GS3
2
THEORY
2
Theory
2.1
Volumetric Water Content
The GS3 sensor uses an electromagnetic field to measure the dielec-
tric permittivity of the surrounding medium. The sensor supplies a
70 MHz oscillating wave to the sensor prongs that charges according
to the dielectric of the material. The stored charge is proportional to
substrate dielectric and substrate volumetric water content. The GS3
microprocessor measures the charge and outputs a value of dielectric
permittivity from the sensor. The dielectric value is then converted
to substrate water content by a calibration equation specific to the
media you are working in.
2.2
Temperature
The GS3 uses a small thermistor to take temperature readings. It is
located underneath the sensor overmold, next to one of the prongs
so it remains in thermal equilibrium with the medium, and reads the
temperature of the prong surface.
The GS3 outputs temperature in
◦
C unless otherwise stated in your
preferences file in either the DataTrac 3 or ECH2O Utility programs.
It is important to note that even though the sensor head is white,
if it is in direct sunshine, the temperature measurement may read
high. Exposure of the sensor head to direct UV radiation may also
degrade the vinyl surface and cause it to discolor.
Use caution when installing the sensor with the overmold in the sun.
2.3
Electrical Conductivity
Electrical conductivity (EC) is the ability of a substance to conduct
electricity and can be used to infer the amount of polar molecules that
are in solution. EC is measured by applying an alternating electri-
cal current to two electrodes, and measuring the resistance between
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