Demonstration of near infrared thermography with silicon image sensor cameras

This paper presents a thermal measurement system based on a Silicon image sensor camera operating in the Near Infrared spectral band (0.7 - 1.1 mu m). The goal of the study is to develop a low-cost imaging system which provides an accurate measurement of temperature. A radiometric model is proposed to characterize the camera response by using physical parameters considering the specific spectral band used. After a calibration procedure of the model, measurements of black body temperatures ranging from 300 to 1000 degrees C has been performed. The Noise Equivalent Temperature Difference (NETD) is lower than +/- 0.18 degrees C at a black body temperature of 600 degrees C. Accurate measurements are provided over the whole temperature range by introducing an automatic exposure time control. The exposure time is adjusted for each frame along the evolution of temperature in order to optimize the temperature sensitivity and the signal-to-noise ratio. The paper also describes the conversion process of the apparent black body temperature to the real temperature of the observed object using its emissivity and surface geometry. The overall method is depicted and the influence of each parameter is analyzed by computing the resulting temperature uncertainty. Finally, preliminary experimental results are presented for monitoring real temperature of moulds in a Super Forming Process (SPF).