SENSING WHEAT MOISTURE-CONTENT INDEPENDENT OF DENSITY

Radio-frequency measurements were taken on four cultivars of hard red winter wheat at 24 degrees C, moisture contents ranging from 9% to 21% , wet basis, and at bulk densities ranging from 0.66 to 0.83 g/cm(3). Moisture content was predicted with an equation developed from the tra nsmission coefficient S-21 at three frequencies between 1 and 350 MHz. Measurements at about 40, 240, and 320 MHz were selected from multipl e linear regression analysis of data collected on static samples in a two-port coaxial flow-through sample holder: Calibration was performed with 49 samples front the four wheat cultivars harvested, and validat ion was performed with 84 different samples of the same cultivars. The standard deviation of the differences (SEP) for the validation data, compared to standard air-oven moisture contents, was 0.36% moisture co ntent, and the bias was -0.06% moisture content. Initial attempts to d evelop a moisture calibration from the intrinsic dielectric properties were unsuccessful. This was attributed to larger errors in the model used to calculate the loss factor values at the lower frequencies.