CAPACITANCE MANOMETER HAVING A RELATIVELY THICK FLUSH DIAPHRAGM UNDER TENSION TO PROVIDE LOW HYSTERESIS

• US 20040187589A1
• Filed: 03/25/2003
• Published: 09/30/2004
• Est. Priority Date: 03/22/2003
• Status: Active Grant

• Current Assignee: STEC Incorporated (Western Digital Corporation)
• Original Assignee: STEC Incorporated (Western Digital Corporation)
• Inventors: Oswald, Michael, Ferran, Robert J., Rohrbach, Daniel M.
• Granted Patent: US 6,837,112 B2
• Time in Patent Office: Days
• US Class Current: 73/718
• CPC Class Codes: G01L 9/0072 using variations in capacitance

Abstract

A capacitance diaphragm gauge (CDG) for measuring pressure includes a flush diaphragm mounted to a body structure via a shim or other raised perimeter portion. The diaphragm and the shim are welded to the body structure while the diaphragm is maintained at an elevated temperature. Contraction of the diaphragm as it cools pretensions the diaphragm to substantially reduce hysteresis effects. An electrode advantageously includes two portions with one portion providing excellent bonding characteristics and the other portion having temperature characteristics corresponding to the body structure and the diaphragm. An alternative CDG includes two identical electrodes with a first electrode positioned proximate to the center of the diaphragm and with a second electrode positioned proximate to the perimeter of the diaphragm. The second electrode provides a second capacitance signal that is used to compensate for changes in capacitance between the diaphragm and the first electrode caused by temperature changes.

Claims

1. A capacitance diaphragm manometer comprising:

a body structure having a front surface and a rear surface;

at least one electrode positioned through the body structure, the electrode having a front face substantially flush with the front surface;

a ring-shaped shim positioned on the front surface of the body structure, the shim having a thickness; and

a diaphragm having a first surface and a second surface, the first surface positioned on the shim and spaced apart from the front surface of the body structure by the thickness of the shim, the first surface of the diaphragm fixed to the shim under tension, the second surface of the diaphragm being a completely smooth and unobstructed exposed surface.

2. The capacitance diaphragm manometer as defined in claim 1, wherein the electrode comprises:

a front portion comprising a material selected to have a first thermal expansion characteristic, the first thermal expansion characteristic being similar to a thermal expansion characteristic of the shim; and

a rear portion comprising a material selected to have a second thermal expansion characteristic, the second thermal expansion characteristic being lower than the first thermal expansion characteristic.

3. A method of constructing a capacitance diaphragm manometer comprising:

mounting an electrode assembly through a bore extending from a front surface to a rear surface of a body structure;

positioning a ring-shaped shim having an outer diameter on the front surface of the body structure, the shim having a thickness;

positioning a diaphragm on the shim, the diaphragm having a first surface and a second surface, the first surface being in contact with the shim and being spaced apart from the front surface of the body structure by the thickness of the shim;

heating the diaphragm to cause the diaphragm to expand;

welding the perimeter of the first surface of the diaphragm to the shim and welding the shim to the front surface of the body structure while the diaphragm is expanded, the perimeter of the first surface of the diaphragm being thereby constrained to a size corresponding to the outer diameter of the shim; and

cooling the diaphragm to cause the diaphragm to contract and become pretensioned by the constraint applied to the perimeter of the first surface of the diaphragm by the shim.

4. The method as defined in claim 3, wherein the diaphragm is heated by applying a removable coating to the second surface of the diaphragm and by applying radiant energy to the coating.

5. The method as defined in claim 3, wherein the diaphragm is forced into contact with the shim and the shim is forced into contact against the front surface of the body structure by pressure from a press.

6. The method as defined in claim 5, wherein the diaphragm is supported in the press by a reusable tooling jig having a melting temperature sufficiently higher than the melting temperature of the diaphragm, the shim and the body structure that the tooling jig is not welded to the diaphragm when the diaphragm, the shim and the body structure are welded.

7. A capacitance diaphragm manometer comprising:

a body structure having a front surface and a rear surface, the front surface having a substantially flat central portion and being bounded by a raised perimeter portion having a thickness perpendicular to the flat central portion;

at least one electrode positioned through the body structure, the electrode having a front face substantially flush with the front surface; and

a diaphragm having a first surface and a second surface, the first surface positioned on the raised perimeter portion and spaced apart from the front surface of the body structure by the thickness of the raised perimeter portion, the first surface of the diaphragm fixed to the raised perimeter portion under tension, the second surface of the diaphragm being a completely smooth and unobstructed exposed surface.

8. The capacitance diaphragm manometer as defined in claim 7, wherein the raised perimeter portion comprises a ring-shaped shim, and wherein the raised perimeter portion is fixed to the front surface of the body structure when the diaphragm is fixed to the raised perimeter portion.

9. A method of constructing a capacitance diaphragm manometer comprising:

mounting an electrode assembly through a bore extending from a front surface to a rear surface of a body structure, the front surface of the body structure having a substantially flat central portion and being bounded by a raised perimeter portion having a thickness perpendicular to the flat central portion and having an outer diameter;

positioning a diaphragm on the raised perimeter portion, the diaphragm having a first surface and a second surface, the first surface being in contact with the raised perimeter portion and being spaced apart from the front surface of the body structure by the thickness of the raised perimeter portion;

heating the diaphragm to cause the diaphragm to expand;

welding the perimeter of the first surface of the diaphragm to the raised perimeter portion while the diaphragm is expanded, the perimeter of first surface of the diaphragm being thereby constrained to a size corresponding to the outer diameter of the raised perimeter portion; and

cooling the diaphragm to cause the diaphragm to contract and become pretensioned by the constraint applied to the perimeter of the first surface of the diaphragm by the raised perimeter portion.

10. The method as defined in claim 9, wherein the raised perimeter portion comprises a ring-shaped shim, and wherein the method further comprises welding the raised perimeter portion to the front surface of the body structure while welding the diaphragm to the raised perimeter portion.

11. A capacitance diaphragm manometer comprising:

a body structure having a front surface and a rear surface, the front surface having a substantially flat central portion and being bounded by a raised perimeter portion having a thickness perpendicular to the flat central portion;

a first electrode positioned through the body structure, the first electrode having a cylindrical body with a front face substantially flush with the front surface, the first electrode being located approximately at the center of the front surface, the front face of the first electrode having a size and a shape;

a second electrode positioned through the body structure, the second electrode having a cylindrical body with a front face substantially flush with the front surface, the second electrode being located proximate to the perimeter of the front surface, the front face of the second electrode having a size and a shape substantially the same as the size and the shape of the first electrode; and

a diaphragm having a first surface and a second surface, the first surface positioned on the raised perimeter portion and spaced apart from the front surface of the body structure by the thickness of the raised perimeter portion, the first surface of the diaphragm fixed to the raised perimeter portion under tension, the second surface of the diaphragm being a completely smooth and unobstructed exposed surface.

12. The capacitance diaphragm manometer as defined in claim 11, wherein each of the first electrode and the second electrode comprises:

a front portion comprising a material selected to have a first thermal expansion characteristic, the first thermal expansion characteristic being similar to a thermal expansion characteristic of the raised perimeter portion; and

a rear portion comprising a material selected to have a second thermal expansion characteristic, the second thermal expansion characteristic being lower than the first thermal expansion characteristic.