Design Of Railway Signal Cable Fault Detectors

The railway signal cable is the carrier of railway signal transmission,and the cable fault detector is one of the basic guarantees of safe train operation.In this thesis,the problems existing in the process of off-line and on-line cable detection were studied,and the off-line and on-line detectors for railway signal cable faults were designed based on the Time Domain Reflectometry(TDR)and Spread Spectrum Time Domain Reflectometry(SSTDR),which can detect faults of railway signal cables in different environments and are of great significance for the transport safety of railway systems.In this thesis,the equivalent circuit model of the cable was established with the structure and characteristics of the transmission line,and the signal attenuation phenomenon,traveling wave transmission speed,traveling wave reflection and transmission phenomenon were studied.A conditioning circuit to improve the transmit signal strength was designed for the problem of large signal attenuation during TDR detection,and a system architecture with FPGA as the core was designed based on the Time Domain Reflectometry.The hardware circuits and PCB were designed according to the system architecture,the TDR fault detection programs were written,and the cable fault off-line detector was developed.By building an experimental platform for cable fault off-line detector,the instrument debugging and experimental testing were conducted.The experimental results show that the cable fault off-line detector can accurately detect faults in railway signal cables within a certain range.In this thesis,the principle of SSTDR fault detection was described through the study of spread spectrum communication principle,signal correlation analysis and time delay estimation algorithm.The selection of pseudo-random sequence,carrier modulation method and carrier modulation ratio was carried out by correlation analysis of test signal through MATLAB software.The algorithm of signal correlation analysis using Discrete Fourier Transform(DFT)was designed for the problem of large amount of operations during SSTDR fault detection,and the system architecture with FPGA as the core was designed based on the Spread Spectrum Time Domain Reflectometry.According to the system architecture,hardware resources were selected and SSTDR fault detection program was written to design the cable fault on-line detector.Through the experimental test,it is known that the cable fault online detector can accurately detect the fault type and fault distance of the cable.At the same time,the correlation analysis of the collected signals was carried out by MATLAB software.The results of the signal correlation waveform comparison showed that the waveform obtained by signal correlation operation through FPGA and the waveform obtained by correlation algorithm of MATLAB software were basically consistent.The experiment verifies the feasibility of using DFT for signal correlation analysis.There are 72 figures,3 tables,and 66 references.