Capacitive pressure transducer with isolated sensing diaphragm

An improved capacitive pressure transducer having a transducer housing,

• a sensor housing disposed in the transducer housing and having a central cavity,
• diaphragm means supported on said sensor housing and extending across the central cavity to thereby divide the central cavity into two central chambers, said diaphragm means being deflectable under pressure and at least a portion thereof being conductive to provide a first plate of a variable sensor capacitor,
• each of said chambers having a conductive surface portion spaced from the diaphragm for providing second plates of a pair of variable sensor capacitors,
• a pair of isolators, said isolators each having an isolator chamber and an isolator diaphragm disposed therein,
• separate passageway means coupling each isolator chamber to a separate central chamber,
• means to permit applying separate pressures to the respective isolator diaphragms at a static line pressure, each isolator chamber, its associated passageway means and connected central chamber enclosing a substantially incompressible fluid such that the diaphragm means is urged to deflect and change the capacitance of the variable sensor capacitors responsive to the differential between the static line pressure applied to the isolator diaphragms,
• means for physically supporting the isolators in a position spaced from the sensor housing,
• the sensor housing being constructed and clamping the diaphragm means so that the diaphragm means is stressed at different amounts when the static line pressure changes to substantially compensate the capacitance output as the sensor housing warps under changes in static line pressure with the same differential pressure.

In a capacitive pressure transducer having a housing with an internal cavity, a deflectable, electrically conducting sensing diaphragm mounted on the transducer and dividing the cavity into first and second cavity sections, said transducer having a central axis lying generally normal to said diaphragm, a filling of insulation material in each of said cavity sections, said insulation material having recessed surfaces adjacent the diaphragm on opposite sides thereof to form chambers permitting deflection of said diaphragm under loads toward the respective recessed surface, means on the respective recessed surfaces forming capacitor plates which in combination with the diaphragm form first and second sensing capacitors generally symmetrical with each other relative to the diaphragm at a rest position and having capacitance values of C.sub.1 and C.sub.2, respectively, means to provide pressure to opposite sides of said diaphragm tending to deflect said diaphragm when pressures on opposite sides are different from each other to thereby lower the capacitance value of one of the sensing capacitors and raise the value of the other sensing capacitor, the reference position of the diaphragm being reached when the pressure on opposite sides of the diaphragm is equal, the improvement comprising selecting the dimensions and the coefficients of elasticity of the diaphragm, the insulation material and the housing in relation to the diaphragm diameter to insure that the product of diaphragm stretch times the capacitance spacing at rest position of the diaphragm remains substantially equal to a constant under changing pressures of equal magnitudes on opposite sides of said diaphragm.

An improved capacitive pressure transducer having a transducer housing,

• a sensor housing disposed in and electrically isolated from the transducer housing,
• diaphragm means, deflectable under pressure, at least a portion of which is conductive, supported on the sensor housing for providing a first plate of a variable sensor capacitor,
• at least one cavity in the sensor housing, said cavity having a conductive surface portion for providing a second plate of a variable sensor capacitor and for providing in combination with the diaphragm means a central chamber,
• at least one isolator, said isolator having an isolator chamber and an isolator diaphragm disposed therein,
• passageway means coupling said isolator chamber to the central chamber, and the isolator chamber, and said passageway means and connected central chamber enclosing a substantially incompressible fluid such that the diaphragm means is urged to deflect and change the capacitance of the variable sensor capacitor responsive to the pressure applied to the isolator diaphragm, and
• means for physically supporting the isolator in a position spaced from the sensor housing, including means to electrically isolate the isolator from the sensor housing.