Capacitive throughput sensor for sugar beets and potatoes

Yield monitoring whilst harvesting, in combination with a positioning system, is a fundamental source of information for generating field yield maps. In this research, a capacitive throughput sensor for potatoes and sugar beets has been tested. The principle of the sensor is based on the fact that the dielectric constant of an air/material mixture between two parallel plates increases with material volume concentration. A theoretical model for a capacitive throughput sensor has been developed; the model incorporates all the most important physical parameters that influence material throughput measurement. Two basic relationships between the sensor electrical capacity and material throughput were derived from the proposed model, a hyperbolic relationship and a linear relationship. The method of presenting the measured material to the sensor was the most important factor in explaining sensor behaviour. The theoretical considerations were confirmed by dynamic laboratory experiments using potatoes and sugar beets.