Campbell CS650, Руководство пользователя

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CS650 and CS655 Water Content Reflectometers
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The thermistor used to measure temperature is in contact with one of the stainless
steel rods at the base of the epoxy probe body. Because of the low thermal
conductivity of stainless steel, the thermistor does not measure the average
temperature along the rod, but instead provides a point measurement of the
temperature within the epoxy. For a valid soil temperature reading, the probe
body must be in thermal equilibrium with the soil. If the probe is installed
vertically with the epoxy probe body above the surface, then the probe body must
be shielded from solar radiation and in direct contact with the soil or media of
interest.
7.2 Proper Insertion
The method used for probe installation can affect the accuracy of the
measurement. The probe rods should be kept as close to parallel as possible when
installed to maintain the design wave guide geometry. The probe is more
sensitive to permittivity close to the rods so probes inserted in a manner which
generates air voids around the rods will have reduced measurement accuracy. In
most soils, the soil structure will recover from the disturbance during probe
insertion.
In some applications, installation can be improved by using the CS650G insertion
guide tool (Figure
7-1 ). The CS650G is inserted into the soil and then removed.
This makes proper installation of the water content reflectometer easier in dense or
rocky soils.
Figure 7-1. CS650G Insertion Guide Tool
7.3 Datalogger Wiring
Our dataloggers typically use SDI-12 to measure the sensor because RS-232
communication requires more control ports per CS650 and RS-232 programming
is more complicated than SDI-12 programming. SDI-12 communication also
allows up to ten probes to be given different addresses and then share a single
control port.