Fibre Optic Sensing Large Amplitude Strain Detection
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Solution Overview
Problem
Conventional distributed fibre optic sensors based on Rayleigh backscatter have limited dynamic range and are insensitive to large amplitude disturbances, leading to signal wrapping and uncertainty in measurements, as well as inability to detect slow acting static strains.
Innovation Solution
A distributed fibre optic sensor system that includes an interrogator and processor to detect a first characteristic signature - a variation in measurement signals affecting all channels simultaneously, using a polarisation modulator to apply controlled modulation to the sensing fibre, allowing identification of large amplitude strains and compensation for static strain changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional Rayleigh backscatter-based distributed fibre optic sensors are used, then dynamic vibration and strain events can be detected with relatively high sensitivity, but the dynamic range is limited and large amplitude disturbances cause signal wrapping leading to measurement uncertainty
Solution Approach 1:
The sensing system segments the measurement range by using two different sensing mechanisms: Rayleigh backscatter for small amplitude dynamic vibrations and polarisation-based sensing for large amplitude strains. The processor segments the analysis by detecting characteristic signatures that distinguish between these different regimes, allowing each mechanism to operate within its optimal range without causing measurement uncertainty
Solution Approach 2:
The system changes the sensing parameter from phase-based Rayleigh backscatter to polarisation state detection when large amplitude disturbances are detected. The processor monitors the measurement signals and switches between sensing modalities based on the amplitude level, thereby extending the dynamic range and preventing signal wrapping issues
2Speed
If conventional Rayleigh backscatter-based distributed fibre optic sensors are used, then dynamic strain monitoring is achieved, but information about slow acting static strain changes is not provided
Solution Approach 1:
The sensing system achieves multi-functionality by using the same optical fibre and interrogator to detect both dynamic vibrations (via Rayleigh backscatter) and static strain changes (via polarisation state). The processor analyzes measurement signals to detect characteristic signatures of static strain when applied through modulation controllers, allowing a single system to provide both dynamic and static strain information without requiring separate sensor systems
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
Enhances measurement accuracy by detecting large amplitude strains and static strain changes, improving the dynamic range and sensitivity of fibre optic sensing, enabling precise monitoring of disturbances and strain variations along the fibre optic cable.
Implementation Method 1
The interrogator may comprise a first polarisation modulator for varying a polarisation state of interrogating radiation output from the interrogator
Implementation Method 2
detects and analyses radiation which is Rayleigh backscattered from within the sensing fibre to provide sensing of disturbances
Data Source
Figure 1~2a
Figure 2b
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AI summary
This application relates to methods and apparatus for distributed fibre optic sensor and especially to Rayleigh based distributed fibre optic sensing that provides enhanced or additional information, such as information regarding large amplitude strains. A sensor has an interrogator (102) for interrogating a sensing optical fibre (101) to perform distributed acoustic sensing and provide a measurement signals from each of a plurality of channels corresponding to sensing portions of the sensing optical fibre. A processor (106, 107) analyses the measurement signals to detect a first characteristic signature (203), the first characteristic signature being a variation in the measurement signal from a plurality of channels that applies for a first channel and substantially all downstream channels and which occurs simultaneously on all such channels.