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E-2
Thermistor equation
Temperature (in Kelvin) is calculated using the Steinhart-Hart equation as follows:
T
=
K
where: T
Table E-1
Model 2790 curve fitting constants for thermistors
Constant
Selecting a thermistor — The thermistor manufacturers specified curve fitting values (A,
B, and C) may not be exactly the same as the ones used by the Model 2790. If they are not
exactly the same, perform the following steps to select a thermistor to use with the
Model 2790:
klqb
1.
2.
3.
4.
1
-----------------------------------------------------------
3
(
)
[
(
)
]
A
+
BlnR
+
C lnR
is the calculated temperature in Kelvin.
K
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 2790 are listed in
2252Ω at 25°C
(Series 44004)
A
0.0014733
B
0.0002372
C
1.074e-7
The specified thermistor temperature measurement accuracy of the Model 2790
(see
Appendix
A) is based on the curve fitting constants listed in
thermistor manufacturer's curve fitting constants are not exactly the same as the
ones listed in
Table
Choose the thermistor type to be used; 2252Ω, 5kΩ, or 10kΩ.
Compare the A, B, and C constants from the thermistor manufacturer with those
used by the Model 2790 (see
Select a thermistor that closely matches the A, B, and C constants in
Analyze the differences between the two sets of curve fitting constants to deter-
mine the affect on measurement accuracy.
Model 2790 SourceMeter
Table
5000Ω at 25°C
10kΩ at 25°C
(Series 44007)
(Series 44006)
0.001288
0.0010295
0.0002356
0.0002391
9.557e-8
1.568e-7
E-1, accuracy will be affected.
Table
E-1).
®
Switch System Reference Manual
E-1.
Table
E-1. If the
Table
E-1.
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