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INDUCTIVELY COUPLED METAL DETECTOR ARRANGEMENT

  • US 3,742,341 A
  • Filed: 08/16/1971
  • Issued: 06/26/1973
  • Est. Priority Date: 08/16/1971
  • Status: Expired due to Term
First Claim
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1. A metal detector arrangement of the type adapted to detect the presence of a metal object and generate detectable signals in response thereto, and comprising, in combination;

  • a case means having peripheral walls, a top wall and a bottom wall transparent to electromagnitic radiation in a preselected bandwith and defining a cavity;

    an electrically operated detector circuit mounted in said case means, and said electrically operated detector circuit comprising;

    oscillator means for generating output signals having a frequency within said preselected bandwith, and said oscillator means having a metal responsive means comprising a tank circuit, and said tank circuit having an inductor and a capacitor, and said inductor comprising a primary of a transformer, and said metal responsive means varying said output signal frequency from a first frequency to other frequencies in response to the presence of the metal object in regions external said cavity;

    search coil means comprising a loop antenna having a first axis and extending around said peripheral walls of said case means in said cavity and connected to said oscillator means for radiating said output signal to regions external said case means, and said search coil means coupled to the secondary of said transformer for varying the inductance of said inductor to vary the frequency of said oscillator output signal for the condition of the metal object in proximity thereto;

    receiver coil means having a second axis substantially perpendicular to said first axis and said second axis substantially coplanar with said search coil, and said receiver coil positioned within said loop of said search coil means and spaced a preselected distance therefrom, said receiver coil means receiving said radiated output signal from said search coil mean;

    tuned amplifier means connected to said receiver coil means for generating an information signal having a magnitude proportional to the difference between said first frequency and said other frequencies;

    switch means connected to said tuned amplifier means for receiving said information signal and having an open condition for blocking said information signal for said information signal having a first magnitude, and a closed condition for transmitting said information signal for said information signal having a second magnitude different from said first magnitude;

    indicator means connected to said switch means for generating the detectable signal in response to said information signal at said second magnitude;

    sensitivity control means mounted on said case means in regions adjacent and spaced from said receiver coil means for varying the magnitude of said information signal; and

    a source of electrical energy for powering said electrically operated detector circuit.

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