On unifying multiblock analysis with application to decentralized process monitoring

Westerhuis et al. (J. Chemometrics 1998; 12: 301-321) show that the scores of consensus PCA and multiblock PLS (Westerhuis and Coenegracht, J. Chemome trics 1997; 11: 379-392) can be calculated directly from the regular PCA an d PLS scores respectively. In this paper we show that both the loadings and scores of consensus PCA can be calculated directly from those of regular P CA, and the multiblock PLS loadings, weights and scores can be calculated d irectly from those of regular PLS. The orthogonal properties of four multib lock PCA and PLS algorithms are explored. The use of multiblock PCA and PLS for decentralized monitoring and diagnosis is derived in terms of regular PCA and PLS scores and residuals. While the multiblock analysis algorithms are basically equivalent to regular PCA and PLS, blocking of process variab les in a large-scale plant based on process knowledge helps to localize the root cause of the fault in a decentralized manner. New definitions of bloc k and variable contributions to SPE and T-2 are proposed for decentralized monitoring. This decentralized monitoring method based on proper variable b locking is successfully applied to an industrial polyester film process. Co pyright (C) 2001 John Wiley & Sons, Ltd.