WHEAT MOISTURE DETERMINATION BY 1 TO 110-MHZ SWEPT-FREQUENCY ADMITTANCE MEASUREMENTS

A technique is presented for rapidly determining the moisture content of hard red winter wheat, Triticum aestivum L., independent of grain b ulk density. Complex admittance measurements from 1 to 110 MHZ on bulk wheat samples were collected for predicting moisture contents ranging from about 9% to 20% wet basis, in samples with densities ranging fro m 0.620 to 0.790 g/cm(3). The data were transformed to density-indepen dent function (D/F) values, and multivariate analysis was used to elim inate spectral and statistical outliers. Principal component analysis was also used to determine the optimum frequencies for predicting mois ture content with the DIF values. Partial least-squares regression was then used to develop a calibration based on measurements at three fre quencies of about 2, 25, and 80 MHz. Calibration was performed with 47 wheat samples representing six cultivars harvested in 1992 and 1992 w ith a standard error of cross validation of 0.34% moisture content, an d validation was tested on 146 different samples from the same cultiva rs. Predicted moisture contents compared well with values determined b y air overt drying with a standard error of performance of 0.39% moist ure content and a bias of +0.03%.