Research Of Rail Flaw Detection System Based On Electromagnetic Acoustic Technique

It is inevitable for the rails get severely damaged after long-term work, which will strongly threaten the safety of the railway. For the present, ordinary flaw detection methods, such as magnetic flux leakage, plused eddy current, alternating current field measurement, can only be used for the rail surface flaw detection. Though piezoelectricity ultrasonic transducer can detect the internal falws of the rails, it needs couplant, as a result, there are blind areas on the surface. The electromagnetic acoustic transducer is independent of the coupling material, so it is quite convenient for it to excitated all kinds of ultrasonic waves to detect the flaws both on the surface and in the inner space with high efficiency and speed. Therefore, it is of great theoretical importance and practical value to research of rail flaw detection system based on electromagnetic acoustic technique.The electromagnetic ultrasonic experiment platform was designed. The transmintting and receiving device was improved, which effectively solved the power source and interference problem and was able to transmit and receive all kinds of ultrasonic waves. The eight-channel data acquisition card based on USB technique was achieved, which can sample eight-channel echo signals simultaneously and supply conditions for multi-transducer rail flaw detection. The upper software was designed based on LabWindows CVI. It can neatly change the frequency, the pluse number, etc, which was convenient to carry out experiments and study digital signal processing algorithm.The digital signal processing algorithm was designed, which was applied in the rail flaw detection system. In order to enhance the reliability of the ultrasonic echo, four-time accumulated average algorithm was used for pre-processing. Through the compare of calculation quantity of FIR and IIR, the IIR ellipse filter was used as basic filter unit. The flaw echo signal can be effectively extracted with cross-correlation detection, self-correlation method and wavelet algorithm. After compare the processing quality and the calculation quantity, the self-correlation method was finally chosen.The electromagnetic ultrasonic rail flaw system was designed. The mechanical structure was designed to make the system work reliably on the rails. The signals can be well processed and displayed with the help of the signal processing circuit based on DSP and ARM. The experiment results proved that the system can achieve the rail flaw detection successfully.