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Fluid level sensor having capacitive sensor

  • US 5,182,545 A
  • Filed: 04/24/1991
  • Issued: 01/26/1993
  • Est. Priority Date: 01/06/1989
  • Status: Expired due to Fees
First Claim
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1. A fluid level detector for detecting the level of a liquid contained within a receptacle having an electrically conductive portion, comprising:

  • a probe mounted in said receptacle and electrically insulated from said receptacle, said probe acting as a first plate of a capacitor and being cooperative with said electrically conductive portion of said receptacle acting as a second plate of said capacitor, the liquid in the receptacle acting as a dielectric between said first plate and said second plate of said capacitor to produce a sensor capacitor having a capacitance which varies in magnitude in accordance with the level of liquid contained within the receptacle;

    detecting circuitry coupled to said probe and responsive to a difference between a voltage decay signal derived from said sensor capacitor and a reference voltage decay signal derived from a reference capacitor to provide an output signal when a predetermined voltage difference is detected therebetween; and

    indicating means coupled to said detection circuitry and responsive to said predetermined voltage difference as detected by said detection circuitry to provide an indication of the level of liquid contained within the receptacle.

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