Location: Quality and Safety Assessment Research UnitTitle: Microwave sensing of moisture content and bulk density in flowing grain
|NELSON, STUART - Retired ARS Employee|
Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/10/2015
Publication Date: 5/2/2016
Citation: Trabelsi, S., Lewis, M.A., Nelson, S. 2016. Microwave sensing of moisture content and bulk density in flowing grain. Transactions of the ASABE. 59(2):429-433.
Interpretive Summary: Dielectric properties of materials are electrical properties that determine how materials interact with electric fields such as those of high-frequency and microwave electromagnetic energy. Dielectric properties of grain and seed are highly correlated with the amount of moisture in these materials. Currently used techniques for rapid moisture measurement in grain and seed through sensing their dielectric properties at lower frequencies require correction for bulk density fluctuations in the grain and therefore are not suitable for reliable measurements on flowing grain because of unknown changes in the bulk density of grain as it flows. Sensing moisture content in grain and seed is possible by utilizing microwave frequencies and has been successfully demonstrated on static grain and seed samples. If desired, the bulk density of the grain or seed can be determined simultaneously with moisture content. Although the theoretical basis for the density-independent grain moisture measurement is expected to be useful on flowing materials, successful use has not been demonstrated. A laboratory flowing grain system was built for tests of microwave moisture measurement that were conducted on shelled field corn, wheat, and soybeans. Appropriate software was written to control a microwave network analyzer for the necessary attenuation and phase measurements, and tests were run on flowing grain and seed materials of high and low moisture levels and at low, medium, and high flow rates. Results confirmed that moisture readings obtained on static and flowing grain and seed agreed well, demonstrating the usefulness of the microwave density-independent technique for monitoring moisture measurements on flowing grain. Bulk densities determined by the microwave measurements on static and flowing grain and seed lots also agreed very well. Such techniques for reliably measuring the moisture content and bulk density of flowing grain may be useful on harvesting and processing equipment for grain and seed materials and provide improvement in efficiencies of managing such operations with benefits for producers, processors and consumers.
Technical Abstract: Moisture content and bulk density were determined from measurement of the dielectric properties of flowing wheat kernels at a single microwave frequency (5.8 GHz). The measuring system consisted of two high-gain microwave patch antennas mounted on opposite sides of rectangular chute and connected to a microwave vector network analyzer. Grain flow was regulated by an iris flow control valve. Software was written to control acquisition of attenuation and phase data on flowing grain and acquiring seven reading per second. The dielectric properties of each flowing sample of wheat were determined from measured attenuation and phase shift. Several algorithms were used to determine simultaneously moisture content and bulk density from measurement of attenuation, phase shift, the dielectric constant and the dielectric loss factor. Results from these prediction algorithms will be shown and their respective performance compared. The standard errors of calibration were 0.2% to 0.5% for moisture and 0.01 to 0.03 g/cm3 for bulk density. Calibration methods presented in this paper offer promise for developing reliable sensors for real-time monitoring of moisture and density in flowing grains.