Acoustic on-line grain moisture meter

Authors:
M. T. Amoodeh;M. H. Khoshtaghaza;S. Minaei
Affiliations:
Department of Agricultural Machinery Engineering, Tarbiat Modares University, P.O. Box 14115-336, Tehran, Iran;Department of Agricultural Machinery Engineering, Tarbiat Modares University, P.O. Box 14115-336, Tehran, Iran;Department of Agricultural Machinery Engineering, Tarbiat Modares University, P.O. Box 14115-336, Tehran, Iran
Venue:
Computers and Electronics in Agriculture
Year:
2006

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Abstract

A prototype of an acoustic on-line grain moisture meter was designed and developed. It consists of a funnel to produce a continuous grain stream with about 72cm^3s^-^1 flow rate falling onto a 30^o inclined sensor surface with 150mm diameter. A microphone, which is placed underneath the surface, receives sound waves generated by kernel impact and converts them to an electronic signal. The sensor was insulated to eliminate the ambient noise effects. Through the experiments the sound pressure level (SPL) variations of the impact sound were measured as output voltage and their relationship with grain moisture content was determined. In the first experiment, effects of grain drop height and types of impact surfaces (glass, wood and metal) on SPL were evaluated. Results showed that a drop height of 10cm with the glass sensor surface had the best calibration equation (R^2=0.94) with the highest accuracy and sensitivity for wheat moisture measurement. In the second experiment, effects of wheat varieties (Mahooty, Karaj-3 and C-73-18) with the selected impact surface (glass) and grain drop height (10cm) on the output voltage related to SPL, were studied. Relationships between the output voltage and kernel moisture content for three wheat varieties were developed as calibration equations. The maximum instrumental error in 8-20% moisture content range was 1.25%.