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Capacitive liquid level sensor having phase detecting circuitry

  • US 5,437,184 A
  • Filed: 10/27/1993
  • Issued: 08/01/1995
  • Est. Priority Date: 10/27/1993
  • Status: Expired due to Fees
First Claim
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1. A liquid level sensor having a capacitive sensor array, wherein said capacitive sensor array is adapted to be disposed in a fluid reservoir along an axis of measurement of fluid contained within said reservoir, and wherein said capacitive sensor array includes a plurality of discrete capacitive input elements and a plurality of discrete capacitive output elements positioned along a length of said array along said axis of measurement, said elements further being positioned such that each one of said input elements overlaps portions of two adjacent ones of said output elements, said apparatus comprising:

  • means for applying an oscillating input signal to at least one said input element of said sensor array at a time, to thereby generate output signals from a corresponding pair of said output elements overlapping said one input element;

    at least one switch coupled to said output elements and to first and second phase detecting means for controllably coupling said output elements to said first and second phase detecting means;

    said first phase detecting means being responsive to an output signal from a first one of said corresponding pair of output elements for generating a first frequency signal indicative of one of the presence and absence of said fluid at said first one of said pair of output elements;

    said second phase detecting means being responsive to an output signal from a second one of said corresponding pair of capacitive output elements for generating a second frequency signal indicative of one of the presence or absence of said fluid at said second one of said pair of output elements;

    phase comparing means for comparing the phase of said first frequency signal with the phase of said second frequency signal and for generating a first output signal indicative of the presence of a phase difference between said first and second frequency signals and a second output signal indicative of no phase difference between said first and second frequency signals;

    said first output signal further indicating that said fluid is at least partially absent at one of said corresponding pair of output elements while fluid is present at the other one of said corresponding pair of output elements; and

    said second output signal further indicating that said fluid is present at both of said first and second capacitive elements.

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