Determination of Transmittance of IR Windows made of CaF2 within Operational Temperatures of Electric Devices

The article presents summaries of works which have resulted in the presentation of a formula making it possible to determine an approximate transmittance of an IR window used in thermographic measurements of electric device temperatures. The equation was formulated after analysing components of the IR radiation reaching the camera lens in case when an IR window was not used and when an IR window was used. Conditions prevailing in course of the thermographic temperature measurement of electric devices contained in the switchgear were recreated in the performance of the works. The measurement system which was used in the experiment has been presented. Components of the IR radiation reaching the camera lens in case when the IR window was used and when the IR window was not used have been discussed. The obtained transmittance results of windows VPFR-75 FRK100-CL have been compared against data from literary sources.