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Abstract

A capacitive type pressure sensing transducer comprised of two dielectric elements bearing four like plates or discs of conducting material and two like conductive pressure sensitive diaphragms which together form two like plate type capacitors of fixed capacitance value and two like plate type capacitors of variable capacitance value. The pressure sensitive diaphragms span like recessed areas in one face of one of the dielectric elements to form two like pressure chambers. The four conducting discs are positioned as matching pairs of capacitive plates on each side of the other dielectric element and together form the two fixed value capacitors. The pressure sensitive diaphragms and one of the conducting disc pairs are aligned to form the two variable value capacitors with their capacitance value depending upon the variable spacing distance of the diaphragms from the aligned discs in response to pressure applied to the diaphragms. The pair of variable value capacitors and pair of fixed value capacitors comprise all of the capacitance elements of a Wheatstone bridge circuit in a single transducer unit in which such capacitive elements are all subjected to the same temperature and pressure environment and are not sensitive to stray capacitances. A source of alternating current is applied across a first set of bridge terminals and a current detection circuit is connected across a second set of bridge terminals and translates current value into a value of pressure applied to the transducer.

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