Capacitive pressure transducer

• US 4,562,742 A
• Filed: 05/24/1985
• Issued: 01/07/1986
• Est. Priority Date: 08/07/1984
• Status: Expired due to Fees

• Current Assignee: Bell Mold Components
• Original Assignee: Bell Mold Components
• Inventors: Bell, Robert L.
• Primary Examiner(s): WOODIEL, DONALD
• Application Number:
  US06/738,539
• Time in Patent Office: 228 Days
• Field of Search: 73/724, 73/718, 361/283
• US Class Current: 73/718
• CPC Class Codes: G01L 19/0636 using particle filters
• CPC Class Codes: G01L 9/0075 using a ceramic diaphragm, e.g. alumina, fused quartz, glass

Abstract

A capacitive pressure transducer is comprised of a deflectable diaphragm and a substantially planar reference plate, both preferably molded of ceramic. The diaphragm includes a sensor electrode ring disposed about a central region thereof and a concentric reference electrode ring substantially encompassing the sensor electrode, with a guard ring between the electrodes to electrically isolate the reference electrode from the sensor electrode. The reference plate is disposed in facing relation to the deformable flat surface of the diaphragm and includes a sensor electrode ring disposed and in opposition to the sensor electrode on the diaphragm to form a sensing capacitor therewith. Spacer means disposed in the central region between the diaphragm and the reference plate intercouple the two elements and maintain a substantially fixed dimension in the central region therebetween while permitting deformation of the diaphragm in response to pressure variations. The spacer means is conductive and facilitates electrical connection to the sensor electrode on the reference plate. A cover is disposed about the reference plate and coupled to the periphery of the diaphragm, and includes a reference electrode ring in facing relation to the reference electrode on the diaphragm to form a reference capacitor therewith.

Claims

1. A capacitive pressure transducer comprising:

a diaphragm comprising a flanged peripheral member having a central web deflectable in response to a pressurized fluid;

a cover coextensive with but spaced apart from the web and attached to the diaphragm at the flanged peripheral member;

first thin film means defining a reference electrode pair on the diaphragm outside the web and on the opposing portion of the cover;

reference plate means disposed between the diaphragm and cover and including spacer means for coupling the reference plate means to the web; and

second thin film means defining a variable electrode pair on the web and the opposing portion of the reference plate means.

2. The invention as set forth in claim 1 above, wherein the spacer means is substantially symmetrically positioned relative to the deflectable portion of the central web and the central web is substantially concentric about a central axis.

3. The invention as set forth in claim 2 above, wherein the spacer means is a single spacer centrally positioned on the central web and having a diameter of the order of 15% of the diameter of the deformable portion of the central web.

4. The invention as set forth in claim 2 above, wherein the spacer means comprises a number of spacers symmetrically spaced about the central axis within a region which has a diameter of the order of 25% of the diameter of deformable region of the central web and the spacers have an area of the order of 3% of the area of the reference plate means.

5. The invention as set forth in claim 4 above, wherein the reference plate means includes a thin web region encompassing the area engaged by the spacers and the spacer means further comprises a number of peripheral spacers between the diaphragm and the cover.

6. The invention as set forth in claim 1 above, wherein the diaphragm has a flat, electrode bearing, surface and is of ceramic material, wherein the spacing between the reference plate means and the diaphragm is of the order of one mil, and wherein the spacer means is conductive and the transducer further includes conductor means coupling the variable electrode element on the reference plate means to a region of the diaphragm via the spacer means.

7. The invention as set forth in claim 1 above, wherein the transducer is configured to deform the diaphragm in response to pressures from either or both sides, wherein the central web of the diaphragm is concentric about a central axis and wherein the electrodes are annuli substantially concentric with the central axis.

8. The invention as set forth in claim 1 above, wherein the first and second thin film means are both within parts of the region on the diaphragm that is coextensive with the flanged peripheral member of the diaphragm and wherein the transducer further comprises an electrically grounded guard band electrode on the diaphragm between the variable electrode and the reference electrode thereon.

