The Rapid Inspection System Study Of The Imperfection For Large-scale Recreational Facilities Based On The New Digital Eddy Current Technology

ACFM electromagnetic detection technology widely used in major industry components defect detection,and the sensor array,diversification and detection of intelligent were shown in development trend with the application value of the upgrade and the increasingly mature computing technology.This paper was studied based on the array of AC detection system.Firstly,the Maxwell equations of the external air layer and the workpiece skin area were listed based on the theoretical basis of Maxwell's equation,and the magnetic induction and electric field intensity of the external air layer and the workpiece skin area were deduced.The magnetic field strength of the skin area was obtained,too.The mathematical model of the magnetic field distribution around the defect was established when the disturbance magnetic field existed.Firstly,the finite element model of AC detection system was established in finite element analysis software ANSYS and the single variables which affect the sensitivity of AC detection were simulated and analyzed.The results showed that either higher or lower of the excitation frequency were not conducive to improve the detection sensitivity.Not only was ensured the detection sensitivity ensures,but also the waste of resources was not caused choosing the appropriate excitation frequency.The detection sensitivity was been little influence on the fluctuation of the current size,so the range of power selection is wide.Compared with the eddy current detection technology,the influence of extraction on the AC detection technology was low;in the detection,the detection sensitivity of ferromagnetic materials was higher than non-ferromagnetic material.Secondly,the excitation coil and the detection coil in the AC detection system were designed.The rectangular coil was selected,and the current excitation method was adopted in the U-type MnZn ferrite core.The factors influencing the electromagnetic field distribution were analyzed.The results showed that the existence of magnetic core was beneficial to improve the strength of the magnetic field on the surface of the workpiece.The distribution of the induced current region on the surface of the workpiece was less affected by the width of the load coil,which increased with the length of the current carrying coil,but not linear.When the wire diameter was chosen to be smaller,it was prone to breakage during the winding process of the coil and damage during the working process,too.The thickness of the coil was large and the detection sensitivity was reduced when the diameter of the coil is larger.According to the design of the detection probe,the coil and the excitation coil were designed separately.The coil selection of the coil was the same as that of the excitation coil but the two coils were composed of two orthogonal coils.Respectively,the magnetic induction intensity were measured in the X and Z direction and was array distribution according to a certain way.Finally,the hardware circuit and software of the AC detection system were designed.In terms of the hardware circuit part,(1)the principle of the locking amplifier circuit and the circuit of each component were discussed.(2)The design of the ACFM hardware circuit was carried out based on the orthogonal locking amplifier.Signal processing including Detection signal processing and Labview-based cross-correlators were mainly designed for the software part.