Study On Eddy Current Testing Virtual Instrument System Under LabWindows/CVI

The frequency spectrum analysis is introduced to the eddy current testing in this paper. Using the virtual instrument technique, the eddy testing virtual instrument system based on LabWindows/CVI is developed to make the metal parameters testing easier and analysis results direct. Also the analysis function is added to the eddy testing instrument through graph describing.Understanding the basic theory of eddy testing is the basis of selecting eddy testing plan. In chapter 2, eddy testing theory is analyzed from several aspects. The equivalent circuit of eddy current testing, frequency response of eddy current testing system and frequency spectrum of eddy current sensor output signal is analyzed respectively. Also, the relation among these analysis methods is discussed. Finally by mathematic derivation, the feasibility of solving the measurement to hardness parameters by frequency spectrum analysis is proved from both theory and experiment data.The development of eddy testing virtual instrument must be based on powerful software tools. The virtual instrumentation technique and LabWindows/CVI with the powerful signal processing and analysis function provide this tool for the project. In chapter 3, the system of eddy testing virtual instrumentation is studied. The virtual instrumentation technique and LabWindows/CVI is firstly introduced. Then the function calling of the third DAQ under LabWindows/CVI is discussed. The multi-virtual panel is designed performing data acquisition function, frequency spectrum analysis, parameters computation, result displaying and graph drawing function etc. Finally, the method of executive program producing and the software packing are given so as to make a true virtual instrumentation.The theory of frequency spectrum analysis is the theoretic basis of processing and analyzing the output signal of the eddy current sensor and also the algorithm reference of software programming. The frequency spectrum idea and the computation tool-Fourier transformation are discussedand the frequency spectrum to the periodic signal is expounded. Finally several problem about frequency spectrum analysis are discussed. With the spectrum analysis theory guided, the data processing about selecting sampling number and the primary phase etc is also analyzed.In chapter 5, the parameters of hardness and distance are obtained by BP neural network computing the three frequency spectrums. And through the comparison with the testing value and theoretic value, it' s concluded that the frequency spectrum analysis method meets the system measurement requirements.In chapter 6, the experiment data is analyzed. And the error reasons in the eddy testing system are analyzed.