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RF Impedance Method for Determining Moisture Content in In-Shell Peanuts Nondestructively
Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org
Citation: Paper number 056080, 2005 ASAE Annual Meeting . (doi: 10.13031/2013.19610) @2005
Authors: Chari V.K. Kandala, Christopher L. Butts
Keywords: RF Impedance, Peanut pods, Parallel-plates, Capacitance
In previous research, the moisture content of single in-shell peanut pods, Arachis hypogea
L., was determined by measuring the complex impedance of a parallel-plate capacitor with a peanut
pod held between the plates. In this method, capacitance, phase angle, and/or dissipation factor
were measured at 1 and 5 MHz.
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.The measured values were used in a derived empirical equation to calculate the moisture content of
the pod. In the present work, similar measurements of the complex impedance at 1, 5, and 9 MHz
were made, to measure the average moisture content of several peanut pods placed between two
parallel-plates. Unlike in the case of a single peanut pod, when several peanut pods are placed
between the plates, all the pods will not be in contact with both plates. This introduces different
patterns of air gaps between the pods and the plates which act as capacitors in series with the pods.
The equation used for single pods was modified to accommodate these changes, and the average
moisture contents were calculated and compared with their air-oven values. The calculated moisture
contents were within 1% of the air-oven values for over 80% of the samples tested in the moisture
range of 5% and 25%. The method is rapid and nondestructive and is suitable for developing a
practical instrument for moisture content measurement of in-shell peanuts.