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United States Department of Agriculture

Agricultural Research Service

Title: Simple Grain Moisture Content Determination from Microwave Measurements

Authors
item Kraszewski, Andrzej
item Trabelsi, S - OICD
item Nelson, Stuart

Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 7, 1997
Publication Date: N/A

Interpretive Summary: Moisture content of grain is an important factor determining suitability for safe storage and processing. Electronic moisture meters have been developed that use the correlation between the electrical or dielectric properties of grain and its moisture content. Such meters are routinely used for rapid testing of grain samples in the grain trade and the grain processing industry. Instruments using the same principles have been developed for on-line use, but their performance has not been generally satisfactory. The desired accuracy has not been achieved for measurements on moving grain, because bulk density fluctuations as the grain moves are reflected in significant moisture measurement errors. Measurements at microwave frequencies that use both the attenuation of microwave signals traversing a layer of grain and the change in the electrical phase of the waves can be used to provide moisture content independent of bulk density variations. The ratio of attenuation and phase shift was studied as affected by grain moisture content and grain temperature, and this simple ratio can be used for rapid sensing of wheat moisture content to within <0.5% moisture content over the moisture range from 10-19% at temperatures from -1C to 42C. Instruments for reliable on-line monitoring of grain moisture content will be useful in maintaining quality of grain for both domestic use and export.

Technical Abstract: Moisture content of wheat, Triticum aestivum L., is expressed as a fraction of the ratio of microwave attenuation and phase shift, measured at 16.8 GHz, and grain temperature. Validation of the calibration equation indicated that moisture content was obtained with an uncertainty less than +/-0.45% moisture at the 95% confidence level, independent of density variation, at temperatuers from -1 C to 42 C, and moisture contents from 10% to 19%. Moisture determination does not depend on the layer thickness of the wheat nor its bulk density. No differences between two wheat cultivars were observed in the measurement data.

Last Modified: 9/20/2014
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