Metal detector system with automatic ground exclusion balance feature

Abstract From the Canadian patent

A portable transmit/receive induction balance type metal detector having an automatic ground exclusion balance (GEB) feature to facilitate the screening out of the effects of mineralized ground. The circuitry provides a static GEB in a single try and then if selected, by the user, continual automatic GEB on a dynamic basis as the system is used. The circuit includes a pair of quadrature phase detectors, one of whose outputs is approximately in phase with the ground component of the loop return signal. That output is modified during an, air balance of the detector to remove the residual off-, sets in the circuit. This modified output in turn is summed with the other phase detector output to …