Fiber optic transducer and method

• US 4,358,678 A
• Filed: 11/19/1980
• Issued: 11/09/1982
• Est. Priority Date: 11/19/1980
• Status: Expired due to Term

• Current Assignee: Wells Fargo Realty Advisors Funding, Incorporated (Wells Fargo & Company)
• Original Assignee: Hersey Products Incorporated
• Inventors: Lawrence, William R.
• Primary Examiner(s): Nelms, David C.
• Assistant Examiner(s): Hostetter, Darwin R.
• Application Number:
  US06/208,245
• Time in Patent Office: 720 Days
• Field of Search: 250/227, 250/231 R
• US Class Current: 250/227.14
• CPC Class Codes: G01B 11/18 using photoelastic elements
• CPC Class Codes: G01D 5/35345 using Amplitude variations to detect the measured quantity
• CPC Class Codes: G01F 1/325 Means for detecting quantities used as proxy variables for swirl
• CPC Class Codes: G01L 11/025 using a pressure-sensitive optical fibre
• CPC Class Codes: G01L 9/0039 using photoelectric means

Abstract

A method and apparatus for detecting and measuring mechanical movement that is directly or indirectly representative of a physical phenomenon. The method and apparatus involve the use of at least one optical fiber that defines a region of bend having a curvature, the radius of which varies in direct relation with the particular mechanical movement that is induced by the physical phenomenon. Light is introduced into one extremity of the optical fiber and propagates through the fiber where the intensity of the light emitted or radiating from the opposite extremity of the fiber is measured. Differentiation between introduced light and emitted light determines the degree of perturbance caused by the region of bend and is thus representative of the physical phenomenon that alters the radius of curvature at the region of bend.

Claims

1. An optical fiber transducer for detecting mechanical movement, comprising:

a length of a single optical fiber defining two extremities and having an intermediate portion thereof formed to define a region of bend having a variable radius of curvature that develops perturbance responsive to change of curvature;

an optical transmitter being optically coupled to one extremity of said optical fiber and transmitting light into said optical fiber;

a light detector means being optically coupled to the opposite extremity of said optical fiber and being capable of detecting the intensity of light being emitted from said opposite extremity of said optical fiber, said light detector means being responsive to the change to light intensity that results from change of curvature of said bend and thus being responsive to the physical phenomenon inducing said change in the radius of curvature of said bend; and

signal generating means being coupled to said light detector means and generating electrical signals that are responsive to the intensity of light being detected by said light detector means, said electrical signals being representative of the state of perturbance of said optical fiber in said region of bend.

2. An optical fiber transducer as recited in claim 1, wherein said transducer detects the velocity of flow of fluid flowing through a flow passage and comprises:

a structural element being at least partially positioned within said flow passage, said structural element having oscillatory movement having a frequency of oscillation responsive to the velocity of fluid flow through said passage, said optical fiber forming loop means positioned within said flow passage, said loop means defining said region of bend, said structural element being interconnected with said loop of said optical fiber and inducing oscillatory movement to said region of bend, thus causing the output signals of said signal generating means to reflect the frequency induced by such oscillatory movement and thereby reflect the velocity of flow through said flow passage.

3. An optical fiber transducer as recited in claim 1 wherein said transducer is adapted to detect the velocity of fluid flowing through a flow passage and comprises:

an obstruction element being positioned within said flow passage and causing development of vortices in the fluid flowing through said flow passage; and

a vortex responsive element being at least partially movably positioned within said flow passage downstream of said obstruction element and being oscillated responsive to the vortices of said flowing fluid, said region of bend of said optical fiber being located within said flow passage and being interconnected with said vortex responsive element in such manner as to induce oscillatory changes in the curvature of said region of bend in response to oscillatory movement of said vortex responsive element, the frequency of oscillatory light intensity changes received by said light detector means being translated in the form of oscillating electrical signals by said signal generating means, the frequency of oscillation of said electrical signals being indicative of the velocity of fluid flow through said flow passage.

4. An optical fiber transducer as recited in claim 3, wherein:

said bend region of said optic fiber defines loop means positioned within said flow passage; and

said vortex responsive element is mechanically coupled to the central portion of said loop means of said optical fiber.

5. An optical fiber transducer as recited in claim 4, wherein:

a support element is positioned within said flow passage; and

a portion of said loop is fixed to said support element.

6. An optical fiber transducer as recited in claim 1, wherein said transducer is adapted to detect the velocity of fluid flowing through a flow passage and comprises:

a structural element being positioned within said flow passage and causing development of vortices in the fluid flowing through said flow passage;

said length of optical fiber being of generally U-shaped form with the extremities thereof being positioned in side-by-side relation and defining a pair of spaced legs, each of said spaced legs being formed to define a loop, said loops being positioned in substantially parallel planes; and

said vortex responsive element being a plate-like member being supported by each of said loops, oscillatory movement of said vortex responsive plate-like member responsive to the velocity of fluid flow causing oscillatory movement of said loops and consequent oscillatory changes in light intensity being received by said light detector means.

7. An optical fiber transducer as recited in claim 1, wherein said transducer is responsive to fluid pressure and comprises:

a mechanical device having opposed sides;

movable means interconnecting said opposed sides and being movable responsive to changes in fluid pressure, movement of said movable means inducing relative movement to said opposed sides, said opposed sides being positionable in particular spaced relation at respective pressures of fluid sensed by said movable means;

said length of optical fiber being interconnected with said opposed sides in such manner that said radius of curvature of said region of bend changes responsive to said relative movement and defines a particular bend radius reflecting the pressure sensed by said movable means thus developing a particular light intensity being transmitted by said optical fiber to said light detector.

