A large-area plate radiator with in situ temperature homogenization for thermographic imager calibration

Large-area plate radiators with a high emissivity and uniform temperature distribution are needed as reference sources for calibrating infrared imagers and camera systems. However, achieving very uniform temperature distribution over a large area is technically challenging, especially at high temperatures. We present a large-area plate radiator with an improved uniformity in its surface temperature distribution for the calibration of infrared thermographic imagers. It is based on an industrial plate radiator which is temperature homogenized in situ by using the Data Reference Method (DRM) developed at the Physikalisch-Technische Bundesanstalt. The DRM takes three spatially shifted pictures of the plate radiator with a thermographic imager, and using this information, it calculates both the nonuniformity in the temperature distribution of the plate radiator and the nonuniformity in the response of the thermographic imager used for imaging the scene. The surface of the applied plate radiator is 300 mm × 300 mm and it operates in a temperature range from 30 °C to 600 °C. The surface is segmented into 9 different parts of identical size whose temperature can be individually controlled. The in situ controlled plate radiator system developed uses an infrared camera, whose detector is corrected for its response inhomogeneity using the DRM. This camera permanently monitors the plate radiator, and from these data, the temperature distribution of the plate is homogenized. Through this method, the homogeneity of the plate radiator can be considerably improved compared to the non-actively regulated mode of operation. For example, at a nominal temperature of 400 °C, without the in situ homogenization procedure, 90% of the plate area has a radiation temperature in the range from 391.7 °C to 403.6 °C. Applying the in situ homogenization procedure leads to 90% of the plate area having a radiation temperature in the range from 394.2 °C to 401.2 °C.