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Digital loop detector with improved detection control

  • US 4,075,563 A
  • Filed: 05/13/1976
  • Issued: 02/21/1978
  • Est. Priority Date: 05/13/1976
  • Status: Expired due to Term
First Claim
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1. In a digital detector device for detecting a metal object in the field of influence of a detector loop controlling the frequency of pulses created by an oscillator, said digital detector device including counter means for counting said pulses created by said oscillator during a counting interval having a selected duration whereby the magnitude of the pulses counted during said controlled interval is indicative of the inductance of said loop and digital means for creating an output signal when the number of pulses counted by said counter means for a given counting interval differs from a selected count by a number greater than a selected threshold number, the improvement comprising:

  • said digital means including means for creating a binary coded signal having a series of binary bits arranged in a selected order for indicating the difference between said number of counted pulses and said selected count;

    a binary logic circuit having a plurality of input lines individually corresponding to said bits and divided into first and second groups, an output line and means for creating said output signal in said output line when the logic on one of said input lines is at a selected binary logic value;

    a source of binary logic value opposite to said selected binary logic value;

    separate sensitivity switch means for selectively shifting said input lines of said first group between a first position where said associated input line has a binary condition controlled by a corresponding one of said binary bits and a second position where said associated input line has a binary condition controlled by said binary logic source;

    means for directing bits of binary logic to corresponding input lines of said second group of input lines; and

    , means for inhibiting creation of said output signal when a selected one of said input lines in said second group is at said selected binary logic value.

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