| 摘要 |
A metal detector system is described for detecting metal objects in a monitoring zone, where the metal detector system comprises: (a) a transmitter coil for generating a magnetic filed in the zone to be monitored, the coil being disposed on a first side of the zone; (b) a first sensing coil disposed on a second side of the zone opposed to the first side, the first sensing coil generating a first sensing signal in response to perturbations in the magnetic field caused by the presence of a metallic object in the zone; (c) a second sensing coil disposed on the second side of the zone, the second sensing coil being spaced apart from the first sensing coil, the second sensing coil generating a second sensing signal in response to perturbations in the magnetic field caused by the presence of a metallic object in the zone; and (d) a sensing circuit for comparing the amplitudes of the first and second sensing signals to generate a difference signal and for generating a first trigger signal for a zero down-crossing of the difference signal and for generating a second trigger signal for a zero uncrossing of the difference signal, wherein the trigger signals indicate direction of travel of a metal object in the zone in relation to the first and second sensing coils.
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