Pressure-sensitive transducer, consisting of a series of spindle-supported electrically conductive metal washers connected to electrical sensing circuitry, determines the force exerted between a mounting bolt and nut on relatively fragile components

Baker, C. D.

English

NASA Technical Reports Server

September 1969
	 Brief 69-10364 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Pressure Transducer 
The problem: 
To devise a simple pressure-sensitive transducer 
for measuring and controlling force or torque. In set-
ting eyelet terminals in relatively fragile substrates in 
the manufacture of electronic components, for ex-
ample, it is essential to exert only that force necessary 
to set the terminal properly without exceeding the 
compressive strength of the substrate. Systems now 
available for this purpose are elaborate and expen-
sive, and they usually involve the use of strain gages 
and amplifiers. Torque wrenches and other similar 
devices place a prescribed tension only on the metal 
of the fastener, and this is unrelated to the crushing 
force applied on the mounted component. 
The solution: 
A novel transducer, consisting of a series of spindle-
supported electrically conductive metal washers con-
nected to electrical sensing circuitry, which can be 
used to determine the crushing force exerted between 
a mounting bolt and its nut on a plastic or other rela-
tively fragile component. This force can be determined 
for any number of turns of the nut and even for por-
tions of each individual turn. Such information will 
be useful for developing fastening specifications for 
installing mounting bolts and nuts used to secure 
electronic components and assemblies. Heretofore 
it has not been possible to develop this information. 
How it's done: 
The transducer is made up of a stack of incompres-
sible metal washers, each of which is separated by 
resilient electrically insulative spacers made of a 
novel material. The spacers are progressively deform-
able in proportion to the applied pressure. The metal 
washers serve as electrical switches, which are closed
in sequence as successive insulative spacers are com-
pressed, to indicate incremental levels of pressure. 
The spacers are fabricated from materials having 
controlled resilience. This makes it possible for 
spacers located in different portions of the stack to 
have various degrees of resilience. The metal washers, 
on the other hand, are virtually incompressible. Thus 
it is possible, by means of controlled resilience of the 
spacers, to determine the magnitude of the fdrce 
exerted between the face of a nut and that of a bolt 
head. Increasing pressure is applied between washers 
as a nut is tightened on a bolt. Progressive compres-
sion and deformation of individual spacers take place 
in an order determined by the specific characteristics 
of resilience of each spacer. Assuming that adjacent 
spacers have characteristics of resilience needing 
progressively increasing amounts of force to effect 
deformation, one spacer would deform first, followed 
in turn by the next as additional pressure is applied. 
As each spacer becomes fully compressed, the ad-
jacent metal faces of neighboring washers come in 
contact with each other. These faces form two ele-
ments of a normally open switch from which electrical 
connections can be made by wires. Visual or aural 
electrical indications can be obtained from the process 
of sequential deformation of the spacers that will show 
the magnitude of pressure exerted on the transducer 
assembly. 
Notes: 
1. This invention is novel in that it provides a broad-
range transducer for measuring pressure or torque. 
Measurements of this type may be useful in such 
applications as the fabrication of wiring-board ter-
minals, the design and manufacture of weight- and 
force-measuring equipment, and the fabrication of 
printed wiring-board connectors. (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.
https://ntrs.nasa.gov/search.jsp?R=19690000360 2020-03-16T18:15:10+00:00Z
2. A prototype version of this device has been de-
vised in which a transducer-punch combination 
is mounted in the ram of a press: With a suitable 
wiring arrangement, the stacked washers acting as 
switch elements can be used to indicate various 
levels of pressure by means of a series of yellow, 
green, and red indicating lights mounted on the 
punch holder in a convenient viewing position. 
3. Documentation is available from: 
Clearinghouse for Federal Scientific 
and Technical Information 
Springfield, Virginia 22151 
Price $3.00 
Reference: TSP69- 10364
Patent status: 
Inquiries about obtaining rights for the com-
mercial use of this invention may be made to NASA, 
Code GP, Washington, D.C. 20546. 
Source: Charles D. Baker of 
Caltech/Jet Propulsion Laboratory 
under contract to

NASA Pasadena Office
(NPO-10853) 
Brief 69-10364	 Category 01


Pressure transducer

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