Liquid capacitance pressure transducer technique

Claim 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.

Claim 12

A method for manufacturing a capacitive pressure sensor for measuring differential liquid pressure between a first liquid and a second liquid, comprising: applying conductive coatings to first and second insulating plates, at least one of which plates is a diaphragm, to form a reference and a variable capacitor when said plates are assembled; assembling said first and second insulating plates, at least one of which is a diaphragm by firing a peripheral path of glass frit to space said conductive coatings on said plates apart by about from 0.5 to 20 thousandths of an inch; evacuating the space between said plates and said conductive coatings; providing a conduit extending to the space between said plates; drawing a low viscosity dielectric liquid into the previously evacuated space between said plates, whereby the very limited space is completely filled with the dielectric liquid with no included air bubbles and with said dielectric liquid extending into said conduit; mounting a thin very flexible membrane or bellows in said conduit in contact with the low viscosity liquid; providing means for coupling said first liquid to the other side of said membrane or bellows; and providing means for coupling said second liquid to the outer side of said diaphragm; whereby the deflection of said diaghragm and the resultant capacitance change reflects the difference in pressure between the first and second liquids.

Claim 13

A method for manufacturing a capacitive pressure sensor for measuring differential liquid pressure between a first liquid and a second liquid, comprising: applying conductive coatings to first and second insulating plates, at least one of which plates is a diaphragm, to form a reference and a variable capacitor when said plates are assembled; assembling said first and second insulating plates, at least one of which is a diaphragm by firing a peripheral path of glass frit to space said conductive coatings on said plates apart by about from 0.5 to 20 thousandths of an inch; evacuating the space between said plates and said conductive coatings; providing a conduit extending to the space between said plates; drawing a low viscosity dielectric liquid into the previously evacuated space between said plates, whereby the very limited space is completely filled with the dielectric liquid with no included air bubbles and with said dielectric liquid extending into said conduit; mounting a thin very flexible membrane or bellows in said conduit in contact with the low viscosity liquid; providing means for coupling said first liquid to the other side of said membrane or bellows; and providing means for coupling said second liquid to the outer side of said diaphragm; whereby the deflection of said diaghragm and the resultant capacitance change reflects the difference in pressure between the first and second liquids.