Capacitance sensors for the nondestructive measurement of moisture content in in-shell peanuts

摘要

Moisture content (MC) in peanuts is measured at various stages of their processing and storage in the peanut industry. A method was developed earlier that would estimate the MC of a small sample of in-shell peanuts (peanut pods) held between two circular parallel-plates, from the measured values of capacitance and phase angle at two frequencies 1 and 5 MHz. These values were used in an empirical equation, developed using the capacitance and phase angle values of samples of known MC levels, to obtain the average MC values of peanut samples with moisture contents in the range of 7 to 18%. In the present work, two rectangular parallel-plates were mounted inside a vertical cylinder made of acrylic material and filled with about 100 g of in-shell peanuts and their average me was determined from a similar empirical equation. The calculated MC values were compared with those obtained by the standard air-oven method. For over 85% of the samples tested in the moisture range between 6% and 22% the MC values were found to be within 1% of the air-oven values. Ability to determine the average MC of slightly larger quantities of in-shell peanuts without shelling and cleaning them, as being done presently, will save time, labor and sampling material for the peanut industry.