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Shielded capacitive load cell apparatus responsive to weight applied to a vehicle seat

  • US 7,119,705 B2
  • Filed: 10/30/2004
  • Issued: 10/10/2006
  • Est. Priority Date: 10/30/2004
  • Status: Active Grant
First Claim
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1. Apparatus for measuring a weight applied to a seating surface of a vehicle seat, comprising:

  • a load cell disposed in said seat including first and second conductive plates separated by a compressible insulator;

    a conductive shield disposed between said seating surface and said load cell; and

    circuitry coupled to said load cell and said conductive shield, including means for maintaining said shield at a reference voltage, an operational amplifier having a first input coupled to said first conductive plate and an output coupled to said second conductive plate, current supply elements for supplying a constant current to said load cell, and means for determining a capacitance of said load cell based on a rate of change in voltage at the output of said operational amplifier, said capacitance providing an indication of the weight applied to said seating surface.

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