Comparison of Rf Impedance and Dc Conductance Sensing for Single-Kernel Moisture Measurement in Corn

TWO electrical methods were compared with a standard forced-air oven method for determining the moisture content of single kernels of com, Zea mays L. One method used the complex impedance of a parallel-plate capacitor with the kernel between the plates, measured at radio frequencies (RF) of 1 and 4.5 MHz. The other used the dc conductance of the kernel as it passed between crushing rollers. Both methods, tested with hybrid yellow-dent field com samples ranging from 11 to 27% moisture content, wet basis, produced nearly comparable results. Standard errors of performance were 0.66% and 0.89% moisture content, for the parallel-plate impedance and crushing roller conductance methods, respectively, as determined by tests on 55 samples with 30 kernels per sample with the instruments described. Variations in measured moisture content of freshly dried samples, by the dc conductance and RF impedance methods, caused by nonequilibrium moisture distribution in the kemel disappeared 3 to 4 hours after drying.