Optical Fiber Temperature Sensing via Differential Thermal Expansion
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Solution Overview
Problem
Optical fiber-based temperature measurement systems face accuracy issues due to strain-induced light refraction, which complicates temperature measurement accuracy along the fiber length.
Innovation Solution
A temperature sensing arrangement where an optical fiber with a lower coefficient of thermal expansion is strain transmissively attached to a member with a higher coefficient of thermal expansion, allowing strain measurements to be correlated with temperature changes, and using materials like Nickel alloys and protective housings to minimize non-temperature related strain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical fiber is used for temperature measurement, then temperature can be measured along the fiber length, but strain causes light refraction that deteriorates measurement accuracy
Solution Approach 1:
The patent extracts the harmful strain effect from the measurement system by using a member with higher coefficient of thermal expansion than the optical fiber. This differential expansion isolates the optical fiber from mechanical strain while maintaining thermal coupling, allowing temperature measurement without strain-induced refraction errors
Solution Approach 2:
The patent changes the thermal expansion parameter relationship between the member and optical fiber, selecting materials where the member has a higher coefficient of thermal expansion. This parameter change ensures that during temperature variations, the member expands or contracts more than the optical fiber, preventing strain transmission to the fiber while maintaining thermal equilibrium for accurate measurement
2Measurement precision
If optical fiber is rigidly attached to the member, then strain can be transmitted for measurement, but non-temperature strain contaminates the measurement signal
Solution Approach 1:
The patent utilizes differential thermal expansion between the member and optical fiber to achieve selective strain transmission. By ensuring the member has a higher coefficient of thermal expansion, the design allows thermal strain to be transmitted to the optical fiber for measurement while preventing non-thermal mechanical strain from being transmitted, thus purifying the measurement signal
Solution Approach 2:
The patent employs a composite structure consisting of a member material with higher thermal expansion coefficient and an optical fiber with lower thermal expansion coefficient. This composite arrangement creates a mechanical coupling that is selective: it transmits thermal-induced strain while filtering out non-thermal strain, enabling accurate temperature measurement through strain correlation
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
This configuration enhances sensitivity and accuracy of temperature measurements by isolating the optical fiber from non-temperature related strain, ensuring that strain measurements accurately reflect temperature changes in the member.
Implementation Method 1
The member has a first coefficient of thermal expansion and the optical fiber has a second coefficient of thermal expansion and the first coefficient of thermal expansion is greater than the second coefficient of thermal expansion
Implementation Method 2
These systems rely on light being reflected or refracted responsive to temperature at points there along returning to an end of the optical fiber for determining temperature at the points
Data Source
AI summary
A temperature sensing arrangement includes a member having a first coefficient of thermal expansion, and an optical fiber having a second coefficient of thermal expansion. The optical fiber is strain transmissively mounted to the member. And the first coefficient of thermal expansion is greater than the second coefficient of thermal expansion such that strain measurable in the optical fiber is correlatable to temperature changes in the member.