Field-mountable fiber optic sensors for long term strain monitoring in hostile environments
First Claim
1. A method for providing a field-mountable fiber optic sensor for sensing strain in a structure, the method comprising the following step:
- (a) bonding a fiber optic element of said fiber optic strain sensor to a metal shim that is of like material as said structure;
wherein said metal shim is spot weldable to said structure.
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Accused Products
Abstract
A metallized glass fiber optic is braze-bonded or solder-bonded to a metal shim to form a sensor unit that may be spot welded to a structure for monitoring structural strain. Preferably shim thermal characteristics are selected to match those of the structure being monitored, and a cover plate protects the fiber after attachment to the shim. Alternatively, a non-metallized optical fiber is attached to the metal shim using a special ceramic adhesive coat whose metal constituents thermally match the thermal expansion co-efficient of the shim. After adhesive curing, a protective cover plate is attached. An embodiment for use with an extrinsic Fabry-Perot type sensor provides a metal plate with a fiber-sized groove that guides the target and the transmit/receive fiber optic elements together to form an air gap. Another embodiment metallizes the fiber optic elements with a mask ring having a depressed region into which a cover plate is attached. Each of the embodiments may be used with a white light interferometer to provide long term strain measurements at temperatures up to about 1,000° F., and may be used in radiation environments.
104 Citations
20 Claims
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1. A method for providing a field-mountable fiber optic sensor for sensing strain in a structure, the method comprising the following step:
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(a) bonding a fiber optic element of said fiber optic strain sensor to a metal shim that is of like material as said structure; wherein said metal shim is spot weldable to said structure. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method for providing a field-mountable extrinsic Fabry-Perot fiber optic sensor that includes spaced-apart first and second fiber optic elements having a common outer diameter, said sensor sensing strain in a structure, the method comprising the following steps:
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(a) providing a first metal plate defining a longitudinally-extending groove having a groove diameter at least equal to said common outer diameter; (b) using said groove as a guide, extending said first and second fiber optic elements into said first metal plate until opposing end faces of said first and second fiber optic elements are spaced apart a chosen gap distance; (c) sandwiching said first metal plate and said first and second fiber optic elements against a second metal plate; (d) spot welding together said first metal plate and said second metal plate, said first and second fiber optic elements being retained therebetween; wherein said second metal plate is spot weldable to said structure. - View Dependent Claims (9, 10, 11, 12, 13, 14)
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15. A system for monitoring strain in a structure using a fiber optic sensor, the system comprising:
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a metal shim having thermal properties substantially similar to thermal properties of said structure; a fiber optic sensor having an exterior surface, a portion of said exterior surface being metallized; said fiber optic sensor being attached to said metal shim using a technique selected from a group consisting of (i) brazing, (ii) soldering, and (iii) electro-plating; said shim being affixed to said structure after attachment of said fiber optic sensor to said shim; and means, coupled to said fiber optic sensor, for monitoring strain in said structure sensed by said fiber optic sensor.
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16. A system for monitoring strain in a structure using a fiber optic sensor that includes first and second fiber optic elements, the system comprising:
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a first metal plate, having thermal properties substantially similar to thermal properties of said structure, defining a longitudinal groove having a diameter at least equal to a diameter of said first and second fiber optic elements; said first and second fiber optic elements being mounted in said longitudinal groove such that end faces of said first and second fiber optic elements are spaced apart a chosen distance to define a Fabry-Perot interference gap; and a second metal plate, spot welded to said first metal plate with said first and second fiber optic elements being sandwiched and retained between said first and said second metal plate; said second metal plate being weldable to said structure to allow said fiber optic sensor to sense stress in said structure; and means, coupled to said fiber optic sensor, for monitoring strain in said structure detected by said fiber optic sensor. - View Dependent Claims (17, 18, 19)
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20. A system for monitoring strain in a structure using a fiber optic sensor, the system comprising:
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said fiber optic sensor including first and second fiber optic elements having a metallized exterior surface that defines a depressed mask ring section; a curved metal plate, having a width less than a width of said mask ring section, and having a diameter at least equal to a diameter of said first and second fiber optic elements; a second metal plate having thermal properties substantially similar to thermal properties of said structure, welded to said curved metal plate such that said first and second fiber optic elements are sandwiched therebetween; said second metal plate being weldable to said structure to allow said fiber optic sensor to sense stress in said structure; and means, coupled to said fiber optic sensor, for monitoring strain in said structure detected by said fiber optic sensor.
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Specification