Operation; Sensor Schematic; Measurement And Output Linearization - Campbell 108 Product Manual

Temperature probe

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Placement of the cable inside a rugged conduit may be necessary for long cable runs, especially

in locations subject to digging, mowing, traffic, use of power tools, or lightning strikes.

8. Operation

Therm108()

CRBasic instruction

the result to temperature. With reference to the previous

applies 1000 mV excitation at the Vx line and measures the voltage drop across the 1 kΩ resistor

at the Vs line.

The ratio of measured voltage (Vs) to excitation voltage (Vx) is related to thermistor resistance

(Rs), and the 1 kΩ and 40 kΩ fixed resistors as described in the following equations:

Vs/Vx = 1000 / (Rs + 40000 Ω + 1000 Ω)

Solving for Rs:

Rs + 41000 Ω = 1000 • (Vx/Vs)

Rs = 1000 • (Vx/Vs) – 41000 Ω

The relationship of Rs to temperature is tabulated in

16), but is calculated by

= (1 / (A + B • ln (R

FIGURE 8-1. 108 thermistor probe schematic

measures the 108 probe thermistor and automatically converts

Therm108()

using the Steinhart-Hart equation, described as follows:

) + C • (ln (R

))

)) – 273.15

FIGURE 8-1

(p. 10),

Thermistor resistance and temperature

108 Temperature Probe 10

Therm108()

(p.

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