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Inductive proximity sensor with periodic switching for sensing the presence of objects

  • US 5,498,958 A
  • Filed: 11/03/1993
  • Issued: 03/12/1996
  • Est. Priority Date: 12/21/1990
  • Status: Expired due to Term
First Claim
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1. An inductive proximity sensor for sensing the presence of objects in close proximity to the sensor, comprising:

  • an inductor;

    a current directing means for supplying a first voltage to the inductor to produce a current in the inductor to induce a magnetic field in the object during a first period, and for supplying a second voltage to the inductor in a direction opposite to the first voltage during a second period which begins upon conclusion of the first period and terminates upon establishing a substantially zero current in the inductor;

    determining means connectable to the inductor for determining when the object is within a predetermined proximity to the inductor, the determining means measuring an induced voltage in the inductor generated by a decaying magnetic field in the object during a third period that begins shortly after the termination of the second period, and comparing the measured induced voltage with a predetermined value.

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