Nondestructive Measurement of Moisture Content Using a Parallel-Plate Capacitance Sensor for Grain and Nuts

A simple, low-cost instrument that measures impedance and phase angle was used along with a parallel-plate capacitance system to estimate the moisture content (MC) of in-shell peanuts and yellow-dent field corn. Moisture content of the field crops is important and is measured at various stages of their processing and storage. A sample of about 150 g of in-shell peanuts or corn was placed separately between a set of parallel plate electrodes and the impedance and phase angle of the system were measured at frequencies 1 and 5 MHz. A semi-empirical equation was developed for peanuts and corn separately using the measured impedance and phase angle values, and the computed capacitance and the MC values obtained by standard air-oven method. The multilinear regression (MLR) method was used for the empirical equation development using an Unscrambler 9.7 data analyzer. In this paper, a low-cost impedance analyzer designed and assembled in our laboratory was used to measure the impedance and phase angles. MC values of corn samples in the moisture range of 7% to 18% and in-shell peanuts in the moisture range of 9% to 20%, not used in the calibration, were predicted by the equations and compared with their standard air-oven values. For over 96% of the samples tested from both crops, the predicted MC values were within 1% of the air-oven values. This method, being nondestructive and rapid, will have considerable application in the drying and storage processes for peanuts, corn, and similar field crops.