Patent ID: 7977938

Claim:
A metal detector for detecting a ferrite or non-ferrite object, the metal detector comprising: an inductively coupled sensor having a transmitter coil and a receiver coil, the detector detecting a phase difference or an amplitude difference between signals in the transmitter and receiver coils in detecting the ferrite or non-ferrite object proximate the sensor; an electronic storage medium having stored therein calibration information for the sensor such that the metal detector does not need to be calibrated before each use; a display for indicating distance of the ferrite or non-ferrite object from the metal detector; a sampling circuit for converting phase difference between the signals in the transmitter and receiver coils into a change in a signal amplitude; and a processor coupled to the sampling circuit, the electronic storage medium, and the display, and programmed to compare the signal amplitude with the calibration information and to output on the display the distance of the ferrite or non-ferrite object from the metal detector.