ARS | Publication request: Microwave Moisture Meter for Granular and Particulate Materials

Submitted to: IEEE Instrumentation & Measurement Society
Publication Type: Proceedings
Publication Acceptance Date: March 1, 2010
Publication Date: May 3, 2010
Citation: Trabelsi, S., Nelson, S.O. 2010. Microwave Moisture Meter for Granular and Particulate Materials. Proceedings of the 2010 IEEE International Instrumentation and Measurement Technology Conference, CD, pp. 1304-1308.

Interpretive Summary: Moisture content of cereal grains and many other agricultural products is the most important characteristic that determines their suitability for storage, and it is also important in determining the selling price. Electronic moisture meters are used almost universally in the grain trade for determining the moisture content of samples taken from lots being delivered to grain elevators, transportation facilities, and processors. However, reliable moisture sensing equipment for continuously monitoring grain and seed moisture content on harvesting equipment, when loading and unloading grain, and in processing is needed to provide better moisture content information for managing these operations. It has been shown that microwave measurements on grain and seed can provide reliable moisture information independent of packing variations that take place while grain is moving in a chute or conveyor. Research has revealed that a single calibration based on the dielectric properties of grain measured at microwave frequencies can reliably sense the moisture content of wheat, corn, grain sorghum, soybeans, and barley. Because these five commodities have very different kernel shapes, sizes, and composition, this new technique offers promise for a universal calibration for grain, soybeans, and similar crops. A prototype microwave moisture meter operating at 5.8 GHz is described that was built with off-the-shelf microwave components and tested for measurements on wheat and soybeans over wide ranges in moisture content. The principles of the moisture measurement are also outlined. The relatively inexpensive instrument provided moisture content independent of bulk density and kind of grain with accuracies better than 1 percent moisture content. It also can provide bulk density from sensed microwave dielectric properties with relative errors of about 2 percent. The results provide an incentive for the development of practical microwave moisture sensing instruments that can provide new tools for the maintenance of high quality in such agricultural products, thus benefiting farmers and consumers as well.

Technical Abstract: A low-cost microwave moisture meter operating at a single frequency for instantaneous and nondestructive determination of moisture content of granular and particulate materials was developed, calibrated and tested with different kinds of grain and seed. The meter operates at a single microwave frequency of 5.8 GHz and uses the principle of free-space transmission measurement for the determination of attenuation, phase shift, and dielectric properties of a layer of material. Moisture content is determined independent of bulk density from the dielectric properties with a permittivity-based algorithm.