Trielectrode capacitive pressure transducer

Claim 2

Apparatus for a capacitive transducer having first and second spaced-apart facing electrodes with a dielectric therebetween and a third electrode which partially shields said first electrode from said second electrode comprising: a transformer having first and second primary windings and a secondary winding; a reference capacitor; means for coupling said secondary primary winding of said transformer between said first primary winding and said reference capacitor, said first primary winding, said second primary winding and said reference capacitor each forming one leg of a bridge; means for inputing an a-c signal to said bridge; means for connecting said ends of said first primary winding to said second and third electrodes, respectively; means for connecting said first electrode to the end of said capacitor remote from said second primary winding; and means coupled to said inputing means and said secondary winding for measuring only the capacitive component of a-c current flowing between said first and second electrodes.

Claim 3

Apparatus as claimed in claim 1 including means for sensing the temperature of said electrodes; and means coupled to said sensing means for compensating said measuring means for the effects of said sensed temperature.

Claim 4

Apparatus comprising: first and second capacitor electrodes each having a sensing portion, said sensing portions being in spaced-apart facing relation with a dielectric material therebetween; an electrical insulator adjoining portions of both of said capacitor electrodes; a third electrode dividing said insulator into two parts; a transformer having first and second primary windings and a secondary winding; a reference capacitor; means for coupling said second primary winding in series between said first primary winding and said reference capacitor; an a-c voltage source connected across said second primary winding and said reference capacitor; means for connecting the ends of said first primary winding to said second and third capacitor electrodes, respectively; means for connecting said second primary winding and said reference capacitor between said first and second capacitor electrodes, respectively; and means coupled to said secondary winding for measuring only the capacitive current component flowing between said sensing portions.

Claim 5

Apparatus comprising: first and second capacitor electrodes each having a sensing portion, said sensing portions being in spaced-apart facing relation with a dielectric material therebetween; an electrical insulator adjoining portions of both of said capacitor electrodes; a third electrode dividing said insulator into two parts; a transformer having first and second primary windings and a secondary winding; a reference capacitor; means for coupling said second primary winding in series between said first primary winding and said reference capacitor; an a-c voltage source connected across said second primary winding and said reference capacitor; means for connecting the ends of said first primary winding to said second and third capacitor electrodes, respectively; means for connecting said second primary winding and said reference capacitor between said first and second capacitor electrodes, respectively; and means coupled to said secondary winding for measuring only the capacitive current component flowing between said sensing portions.

Claim 6

The apparatus of claim 3 wherein said two means for connecting comprise a triaxial cable, said inner conductor of said cable being connected to said second capacitor electrode, said middle cable conductor being connected to said third electrode, and said outer cable conductor being connected to said first capacitor electrode.

Claim 7

Apparatus as set forth in claim 3 further comprising: means for sensing the temperature of said capacitor electrodes; and means coupled to said sensing means for compensating said measuring means for the effects of said sensed temperature.

Claim 8

Apparatus as set forth in claim 3 further comprising: means for sensing the temperature of said capacitor electrodes; and means coupled to said sensing means for imposing a capacitance in shunt with said reference capacitor which capacitance is a function of said sensed temperature.

Claim 9

Apparatus as set forth in claim 3 wherein said measuring means comprises: an indicator; a phase-sensitive demodulator coupled between the output of said transformer secondary and said indicator; and means for supplying an a-c voltage to said phase-sensitive demodulator that has the same frequency as the voltage from said a-c voltage source and a phase relation that enables said demodulator to detect the capacitive current component through said sensing portions.

Claim 10

Apparatus comprising: first and second capacitor electrodes each having a sensing portion, said sensing portions being in spaced-apart facing relation with a dielectric material therebetween; an electrical insulator adjoining portions of both of said capacitor electrodes; a third electrode dividing said insulator into two parts; a transformer having first and second primary windings and a secondary winding; a reference capacitor; means for coupling said second primary winding in series between said first primary winding and said reference capacitor; an a-c voltage source connected across said second primary winding and said reference capacitor; means for connecting the ends of said first primary winding to said second and third capacitor electrodes, respectively; means for connecting said second primary winding and said reference capacitor between said first and second capacitor electrodes, respectively; a differential amplifier having first and second inputs and an output; a phase-sensitive demodulator having first and second inputs and an output; a phase shifter; an indicator; said first input of said demodulator being coupled to said transformer secondary, said phase shifter being coupled between said a-c voltage source and said second demodulator input, said demodulator output being coupled to said first input of said differential amplifier, said differential amplifier output being coupled to said indicator; means for generating a signal representative of the temperature of said capacitor electrodes; and means for coupling said signal to said second input of said differential amplifier.

Claim 11

Apparatus comprising: first and second capacitor electrodes each having a sensing portion, said sensing portions being in spaced-apart facing relation with a dielectric material therebetween; an electrical insulator adjoining portions of both of said capacitor electrodes; a third electrode dividing said insulator into two parts; a transformer having first and second primary windings and a secondary winding; a reference capacitor; means for coupling said second primary winding in series between said first primary winding and said reference capacitor; an a-c voltage source connected across said second primary winding and said reference capacitor; means for connecting the ends of said first primary winding to said second and third capacitor electrodes, respectively; means for connecting said second primary winding and said reference capacitor between said first and second capacitor electrodes, respectively; a differential amplifier having first and second inputs and an output; a phase-sensitive demodulator having first and second inputs and an output; a phase shifter; an indicator; said first input of said demodulator being coupled to said transformer secondary, said phase shifter being coupled between said a-c voltage source and said second demodulator input, said demodulator output being coupled to said first input of said differential amplifier, said differential amplifier output being coupled to said indicator; means for generating a signal representative of the temperature of said capacitor electrodes; and means for coupling said signal to said second input of said differential amplifier.