Multiscale classification has potential advantages for monitoring industrial processes generally driven by events in different time and frequency domains.In this study, we adopt stationary wavelet transform for multiscale analysis and propose an applicable scale selection method to obtain the most discriminative scale features.Then using the multiscale features, we construct two classifiers:(1) a supported vector machine(SVM) classifier based on classification distance, and(2) a Bayes classifier based on probability estimation.For the SVM classifier, we use 4-fold cross-validation and grid-search to obtain the optimal parameters.For the Bayes classifier, we introduce dimension reduction techniques including kernel Fisher discriminant analysis(KFDA) and principal component analysis(PCA) to investigate their influence on classification accuracy.We tested the classifiers with two simulated benchmark processes:the continuous stirred tank reactor(CSTR) process and the Tennessee Eastman(TE) process.We also tested them on a real polypropylene production process.The performance comparison among the classifiers in different scales and scale combinations showed that when datasets present typical scale features, the multiscale classifier had higher classification accuracy than conventional single scale classifiers.We also found that dimension reduction can generally contribute to a better classification in our tests.
Yu-ming LIU Lu-bin YE Ping-you ZHENG Xiang-rong SHI Bin HU Jun LIANG
Data-driven tools,such as principal component analysis(PCA)and independent component analysis (ICA)have been applied to different benchmarks as process monitoring methods.The difference between the two methods is that the components of PCA are still dependent while ICA has no orthogonality constraint and its latent variables are independent.Process monitoring with PCA often supposes that process data or principal components is Gaussian distribution.However,this kind of constraint cannot be satisfied by several practical processes.To ex- tend the use of PCA,a nonparametric method is added to PCA to overcome the difficulty,and kernel density esti- mation(KDE)is rather a good choice.Though ICA is based on non-Gaussian distribution information,KDE can help in the close monitoring of the data.Methods,such as PCA,ICA,PCA with KDE(KPCA),and ICA with KDE (KICA),are demonstrated and compared by applying them to a practical industrial Spheripol craft polypropylene catalyzer reactor instead of a laboratory emulator.
