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Title: DETERMINING BULK DENSITY OF GRANULAR MATERIALS FROM MICROWAVE MEASUREMENTS OF THEIR DIELETRIC PROPERTIES

Author
item TRABELSI, SAMIR - UNIVERSITY OF GEORGIA
item Kraszewski, Andrzej
item Nelson, Stuart

Submitted to: Instrumentation and Measurement Technology Conference Record
Publication Type: Proceedings
Publication Acceptance Date: 3/1/2001
Publication Date: N/A
Citation: N/A

Interpretive Summary: Granular materials such as agricultural grains have a characteristic known as bulk density, which is a measure of the weight of grain that occupies a given volume of space. In the grain trade, the term "test weight" is used for the bulk density of grain determined by a standard method. The test weight for a given lot of grain is used as one of the quality factors for that grain lot. The standard test weight for a given type of grain is used for determining yields in bushels per acre. For example the standard test weight for wheat is 60 lb/bushel, and the weight of wheat harvested from a field is divided by 60 to determine the number of bushels the field yielded. Then dividing that number of bushels by the number of acres in the field gives the yield in bushels per acre. The bulk density of grain that is moving in a conveyor or through a chute is quite variable, because the bulk density depends on the degree of packing that takes place in the bulk grain. Knowledge of the bulk density can be important in operations such as yield monitoring on combines, but it is a difficult quantity to measure in flowing grain. The research reported describes a new technique for determining bulk density of grain and other granular materials through sensing the electrical properties of the grain at microwave frequencies. Use of these microwave dielectric properties can provide accurate values for the bulk density of the grain. Development of suitable microwave instruments for monitoring the bulk density of flowing grain can provide a new tool that will be useful in modern farming and processing operations for American agriculture.

Technical Abstract: A dielectric method for determining bulk density of granular materials from measurement of their dielectric properties at microwave frequencies is presented. A complex-plane representation of the dielectric properties, normalized to bulk density, is used to generate calibration equations at 7 GHz for cereal grain and seed over wide ranges of moisture content and temperature. The technique provided bulk density values with relative errors of less than 1.5% for wheat, corn, and soybeans and less than 4% for oats. It provides a technique adaptable to on-line monitoring of bulk density of grain and seed under dynamic conditions.