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Person detecting device

  • US 4,887,024 A
  • Filed: 10/27/1988
  • Issued: 12/12/1989
  • Est. Priority Date: 10/27/1987
  • Status: Expired due to Term
First Claim
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1. A person detecting device for detecting the presence and absence of a person comprising:

  • sensing means for sensing capacitance between at least a pair of electrodes facing to each other with a space, said capacitance varying depending upon the presence and absence of the person in said space;

    oscillating means for providing a first pulse signal;

    delay means for delaying said first pulse signal and providing a second pulse signal delayed in response to said capacitance of said sensing means;

    duty ratio converting means for receiving said first and second pulse signal and providing a third pulse signal of a duty ration determined in response to said capacitance to convert said third pulse signal to a value representing said duty ratio;

    comparing means for comparing said value representing said duty ratio with at least a reference value preset for judging as to the presence and absence of the person to provide a resultant signal of comparison; and

    output means for receiving said resultant signal of said comparing means and judging as to the presence and absence of the person to output a signal of the result of judgement;

    wherein said oscillating means includes means for generating a clock pulse signal at a predetermined frequency and means for dividing said clock pulse signal into a plurality of divided pulse signals of different frequencies and providing one of said divided pulse signals as said first pulse signal, and wherein said duty ratio converting means includes means for converting said third pulse signal to a digital value corresponding to said duty ratio based on said clock pulse signal.

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