CCD cameras as thermal imaging devices in heat treatment processes

In many industrial processes knowledge of the two-dimensional thermal distribution is of great importance. Conventional infrared based systems (MIR, FIR) provide very accurate results, but their quality also comes at high cost, and moreover these systems cannot always be properly applied in every case, e.g. due to problems concerning IRradiation absorption through certain IR-blocking materials such as inspection windows We present a "low cost" NIR thermal imaging device based on a grayscale CCD camera used in combination with image processing software applied to the thermal imaging of heated metal parts in a plasma reactor. The aim of this work is to measure the temperature distribution of objects at relatively low temperatures of approx. 350°C and below by applying image processing techniques, assuming constancy of temperature for a few seconds. Special emphasis is put on the influence of the emission factor, which plays an important role in the field of non-contact temperature measurements, especially when thermo-chemically processed surfaces are considered. In addition, the noise characteristics of the imaging system have to be taken into account to ensure reproducible results. The underlying imaging model and a camera characterization procedure based on the 'Photon Transfer Technique' are presented which are used to adjust the relevant parameters to predict the measurement limits of such systems.