Multiplexed optical fiber crack sensor

• US 8,576,392 B2
• Filed: 04/13/2011
• Issued: 11/05/2013
• Est. Priority Date: 02/09/2011
• Status: Active Grant

• Current Assignee: Siemens Energy Incorporated (Siemens AG)
• Original Assignee: Siemens Energy Incorporated (Siemens AG)
• Inventors: Johnston, Robert T.
• Primary Examiner(s): STAFIRA, MICHAEL PATRICK
• Application Number:
  US13/085,617
• Publication Number:
  US 20120198849A1
• Time in Patent Office: 937 Days
• Field of Search: 3562371-2375, 356 32- 355, 356/73.1
• US Class Current: 356/237.1
• CPC Class Codes: F01D 17/02 Arrangement of sensing elements
• CPC Class Codes: F01D 21/003 Arrangements for testing or measuring for measuring vibrations G01H
• CPC Class Codes: F05D 2270/804 Optical devices
• CPC Class Codes: G01B 11/16 for measuring the deformation in a solid, e.g. optical strain gauge
• CPC Class Codes: G01M 11/086 Details about the embedment of the optical fiber within the DUT
• CPC Class Codes: G01M 5/0033 by determining damage, crack or wear
• CPC Class Codes: G01M 5/0091 by using electromagnetic excitation or detection
• CPC Class Codes: G01N 21/00 Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light G01N3/00 - G01N19/00 take precedence

Abstract

An optical fiber crack detector that includes a plurality of FBG sensors positioned within one or more fibers that are operable to reflect a defined wavelength of an optical input beam. The crack detector includes a light source for generating the optical input beam that propagates down the optical fiber and interacts with the FBG sensors. A wavelength of the optical beam that is reflected by the FBG sensors is detected, and if a crack in the component damages the fiber between an FBG sensor and the detector circuit, where one or more of the reflected signals are not received, the detector knows that a crack has occurred. By strategically placing a plurality of the FBG sensors along the fiber, a crack that damages the fiber in multiple locations between multiple FBG sensors, or in multiple fibers, can provide an indication of the length of the crack.

Claims

1. A crack sensor for detecting cracks in a component, said sensor comprising:

at least one light source generating an optical beam;

at least one optical fiber receiving the optical beam from the at least one light source, said optical fiber including a fiber core through which the optical beam propagates and a plurality of spaced apart fiber Bragg gratings formed in the core, each fiber Bragg grating being operable to reflect a predefined and different wavelength of the optical beam back along the optical fiber and allow other wavelengths in the optical beam to propagate through the fiber Bragg grating; and

a detector for detecting the reflected wavelengths of the optical beam from the fiber Bragg gratings, wherein a crack that forms in the component that damages or severs the fiber between fiber Bragg gratings causes loss of reflected wavelengths from at least some of the fiber Bragg gratings to identify the location of the crack.

2. The sensor according to claim 1 wherein the at least one optical fiber is mounted to the component in a meandering orientation, and wherein a separate one of the fiber Bragg gratings is positioned at each location where the optical fiber makes a 180°

turn.

3. The sensor according to claim 2 wherein the meandering orientation of the optical fiber provides a plurality of substantially parallel fiber sections so that if the crack severs multiple fiber sections between the fiber Bragg gratings at the turns, the loss of the reflected wavelength from the particular fiber Bragg gratings provides an indication of the length of the crack.

4. The sensor according to claim 2 wherein the turns are semi-circular turns.

5. The sensor assembly according to claim 1 wherein the at least one optical fiber is a single optical fiber including a plurality of spaced apart fiber Bragg gratings where each fiber Bragg grating reflects a different wavelength of the optical beam, and wherein opposite ends of the optical fiber are coupled to different channels that provide different input optical beams.

6. The sensor according to claim 1 wherein the at least one optical fiber is mounted to the component in a straight line where the spaced apart fiber Bragg gratings are spaced apart along the line.

7. The sensor according claim 6 comprising a plurality of optical fibers each including a plurality of spaced apart fiber Bragg gratings, and wherein the length of the optical fibers is in a direction substantially perpendicular to a crack formation direction where damage or severing of multiple optical fibers provides an indication of the length of the crack.

