Submitted to: Southeastcon, IEEE
Publication Type: Proceedings
Publication Acceptance Date: 3/9/2015
Publication Date: 4/9/2015
Citation: Lewis, M.A., Trabelsi, S., Nelson, S.O. 2015. Circuits and signal conditioning for a peanut-drying monitoring system. Southeastcon, IEEE. p. 123-127.
Interpretive Summary: Peanut drying is an essential task that takes place at peanut buying stations and shelling plants, preceding grading and sales. Although peanuts are left in windrows to dry naturally before being harvested with combines, they arrive at buying stations considerably high in moisture content. It is imperative for peanuts to be dried to less than 10.5% kernel moisture content for grading and storage purposes. To facilitate the drying process, peanuts are loaded into drying wagons or trailers. Then, dryers using propane or natural gas fuels are connected to the wagons and trailers through canvas ducts, and heated air is blown into the airspace below the peanut bed. The air is forced up through the peanuts to decrease their moisture content. Peanuts are dried in this fashion until they are expected to have less than 10.5% moisture content. Modern peanut drying processes utilize decision support software based on modeling and require substantial human interaction for moisture sampling. The samples must be taken, shelled and cleaned before testing for kernel moisture content with current moisture meters. The kernel moisture content is the main parameter of interest in the drying process, and it is the only parameter, besides temperature, that the drying system is working to control. However, since it is difficult to obtain, the control for kernel moisture content is often indirect and misguided. These procedures increase the likelihood of peanuts being overdried or underdried. An automated controller with real-time, in-shell kernel moisture content determination capabilities has been developed to control and monitor the peanut drying process. By using a microwave moisture meter, developed within USDA, ARS, the moisture content of the peanut kernel can be determined without having to shell the pod peanuts. The kernel moisture content and atmospheric conditions serve as continuous inputs to the controller, and thus, air temperature and drying time are controlled automatically. Such implementation reduces overdrying and underdrying, preserves quality of peanuts, and minimizes energy consumption through efficient control of the heater. A quarter-scale peanut drying system was used in developing and testing the automated drier controller. This development led to the implementation of a portable peanut-drying monitoring system, capable of measuring drying parameters in real-time on 45-ft semi-trailers. The monitoring system uses a sensor network containing five sensors, one of which is a microwave moisture sensor, capable of in-shell kernel moisture content determination, to monitor drying parameters. These parameters include temperature and relative humidity of the ambient air, temperature and kernel moisture content of the peanut bed, and the temperature of the inlet air. Appropriate signal conditioning was applied to each sensor output so that all voltages would be suitable for the analog-to-digital converter of the microcontroller. Laboratory testing, field testing, and demonstrations have shown that the circuits are robust and maintain stability even after the system has been moved and installed in commercially operated drying trailers. Data from sensors used to measure atmospheric conditions compare well to weather data from that time period in laboratory trails and field testing. Kernel moisture content was determined in-shell with an accuracy of about 1/2% or less when compared to standard oven drying tests. Results from this research show promise for further implementation on a commercial scale. When implemented commercially, such control systems would save significant labor and energy costs while improving product quality for the peanut industry and consumers.
Technical Abstract: Post-harvest processes at peanut buying points and other peanut grading facilities have a direct impact on the quality of the product. Peanut drying is an essential task for safe peanut storage. The rate at which peanuts are dried can also affect the flavor and milling qualities. Current peanut drying processes require substantial human interaction and often lack efficiency. Therefore, a quarter-scale peanut drying system was developed to study automation of the drying process. This development led to the implementation of a portable peanut-drying monitoring system, capable of measuring drying parameters in real-time on 45-ft semi-trailers. The monitoring system uses a sensor network containing five sensors, one of which is a microwave moisture sensor, capable of in-shell kernel moisture content determination, to monitor drying parameters. These parameters include temperature and relative humidity of the ambient air, temperature and kernel moisture content of the peanut bed, and the temperature of the inlet air. Appropriate signal conditioning was applied to each sensor output so that all voltages would be suitable for the analog to digital converter of the microcontroller. Such implementation would reduce overdrying and underdrying, preserve peanut quality, and provide more efficient control of the heater, minimizing energy consumption and labor requirements.