Fuel Level Sensor Having Dual Fluorescent Plastic Optical Fibers

• US 20190107431A1
• Filed: 11/29/2018
• Published: 04/11/2019
• Est. Priority Date: 02/09/2017
• Status: Active Grant

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Chan, Eric Y., Koshinz, Dennis G., Truong, Tuong K.
• Granted Patent: US 10,451,469 B2
• Time in Patent Office: Days
• CPC Class Codes: B64D 37/005 Accessories not provided for in the groups B64D37/02 - B64D37/28
• CPC Class Codes: B64D 37/02 Tanks tanks constructed integrally with aircraft wings B64C; shape or construction of tanks per se B65D
• CPC Class Codes: B65H 57/16 formed to maintain a plurality of filaments in spaced relation
• CPC Class Codes: G01F 23/292 Light , e.g. infrared or ultraviolet
• CPC Class Codes: G01F 23/2927 for several discrete levels, e.g. with more than one light-conducting sensing element
• CPC Class Codes: G02B 6/0003 the light guides being doped with fluorescent agents
• CPC Class Codes: G02B 6/001 the light being emitted along at least a portion of the lateral surface of the fibre
• CPC Class Codes: H02G 7/12 Devices for maintaining distance between parallel conductors, e.g. spacer

Abstract

An airplane fuel level optical sensor using one side-emitting plastic optical fiber (SPOF) and two fluorescent plastic optical fibers (FPOFs) to detect the airplane fuel level without using any electrically conductive component or element placed inside the fuel tank. This dual-FPOF sensor is capable of achieving high resolution and high accuracy with a one-time calibration in the actual airplane'"'"'s fuel tank environment. One embodiment of the dual-FPOF sensor uses one SPOF and two FPOFs to detect fuel level change based on the optical signal output from the two FPOFs. The sensor design uses large-diameter (core and cladding), lightweight, low-cost and high-durability plastic optical fiber, which is very desirable for airplane installation.

Claims

1. An optical fiber assembly comprising:

first, second and third holding rods;

first, second and third glass tubes respectively partially embedded in and partially protruding from the first, second and third holding rods;

a side-emitting optical fiber having a portion embedded in the first glass tube;

a first fluorescent optical fiber having a portion embedded in the second glass tube;

a second fluorescent optical fiber having a portion embedded in the third glass tube; and

a supporting structure that supports the first, second and third holding rods in locations such that that light emitted by the side-emitting optical fiber will be received by the first and second fluorescent optical fibers.

2. The optical fiber assembly as recited in claim 1, wherein the side-emitting optical fiber and the first and second fluorescent optical fibers are made of plastic material.

3. The optical fiber assembly as recited in claim 1, wherein the embedded portions of the side-emitting optical fiber and the first and second fluorescent optical fibers are mutually parallel.

4. The optical fiber assembly as recited in claim 1, wherein the supporting structure comprises:

an outer tube having first and second ends;

a first end cap affixed to the first end of the outer tube; and

a second end cap affixed to the second end of the outer tube,

wherein the first, second and third holding rods are disposed inside the outer tube.

5. The optical fiber assembly as recited in claim 4, wherein the outer tube, first and second end caps, and first, second and third holding rods are made of composite material.

6. The optical fiber assembly as recited in claim 4, further comprising an optical fiber holding cylinder having first, second and third openings, wherein the first end cap has a recess which is configured to receive the optical fiber holding cylinder and also has first, second and third openings respectively aligned with the first, second and third openings in the optical fiber holding cylinder, the side-emitting plastic optical fiber passes through the first openings in the first end cap and optical fiber holding cylinder, the first fluorescent plastic optical fiber passes through the second openings in the first end cap and the optical fiber holding cylinder, and the second fluorescent plastic optical fiber passes through the third openings in the first end cap and the optical fiber holding cylinder.

7. The optical fiber assembly as recited in claim 6, wherein:

the first end cap comprises a first portion integrally formed with a second portion;

the first portion has a circular cylindrical outer surface with a first radius;

the second portion has a circular cylindrical outer surface with a second radius less than the first radius;

the recess is formed in the first portion of the first end cap; and

the first, second and third openings of the first end cap being formed in the second portion of the first end cap.

