Sentek RT6, Руководство по оборудованию

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SENTEK
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dielectric constant of the material between the plates.
The conductive rings of the sensor forms the plates of
the "capacitor". As the area of the plates/rings and the
distance between the plates/rings are fixed on the
EnviroSCAN/EasyAG sensor, the capacitance (C)
varies with varying complex dielectric constant of the
material (dielectric) surrounding the plates/rings.
This “capacitor” is connected to circuitry which
forms an oscillator. The frequency of oscillation is
depending on the capacitance (C) which is effected
by the changing complex dielectric constant of the
material in the sensors sphere of influence. The
oscillating capacitance field generated between the
two rings of the sensor extends beyond the PVC
access tube into the surrounding medium/soil
(dielectric). Sensor sensitivity (sphere of influence)
has been independently identified in laboratory
conditions to be horizontally - 130 mm to 150 mm
radius of axial centre in free air and vertically – 85
mm to 120 mm either side of axial centre.
If we assume that the soil and organic matter remains
constant then capacitance varies with varying
fertilizer (salinity), water and air. The frequency of
oscillation was selected from scientific studies on
high frequency excitation of various soil types with
varying salinity, temperature and moisture content.
The EnviroSCAN/EasyAG sensor has been designed
to oscillate at frequencies where variations in salinity
and temperature have minimal effect. Therefore the
sensor is relatively immune to salinity/fertilizer
variations at levels typically found in irrigated crops
so responds by varying frequency of oscillation
proportional to varying moisture content.
Due to logistics of transmitting (along cable) and
recording very high frequencies (VHF) the frequency
of oscillation of the sensor has been divided down by
a factor of 2048 thus providing an output frequency
proportional to frequency of oscillation. The data
logger powers the sensor up for 0.5 seconds then