Capacitive pressure sensor having a pedestal supported electrode

• US 5,442,962 A
• Filed: 08/20/1993
• Issued: 08/22/1995
• Est. Priority Date: 08/20/1993
• Status: Expired due to Fees

• Current Assignee: Setra Systems Incorporated (Fortive Corp.)
• Original Assignee: Setra Systems Incorporated (Fortive Corp.)
• Inventors: Lee, Shih-Ying
• Primary Examiner(s): Chilcot, Jr., Richard E.
• Assistant Examiner(s): FELBER, JOSEPH LEON
• Application Number:
  US08/110,075
• Time in Patent Office: 732 Days
• Field of Search: 73/718, 73/724, 73/729.2, 73/731, 361/283.3, 361/283.4
• US Class Current: 73/718
• CPC Class Codes: G01L 9/0072 using variations in capacitance

Abstract

A capacitance pressure sensor includes a conductive diaphragm positioned between two pneumatically separate chambers. The diaphragm is supported at its periphery by a concave base member. An electrode assembly establishes a substantially planar conductive surface opposite to, and spaced apart by a nominal gap from, the conductive diaphragm. The electrode assembly includes the conductive surface and a single support element secured to, and extending through the base member. A glass dielectric fixes the support element to a collar which may be welded, brazed or soldered to the base member. The glass dielectric provides both mechanical support and high quality electric insulation between the electrode and the housing. By prefabricating the electrode support element with the collar and securing the collar to the housing after the dielectric has cured, problems associated with thermal expansion and contraction are avoided and the dimension of the nominal gap may be precisely controlled at a relatively low cost.

Claims

1. A capacitive pressure sensor comprising:

A) a housing disposed about a central axis, said housing including

i) a first concave base member disposed symmetrically about said central axis and having a peripheral rim disposed in a first plane, said first plane being substantially perpendicular to said central axis, said first concave base member having a first aperture extending about said central axis; and

ii) a second concave base member opposite said first concave base member disposed symmetrically about said central axis and having a peripheral rim disposed in said first plane, said peripheral rim of said second concave base member being fixedly coupled to said peripheral rim of said first concave base member;

B) a diaphragm having peripheral portion fixedly coupled to at least one of said peripheral rim of said first base member and said peripheral rim of said second base member;

C) a pre-assembled first electrode assembly including

i) a first electrode having a first electrically conductive surface;

ii) a first electrode support fixedly coupled to said first electrode and extending along a first electrode axis, said first electrode axis extending substantially transverse to said first electrically conductive surface;

iii) a first tubular collar substantially concentrically disposed about said first electrode support;

iv) a dielectric material rigidly coupling said first electrode support to said first tubular collar; and

said first electrode assembly being rigidly coupled to said first concave base member according to the following sequential steps;

1) positioning said first tubular collar in said first aperture, whereby said first electrically conductive surface is uniformly spaced apart from said first plane by a predetermined distance;

2) rigidly coupling said first tubular collar to said first concave base member maintaining said first electrically conductive surface opposite said first plane and uniformly spaced apart therefrom by said predetermined distance.

2. A capacitive pressure sensor according to claim 1, wherein said first electrically conductive surface is uniformly spaced apart from said diaphragm by a nominal gap, d.

3. A capacitive pressure sensor according to claim 1, wherein step 2 includes the sub-steps of

2a) providing a formable filler material between said first tubular collar and said first concave base member, and

2b) hardening said filler material whereby said filler material rigidly couples said first tubular collar to first concave base member.

4. A capacitive pressure sensor according to claim 1, wherein said dielectric material contains a glass material.

5. A capacitive pressure sensor according to claim 1, wherein said first electrically conductive surface is substantially planar.

6. A capacitive pressure sensor according to claim 5, wherein said first electrically conductive surface includes a central recessed portion separated from said first plane by a distance greater than said predetermined distance.

7. A capacitive pressure sensor according to claim 1, wherein said first electrically conductive surface is substantially concave.

8. A capacitive pressure sensor according to claim 1, wherein said first electrode support is fusion welded to said first electrode.

9. A capacitive pressure sensor according to claim 1, wherein said first electrode assembly is formed by the steps of:

A) fixedly coupling said first electrode support to said first electrode, whereby said first electrode axis extends substantially transverse to said first electrically conductive surface;

B) positioning said first tubular collar substantially concentrically about said first electrode support, whereby an interior surface of said first tubular collar is opposite and substantially uniformly spaced apart from an exterior surface of said first electrode support;

C) rigidly coupling said interior surface of said first tubular collar and said exterior surface of said first electrode support to a substantially rigid dielectric material.

