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Resonator sensors employing piezoelectric benders for fluid property sensing

  • US 6,044,694 A
  • Filed: 08/28/1996
  • Issued: 04/04/2000
  • Est. Priority Date: 08/28/1996
  • Status: Expired due to Fees
First Claim
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1. A method of monitoring liquid viscosity to maintain the level of a liquid contained in a vessel comprising the steps of:

  • (a) locating at least the vibrating portion of a piezoelectric bender in said vessel containing said liquid;

    (b) applying a stimulation voltage to said bender at an amplitude and frequency to cause the bender to resonate;

    (c) varying said stimulation voltage frequency as a function of said output voltage frequency to maintain said bender at resonance;

    (d) monitoring an output voltage from said bender, the amplitude of said output voltage varying as an inverse function of the liquid viscosity, whereby an increase in liquid viscosity produces a decrease in output voltage amplitude and vice-versa;

    (e) detecting when the output voltage amplitude signals a change in viscosity indicating that the bender is no longer in contact with said liquid; and

    (f) automatically replenishing the liquid in said vessel when the liquid is no longer in contact with said bender.

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