| The occurrence of vibration phenomena in machinery manufacturing,aerospace and other fields is often unavoidable.Many mechanical failures and engineering accidents are accompanied by abnormal vibrations.Therefore,it is of great significance to detect the vibration phenomenon in advance and find out the vibration abnormality in engineering monitoring and equipment maintenance.With the continuous development of society,various engineering applications,mechanical flaw detection,and monitoring of natural phenomena have imposed higher requirements on frequency of vibration detection,demodulation accuracy,and sensor multiplexing capacity.In this paper,an ultra-weak reflection-based all-in-one fiber grating is used to build the sensor network,and an optical path is constructed based on the optical time-domain reflection technique.Through the research of demodulation principle,demodulation algorithm and experimental verification,a quasi-distributed vibration sensing technology with high speed,high capacity and high precision is realized.The main research contents of this article are as follows:(1)The grating vibration sensor demodulation system based on pulse modulation Mach–Zehnder interferometer is studied.The system consists of a light source modulation unit,a sensing unit,and a signal processing unit.The light source modulation unit uses a pulse-driven semiconductor optical amplifier to modulate the broadband light source to generate a pulsed light with a frequency of 10 kHz and a pulse width of 20 ns.The sensing unit is composed of a circulator and an isomorphous weak grating array to increase the system multiplexing capacity;The processing unit is composed of a Mach-Zehnder interferometer and three high-speed,high-gain avalanche diodes.The interferometer arm of the fixed interferometer is long.The original vibration measurement through the interferometer arm is replaced by a sensor grating for vibration detection.Sensing has become point-based sensing,which enables quasi-distributed measurements.The reflected light from the sensor grating undergoes photoelectric conversion by an avalanche diode after interferometer interference,and finally data processing is performed..(2)The demodulation principle of the demodulation system and the causes of pulse jitter are analyzed and solutions are proposed.The expression of vibration information is deduced by the formula,and at the same time,a delay fiber is added before the sensor grating to reduce the pulse jitter and improve the system demodulation accuracy.(3)The demodulation algorithm of the grating vibration sensor demodulation system has been studied and optimized to quickly obtain the position information and vibration information of each grating in the weak grating array.By processing the 3-way data,it is possible to avoid the occurrence of a homodyne when the phase is an integer multiple of 0 or ?.The Fourier transform of the 3-way data overcomes the interference of external factors such as temperature changes and extracts useful vibrations signal.(4)The experimental platform is built to measure the stability of the experiment,and the vibration demodulation capability and stability of the system's identical and weak grating array are verified.The measurement results show that the demodulation accuracy of the sensor system reaches 2pm under static experimental conditions.The system performs distributed experiments and completes the vibration demodulation of 100 identical 3M weak gratings with a reflectivity of only 0.1% in series on a single fiber,realizing a dynamic demodulation accuracy of 90 pm,and finally the aviation hydraulic hose.The vibration detection is performed.Finally,the vibration detection of aviation hydraulic tubing is carried out,and the reliability and practicability of the system are verified by vibration detection under normal condition and fault condition. |
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