Working with a Set of Filter near Infrared Instruments

Abstract

There is an increasing need for using a set of near infrared (NIR) instruments in industrial activities. In this study, three methodologies of working with a set of NIR instruments are reviewed: the standardisation of the predicted values, the standardisation of the absorbances and the modelling of the instrument differences. Modelling the NIR differences is performed by including in the calibration/validation sets spectra recorded in any of the different instruments of the set without any pre-treatment or after transfer by orthogonal projection (TOP) pre-transformation. In the latter case, TOP calculations from different sets of products are assayed. The methods are briefly presented and discussed through the results of a set of four InfraAlyzer 2000 instruments, 19-filter spectrometers which are used in the quality control of fresh alfalfa. Although the optimal procedure depends on the particular conditions of the industrial work (number of products, number of properties, number of instruments, etc.), all the above methods have been found to be suitable for operating with a set of NIR instruments. The present results also indicate an independence of the TOP results from the product used to compute the TOP factors, at least for the present set of NIR instruments which all belong to the same model and company.