8. The sensor according to claim 6 wherein each optical fiber includes fifteen fiber Bragg gratings.

9. The sensor according to claim 7 wherein each aligned fiber Bragg grating in parallel optical fibers reflects the same wavelength.

10. The sensor according to claim 1 wherein the component is part of a turbine.

11. A crack detector for detecting cracks in a component, said crack detector comprising an optical fiber including a fiber core through which an optical beam propagates and a plurality of spaced apart fiber Bragg gratings formed in the core, each fiber Bragg grating being operable to reflect a predefined and different wavelength of the optical beam back along the optical fiber and allow other wavelengths in the optical beam to propagate through the fiber Bragg grating, said optical fiber being mounted to the component in a meandering orientation defining a plurality of substantially parallel fiber sections where a separate one of the fiber Bragg gratings is positioned at each location where the optical fiber makes a 180°

turn.

12. The crack detector according to claim 11 wherein the turns are semi-circular turns.

13. A crack detector for detecting cracks in a component, said crack detector comprising at least one optical fiber including a fiber core through which an optical beam propagates and a plurality of spaced apart fiber Bragg gratings formed in the core, each fiber Bragg grating being operable to reflect a predefined and different wavelength of the optical beam back along the optical fiber and allow other wavelengths in the optical beam to propagate through the fiber Bragg gratings, said optical fiber being mounted to the component in a straight line, wherein a crack that forms in the component that damages or severs the fiber between fiber Bragg gratings and causes loss of reflected wavelengths from at least some of the fiber Bragg gratings allows the detector to identify the location of the crack.

14. The crack detector according claim 13 comprising a plurality of optical fibers each including a plurality of spaced apart fiber Bragg gratings, and wherein the length of the optical fibers is in direction substantially perpendicular to a crack formation direction where damage to or severing of multiple optical fibers provides an indication of the length of the crack.

15. The crack detector according to claim 13 comprising a single optical fiber including a plurality of spaced apart fiber Bragg gratings where each fiber Bragg grating reflects a different wavelength of the optical beam, and wherein opposite ends of the optical fiber are coupled to different channels that provide different input optical beams.

16. A gas turbine comprising:

a shaft rotatably provided along a center line of the turbine;

a compressor section responsive to a working fluid and being operable to compress the working fluid to produce a compressed working fluid;

a combustion section in fluid communication with the compressor section that receives the compressed working fluid, said combustion section mixing the compressed working fluid with a fuel and combusting the compressed fluid and fuel mixture to produce a hot working fluid;

a turbine section in fluid communication with the combustion section, said turbine section expanding the hot working fluid to produce mechanical power through rotation of the shaft; and

at least one crack sensor operatively coupled to a component in the engine, said at least one crack sensor including at least one optical fiber receiving an optical beam, said at least one optical fiber including a fiber core through which the optical beam propagates and a plurality of spaced apart fiber Bragg gratings formed in the core, each fiber Bragg grating being operable to reflect a predefined and different wavelength of the optical beam back along the optical fiber and allow other wavelengths in the optical beam to propagate through the fiber Bragg grating, wherein a crack that forms in the component that damages or severs the fiber between fiber Bragg gratings and causes loss of reflected wavelengths from at least some of the fiber Bragg gratings allows the sensor to identify the location of the crack.

17. The turbine according to claim 16 wherein the at least one optical fiber is mounted to the component in a meandering orientation, and wherein a separate one of the fiber Bragg gratings is positioned at each location where the optical fiber makes a 180°

turn.

18. The turbine according to claim 17 wherein the meandering orientation of the optical fiber provides a plurality of substantially parallel fiber sections so that if the crack severs multiple fiber sections between the fiber Bragg gratings at the turns, the loss of the reflected wavelength from the particular fiber Bragg gratings provides an indication of the length of the crack.

19. The turbine according to claim 16 wherein the at least one optical fiber is mounted to the component in a straight line where the spaced apart fiber Bragg gratings are spaced apart along the line.

20. The turbine according claim 19 comprising a plurality of optical fibers each including a plurality of spaced apart fiber Bragg gratings, and wherein the length of the optical fibers is in a direction substantially perpendicular to a crack formation direction where damage or severing of multiple optical fibers provides an indication of the length of the crack.