CAPACITIVE PRESSURE TRANSDUCER

• US 3,808,480 A
• Filed: 04/16/1973
• Issued: 04/30/1974
• Est. Priority Date: 04/16/1973
• Status: Expired due to Term

• Current Assignee: Samuel Andrew Johnston
• Original Assignee: Samuel Andrew Johnston
• Inventors: Johnston, Samuel Andrew
• Primary Examiner(s): Goldberg, E. A.
• Application Number:
  US05/351,664
• Time in Patent Office: 379 Days
• Field of Search: 317/256,246 73/398C
• US Class Current: 361/283.4
• CPC Class Codes: C01B 17/60 Isolation of sulfur dioxide from gases
• CPC Class Codes: G01L 19/14 Housings G01L19/0007, G01L19/0084, G01L19/0092, G01L19/04, G01L19/06 take precedence
• CPC Class Codes: G01L 9/0072 using variations in capacitance
• CPC Class Codes: G01L 9/0086 using variations in capacitance
• CPC Class Codes: G01L 9/12 by making use of variations in capacitance , i.e. electric circuits therefor

Abstract

Pressure responsive diaphragms, in their movement with respect to fixed plates, constitute variable capacitors. Dual diaphragms, on opposite sides of a substrate carrying the corresponding fixed plates, eliminate flexure of the substrate as a factor in the performance of the device. An electrical circuit for converting the varying capacitance to a correspondingly varying electrical signal is housed in the space between the diaphragms. The pressure transducer so formed is contained in a casing which communicates by tubing to any desired source of pressure; such pressure in the interior of the casing is imposed on the transducer. Terminals for external electrical connections are formed by screws which hold the casing members together, and which are electrically continuous with internal conductors.

Claims

1. A variable capacitance pressure responsive device comprising a thin, flat, plate-like electrically nonconductive substrate having a supporting surface, a first electrode comprising a first electrically conductive film affixed to a portion of said supporting surface a second electrode comprising a second electrically conductive film hermetically affixed to said supporting surface and surrounding the periphery of but spaced apart and electrically isolated from said first electrode a thin flexible electrically conductive diaphragm hermetically sealed to and in electrical contact with said second film, said diaphragm being spaced from said first electrode, said first electrode and said diaphragm forming the plates of a capacitor, and means for providing a difference of pressure on opposite sides of said diaphragm.

2. A pressure responsive capsule comprising a plate-like substrate of electrically non-conductive material, electrodes laminated to opposite faces of said substrate, and a pair of electrically conductive diaphragms attached to opposite faces of said substrate, each enclosing at least one of said Electrodes, but electrically insulated therefrom.

3. A pressure responsive capsule in accordance with claim 2, wherein a passage through said substrate is provided, permitting equalization of pressure between the spaces on opposite sides of said substrate enclosed by said diaphragms.

4. A pressure responsive capsule in accordance with claim 2, further including a lead extending from at least one of said electrodes to a point external to said diaphragms.

5. A pressure responsive capsule in accordance with claim 2, wherein the spaces enclosed by said diaphragms are evacuated and sealed.

6. A pressure transducer system including a plate-like substrate of electrically non-conductive material, electrodes attached to opposite faces of said substrate, a pair of electrically conductive diaphragms attached to opposite faces of said substrate, each enclosing at least one of said electrodes but insulated therefrom, the spaces enclosed by said diaphragms being at least partially evacuated and sealed, and said substrate having a passage therethrough communicating between said spaces and permitting equalization of pressure between said spaces, and an electrical circuit housed in said at least partially evacuated space, said circuit having input terminals connected to at least one of said electrodes and to at least one of said diaphragms, and being adapted to produce an output signal having a frequency varying in accordance with the capacitance presented to said input terminals.

7. A pressure transducer system including a plate-like substrate of electrically non-conductive material, electrodes attached to opposite faces of said substrate, a pair of electrically conductive diaphragms attached to opposite faces of said substrate, each enclosing at least one of said electrodes but insulated therefrom, the spaces enclosed by said diaphragms being at least partially evacuated and sealed, and said substrate having a passage therethrough communicating between said spaces and permitting equalization of pressure between said spaces, a closed casing surrounding said substrate and said diaphragms, said casing having means whereby its interior may be connected to a source of pressure to be sensed, and an electrical circuit housed in said at least partially evacuated space, said circuit having input terminals connected to at least one of said electrodes and to at least one of said diaphragms, and having output terminals, said circuit being adapted to produce a signal at said output terminals having a frequency varying in accordance with the capacitance presented to said input terminals.

8. A pressure transducer in accordance with claim 7, wherein said casing comprises parts which are maintained in assembled relation by a plurality of electrically conductive fasteners passing through said parts, at least one of said fasteners being then in electrical contact with one of said output terminals.

9. A pressure transducer comprising a platelike, electrically non-conductive substrate, a fixed electrode laminated to said substrate, a flexible, electrically conductive diaphragm enclosing said fixed electrode, but electrically insulated therefrom, and sealed to said substrate, the space between said diaphragm and said substrate being at least partially evacuated, a variable frequency oscillator mounted on said substrate in the space between said diaphragm and said substrate, said electrode and said diaphragm being connected to the input of said oscillator, whereby a change in capacitance between said electrode and said diaphragm varies the output frequency of said oscillator.

