Electrostatic pressure sensor with porous dielectric diaphragm

• US 8,079,269 B2
• Filed: 05/16/2007
• Issued: 12/20/2011
• Est. Priority Date: 05/16/2007
• Status: Active Grant

• Current Assignee: Rosemount Incorporated (Emerson Electric Company)
• Original Assignee: Rosemount Incorporated (Emerson Electric Company)
• Inventors: Chakraborty, Swapan
• Primary Examiner(s): Caputo, Lisa
• Assistant Examiner(s): JENKINS, JERMAINE L
• Application Number:
  US11/803,971
• Publication Number:
  US 20080282806A1
• Time in Patent Office: 1,679 Days
• Field of Search: 73700-756, 3612831-2834
• US Class Current: 73/715
• CPC Class Codes: G01L 13/025 using diaphragms
• CPC Class Codes: G01L 9/0005 using variations in capacitance G01L9/0072 takes precedence
• CPC Class Codes: G01L 9/0042 Constructional details associated with semiconductive diaphragm sensors, e.g. etching, or constructional details of non-semiconductive diaphragms details about the integration or bonding of piezoresistor in or on the diaphragm G01L9/0052 and G01L9/0057 respectively
• CPC Class Codes: G01L 9/0044 Constructional details of non-semiconductive diaphragms
• CPC Class Codes: G01L 9/0072 using variations in capacitance

Abstract

A pressure sensor comprises a first pressure chamber containing fill fluid at a first pressure, a second pressure chamber containing fill fluid at a second pressure, a porous dielectric diaphragm having first and second major surfaces exposed to the first and second pressure chambers, and first and second electrodes positioned with respect to the first and second major surfaces. A method for sensing pressure is also disclosed, comprising applying first and second pressures to fill fluid in first and second pressure chambers of a pressure sensor having a porous dielectric diaphragm, and producing an output representative of a pressure differential between the pressures, as a function of surface charges on first and second major surfaces of the porous dielectric diaphragm.

Claims

1. A pressure sensor comprising:

a first pressure chamber containing fill fluid at a first pressure;

a second pressure chamber containing fill fluid at a second pressure;

a porous dielectric diaphragm comprising a porous polymer membrane having a first major surface exposed to the first pressure chamber and a second major surface exposed to the second pressure chamber;

a first contact electrode positioned in contact with the first major surface; and

a second contact electrode positioned in contact with the second major surface;

wherein a potential signal is induced across the first and second electrodes by a potential generated across the first and second major surfaces of the porous dielectric diaphragm.

2. The pressure sensor of claim 1, wherein the potential signal on the first and second contact electrodes is induced in response to surface charges on the first and second major surfaces of the porous dielectric diaphragm.

3. The pressure sensor of claim 1, additionally comprising first and second parallel spaced electrodes positioned generally parallel to the porous dielectric diaphragm and spaced from the first and second major surfaces of the porous dielectric diaphragm.

4. The pressure sensor of claim 1, wherein the potential generated across the first and second major surfaces of the porous dielectric diaphragm comprises a reverse electro-osmotic potential generated by a streaming current that flows across the porous dielectric diaphragm.

5. The pressure sensor of claim 1, wherein the potential across the first and second major surfaces of the porous dielectric diaphragm has a polarity indicative of the greater of the first pressure and the second pressure.

6. The pressure sensor of claim 1, wherein the fill fluid comprises a non-polar phase.

7. The pressure sensor of claim 1, wherein the fill fluid comprises an electrolytic phase, the electrolytic phase comprising ionic particles.

8. The pressure sensor of claim 1, wherein the first pressure and the second pressure are dynamic line pressures.

9. The pressure sensor of claim 1, wherein the first pressure is a dynamic line pressure and the second pressure is a reference pressure.

10. The pressure sensor of claim 1, wherein the first pressure is a dynamic line pressure and the second pressure is a vacuum pressure.

11. The pressure sensor of claim 1, wherein the fill fluid comprises a fluid colloid, the fluid colloid comprising a non-polar dispersing phase and one of an electrolytic dispersed phase or a polar dispersed phase.

12. A pressure sensor, comprising:

a first pressure chamber;

a second pressure chamber;

a porous dielectric diaphragm that divides the first pressure chamber, at a first major surface of the diaphragm, from the second pressure chamber, at a second major surface of the diaphragm;

a first contact electrode positioned in contact with the first major surface of the porous dielectric diaphragm, such that the first contact electrode responds to a first surface charge on the first major surface of the diaphragm;

a second contact electrode positioned in contact with the second major surface of the porous dielectric diaphragm, such that the second contact electrode responds to a second surface charge on the second major surface of the diaphragm;

first and second parallel spaced electrodes positioned generally parallel to the porous dielectric diaphragm and spaced from the first and second major surfaces of the porous dielectric diaphragm; and

a fill fluid that flows through the diaphragm in response to a pressure differential between the first pressure and the second pressure.

