Optical Impedance Modulation for Fuel Quantity Measurement

• US 20160138958A1
• Filed: 11/19/2014
• Published: 05/19/2016
• Est. Priority Date: 11/19/2014
• Status: Active Grant

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Thomas, Todd C., Wahlin, Sigvard J., Vento, John L., Truong, Tuong K., Koshinz, Dennis G., Chan, Eric Y., Groat, J. Everett, Hariram, Sham S., Nesting, Richard J.
• Granted Patent: US 9,645,004 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: B64D 37/005 Accessories not provided for in the groups B64D37/02 - B64D37/28
• CPC Class Codes: G01F 22/00 Methods or apparatus for measuring volume of fluids or fluent solid material, not otherwise provided for
• CPC Class Codes: G01F 23/292 Light , e.g. infrared or ultraviolet
• CPC Class Codes: Y02T 50/40 Weight reduction

Abstract

Systems and methods that use an optical impedance sensor that eliminates electricity for measuring fuel quantity in fuel tanks. The optical impedance sensor comprises two optical fibers spaced apart inside a meniscus tube, one to transmit light along its length and the other to receive light along its length. The meniscus tube minimizes the sloshing of fuel level. The fuel level in the tank modulates the optical impedance between the two optical fibers, resulting in changes in the total light received by an optical detector. Depending on fuel tank height, the optical impedance sensor may comprise different embodiments in which the detection apparatus shapes the light to be unidirectional (emitted and collected only on one side of the fiber) or omnidirectional (all directions).

Claims

1. An optical impedance sensor comprising:

a tube having an internal volume;

a first light guide comprising a first optical fiber and a first tube which encases said first optical fiber, wherein said first tube comprises a first jacket having a longitudinal slot and a first lens disposed in said longitudinal slot of said first jacket and optically coupled to said first optical fiber, and said first optical fiber comprises a cladding having a non-uniform surface in an area bounded by said longitudinal slot of said first jacket; and

a second light guide comprising a second optical fiber spaced apart from said first optical fiber, wherein said second optical fiber comprises a cladding having a non-uniform surface in an area confronting said longitudinal slot of said first jacket.

2. The optical impedance sensor as recited in claim 1, wherein said second light guide further comprises a second tube which encases said second optical fiber, said second tube comprising a second jacket having a longitudinal slot and a second lens disposed in said longitudinal slot of said second jacket and optically coupled to said second optical fiber, wherein said longitudinal slots of said first and second jackets are arranged in mutual opposition so that at least some light emitted from said longitudinal slot of said first jacket will directly enter said longitudinal slot of said second jacket.

3. The optical impedance sensor as recited in claim 1, further comprising a third light guide comprising a third optical fiber and a second tube which encases said third optical fiber, wherein said second tube comprises a second jacket having a longitudinal slot and a second lens disposed in said longitudinal slot of said second jacket and optically coupled to said third optical fiber, and said third optical fiber comprises a cladding having a non-uniform surface in an area bounded by said longitudinal slot of said second jacket.

4. The optical impedance sensor as recited in claim 1, further comprising a curved reflective surface disposed between said first optical fiber and said first jacket.

5. The optical impedance sensor as recited in claim 1, wherein said first jacket is made of a material which is not optically transparent or translucent.

6. A system for measuring a level of liquid in a reservoir, comprising:

a tube having an internal volume, said tube being disposed in the reservoir;

an optical source for outputting light;

an optical detector for converting impinging light into an electrical signal representing an optical power of the impinging light;

a first light guide comprising a first optical fiber and a first tube which encases said first optical fiber, wherein said first tube comprises a first jacket having a longitudinal slot and a first lens disposed in said longitudinal slot of said first jacket and optically coupled to said first optical fiber, and said first optical fiber comprises a cladding and a core inside said cladding, said cladding of said first optical fiber having a non-uniform surface in an area bounded by said longitudinal slot of said first jacket, and said core of said first optical fiber being optically coupled to receive light from said optical source; and

a second light guide comprising a second optical fiber spaced apart from said first optical fiber, wherein said second optical fiber comprises a cladding and a core inside said cladding, said cladding of said second optical fiber having a non-uniform surface which receives light emitted by said first optical fiber through said longitudinal slot of said first jacket, and said core of said second optical fiber being optically coupled to output light to said optical detector.

