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Method and apparatus for protecting alternating current circuits

  • US 4,271,449 A
  • Filed: 04/04/1979
  • Issued: 06/02/1981
  • Est. Priority Date: 04/04/1979
  • Status: Expired due to Term
First Claim
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1. An apparatus for protecting a circuit from excessive current flow, comprising:

  • sense transformer means for sensing the current flow through the circuit;

    pulse shaping means for generating a sense pulse whose width is related to the rate of current flow into the sense transforming means;

    1st single shot multivibrator means for generating a reference period at the occurrence of each sense pulse;

    2nd single shot multivibrator means for providing a second pulse each time a sense pulse occurs;

    comparator means for providing an enabling command as long as the sense pulse'"'"'s width is greater than the reference period and to provide a reset at a fault condition when the sense pulse'"'"'s width is less than the reference period;

    selectable time delay means for providing a command signal after a fault condition and the occurrence of a selectable number of the second pulses; and

    relay means activated by the command signal.

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