How MoistScan® Works
Measurement of moisture content in bulk materials using
microwaves has been investigated extensively over the past 20
years. Moisture measurement using this technique is based upon
the relatively high dielectric constant of water in comparison
to the dielectric properties of other materials.
To illustrate this technique, common sand (silicon dioxide)
produces a dielectric constant of 4.2 compared to the dielectric
constant of water of 80.4. The variation of water within the
sand would result is a large variation in the combined
dielectric constant which would then be measured by monitoring
the change in the microwave signal. Both the velocity of the
microwave signal (or phase shift) and the ultimate signal
strength (or attenuation) would be affected by the change in the
dielectric constant of the analysed material. Put simply, the
microwave measurement is effected mainly by the excitation of
free moisture molecules rather than many other types of
materials.
Transferring this technology to an on-line situation such as a
conveyor belt has posed many challenges. Subsequently Callidan
Instruments has invested an extensive amount of research into
optimising the operation of its MA-500 moisture meter. One of
MoistScan®’s greatest strengths is its flexibility to scan over
a broad bandwidth. This enables microwave anomalies such as
standing wave reflection and interference, alternate path and
signal/noise ratio difficulties to be minimized. Further
optimisation of parameters such as the measurement technique,
antenna design, and signal strength have all been paramount in
developing an analyser that has optimal performance at an
affordable price.
Possibly the largest benefit of the microwave technology is the
fact it is a transmission technique and measures practically all
the material on the conveyor belt. Optimal antenna design
increases the measurement area while reducing alternate path
microwaves or strenuous readings. The microwave measurement
cycle ensures that the measurement is in fact continuous and no
material within the analysis zone goes unmeasured. This is a
major benefit compared to many previous and outdated surface
measurement techniques.
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