To measure fluid pressure with minimum disturbance to fluid flow, a miniature pressure transducer can be imbedded and faired into the test surface. Incorporated in the design are piezoresistive elements mounted on a diaphragm, which transform pressure strains into an electrical signal

Schaffer, R. J.

English

NASA Technical Reports Server

May 1964	 Brief 64-10021 
NASA TECH BRIEF 
This NASA Tech Brief is issued by the Technology Utilization Division to acquaint industry 
with the technical content of an innovation derived from the NASA space program. 
Pressure Transducer 3/8-Inch in Size Can Be Faired into Surface 
Flange 
-.__..E:22:J-----	 Body 
Stiffening Ring
ring Plug 
Diaphragm
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Fastener 
TRANSDUCER ASSEMBLY 
The problem: To design a small pressure trans-
ducer that can be imbedded and faired into the 
surface of a model or a device under test. Fairing 
allows fluid pressure measurements to be made with 
minimum disturbance to the fluid flow about a test 
item. Small faired pressure transducers should be 
useful in making point-to-point measurements of high 
pressure-gradient areas and measurements of flow 
through marginally accessible or narrow-clearance 
spaces. 
The solution: A miniature pressure transducer that 
can be imbedded and faired into the selected test 
surface. Piezoresistive elements mounted on a dia-
phragm transform strains induced by pressure into a 
proportional electrical signal. It has a range of more 
than 500 pounds per square inch and furnishes an
electrical output suitable for recording instruments, 
without amplification. This device provides a stress-
free system. 
How it's done: Three parts are needed: a flange 
which is imbedded or threaded into the test surface, 
a fairing plug, and a diaphragm on which the piezo-
electric sensing element is mounted. Only normal 
machining is needed for parts, and the mounting hole 
can be made quickly and easily. Transducers as small 
as 0.350-inch in diameter by 0.190-inch in thickness, 
weighing 0.05 ounce, have been used. 
With this design the sensing element is assembled 
so that it is free to reflect the static and dynamic 
forces of the liquid or gas pressure, and not unwanted 
forces affecting the body in which the transducer is 
imbedded. Thus, the mounting flange provides an 
(continued overleaf) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States Govern-
ment, nor NASA, nor any person acting on behalf of NASA: A. Makes 
any warranty or representation, express or implied, with respect to the 
accuracy, completeness, or usefulness of the information contained in.
this document, or that the use of any information, apparatus, method, 
or process disclosed in this document may not infringe privately-owned 
rights: or B. Assumes any liabilities with respect to the use of, or for 
damages resulting from the use of, any information, apparatus, method, 
or process disclosed in this document.
https://ntrs.nasa.gov/search.jsp?R=19640000013 2020-03-11T17:06:54+00:00Z
elastic suspension, maintains axial and radial align-
ment, and, in some cases, seals the exterior portion of 
the diaphragm. 
The fairing plug or core receives all compressive 
forces from the mounting flange and serves as a trim 
surface which can be contoured to the material in 
which the transducer is mounted. It also supplies a 
small sensing orifice, provides a smooth run for fluid 
away from the parting line, and dampens vibratory 
elastic energy. 
Units of this type offer considerable utility since 
they can measure absolute pressure or can sense rela-
tive pressure between one side of a test body and the 
other. Transducers of this type can be installed on 
either the high-pressure or the low-pressure side of a 
rotating blade if one side is inaccessible, as in an 
array of blades of an axial flow pump. 
An alternate design can be used having an orifice in 
both sides of the transducer. Sensing elements would 
then be mounted on two sides of a separate diaphragm 
placed between the stiffening ring and an inner core 
surface. A variety of diaphragms, such as flat, hat
type, rimmed, or dished, can be used. The cavity, on 
one or both sides of the diaphragm, can be utilized for 
damping the undesirable effects of fluids in certain 
installations by filling the cavity with a suitable 
substance. 
Notes: 
1. This innovation is suitable for use in models when 
testing hydrofoils, airfoils, fluid flow nozzles, nose 
cones, and aircraft surfaces, particularly when it is 
desirable to fair the transducer to the surface. 
2. For further information about this innovation 
inquiries may be directed to: 
Technology Utilization Officer 
Western Operations Office 
160 Pico Boulevard 
Santa Monica, California 90406 
Reference: B64-10021 
Patent status: NASA encourages commercial use 
of this innovation. No patent action is contemplated. 
Source: Robert J. Schaffer 
(WOO-065) 
Brief 64-10021


Pressure transducer 3/8-inch in size can be faired into surface

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