ONLINE MONITORING OF POWDER BLENDING WITH NEAR-INFRARED SPECTROSCOPY

Powder blending was monitored on-line by taking near-infrared measurem ents at regular time intervals during the mixing process. The average standard deviation between the measurements taken at each time and the dissimilarity between each mixture spectrum and the ideal mixture spe ctrum were used to monitor the changes in the pow der blend over time. The distribution of the pure compounds in the blend can be investigat ed by looking at the score plot for the first two principal components (PCs), the contribution of each variable to the dissimilarity and, in particular, the contrasts between two characteristic wavelengths for each compound. Statistical process monitoring charts were used to dete rmine the blending time at which the mixture was within (spectroscopic ) specifications. Shewhart charts monitor the blend at characteristic wavelengths for each substance separately. The Hotelling's T-2 test de fines a multivariate confidence interval. For spectral data, feature r eduction is needed, This procedure is accomplished by using characteri stic wavelengths for the pure compounds or the significant PCs after p erforming principal components analysis (PCA).