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Model 108 Temperature Probe
7.4
Water Temperature Installation
7.5
Soil Temperature
8.
Operation
8.1
Sensor Schematic
8.2
Measurement and Output Linearization
8
The 108 is held in the RAD06 radiation shield by inserting the sensor through
the sensor gland at the bottom of the shield FIGURE
on the gland, and insert the probe into the shield. Tighten the nut on the sensor
gland using an adjustable wrench until the sensor is securely held in place.
Route the sensor cable to the instrument enclosure.
Secure the cable to the tripod or tower using cable ties.
108 probes can be submerged to 15 m (50 ft) or 21 psi. The 108 is not
weighted, so a weighting system should be added, or the probe secured to a
submerged object such as a piling.
The 108 tends to measure the average temperature over its length, so it is
usually buried such that the measurement tip is horizontal to the soil surface at
the desired depth. 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.
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.
Black
Vx
Red
Vs
Purple
⏚
⏚
Clear
⏚ — Analog Ground
FIGURE 8-1. 108 thermistor probe schematic
CRBasic instruction Therm108() measures the 108 probe thermistor and
automatically converts the result to temperature. With reference to the previous
7-2
right). Loosen the nut
Thermistor
40 kΩ, 0.1% 10 ppm
1 kΩ, 0.1% 10 ppm
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