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Transmitter-receiver loop buried metal object locator with switch controlled reference voltage

  • US 4,348,639 A
  • Filed: 05/18/1979
  • Issued: 09/07/1982
  • Est. Priority Date: 05/18/1979
  • Status: Expired due to Term
First Claim
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1. An electronic subterranean longitudinal metal object locator comprising:

  • (a) first and second closed rectangular loops, said first loop being oriented in a vertical plane and said second loop being oriented in a horizontal plane perpendicular to said first loop and spaced apart therefrom;

    (b) means for energizing said first loop with an alternating electrical current whereby a varying electromagnetic field is produced;

    (c) means for positioning said first loop in a plane perpendicular to said longitudinal metal object and said second loop in a plane parallel thereto, whereby a current is produced in said metal object from said first loop which produces a varying electromagnetic field for inducing a receive current in said second loop the magnitude of said received current being controlled by the relative position of said loops with respect to said metal object;

    (d) an amplifier for providing a voltage proportional to a current induced in said second loop;

    (e) a phase detector having a first input for receiving a voltage from said amplifier and a second input coupled to a source of a phase reference signal, said phase reference signal desensitizing said phase detector to ground signals;

    (f) a comparator for providing an output voltage proportional to the difference between a reference voltage and the output voltage provided by said phase detector, said comparator output voltage being proportional to said received current;

    (g) means for indicating the relative output voltage of said comparator, whereby changes in the relative level of said received current may be monitored; and

    (h) means for manually varying the level of said reference voltage to alter said comparator output voltage in response to monitored increases in the magnitude of the received current in said second loop, said means including a switch connected to receive said comparator output voltage, said means providing a voltage related to said received current for restoring said comparator output voltage to a predetermined level in response to a momentary closure of said switch, whereby the relative magnitude of said current is monitored for accurately positioning said second loop with respect to said longitudinal metal object, the position of said second loop determining the position of said metal object.

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