Parallel-Plate Capacitance Moisture Sensor for Hay and Forage
Abdel Moneim Osman, Philippe Savoie, Dominic Grenier, R. Thériault · 2002 Chicago, IL July 28-31, 2002 · 2002
A parallel-plate capacitor connected to an integrated circuit timer (LM555) was used in astatic mode to estimate the moisture content and the total amount of water in chopped forage placedin a plexiglass box (0.10 m x 0.20 m x 0.20 m). Experiments were performed with a first set ofwhole-plant corn at five levels of moisture content, a second set of corn at three levels of moistureand alfalfa at three levels of moisture. Forage samples were prepared at two levels of density (lowand high) and at four levels of capacitor volume fill (25, 50, 75 and 100%), and repeated randomlythree 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 waterincreased. The coefficient of determination R2 between frequency drop and amount of water was0.92 for corn-set-1, 0.87 for corn-set-2 and 0.67 for alfalfa. The frequency drop was more highlycorrelated with mass of water at low water density than at high water density in the capacitorsvolume. The frequency drop was not well correlated with moisture content alone. The moisturecontent could be determined by measuring the total wet mass and the mass of water.