Process near infra red calibration spectra and references samples can always be made to match properly

A process stream could easily have 4–10 constituents of interest and 2–5 physical attributes that will
contribute significantly to the spectrum. Except for vary rare situations at any given time, these constituents and physical variables will have a certain value which, however, will necessarily change as the process unfolds, perhaps even in a few moments. Process heterogeneity in this sense can, for example, be defined as the “short vs longer term stability” of these attributes. Process heterogeneity will always
play an important role in establishing a multivariate calibration and validation scheme for any on-line NIR installation. There may be a time match or mismatch between calibration spectra and extracted reference samples—or there may be a match/mismatch
between the actual stream volume “seen” by the probe and the volume extracted and sent for analysis. We here discuss these situations which are often met in practical process sensor calibration.