Title: Integrating an embedded system in a microwave moisture meter Authors
Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 23, 2012
Publication Date: December 21, 2012
Citation: Lewis, M.A., Trabelsi, S. 2012. Integrating an embedded system in a microwave moisture meter. Applied Engineering in Agriculture. 28(6):923-931. Interpretive Summary: Electrical characteristics, known as dielectric properties, of grain and oilseed are closely related to the amount of water that they contain. Consequently, instruments can be designed to sense these dielectric properties and be calibrated to read moisture content. Such instruments, called moisture meters, are widely used in the grain and seed trade for rapid determination of moisture content. Moisture content is especially important in the sale and storage of peanuts so that spoilage and development of toxins can be avoided. If kernel moisture contents of peanut lots exceed 10.49 percent, they cannot be sold and have to be dried before they can be reconsidered for sale. Research on microwave dielectric properties of peanuts has revealed that measurements at these higher frequencies can reliably measure the moisture content of the peanut kernels from measurements on the unshelled peanut pods. A low-cost microwave moisture meter was built for rapidly and nondestructively determining the kernel moisture content from measurements on unshelled peanut pods. However, this meter was controlled by a laptop computer, which reduced its portability, and occasional computer-related problems interfered with normal operation. Therefore a microcontroller was used in the design of an embedded control system for the moisture meter to replace the separate computer. The microcontroller provides a graphical 144 x 32 pixel LCD and 16-button keypad to facilitate user interaction. The embedded system thus provides a user interface, event execution, process control, data acquisition and data storage. Testing showed that the moisture meter with the new embedded system maintained the performance and accuracy observed for the original meter with laptop computer control. Results showed close similarity of measurements taken with the microwave meter, both with laptop control and with embedded microcontroller, and measurements taken with a laboratory vector network analyzer. The integration of the embedded system with the microwave moisture meter provides a cost-effective, portable, and robust solution for microwave moisture testing of peanuts and other crops. The microwave moisture meter with embedded microcontroller system offers promise for improving efficiencies of grading and processing as well as preventing losses due to spoilage and will be a useful tool for peanut farmers, handlers, and processors, thus providing safe and high quality products for consumers.
Technical Abstract: The conversion of a PC- or laptop-controlled microwave moisture meter to a stand-alone meter hosting its own embedded system is discussed. The moisture meter measures the attenuation and phase shift of low power microwaves traversing the sample, from which the dielectric properties are calculated. The power level of the microwaves is similar to that of Wi-Fi. Therefore, the sample is unharmed and no heating occurs. The dielectric properties are then used for rapid, nondestructive determination of the moisture content in the grain or seed sample. The initial system consisted of the moisture meter being controlled via USB interface by an external laptop or PC. Though effective, the system lacked full portability and was susceptible to computer crashes and interruptions in communication between the meter and laptop. To improve the system, a microcontroller was selected in the design of an embedded system for the moisture meter. The microcontroller provides a graphical 144 x 32 pixel LCD and 16-button keypad to facilitate user interaction. The embedded system provides the following functionalities: user interface (input/output), event execution, process control, data acquisition and data storage. Testing showed that the moisture meter with the new embedded system maintained the performance and accuracy observed for the original meter with PC or laptop control. Results are included to show the similarity of measurements taken with the microwave meter (both versions) to measurements taken with a vector network analyzer. The integration of the embedded system with the microwave moisture meter provides a cost-effective, portable, and robust solution for microwave moisture sensing.