Electricity: measuring and testing – Of geophysical surface or subsurface in situ – For small object detection or location
Patent
1980-05-05
1982-08-10
Strecker, Gerard R.
Electricity: measuring and testing
Of geophysical surface or subsurface in situ
For small object detection or location
G01V 311
Patent
active
043440347
ABSTRACT:
A metal detector circuit derives a first sine wave signal in response to metal objects in proximity to the search head. A second sine wave signal at the operating frequency of the circuit is applied to a center tapped inductor. The initial and final turns of the inductor are connected through a system of capacitors, resistors, and diodes so that conduction occurs during a brief period of each cycle of the applied sine wave. The electrical switching action thus afforded is used to charge a capacitor to the instantaneous voltage of a specified component of the first sine wave. A phase shift network provides a means of adjustment of the phase angle at which switching occurs, to permit a predetermined component of the first sine wave to be detected. When the proper component of the first sine wave is detected, a selective or discriminatory response may be derived, resulting in signals of opposite polarity for high Q objects, such as coins, and low Q objects, such as aluminum pull tabs.
In addition, a metal detector system is presented wherein two of the detector circuits of the invention are advantageously combined so that the output is both selective and ground neutralized. In this system, a first detector circuit provides a selective response to metal objects. A second detector circuit provides a response to metal objects, while excluding ground effects. A clamping circuit controlled by the second detector circuit removes ground effects from the output of the first detector circuit.
REFERENCES:
patent: 3337796 (1967-08-01), Hentschel et al.
patent: 3826973 (1974-07-01), Pflaum
patent: 4030026 (1977-06-01), Payne
patent: 4096432 (1978-06-01), Spencer
patent: 4110679 (1978-08-01), Payne
patent: 4128803 (1978-12-01), Payne
patent: 4249129 (1981-02-01), Karbowski
Gardiner Robert F.
Strecker Gerard R.
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