Research On Applying Optical Fiber Grating In Track Monitoring

The railway track is the most basic facility of railway operation in the railway system.A mass of information can be obtained by track monitoring.However,the hash environment around the railway track can affect the reliability of track monitoring equipments,malfunctions,such as bad shunting,red belt,incorrect axles counting et al,may occur and influence the efficiency and security railway operation. Fiber grating has the advantages of simple method of making,high reliability,small size,immune of electromagnetic interference,flexibility,and it is apt to integrate with optical fiber.In addition to the matured encapsulation technology,fiber grating sensor can provide stable and reliable detecting information under harsh conditions.The above-mentioned points are the basis of the Research on applying optical optical fiber grating in track monitoring.The research project presents two sensing detecting solutions based on FBG(Fiber Bragg Grating) and FCG(Chirped Fiber Bragg Grating).This paper illustrates the following research contents in detail:the sensing principles and related experiments, the optimal design for positing sensors,the overall design and the implementation of software and hardware,data acquisition and processing.The related research result is presented in this paper.The main research contents and conclusions are as follow:Ⅰ.According to the Coupled-mode Theory and the method of Transmission Matrix, the spectral characteristics of FBG and FCG are analyzed by using the method of numerical simulation.The results show that:in the sensing field,FBG is suit for wavelength detecting,it can provide the information of absolutely wavelength shift; FCG is suit for light intensity detecting,it can realize low-cost dynamic measurement.Ⅱ.The strain sensing characteristics of FBG ang FCG are analysed,and relatied experiments have done to verify the characteristics.The results show that:Both sensing output of FBG and FCG have good linear relations highly sensitivity with strain.The axial direction sensitivity of FBG,which central wavelength is about 1300nm,is 1.0344 pm/με.The sensitivity of spectrum shfting with strain is about 1 pm/μεalso.Ⅲ.This paper presents an approach to analyze track strain field.This field is decomposed into three vector fields(x,y and z axis-direction).FEA(Finite Element Analysis) is used to analyze characteristics of the three fields under different operational conditions.The result of FEA shows that the small place at the central bottom and along the centerline of the track meets the conditions.Experiment shows that if the FBG sensor is fixed at right place,the wavelength shift of FBG sensors can be up to 150pm,when a multiple unit train past the detecting point at the speed of 140km/h.Ⅳ.According to the characteristics of FBG sensor and FCG sensor,hardwear solutions are designed individually for them. Ⅴ.The cases of interaction between software system and paticipants is found out. The multithreading technique is adopted to ensure the stable operation and efficiency.Ⅵ.According to contrast and analysis on derivative method,Gauss fitting method, cycle counting method et al,a real time algorithm for peak finding is presented in this paper.The function of the algorithm is realized in the main calculation thread and achieves good reality and real time effect.