
Figure 2.15: Thermistor Probe Schematic
[Manual - Model 107 Temperature Probe, 4/07]
The ration of measured voltage (Vs) to the excitation voltage (Vx) is related to
the thermistor resistance (Rs), and the 1000 and 249K ohm fixed resistor shown in
equation 2.3 below.
V s/V x =
1000
Rs + 249000 + 1000
(2.3)
The sensor calculates Rs from the voltage ration, and converts Rs to temperature
using the Steinhart-Hart equation in 2.4.
T =
1
A + B(LnRs)+C(LnRs)
3
) − 273.15
(2.4)
• T = temperature returned in °C
• A, B, C = coefficients provided by the thermistor manufacteur
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