Non-contact Fuel Level Sensor Using Plastic Optical Fiber
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Solution Overview
Problem
Existing liquid-level measurement systems in storage tanks, particularly in aircraft fuel tanks, face issues with weight, maintenance, and accuracy due to the use of electrical capacitance probes and optical fiber sensors, which are prone to degradation and interference from fuel chemicals.
Innovation Solution
A non-contact plastic optical fiber (POF) system using the time-of-flight principle for measuring liquid levels, employing a graded-index POF with a high-numerical aperture and an avalanche photodiode for accurate and repeatable measurements without electrical contact or immersion in the fuel, reducing weight and maintenance needs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If electrical capacitance probes with metal mounting structures are used, then liquid level measurement can be achieved, but weight increases and cost increases
Solution Approach 1:
The patent replaces electrical capacitance probes with an optical time-of-flight measurement system. Instead of using metallic components and electrical fields, the system uses light propagation through plastic optical fiber to measure liquid level, thereby eliminating heavy metal mounting structures and reducing overall sensor weight.
Solution Approach 2:
The patent introduces plastic optical fiber as an intermediary medium to transmit optical signals. This intermediary allows the measurement system to operate without direct electrical contact or heavy metal structures, enabling weight reduction while maintaining measurement capability through optical signal transmission.
2Measurement precision
If electrical capacitance probes requiring electrical current through fuel tank are used, then liquid level measurement can be achieved, but weight increases due to heavily shielded electrical cables
Solution Approach 1:
The patent substitutes electrical signal transmission with optical signal transmission through plastic optical fiber. This replacement eliminates the need for heavily shielded electrical cables that would otherwise be required to feed power and signals through the fuel tank, significantly reducing cable weight.
Solution Approach 2:
The patent uses plastic optical fiber as an intermediary to transmit measurement signals through the fuel tank environment. This optical intermediary replaces heavy shielded electrical cables, enabling signal transmission without the weight penalty of electrical shielding while maintaining measurement functionality.
3Measurement precision
If plastic optical fiber sensing element is immersed in fuel tank, then liquid level measurement can be achieved, but long-term degradation occurs due to chemical reaction with fuel
Solution Approach 1:
The patent extracts the sensing element from direct contact with the fuel environment. By using non-contact optical measurement through the plastic optical fiber, the sensing mechanism is removed from the harmful chemical environment, preventing degradation while maintaining measurement capability.
Solution Approach 2:
The patent introduces plastic optical fiber as an intermediary that transmits optical signals without requiring the sensing element to be immersed in fuel. This intermediary allows the measurement system to operate remotely, protecting the sensing mechanism from chemical degradation while maintaining continuous measurement capability.
4Measurement precision
If plastic optical fiber sensing element is immersed in fuel tank, then liquid level measurement can be achieved, but optical transmission property degrades due to fuel gunk deposition
Solution Approach 1:
The patent extracts the optical sensing mechanism from direct exposure to fuel. By using non-contact measurement where the plastic optical fiber remains outside the fuel or in a protected position, the system prevents fuel gunk deposition on the sensing element, maintaining stable optical transmission properties and repeatable measurements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides highly accurate, repeatable, and safe fuel level measurements, eliminating concerns of fuel gunk deposition and chemical degradation, while reducing weight and eliminating the need for electrical cables and shielding.
Implementation Method 1
The plastic optical fiber sensing element is immersed in the fuel tank
Implementation Method 2
detecting impingement on a photodetector of first photons from the emitted laser pulse which were reflected at the end face of the plastic optical fiber
Implementation Method 3
detecting a time delay between the times of arrival of the first and second photons; and determining a level of the liquid in the storage tank by processing data representing the time delay
Data Source
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AI summary
A fuel sensing system (50) utilizes non-contact plastic optical fiber (POF) (14) to optically sense a level of liquid fuel (2) in a fuel tank (10). In one implementation, the fuel level sensing system (50) includes the following elements: (i) a high-speed and high-power red laser diode (28); (ii) an ultra-high-sensitivity photon-counting avalanche photodiode (32); and (iii) a large-diameter and large-numerical-aperture graded-index POF (14). The fuel level is sensed when the avalanche photodiode (32) first detects impinging light reflected by the POF end face (1) and then detects impinging light reflected by the fuel surface (3) in response to emission of a laser pulse (18) by the red laser diode (28). A time delay detection circuit (30) calculates the time interval separating the respective times of arrival. A fuel level calculator (34) calculates the fuel level based on the time interval provided by the time delay detection circuit (30).