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7 October 2014 Modeling transient thermal behavior of shutter-less microbolometer-based infrared cameras
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This paper concerns with the problem of disturbing radiation derived from the interior of radiometric microbolometer-based infrared cameras. The amount of internal radiation depends particularly on the ambient temperature. Variation of ambient temperature leads to a change of the temperature distribution inside the camera. The approach proposed here is determining the disturbing radiation without using a shutter by measuring the internal thermal state with several temperature probes and deducing the disturbing radiation flux. Because of this discrete temperature measurement it is not possible to determine the present thermal state of the camera interior as precise as performing a shutter process. Therefore, the position of the temperature measurement is crucial for the significance of the relation between measured temperature and disturbing radiation flux. Furthermore, the transient thermal behavior during a cooling or heating period of the camera enclosure is a non-ergodic process [1]. Two approaches facing these problems are analyzed. The first approach is based on the usage of more than one temperature probe at different positions inside the camera. Each position of temperature measurement has its own characteristic of heat conductance and convection parameters. Therefore, the low-pass behavior and the corresponding response time of the measured temperature in relation to the ambient temperature differ. Developing a thermal model using different probes with a higher significance of the transient thermal trend reduces the calculation uncertainty. A second approach is to separate the transient and the steady-state behavior of the calculation model. If the camera is able to follow a slow change of ambient temperature completely, then it stays always in steady state and the process is ergodic. Only in case of an abrupt change of ambient temperature the thermal behavior leaves the steady state and a transient correction factor is necessary. This factor has to take the history of the measured temperature into account.
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A. Tempelhahn, Helmut Budzier, V. Krause, and G. Gerlach "Modeling transient thermal behavior of shutter-less microbolometer-based infrared cameras", Proc. SPIE 9249, Electro-Optical and Infrared Systems: Technology and Applications XI, 924904 (7 October 2014);

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