Electricity: measuring and testing – Of geophysical surface or subsurface in situ – For small object detection or location
Patent
1979-02-16
1982-03-23
Strecker, Gerard R.
Electricity: measuring and testing
Of geophysical surface or subsurface in situ
For small object detection or location
331 37, G01V 311, G01V 3165
Patent
active
043215394
ABSTRACT:
An improved metal detecting device of the beat frequency oscillator type is provided which incorporates a method for determining the side of the zero beat frequency at which a search oscillator is operating. The device includes a search coil conveniently mounted which is part of a search oscillator. A reference oscillator is also provided, the output of which is digitally compared to that of the search oscillator by a digital phase comparator. The digital phase comparator output is applied through a low pass filter to a slope detector circuit. The slope detector output signal is supplied to both an audio output circuit and a filter/comparator. The audio output is sufficient to facilitate location of permeable and conductive substances. The output of the slope detector also contains information which is extracted by the filter/comparator and translated to an audible signal by an oscillator and the audio output circuit. This audible signal serves to facilitate the determination of whether a permeable or a conductive substance is being detected.
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Macario, R.C.V., "Discriminative Metal Detector" Wireless World, Jul. 1978, pp. 43-46.
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Coult John H.
Hill Thomas E.
Strecker Gerard R.
Zenith Radio Corporation
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