Apparatus and method for on-line inspection of electrically conductive

Abstract

Inclusions such as encysted parasites and spoilage in food products such as fish fillets are detected by immersing the food products in a bath of an electrolyte, such as a saline solution, having substantially the same electrical conductivity as the uncontaminated food product. An electrical current passed through the electrolyte also passes through the food product. Perturbations in the resulting magnetic field produced by the discontinuities in conductivity at the boundaries of the inclusions or of the spoiled article which have substantially different conductivities from that of the electrolyte and unspoiled food products, provide an indication of the presence of the contamination. Production line inspection rates are achieved by conveying the food products through a container filled with electrolyte and past an array of stationary magnetometers. Perturbations in the magnetic field at the edges of the container are cancelled by directing the current which flows through the electrolyte in a first direction back over the container in the opposite direction through a cancelling conductor, while fields produced by the supply leads are cancelled by using coaxial cable.