Keithley 2701

Model 2701 User’s Manual Temperature Equations F-7
NOTE The specified thermistor temperature measurement accuracy of the Model 2701
(see Appendix A) is based on the curve fitting constants listed in Table F-9. If the
thermistor manufacturer’s curve fitting constants are not exactly the same as the
ones listed in Table F-9, accuracy will be affected.
1. Choose the thermistor type to be used; 2252Ω, 5kΩ, or 10kΩ.
2. Compare the A, B, and C constants from the thermistor manufacturer with those
used by the Model 2701 (see Table F-9).
3. Select a thermistor that closely matches the A, B, and C constants in Table F-9.
4. Analyze the differences between the two sets of curve fitting constants to
determine the affect on measurement accuracy.
Converting K to °C — The temperature in Kelvin can be converted to °C as follows:
T
°C
= T
K
- 273.15
where: T
°C
is the temperature in °C.
T
K
is the calculated Kelvin temperature.
Example — Calculate the temperature for a Series 44007 thermistor that measures
5kΩ (R):
lnR = ln(5000) = 8.5172
A = 0.001288
B = 0.0002356
C = 9.557e-8
T
K
= 1 / {A + (BlnR) + [(C)(lnR)
3
]}
= 1 / {0.001288 + [(0.0002356)(8.5172)] + [(9.557e-8)(8.5172
3
)]}
= 1 / (0.001288 + 0.002007 + 0.000059)
= 1 / 0.003354
= 298.15
T
°C
= T
K
- 273.15
= 298.15 - 273.15
= 25°C