A special spot welding technique is used to make miniature capacitance transducers for placing in a wind tunnel model. Rugged and relatively low in cost, they have a flat response up to one-third of the resonant frequency

Coon, G. W.

English

NASA Technical Reports Server

A.,	 (.001" to .0021 
Id Reference Plate 
all Body 
ass Insulator 
d-Thru 
Spot Welded Diaphragm 
CE 
Electrical 
M'rch- 1964 
S	 NASA TECH BRIEF
Brief 63-10429 
This NASA Tech Brief is issued by the Technology Utilization Division to acquaint industry 
with the technical content of an innovation derived from the NASA space program. 
Welded Pressure Transducer Made as Small as 1/8th-Inch in Diameter 
The problem: Construction of a miniature differen-
tial pressure transducer small enough to put in a wind 
tunnel model and still have desirable response 
characteristics. The transducer must be rugged and 
relatively low in cost. 
The solution: Capacitance transducers as small as 
1/8th-inch in diameter, made by a special spot-weld-
ing technique and having a flat response (within five 
percent) up to one-third of the resonant frequency. 
How it's done: The smallest transducers possible 
are required in shock-tube, wind tunnel testing when 
conducting experiments on boundary layer flow. 
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 
anywarranty or representation, express or implied, with respect to the 
accuracy, completeness, or usefulness of the information contained in
Small transducers cause a minimum of disturbance 
in the airflow. Capacitance cells as small as 0.12 
inch in diameter, having a diaphragm thickness of 
0.0005 inch, and a sensitivity as low as plus or minus 
1 lb/in. 2 have been made by this method. Resonant 
frequency is 34,000 cycles per second. 
The center electrode and glass insulator are recessed 
below the level of the outer body shell approximately 
0.003 inch. A conducting gold film is painted over 
the center of the insulator and the center electrode, 
then baked to form the stationary capacitance-sensing 
plate. The diaphragm (in a stretching frame) and the 
(continued overleaf) 
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=19630000074 2020-03-11T16:47:45+00:00Z
body of the transducer- are mounted in the indexing 
head of a commercial condenser-discharge spot 
welder. Spot welds are placed about one electrode 
radius apart. Distortion from local heating and 
local burning of the diaphragm are reduced by the 
addition of a small droplet of water under the 
spot-weld electrode. 
Notes: 
1. Techniques developed-in the process of welding the 
transducer diaphragm to the transducer cell body 
may have other applications in miniaturization 
technology. Welded electronic modules appear to 
be one possibility. 
2. Capacitance transducers have been found in this 
work to be more desirable than reactive or resis-
tive transducers because the capacitance type is 
simple mechanically and generates less electrical 
heat. In addition, the welding technique avoids 
manufacturing problems associated with the 
method of machining the cell body and diaphragm 
from a single block of material. 
Patent status: NASA encourages the commercial 
use of this invention. It was invented by a NASA 
employee and U.S. Patent Number 3,027,769 has been 
issued to him. Inquiries about obtaining license 
rights for its commercial development should be 
addressed to the inventor, Mr. Grant W. Coon, of 
Ames Research Center, Moffett Field, Mountain View, 
California.
Source: Ames Research Center (ARC-l1) 
Brief 63-10429


Welded pressure transducer made as small as 1/8th-inch in diameter

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