Sensor is easy to construct, requires only one operational amplifier, and has very fast response. It provides direct readout of temperature on digital voltmeter

Love, A. W.

English

NASA Technical Reports Server

*	 October 1975	 B7540260 
NASA TECH BRIEF 
Langley Research 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. 
Simple Temperatue Sensor With Direct Readout 
. 
S
A new temperature sensor is easy to construct, 
requires only one operational amplifier, and has very 
fast response. It provides direct readout of tempera-
ture on a digital voltmeter (a scale factor of precisely 
100 K per volt for example). Parameters can be 
changed to give different scale factors (e.g., joO C or 
100 F per volt). The system is capable of accuracy to 
±0.1° C, if calibrated over the range of 0° to 40° C. 
This sensor could be applied in any instance 
requiring fast response and a direct temperature 
indication. This could be in a temperature-controlled 
oven or any other place where a small diode could be 
placed in contact with an object to determine its 
temperature. 
A silicon diode (Fairchild FDH600) can be used as 
the temperature sensor because the forward voltage 
across the diode is a nearly linear function of 
temperature, from cryogenic temperatures (e.g., 77 
K) to above 300 K, provided that the forward current 
in the diode is constant. Data from tests of a diode 
operating at 8.5 A current reveal that the voltage is 
linear with temperature to about ±0.10 over, a range of 
0° to 40° C (i.e., 273 to 313 K). Linearity is poorer 
when the range is extended further, about ±1.00 over 
the range of 77 to 313 K. 
The schematic diagram is of a circuit for supplying 
approximately constant current to the diode and 
includes an operational amplifier that performs a 
simple analog operation on the diode voltage, such 
that the output of the amplifier is a voltage that is 
directly proportional to the diode temperature in 
degrees Kelvin. Resistance values may be chosen to 
select a suitable scale factor for 100 K per volt, the 
temperature is 100 times the indicated output 
voltage). A digital voltmeter (DVM) is used as an 
indicator, and a ±15-V regulated supply is used for 
the operational amplifier, the DVM, and the Diode 
bias.
—e1	 I	 R1*	 i,	 il	 A2 
50K*	 i8.51A	
[__r115V FDH600 
eD	 T0DVM 
200 K*	 A = 1.75M 
—15 V
Note: All Resistances Are in Ohms. 
R 8.5 MA 
eD+el e—eD 
'1=	 R 1	 A2 
8 2	 A2 
• e = eD 0 + - ) , + - e1 A 1	 R1 
— Low Tempco 
Diode Circuit for Temperature Sensor 
Test data also show that the voltage drop across the 
diode is not too sensitive to current changes. 
Typically, a 1-percent change in diode current 
produces only a 0.4-mV change in voltage. For this 
reason the simple circuit shown is adequate for ±0.1 
K accuracy over the range of 273 to 313 K. A greater 
temperature range is obtained by adding an 
additional operational amplifier to form a constant-
current regulator, thereby holding diode current 
strictly constant over the whole temperature range. A 
slight nonlinearity in the diode characteristic will 
degrade accuracy as the temperature range is 
increased.
(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=19750000260 2020-03-19T20:14:55+00:00Z
Note: 
Requests for further information may be directed 
to:
Technology Utilization Officer 
Langley Research Center 
Mail Stop 139-A 
Hampton, Virginia 23665 
Reference: B75-10260
Patent status: 
• Inquiries concerning rights for the commercial use 
of this invention should be addressed to: 
Patent Counsel 
Langley Research Center 
Mail Stop 313 
Hampton, Virginia 23665 
Source: Allan W. Love of

Rockwell International Corp.

(LAR-1 1818)
. 
Categories: 01 (Electronics - Components 
and Circuitry) 
B75-10260
	 03 (Physical Sciences)


Simple temperature sensor with direct readout

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server