Submitted to: IEEE Transactions on Instrumentation and Measurement
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/16/2004
Publication Date: 12/10/2004
Citation: Kandala, C., Nelson, S.O. 2004. Moisture determination in single peanut pods by complex rf impedance measurement. IEEE Transactions on Instrumentation and Measurement. Interpretive Summary: Moisture content (mc) is an important property to be measured and monitored in harvesting, storing, selling, buying and processing of peanuts. Freshly harvested peanuts have a mc usually in the range of 20% to 40%. According to the grading standards the mc value has to be less than 10.49% and to achieve this these peanuts have to be immediately dried. Peanuts are dried in trailers that have perforated floor and an air plenum till they dry to the required mc value. In the drying facilities one can see peanuts being dried this way in over 80 trailers at a time. During the drying process it would be necessary to measure the mc value of the peanuts in each trailer at regular intervals to determine the point in time at which the drying can be stopped. Over-drying results in waste of energy and lowers the quality of peanuts while under-drying is not acceptable in the industry.
Technical Abstract: It was earlier determined that moisture content (mc) in a single in-shell peanut (peanut pod) can be estimated from the complex impedance measurements on a parallel-plate capacitor with the pod held between the plates. In this method, capacitance (C), phase angle (')'' and/or dissipation factor (D) were measured with the pod between the plates at two frequencies of 1.0 and 5.0 MHz, and these values were used in an empirical equation to calculate the mc of the pod . Moisture content values obtained by this method were independent of variation in the size of the peanut pods, and the mc of the pods tested was between 5% and 20%. The predicted moisture contents were within 1% of the standard air-oven values for over 85% of the single pods tested. In the new work reported in this paper the feasibility was assessed for estimating the average mc of a small sample of peanuts, consisting of seven or eight pods, from the complex impedance measurements made on a parallel-plate capacitor holding the pods, at the frequencies 1, 5 and 9 MHz.