Distributed Fibre Optic Sensing With Gauge Length Drift Compensation
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Solution Overview
Problem
Coherent Rayleigh based distributed fibre optic sensors suffer from low frequency drift due to changes in operating conditions over time, which can affect the accuracy of measurements for low frequency signals such as strains or temperature changes.
Innovation Solution
The apparatus and method involve modulating the wavelength of coherent interrogating optical radiation between successive interrogations according to a modulation characteristic, allowing for the identification and compensation of variations in effective gauge length by determining the amplitude of an induced signal component, which is used to correct measurement signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If coherent Rayleigh based distributed fibre optic sensors are used to provide quantitative data about stimuli, then measurement capability is improved, but low frequency drift occurs due to changes in operating conditions over time
Solution Approach 1:
The patent applies periodic action by modulating the wavelength of the coherent interrogating optical radiation according to a modulation characteristic between successive interrogations. This periodic wavelength modulation creates an induced signal component that can be identified and used to determine variations in effective gauge length, thereby compensating for low frequency drift and maintaining measurement stability over time.
Solution Approach 2:
The patent implements parameter changes by varying the wavelength parameter of the interrogating optical radiation. By modulating the wavelength between successive interrogations, the system creates a detectable induced signal that provides information about gauge length variations, enabling compensation for drift while maintaining measurement precision.
2Measurement precision
If the wavelength of coherent interrogating optical radiation is modulated to compensate for gauge length variations, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The patent employs feedback by using the induced signal component generated through wavelength modulation to determine variations in effective gauge length. This information is then fed back to compensate for gauge length variations in the measurement process, creating a closed-loop system that improves accuracy without requiring complex additional hardware.
Solution Approach 2:
The system performs self-service by using its own modulated wavelength signal to generate the induced signal component that reveals gauge length variations. The same interrogating radiation that probes the fibre also provides the reference signal needed for compensation, eliminating the need for separate reference measurements or additional complex subsystems.
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 improves the accuracy of measurements by compensating for variations in gauge length, reducing errors in both high and low frequency signals, and maintaining consistent measurement precision over time.
Implementation Method 1
detecting a backscatter signal comprising optical radiation which is Rayleigh backscattered from within the sensing fibre in response to an interrogation
Implementation Method 2
The apparatus is operable to controllably modulate a wavelength of the coherent interrogating optical radiation to vary between successive interrogations according to a modulation characteristic
Implementation Method 3
determine, for each of a plurality of channels of the sensing optical fibre, a measurement signal indicative of a phase modulation of the detected backscatter signal
Data Source
AI summary
This application relates to methods and apparatus for distributed fibre optic sensing. A sensing apparatus includes an optical arrangement which repeatedly interrogates a sensing optical fibre by launching coherent interrogating optical radiation into the sensing optical fibre. A detector detects Rayleigh backscatter from within the sensing fibre and a processor processes the detected backscatter to determine a measurement signal for each of a plurality of channels of the sensing optical fibre. The wavelength of the coherent interrogating optical radiation is modulated so as to vary between successive interrogations according to a modulation characteristic. The processor is operable to identify, for a given channel, an induced signal component corresponding to the modulation characteristic and determine an amplitude of the induced signal component so as to determine a compensation to be applied to the measurement signal for that channel to compensate for any variation in effective gauge length.