Solid dielectric capacitance gauge for measuring fluid pressure having temperature compensation and guard electrode

Claim 1

A method of measuring pressures up to 35,000 p.s.i. in a fluid comprising the following steps: a. disposing a crystal of calcium fluoride entirely in said fluid; b. mounting a first electrode on a first side of said crystal in intimate physical engagement therewith; c. mounting a second electrode on said first side of said crystal in intimate physical engagement therewith, surrounding said first electrode and insulated electrically therefrom to comprise a guard ring; d. mounting a third electrode on a second side of said crystal opposite to said first side and in intimate physical engagement with said second side, the combination of said first, second, and third electrodes and said crystal constituting a guard-ring capacitor; e. maintaining the temperature of said crystal at a relatively constant value; f. measuring the capacitances between said first and third and said second and third electrodes at said maintained temperature; and g. subtracting measured capacitances to determine the capacitance between said first and third electrodes, which capacitance is a measure of the dielectric constant and hence Of the pressure in said fluid.

Claim 2

A method of measuring pressures up to 35,000 p.s.i. in a fluid comprising the following steps: a. disposing a crystal of calcium fluoride entirely in said fluid; b. mounting a first electrode on a first side of said crystal in intimate physical engagement therewith; c. mounting a second electrode on said first side of said crystal in intimate physical engagement therewith, surrounding said first electrode and insulated electrically therefrom to comprise a guard ring; d. mounting a third electrode on a second side of said crystal opposite to said first side and in intimate physical engagement with said second side, the combination of said first, second, and third electrodes and said crystal constituting a guard-ring capacitor; e. maintaining the temperature of said crystal at a relatively constant value; f. measuring the capacitances between said first and third and said second and third electrodes at said maintained temperature; and g. subtracting measured capacitances to determine the capacitance between said first and third electrodes, which capacitance is a measure of the dielectric constant and hence Of the pressure in said fluid.

Claim 3

An apparatus for measuring pressure in a fluid comprising: a solid dielectric material disposed entirely in said fluid and subject to the pressure thereof; a first electrode mounted on one side of said solid dielectric material in intimate physical engagement therewith; a second electrode mounted on the side of said solid dielectric material opposite to said first electrode in intimate physical engagement with said solid dielectric material; guard electrode means cooperatively disposed to inhibit fringing electric fields between said first and second electrodes; and three-terminal-capacitance-measuring means connected electrically to said first and second electrodes and to said guard electrode means for measuring the capacitance between said first and second electrodes, which capacitance is a measure of the dielectric constant of said solid dielectric material and hence the pressure of said fluid.

Claim 4

An apparatus for measuring pressure in a fluid comprising: a solid dielectric material disposed entirely in said fluid and subject to the pressure thereof; a first electrode mounted on one side of said solid dielectric material in intimate physical engagement therewith; a second electrode mounted on the side of said solid dielectric material opposite to said first electrode in intimate physical engagement with said solid dielectric material; guard electrode means cooperatively disposed to inhibit fringing electric fields between said first and second electrodes; and three-terminal-capacitance-measuring means connected electrically to said first and second electrodes and to said guard electrode means for measuring the capacitance between said first and second electrodes, which capacitance is a measure of the dielectric constant of said solid dielectric material and hence the pressure of said fluid.