10. A capacitive pressure sensor comprising:

A) a housing disposed about a central axis, said housing including

i) a first concave base member disposed symmetrically about said central axis and having a peripheral rim disposed in a first plane, said first plane being substantially perpendicular to said central axis, said first concave base member having an aperture extending about said central axis; and

ii) a second concave base member opposite said first concave base member disposed symmetrically about said central axis and having a peripheral rim disposed in said first plane, said second concave base member having an aperture extending about said central axis, said peripheral rim of said second concave base member being fixedly coupled to said peripheral rim of said first concave base member;

B) a pre-assembled first electrode assembly including

i) a first electrode having a first electrically conductive surface;

ii) a first electrode support fixedly coupled to said first electrode and extending along a first electrode axis, said first electrode axis extending substantially transverse to said first electrically conductive surface;

iii) a first tubular collar substantially concentrically disposed about said first electrode support;

iv) a first dielectric material rigidly coupling said first electrode support to said first tubular collar; and

said first electrode assembly being rigidly coupled to said first concave base member according to the following sequential steps;

1) positioning said first tubular collar in said aperture of said first concave base member, whereby said first electrically conductive surface is uniformly spaced apart from said first plane by a first predetermined distance;

2) rigidly coupling said first tubular collar to said first concave base member maintaining said first electrically conductive surface opposite said first plane and uniformly spaced apart therefrom by said first predetermined distance;

C) a pre-assembled second electrode assembly including

i) a second electrode having a second electrically conductive surface;

ii) a second electrode support fixedly coupled to said second electrode and extending along a second electrode axis, said second electrode axis extending substantially transverse to said second electrically conductive surface;

iii) a second tubular collar substantially concentrically disposed about said second electrode support;

iv) a second dielectric material rigidly coupling said second electrode support to said second tubular collar; and

said second electrode assembly being rigidly coupled to said second concave base member according to the following sequential steps;

3) positioning said second tubular collar in said aperture of said second concave base member, whereby said second electrically conductive surface is uniformly spaced apart from said first plane by a second predetermined distance;

4) rigidly coupling said second tubular collar to said second concave base member maintaining said second electrically conductive surface opposite said first plane and uniformly spaced apart therefrom by said second predetermined distance.

11. A capacitive pressure sensor according to claim 10, wherein said first electrically conductive surface is uniformly spaced apart from said second electrically conductive surface by a nominal gap, D.

12. A capacitive pressure sensor according to claim 10, further comprising

a diaphragm having peripheral portion fixedly coupled to at least one of said peripheral rim of said first base member and said peripheral rim of said second base member.

13. A capacitive pressure sensor according to claim 12, wherein said first electrically conductive surface is uniformly spaced apart from said diaphragm by a nominal gap, d.

14. A capacitive pressure sensor according to claim 12, wherein said second electrically conductive surface is uniformly spaced apart from said diaphragm by a nominal gap, d'"'"'.

15. A capacitive pressure sensor according to claim 10, wherein step 2 includes the sub-steps of

2a) providing a formable filler material between said first tubular collar and said first concave base member, and

2b) hardening said filler material whereby said filler material rigidly couples said first tubular collar to first concave base member.

16. A capacitive pressure sensor according to claim 10, wherein step 4 includes the sub-steps of

4a) providing a formable filler material between said second tubular collar and said second concave base member, and

4b) hardening said filler material whereby said filler material rigidly coupling said second tubular collar to second concave base member.

17. A capacitive pressure sensor according to claim 10, wherein said first dielectric material contains a glass material.

18. A capacitive pressure sensor according to claim 10, wherein said second dielectric material contains a glass material.

19. A capacitive pressure sensor according to claim 10, wherein said first electrically conductive surface is substantially planar.

20. A capacitive pressure sensor according to claim 19, wherein said first electrically conductive surface includes a central recessed portion separated from said first plane by a distance greater than said first predetermined distance.

21. A capacitive pressure sensor according to claim 10, wherein said second electrically conductive surface is substantially planar.

22. A capacitive pressure sensor according to claim 21, wherein said second electrically conductive surface includes a central recessed portion separated from said first plane by a distance greater than said second predetermined distance.

23. A capacitive pressure sensor according to claim 10, wherein said first electrically conductive surface is substantially concave.

24. A capacitive pressure sensor according to claim 10, wherein said second electrically conductive surface is substantially concave.

