INVESTIGATING THE INFLUENCE OF GRAIN VARIETY ON CALIBRATION OF MICROWAVE MOISTURE SENSORS.

Microwave moisture sensors represent a sound solution for real-time, nondestructive determination of moisture content in grains, seeds, nuts, and other agricultural products. One of the most critical phases in developing these sensors is their calibration against standard methods, in this instance, the oven-drying technique. In this study, dielectric properties of different varieties of wheat, and corn were measured at 10 GHz and an average room temperature of 25.2°C to investigate the influence of variety in calibrating microwave moisture sensors. Dielectric properties measured for all varieties tested for a given material were nearly superimposed, and the same was observed when plotting density-independent calibration function, ψ, as a function of moisture content. Performance of individual moisture calibration equations in predicting moisture content was compared to that from a single moisture calibration equation established for all varieties combined through computation of the standard error of calibration (SEC). In most instances, for both wheat and corn the SEC corresponding to individual varieties were nearly the same as that corresponding to all varieties combined. In addition, it was observed that a unified calibration can be established for both wheat and corn whereby moisture can be predicted from a single moisture calibration equation based on measurement of the dielectric properties at a single microwave frequency. Here, such an equation provided moisture content in wheat and corn with a SEC of 0.87%. [ABSTRACT FROM AUTHOR]