Constantan wire worked to a needle point and covered with a copper coating produces a small, concentric, fast-reaction thermocouple that has the fast response time necessary to measure rapid temperature changes accurately and only slightly alters the environment being measured

Stover, C. M.

English

NASA Technical Reports Server

October 1968
	
Brief 68-10389 
•	 AEC-NASA TECH BRIEF 
W 
YES
AEC-NASA Tech Briefs describe innovations resulting from the research and development program 
of the U.S. AEC or from AEC-NASA interagency efforts. They are issued to encourage commercial 
application. Tech Briefs are published by NASA and may be purchased, at 15 cents each, from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Method for Making Small Pointed Thermocouples 
The problem: 
To devise a method for making single-ended I mil 
or smaller thermocouples that have the fast response 
time necessary to measure rapid temperature changes 
accurately and that will not significantly alter the en-
vironment being measured. 
The solution: 
A constantan wire is worked to a needle point and 
covered with a copper coating to produce a small, 
concentric, fast-reaction thermocouple that alters the 
environment only slightly because of the small mass 
involved. 
How it's done: 
A straight piece of 0.032 inch diameter constantan 
wire, 1 1/2 inches long, is mounted in a pin vise so that 
approximately I inch of wire extends from the vise. A 
tip is formed by rotating the wire against an aluminum 
block and shaping it with a fine file down to 0.005 
inch or less. The filing motion must be parallel with 
the wire and in a direction away from the pin vise. 
After as much work as possible is done with the file, 
the tip is worked with successively smaller emery 
cloths, and finished with crocus cloth. All shredding 
caused by the file must be removed. After the tip is 
formed, the space ¼ to ½ inch from the butt end 
is knurled by rolling a file over the constantan while 
it is lying on a piece of hardwood; this will help hold 
the sleeve in place. The wire is then lightly oxidized 
to free the surface of grease and oil. 
A refractory cement is used to attach a sleeve of 
'/s inch copper pipe, ¼ inch long, to the butt end of 
the wire. After the cement has been cured by heat, a
thin, uniform coating of a clear glaze ceramic paint is 
applied to about /8 inch of the tip and fused by heat-
ing to 1700° F. in an oven. An insulating cement is 
applied from the base of the sleeve to within ¼ inch 
of the tip, the refractory cement being covered. The 
copper sleeve is then cleaned of all oxide caused by 
the heating, and the assembly is mounted vertically 
and rotated in a vacuum chamber for copper coating. 
After 2 x 10 to 20 x 101 inch of copper is deposited 
on the assembly, it is removed froni the vacuum 
chamber, and about 1/32 of an inch of the tip is 
cut off with jewelers' end cutters. The thermocouple 
is then given another vacuum coating of copper which 
completes the contact to the constantan tip. 
After a continuity check with a low voltage ohm-
meter, the thermocouple is given a final electroplat-
ing with copper. The base is covered with wax, and 
the assembly is placed in a copper electroplating bath 
with 1/16 inch of the tip not immersed. The tip is 
gradually moved further above the level of the plating 
solution so that the copper plating is heavy on the 
base to ensure a good contact and thin near the tip to 
keep the mass small near the thermocouple junction. 
Notes: 
I. The average decay response time on a small tip 
is about ¼ second in slow moving air, although 
several thermocouples had much better response 
times. 
2. A needle point thermocouple can be used to 
measure the internal temperature of animal tissue. 
Its rapid response time makes it useful for control 
purposes.
(continued overleaf) 
This document was prepared under the sponsorship of the Atomic 
Energy Commission and/or the National Aeronautics and Space 
Administration. Neither the United States Government nor any per-
son 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 the use of any information, apparatus, 
method, or process disclosed in this document may not infringe pri-
vately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19680000389 2020-03-12T05:57:50+00:00Z
3. Inquiries concerning this innovation may be 
directed to: 
Sandia Office of Industrial Cooperation, 
Org. 3416 
Sandia Laboratories 
Post Office Box 5800 
Albuquerque, New Mexico 87115 
Reference: B68-10389
Patent status: 
No patent action is contemplated by AEC or 
NASA.
Source: C. M. Stover 
(SAN-10014)
S 
Brief 68-10389	 Category 01


Method for making small pointed thermocouples

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