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Liquid capacitance pressure transducer technique

  • US 4,425,799 A
  • Filed: 06/03/1982
  • Issued: 01/17/1984
  • Est. Priority Date: 06/03/1982
  • Status: Expired due to Term
First Claim
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1. A capacitive sensor for measuring differential pressure between a first and a second liquid comprising:

  • first and second flat insulating plates, at least one of said plates being a diaphragm;

    means for mounting said plates spaced apart from one another and sealed to one-another along a narrow zone spaced out from the center of said plates for facilitating free movement of said plates toward and away from one-another as the pressure across the diaphragm varies, the spacing between said plates being in the order of 0.5 to 20 thousandths of an inch,means including conductive coatings on the inner surfaces of the facing opposed portions of said plates for forming a variable capacitor located toward the center of said plates which changes substantially with changes in differential pressure, and a reference capacitor located outward from the center of said plates near said narrow zone, said reference capacitor only charging slightly with changes in capacitance;

    means for coupling and directing said first liquid to the outside of said diaphragm;

    a conduit containing a thin membrane or bellows; and

    a low viscosity dielectric fluid completely filling the space between said plates and said conductive coatings and filling said conduit up to and engaging said membrane or bellows;

    means for conducting and directing said second liquid to the other side of said bellows,whereby the changes in capacitance of said sensor directly indicate the pressure differential between said first and second liquid.

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