Skip to main content
ARS Home » Research » Publications at this Location » Publication #227706

Title: Practical Microwave Meter for Sensing Moisture and Density in Granular Materials

item Trabelsi, Samir
item Nelson, Stuart
item Lewis, Micah

Submitted to: Instrumentation and Measurement Technology Conference Record
Publication Type: Proceedings
Publication Acceptance Date: 3/24/2008
Publication Date: N/A
Citation: N/A

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. A prototype microwave moisture sensor has been assembled with off-the-shelf microwave components and tested for measurements on grain and seed. Three algorithms were used to determine both bulk density and moisture content. Results from measurements on wheat show that bulk density can be determined with an accuracy of less than 2% and moisture content with a standard error of calibration of 0.5%. These 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 sensor for rapid and nondestructive sensing of bulk density and moisture content in granular and particulate materials has been built and tested. The sensor was made with inexpensive, off-the-shelf components and operates at 5.8 GHz. Three permittivity-based algorithms were used to determine simultaneously bulk density and moisture content from dielectric properties measurement. Results obtained for wheat indicate the bulk density can be determined with less than 2% relative error and that moisture content can be determined with a standard error of calibration of 0.5%. Keywords – Low-cost microwave sensor, dielectric constant, loss factor, moisture content, bulk density, wheat.