Keithley 3720-ST

Series 3700A System Switch/Multimeter Reference Manual Section 4: Basic DMM operation
3700AS-901-01 Rev. D/June 2018 4-39
Example
Calculate the temperature for a Series 44007 thermistor that measures 5 kΩ (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
RTD equations
The temperature versus resistance readings listed in the RTD reference tables are calculated using
the Callendar-Van Dusen equation. There are two equations based on different temperature ranges.
There is an equation for the –200 °C to 0 °C range and one for the 0 °C to 630 °C range.
Equation for –200 °C to 0 °C temperature range
R
RTD
= R
0
[1 + AT + BT
2
+ CT
3
(T–100)]
Where:
R
RTD
= The calculated resistance of the RTD
R
0
= The known RTD resistance at 0 °C
T = The temperature in °C
A = Alpha [1 + (delta/100)]
B = –1 (alpha)(delta)(1e-4)
C = –1 (alpha)(beta)(1e-8)
The alpha, beta, and delta values are listed in RTD parameters for equations (on page 4-40).