Transducer measures gas pressure profiles in high temperature, short duration, gas flows usually found in devices where pressure pulses may have durations of few microseconds to several milliseconds. Assembly includes fluid delay line, delay chamber, and flow restrictor for equalizing steady state pressure on diaphragm's side

Seegmiller, H. L. B.

English

NASA Technical Reports Server

June 1971	 Brief 71-10200 
S	 NASA TECH BRIEF 
Ames Research Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield; Virginia 22151. Requests for individual copies or questions relating to the. Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D. f. 20546. 
Inertia Diaphragm Pressure Transducer 
S
The problem: 
To devise a sensitive pressure transducer which can 
measure gas pressure profiles in the high temperature, 
short duration, gas flows characteristically found in 
shock tubes, wind tunnels, or other devices where 
pressure pulses may have durations of a few micro-
seconds to several milliseconds. In available devices, 
diaphragm displacement depends upon elastic defor-
mation under pressure, but the transducers are too 
insensitive for measurement of pressure pulses of 
short duration because an elastic system with the req-
uisite rapid response requires a large spring return 
force. 
The solution: 
A new transducer consisting of a diaphragm 
mounted in such a way that its resistance to sudden 
movement is provided primarily by its inertia; in the 
new transducer, the acceleration of the diaphragm is 
measured instead of its displacement. 
How it's done: 
A diaphragm is freely supported so that only its 
inertia can resist the force of a pressure pulse. The 
periphery of the diaphragm is concentrically cor-
rugated to provide a low spring constant and the 
diaphragm is mounted in a housing that is partially 
filled with an electrically insulating support for a 
fixed conducting plate. In operation, a pressure pulse 
of short duration and a very high rise time accelerates 
the diaphragm in the direction of the fixed plate. The 
diaphragm is accelerated in accordance with New-
ton's second law: F=Ma, where a is the acceleration,
triction 
Chamber Oher 
Insulation 
Diaphragm
Reading and Insulator Recording Plate F	 Circuit
Fixed 
Plate 
F is the force exerted by the gas against the dia-
phragm, and the mass M is a fixed and known quan-
tity. Since the diaphragm and the fixed plate form a 
capacitor, motion of the diaphragm toward the fixed 
plate can provide an electrical quantity related to the 
spacing between the diaphragm and the fixed plate. 
Thus, by recording the time-displacement history of 
the diaphragm movement, the acceleration and the 
displacement force (pressure) can be evaluated. 
The transducer assembly includes a fluid delay 
line, a delay chamber, and a flow restrictor for equal-
izing the steady state pressure on both sides of the 
diaphragm; the delay prevents the pressure pulse 
from appearing simultaneously on both sides of the 
diaphragm.
(Continued overleaf) 
This document was prepared under the sponsorship of the National 	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States 	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States 	 will be free from privately owned-rights. 
https://ntrs.nasa.gov/search.jsp?R=19710000199 2020-03-17T02:19:34+00:00Z
Notes: 
1. Diaphragms are preferably made of soft, heavy, 
metals such as platinum; however, for certain ap-
plications, plastics with metallized surfaces may be 
preferable. 
2. If the diaphragm is made of magnetic material, or 
if a magnetic plate is fastened to the diaphragm 
and a coil of wire is mounted close to it and within 
insulating material, the velocities of the diaphragm 
can be sensed as an induced output voltage. 
3. No additional documentation is available. Specific 
questions, however, rny be directed to: 
Technology Utilization Officer 
Ames Research Center 
Moffett Field, California 94035 
Reference: B71-10200
Patent status: 
This invention has been patented by NASA (U.S. 
Patent No. 3,352,157) and royalty-free license rights 
will be granted for its commercial development. In-
quiries about obtaining a license should be addressed 
to:
Patent Counsel 
Mail Code 200-1 1A 
Ames Research Center 
Moffett Field, California 94035 
Source: Henry L. B. Seegmiller of 
NASA - Ames Research Center 
(XAC-2981)
. 
E 
Brief 71-10200
	
Category 05


Inertia diaphragm pressure transducer

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