13. The pressure sensor of claim 12, wherein the surface charges characterize a reverse electro-osmotic potential generated by a streaming current that flows across the porous dielectric diaphragm.

14. The pressure sensor of claim 12, additionally comprising a voltmeter that measures a potential signal across the first contact electrode and the second contact electrode.

15. The pressure sensor of claim 12, additionally comprising:

a first ammeter that measures a first current signal between the first contact electrode and the first parallel spaced electrode; and

a second ammeter that measures a second current signal between the second contact electrode and the second parallel spaced electrode.

16. The pressure sensor of claim 15, additionally comprising a potential supply that provides a variable potential across the first contact electrode and the second contact electrode.

17. The pressure sensor of claim 16, wherein the variable potential approximately minimizes the current signals.

18. The pressure sensor of claim 15, additionally comprising:

a first capacitive correction voltmeter that measures a capacitive signal across the first contact electrode and the first parallel spaced electrode; and

a second capacitive correction voltmeter that measures a capacitive signal across the second contact electrode and the second parallel spaced electrode.

19. A method for sensing pressure, the method comprising:

applying first and second pressures to fill fluid in first and second pressure chambers of a pressure sensor having a porous dielectric diaphragm, the porous dielectric diaphragm comprising a porous polymer membrane having first and second major surfaces exposed to the first and second pressure chambers;

sensing a potential induced on first and second contact electrodes positioned in contact with the first and second major surfaces of the porous dielectric diaphragm; and

producing an output representative of a pressure differential between the first and second pressures based on the potential induced on the first and second contact electrodes, wherein the potential is a function of surface charges on the first and second major surfaces of the porous dielectric diaphragm.

20. The method of claim 19, wherein applying first and second pressures comprises applying one or more of a dynamic line pressure, a reference pressure, or a vacuum pressure.

21. The method of claim 19, wherein producing an output comprises sensing a potential signal across first and second parallel spaced electrodes positioned parallel to the porous dielectric diaphragm and spaced from the first and second major surfaces of the porous dielectric diaphragm.

22. The method of claim 21, wherein producing an output comprises sensing a first current signal between the first contact electrode and the first parallel spaced electrode, and a second current signal between the second contact electrode and the second parallel spaced electrode.

23. The method of claim 22, wherein producing an output further comprises applying a variable potential across the first and second contact electrodes.

24. The method of claim 21, wherein producing an output comprises sensing a first capacitive signal between the first contact electrode and the first parallel spaced electrode, and a second capacitive signal between the second contact electrode and the second parallel spaced electrode.

25. A pressure sensor comprising:

a first pressure chamber containing fill fluid at a first pressure;

a second pressure chamber containing fill fluid at a second pressure;

a porous dielectric diaphragm having a first major surface exposed to the first pressure chamber and a second major surface exposed to the second pressure chamber;

a first electrode positioned with respect to the first major surface; and

a second electrode positioned with respect to the second major surface;

wherein a potential signal is induced across the first and second electrodes by a potential generated across the first and second major surfaces of the porous dielectric diaphragm; and

wherein the porous dielectric diaphragm comprises one or more of a porous thin film of carbon nanotubes, a porous thin film of carbon nanofibers, or a porous carbon nanotube mat.

26. The pressure sensor of claim 25, wherein the porous dielectric diaphragm comprises a porous thin film of carbon nanotubes.

27. The pressure sensor of claim 25, wherein the porous dielectric diaphragm comprises a porous thin film of carbon nanofibers.

28. The pressure sensor of claim 25, wherein the porous dielectric diaphragm comprises a porous carbon nanotube mat.

29. A pressure sensor comprising:

a first pressure chamber containing fill fluid at a first pressure;

a second pressure chamber containing fill fluid at a second pressure;

a porous dielectric diaphragm having a first major surface exposed to the first pressure chamber and a second major surface exposed to the second pressure chamber;

a first electrode positioned with respect to the first major surface; and

a second electrode positioned with respect to the second major surface;

wherein a potential signal is induced across the first and second electrodes by a potential generated across the first and second major surfaces of the porous dielectric diaphragm; and

wherein the fill fluid comprises a fluid colloid, the fluid colloid comprising a non-polar dispersing phase and one of an electrolytic dispersed phase or a polar dispersed phase.