9. In a pressure responsive capacitive transducer in which a reference plate bearing an electrode is mounted on the deformable portion of a diaphragm having a substantially coextensive electrode, the improvement comprising:

a conductive spacer centrally disposed on the deformable portion of the diaphragm and coupled to both the reference plate and the diaphragm, the spacer comprising a conductive element having a height of less than 2 mils and a width of less than about 25% of the diameter of the deformable portion of the diaphragm;

means providing an electrical signal conductor on the diaphragm; and

means coupling the electrode on the reference plate to the electrical signal conductor through the spacer.

10. The invention as set forth in claim 9 above, wherein the diaphragm includes an outer flange concentrically disposed about and integral with the deformable portion, and on the opposite side from the reference plate, the outer flange being substantially non-deforming in response to pressure, and wherein the electrode on the diaphragm is coextensive with a portion of the flange and not within the deformable portion such that deformation of the deformable portion results in movement of the reference plate electrode only.

11. The invention as set forth in claim 10 above, wherein the diaphragm has a substantially flat electrode bearing surface including a sensing capacitor electrode at an inner radius coextensive with a portion of the outer flange and a reference electrode at a greater radius thereabout and wherein the transducer further includes a cover encompassing the reference electrode and coupled to the flange region of the diaphragm outside the reference electrode, the cover including a reference surface spaced apart from the diaphragm by a predetermined distance, and reference electrode means thereon substantially coextensive with the reference electrode on the diaphragm.

12. The invention as set forth in claim 9 above, wherein the spacer is substantially centrally disposed on the deformable portion of the diaphragm such that stresses of deformation are minimized and absorbed within the spacer, wherein the electrodes are thin films, and wherein the electrode area on the diaphragm is greater than on the reference plate.

13. A capacitive pressure transducer comprising:

a diaphragm having a substantially flat deformable surface, the diaphragm including a sensor electrode disposed about a central region thereof, and a reference electrode substantially encompassing the sensor electrode;

means coupled to at least one side of the diaphragm for providing a fluid, whose pressure is to be measured into contact with the diaphragm to deform the same;

a substantially planar reference plate disposed in facing relation to the deformable surface of the diaphragm and including a sensor electrode disposed about the central region and in opposition to the sensor electrode on the diaphragm to form a sensing capacitor therewith;

spacer means disposed in the central region and between the diaphragm and the reference plate to maintain a substantially fixed dimension in the central region therebetween while permitting deformation of the diaphragm; and

cover means disposed about the reference plate and coupled to the periphery of the diaphragm and including a reference electrode in facing relation to the reference electrode on the diaphragm to form a reference capacitor therewith.

14. The invention as set forth in claim 13, wherein the spacer means is disposed in a region of convex curvature of the diaphragm when the diaphragm is deformed toward the reference plate.

15. The invention as set forth in claim 14 above, wherein the spacer means comprises a single centrally disposed conductive spacer pad.

16. The invention as set forth in claim 13 above, wherein the spacer means comprises a plurality of symmetrically placed pads and the reference plate has a thin central web in the region encompassing the pads.

17. The pressure transducer of claim 13, including an annular grounded guard electrode on the diaphragm between the sensor electrode from the reference electrode thereon to electrically isolate the same.

18. The pressure transducer of claim 13, wherein said sensor electrode on the diaphragm and said reference electrode on the diaphragm are each substantially in the form of an annulus concentric with the center, and said sensor electrode on the reference plate and said reference electrode on the cover are also substantially in the form of annuli.

19. The pressure transducer of claim 13, said diaphragm, reference plate and cover means are comprised of materials from the class including high density ceramic materials, quartz, silicon, silica and the like which are mechanically elastic but do not exhibit significant plasticity.

