also possess an automatic sweep function SUMMARY OF THE INVENTION 
The present invention involves a method and appara- to provide for the- continuous variation of mplitude 
tus for the dynamic calibration of pressure transducers and frequency across the desired spectrum. A generator 
installed in models and flight vehicles, over a range of of this type that was used and that is commercially 
frequencies and oscillating pressures typically encoun- 60 available is a Bafco Model SD 330A Real-Time Spectro 
tered during an unsteady pressure measure test. A cer- Analyzer. Hydraulic valve 29 is also controlled by a 
tain oscillating pressure is produced and transmitted to servo feedback means by closing a switch 34 which 
the surface of the installation configuration under applies the output from LVDT 27 through a signal 
which lie the transducers to be calibrated. The resulting conditioner 35 to difference circuit 33. In addition, hy- 
outputs of the transducers are compared with the oscil- 65 draulic valve 29 can be controlled by a second servo 
lating pressure or with the output from a standard trans- feedback means by closing a switch 36 which applies 
ducer to perform a dynamic calibration of the transduc- the signal from transducer 18 through a signal condi- 
ers located under the surface. tioner 37 to difference circuit 33. 
\ 
3 
4,698,997 
In the operation of this invention, calibration head 15 
is placed over hole 13 thereby enclosing chamber 16 at 
atmospheric pressure. The type of control is selected by 
closing one of the switches 34 or 36. Then a signal is 
generated by signal generator 32 thereby moving piston 
25, changing the volume of chamber 22 and changing 
the pressure inside chamber 16. The outputs of trans- 
ducers 11 and 17 are then measured. Inasmuch as the 
system has been calibrated to know the pressure in 
chamber 16 corresponding to the signal output of signal 
generator 32 all of the data is available for calibrating 
transducer 11. 
The advantages of the present invention are numer- 
ous. It is especially useful as a portable transducer cali- 
brator. The invention provides a means of dynamically 
and statically calibrating a pressure transducer mounted 
in its installation configuration in a model or aircraft 
over a range of frequencies and amplitudes not available 
in commercial acoustic calibration devices. Addition- 
ally, the invention accurately calibrates these transduc- 
ers by maintaining a constant oscillating pressure 
through the use of a servo feedback system. Further- 
more, the constant oscillating pressure is developed 
using an open air bellows apparatus thereby removing 
the requirmeent of a closed gaseous or liquid pressure 
producing system. 
The above described description and drawings are 
only illustrative of preferred embodiments which 
achieve the objects, feature, and advantages of the pres- 
ent invention, and it is not intended that the present 
invention is limited thereto. Any modifications of the 
present invention which come within the spirit and 
scope of the following claims are considered part of the 
present invention. One such modification would be the 
use of a linear magnetic shaker to drive the system in 
place of the oscillating drive system shown and de- 
scribed 
What is claimed to be new and desired to be secured 
by Letters Patent of the United States is: 
1. A method for dynamically calibrating a transducer 
operating in the unsteady aerodynamic pressure range 
and located below the surface of a model comprising 
the steps of: 
locating a standard transducer adjacent to the surface 
of a model nearby the transducer being calibrated 
whereby pressure measurements along the top of 
the model are obtained; 
enclosing a volume of air at atmospheric pressure 
with the transducer located below the surface and 
the standard transducer adjacent to the surface 
subjected to the pressure inside the volume; 
changing the volume by a controlled amplitude and 
frequency; and 
varying the controlled amplitude and its frequency 
continuously whereby the transducer located 
below the surface is subjected to a pressure in the 
unsteady aerodynamic pressure range and the re- 
sulting output of the transducer located below the 
surface can be calibrated against the actual pres- 
sures along the top of the model as measured by the 
standard transducer located adjacent to the sur- 
face. 
2. Apparatus for dynamically calibrating a transducer 
operating in the unsteady aerodynamic pressure range 
and located below the surface of a model comprising: 
an enclosure for enclosing a chamber of air at atmo- 
spheric pressure; 
means for locating a standard transducer adjacent to 
the surface of a model nearby the transducer being 
calibrated whereby pressure measurements along 
the top of the model are obtained; 
4 
means for connecting the transducer located below 
the surface of a model and said standard transducer 
to said chamber to thereby subject the transducer 
and said standard transducer to the pressure inside 
said chamber; 
means for changing the volume inside said chamber 
by controlled amplitudes and frequencies to 
thereby change the pressure on said transducer; 
and 
means for varying the controlled amplitudes and 
frequencies continuously whereby said transducer 
can be calibrated while operating in the unsteady 
aerodynamic pressure range. 
3. Apparatus according to claim 2 wherein said enclo- 
sure is a bellows that can be either contracted or ex- 
4. Apparatus according to claim 3 wherein said means 
for changing the volume inside said chamber is a hy- 
draulic actuator connected to said bellows, a pressure 
supply and a hydraulic valve under the control of a 
20 signal generator for controlling the pressure to said 
hydraulic actuator. 
5. Apparatus according to claim 4 including means 
for producing a signal proportional to the pressure in- 
side said chamber and means for subtracting said signal 
from the signal from said signal generator to obtain a 
25 difference signal that is used to control said hydraulic 
valve. 
6. Apparatus according to claim 2 wherein said means 
for connecting said transducer to said chamber is a 
calibration head with a flexible tubing connecting the 
30 calibration head to said chamber whereby the calibra- 
tion head can be portable. 
7. Apparatus according to claim 6 wherein said cali- 
bration head provides the means for connecting said 
standard transducer to said chamber whereby said 
35 transducer can be calibrated against said standard trans- 
ducer. 
8. Apparatus according to claim 6 wherein said cali- 
bration head provides said means for locating said stan- 
dard transducer adjacent to the surface. 
9. Apparatus according to claim 2 wherein said means 
40 for varying the controlled amplitudes and frequencies 
includes a signal generator whereby said signal genera- 
tor produces signals that control the amplitude and 
frequency of the pressure inside said chamber so that 
the transducer can be calibrated while operating in the 
10. Apparatus for dynamic calibration of a pressure 
transducer over a range of frequencies of oscillating 
pressures and located below the surface of a model 
comprising: 
means for enclosing a chamber of air with the trans- 
ducer and a standard transducer only subject to the 
pressure inside said chamber; 
means for locating said standard transducer adjacent 
to the surface of a model nearby the transducer 
being calibrated whereby pressure measurements 
along the top of the model are obtained; 
means for producing a back and forth motion of an 
object at selected low frequencies; 
means for continuously varying the back and forth 
motion of said object whereby a range of ampli- 
tudes and frequencies of oscillating pressures is 
developed; and 
means responsive to the motion of said object for 
changing the volume of said chamber whereby said 
transducer located below the surface of the model 
can be calibrated against said standard transducer 
over the range of amplitudes and frequencies of 
oscillating pressures. 
lo 
15 panded. 
45 unsteady aerodynamic pressure range. 
50 
55 
6o 
65 
* * * * *  


Oscillation pressure device for dynamic calibration of pressure transducers

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