Ultrasonic Testing Signal Processing of Weld Flaw Based on the Second Generation Wavelet

Abstract

The de-noise result of traditional wavelet is related to the wavelet basis function. In the process of ultrasonic testing, flaw echo signal exited the characteristics of electrical noise, scattering noise in ultrasonic testing, which was sometimes very difficult to eliminate. Considering the distinctness of distribution between defects signals and noises, the second generation wavelet transform (SGWT) de-noising ultrasonic testing signal processing was proposed. Wavelet basis function with some special characteristic can be obtained by means of designing prediction and updating coefficient. Study mathematics properties of flaw echo signals and analyze the composition of noises and their characters in ultrasonic echo signals. The processed detail coefficient and the approximate coefficient are used to construct the signal. Wavelet transform coefficients of noise were filtered by changing threshold on the different scale and reconstructed the detection echo in order to enhance signal-to-noise ratio. The Experiments result shows that the method can improve the signal noise ratio and the distinguish ability of signals of different defects classes, and suppress energy attenuation as well as signal distortion efficiently. And flaw location accuracy and longitudinal resolution are advanced too.