Principle of operation
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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.
fig 2. Principle of operation
When the measuring channel is empty, the resonator has resonant frequency
F
0
and amplitude
A
0
(fig. 2). When the channel is filled with grain with certain mois-
ture content, the resonant frequency and amplitude decrease to
F
1
and
А
1
respective-
ly. With the increase of moisture content in measured product, resonant frequency
and amplitude decrease even more (
F
2
and
А
2
). Simultaneous measurement of res-
onant frequency and amplitude allows determining moisture content independently of
grain density.