8. An optical fiber transducer as recited in claim 7, wherein said movable means comprises:

a bellows interconnected with a source of pressure and having the capability of expanding and contracting responsive to the pressure of said source of pressure, said bellows being in operative engagement with said opposed sides and causing movement of said opposed sides in response to expansion and contraction of said bellows.

9. An optical fiber transducer as recited in claim 7, wherein said movable means comprises:

a sealed bellows adapted to be positioned within a pressurized fluid medium and having the capability of expansion and contraction responsive to changes in the pressure of said fluid medium, said bellows being in operative engagement with said opposed sides and causing movement of said opposed sides in response to expansion and contraction of said bellows.

10. An optical fiber transducer as recited in claim 7, wherein said mechanical device comprises:

a first structural element defining one of said opposed sides;

a second structural element defining the other of said opposed sides;

connector means extending from each of said first and second structural elements and being pivotally interconnected; and

said length of optical fiber being formed to a U-shaped configuration with opposed end portions thereof defining spaced leg portions and with the intermediate portion thereof defining said region of bend, one of said leg portions being secured in substantially immovable relation with said first structural element and the other of said leg portions being secured in substantially immovable relation with said second structural element, relative movement of said leg portions of said optical fiber responsive to relative movement of said first and second structural elements causing change in the curvature of said region of bend.

11. An optical fiber transducer as recited in claim 10, wherein said movable means comprises:

a fluid pressure responsive element being in contact with said first and second structural elements and being capable of movement that is responsive to change in the pressure of the fluid within which said pressure responsive element is located, said movement of said fluid pressure responsive element inducing relative movement to said first and second structural elements.

12. An optical fiber transducer as recited in claim 11, wherein said fluid pressure responsive element comprises:

an evacuated bellows located within a pressurized fluid and having the capability of expanding and contracting responsive to the pressure of said fluid, said bellows being in operative engagement with said opposed sides.

13. An optical fiber transducer is recited in claim 1 which is adapted to provide signals representing the physical cross-sectional dimension of a body and signals representing changes in the physical cross-sectional dimension of the body, said transducer comprising:

first constraining means;

said length of optical fiber having end portions thereof that are constrained against relative movement by said first constraining means, said optical fiber being formed to define first and second loops, said first loop defining said region of bend and said second said loop adapted to circumscribe said body, said first and second loops being so related that expansion and contraction of said second loop by changes in the cross-sectional dimension of said body induces a change in the dimension of said first loop and thus changes the curvature of said region of bend.

14. An optical fiber transducer as recited in claim 13, wherein said transducer includes:

means controlling the minimum radius of curvature of said region of bend.

15. An optical fiber transducer as recited in claim 13, wherein said transducer includes:

calibration means fixing end portions of said length of optical fiber in relation to one another and setting the response parameters of said first and second loops.

16. An optical fiber transducer as recited in claim 13, wherein:

said first and second loops substantially define a FIG. "8" and said length of optical fiber crosses itself to define an intersection between said first and second loops; and

second constraining means receiving said intersection of said optical fiber in such manner as to allow relative movement of said fiber at said intersection permitting said change in the relative dimensions of said first and second loops.

17. An optical fiber transducer as recited in claim 16, wherein said transducer includes:

means controlling the minimum radius of curvature of said region of bend; and

calibration means fixing end portions of said length of optical fiber in relation to one another and setting the response parameters of said first and second loops.

18. An optical fiber transducer as recited in claim 13, wherein:

the combined dimensions of said first and second loops remains constant regardless of the relative dimensions of said first and second loops.

19. An optical fiber transducer as recited in claim 13, wherein said second constraining means comprises:

an annular element defining an aperture of sufficient diameter that said intersection of said optical fiber is loosely received therein, said annular element permitting movement of said optical fiber through said aperture to permit dimensional changes of said first and second loops.

20. A method of detecting mechanical movement and providing signals representative of such movement, said method comprising:

providing single strand optical fiber means which is oriented in such manner as to define a region of bend intermediate the extremities thereof;

introducing light into one extremity of said optical fiber means;

positioning said optical fiber means in physical fiber moving relation with a movable object in such manner that movement of said movable object causes alteration of the curvature of said region of bend and thus alters the total internal reflection of said optical fiber means resulting in alteration of the intensity of light radiating from the opposite entremity of said optical fiber means, the intensity of emitted light being a variable signal the variations of which represent mechanical movement of said object;

detecting changes in the intensity of said light being emitted from said opposite extremity of said optical fiber; and

converting the intensity of light signals being received into electrical signals responsive to the intensity of light signals and providing electrical output signals representing light intensity.

21. A method as recited in claim 20, including:

inducing mechanical movement to said object in response to the rate of fluid flow through a flow conduit.

22. A method as recited in claim 20 including:

inducing oscillatory movement to said object wherein the oscillations represent the rate of fluid flow through a flow conduit.

23. A method as recited in claim 20, including:

inducing said mechanical movement to said object responsive to the fluid pressure of a pressure source, whereby said emitted light intensity is representative of the pressure of said pressure source.

24. A method as recited in claim 20, including:

positioning a loop of said optical fiber means about an object capable of changing the physical dimension thereof, said mechanical movement being changes in the physical dimension of said object; and

inducing alteration of said loop and said region of bend responsive to changes in the physical dimensions of said object.