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ARS Home » Research » Publications at this Location » Publication #112723
Title: DIELECTRIC CALIBRATION METHODS FOR INDUSTRIAL MICROWAVE MOISTURE SENSORS

Author
item TRABELSI, SAMIR - OICD
item Kraszewski, Andrzej
item Nelson, Stuart

Submitted to: World Congress on Microwave and Radio Frequency Processing
Publication Type: Proceedings
Publication Acceptance Date: 5/20/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: Radio-frequency electrical characteristics of cereal grains, known as dielectric properties, have been used for many years for measuring moisture content in grain samples with electrical moisture meters. The usefulness of this method is based on the high correlation between the moisture content and the dielectric properties of the grain. Serious problems have been experienced in attempting to extend these measurement techniques for monitoring moisture content in grain samples moving through chutes or on conveyors. The errors in resulting moisture determinations are related to variations in bulk density (packing) of the moving granular materials that produce changes in dielectric properties similar to those changes resulting from differences in moisture content. Research has shown that certain relationships between the dielectric properties and moisture content determined from microwave measurements on grain samples can be used to minimize the influence of bulk density changes on the resulting moisture content determinations. The effectiveness of three of these relationships, expressed as mathematical functions of the dielectric properties, were compared for sensing moisture content in wheat and soybeans accurately and independent of the bulk density of these two commodities. One of these functions was identified which shows promise for simplifying the calibration of microwave moisture sensors, thus facilitating their development for practical use. Such reliable moisture sensors will be very helpful in managing moisture content in grain and soybean lots and improving quality maintenance in such commodities.

Technical Abstract: Permittivity-based calibration functions for moisture determination in granular materials independent of bulk density are suitable for implementation in industrial moisture sensors. Performance of three of these functions is discussed for moisture prediction in wheat and soybeans from measurement of their dielectric properties in free space at 9.46 GHz and at room temperature. One of these functions shows potential for a universal calibration.