Pressure sensor with fibre-integrated bragg grating, comprising an integrated temperature sensor with fibre-integrated bragg grating

• US 6,563,970 B1
• Filed: 08/25/2000
• Issued: 05/13/2003
• Est. Priority Date: 02/27/1998
• Status: Expired due to Term

• Current Assignee: GE Oil & Gas (General Electric Company)
• Original Assignee: ABB Research Ltd. (ABB Ltd.)
• Inventors: Bodor, Patrick, Bohnert, Klaus, Brändle, Hubert
• Primary Examiner(s): NGO, HUNG NHAT
• Application Number:
  US09/623,056
• Time in Patent Office: 991 Days
• Field of Search: 385/13, 385/37, 385/137
• US Class Current: 385/13
• CPC Class Codes: G01L 11/025 using a pressure-sensitive optical fibre
• CPC Class Codes: G01L 9/0007 using photoelectric means G01L9/0076 takes precedence
• CPC Class Codes: G01L 9/0032 using photoelectric means

Abstract

The subject-matter of the present invention is a wavelength-coded fiber Bragg grating pressure sensor 1 which is suitable, in particular, for use in the case of high pressures and temperatures in oil drill holes. The sensor principle according to the invention is based on the fact that the hydrostatic pressure of a liquid or gaseous medium 11 is converted with the aid of a transducer 1 into a longitudinal fiber elongation or fiber compression. The transducer 1 comprises a measuring or pressure cylinder 7a which exchanges pressure with the medium 11, and a reference cylinder 7b which is shielded from the medium 11 or oppositely pressure-loaded. Temperature-compensated transducers 1 with a temperature-independent Bragg wavelength λ_B can be realized by introducing a suitable temperature dependence of the mechanical prestressing of the pressure sensor fiber 3 by selecting the materials, lengths and arrangements of the fiber holder supports 5a, 5b. A fiber Bragg grating temperature sensor 19, 20 can be provided, in addition. Also specified are transducers 1 with other cylinder arrangements 7a, 7b, and a wavelength-division multiplex configuration with several transducers 1.

Claims

1. A fiber-optic sensor particularly suitable for pressure and temperature measurement in oil drill holes comprising:

a transducer with fiber holders for a pressure sensor fiber;

the fiber holders being mounted on at least one support, the at least one support comprises a pressure membrane for converting an all around pressure of a medium into a longitudinal elongation or compression of the pressure sensor fiber;

wherein the pressure sensor fiber has at least one fiber Bragg grating, said fiber being prestressed or precompressed in the region of the at least one fiber Bragg grating.

2. The fiber optic sensor in accordance with claim 1, wherein

a) the transducer includes a pressure-insulated chamber with pressure-tight fiber lead-ins for the pressure sensor fiber, and having

b) exactly two supports which are composed of materials with different coefficients of thermal expansion (α ₁, α

₂), and wherein

c) a differential thermal expansion between the supports counteracts a thermally-induced shift in the Bragg wavelength (λ

_B) of the pressure sensor fiber and

d) at least one of the supports has at least two segments with different coefficients of thermal expansion and predefinable lengths.

3. The fiber-optic sensor in accordance with claim 1, wherein

a) a sensor fiber comprises both the pressure sensor fiber and also a temperature sensor fiber and

b) the temperature sensor fiber has a fiber-integrated Bragg grating.

4. The fiber optic sensor in accordance with claim 1, wherein

a) the pressure chamber is a pressure membrane,

b) the pressure membrane having a cavity with an opening and at least one piston surface and

c) the piston surface being interactively connected with a fiber holder.

5. The fiber optic sensor in accordance with claim 4, wherein

a) a first support in the form of a pressure cylinder includes an inner cylinder which can be expanded by internal pressure,

b) a second support includes an outer cylinder shielded from a surrounding medium, and wherein

c) the cylinders are fixed to a transducer wall and encapsulated in a transducer casing.

6. The fiber optic sensor in accordance with claim 4, wherein

a) a first support in the form of a pressure cylinder includes an inner cylinder which can be expanded by internal pressure,

b) a second support includes an outer cylinder which can be compressed by external pressure, and

c) the cylinders are fixed to a transducer wall.

7. The fiber optic sensor in accordance with claim 4, wherein

a) the supports in the form of a pressure cylinder include a ring cylinder which can be expanded by internal pressure,

b) the ring cylinder being mounted in a transducer casing by means of positioning elements and

c) the fiber holders are interactively connected with the ring cylinder by axial cylinders.

8. The fiber-optic sensor in accordance with claim 4, wherein

a) the supports include a supporting cylinder which can be expanded by external pressure and

b) the fiber holders are fixed to the piston surfaces of the axial cylinders.

9. The fiber optic sensor in accordance with claim 1, wherein

a) several transducers of different Bragg wavelength (λ

_B⁽ⁱ⁾) are optically connected with a wide-band light source and a detection unit by means of a fiber coupler and

b) the detection unit includes a wavelength demultiplexer and a detector which is connected to evaluation electronics.

10. The fiber optic sensor in accordance with claim 1, wherein

a) a block with a bore is provided to receive the pressure sensor fiber,

b) the pressure chamber membrane is filled with a fluid, and

c) the pressure-isolated chamber is filled with a low-pressure gas or a vacuum.

11. The fiber optic sensor in accordance with claim 10, wherein the fluid is silicone oil.