Distributed Optical Fiber Temperature And Strain Sensing System Based On Raman And Rayleigh Scattering

The development of optical fiber technology and optical time-domain reflection technology has laid the foundation of distributed optical fiber sensing technology.Distributed optical fiber sensing technology is particularly prominent in the long-distance measurement of temperature,strain and vibration.Due to the fixed point-sensing characteristics of the traditional electronic sensing devices,there are blind spots in the measurement that is also susceptible to electromagnetic interference.The distributed optical fiber sensing system has the advantages of light weight,small size,long distance and strong anti-interference.It has a very wide range of practical applications in the power plant fire alarm,bridge and dam defect detection and mine safety monitoring.Nowadays,the distributed fiber-optic temperature and strain sensing measurement mostly adopts the Brillouin scattering effect as the main technology.However,the Brillouin frequency shift measured in this solution is sensitive to temperature and strain,which leads to the cross-sensitivity phenomenon of the fiber temperature and strain measurement.To one certain degree,this also limits the measurement sensitivity.Usually,a temperature or strain compensation device is required to eliminate this phenomenon.In order to simplify the system structure and improve the measurement accuracy,this paper proposes a fiber-optic sensing system based on Raman and Rayleigh scattering.Based on this hybrid scheme,simultaneous measurement of fiber temperature and strain is achieved.Experiments show that the system has the advantages of simple principle,compact structure,and low cost.After using the RBF neural network model to replace the traditional data processing method,the measurement error can be reduced and the temperature measurement accuracy can be improved.The work is briefly introduced below.First of all,this article describes the spatial positioning principle of optical timedomain reflection technology,analyzes the measurement principles of Rayleigh scattering,Brillouin scattering and Raman scattering,and compares the advantages and disadvantages of these three scattering in temperature,strain and vibration measurement.Finally,based on this system,a mixed scheme of Rayleigh and Raman scattering was selected to measure temperature and strain.Then the design scheme of distributed optical fiber temperature and strain sensing system is introduced,and the performance parameters of each device and device are described in detail,including 1550 nm center wavelength pulse laser,optical circulator,three-bandwidth wavelength division multiplexer,photoelectric detection Device,data acquisition card,multi-mode sensing optical fiber,temperature and strain modulation device,etc.The related codes and software interface of A/D conversion realized by data acquisition card are briefly introduced.Subsequently,the optimization scheme of the system in signal processing is introduced,including cumulative averaging algorithm,dispersion compensation shift algorithm and so on.Finally,the RBF(Radial Basis Function)neural network model is used in combination to calculate the temperature and compared with the traditional twoway demodulation algorithm.Experiments verify that after using the RBF neural network model to replace the traditional data processing method,it can reduce the measurement error and improve the temperature measurement accuracy.Finally,the effectiveness of the system designed in this paper in distributed optical fiber temperature and strain sensing measurement is verified.The temperature measurement accuracy is about ± 0.25?,the strain measurement accuracy is about ± 0.1mm,the system spatial resolution is 1m,and the optical fiber sensing distance is 5km.This system has the advantages of simple principle,compact structure and low cost.It has certain reference and use value as a low-cost distributed optical fiber sensing system for the simultaneous temperature and strain measurement.