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The Development of Eddy Current Testing System and the Research of Classification Methods about Inversion Problem

Author: HeGuangLin
Tutor: ZhouZeKui；HuangPingJie
School: Zhejiang University
Course: Detection Technology and Automation
Keywords: Eddy Current Testing technology Direct Digital Synthesis technology de-noise methods feature extraction classification methods
CLC: TP274.4
Type: Master's thesis
Year: 2008
Downloads: 256
Quote: 4
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Abstract


Eddy Current Testing(ECT)technology is a kind of Non-destructive testing technology;it’s widely used in many crucial fields such as aerospace,atomic engineering and manufacture.The dissertation is combined with an actual project,which is supported by the National Natural Science Fund.The whole dissertation concentrate on two keystones:one is the development of ECT system, the other is the research of Classification Methods about Inversion Problem.The major contributions in the dissertation are as follows:At the beginning,the sense of the dissertation is briefly introduced.Then,the development history about ECT and Direct Digital Synthesis technology is stated later.As inversion problem is the other key point,the research status of inversion problem is also disscussed.The research content and concrete work are also discussed in the beginning statement.As we know,actual project is based on corresponding theories.So,some important theorie must be studied,as the impedance of coil probe and the lift-off effect.From the study about the transformer impedance model of coil probe,it can be concluded that,as the height of lift-off increases,the effect that eddy current reflect on coil probe decreases.The concrete rule is that:the resistance of coil probe decreases,and the inductance of the probe increases.Following that, impedance signal decomposition theory is presented to confirm the way of getting magnitude value and phase value.Another important theory point about skin effect is referred in this chapter for the coming chapter.The development about ECT system is started from the scheme discussion,especially about the possibility of DDS technology application.After scheme’s desicription,ECT system is analyzed from hardware design and software design.Some debug results show that:the system is able to achieve the design goal.Signal-processing techniques for noise elimination including time-domain methods, frequency-domain methods and time-frequency domain methods are studied.The study of time-domain de-noise method includes mean filtering algorithm and one order lag algorithm.Fast Fourier Transform is applied in frequency-domain de-noise method.The Wavelet transform is used in time-frequency domain method,the effect of four different wavelet groups with different threshold selection rules are studied in the chapter.The experiment result indicates that the best de-noise wavelet of the four groups is Biorthogonal wavelet group and the best rule is rigrsure rule.Feature extraction and classification methods are the last key study point.According to feature extraction,the chapter mainly analyzes principal component analysis and kernel principal component analysis.The classification methods study includes nearest mean method,K-near method,back propagation artificial neural network method and Support vector machine method. The experiment results concludes that the SVM classification method based on KPCA have the better classification effect than the other three.

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CLC: > Industrial Technology > Automation technology,computer technology > Automation technology and equipment > Automation systems > Data processing, data processing system > Centralized testing and roving detection system
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