Capacitive pressure sensor
First Claim
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1. A capacitive pressure sensor comprising:
- a housing including a pair of spaced apart diaphragms matched in compliance to vibrate and deflect in substantial unison in response to vibratory and acceleration forces, respectively;
an outer pressure responsive one of said pair of diaphragms movably cooperating with said housing to bound a reference-pressure chamber within which is movably disposed the other of said pair of diaphragms;
said other diaphragm carrying a first pair of spaced apart planar electrodes confronting said one diaphragm and each of a certain geometric shape, and a first planar shield electrode having a portion circumscribing said first pair of electrodes and a cross bar portion interposing between said first pair of electrodes;
said one diaphragm carrying a second pair of spaced apart planar electrodes confronting said other diaphragm and said first pair of electrodes thereon and each of said certain geometric shape;
said first pair of electrodes and said second pair of electrodes being congruent to define a respective pair of variable capacitors each of substantially identical value and varying in capacitance value simultaneously in union as said one diaphragm moves in response to external fluid pressure, whereby said variable capacitors remain of substantially identical value in response to external fluid pressure acting on said sensor, and said capacitance values being substantially immune from said vibration and acceleration forces.
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Abstract
A dual capacitive pressure sensor includes matched variable capacitors which are immune to vibration and acceleration, but which respond equally to changes in external fluid pressure level. The structure of the sensor is configured to avoid calibration drift as the sensor ages, as well as to provide electrical shielding for the variable capacitors of the sensor.
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Citations
32 Claims
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1. A capacitive pressure sensor comprising:
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a housing including a pair of spaced apart diaphragms matched in compliance to vibrate and deflect in substantial unison in response to vibratory and acceleration forces, respectively;
an outer pressure responsive one of said pair of diaphragms movably cooperating with said housing to bound a reference-pressure chamber within which is movably disposed the other of said pair of diaphragms;said other diaphragm carrying a first pair of spaced apart planar electrodes confronting said one diaphragm and each of a certain geometric shape, and a first planar shield electrode having a portion circumscribing said first pair of electrodes and a cross bar portion interposing between said first pair of electrodes; said one diaphragm carrying a second pair of spaced apart planar electrodes confronting said other diaphragm and said first pair of electrodes thereon and each of said certain geometric shape; said first pair of electrodes and said second pair of electrodes being congruent to define a respective pair of variable capacitors each of substantially identical value and varying in capacitance value simultaneously in union as said one diaphragm moves in response to external fluid pressure, whereby said variable capacitors remain of substantially identical value in response to external fluid pressure acting on said sensor, and said capacitance values being substantially immune from said vibration and acceleration forces. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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17. A capacitive pressure sensor comprising a housing including a pair of spaced apart circular diaphragm members matched in compliance to vibrate and deflect in substantial unison in response to vibratory and acceleration forces effective thereon, an outer one of said pair of diaphragm members bounding a reference-pressure chamber within which is movably disposed the other of said pair of diaphragm members;
- and said one diaphragm member deflecting in response to fluid pressure differential thereacross to move relative said other diaphragm member, first surface metalization film means carried by said pair of diaphragm members on confronting surfaces thereof for defining a pair of matched variable capacitors varying in capacitance value equally in response to relative movement of said pair of diaphragm members and for defining a plane of bilateral symmetry for said sensor, and second surface metalization film means carried also by said pair of diaphragm members on oppositely disposed surfaces thereof for balancing surface metalization residual stresses on each of said pair of diaphragm members, said second surface metalization film means including a portion thereof carried upon said one diaphragm member externally of said sensor for electrically shielding said pair of capacitors.
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18. A capacitive pressure sensor comprising a housing defining a closed reference pressure chamber therewithin, a pair of yieldable shape retaining diaphragm members matching in weight and resilience to vibrate and deflect substantially equally in unison in response to vibratory and acceleration forces, respectively;
- one of said pair of diaphragm members cooperating with said housing to bound said reference-pressure chamber on one side thereof and having another opposite side thereof exposing to ambient pressure to movingly respond according to pressure differences thereacross, the other of said pair of diaphragm members being movably disposed within said reference pressure chamber in isolation from ambient pressure, and means carried by said pair of diaphragm members for defining a pair of variable capacitors matching in capacitance value and changing capacitance value in unison equally in response to differential movement of said pair of diaphragm members resulting from deflection of said one diaphragm member in response to said pressure differential thereacross, whereby said pair of variable capacitors are not changing in capacitance value in response to vibration or acceleration forces affecting the pair of diaphragms equally, said variable capacitor defining means including said pair of diaphragm members defining respective confronting circular shaped axially spaced apart surfaces thereon, a pair of laterally spaced apart metallic film coatings on each of said circular surfaces of said pair of diaphragm members, each individual metallic film coating being of circular segment shape confrontingly congruent and spaced from a matching respective metallic film coating on the other of said pair of diaphragm members, and a metallic film coating shield electrode carried upon said other diaphragm member and including an annular portion circumscribing said pair of film coatings thereon and a diametral cross bar portion interposing between said pair of laterally spaced apart film coatings on said other diaphragm member.
