The Railway Links Up Grounding Wire Theft Deterrent Research Based On OTDR

As comprehensive ground wire which include safe ground,anti-lighting ground and frame ground,railway through grounding wires is laid in each line widely.However,As a result of railway line located at remote areas,the environment of line is quite complicated,it is stolen frequently.If the ground line were stolen,the signal equipment which connected to ground wire is not grounded,will be seriously damage devices and cause casualties,threatening railway traffic and person safety.Comparing to other sensing mode,optical fiber sensing has the advantages of high sensitivity,good reliability and strong electromagnetic interference resistance,especially in remote sensing applications.To solve the above problem,in this paper,an optical fiber sensing system based on the principle optical time domain reflection(OTDR)is proposed,which can realize active and real-time monitoring of railway through ground wire.It can able to quickly alert and monitor the location of the accident in a short time when the wire was cutting,actualize automation and real-time monitoring,to effectively combat theft arrest activists,reduce the economic losses caused by the wire theft.Main works in this paper contain:Firstly,the paper briefly introduces the characteristics and advantages of optical fiber sensing technology based on currents anti-theft system,on this basis,it proposed the design of anti-theft system of railway through ground wire,and introduce the detail of OTDR working principle,performance indicators and other parameters.Secondly,the dynamic range and range resolution of OTDR are the two most important parameters,which determine the detection range and positioning accuracy of the system.The increase of dynamic range can be achieved by enlarge pulse width,but it will result in the decrease of range resolution.Traditionally,OTDR launch the single pulse as the detection signal of the fiber,with the cumulative average method to improve the dynamic range,the method proposed in this paper using the correlation operation,the use of pseudo random sequence as the probe signal and selected the CCPONS code as the input signal which has better performance in pseudo random sequences.Then,by introducing the characteristics of Fourier transform,short-time Fourier transform and wavelet transform,explained the advantages of wavelet transform in signal processing.According to the features of OTDR,it selected Harr wavelet as wavelet basis function of the system,besides,proposing the combination of wavelet transform and slope method to located reflection events and non-reflection event respectively.Finally,designed the signal generation part and signal collection part of the ground line anti-theft system which based on OTDR,and shows the simulation result of the system under MATLAB respectively,the results shows that when using 128 bits CCPONS code,the energy of system signal increase 25dB,and SNR increase increased 8dB without losing range resolution.Afterwards the paper uses wavelet transform to analyses the signal of the system includes events those occurred in railway systems,judges the various events and location of events respectively,verified the feasibility of the system.