Process for identifying objects using an optical spectrometer and a transport system

Process for identifying articles which are at least partly made from at least one polymer, using an optical spectrometer and a transport system, said transport system comprising a transport rail and transport units, the transport units comprising a body, coupling means for fixing the articles to the transport units, the transport units being movably connected to the transport rail and a guide system which is capable of cooperating with the body and/or coupling means, said guide system at least being present in the area of the optical spectrometer, wherein the guide system comprises a pair of guiding elements which are essentially parallel to the transport rail and which are capable of receiving the body and/or coupling means, said process comprising the steps of:

• a) moving the articles past the optical spectrometer using the transport system;
• b) irradiating the articles and measuring the response of the irradiated articles using the optical spectrometer, analyzing the response to identify the articles as to the type of polymer;
• c) at least periodically irradiating at least one external reference object, using the transport system to move the at least one external reference object past the optical spectrometer, measuring the response of the at least one irradiated reference object using the optical spectrometer, and using the measured response of the at least one external reference object for the analysis of step b) and for correction of background signals and/or for correction for drift.