Quality control using electromagnetic induction sensors

Electromagnetic induction sensors have been used since the 1950´s for quality control on manufacturing production lines to safeguard against contamination of products and ensure consistency of quality. However, manufacturers of these sensors have concentrated on improving sensitivity and reducing noise rather than determining the properties of nearby products such as size, position or conductivity. Partly, this is because the complex interactions between the sensor, the product and the environment are difficult to interpret, but digital signal processing (DSP) techniques could be used to extract certain properties of conductive objects from a signal. This paper discusses the implementation of an electromagnetic sensor based on DSP techniques. The operation of the electromagnetic sensor is discussed. Two possible algorithms for parameter extraction are introduced, and differentiation between aluminium and ferromagnetic materials is demonstrated. This `intelligent´ electromagnetic sensor could be used to automate, for example, the sorting of conductive materials for recycling