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Parallel-Plate Capacitance Moisture Sensor for Hay and Forage

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  Paper number  021055,  2002 ASAE Annual Meeting . (doi: 10.13031/2013.9309) @2002
Authors:   Abdel Moneim Osman, Philippe Savoie, Dominic Grenier, Roger Thériault,
Keywords:   Moisture content, sensor, forage, hay, dielectric, capacitance, precision agriculture

A parallel-plate capacitor connected to an integrated circuit timer (LM555) was used in a static mode to estimate the moisture content and the total amount of water in chopped forage placed in a plexiglass box (0.10 m x 0.20 m x 0.20 m). Experiments were performed with a first set of whole-plant corn at five levels of moisture content, a second set of corn at three levels of moisture and alfalfa at three levels of moisture. Forage samples were prepared at two levels of density (low and high) and at four levels of capacitor volume fill (25, 50, 75 and 100%), and repeated randomly three times. The output was expressed as the timers frequency drop from the reference frequency (average 854 kHz). The frequency drop increased as volume fill and total amount of water increased. The coefficient of determination R2 between frequency drop and amount of water was 0.92 for corn-set-1, 0.87 for corn-set-2 and 0.67 for alfalfa. The frequency drop was more highly correlated with mass of water at low water density than at high water density in the capacitors volume. The frequency drop was not well correlated with moisture content alone. The moisture content could be determined by measuring the total wet mass and the mass of water.

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