Low cost, center-mounted capacitive pressure sensor
First Claim
1. A sensor for a variable capacitance type transducer that transforms the pressure of a fluid into a corresponding capacitance value, comprising:
- a pressure fitting with a passage extending axially to direct the fluid from a first end to a second end,a diaphragm secured at its peripheral edges to said fitting at said second end in a first joint,an assembly comprising a first metallic post secured at one of its ends to the center of said diaphragm, a metallic collar in a spaced relationship with and at least in part lying radially outside of said post, and an inorganic dielectric spacing ring secured between said post and said collar,means for securing said post to the center of said diaphragm at a second butt joint,an electrode, andan adherent filler that secures said electrode to said collar without said filler contacting said diaphragm to establish a generally parallel spaced relationship between said electrode and said diaphragm to form a variable capacitor whereby changes in the electrode-to-diaphragm gap produced by a flexure of said diaphragm in response to the fluid pressure spacing provide a capacitive measure of the fluid pressure.
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Accused Products
Abstract
A variable capacitance type pressure sensor with excellent manufacturability center-mounts an electrode on an edge-mounted diaphragm using a metal-glass-metal subassembly. An inner metal post of the assembly is welded to the diaphragm. A solder or flowable cement secures the electrode to an outer metal collar of the assembly with the initial diaphragm-to-electrode spacing set by a temporary shim. The position of the glass and the physical lengths of the metallic members of the assembly are adjusted to provide self-compensation for temperature variations. In a preferred form for low and medium pressure applications, the diaphragm is stamped from sheet metal with a central dimple that resists rotation of the attached assembly and isolates diaphragm deformation stresses from the post-to-diaphragm weld. In a high pressure form, a machined central boss isolates this weld from stress. A fitting that edge-mounts the diaphragm has a thinned end wall, or the diaphragm has a thin-walled skirt, to relieve stress on the diaphragm-to-fitting joint.
98 Citations
23 Claims
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1. A sensor for a variable capacitance type transducer that transforms the pressure of a fluid into a corresponding capacitance value, comprising:
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a pressure fitting with a passage extending axially to direct the fluid from a first end to a second end, a diaphragm secured at its peripheral edges to said fitting at said second end in a first joint, an assembly comprising a first metallic post secured at one of its ends to the center of said diaphragm, a metallic collar in a spaced relationship with and at least in part lying radially outside of said post, and an inorganic dielectric spacing ring secured between said post and said collar, means for securing said post to the center of said diaphragm at a second butt joint, an electrode, and an adherent filler that secures said electrode to said collar without said filler contacting said diaphragm to establish a generally parallel spaced relationship between said electrode and said diaphragm to form a variable capacitor whereby changes in the electrode-to-diaphragm gap produced by a flexure of said diaphragm in response to the fluid pressure spacing provide a capacitive measure of the fluid pressure. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A sensor for measuring the pressure of a fluid capacitively, comprising,
a generally tubular fitting extending along a first axis from a first end in fluid communication with the vessel to a second end, a diaphragm edge-mounted to said second end at a first joint and deformable along a first axis normal to the diaphragm in response to the fluid pressure, an electrode, a mounting assembly for supporting said electrode over said diaphragm in a spaced relationship to define a generally annular capacitive gap between said diaphragm and said electrode while electrically insulating said electrode from said diaphragm, said mounting assembly having a central post secured at one generally flat end to the center of said diaphragm and extending along said first axis, a metallic collar surrounding said post in a spaced relationship and also spaced axially from said diaphragm, and an inorganic dielectric ring secured between said post and said collar, a nib projecting from said generally flat post end that is welded to secure said central post end to said diaphragm center at a generally flat, rigid joint, and an annular filler that rigidly secures said electrode to said collar, said filler being spaced from said diaphragm.
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20. A process for measuring fluid pressure with a variable capacitor formed by a diaphragm edge-mounted on a fitting at a first joint and an electrode spaced closely from the diaphragm, comprising
directing the fluid to act on one side of the diaphragm and deform it in response to the pressure, supporting the electrode from the center of the diaphragm with a gap of predetermined spacing therebetween so that movement of the diaphragm produces a corresponding movement of the electrode said supporting including providing a mutually concentric metallic post and collar, isolating the diaphragm and the electrode electrically with an inorganic dielectric material bridging said post and collar, securing said post to the diaphragm at a second butt joint, cementing said electrode to said second metal member with a an annular filler of a flowable adhesive that is spaced from said diaphragm, flowable adhesive, and rigidifying said diaphragm to isolate stress in said diaphragm from said second joint.
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23. A process for capacitively measuring the pressure of a fluid via a fitting with a variable capacitor formed by a diaphragm and an electrode, comprising the steps of
converting a fluid pressure change into a corresponding mechanical movement along a first axis by applying the fluid to one side of the diaphragm edge-mounted on the fitting and thereby flexing the diaphragm, supporting the electrode on a generally flat surface of the diaphragm at the center of the diaphragm opposite the fitting with a pre-assembled metal-post inorganic dielectric material-metal collar mounting assembly, isolating stress in said diaphragm produced by said flexing from said center mounting by enhancing the rigidity of said diaphragm at its center, electrically isolating the diaphragm from the electrode with the inorganic dielectric material in said mounting assembly, and cementing the electrode to the collar of said mounting assembly with an annular ring of a filler cement that is spaced from the diaphragm.
Specification