20. A capacitive pressure transducer comprising:

a diaphragm having a substantially flat deformable surface, the diaphragm including an annular sensor electrode disposed about a central deformable region thereof concentric with a central axis, an annular reference electrode, said electrodes each terminating in a conductive contact path to the exterior, an electrically grounded guard electrode and positioned between said sensor electrode and said reference electrode, said sensor electrode, said reference electrode, and said guard electrode being concentric about the central axis, and said diaphragm further including thin film conductive means in the central region of said diaphragm including a conductive path to the exterior of the transducer;

means communicating with at least one side of the diaphragm for introducing a fluid whose pressure is to be determined into contact with the diaphragm to deform same;

a substantially planar reference plate disposed in facing relation to the deformable surface of the diaphragm, said reference plate having an annular sensor electrode disposed about the central region and facing the sensor electrode on the diaphragm to form a sensing capacitor therewith, and thin film conductive means in the central region of said reference plate, including a conductive path to said sensor electrode on said reference plate;

conductive spacer means interconnecting the diaphragm and the reference plate in the central region thereof to maintain a substantially fixed dimension in the central region between the diaphragm and the reference plate while permitting deformation of the diaphragm, said spacer means interconnecting the thin film conductive means on said diaphragm with the thin film conductive means on the reference plate, whereby an electrical connection from the sensor electrode on the reference plate is taken through the spacer means; and

a cover disposed about the reference plate, said cover comprising a depending flange connected to the outer periphery of the diaphragm, and including an annular reference electrode in facing relation to the reference electrode on the diaphragm, to form a reference capacitor therebetween, said reference electrode on said cover terminating in a conductive path to the exterior.

21. The invention as set forth in claim 20 above, wherein said spacer means interconnecting the diaphragm and the reference plate are comprised of a vitrified glass-containing composition.

22. The invention as set forth in claim 20 above, further including a vitrified glass-containing bead mounted around the periphery of the outer lower edge of the flange of said cover and coupling the cover to the outer periphery of the diaphragm.

23. The invention as set forth in claim 20 above, wherein the means for introducing a fluid comprises means for providing a fluid of variable pressure to the side of the diaphragm opposite the reference plate.

24. The invention as set forth in claim 23 above, wherein the spacer means comprises a single spacer centrally disposed on the diaphragm.

25. The invention as set forth in claim 20 above, wherein the spacer means comprises a first number of spacers symmetrically disposed about the center of the diaphragm at a diameter less than 25% of the diameter of the deformable portion of the diaphragm, and wherein a second number of spacers are symmetrically disposed about the periphery of the diaphragm and the cover, outside the radius of the reference capacitor.

26. The invention as set forth in claim 25 above, further including thin film conductive means coupling the reference electrode on the cover to one of the second number of spacers, and wherein the means for introducing fluid comprises means for providing fluids to the opposite sides of the diaphragm such that differential pressure may be measured, and further including filter means coupled between the means for introducing fluid and the transducer interior for blocking conductive media therefrom.

27. A capacitive pressure transducer comprising:

a diaphragm having a central web deflectable in response to a pressurized fluid acting against a first side thereof, the diaphragm including a peripheral flange;

a cover adjacent the second side of the diaphragm and coupled thereto at the peripheral flange;

reference capacitor means disposed between the diaphragm and cover in the peripheral flange region;

reference plate means mounted on the second side of the central web and movable with deflection thereof; and

sensing capacitor means disposed between the second side of the diaphragm and the reference plate means.

28. A capacitive pressure transducer comprising a diaphragm having a peripheral flange bounding a central deflectable web that deflects in response to a pressurized fluid acting on a first side thereof, without substantial deflection of the flange;

cover means adjacent the second side of the diaphragm and coupled thereto at the peripheral flange;

plate means mounted on but principally spaced apart from the second side of the diaphragm at the web and movable therewith;

first capacitor means responsive to the distance between the web and the plate means; and

second capacitor means responsive to the distance between the flange and the cover means.

29. A pressure responsive capacitive transducer comprising:

a diaphragm having a deformable central region responsive to pressure applied to one side thereof, the diaphragm including a thin film electrode thereon;

a planar element disposed adjacent but spaced apart from the deformable central region of the diaphragm and including a thin film electrode in facing relation to the thin film electrode on the diaphragm; and

conductive spacer means disposed in the maximum deflection portion of the deformable central region of the diaphragm for (1) mechanically coupling the planar element to move with the deformable central region of the diaphragm and (2) providing electrical coupling to the thin film electrode on the diaphragm.

30. The invention as set forth in claim 29 above, wherein the conductive spacer means has a width of less than about 25% of the diameter of the deformable portion of the diaphragm.