Capacitive accelerometer design enables the construction of highly miniaturized instruments having full-scale ranges from 1 g to several hundred g. This accelerometer is applicable to telemetry and can be tailored to cover any of a large number of acceleration ranges and frequency responses

Coon, G. W.

Harrison, D. R.

English

NASA Technical Reports Server

November 1966	 Brief 66-10491 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U. S. space 
program and to encourage their commercial application. Copies are available to the public from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Miniature Capacitive Accelerometer Is Especially Applicable to Telemetry 
Cap 
Diaphragm
	 Tantalum Disks 
4 Holes
	 Platinum Film 
Equally Spaced 
In Diaphragm	 Base 
The problem: 
To design a class of miniature, general purpose 
accelerometers which are applicable to telemetry and 
which maybe tailored to cover any of a large number 
of acceleration ranges and frequency responses. The 
accelerometers must be rugged, easily calibrated, in-
expensive, and insensitive to temperature changes. 
The solution: 
A capacitive accelerometer design which enables 
the construction of highly miniaturized instruments 
having full-scale ranges from I g to several hundred g.
Frequency responses are flat to 3 percent from 0 to 
1000 cycles per second for the lower acceleration 
ranges and from 0 to 3000 cycles per second for the 
higher ranges. The accelerometers are 0.25 inch in 
diameter but have been constructed as small as 0.15 
inch in diameter. Since the capacitive transducer 
modulates the "C" of the "L-C" circuit in the teleme-
try oscillator, the circuitry is extremely simple. 
How its's done: 
The capacitive accelerometer senses acceleration as 
a change in capacitance between a mass-diaphragm as-
sembly and a platinized fixed electrode.
(continued overleaf) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
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The base of the accelerometer is machined from a 
commercially available glass-metal, single terminal, 
electrical feedthrough. A metal diaphragm with equal 
masses attached to the center of each side is welded 
at its periphery to the rim of the base. The diaphragm, 
with attached mass, functions as the variable plate of 
the capacitor. A metal cap soldered to the base com-
pletes the assembly. To provide vibration damping, 
atmospheric pressure is hermetically sealed inside 
the accelerometer. Pressure is equalized across the 
diaphragm by four small holes through the dia-
phragm. 
The mass, spring constant, and required damping 
are provided in a minimum space. The mass consists 
of two thin, tantalum discs welded to the center of 
the stretched circular diaphragm.. The prestressed 
diaphragm provides the spring restoring force. The 
damping is produced by the energy dissipation of the 
air set in motion by mass-diaphragm displacements. 
The frequency response can be controlled by varying 
the plate spacings and the size of the air sumps. 
Notes; 
1. These accelerometers have been successfully in-
corporated in a telemetry circuit for use with free-
flight model instrumentation. Four channels were 
obtained by using four separate telemeter units, 
each operating at a different frequency and work-
ing into a separate receiver. Standard fm telemetry 
receivers were used to acquire the data.
2. The capacitive accelerometer has proved to be 
rugged, applicable to low or high g measurements, 
easily calibrated, and of adequate linearity and 
frequency response. 
3. This capacitive accelerometer is similar to a ca-
pacitive pressure cell described in NASA Tech 
Brief B63-10429, "Welded Pressure Transducer 
Made as Small as 1/8-inch in Diameter," March 
1964. 
4. Inquiries concerning this invention may be di-
rected to:
Technology Utilization Officer 
Ames Research Center 
Moffett Field, California 94035 
Reference: B66-10491 
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to NASA, Code 
GP, Washington, D.C., 20546. 
Source: G. W. Coon and D. R. Harrison 
(ARC-72)
.j 
Brief 66-10491	 Category 01


Miniature capacitive accelerometer is especially applicable to telemetry

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