INFRARED-THERMOGRAPHY THROUGH WINDOWS AT LOW-TEMPERATURES

Infrared thermography offers itself for non-intrusive measuring of loc al temperature distributions at internal surfaces of channels and holl ow objects. The temperature distribution at an internal surface can on ly be measured through an IR-transparent window, if the IR-camera is p ositioned outside. Thermal radiation and reflection by this window may falsify the temperature distribution indicated by the IR-camera, the required correction is analyzed in this paper. For this study the radi ation reaching the IR-camera within the detected range of wavelength i s considered by a balance of radiative energy fluxes. The assumptions made to evaluate this balance are verified by comparing calculated and measured temperature values and the validity is confirmed. Results sh ow, that linear calibration curves for measurements through a window m ay be applied with reasonable accuracy in a range of temperature 295 K less-than-or-equal-to T(O) less-than-or-equal-to 365 K of both window and environment. The influence of both temperatures on the calibratio n curve has been studied by considering the balance of radiative fluxe s. In addition, the influences of different angles of view of the IR-c amera and of different window orientations are examined.