Inductive vibration sensor measures the surface displacement of nonferrous metal panels subjected to vibration or flutter. This transducer does not make any physical contact with the test panel when measuring

Pea, R. O.

English

NASA Technical Reports Server

March 1965	 Brief 65-10085 
NASA TECH 
NASA Tech Briefs are issued by the Technology Utilization Division to summarize specific 
technical innovations derived from the space program. Copies are available to the public from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia, 22151. 
Transducer Senses Displacements of Panels Subjected to Vibration 
Vibrating
	 0 
Coils, 200 Turns Each 
Input
	 Aluminum Tube 
20 Kc Power 
Output Terminals 
The problem: Measuring the surface displacements 
of nonferrous metal panels subjected to vibration or 
flutter such as produced by high-velocity winds. The 
transducer to be used for the measurements must not 
be placed in physical contact with any portion of the 
test panel. 
The solution: An inductive vibration sensor, 0.25 
inch in diameter by 2 inches in length, that can be po-
sitioned 0.02 to 0.7 inch from the surface of a non-
ferrous metal panel. 
How it's done: The sensor employs a simple circuit 
consisting of two counter-wound coils on a common 
core enclosed in an aluminum tube. A bridge circuit is 
formed by the addition of two resistors of equal value.
Electrical power is supplied to the unit by a commer-
cially available 20 kc signal generator. The input and 
output leads must be individually shielded. The coil at 
the sensing end, placed in proximity to the test surface, 
varies in inductance as the surface vibrates. The op-
posite coil is not affected and serves as a stable refer-
ence. The device has a flat frequency response of I kc 
and produces a voltage output which varies approxi-
mately as the inverse square of the distance of the 
sensing end of the coil from the panel surface. Because 
of the nonlinear characteristic of the sensor, a calibra-
tion curve is needed for each position relative to the 
surface where a null point is established. The device 
can detect a displacement of 0.00002 inch when it is 
positioned at 0.05 to 0.1 inch from a surface. When the 
Icnnlintied overleali 
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=19650000084 2020-03-11T17:22:16+00:00Z
device is positioned at a distance of 0.5 to 0.7 inch 
from the surface, its detection capability decreases to 
0.002 inch. 
Notes: 
I. The sensor can best measure surface displacements 
in a flat plate of nonferrous metal that is a moder-
ately good electrical conductor and more than 
0.005-inch thick. It can also be used to a limited 
extent for ferrous metals and surfaces of unsym-
metrical configuration.
2. Inquiries concerning this innovation may be di-
rected to: 
Technology Utilization Officer 
Ames Research Center 
Moffett Field, California, 93523 
Reference: B65-10085 
Patent status: NASA encourages commercial use
of this innovation. No patent action is contemplated. 
Source: Richard 0. Pea 
(ARC-37) 
Brief 65-10085	 Category No. 01


Transducer senses displacements of panels subjected to vibration

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