Transducer measures pressure by sensing the damping of a vibrating diaphragm immersed in the atmosphere to be measured. Improved sensor can be included in rugged, lightweight package for use aboard aircraft, meteorological vehicles, and space probes

Dimeff, J.

Lane, J. W.

English

NASA Technical Reports Server

$ Gas 
Inlet 
May 1972	 B72-10196 
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. Tecli 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.C. 20546. 
Wide-Range Dynamic Pressure Sensor 
The problem: 
To develop a sensor which can measure pressure 
over the range 10 to 103 torr (1.83 x 10 to 
133 kN/m2) and can be included in a rugged, light-
weight package for use aboard aircraft, meteoro-
logical vehicles, and space probes.
other is used to detect the amplitude or frequency of 
vibration. Since the space between the plates and 
diaphragms is filled with gas at the pressure to be 
measured, the gas dampens motion of the diaphragm 
and causes loss of energy, and it is necessary to in-
crease the electrical power input to the driver plate 
to maintain a given amplitude of vibration. Thus, by 
Damping Plate	 Diaphragm
ceramic 
Schematic Representation of 
Grid-Type Transducer Half 
The solution: 
A transducer which measures pressure by sensing 
the damping of a vibrating diaphragm immersed in 
the atmosphere to be measured. 
How it's done: 
A vibrating diaphragm pressure transducer con-
sists essentially of a thin metallic diaphragm under 
radial tension that is situated between closely spaced 
insulated metal plates or grids. One of the plates or 
grids serves as a driver and provides a means of elec-
trostatically forcing the diaphragm into vibration; the
Simplified Sketch of 
Damping Plate 
vibrating the diaphragm at its resonant frequency and 
at constant amplitude, the driving force needed to 
overcome gas dampening can be measured and cor-
related with the density or pressure of the gas sur-
rounding the diaphragm. Alternatively, the frequency 
is a function of gas pressure. 
The damping effect of the enclosed gas in a vibrat-
ing diaphragm pressure transducer increases with 
increasing pressure to the point where the sensor may 
cease to function as a simple mechanical resonant 
system and is not able to provide pressure indications 
above 1000 torr (133 kN/m 2 '). In many instances, the 
(continued overleaf) 
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mechanical frequency of the diaphragm is altered due 
to gas stiffness to the point where, it overlaps an 
acoustic resonance associated with the interior dimen-
sions of the transducer body. These problems have 
been minimized by the transducer configuration shown 
in the diagram. The performance of vibrating dia- 
phragm sensors at high pressures has been signifi-
cantly improved by substituting a grid-damping plate 
structure. The functions of the forcing plate and the 
sensing plate have now been taken over by forcing 
and sensing grids which are maintained close to the 
diaphragm (a few thousandths of a centimeter) while 
the solid plates that control the stiffness introduced 
by the gas are moved farther from the membrane. 
One of the main, advantages of this configuration is 
That it provides considerable freedom in choosing the 
interior transducer geometry without sacrificing effec-
tive driving force or displacement sensing sensitivity. 
Moreover, by orienting the grid area concentric and 
parallel to the membrane and by proper selection of 
the grid area, it is possible to suppress the sensing of 
higher modes of resonant vibration. 
The body of the grid-type transducer shown in the 
diagram is made of 42% nickel-iron alloy; the ceramic 
insulators are of alumina, and were chosen to provide 
the necessary thermal expansion coefficient. The dia-
phragm is 44% nickel-iron annealed at 516°C and it is 
mounted under tension to one-half of the sensor body 
by an overlapping spot weld. The grid structure is of 
0.1- mil (0.0025-mm) nickel wire mesh (50% open area) 
spot welded to the top of the damping structure. 
An electronic system' has also been designed to 
drive the pressure transducer to yield pressure meas-
urements over the range 10 to 4000 torr (1.38 x 10'6 
to 183 kN/m2). The displacement of the diaphragm 
causes a capacitance change which, in turn, generates 
an input to a velocity sensing preamplifier. The out-
put of the preamplifier is then amplified, filtered, 
rectified, and compared to a preset DC reference 
voltage. Any voltage difference is used to provide 
driving power at the resonant frequency of the dia-
phragm and at an amplitude sufficiently large so that 
the voltage difference is reduced to zero, that is, the 
rectified output of the preamplifier is constant and 
equal to the reference voltage. 
References: 
1. Dimeff, J
. , Lane, J . W., and Coon, C. S.: New Wide 
Range Pressure Transducer. Review of Scientific 
Instruments, vol. 33, p. 804, 1962. 
2. Southwest Research Institute: Vibrating Diaphragm 
Pressure Transducer. NASA SP-5020, August 1966. 
Notes: 
1. One version of the improved sensor gives pressure 
readings which are substantially independent of 
gas composition. 
2. Reference (2) may be obtained from: 
Superintendent of Documents 
U. S. Government Printing Office 
Washington, D.C. 20402 
Price $0.80. 
8. Additional information may be obtained from: 
Technology Utilization Officer 
Ames Research Center 
Moffett Field, California 94085 
Reference: TSP 72-10196 
Patent status: 
This invention is owned by NASA, and a patent 
application has been filed. Royalty-free, nonexclusive 
licenses for its commercial use will be granted by 
NASA. Inquiries concerning license rights should be 
made to: 
Patent Counsel 
Mail Code 200-1A 
Ames Research Center 
Moffett Field, California 94085 
Source: John Dimeff and James W. Lane 
Ames Research Center 
(ARC-10263) 
B72-10196	 Category 03


Wide-range dynamic pressure sensor

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