25. A capacitive pressure sensor according to claim 10, wherein said first electrode support is fusion welded to said first electrode.

26. A capacitive pressure sensor according to claim 10, wherein said second electrode support is fusion welded to said second electrode.

27. A capacitive pressure sensor according to claim 10, wherein said first electrode assembly is formed by the steps of:

A) fixedly coupling said first electrode support to said first electrode, whereby said first electrode axis extends substantially transverse to said first electrically conductive surface;

B) positioning said first tubular collar substantially concentrically about said first electrode support, whereby an interior surface of said first tubular collar is opposite and substantially uniformly spaced apart from an exterior surface of said first electrode support;

C) rigidly coupling said interior surface of said first tubular collar and said exterior surface of said first electrode support to a substantially rigid dielectric material.

28. A capacitive pressure sensor according to claim 10, wherein said second electrode assembly is formed by the steps of:

A) fixedly coupling said second electrode support to said second electrode, whereby said second electrode axis extends substantially transverse to said second electrically conductive surface;

B) positioning said second tubular collar substantially concentrically about said second electrode support, whereby an interior surface of said second tubular collar is opposite and substantially uniformly spaced apart from an exterior surface of said second electrode support;

C) rigidly coupling said interior surface of said second tubular collar and said exterior surface of said second electrode support to a substantially rigid dielectric material.

29. A capacitive pressure sensor according to claim 10, wherein said first base member and said second base member form a hermetically sealed chamber having a predetermined pressure.

30. A capacitive pressure sensor comprising:

A) a housing disposed about a central axis, said housing including

i) a first concave base member disposed symmetrically about said central axis and having a peripheral rim disposed in a first plane, said first plane being substantially perpendicular to said central axis, said first concave base member having a first aperture extending about said central axis; and

ii) a second concave base member opposite said first concave base member disposed symmetrically about said central axis and having a peripheral rim disposed in said first plane, said peripheral rim of said second concave base member being fixedly coupled to said peripheral rim of said first concave base member;

B) a diaphragm having peripheral portion fixedly coupled to at least one of said peripheral rim of said first base member and said peripheral rim of said second base member;

C) a pre-assembled first electrode assembly and associated coupling means including

i) a first electrode having a first electrically conductive surface;

ii) a first electrode support fixedly coupled to said first electrode and extending along a first electrode axis, said first electrode axis extending substantially transverse to said first electrically conductive surface, said first electrode support having an outer surface;

iii) a first tubular collar substantially concentrically disposed about said first electrode support, said first tubular collar having an outer surface and an inner surface;

iv) a dielectric material rigidly coupling said outer surface of the first electrode support to the inner surface of said first tubular collar;

iv) coupling means for rigidly coupling the outer surface of said first tubular collar to said first concave base member at said first aperture whereby said first tubular collar extends through said first aperture and said first electrically conductive surface is opposite said first plane and uniformly separated therefrom by a predetermined distance;

whereby said first electrode support is rigidly coupled to said first concave base member at said first aperture solely by way of said dielectric material, said collar and said coupling means.

31. A capacitive pressure sensor according to claim 30, wherein said first electrically conductive surface is uniformly spaced apart from said diaphragm by a nominal gap, d.

32. A capacitive pressure sensor according to claim 30, wherein said coupling means includes a formable filler material disposed between said first tubular collar and said first concave base member for rigidly coupling said first tubular collar to said first concave base member.

33. A capacitive pressure sensor according to claim 30, wherein said dielectric material contains a glass material.

34. A capacitive pressure sensor according to claim 30, wherein said first electrically conductive surface is substantially planar.

35. A capacitive pressure sensor according to claim 34, wherein said first electrically conductive surface includes a central recessed portion separated from said first plane by a distance greater than said predetermined distance.

36. A capacitive pressure sensor according to claim 30, wherein said first electrically conductive surface is substantially concave.

37. A capacitive pressure sensor according to claim 30, wherein said first electrode support is fusion welded to said first electrode.

