Non-contact measurement of the temperature profile of PET preforms

This paper describes a method for the measurement of the internal and external temperature profiles of PET preforms used in the Injection Stretch Blow Moulding (ISBM) process. Temperature is the most critical parameter for the process quality, but no online measuring system has yet been implemented. The proposed system is based on two thermopiles for the identification of the internal temperature profile and a thermal camera for the measurement of the external temperature profile. The adopted sensors have been individually calibrated and the measurement uncertainty budget proved that the sensor's instrumental uncertainty is not the actual limiting factor for the system accuracy. The main accuracy limitations derive from the emissivity of the materials of PET preforms. The use of average emissivity values increases the measurement uncertainty to 1.4°C, a value that is judged acceptable in this specific application.