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United States Department of Agriculture

Agricultural Research Service

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

item Kandala, Chari
item Sundaram, Jaya

Submitted to: IEEE Sensors Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 15, 2009
Publication Date: January 1, 2010

Interpretive Summary: Moisture content (mc) measurement of grain samples is very useful in determining their quality, storability and processing. A nondestructive rapid method is described here to determine the moisture content of in-shell peanut and corn samples in the moisture range of 6 % to 20 % from their impedance and phase angle measurements. The system was initially calibrated using peanut and corn samples of known mc values in the moisture range of 6 to 20 %. The calibration constants generated were used in a semi-empirical equation developed, and the mc of peanut and corn samples were calculated using the measured impedance and phase angle values at the frequencies of 1 and 5 MHz. The calculated mc values of these samples were compared with the mc values of the samples obtained by the standard air-oven method and were found to be within 1% of the air-oven values for over 90% of the samples tested. This method is rapid and nondestructive and can be used for different types of grains and nuts.

Technical Abstract: 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 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 and corn were 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. Multi Linear Regression (MLR) method was used for the empirical equation development using Unscrambler 9.7 data analyzer. In the present work, 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 equation 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 of peanuts, corn and similar field crops.

Last Modified: 4/22/2015
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