Research Of Technology Used In New And Portable Electromagnetic Detectors Project

There are many kinds of workpiece crack detectors based on electromagnetic principles. Magnetic particle inspection is a very important way among them. Normally, it is used to find surface cracks in workpiece. And it can be used in many industrial areas, such as aerospace, weapons manufacturing, shipbuilding, railways, construction, electricity, chemicals, boiler and pressure vessel industry, pressure piping industry, etc.We analyze the basic principle and the shortages of magnetic particle inspection. Then we contrast several magnetic flux leakage detection methods, and we finally designed a new workpiece crack detector called New Portable Electromagnetic Detection System which is based the traditional magnetic particle inspection. The system overcome lots of shortcomings of magnetic particle inspection. It has great improvement in terms of the way of magnetization and the workpiece crack indications.This system still use the cross magnetic yoke to generate a rotating magnetic field. In this system the cross magnetic yoke are powered by the square-wave current which replace the AC sine wave in magnetic particle inspection. This way can not only keep the good effect of magnetization, but also it can largely improve the safety and the portability of the system. The magnetic field generation module mainly include three sub-modules, the master chip module, the full-bridge inverter module and the power detection module. We choose ATmega48 PA, one of AVR microcontrollers, as the control core of master chip module. The ATmega48 PA is mainly used to control the full-bridge inverter module to produce two square-wave currents, which have a fixed phase difference. The power detection module can monitor the change of battery voltage. It can help the magnetic field generation module generate a stable magnetic field.The main function of the magnetic field detection module is to detect the cracks in the surface of workpiece and show the testing result in screen, which replace the role of magnetic powder in magnetic particle inspection. The magnetic field detection module has four sub-modules, the hall sensors array, the data acquisition module, the data analysis module and the image processing module. Firstly, the hall sensors array tests the magnetic flux leakage of workpiece surface. Then it passes the corresponding data to the data acquisition module. The data acquisition module reorder the data, process them with wavelet de-noising and remove power frequency interference of the data with independent variable analysis techniques. After that it passes the data to the data analysis module. This module analyses the data with PNN algorithm, determines the locations of magnetic flux leakage and divides ratings of magnetic flux leakage. Finally, it passes the result to the image processing module. The image processing module illume the locations of magnetic flux leakage. These luminous points can reflect the cracks in workpiece surface and near-surface. This system reduces the requirement of workpiece surface flatness, which is very necessary in magnetic particle inspection. And this system is much greener, cleaner and safer than the traditional magnetic particle inspection.In the last part of this paper we illuminate the testing result of the magnetic field generation module and the MATLAB simulation result of several key algorithms in magnetic field detection module.