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3. Principle of operation
The principle of sensor A315 operation is based on the considerable difference
of the permittivity of dry substances and water at ultra-high frequencies (UHF).
The feature and important advantage of A315 moisture content sensor is that
due to simultaneous measurement of resonant frequency and amplitude of the reso-
nance and special processing algorithm, moisture content measurements become
practically independent of product bulk density.
The sensing element is based on a ring resonator. The resonator has a cavity
formed by a PTFE tube for grain flow. Interaction of grain flow with resonator field in-
side the tube influences parameters of the resonator. Temperature sensors in meas-
uring channel allow automatic correction of measured value of moisture content from
the grain temperature.
Electronics of the sensor consists of two units – UHF module and data pro-
cessing module that control frequency response of measurement resonator, provide
necessary calculations and transfer of data to control panel via RS-485 interface.
When the measuring channel is empty, the resonator has resonant frequency
and amplitude A
F
0
0
ture content, the resonant frequency and amplitude decrease to F
ly. With the increase of moisture content in measured product, resonant frequency
and amplitude decrease even more (F
onant frequency and amplitude allows determining moisture content independently of
grain density.
fig 2. Principle of operation
(fig. 2). When the channel is filled with grain with certain mois-
and А
2
Principle of operation
and А
1
). Simultaneous measurement of res-
2
respective-
1
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