Patent ID: 7202661

Claim:
Apparatus for establishing the positions of metal objects in a mixed input stream of both metal and non-metal objects, the apparatus comprising a differential metal-detecting coil having a first coil portion wound in a first sense and a second coil portion of generally similar shape and size to the first, wound in a second sense opposite to the first sense, and conveying means for moving objects with respect to, and past, the differential metal-detecting coil in a plane and in a direction with unit vector â, characterised in that the second coil portion is displaced from the first coil portion by a displacement B having a component in the plane in a direction with unit vector {circumflex over (b)}, wherein 0 < cos - 1 ⁢ a ^ · b ^ < π 2 , and in that the apparatus further comprises a signal processor for analysing the form of the output voltage of the coil as a function of time to establish the position of said metal objects in a direction ĉ in the plane, where ĉ is defined by â·ĉ=0.