10. A pressure transducer system including a plate-like substrate of electrically non-conductive material, an electrode of circular outline attached to one face of said substrate, an annular electrode attached to the same face of said substrate, surrounding and spaced from said circular electrode, an electrically conDuctive diaphragm hermetically sealed to said annular electrode and spaced from said circular electrode, the space between said diaphragm and said circular electrode being at least partially evacuated and sealed, said substrate having a recess formed therein, in the space between said electrodes, and an integrated electronic circuit device located in said recess, said device having input terminals connected to said electrodes, and having output terminals, and hermetically sealed conductors from said output terminals to points on said substrate outside of said diaphragm.

11. A pressure transducer system comprising a plate-like substrate of electrically non-conductive material, a first electrical conductor constituting a fixed capacitor plate carried on said substrate, an electrically conductive flexible diaphragm hermetically sealed to said substrate and constituting a variable capacitor plate, an electronic circuit carried on said substrate, and having input and output terminals, said first electrical conductor and said diaphragm being connected to said input terminals, an outer enclosure for said substrate and said diaphragm whereby the outside of said diaphragm is subjected to the pressure of whatever fluid may be contained in said enclosure, said enclosure comprising parts which are maintained in assembled relation by a plurality of electrically conductive fasteners passing through said parts and through said substrate, at least one of said fasteners being in electrical contact with one of said output terminals.

12. A pressure transducer comprising in combination a plate-like ceramic substrate carrying on each face a conductor constituting a fixed capacitor plate, and a flexible diaphragm hermetically sealed to the substrate and constituting a movable capacitor plate, an electrical circuit having input terminals and output terminals and including an integrated circuit device, said substrate being comprised of at least two coterminous laminae, one of said laminae having said integrated circuit device carried thereon, the other of said laminae having an aperture therein providing a clearance space around said device, and one of said laminae carrying conductors in the interface between said laminae, said conductors providing connections to and from said device, and including conductors from said fixed and movable capacitor plates to said input terminals.

13. A variable capacitance pressure transducer comprising:

a. a support member having an electrically non-conductive gas impervious surface upon which a first and second electrode are supported;

b. said second electrode surrounding the periphery of and spaced apart from said first electrode and hermetically sealed to said surface;

c. a thin flexible electrically conductive diaphragm, impermeable to gas, electrically and hermetically attached to said second electrode and spaced apart therefrom, the surface of said support member and said diaphragm forming a hermetically closed chamber for maintaining a predetermined gas pressure; and

d. an electrically conductive path extending from said first electrode, under said diaphragm and electrically insulated therefrom and from said second electrode, to a position on said support member beyond the outer extremity of said second electrode and said diaphragm, whereby ambient pressure acting upon the surface of said flexible diaphragm can be monitored by sensing the electrical capacitance between said electrically conductive path and said diaphragm.

14. Apparatus according to claim 13 wherein said path is insulated from said diaphragm and said second electrode by a dielectric material interposed between said path and an area under the outer extremity of said diaphragm path.

15. An apparatus according to claim 14 wherein the electrically capacitance between that portion of the electrical path which is in close juxtaposition to said diaphragm is relativeLy small compared to the electrical capacitance between said disphragm and said first electrode.

16. A variable capacitance pressure transducer comprising:

a. a support member having an electrically non-conductive gas impervious surface upon which an electrode is supported;

b. a thin flexible electrically conductive diaphragm impermeable to gas hermetically attached to said surface and spaced apart from said electrode, the surface of said support member and said diaphragm forming a hermetically closed chamber for maintaining a predetermined gas pressure; and

c. an electrically conductive path extending from said electrode under said diaphragm and electrically insulated therefrom to a position on said support member beyond the outer extremity of said diaphragm, whereby ambient pressure acting upon the surface of said flexible diaphragm can be monitored by sensing the electrical capacitance between said electrically conductive path and said diaphragm.

17. An apparatus according to claim 16 wherein the electrical capacitance between that portion of the electrical path which is under and in close juxtaposition to said diaphragm is relatively small compared to the electrical capacitance between said diaphragm and said electrode.

18. A variable capacitance pressure transducer comprising:

a. a laminated support member having two opposing electrically non-conductive gas impervious surfaces upon which a first and a second electrode are respectively supported in spaced apart opposing relationship to one another;

b. first and a second thin flexible electrically conductive diaphragms impermeable to gas, each respectively hermetically attached to a different one of said surfaces and spaced apart from one of said electrodes, the surfaces of said support member and said diaphragms forming two hermetically closed chambers each maintaining a predetermined gas pressure; and

c. electrically conductive paths extending from each electrode under its respective diaphragm and electrically insulated therefrom to a position on said support member beyond the outer extremity of said diaphragm, whereby ambient pressure acting upon the surface of said flexible diaphragm can be monitored by sensing the electrical capacitance between said electrically conductive paths and said diaphragms.