- View Dependent Claims (19, 20, 21, 22, 23)
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24. The method of providing a pair of variable capacitances of substantially equal value which vary in value in unison and substantially equally in accord with the level of a physical parameter to be measured and which do not substantially vary in response to vibratory and acceleration forces acting thereon, said method comprising the steps of:
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providing a pair of juxtaposed spaced apart yieldably shape-retaining diaphragm members matched in weight and resilience to vibrate and deflect substantially in unison in response to said vibratory and acceleration forces, respectively, to maintain a substantially constant spacing therebetween in response to said forces; exposing only one of said pair of diaphragm members to said physical parameter to deflect relative to the other of said diaphragm members to change said spacing therebetween predictably in accord with the level of said parameter; carrying a pair of variable capacitors on said pair of diaphragm members, defining said pair of variable capacitors by providing for each one an electrode carried by said one diaphragm member and a matching congruently confronting electrode carried by the other of said diaphragm members; configuring said matching congruently confronting electrodes of said pair of varible capacitors to have area equality, geometric similarity and bilateral symmetry with respect to said pair of diaphragm members such that said pair of variable capacitors are substantially matched, change substantially equally in response to variation of said physical parameter; and further including the steps of providing a shield electrode upon one of said pair of capacitors, and configuring said shield electrode to share said bilateral symmetry with said pair of variable capacitors. - View Dependent Claims (25, 26)
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27. A capacitive pressure sensor comprising a housing including a pair of spaced apart circular diaphragm members matched in compliance to vibrate and deflect in substantial unison in response to vibratory and acceleration forces effective thereon, an outer one of said pair of diaphragm members bounding a reference-pressure chamber within which is movably disposed the other of said pair of diaphragm members;
- and said one diaphragm member deflecting in response to fluid pressure differential thereacross to move relative said other diaphragm member, first surface metalization film means carried by said pair of diaphragm members on confronting surfaces thereof for defining a pair of matched variable capacitors varying in capacitance value equally in response to relative movement of said pair of diaphragm members and for defining a plane of bilateral symmetry for said sensor, and second surface metalization film means carried also by said pair of diaphragm members on oppositely disposed surfaces thereof for balancing surface metalization residual stresses on each of said pair of diaphragm members, said second surface metalization film means including a portion thereof carried upon said one diaphragm member externally of said sensor for electrically shielding said pair of capacitors, further including a surface film shield metalization carried by said other diaphragm member and electrically connecting with said shielding portion of said second surface metalization film means.
- View Dependent Claims (28, 29)
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30. Capacitive pressure sensor apparatus comprising:
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a chambered housing of substantially non-conductive shape-retaining material;
said housing including a comparatively thick and unyielding base portion, and a middle portion and top portion both of which are comparatively thinner and at least in part compliant, said housing portions being stacked and sealingly interbonded at outer regions thereof to cooperatively define a reference pressure chamber therewithin, a central region of each of said middle portion and top portion defining a respective diaphragm part, said diaphragm parts of said middle portion and top portion being spaced apart and matched in compliance to deflect and vibrate substantially in unison in response to acceleration and vibratory forces, respectively, acting upon said sensor apparatus;
said diaphragm part of said top portion being outwardly exposed to ambient pressure and inwardly bounding said reference pressure chamber and movingly responding to pressure differences therebetween to move relative to said other diaphragm part;
said diaphragm part of said middle portion spanning and being encompassed by said reference pressure chamber in isolation from ambient pressure;four separate areas of capacitive surface metallization disposed two upon each one of said diaphragm parts of said top portion and middle portion within said reference pressure chamber as confronting spaced apart pairs, said four areas of surface metalization being of substantially identical geometric shape and area to define a plane of bilateral symmetry in said sensor, and each pair of surface metalization areas defining one of a pair of variable capacitors of equal value varying simultaneously and equally in response to movement of said one diaphragm part as the latter movingly responds to varying ambient pressure; conductive means for individually connecting each of said four surface metalization areas externally of said sensor apparatus, said four separate metalization areas each being of circular segment shape or semi-circular, wherein the two surface metalization areas upon each of said diaphragm parts cooperatively define a substantially complete circular area, and each of said diaphragm parts also carrying a counter balancing area of surface metalization on the side thereof opposite to the two capacitive areas of surface metallization, each of said counter balancing areas of surface metalization being of similar area and shape to the combination of the two capacitive areas of surface metalization thereon. - View Dependent Claims (31, 32)
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Specification