Thin film convective heat transfer gage functions effectively for prolonged periods at temperatures up to 1000 degrees F. An initial resistance shift does not inhibit the performance or accuracy of the gages, as the original resistance-temperature relationship remains unchanged

Loyd, J. R.

Pickard, R. F.

English

NASA Technical Reports Server

March 1968	 Brief 68-10051 
NASA TECHBRIEF. 
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. 
Thin Film Heat Transfer Gage Is Stable at Higher Temperatures 
Electric Leads 
Cement 
Gold Coating 
Platinum Film 
Glass Substrate
Potting Resin 
A new thin film convective heat transfer gage that 
has been designed will function effectively for pro-
longed periods at temperatures up to 1000° F. Previous 
designs which employ metal-to-glass seals for the 
electrical leads from the thin film sensing element 
(as in the rod and tube design summarized in Tech 
Brief 66-10180) are subject to failure at the higher 
temperatures. The failures are primarily due to rup-
ture of the thin film under the stresses produced by 
the large difference in thermal expansion between the 
glass and metal leads in the earlier designs. 
The new gageeliminates the problems due to dif-
ferences in coefficient of thermal expansion between 
glass and metal by replacing the earlier metal-to-glass 
seals with spring-like (S-shaped) pressure contacts 
between a gold thin film deposit and electrical leads 
to the monitoring circuit. The gold thin film is formed 
by painting a commercial gold suspension (liquid 
gold) from both ends of the normal platinum thin film 
sensing element, around the sides of the glass sub-
strate, and onto its back side to form a gold pad. Each
of two S-shaped (0.OlOxO.002 inch) pieces of gold-
plated lnconel-X wire is forced at one end into contact 
with the gold pad and at the other end is spot welded 
to an electrical lead. The two leads are made of a copper 
alloy whose thermal expansion coefficient matches 
that of the glass tubing used as electrical insulation 
for the leads. Potting material, which is placed around 
the S-shaped wires in the gage holder, is cured while 
the compressed spring condition of the S-bend is 
maintained in a small vise. An appropriate cement is 
used to secure the heat sensing assembly to a gage 
holder. 
Notes: 
I. The platinum film must be coated with silicon 
monoxide to prevent contamination by foreign 
materials under vacuum and high temperature. 
2. An initial resistance shift does not inhibit the per-
formance or accuracy of the gages, as the original 
resistance—temperature relationship remains 
unchanged. (continucd over ea 
This document was prepared under the sponsorship of the National	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States 	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States 	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19680000051 2020-03-12T05:45:44+00:00Z
3. The small effective surface area of the gage, 0.025 
square inch, minimizes radiation losses. 
4. The gage was designed for use in conjunction with 
- a base which could be regulated to operate at any 
preselected temperature between 750 and 1000°F. 
5 Inquiries concerning this convective thin film heat 
transfer gage may be directed to: 
Technology Utilization Officer 
Marshall Space Flight Center 
Huntsville, Alabama 35812 
Reference: B68-10051
Patent status: 
No patent action is contemplated by NASA. 
Source: R. F. Pickard and J. R. Loyd 
of Astro-Space Laboratories, Inc. 
under contract to 
Marshall Space Flight Center 
(MFS-12396) 
Brief 68-'10051
	 Category 01


Thin film heat transfer gage is stable at higher temperatures

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server