Metal detector with circuits for automatically screening out the

Details Metal detector with circuits for automatically screening out the Metal detector with circuits for automatically screening out the

1986-03-27

1988-11-08

Eisenzopf, Reinhard J.

Electricity: measuring and testing

Of geophysical surface or subsurface in situ

For small object detection or location

324233, G01V 311, G01R 3300

Patent

active

047836300

ABSTRACT:
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 offsets in the circuit. This modified output in turn is summed with the other phase detector output to produce a phase detection signal that can be adjusted by automatic means to be precisely in quadrature with the ground component of the loop return signal. A controller is provided, with selectable user inputs, to initiate the static and dynamic GEB operations. An error amplifier in conjunction with two sample/hold elements and a variable duty cycle chopper operate in a feedback loop to appropriately adjust the phase detection signal. Audible beep indications are generated to signal the user when the steps in the automatic GEB are completed.

REFERENCES:
patent: 4303897 (1981-12-01), Podhrasky
patent: 4387338 (1983-06-01), Hecht et al.
patent: 4470015 (1984-09-01), Hirschi et al.

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