Capacitive pressure sensing with moving dielectric

• US 6,505,516 B1
• Filed: 01/06/2000
• Issued: 01/14/2003
• Est. Priority Date: 01/06/2000
• Status: Expired due to Term

• Current Assignee: Rosemount Incorporated (Emerson Electric Company)
• Original Assignee: Rosemount Incorporated (Emerson Electric Company)
• Inventors: Willcox, Charles R., Frick, Roger L.
• Primary Examiner(s): OEN, WILLIAM L
• Application Number:
  US09/478,434
• Time in Patent Office: 1,104 Days
• Field of Search: 737/18, 737/24, 737/17, 737/16, 737/15, 737/20, 737/21, 737/27, 737/56, 361/283, 361/283.4
• US Class Current: 73/718
• CPC Class Codes: G01L 19/0092 Pressure sensor associated with other sensors, e.g. for measuring acceleration or temperature G01L9/025, G01L9/045, G01L9/065, G01L9/085, G01L9/105, G01L9/125, G01L19/02, G01L19/04 take precedence; measuring two or more variable G01D21/02; temperature sensors with pressure compensation G01K1/26
• CPC Class Codes: G01L 9/0072 using variations in capacitance

Abstract

A pressure sensor with a diaphragm that has a dielectric portion that moves in a cavity near capacitor plates that are fixed relative to a mounting frame. The diaphragm is supported on the frame and the frame surrounds the cavity. The diaphragm has an outer surface that receives pressure and has an inner surface facing the cavity. The capacitor plates, which are fixed, sense movement of the nearby dielectric portion and generate an electrical output representative of pressure. Creep of metallizations on a flexible diaphragm are avoided. Manufacture is simplified because metallization of the diaphragm is avoided.

Claims

1. A pressure sensor, comprising:

a frame surrounding a cavity;

a diaphragm supported on the frame and having an outer surface receiving pressure and having an inner surface facing the cavity;

a dielectric portion carried on the inner surface, the dielectric portion being movable relative to the frame by the pressure; and

capacitor plates fixed relative to the frame in the cavity near the movable dielectric portion, the capacitor plates sensing movement of the nearby dielectric portion and generating an electrical output representative of pressure.

2. The pressure sensor of claim 1 wherein the capacitor plates include a first capacitor plate separated from a second capacitor plate by a space in the cavity, the movable dielectric portion being movable through the space to vary the electrical output.

3. The pressure sensor of claim 2 wherein the space in the cavity intersects with a straight line between the first and second capacitor plates.

4. The pressure sensor of claim 2 wherein the space in the cavity does not intersect with a straight line between the first and second capacitor plates.

5. The pressure sensor of claim 1 wherein the movable dielectric is free of conductors.

6. The pressure sensor of claim 1 wherein the cavity is evacuated and sealed.

7. The pressure sensor of claim 1 wherein the frame is elongated and has a first end including the diaphragm and a second end opposite the first end that is isolated from the pressurization and includes electrical connections for the capacitor plates.

8. The pressure sensor of claim 1 wherein the capacitor plates are interdigitated.

9. The pressure sensor of claim 8 further comprising a support plate upon which the capacitor plates are disposed and comprising screen electrodes disposed on the support plate.

10. The pressure sensor of claim 9 further comprising unity gain buffers coupled to the screen electrodes.

11. A pressure sensor, comprising:

a beam formed around a central channel and having a support surface in the central channel, the beam including a diaphragm having an outer diaphragm surface receiving pressure and having an inner diaphragm surface formed of dielectric and spaced away from the support surface in the central channel, the dielectric being movable relative to the support surface by the pressure; and

capacitor plates fixed on the support surface near the movable dielectric, the capacitor plates sensing movement of the nearby dielectric and providing an electrical output representing pressure.

12. The pressure sensor of claim 11 wherein the capacitor plates include a first capacitor plate separated from a second capacitor plate by a space in the central channel, the movable dielectric portion being movable through the space to vary the electrical output.

13. The pressure sensor of claim 11 wherein the space in the central channel intersects with a straight line between the first and second capacitor plates.

14. The pressure sensor of claim 11 wherein the space in the central channel does not intersect with a straight line between the first and second capacitor plates.

15. The pressure sensor of claim 11 wherein the movable dielectric is free of conductors.

16. The pressure sensor of claim 11 wherein the central channel is evacuated and sealed.

17. The pressure sensor of claim 11 wherein the frame is elongated and has a first end including the diaphragm and a second end opposite the first end that is isolated from the pressurization and includes. electrical connections for the capacitor plates.

18. The pressure sensor of claim 11 wherein the capacitor plates are interdigitated.

19. The pressure sensor of claim 18 further comprising screen electrodes disposed on the support surface.

20. The pressure sensor of claim 19 further comprising unity gain buffers coupled to the screen electrodes.

21. A pressure sensor, comprising:

a frame surrounding a cavity;

a diaphragm supported on the frame and having an outer surface receiving pressure and having an inner surface facing the cavity;

a dielectric portion carried on the inner surface, the dielectric portion being movable relative to the frame by the pressure; and

means for sensing movement of the dielectric portion including capacitor plates fixed relative to the frame in the cavity near the movable dielectric portion, the capacitor plates generating an electrical output representative of pressure.

22. A pressure sensor, comprising:

a beam formed around a central channel and having a support surface in the central channel, the beam including a diaphragm having an outer diaphragm surface receiving pressure and having an inner diaphragm surface formed of dielectric and spaced away from the support surface in the central channel, the dielectric being movable relative to the support surface by the pressure; and

means for sensing movement of the dielectric including capacitor plates fixed on the support surface near the movable dielectric, the capacitor plates providing an electrical output representing pressure.