Fuel level sensor having dual fluorescent plastic optical fibers

• US 10,175,087 B2
• Filed: 02/09/2017
• Issued: 01/08/2019
• 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.
• Primary Examiner(s): Rogers, David A
• Application Number:
  US15/428,626
• Publication Number:
  US 20180224317A1
• Time in Patent Office: 698 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. A system for measuring a level of liquid in a reservoir, comprising:

a light source for outputting light;

a side-emitting optical fiber having one end optically coupled to the light source;

first and second optical detectors for converting impinging light into an electrical signal representing an optical power of the impinging light;

a first fluorescent optical fiber positioned parallel to and at a distance from the side-emitting optical fiber and having one end optically coupled to the first optical detector; and

a second fluorescent optical fiber positioned parallel to and at the distance from the side-emitting optical fiber and having one end optically coupled to the second optical detector, wherein the first and second fluorescent optical fibers have different photo response efficiencies,

a first variable optical attenuator that optically couples the first fluorescent optical fiber to the first optical detector;

a second variable optical attenuator that optically couples the second fluorescent optical fiber to the second optical detector;

a computing system configured to send first control signals to the first and second variable optical attenuators, which first control signals set the levels of attenuation provided by the first and second variable optical attenuators;

a light source power controller for controlling the electrical power provided to the light source, wherein the computing system is further configured to send second control signals to the light source power controller, which second control signals set the level of electrical current provided to the light source,

a first current-to-voltage converter coupled to receive photo-current output by the first optical detector and transmit a first voltage to the computing system; and

a second current-to-voltage converter coupled to receive photo-current output by the second optical detector and transmit a second voltage to the computing system,

wherein the computing system is further configured to calculate a ratio of the first and second voltages, and the first and second control signals are based in part on the ratio.

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

3. The system as recited in claim 1, further comprising a fuel level indicator electrically coupled to the computing system, wherein the computing system is further configured to output a fuel level to the fuel level indicator, which fuel level is based in part on a third voltage received from the first current-to-voltage converter after sending of the first and second control signals.

4. A method for measuring a height of liquid in a reservoir, comprising:

placing a side-emitting optical fiber and a first fluorescent optical fiber in the liquid contained in the reservoir having respective locations whereat the side-emitting optical fiber and the first fluorescent optical fiber are mutually parallel and separated by a distance, and the first fluorescent optical fiber has a first photo response efficiency;

inputting light from a light source into one end of the side-emitting optical fiber;

side-emitting at least some of the inputted light from the side-emitting optical fiber;

absorbing at least some of the side-emitted light inside the first fluorescent optical fiber;

producing light by fluorescence inside the first fluorescent optical fiber in response to absorption of side-emitted light;

emitting light produced by fluorescence from one end of the first fluorescent optical fiber;

converting at least some of the light emitted by the first fluorescent optical fiber into a first photo-current;

converting the first photo-current into a first voltage;

calculating the height of the liquid in the reservoir based in part on a magnitude of the first voltage; and

visually indicating the height on a display;

wherein the placing step further comprises placing a second fluorescent optical fiber in the liquid contained in the reservoir having a location whereat the side-emitting optical fiber and the second fluorescent optical fiber are mutually parallel and separated by the distance, and the second fluorescent optical fiber has a second photo response efficiency different than the first photo response efficiency, the method further comprising;

absorbing at least some of the side-emitted light inside the second fluorescent optical fiber;

producing light by fluorescence inside the second fluorescent optical fiber in response to absorption of side-emitted light;

emitting light produced by fluorescence from one end of the second fluorescent optical fiber;

converting at least some of the light emitted by the second fluorescent optical fiber into a second photo-current;

converting the second photo-current into a second voltage;

calculating a ratio of the first and second voltages; and

comparing the calculated ratio to a predetermined constant,

wherein the height is calculated if the calculated ratio and the predetermined constant are equal.

5. The method as recited in claim 4, further comprising attenuating the light emitted by the first and second fluorescent optical fibers if the calculated ratio and the predetermined constant are not equal.

6. The method as recited in claim 4, further comprising changing the optical power of the light inputted into the one end of the side-emitting optical fiber if the calculated ratio and the predetermined constant are not equal.

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

a light source for outputting light;

a light source power controller for controlling the electrical power provided to the light source,

a side-emitting optical fiber having one end optically coupled to the light source;

first and second optical detectors for converting impinging light into an electrical signal representing an optical power of the impinging light;

a first fluorescent optical fiber positioned parallel to and at a distance from the side-emitting optical fiber and having one end optically coupled to the first optical detector, wherein the first fluorescent optical fiber has a first photo response efficiency;

a second fluorescent optical fiber positioned parallel to and at the distance from the side-emitting optical fiber and having one end optically coupled to the second optical detector, wherein the second fluorescent optical fiber has a second photo response efficiency different than the first photo response efficiency;

a first current-to-voltage converter configured to convert photo-current output by the first optical detector into a first voltage;

a second current-to-voltage converter configured to convert photo-current output by the second optical detector into a second voltage; and

a computing system configured to calculate a ratio of the first and second voltages and then send control signals to the light source power controller to set a level of electrical current provided to the light source based at least partly on the calculated ratio.

8. The system as recited in claim 7, wherein the side-emitting optical fiber and the first and second fluorescent optical fibers are made of plastic.

9. The system as recited in claim 7, further comprising:

a first variable optical attenuator that optically couples the first fluorescent optical fiber to the first optical detector; and

a second variable optical attenuator that optically couples the second fluorescent optical fiber to the second optical detector,

wherein the computing system is further configured to send control signals to the first and second variable optical attenuators to set the levels of attenuation provided by the first and second variable optical attenuators based at least partly on the calculated ratio.