Validation of phosphor thermometry for industrial surface temperature measurements

Surface temperature measurements are required by the aerospace and automotive industries to guarantee high-quality products and optimize production processes. Accurate and reliable measurement of surface temperature is very challenging in an industrial environment. Surface contact probes are widely used but poorly characterized, while non-contact infrared thermometry is severely hampered by the unknown emissivity of the surface and by problems caused by stray radiation from the background. An alternative approach to the above techniques is phosphor thermometry, used here in a hybrid contact/non-contact approach. In this work, the development of a lifetime-based phosphor thermometer, its application to industrial surface temperature measurement and its validation are reported in a metrologically sound manner. The phosphor thermometer was initially calibrated by contact on a reference calibrator system at the Istituto Nazionale di Ricerca Metrologica to provide SI traceability to the measurements at the industrial level; the system was later validated by exploiting a metal phase-change method. The robustness of the approach against a strong radiative background was also investigated. A comprehensive uncertainty analysis was carried out, resulting in an expanded uncertainty (k  =  2) lower than 1.4 °C over the temperature range from the ambient to 450 °C. The phosphor-based thermometer was then tested at industrial manufacturing premises to measure the surface temperature of aluminium alloy billets during the pre-heating phase before forging. The phosphor-based approach was compared with radiation and contact thermometry in both static and dynamic measurement conditions. The experimental results proved that phosphor thermometry, besides being a valid alternative to conventional techniques, may offer better performance in an industrial setting.