On-line monitoring system for grain moisture content during dryer processing

A monitoring system was developed for the purpose of measuring and controlling the grain moisture content from the outlet of a dryer during drying process. Concentric cylinder type of capacitance sensor was used to measure the capacitance, which varied with the change of the moisture content and the dielectric constant of grain. The relationship between grain moisture content and oscillation frequency of the sensor as well as grain temperature under uniform flow was determined, and a mathematical model was then developed. In order to achieve the required grain moisture content, the PI control algorithm was used to control the unloading auger speed. Test were conducted with wheat and corn. The experimental result showed that control accuracy at the dryer's outlet was within 0.5% of the required moisture content.