Metal detector with nulling of imbalance

Details Metal detector with nulling of imbalance Metal detector with nulling of imbalance

1996-06-03

1998-03-17

Snow, Walter E.

Electricity: measuring and testing

Of geophysical surface or subsurface in situ

For small object detection or location

324233, 324225, G01V 308, G01V 310, G01N 3312, G01R 2772

Patent

active

057291438

ABSTRACT:
A metal detector includes a receive coil and a transmit coil connected in an inductive bridge. To overcome imbalances in the bridge due for instance to misalignment of the coils or the presence of mineralization in the medium which is being examined, the metal detector automatically produces a nulling (bucking) signal to cancel out the effects of any unwanted receive coil signals detected during calibration. This nulling signal is a nulling current both in terms of level and phase, and its level and phase are determined during a calibration process prior to actual metal detection. By inclusion in the metal detector of a microprocessor (microcontroller) operating at a much higher frequency than the variations in the magnetic field used to detect metal, the nulling signal generation is performed with a high degree of time resolution, resulting a precision metal detector which adaptively ignores any unwanted signals.

REFERENCES:
patent: 4030026 (1977-06-01), Payne
patent: 4423377 (1983-12-01), Podhrosky
patent: 4628265 (1986-12-01), Johnson et al.
patent: 4783630 (1988-11-01), Shoemaker
patent: 4868910 (1989-09-01), Maulding
patent: 4894618 (1990-01-01), Candy
patent: 5247257 (1993-09-01), Chulick
patent: 5506506 (1996-04-01), Candy

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