Electricity: measuring and testing – Of geophysical surface or subsurface in situ – For small object detection or location
Patent
1980-06-23
1984-03-27
Strecker, Gerard R.
Electricity: measuring and testing
Of geophysical surface or subsurface in situ
For small object detection or location
331 1R, 331 65, G01V 311, H03L 700
Patent
active
044397348
ABSTRACT:
A frequency shift responsive metal detector having a sense oscillator coupled with an inducer loop. When the inducer nears a metal object, the effective inductance is changed which correspondingly shifts the natural frequency of the sense oscillator. The sense oscillator couples with a frequency shift detector. The detector produces a d.c. feedback signal which is proportional to the sense oscillator shift and acts therewith to re-establish the oscillator to it's original natural frequency by way of a voltage controlled reactance. The detector also produces a d.c. output that serves to drive an audio frequency rate voltage controlled oscillator wherein the pitch, or resultant frequency therefrom produced is proportional to the effect of the metal object on the inducer loop. A d.c. signal from the detector also serves to drive a visual indicator, such as a meter. The change in the loop inductance may be either positive or negative, resulting in a unique indication distinction between diamagnetic materials, and those which are ferromagnetic or paramagnetic. The use of a dual channel, stereo-like apparatus also provides the operator with directivity, which may be coupled with an enhancement gate signal which alternates the stereo-response back and forth between the earphones of a stereo-headset, thereby improving operator acuity.
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Dayton et al., "Capacitive Micrometer," Electronics, Sep. 1946, pp. 106-111.
Todd, Carl David, "Metal Detector Finds Ducts and Pipes," Electronics, Jan. 1, 1957, pp. 172-174.
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