Keithley 2750 - Thermistor Equation

F-6 Temperature Equations Model 2750 Multimeter/Switch System User’s Manual
Thermistor equation
Temperature (in Kelvin) is calculated using the Steinhart-Hart equation as follows:
where: T
K
is the calculated temperature in Kelvin.
lnR is the natural log of the measured resistance of the thermistor.
A, B, and C are the curve fitting constants. The constants for the three thermistor
types used by the Model 2750 are listed in Table F-9.
Table F-8
Type T inverse function polynomial
-200°C to 0°C
(-5,603µV to 0µV)
0°C to 400°C
(0µV to 20,872µV)
c
0
= 0.0 0.0
c
1
= 2.594 919 2 × 10
-2
2.592 800 × 10
-2
c
2
= -2.131 696 7 × 10
-7
-7.602 961 × 10
-7
c
3
= 7.901 869 2 × 10
-10
4.637 791 × 10
-11
c
4
= 4.252 777 7 × 10
-13
-2.165 394 × 10
-15
c
5
= 1.330 447 3 × 10
-16
6.048 144 × 10
-20
c
6
= 2.024 144 6 × 10
-20
-7.293 422 × 10
-25
c
7
= 1.266 817 1 × 10
-24
Error: 0.04°C to -0.02°C 0.03°C to -0.03°C
t
90
= c
0
+ c
1
E + c
2
E
2
+ c
3
E
3
... c
i
E
i
where: t
90
is the calculated temperature in °C.
E is the measured voltage in microvolts.
Table F-9
Model 2750 curve fitting constants for thermistors
Constant
2252Ω at 25°C
(Series 44004)
5000Ω at 25°C
(Series 44007)
10kΩ at 25°C
(Series 44006)
A 0.0014733 0.001288 0.0010295
B 0.0002372 0.0002356 0.0002391
C 1.074e-7 9.557e-8 1.568e-7
T
K
1
ABlnR()ClnR()
3
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2750-900-01.book Page 6 Wednesday, August 3, 2011 7:56 AM