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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 This is a major benefit compared to many previous and outdated surface measurement techniques.

 

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