REDUCTION OF THE SIZE-OF-SOURCE EFFECT AND DISTANCE DEPENDENCY OF A HIGH PRECISION INFRARED RADIATION THERMOMETER

摘要

Radiation thermometers to be used as transfer normals in calibration laboratories should be equipped with a variable focus and selectable wavelength filters. For such application a new instrument with an InGaAs detector and a stepper motor driven filter wheel has been developed. Key feature is the specially designed objective, which enables visual focussing for measurements performed at wavelengths from the visible up to 1.6 μm. Besides the excellent apochromatic correction for three wavelengths, the new objective has a largely reduced Size-of-Source Effect. The problem of the distance dependency leading to signal deviations up to 1% with the maximum distance variation has been solved by means of a specially developed electronic correction technique.