OFDR Vibration Measurement Frequency Modulation Compensation
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Solution Overview
Problem
Existing vibration distribution measurement systems using optical frequency domain reflectometry (OFDR) face challenges in accurately measuring the distribution of dynamic distortion due to frequency modulation, which affects the measurement results and cannot clearly determine the time waveform of dynamic distortion.
Innovation Solution
A vibration distribution measurement system that includes a frequency sweep light source, an optical splitter, an optical mixer, and an analysis unit to analyze the beat signal, estimating a distance offset using cross-correlation between the distribution waveform and a reference waveform, and correcting the distance to compensate for frequency modulation effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If frequency sweep light is used for vibration distribution measurement, then measurement capability is provided, but frequency modulation causes distance offset and reduces measurement precision
Solution Approach 1:
The patent converts the harmful frequency modulation effect into a useful measurement signal. By detecting the spectral shift caused by frequency modulation and using cross-correlation analysis, the system transforms the distance offset error into information about vibration amplitude and phase, thereby measuring vibration distribution while compensating for the frequency modulation effect.
Solution Approach 2:
The patent applies asymmetric measurement by using different reference frequencies for up-sweep and down-sweep frequency modulation. This asymmetric approach allows the system to distinguish between static distance offset and dynamic vibration signals, enabling accurate vibration measurement while compensating for frequency modulation effects.
2Productivity
If measurement repetition frequency is increased to capture dynamic distortion, then time waveform measurement capability is improved, but frequency modulation effects become more significant and reduce accuracy
Solution Approach 1:
The patent implements feedback by continuously monitoring the spectral shift amount and using cross-correlation analysis to determine both distance offset and vibration characteristics. The system uses the measured vibration information to compensate for frequency modulation effects in real-time, maintaining measurement accuracy even at high repetition frequencies.
Solution Approach 2:
The patent performs preliminary measurement of the spectral shift amount before analyzing vibration characteristics. By first determining the distance offset caused by frequency modulation and compensating for it, the system establishes an accurate reference frame for subsequent vibration amplitude and phase measurements.
3Loss of information
If spectral shift amount is used to measure distance, then position information is obtained, but frequency modulation causes spectral shift that mimics distance change and reduces measurement accuracy
Solution Approach 1:
The patent segments the spectral shift analysis into two distinct components: distance offset determination and vibration characteristic extraction. By using cross-correlation analysis to separately identify the spectral shift caused by frequency modulation from the spectral shift caused by vibration, the system recovers accurate position information while measuring vibration distribution.
Solution Approach 2:
The patent transitions from static distance measurement to dynamic vibration measurement by analyzing temporal changes in spectral shift amount. The system uses the time-varying characteristics of spectral shift to distinguish between static distance offset and dynamic vibration signals, enabling accurate measurement of both position and vibration characteristics.
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
Enables accurate measurement of the time waveform of dynamic distortion by compensating for distance offsets caused by frequency modulation, improving measurement accuracy and clarity of vibration distribution.
Implementation Method 1
a frequency sweep light source configured to output frequency sweep light
Implementation Method 2
an optical splitter configured to split the frequency sweep light into probe light and local light
Implementation Method 3
an optical mixer configured to mix backscattered light from the sensing fiber as signal light with the local light
Implementation Method 4
a beat signal obtained from output light of the optical mixer
Implementation Method 5
estimating a distance offset from a measurement result obtained from a distribution waveform of the beat signal
Implementation Method 6
The Fourier transform (the square of an absolute value) of the distribution waveform of the distortion sensor interval indicates an optical frequency spectrum
Implementation Method 7
distributed dynamic strain measurement using optical frequency-domain reflectometry
Implementation Method 8
the backscattered light of the sensing fiber to be frequency-modulated
Data Source
AI summary
A vibration distribution measurement system includes a frequency sweep light source that outputs frequency sweep light, an optical splitter that splits the frequency sweep light into probe light and local light, an optical mixer that mixes backscattered light from the sensing fiber as signal light with the local light, the backscattered light being obtained by causing the probe light to be incident on the sensing fiber, and an analysis unit that analyzes a beat signal obtained from output light of the optical mixer. The analysis unit estimates a distance offset from a measurement result obtained by measuring a distribution waveform of the signal light by measuring the beat signal at a measurement time sufficiently shorter than a cycle of the vibration of the sensing fiber, and measures a distribution of a vibration at any position by compensating for the distance offset.