8. The optical fiber assembly as recited in claim 7, wherein the second portion of the first end cap has first, second and third recesses, the first recess being configured to receive ends of the first composite holding rod and the first glass tube, the second recess being configured to receive ends of the second composite holding rod and the second glass tube, and the third recesses being configured to receive ends of the third composite holding rod and the third glass tube.

9. The optical fiber assembly as recited in claim 4, wherein the second end cap has first, second and third openings, the first opening being configured to receive ends of the first composite holding rod and the first glass tube, the second opening being configured to receive ends of the second composite holding rod and the second glass tube, and the third opening being configured to receive ends of the third composite holding rod and the third glass tube.

10. The optical fiber assembly as recited in claim 9, wherein the second end cap has at least one opening configured to allow liquid to flow into the outer tube when the optical fiber assembly is immersed in a reservoir containing liquid.

11. The optical fiber assembly as recited in claim 1, wherein a core of the first fluorescent optical fiber has a first fluorescing dopant, whereas a core of the second fluorescent optical fiber has a second fluorescing dopant different than the first fluorescing dopant.

12. The optical fiber assembly as recited in claim 1, wherein a core of the first fluorescent optical fiber has a first concentration of a fluorescing dopant, whereas a core of the second fluorescent optical fiber has a second concentration of the fluorescing dopant different than the first concentration.

13. A system for containing a liquid, the system comprising a reservoir and an optical fiber assembly installed in the reservoir, wherein the optical fiber assembly comprises:

an outer tube having first and second ends;

a first end cap having a portion seated inside the first end of the outer tube;

a second end cap seated inside the second end of the outer tube;

a side-emitting optical fiber extending from the second end cap to and through the first end cap;

a first fluorescent optical fiber extending from the second end cap to and through the first end cap; and

a second fluorescent optical fiber extending from the second end cap to and through the first end cap,

wherein the first and second end caps support the side-emitting optical fiber and the first and second fluorescent optical fibers such that light emitted by the side-emitting optical fiber and not obstructed by intervening matter will be received by the first and second fluorescent optical fibers.

14. The system as recited in claim 13, wherein the optical fiber assembly further comprises:

first, second and third holding rods supported at opposing ends by the first and second end caps; and

first, second and third glass tubes respectively partially embedded in and partially protruding from the first, second and third holding rods, and

further wherein the side-emitting optical fiber has a portion embedded in the first glass tube, the first fluorescent optical fiber has a portion embedded in the second glass tube, and the second fluorescent optical fiber has a portion embedded in the third glass tube.

15. The system as recited in claim 13, wherein a core of the first fluorescent optical fiber has a first photo response efficiency, and a core of the second fluorescent optical fiber has a second photo response efficiency different than the first photo response efficiency.

16. The system as recited in claim 13, wherein the second end cap has at least one opening configured to allow liquid to flow into the outer tube when the optical fiber assembly is in a reservoir containing liquid.

17. An aircraft comprising a fuel tank and an optical sensor disposed inside the fuel tank, wherein the optical sensor comprises:

an outer tube having first and second ends;

a first end cap having at least a portion seated inside the first end of the outer tube;

a second end cap seated inside the second end of the outer tube;

a side-emitting optical fiber extending from the second end cap to and through the first end cap;

a first fluorescent optical fiber extending from the second end cap to and through the first end cap; and

a second fluorescent optical fiber extending from the second end cap to and through the first end cap,

wherein the first and second end caps support the side-emitting optical fiber and the first and second fluorescent optical fibers such that light emitted by the side-emitting optical fiber and not obstructed by intervening matter will be received by the first and second fluorescent optical fibers.

18. The aircraft as recited in claim 17, wherein the optical sensor further comprises:

first, second and third holding rods supported at opposing ends by the first and second end caps; and

first, second and third glass tubes respectively partially embedded in and partially protruding from the first, second and third holding rods, and

wherein the side-emitting optical fiber has a portion embedded in the first glass tube, the first fluorescent optical fiber has a portion embedded in the second glass tube, and the second fluorescent optical fiber has a portion embedded in the third glass tube.

19. The aircraft as recited in claim 17, wherein a core of the first fluorescent optical fiber has a first photo response efficiency, and a core of the second fluorescent optical fiber has a second photo response efficiency different than the first photo response efficiency.

20. The aircraft as recited in claim 17, wherein the second end cap has at least one opening configured to allow fuel contained by the fuel tank to flow into the outer tube.