Campbell Scientific 109SS Temperature Probe - Manual (Page 15)

Model 109SS Temperature Probe
7.3 Water Temperature Installation
109SS probes can be submerged to 45 m (150 ft) or 63 psi. The 109SS is not
weighted, so a weighting system should be added, or the probe secured to a
fixed submerged object such as a piling.
7.4 Soil Temperature Installation
The 109SS tends to measure the average temperature over its length, so it
should generally be buried such that the measurement tip is horizontal to the
soil surface at the desired depth.
One or two coils of cable should also be buried in a shallow installation. Burial
of some cable mitigates the effect of solar heating of the above ground cable on
the temperature measurement.
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.
The maximum burial depth for soil that could become saturated with water is
dictated by the maximum water pressure allowed for the sensor, which is 21
psi.
8. Operation
8.1 Sensor Schematic
FIGURE 8-1. 109SS thermistor probe schematic
8.2 Measurement and Output Linearization
Campbell Scientific dataloggers measure the 109SS probe thermistor and
convert the result to temperature. With reference to the previous FIGURE 8-1,
109SS thermistor probe schematic, a precise excitation voltage is applied at the
Vx line and the voltage drop across the 24.9 kΩ resistor is measured at the Vs
line.
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