Multi-core Fiber Temperature Sensing with Strain Correction
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Solution Overview
Problem
Distributed temperature systems face challenges in calibrated temperature measurements due to spectral-dependent loss changes caused by hydrogen and stress, particularly in downhole configurations, and require complex dual-ended configurations with U-tube setups, which increase installation costs and complexity, and are plagued by strain and drift issues in harsh environments.
Innovation Solution
A multi-core distributed temperature sensing optical fiber with at least two light guiding cores, where one core is a Raman DTS fiber and the other includes fiber Bragg gratings, allowing differential responses to temperature and strain changes, enabling spectral attenuation correction and self-calibration without the need for U-tube configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a dual-ended DTS configuration with U-tube and dual capillary lines is used to correct non-linear spectral attenuation, then measurement accuracy is improved, but device complexity and installation cost increase significantly
Solution Approach 1:
The patent combines the temperature sensing function and the spectral attenuation reference function into a single optical fiber by incorporating two cores: one core for Raman DTS temperature sensing and another core for spectral attenuation measurement. This merging eliminates the need for separate U-tube and dual capillary line configurations, reducing system complexity while maintaining measurement accuracy through differential measurement between the two cores.
Solution Approach 2:
The multi-core optical fiber serves multiple functions simultaneously: one core performs distributed temperature sensing while the other core measures spectral attenuation characteristics. This multi-functionality allows a single component to replace the traditional dual-ended configuration with U-tube and capillary lines, simplifying the overall system architecture.
2Measurement precision
If dual-ended DTS configuration with U-tube is deployed to correct spectral attenuation errors, then temperature measurement accuracy improves, but installation cost and complexity increase
Solution Approach 1:
The patent merges the temperature sensing and spectral reference measurements into a single multi-core fiber cable, eliminating the need for complex U-tube installations and dual capillary line deployments. This integration makes installation easier while maintaining the ability to correct spectral attenuation errors through differential measurement between cores.
3Measurement precision
If FBG-based DTS fiber is used for temperature sensing, then temperature measurement capability is provided, but strain cross-sensitivity causes measurement errors
Solution Approach 1:
The patent uses the second core as an intermediary reference that is insensitive to temperature changes (or has different temperature sensitivity). By comparing the Bragg wavelength shift in the FBG core with the Raman temperature measurement from the second core, the system can separate and eliminate strain-induced errors from the temperature measurement, correcting the strain cross-sensitivity problem.
4Measurement precision
If additional pressure sensors are deployed to compensate for temperature drift, then drift correction capability is provided, but system complexity and cost increase
Solution Approach 1:
The patent combines temperature sensing and drift reference measurements into the same multi-core fiber structure. The second core provides a reference measurement that is either insensitive to temperature or has known temperature dependence, allowing drift correction to be performed using the differential signal between cores, eliminating the need for separate additional sensors.
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 solution improves measurement accuracy by correcting for strain and drift, reducing installation complexity, and enabling accurate temperature measurements in harsh environments with reduced risk of fiber damage and increased fluid pressures.
Implementation Method 1
one core is a Raman DTS fiber
Implementation Method 2
the other includes fiber Bragg gratings
Data Source
AI summary
A multi-core distributed temperature sensing optical fiber is described, wherein the arrangement and construction of at least two cores provides a spectral attenuation corrected (e.g., corrected for hydrogen and/or stress on the fiber) temperature measurement.