| In recent years,a variety of heat resistance,high temperature resistance,corrosion resistance,high hardness,strong electrical conductivity of the alloy and metal material application more and more,but in the use of metal materials,will be accompanied by a series of problems such as metal eligibility,safety.Metal thickness,as one of the important indexes to measure metal eligibility and safety,has important research significance.Compared with other detection technologies,eddy current testing has many advantages,such as fast detection speed,low detection environment requirements,elimination of interference factors,no coupling agent and high sensitivity for metal surface and near-surface defect detection.Therefore,Eddy current detection is widely used in metal thickness detection.Frequency sweep eddy current detection technology is a method to collect eddy current data in a specific frequency band to detect conductive specimens.Its wide frequency range can not only make the optimal excitation frequency easy to determine,but also ensure the continuity of detection.Compared with the traditional method of using impedance analyzer for sweep eddy current detection,the integrated sweep eddy current detection system is low in cost,easy to carry and has higher sensitivity.Therefore,it is especially important to develop a sweep eddy current testing system.Firstly,the finite element modeling of eddy current thickness measurement is established.According to the boundary conditions of Maxwell's equations and time-varying electromagnetic field,the vector magnetic position and the impedance variation of the detection coil are solved.The correctness of the model is verified by comparison with the analytical model.The effects of conductivity,lift and permeability on eddy current modeling are simulated,which provides a theoretical basis for the thickness measurement of ferromagnetic plates.Secondly,on the basis of the eddy current finite element modeling of the thickness of the ferromagnetic metal detection model is established to verify the feasibility of inductance to detect the thickness of the imaginary part of the analysis of the lift-off of the ferromagnetic plate conductivity and thickness of the influence of the peak and the peak frequency,and puts forward the ferromagnetic plate according to the analysis results under different circumstances the best thickness method,and respectively will peak and peak frequency as characteristic parameter,thickness is analyzed theoretically determine the thickness of the two range and usability.Based on the intersections of different conductiveness-reactance curves found in the influence curve of permeability on coil reactance in chapter 2,a tentative idea of measuring the thickness of ferromagnetic plates by shielding permeability is proposed.Thirdly,the sweep eddy current thickness measuring system is designed.The hardware circuit and software design are expounded;The influence of sampling period and number of sampling points on the detection is simulated,and the optimal sampling scheme with 1024 sampling points and 4 sampling periods is determined.The error is reduced and the accuracy and reliability of the thickness measuring system are greatly improved.Finally,The performance of the sweeping eddy current thickness measuring system is evaluated,the blank correction is made by using the difference principle,and the error is analyzed.The correctness of the thickness measurement theory of non-ferromagnetic plate in chapter 3 is verified by the thickness measurement experiment.This paper optimizes the thickness measurement method of non-ferromagnetic plates and develops a sweeping eddy current thickness measurement system.The sensitivity,accuracy and reliability of the system are improved from the aspects of eigenvalue selection,hardware optimization,detection optimization and difference. |
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