| Coal mine industry is the most important basic energy industry in China,and plays a very important role in China's economic and social development.Coal mine safety is an important prerequisite for the sustainable and stable development of coal industry.At present,the situation of coal mine safety in China is grim,and the frequent occurrence of safety accidents has caused serious economic losses,casualties and adverse social impact.Traditional coal mine safety monitoring methods have various shortcomings in practical application.In recent years,with the breakthrough progress of electronic technology and equipment,especially the improvement of computer data processing ability,microseismic monitoring technology has been developed rapidly.Microseismic monitoring technology realizes the monitoring and early warning of coal mine disasters by monitoring the micro-fracture phenomena of coal and rock.At present,the front-end sensors of most microseismic monitoring systems at home and abroad are electrical acceleration sensors.There are serious potential safety hazards in the use electrical acceleration sensors in underground gas environment.Therefore,it is important to develop intrinsically safe optical fiber microseismic monitoring instrument for coal and gas outburst mine safety monitoring and early warning based on all-fiber acceleration sensing technology.This paper studies the phase generated carrier(PGC)modulation technology and noise reduction technology suitable for all-fiber microseismic monitoring system,and carries out a 1*4 time division multiplexing experiment and verifies the feasibility of time division multiplexing.Conducts field tests in the No.4 tunnel of Hanjiang to Weihe River Project of China Railway Group,the data obtained are analyzed and processed in three aspects:time,space and strength.The concrete results are as follows:1.A PGC digital demodulation system is designed based on LabVIEW.Then,the reference clock of the carrier signal source is used to solve the phase drift problem when the data acquisition card collects the signal.Aiming at the carrier phase delay of the PGC demodulation,the method of extracting the single frequency signal is adopted to compensate the inherent phase delay in the demodulation system by finding the extremum to determine the carrier phase.2.The principle of two-way balanced noise reduction methods and reference interferometer PGC modulation method are elaborated in detail.Firstly,the system intensity noise decreases about 10 dB in the frequency band above 200 Hz by using the two-way balanced noise reduction methods.Then,the reference interferometer PGC modulation scheme is simulated and analyzed and tested experimentally.At 30 Hz of low frequency signal,the system phase noise decreases most.In the frequency band above 100 Hz,the phase noise suppression effect decreases with the increase of frequency.Experiments show that the low frequency noise of the system from 20 Hz to 200 Hz is effectively controlled.3.The cost and technical difficulty of various multiplexing schemes are evaluated comprehensively,multiplexing schemes of time division multiplexing and space division multiplexing is determined.A 1*4 time division multiplexing optical path is constructed.The demultiplexing program is designed based on LABVIEW.The minimum detectable acceleration is 70?g after PGC demodulation of the time division multiplexing optical signal,which verifies the feasibility of the time division multiplexing scheme.4.The basement simulation field experiment of 8-channel all-fiber microseismic monitoring system and the outfield experiment of No.4 tunnel of China Railway Group's Hanji-Weihe Project are carried out.The arrival time of microseismic event waveform was determined,and the location algorithm of the seismic source and the calculation method of energy magnitude are verified. |
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