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Heating element operated as capacitive sensing electrode

  • US 9,656,575 B2
  • Filed: 02/21/2012
  • Issued: 05/23/2017
  • Est. Priority Date: 02/21/2011
  • Status: Active Grant
First Claim
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1. A combined seat heater and capacitive occupancy sensor, comprisinga heater network including a heating element connected between a first node and a second node to dissipate heat when a heating current is caused to flow between said first and second nodes,a capacitive sensing circuit connected to said heating element to sense a capacitive load of said heating element;

  • wherein said heater network comprises a first interface for connecting said first node to a first terminal of a power source and a second interface for connecting said second node to a second terminal of said power source,wherein said first interface comprises a first electronically controlled switch and a second electronically controlled switch arranged in series so as to define a first intermediate node there between;

    wherein said second interface comprises a third electronically controlled switch and a fourth electronically controlled switch arranged in series so as to define a second intermediate node there between;

    wherein said capacitive sensing circuit comprisesan oscillator that is AC-coupled to said first and second nodes through said first and second intermediate nodes to apply an oscillating voltage to said first and second nodes; and

    current measuring means AC-coupled between said oscillator and said heating element configured to keep the AC-potential of said heating element equal, or at least substantially equal, in amplitude and phase, to said oscillating voltage and to derive said capacitive load from a current flowing into said heating element in response to said AC-potential of said heating element being kept equal, or at least substantially equal, in amplitude and phase, to said oscillating voltage.

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