Research On ACFM Detection Signal Processing Method And Its Application

The alternating current field measurement (ACFM) technique is a new kind of the electromagnetic non-destructive testing (NDT) technique. This method can size the lengh and depth of crack on structure surface, which has no effect with lift-off, property of metal material and boundary effect. Based on the relevant research contents of the project of ACFM defect detection intelligent visualization system development and industrial applications which is sponsored by Science and Technology Development Plan of Shandong Province, this paper conducts the systematic research to the ACFM detection signal's processing method and the application. The mathemactical model of alternating current field measurement is disscussed. Using the finite element numerical simulation method and the method of far-field element adopted to dispose a three-dimensionna unbounded field problem, rectangle and u-shaped incentive detector model and finite element model of ACFM is built up. Analysis of the distribution of perturbed magnetic is studied.The experiments verify the correctness of the simulation results,these can be used as the theoretic base to achieve quantitative measurement of surface cracks.The detecting coil size is designed to meet the "point" of the magnetic measurement,.Series probe is developed based on the rectangular, U-type magnetic core and a single, serialized array detecting coil.Based on the probe mentioned above,a kind of signal source and practicing circuit are designed.The testing system software based on virtual instrument is developed with application of object-oriented programming idea. Using digital filtering, wavelet analysis and other modern signal processing technology, combined with Labview and Matlab programming mixed method, to detect the weak signal de-noising processing and extract useful signal.Butterfly diagram used for qualitative to identify defects and to alarm,eliminating the effect of the speed of mobile sensors.Form the view of the quantitative point to give the length and depth of cracks.A testing system of the hardware experiment platform and the software analysis platform is built up,combined with the theory ,model and working Principle of alternating magnetic field technology.and based on sensors, signal detection,computer and signal processing. The workpiece crack is detected through many experiments carried out on and the test data are analyzed.