Eddy Current Testing Application In Railway Catenary's Defect

Eddy current Testing is one of five normal nondestructive testing methods. In comparison to the others, it can test in higher speed and non-contact, as well as, is sensible to the defect on the surface or near the surface, especially for conductors with thin size. Considering problem of catenary rupture, the eddy current testing method for catenary's defect is researched in the paper,Firstly, several methods of testing catenary's defect are put forward and compared. Considering of configuration and using characteristic of catenary, we get the result that the catenary's defect can be only detected by portable testing instrument. Secondly, the principle of eddy current test is introduced. Based on electromagnetic field theory, some important formulas are deduced. Impedance analytical method is presented, through which we analyze some factors that alter testing coil impedance's value. Then, characteristic frequency of laid test coil is calculated, it is important to select the test frequency. Thirdly, the eddy current testing system is simplified as a model of column coil straight facing to infinite flat conduct, then the model is simulated by ANSYS software that is based on FEM, and some simulation's conclusions are given, which is good guidance to make the sensor. Fourthly, the magnetic field on coil axes is calculated when coil size is changed, which guide design of probe coil. Finally the sensor's all parameters are designed.As for hardware design, in signal converter, in order to improve sensitivity, the parameter of signal converter is gotten through math illation. The sensor's signal is decomposed to two signals by circuit of 90 degree move-phase and two circuits of phase-sensitive detecting rectification. The hardware of system with AT89C51 microprocessor is designed to satisfy the design demand.As for software design, software is modularized, and every module is designed, then each flow chart is given. The BP neural network is used to fit data, through which quantitative analysis of defect signal can be obtained.