Location: Peanut Research
Title: Parallel-Plate Sensors for Measurement of Moisture Content in in-Shell Peanuts Non-Destructively Authors
Submitted to: Proceedings of the American Society of Agricultural and Biological Engineers International (ASABE)
Publication Type: Proceedings
Publication Acceptance Date: July 1, 2006
Publication Date: July 12, 2006
Citation: Kandala, C., Butts, C.L., Nelson, S.O. 2006. PARALLEL-PLATE SENSORS FOR MEASUREMENT OF MOISTURE CONTENT IN IN-SHELL PEANUTS NON-DESTRUCTIVELY. Proceedings of the American Society of Agricultural and Biological Engineers International (ASABE). Paper No. 66041.. Interpretive Summary: In the southeastern United States, freshly dug peanuts, may have moisture contents as high as 40%. Soon after they are combined, the peanuts have to be dried to reduce the mc to less than 10.5% to meet the grading standards. They also can be stored at this mc level with adequate ventilation. Measuring and controlling mc is an important aspect in the harvesting, storage, marketing and processing of peanuts. Commercial moisture meters presently used can only measure the mc of peanuts that are shelled and cleaned. This process is laborious. The samples used for testing are usually discarded, resulting in cumulative loss of large quantities of peanuts of considerable dollar value. The RF Impedance method determines the mc of peanuts by measurements on the pods themselves and saves time and labor expended in shelling and cleaning the peanuts. The method is nondestructive and the parallel-plate sensors used are simple to construct and easy to operate. There are no moving parts involved and thus the sensors can be used continuously and over long periods of time. Earlier experiments showed a good correlation between the pod and kernel moistures in peanuts and thus from a knowledge of the pod moisture the kernel moisture can be determined to acceptable accuracies. The RF Impedance method with parallel-plate sensors described here can be used in the development of a practical instrument for measurement of moisture content in in-shell peanuts.
Technical Abstract: In earlier work reported, parallel-plate capacitance sensors were used to determine the average moisture content (MC) of small samples of in-shell peanuts (peanut pods). In this method, seven or eight peanut pods were held between two parallel metal electrodes and the capacitance, phase angle and/or dissipation factor of the system were measured at frequencies of 1, 5 and 9 MHz. The measured values were used in an empirical equation and the average MC values were calculated. In the present work two parallel-plate electrodes were mounted inside a cylinder, made of acrylic material, and the space between the plates was filled with peanut pods. The impedance measurements were made on the cylinder system and the average MC of the peanut pods was determined from a similar empirical equation. The calculated MC values were compared with their oven-determined values and were found to be within 1% of the standard oven values for 90% of the samples tested in the moisture range between 6 and 20%. Two parallel-plate sensors with different plate separations, and peanuts from 2004 and 2005 harvests, were used in these measurements. The method being rapid and nondestructive, is suitable for the development of a practical instrument for measurement of moisture content in in-shell peanuts.