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Capacitance measuring circuit and method for liquid leak detection by measuring charging time

  • US 5,159,276 A
  • Filed: 07/08/1991
  • Issued: 10/27/1992
  • Est. Priority Date: 07/08/1991
  • Status: Expired due to Fees
First Claim
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1. A capacitance measuring circuit for use with a leak detection cable, said circuit comprising:

  • (a) inverter means for receiving a DC input voltage and for inverting said DC input voltage to produce a mirror-image inverter DC voltage;

    (b) current source means for receiving a DC voltage (VX) and for producing a constant current (IC) proportional to said DC voltage (VX), said constant current (IC) being defined by the equation IC =-k·

    VX, where k is equal to a predetermined constant, and where VX is equal to one of said DC input voltage and said mirror-image inverted DC voltage;

    (c) means for supplying said constant current (IC) to the leak detection cable such that the leak detection cable is charged from a first potential to a second potential;

    (d) comparator means for comparing said second potential to the other one of said DC input voltage and said mirror-image inverted DC voltage and for producing a match signal when a predetermined relationship exists therebetween; and

    (e) timer means responsive to said match signal for measuring a time required for the leak detection cable to be charged from said first potential to said second potential.

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