7. The system as recited in claim 6, further comprising a computer system programmed to compute a level of liquid in said reservoir based on optical power data received from said optical detector.

8. The system as recited in claim 6, wherein said optical source comprises a laser and said optical detector comprises a photodiode.

9. The system as recited in claim 6, wherein the reservoir is a fuel tank on an airplane.

10. The system as recited in claim 6, wherein said second light guide further comprises a second tube which encases said second optical fiber, said second tube comprising a second jacket having a longitudinal slot and a second lens disposed in said longitudinal slot of said second jacket and optically coupled to said second optical fiber, wherein said longitudinal slots of said first and second jackets are arranged in mutual opposition so that at least some light emitted from said longitudinal slot of said first jacket will directly enter said longitudinal slot of said second jacket.

11. The system as recited in claim 6, further comprising a third light guide comprising a third optical fiber and a second tube which encases said third optical fiber, wherein said second tube comprises a second jacket having a longitudinal slot and a second lens disposed in said longitudinal slot of said second jacket and optically coupled to said third optical fiber, and said third optical fiber comprises a cladding having a non-uniform surface in an area bounded by said longitudinal slot of said second jacket.

12. The system as recited in claim 11, wherein said first and second lenses are disposed at different elevations.

13. The system as recited in claim 6, further comprising a curved reflective surface disposed between said first optical fiber and said first jacket.

14. A light guide comprising:

an optical fiber having an axis and a circumferential surface;

a jacket having a longitudinal slot that extends parallel to said axis of said optical fiber, said jacket being in contact with said circumferential surface of said optical fiber except in an area of said longitudinal slot; and

a lens disposed in said longitudinal slot of said jacket and interfaced with said circumferential surface of said optical fiber,

wherein said optical fiber comprises a cladding having a non-uniform surface in an area bounded by said longitudinal slot of said jacket.

15. The light guide as recited in claim 14, further comprising a curved reflective surface disposed between said optical fiber and said jacket.

16. The light guide as recited in claim 14, wherein said jacket is made of a material which is not optically transparent or translucent.

17. A method for measuring a level of fuel in a fuel tank having multiple compartments, comprising:

placing a first tube in a first compartment;

placing a first light guide inside the first tube with an orientation that will be generally perpendicular to a surface of the fuel when the first compartment is at least partially filled with fuel, wherein the first light guide comprises a first optical fiber that is encased to prevent wetting of the first optical fiber when the first light guide is immersed in the fuel;

placing a second light guide inside the first tube spaced apart from and generally parallel with the first light guide, wherein the second light guide comprises a second optical fiber that is encased to prevent wetting of the second optical fiber when the second light guide is immersed in the fuel;

emitting light along a length of the first light guide toward a length of the second light guide;

detecting the optical power output from the second light guide; and

determining a level of the fuel in the first compartment based on the detected optical power output from the second light guide.

18. The method as recited in claim 17, wherein said step of determining the level of fuel comprises comparing the detected optical power with a database of calibrated fuel level versus optical power.

19. The method as recited in claim 17, further comprising:

placing a second tube in a second compartment having a height less than a height of the first compartment;

placing a third light guide inside the second tube with an orientation that will be generally perpendicular to a surface of the fuel when the second compartment is at least partially filled with fuel, wherein the third light guide comprises a third optical fiber that is encased to prevent wetting of the third optical fiber when the third light guide is immersed in the fuel;

placing a fourth light guide inside the second tube spaced apart from and surrounding the third light guide, wherein the fourth light guide has a spiral shape and comprises a fourth optical fiber that is encased to prevent wetting of the fourth optical fiber when the fourth light guide is immersed in the fuel;

emitting light along a length of the third light guide toward a length of the fourth light guide;

detecting the optical power output from the fourth light guide; and

determining a level of the fuel in the second compartment based on the detected optical power output from the fourth light guide.

20. The method as recited in claim 17, wherein the fuel tank is incorporated in a wing of an aircraft.