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CS650 and CS655 Water Content Reflectometers
9
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
sensor body must be in thermal equilibrium with the soil. Also bury the sensor
head in the soil so that it is insulated from diurnal temperature fluctuations.
7.2 Proper Insertion
The method used for sensor installation affects the accuracy of the
measurement. Insert the sensor rods as close to parallel as possible. The sensor
is more sensitive to permittivity close to the rods. Air voids around the rods
result in reduced measurement accuracy. Most soils recover from disturbances
caused by installation.
The CS650G Rod Insertion Guide Tool with Pilot Rod helps maintain the
proper spacing and parallel orientation of the rods during sensor insertion. It
also helps the insertion of the sensor in high density or rocky soils.
FIGURE 7-1. CS650G Rod Insertion Guide Tool with Pilot Rod
7.3 Datalogger Wiring
Campbell Scientific dataloggers typically use SDI-12 to measure the sensor
because RS-232 communications require more terminals per CS650 and
RS-232 programming is more complicated than SDI-12 programming.
shows the SDI-12 wiring for the CS650 water content
reflectometer. SDI-12 data is transmitted to a CRBasic datalogger
odd-numbered control or
U
terminal. Wiring information for RS-232
communications is provided in Section
(p. 11)
.