Calibration of a microwave system for measuring grain moisture content

This paper relates to a microwave system for grain moisture content determination which is based on simultaneous measurements of two parameters: attenuation and phase shift, of the electromagnetic wave transmitted through the layer of material. The calibration of such a system consists of identifying a function modeling the relationship between these parameters and the measured moisture content, taking into account an influence quantity-temperature T. Two algorithms for calibration are proposed and studied. The results of calibration show that the moisture of hard red winter wheat can be determined with uncertainty less than 0.5% moisture, at the 95% confidence level, in the moisture range of 10% to 19% at grain temperatures between -1/spl deg/C and 42/spl deg/C, independent of the grain bulk density.