Radiometric Temperature Reference uses a thermistor as both a heating and sensing element to maintain its resistance at a preselected level to continuously control the power supplying it. The fixed infrared radiation level must be simple, rugged, and capable of high temperature operation

Monford, L. G., Jr.

English

NASA Technical Reports Server

C 
October 1969	 Brief 69-10507 
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. 
Radiometric Temperature Reference
The problem: 
In the measurement of infrared radiation an internal 
calibration source or reference of a known, fixed 
radiation level is required to provide quantitative 
information. Frequently, the reference radiation must 
be made large with respect to that from the sample 
being measured. Thus, a reference source is desired 
that is simple, rugged, and capable of high tempera-
ture operation. 
The solution: 
A Radiometric Temperature Reference (RTR) has 
been designed that uses a thermistor as both heating 
and sensing element to maintain its resistance at a 
level that is preselected to continuously control the 
power supplying it. 
How it's done: 
The mechanical configuration of the thermistor 
assembly and the electronic control circuit are shown 
on the above figure. Although the circuit uses a 
minimum of components, it is theoretically capable
of maintaining selected temperatures to within the 
temperature-resistance repeatability figures of state-
of-the-art thermistors. With components as shown 
the circuit is sensitive enough to drive the thermistor 
at saturation voltage with an instantaneous 0.01% 
change of the thermistor resistance. For this reason, 
the thermistor must be thermally isolated from its 
environment, its thermal mass must be increased, or 
the system must be electronically damped to prevent 
oscillations. 
The operating temperature of the RTRis controlled 
by varying the value of RI at the input of opera-
tional amplifier #1 which is operating in a constant 
current configuration. Operational amplifier #2 
operates in a unity gain mode and inverts the signal 
polarity for positive feedback through resistor Ri. 
When the circuit is energized, the resistance value of 
RI is less than the resistance of the thermistor (T), 
establishing a gain greater than unity. Under this con-
dition the voltage across the thermistor increases until 
it approximates the power supply voltage. This voltage 
heats the thermistor until its resistance is approxi-
(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=19690000486 2020-03-16T18:06:34+00:00Z
mately equal to RI and then decreases to a value 
necessary to maintain resistance equilibrium. 
Notes: 
Documentation is available from: 
Clearinghouse for Federal Scientific 
and Technical Information 
Springfield, Virginia 22151 
Price $3.00 
Reference: TSP69- 10507
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to NASA, Code 
GP, Washington, D.C. 20546. 
Source: L. G. Monford, Jr. 
Manned Spacecraft Center 
(MSC- 13276)
. 
. 
Brief 69-10507	 Category 01


Radiometric temperature reference

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