Campbell-scientific 107-L Temperature Probe Manual do Utilizador descarregar pdf (Página 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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