Method and apparatus for determining the nature or a property of a non-metallic, conductive material with the aid of an electromagnetic alternating field.

摘要

A food sample is passed through a time-varying electromagnetic field generated by a transmitter coil (1) whereby a signal is induced in a receiving signal (3) due to the generation of eddy-currents. A balance coil (4) offsets the large voltage induced in the receiving coil (3) by the field alone and thereby improves the sensitivity of detection. A food sample has been found to generate both reactive and resistive components which can be detected by respective phase detectors (5,6) that supply digital values to microprocessor (9) and the reactive and resistive components can be used to provide a measure of freshness or ripening of e.g. vegetable matter. Adjustments for variations in the cross-sectional area of the sample are made with regard to a factor Kr which relates to the reactive and resistive components.