Oil-less differential pressure sensor

• US 20010032515A1
• Filed: 02/09/2001
• Published: 10/25/2001
• Est. Priority Date: 02/11/2000
• Status: Active Grant

• Current Assignee: Rosemount Incorporated (Emerson Electric Company)
• Original Assignee: Rosemount Incorporated (Emerson Electric Company)
• Inventors: Romo, Mark G., Willcox, Charles R., Rud, Stanley E. Jr., Lutz, Mark A.
• Granted Patent: US 6,425,290 B2
• Time in Patent Office: Days
• US Class Current: 73/715
• CPC Class Codes: G01L 11/02 by optical means
• CPC Class Codes: G01L 13/026 involving double diaphragm
• CPC Class Codes: G01L 9/0007 using photoelectric means G01L9/0076 takes precedence
• CPC Class Codes: G01L 9/0055 bonded on a diaphragm
• CPC Class Codes: G01L 9/0072 using variations in capacitance
• CPC Class Codes: G01L 9/0073 using a semiconductive diaphragm
• CPC Class Codes: G01L 9/0075 using a ceramic diaphragm, e.g. alumina, fused quartz, glass
• CPC Class Codes: G01L 9/0076 using photoelectric means

Abstract

A pressure sensor is provided for measuring a pressure difference between two fluids which does not require isolation fluid. The pressure sensor includes a diaphragm support member having an outer periphery and diaphragms coupled thereto. Movement of the diaphragms are the movement of a moveable member. The movement can be sensed to determine the applied differential pressure. The coupling member is joined to the outer periphery with a web. The web is recessed from opposed outwardly facing surfaces of the outer periphery, and first and second diaphragms disposed on opposite sides of the diaphragm support member. Each diaphragm is joined to the outer periphery and to the coupling member.

Claims

1. A pressure sensor for measuring a pressure difference between two fluids, the pressure sensor comprising:

a diaphragm support member having an outer periphery and an opening formed therethrough;

a first diaphragm covering one side of the opening through the support member;

a second diaphragm covering the other some of the opening through the support member; and

a moveable member extending through the opening and coupled between the first and second diaphragms, wherein the moveable member moves in response to a difference between pressures applied to the first and second diaphragms.

2. The pressure sensor of

claim 1

wherein the first and second diaphragms are joined to the outer periphery of the diaphragm support member.

3. The pressure sensor of

claim 1

including an electrode on the first diaphragm and an electrode on the diaphragm support member and wherein deflection of the first diaphragm causes a change in capacitance between the first and second electrodes.

4. The pressure sensor of

claim 1

including a first electrode carried on the moveable member and a second electrode carried on the diaphragm support member and wherein a capacitance between the first and second electrode is related to movement of the moveable member within the diaphragm support member.

5. The pressure sensor of

claim 2

including at least one additional electrode configured to have a capacitance which changes in response to a localized deflection in the first diaphragm.

6. The pressure sensor of

claim 1

wherein the coupling member is joined to the outer periphery of the diaphragm support structure by a web, the web being recessed from opposed outwardly facing surfaces of the outer periphery.

7. The pressure sensor of

claim 1

wherein the diaphragm support member includes a second web joining the coupling member to a different portion of the outer periphery.

8. The pressure sensor of

claim 7

and wherein the diaphragm support member includes a support joined between the web and the outer periphery, the support being recessed from the outwardly facing surfaces.

9. The pressure sensor of

claim 8

and further comprising a pair of capacitive displacement sensors to measure displacement of the diaphragms relative to the diaphragm support member, each capacitive displacement sensor comprising a first capacitor plate disposed on the support and a second capacitor plate disposed on a surface of the corresponding diaphragm facing the first capacitor plate.

10. The pressure sensor of

claim 1

wherein the diaphragm support member includes a plurality of coupling members joined to the first and second diaphragms at opposite ends, each coupling member having a web joining the coupling member to the outer periphery.

11. The pressure sensor of

claim 1

wherein the diaphragm support member includes an overstop member joined to the outer periphery and extending inwardly configured to limit movement of the first diaphragm.

12. The pressure sensor of

claim 11

wherein the overstop member has opposed surfaces spaced-apart from each of the diaphragms.

13. The pressure sensor of

claim 1

wherein diaphragm support member includes a recess and the portion of the first diaphragm deflects proximate the recess.

14. The pressure sensor of

claim 12

and a sensing device for measuring deflection of the portion of the first isolator diaphragm.

15. The pressure sensor of

claim 14

wherein the sensing device comprises a capacitive electrode disposed on the diaphragm support structure within the recess, and a second capacitive electrode disposed on the portion of the first isolator diaphragm and facing the first capacitive electrode.

16. The pressure sensor of

claim 1

wherein the diaphragm support structure comprises sapphire.

17. The pressure sensor of

claim 1

wherein the first and second diaphragms are coupled to the diaphragm support member by fusion bond.

18. A process transmitter including a pressure sensor in accordance with

claim 1

.

19. The pressure sensor of

claim 1

wherein the first diaphragm and the moveable member are integral.

20. The pressure sensor of

claim 1

wherein the first and second diaphragms are in direct contact with a process fluid.

21. A pressure transmitter in a process control system for measuring and sensing a pressure difference between two fluids, the transmitter comprising:

a pressure sensor comprising,

a diaphragm support member having an outer periphery and a coupling member disposed inward of the outer periphery and joined to the outer periphery with a web, the web being recessed from opposed outwardly facing surfaces of the outer periphery; and

first and second diaphragms disposed on opposite sides of the diaphragm support member, each diaphragm joined to the outer periphery and to the coupling member, and wherein the first diaphragm receives the first pressure and the second diaphragm receives the second pressure;

a sensing device operably coupled to the pressure sensor to provide an output signal indicative of a difference in pressure between the first pressure and the second pressure; and

circuitry receiving the output signal and transmitting information on the loop.

22. The pressure transmitter of

claim 21

wherein the sensing device comprises a capacitive sensing device.