38. A capacitive pressure sensor comprising:

A) a housing disposed about a central axis, said housing including

i) a first concave base member disposed symmetrically about said central axis and having a peripheral rim disposed in a first plane, said first plane being substantially perpendicular to said central axis, said first concave base member having an aperture extending about said central axis; and

ii) a second concave base member opposite said first concave base member disposed symmetrically about said central axis and having a peripheral rim disposed in said first plane, said second concave base member having an aperture extending about said central axis, said peripheral rim of said second concave base member being fixedly coupled to said peripheral rim of said first concave base member;

B) a pre-assembled first electrode assembly and associated first coupling means including

i) a first electrode having a first electrically conductive surface;

ii) a first electrode support fixedly coupled to said first electrode and extending along a first electrode axis, said first electrode axis extending substantially transverse to said first electrically conductive surface, said first electrode support having an outer surface;

iii) a first tubular collar substantially concentrically disposed about said first electrode support, said first tubular collar having an outer surface and an inner surface;

iv) a dielectric material rigidly coupling said outer surface of the first electrode support to the inner surface of said first tubular collar;

iv) first coupling means for rigidly coupling the outer surface of said first tubular collar to said first concave base member at said aperture of said first concave base member whereby said first tubular collar extends through said aperture of said first concave base member and said first electrically conductive surface is opposite said first plane and uniformly separated therefrom by a first predetermined distance;

whereby said first electrode support is rigidly coupled to said first concave base member at said aperture of said first concave base member solely by way of said first dielectric material, said first tubular collar and said first coupling means, therefore permitting substantially no net relative movement of said first electrode support with respect to said first tubular collar as a result of thermal expansion or contraction;

C) a second electrode assembly and associated second coupling means including

i) a second electrode having a second electrically conductive surface;

ii) a second electrode support fixedly coupled to said second electrode and extending along a second electrode axis, said second electrode axis extending substantially transverse to said second electrically conductive surface, said second electrode support having an outer surface;

iii) a second tubular collar substantially concentrically disposed about said second electrode support, said second tubular collar having an outer surface and an inner surface;

iv) a second dielectric material rigidly coupling said outer surface of the second electrode support to the inner surface of said second tubular collar;

iv) second coupling means for rigidly coupling the outer surface of said second tubular collar to said second concave base member at said aperture of said second concave base member whereby said second tubular collar extends through said aperture of said second concave base member and said second electrically conductive surface is opposite said first plane and uniformly separated therefrom by a second predetermined distance;

whereby said second electrode support is rigidly coupled to said second concave base member at said aperture of said second concave base member solely by way of said dielectric material, said tubular collar and said second coupling means.

39. A capacitive pressure sensor according to claim 38, wherein said first electrically conductive surface is uniformly spaced apart from said second electrically conductive surface by a nominal gap, D.

40. A capacitive pressure sensor according to claim 38, further comprising a diaphragm having peripheral portion fixedly coupled to at least one of said peripheral rim of said first base member and said peripheral rim of said second base member.

41. A capacitive pressure sensor according to claim 40, wherein said first electrically conductive surface is uniformly spaced apart from said diaphragm by a nominal gap, d.

42. A capacitive pressure sensor according to claim 40, wherein said first electrically conductive surface is uniformly spaced apart from said diaphragm by a nominal gap, d'"'"'.

43. A capacitive pressure sensor according to claim 38, wherein said first coupling means includes a formable filler material disposed between said first tubular collar and said first concave base member for rigidly coupling said first tubular collar to said first concave base member.

44. A capacitive pressure sensor according to claim 38, wherein said second coupling means includes a formable filler material disposed between said second tubular collar and said second concave base member for rigidly coupling said second tubular collar to said second concave base member.

45. A capacitive pressure sensor according to claim 38, wherein said first dielectric material contains a glass material.

46. A capacitive pressure sensor according to claim 38, wherein said second dielectric material contains a glass material.

47. A capacitive pressure sensor according to claim 38, wherein said first electrically conductive surface is substantially planar.

48. A capacitive pressure sensor according to claim 47, wherein said first electrically conductive surface includes a central recessed portion separated from said first plane by a distance greater than nominal gap, d.

49. A capacitive pressure sensor according to claim 38, wherein said second electrically conductive surface is substantially planar.

50. A capacitive pressure sensor according to claim 49, wherein said second electrically conductive surface includes a central recessed portion separated from said first plane by a distance greater than nominal gap, d'"'"'.

51. A capacitive pressure sensor according to claim 38, wherein said first electrically conductive surface is substantially concave.

52. A capacitive pressure sensor according to claim 38, wherein said second electrically conductive surface is substantially concave.

53. A capacitive pressure sensor according to claim 38, wherein said first electrode support is fusion welded to said first electrode.

54. A capacitive pressure sensor according to claim 38, wherein said second electrode support is fusion welded to said second electrode.

55. A capacitive pressure sensor according to claim 38, wherein said first base member and said second base member form a hermetically sealed chamber having a predetermined pressure.