Dual-Laser Attenuation Correction for Distributed Temperature Sensors
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Solution Overview
Problem
Distributed temperature sensors using Raman scattering face inaccuracies and drift due to dynamically varying attenuation, particularly in downhole applications where mechanical stress and chemical degradation of optical fibers occur, leading to unreliable temperature measurements.
Innovation Solution
Employing a dual-laser system where one laser source collects Stokes and anti-Stokes Raman scattering and another collects Rayleigh scattering, with specific wavelengths to cancel out attenuation effects, allowing for accurate temperature determination by using ratios of these signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single laser source is used to measure temperature via Raman scattering, then the device complexity is reduced, but measurement precision deteriorates due to attenuation effects
Solution Approach 1:
The patent divides the temperature measurement process into two separate measurement paths: one using Stokes Raman scattering and another using anti-Stokes Raman scattering. Each path uses a dedicated laser source optimized for its specific wavelength requirements. This segmentation allows independent optimization of each measurement channel while enabling mathematical combination of results to eliminate attenuation effects.
Solution Approach 2:
The patent introduces Rayleigh scattering as an intermediary measurement that provides information about attenuation characteristics. By measuring Rayleigh scattering alongside Raman scattering, the system can calculate attenuation coefficients and use these to correct the temperature measurements, effectively using Rayleigh scattering as a mediator between the light source and the temperature determination.
2Ease of operation
If Stokes or anti-Stokes Raman scattering alone is used for temperature measurement, then the measurement process is simplified, but reliability deteriorates due to attenuation variance
Solution Approach 1:
The patent merges two previously separate measurement approaches (Stokes Raman and anti-Stokes Raman) into a unified temperature measurement system. By combining measurements from both scattering types and using their ratio, the system achieves temperature determination that is independent of attenuation effects, thereby improving reliability while maintaining operational feasibility.
Solution Approach 2:
The system continuously monitors attenuation characteristics through Rayleigh scattering measurements and uses this feedback to correct temperature calculations in real-time. The attenuation coefficients derived from Rayleigh scattering are fed back into the temperature calculation algorithm, allowing dynamic compensation for changing attenuation conditions throughout the measurement process.
3Measurement precision
If multiple laser sources with different wavelengths are used, then attenuation effects are canceled out, but device complexity increases
Solution Approach 1:
The patent designs the dual-laser system where each laser source is not only responsible for its primary Raman scattering measurement but also contributes to Rayleigh scattering measurements. This multi-functionality allows the system to extract multiple types of information (temperature, attenuation) from each laser source, reducing the need for additional dedicated components and mitigating the complexity increase.
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 approach eliminates inaccuracy in temperature measurements by canceling out attenuation terms, providing a robust and precise temperature profile along optical fibers, even in challenging environments like downhole applications.
Implementation Method 1
When light is transmitted in an optical fiber, the photons may be elastically scattered (Rayleigh scattering)
Implementation Method 2
In Raman scattering, the scattered photon may have less energy than the incident photon (Stokes Raman scattering) due to absorption of energy by the optical fiber
Implementation Method 3
the scattered photon may have more energy than the incident photon (anti-Stokes Raman scattering) due to loss of energy by the optical fiber
Data Source
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AI summary
A distributed temperature sensor, a method of determining temperature, and a processing system to compute temperature are described. The sensor includes an optical fiber disposed in an area where temperature is to be measured, a primary light source to inject light into the optical fiber, and a secondary light source to inject light into the optical fiber. The sensor additionally includes a photo detector to detect backscatter light energy from the optical fiber the backscatter light energy including Stokes Raman scatter or anti-Stokes Raman scatter and primary Rayleigh scatter resulting from the primary light source and secondary Rayleigh scatter resulting from the secondary light source, and a processor to determine temperature based on a ratio of the Stokes Raman scatter or the anti-Stokes Raman scatter and a combination of the primary Rayleigh scatter and the secondary Rayleigh scatter.