An ultrasonic test of spot welding for stainless steel is conducted. Based on wavelet packet decomposition, the ultrasonic echo signal has been analyzed deeply in time - frequency domain, which can easily distinguish ...An ultrasonic test of spot welding for stainless steel is conducted. Based on wavelet packet decomposition, the ultrasonic echo signal has been analyzed deeply in time - frequency domain, which can easily distinguish the nugget from the corona bond. The 2D C-scan images produced by ultrasonic C scan which contribute to quantitatively calculate the nugget diameter for the computer are further analyzed. The spot welding nugget diameter can be automatically obtained by image enhancement, edge detection and equivalent diameter algorithm procedure. The ultrasonic detection values in this paper show good agreement with the metallographic measured values. The mean value of normal distribution curve is 0.006 67, and the standard deviation is 0.087 11. Ultrasonic C-scan test based on wavelet packet signal analysis is of high accuracy and stability.展开更多
A new time-domain analysis method that uses second generation wavelettransform (SGWT) for weak fault feature extraction is proposed. To extract incipient fault feature,a biorthogonal wavelet with the characteristics o...A new time-domain analysis method that uses second generation wavelettransform (SGWT) for weak fault feature extraction is proposed. To extract incipient fault feature,a biorthogonal wavelet with the characteristics of impact is constructed by using SGWT. Processingdetail signal of SGWT with a sliding window devised on the basis of rotating operation cycle, andextracting modulus maximum from each window, fault features in time-domain are highlighted. To makefurther analysis on the reason of the fault, wavelet package transform based on SGWT is used toprocess vibration data again. Calculating the energy of each frequency-band, the energy distributionfeatures of the signal are attained. Then taking account of the fault features and the energydistribution, the reason of the fault is worked out. An early impact-rub fault caused by axismisalignment and rotor imbalance is successfully detected by using this method in an oil refinery.展开更多
Baseline wander is a common noise in electrocardiogram (ECG) results.To effectively correct the baseline and to preserve more underlying components of an ECG signal,we propose a simple and novel filtering method based...Baseline wander is a common noise in electrocardiogram (ECG) results.To effectively correct the baseline and to preserve more underlying components of an ECG signal,we propose a simple and novel filtering method based on a statistical weighted moving average filter.Supposed a and b are theminimum and maximum of all sample values within a moving window,respectively.First,the whole region [a,b] is divided into M equal sub-regions without overlap.Second,three sub-regions with the largest sample distribution probabilities are chosen (except M<3) and incorporated into one region,denoted as [a 0,b 0 ] for simplicity.Third,for every sample point in the moving window,its weight is set to 1 if its value falls in [a 0,b 0 ];otherwise,its weight is 0.Last,all sample points with weight 1 are averaged to estimate the baseline.The algorithm was tested by simulated ECG signal and real ECG signal from www.physionet.org.The results showed that the proposed filter could more effectively extract baseline wander from ECG signal and affect the morphological feature of ECG signal considerably less than both the traditional moving average filter and wavelet package translation did.展开更多
基金Funded by Key Laboratory of Automobile Materials of Ministry of Education and Department of Materials Science & Engineering,Jilin University
文摘An ultrasonic test of spot welding for stainless steel is conducted. Based on wavelet packet decomposition, the ultrasonic echo signal has been analyzed deeply in time - frequency domain, which can easily distinguish the nugget from the corona bond. The 2D C-scan images produced by ultrasonic C scan which contribute to quantitatively calculate the nugget diameter for the computer are further analyzed. The spot welding nugget diameter can be automatically obtained by image enhancement, edge detection and equivalent diameter algorithm procedure. The ultrasonic detection values in this paper show good agreement with the metallographic measured values. The mean value of normal distribution curve is 0.006 67, and the standard deviation is 0.087 11. Ultrasonic C-scan test based on wavelet packet signal analysis is of high accuracy and stability.
文摘A new time-domain analysis method that uses second generation wavelettransform (SGWT) for weak fault feature extraction is proposed. To extract incipient fault feature,a biorthogonal wavelet with the characteristics of impact is constructed by using SGWT. Processingdetail signal of SGWT with a sliding window devised on the basis of rotating operation cycle, andextracting modulus maximum from each window, fault features in time-domain are highlighted. To makefurther analysis on the reason of the fault, wavelet package transform based on SGWT is used toprocess vibration data again. Calculating the energy of each frequency-band, the energy distributionfeatures of the signal are attained. Then taking account of the fault features and the energydistribution, the reason of the fault is worked out. An early impact-rub fault caused by axismisalignment and rotor imbalance is successfully detected by using this method in an oil refinery.
基金supported by the Science and Technology Project of Guangdong Province (No.2009B060700124)the Science and Technology Project of Guangzhou Municipality,Guangdong Province,China (No.2010Y1-C801)
文摘Baseline wander is a common noise in electrocardiogram (ECG) results.To effectively correct the baseline and to preserve more underlying components of an ECG signal,we propose a simple and novel filtering method based on a statistical weighted moving average filter.Supposed a and b are theminimum and maximum of all sample values within a moving window,respectively.First,the whole region [a,b] is divided into M equal sub-regions without overlap.Second,three sub-regions with the largest sample distribution probabilities are chosen (except M<3) and incorporated into one region,denoted as [a 0,b 0 ] for simplicity.Third,for every sample point in the moving window,its weight is set to 1 if its value falls in [a 0,b 0 ];otherwise,its weight is 0.Last,all sample points with weight 1 are averaged to estimate the baseline.The algorithm was tested by simulated ECG signal and real ECG signal from www.physionet.org.The results showed that the proposed filter could more effectively extract baseline wander from ECG signal and affect the morphological feature of ECG signal considerably less than both the traditional moving average filter and wavelet package translation did.
