Campbell Scientific 107-L Temperature Probe - Manual (Page 16)

Model 107 Temperature Probe
8. Operation
8.1 Sensor Schematic
FIGURE 8-1. 107 thermistor probe schematic
8.2 Measurement and Output Linearization
Campbell Scientific dataloggers measure the 107 probe thermistor and convert
the result to temperature. With reference to the previous FIGURE 8-1, 107
thermistor probe schematic, a precise excitation voltage is applied at the Vx
line and the voltage drop across the 1 kΩ resistor is measured at the Vs line.
The ratio of measured voltage (Vs) to excitation voltage (Vx) is related to
thermistor resistance (Rs), and the 1 kΩ ohm and 249 kΩ fixed resistors as
described in the following equations:
Vs/Vx = 1000 / (Rs + 249000 Ω + 1000 Ω)
Solving for Rs:
Rs + 250000 Ω = 1000 • (Vx/Vs)
Rs = 1000 • (Vx/Vs) – 249000
TABLE 8-1, 107 Measurement Details, and TABLE 8-2, 107 Temperature
Calculation, describe how measurement results Vs/Vx and Rs are converted to
temperature by Campbell Scientific dataloggers.
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