Patent ID: 6456079
Filing Date: 2002-09-24
Classification: G01V

Abstract:
A metal detection circuit for detecting the metal type of a metal target object, the circuit comprising:(a) a pulse generator; (b) a transmitting coil connected to the pulse generator for generating a time changing magnetic field in response to electrical pulses applied to the coil; (c) a resistive energy damper coupled to a receiving coil for attenuating the energy in the magnetic field; (d) a sampling and storing circuit connected to the receiving coil for sampling a signal representing the magnitude of the coil current at a sampling time within a time interval beginning after termination of a pulse and ending before the time at which inductor current in the presence of a high conductivity metal target object decays to a current which exceeds the current to which the inductor current decays in the absence of a metal target object; and (e) a signaling circuit connected to the sampling and storing circuit for signaling changes in the detected coil current at the sampling time as the coil is moved to indicate the metal type of metal target object.