Fiber Optic Temperature Sensor Insert for High Temp Environments
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Solution Overview
Problem
Existing measurement systems for high-temperature characterization of thermal protection systems in aerospace vehicles, such as those using thermocouples, suffer from inaccuracies due to multiple ingresses and egresses, which introduce discontinuities in the insulating material and differ in thermal conductivity from the surrounding material, making it difficult to obtain accurate temperature profiles.
Innovation Solution
A thermal profile system utilizing a test plug with a string-like sensor formed from fiber Bragg gratings (FBGs) embedded in optical fibers, which are fabricated to match the material and form of the surrounding TPS, allowing for simultaneous temperature measurements with minimal ingresses and egresses, and providing a more accurate representation of the thermal conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple discrete thermocouples are used for temperature measurements, then temperature profile data can be obtained, but the number of ingresses and egresses increases, creating discontinuities in the insulating material and measurement inaccuracies
Solution Approach 1:
Multiple discrete thermocouple measurements are merged into a single integrated optical fiber sensor. The patent combines multiple temperature sensing points along one continuous optical fiber string, eliminating the need for multiple separate thermocouple ingresses and egresses. This single integrated sensor provides comprehensive temperature profile data while maintaining material continuity.
Solution Approach 2:
The patent introduces an optical fiber as an intermediary sensing medium that does not disrupt the thermal insulation properties of the TPS material. Unlike metallic thermocouple wires that conduct heat and create thermal bridges, the optical fiber serves as a non-conductive intermediary that measures temperature without affecting the thermal field or creating significant thermal discontinuities.
2Measurement precision
If metallic thermocouple wires are used, then temperature measurements can be taken, but the thermal conductivity of the wire differs significantly from the TPS material, introducing measurement errors
Solution Approach 1:
The patent applies homogeneity by using an optical fiber sensor whose thermal properties match the surrounding TPS material. The optical fiber has thermal conductivity comparable to the ablative material, creating a homogeneous thermal environment that eliminates the thermal bridge effect and measurement errors associated with metallic thermocouples.
Solution Approach 2:
The patent replaces the electrical measurement system (metallic thermocouples) with an optical measurement system (optical fiber with FBG sensors). This substitution eliminates the thermal conductivity mismatch problem because optical fibers are dielectric materials whose thermal properties can be matched to the TPS material, unlike conductive metal wires.
3Device complexity
If a single string sensor is used, then the number of ingresses and egresses is minimized, but the sensor must be fabricated from material matching the TPS to ensure accurate thermal conductivity
Solution Approach 1:
The patent segments the optical fiber into multiple sensing zones along its length, with FBG sensors positioned at different locations to measure temperature at various points within the TPS material. This segmentation allows a single continuous fiber to provide multiple measurement points without requiring multiple ingresses and egresses.
Solution Approach 2:
The single optical fiber string serves multiple functions: it provides structural integration with the TPS material, acts as a thermal insulator matching the surrounding material, and contains multiple temperature sensing points along its length. This multi-functionality eliminates the need for separate sensing elements and simplifies the overall sensor system.
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 system achieves improved accuracy and reduced measurement errors by using FBGs in optical fibers that closely match the thermal conductivity of the TPS materials, enabling precise temperature profiling with a single string sensor, reducing the need for multiple thermocouples and minimizing material discontinuities.
Implementation Method 1
a first sensor formed using a first linear array of fiber Bragg gratings (FBG)... Each particular sensor reflects optical energy in a unique range of wavelengths, and each sensor in the sequence which receives optical energy outside its unique range of wavelengths from another sensor passes this reflected optical energy along
Data Source
AI summary
A thermal protection system (TPS) test plug has optical fibers with FBGs embedded in the optical fiber arranged in a helix, an axial fiber, and a combination of the two. Optionally, one of the optical fibers is a sapphire FBG for measurement of the highest temperatures in the TPS plug. The test plug may include an ablating surface and a non-ablating surface, with an engagement surface with threads formed, the threads having a groove for placement of the optical fiber. The test plug may also include an optical connector positioned at the non-ablating surface for protection of the optical fiber during insertion and removal.