Proposed heater uses its own temperature coefficient for sensing function. Heating power is supplied from current source, heater voltage containing temperature information. Dynamic stability is very high since there is no thermal lag as would exist with separate heater and sensor

Strange, M. G.

English

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Ov X 
VV 
December 1974	 B74-10241 
NASA TECH BRIEF 
Goddard Space Flight Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Implementation of a Self-Controlling Heater: A Concept 
.
The problem: 
Precision temperature control,a common requirement 
in modern instrumentation, is accomplished either with 
"on-off" thermostats or with proportional control de-
vices. Of the two methods, proportional control is 
usually preferred because it prevents cyclical tempera-
ture excursions in the controlled body and possible 
electrical interferences. Either method, however, normal-
ly requires installation of a separate heater and sensor 
on the part to be controlled. With very small parts or 
thin filaments, these often cannot be mounted without 
perturbing the temperature distribution, increasing heat 
losses, or producing instability due to excessive lag 
between heater and sensor. 
The solution: 
A self-controlling heater is proposed which combines 
the heating and sensing functions.
How it's done: 
The proposed heater uses its own temperature co-
efficient for the sensing function. Heating power is 
supplied from a current source, the heater voltage con-
taining the temperature information. In the closed loop 
configuration, a simple analog computation separates 
the heater voltage drop due to its temperature from the 
component due to the instantaneous drive level. The 
resulting measure of actual temperature is used as an 
input to conventional error control circuitry. A con-
tinuous, true proportional control system results. 
In the simplified schematic of the self-controlling 
heater shown in the figure, amplifiers A 1
 and A2 
perform the current-drive and offset/gain functions; 
amplifier A 3
 is used for error comparison. Reference 
voltage VR sets the temperature control point. The 
analog divider removes the component of heater voltage 
due to its heating current by dividing by error signal 
V 
(Temperature
Reference)
Heater Driver

Voltage Gain = Average at 
by Average
Differential
Amplifier
Voltage Gain = AD
V O 
+R S 
Heater Resistance, r  = R0+R0Q(T2—T1)	
v	 R 
- R 
a	 S
v  
= v, at T 1 , where r  = R0 
.
Simplified Schematic of the Self-Controlling Heater
(continued overleaf) 
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 Stales
	 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=19740000241 2020-03-17T13:53:33+00:00Z
v; the resulting voltage vd then represents actual heater 
temperature. The design equation is 
10ADaR0(T2—T ) 
vI =
1sO+1S 
where VR = temperature-set reference voltage 
T 1 = reference temperature, 
T2 = desired temperature, 
R0 = heater resistance at temperature T1, 
R5 = current-sampling resistance, 
AD = gain of differential amplifier A2 , and 
a	 = temperature coefficient of resistivity of 
the heater. 
An experimental circuit constructed using a copper 
heater (a = 0.00381) has controlled temperatures at set 
points between 300 and 70° C. The accuracy is within 
W.5° C over an ambient range of 50°C. 
Notes: 
1. The proposed design may be used for controlling the 
temperature of thin wire filaments by employing the 
filaments themselves as self-controlling heaters. One 
application might be to control low-temperature 
incandescent calibration lamps for radiation standards. 
It may also be applied in many other areas that use 
conventional temperature controls. 
2. Temperature may be easily programed by varying the 
reference voltage. The closed-loop control provides 
fast stabilization as well as immunity to outside 
thermal disturbances.
3. Dynamic stability is very high since there is no 
thermal lag as would exist with a separate heater and 
sensor. 
4. The following documentation may be obtained from: 
National Technical Information Service 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $2.25) 
Reference: NASA TND-7248 (N73-24479), Imple-
mentation of a Self-Controlling Heater 
5. Technical questions may be directed to: 
Technology Utilization Officer 
Goddard Space Flight Center 
Code 207.1 
Greenbelt, Maryland 20771 
Reference: B74-10241 
Patent status: 
This invention is owned by NASA and a patent 
application has been filed. Inquiries concerning non-
exclusive or exclusive license for its commercial develop-
ment should be addressed to: 
Patent Counsel 
Goddard Space Flight Center 
Code 204 
Greenbelt, Maryland 20771 
Source: Maxwell G. Strange
Goddard Space Flight Center
(GSC-1 1752)
is 
. 
B74-10241	 Category 06


Implementation of a self-controlling heater: A concept

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