Capacitive pressure transducer

A capacitive type pressure sensing transducer assembly comprising:

• (a) a transducer housing with walls defining a fluid chamber and incompressible fluid within and filling said chamber;
• (b) a pressure sensitive element spanning a port in one wall of said housing, said element interfacing with an applied pressure force to be sensed and measured and being deflectable in response to said pressure force to vary the volume of the fluid chamber of said transducer housing;
• (c) four electrically conductive capacitor elements each formed to present two electrically conductive capacitive plates;
• (d) means for mounting said capacitor elements in fixed spaced relationship from one another and for positioning said elements so that each capacitive plate thereof defines with a capacitive plate of the next adjacent capacitor element a dielectric space therebetween whereby said mounted capacitor elements with their respective plates together form a sensor having four plate type capacitors;
• (e) dielectric material within the dielectric spaces of a first pair of the capacitors of said sensor whereby said pair of capacitors have like fixed electrical capacitive value;
• (f) means connecting the dielectric spaces of a second pair of the capacitors of said sensor in fluid flow communication with the fluid chamber of said housing so that fluid from said chamber is maintained as like variable height fluid columns of dielectric material within said spaces whereby the electrical capacitive value of said second pair of capacitors varies directly with the increasing or decreasing volume of said fluid chamber and corresponding decreasing or increasing height of said fluid columns in response to a pressure force applied to said pressure sensitive element;
• (g) means electrically connecting the first and second pairs of capacitors of said sensor together to form the four capacitive sides of a Wheatstone bridge circuit, the first pair of capacitors connected as two opposing sides of said bridge and the second pair of capacitors connected as the remaining two opposing sides of said bridge;
• (h) a source of alternating current of constant voltage and set frequency connected across said bridge circuit to a first set of terminals at opposite corners of the bridge, each of said terminals located between a capacitor of the first pair of capacitors and a capacitor of the second pair of capacitors of said sensor;
• and
• (i) a current detection circuit connected across the bridge to a second set of terminals independent of said first set of terminals and at opposite corners of the bridge, each of said second terminals located between a capacitor of the first pair of capacitors and a capacitor of the second pair of capacitors of said sensor, said detection circuit including current value measuring and current value indication circuitry for expressing in direct relationship said current value as a pressure force value.