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Capacitive occupancy or proximity detector

  • US 10,126,149 B2
  • Filed: 08/20/2015
  • Issued: 11/13/2018
  • Est. Priority Date: 09/10/2014
  • Status: Active Grant
First Claim
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1. A capacitive occupancy or proximity detector, comprising:

  • a heating circuit including a heating element, a heating current source and a common mode choke having a first and a second winding, said heating element being connectable to said heating current source via said first and second windings of said common mode choke;

    an impedance measurement circuit connected to said heating element for measuring impedance between said heating element and a node at ground potential; and

    a diagnostic circuit configured for determining integrity of said heater element,wherein said diagnostic circuit comprises;

    at least one first controllable switching element having a first terminal connected to said second winding of said common mode choke, and a second terminal connected to ground potential, such that said at least one first controllable switching element is coupled across said second winding of said common mode choke;

    means for injecting a DC current into a series connection formed by said first winding of said common mode choke, said heating element and a parallel connection of said second winding of said common mode choke and said at least one first controllable switching element, wherein the injected DC current flows through said first winding, through said heating element, and divides at the parallel connection such that part of the injected DC current flows through said second winding, and another part of the injected DC current flows through said at least one first controllable switching element; and

    at least one detection circuit for detecting a voltage variation across said second winding of said common mode choke, said voltage variation being induced upon opening said first controllable switching element.

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