Instruction manual

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
submerged object such as a piling.
7.4 Soil Temperature Installation
The 109SS tends to measure the average temperature over its length, so
burying the probe such that the measurement tip is horizontal to the soil surface
at the desired depth is usually preferred. 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.
8. Operation
8.1 Sensor Schematic
FIGURE 8-1. 109SS thermistor probe schematic
8.2 Measurement and Output Linearization
CRBasic instruction Therm109() measures the 109SS probe thermistor and
automatically converts 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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