Image Number 4 for United States Patent #8473235.
The present invention provides apparatus for scanning a product to detect metal in that product. The apparatus comprises a drive coil (4), for generating an electromagnetic field in the product, and a detection coil arranged to detect fluctuations in the magnetic field caused by the presence of a metallic particle in the product. A drive circuit (26) for the drive coil (4) comprises a plurality of switches (19 to 22) driven by a controller (16), which switch alternately connect the drive coil across a potential difference to cause the drive coil to be driven at an operating frequency determined by operation of the switches. Using a switching circuit to drive the drive coil (4) greatly increases the number of frequencies at which the drive coil may be operated. The invention has particular application to the food industry.