Optical Fabry-Perot Liquid Level Sensor for Aircraft Fuel Tanks
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Solution Overview
Problem
Current electrically based sensors for liquid level and quantity measurement in aircraft fuel tanks face challenges in intrinsic safety, making installation difficult due to electrical clearance rules.
Innovation Solution
An optical sensor system using an optic fiber optically coupled to an open cavity in fluid communication with the environment, detecting changes in refractive index to determine liquid level and quantity, and utilizing a plurality of sensors for accurate measurements across the container.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electrically based sensors are used for liquid level measurement, then measurement functionality is achieved, but installation safety and reliability deteriorate due to electrical clearance requirements
Solution Approach 1:
The patent replaces electrically based sensors with an optical sensor system that uses light transmission through a cavity to detect liquid level. The optical fiber transmits light through the cavity containing the liquid, and changes in light transmission indicate liquid presence or level. This substitution eliminates electrical components from the measurement environment, achieving intrinsic safety while simplifying installation in aircraft fuel tanks.
Solution Approach 2:
The patent introduces an optical cavity as an intermediary between the optical fiber and the liquid environment. The cavity allows light to interact with the liquid without requiring direct electrical contact, enabling safe measurement of liquid levels in flammable environments. The cavity acts as a mediator that translates liquid presence into optical signal changes.
2Reliability
If optical sensor with open cavity is used, then intrinsic safety is achieved, but sensitivity to detect refractive index changes may worsen due to environmental exposure
Solution Approach 1:
The patent maintains continuous optical interaction with the liquid through the open cavity design. Light continuously passes through the cavity, allowing real-time detection of refractive index changes as liquid enters or leaves the cavity. This continuous optical measurement ensures both safety and precision by constantly monitoring liquid presence without interruption.
Solution Approach 2:
The patent optimizes the local optical properties within the cavity to enhance detection sensitivity. The cavity dimensions, optical fiber positioning, and material selection are specifically designed to maximize light-liquid interaction in the measurement zone. This localized optimization ensures high measurement precision while maintaining the safety benefits of the open cavity design.
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 optical sensor system provides accurate and safe liquid level and quantity measurements by detecting refractive index changes, overcoming the limitations of electrically based sensors and ensuring intrinsic safety for installation in aircraft fuel tanks.
Implementation Method 1
detection of changes in index of refraction inside the cavity
Data Source
AI summary
An optical sensor includes an optic fiber optically coupled to a cavity. An optical path is defined from the fiber, across the cavity, and reflected back across the cavity back into the fiber. The cavity is an open cavity that is in fluid communication with an environment ambient to the cavity for detection of changes in index of refraction inside the cavity due to whether the environment ambient to the cavity is gaseous or liquid.