Fluid diffusion resistant glass-encased

• US 20040040381A1
• Filed: 05/01/2003
• Published: 03/04/2004
• Est. Priority Date: 01/31/2000
• Status: Active Grant

• Current Assignee: Weatherford Technology Holdings, LLC (Weatherford International PLC)
• Original Assignee: Alan D. Kersey, Mark R. Fernald, Martin A. Putnam, Timothy J. Bailey, Trevor W. Macdougall
• Inventors: Kersey, Alan D., Fernald, Mark R., Bailey, Timothy J., Putnam, Martin A., MacDougall, Trevor W.
• Granted Patent: US 6,877,378 B2
• Time in Patent Office: Days
• US Class Current: 73/705
• CPC Class Codes: G01L 1/246 using integrated gratings, e.g. Bragg gratings
• CPC Class Codes: G01L 11/025 using a pressure-sensitive optical fibre
• CPC Class Codes: G01L 9/0077 for measuring reflected light

Abstract

A fluid diffusion resistant tube-encased fiber grating pressure sensor includes an optical fiber 10 having a Bragg grating 12 impressed therein which is encased within a sensing element, such as a glass capillary shell 20. A fluid blocking coating 30 is disposed on the outside surface of the capillary shell to prevent the diffusion of fluids, such as water molecules from diffusing into the shell. The fluid diffusion resistant fiber optic sensor reduces errors caused by the diffusion of water into the shell when the sensor is exposed to harsh conditions.

Claims

1. A fluid blocking fiber optic pressure sensor, comprising:

an optical fiber, having at least one pressure reflective element embedded therein, said pressure reflective element having a pressure reflection wavelength;

a sensing element, having said optical fiber and said reflective element encased therein, said sensing element being fused to at least a portion of said fiber and said sensing element being strained due to a change in external pressure, said strain causing a change in said pressure reflection wavelength, and said change in said pressure reflection wavelength being indicative of said change in pressure; and

a fluid blocking coating disposed on the external surface of said sensing element.

2. The pressure sensor of claim 1 wherein said sensing element comprises a tube.

3. The pressure sensor of claim 1 wherein said fluid blocking coating comprises at least one layer.

4. The pressure sensor of claim 1 wherein said fluid blocking coating comprises a fluid blocking material of gold, chrome, silver, carbon or silicon nitride.

5. The pressure sensor of claim 1 wherein said fluid blocking coating capable of preventing the diffusion of water molecules into to said sensing element.

6. The pressure sensor of claim 1 wherein said coating comprises:

a first layer comprised of chrome disposed on said outside surface of said sensing element; and

a second layer comprised of gold disposed on said first layer.

7. The pressure sensor of claim 6 wherein said first layer has a thickness of about 250 Å

and wherein said second layer has a thickness of about 20,000 Å

.

8. A fluid blocking fiber optic pressure sensor, comprising:

an optical sensing element, having at least one pressure reflective element disposed therein, said pressure reflective element having a pressure reflection wavelength;

said sensing element being axially strained due to a change in external pressure, said axial strain causing a change in said pressure reflection wavelength, and said change in said pressure reflection wavelength being indicative of said change in pressure;

at least a portion of said sensing element having a transverse cross-section which is contiguous and made of substantially the same material and having an outer transverse dimension of at least 0.3 mm;

a fluid blocking coating disposed on the external surface of said sensing element.

9. The pressure sensor of claim 8 wherein said fluid blocking coating comprises at least one layer.

10. The pressure sensor of claim 8 wherein said fluid blocking coating comprises a fluid blocking material of gold, chrome, silver, carbon or silicon nitride.

11. The pressure sensor of claim 8 wherein said fluid blocking coating capable of preventing the diffusion of water molecules into to said sensing element.

12. The pressure sensor of claim 8 wherein said coating comprises:

a first layer comprised of chrome disposed on said outside surface of said sensing element; and

a second layer comprised of gold disposed on said first layer.

13. The pressure sensor of claim 12 wherein said first layer has a thickness of about 250 Å

and wherein said second layer has a thickness of about 20,000 Å

.

14. A method for providing a fiber optic sensing pressure resistant to fluid diffusion, comprising:

obtaining an optical fiber with at least one pressure reflective element encased in a sensing element, said sensing element being fused to at least a portion of said fiber, and said pressure reflective element having a pressure reflection wavelength; and

coating the external surface of said sensing element with a fluid blocking material.

15. The method of claim 14 wherein said coating comprises a sputtering process.

16. The method of claim 14 further comprising preparing said external surface prior to said coating step.

17. The method of claim 16 wherein said preparing comprises:

degreasing said external surface; and

etching said external surface.

18. The method of claim 17 wherein said etching step comprises an oxygen-ion process.