Abstract
Infrared radiation thermometers measuring low temperature have an inherent problem of background radiation originated in themselves because inner parts of radiation thermometers radiate as bright as measurement objects. The problem is important to multielement radiation thermometers.
To investigate background radiation of a multielement detector, angular dependence of responsivity of a 10-element InSb linear array was measured. The detector elements responded to radiation incidence from the outside of the field of view. Radiation from the outside of the field of view is mainly background radiation in an actual radiation thermometer.
We developed a new optical method to reduce background radiation incidencee of thermal infrared detectors with cooling. A mirror iris was used in the method; it was a concave mirror having an aperture for signal radiation at the center. When the mirror iris is inserted into an optical pass between the detector and a lens, the detector observes the cold image reflected in the mirror surface.
A thermal infrared radiation thermometer having the InSb array detector and the mirror iris was developed to evaluate the effect of the optical method. Zero drift of the radiation thermometer was largely reduced by the mirror iris without an optical chopper.
Stability of the radiation thermometer observing a blackbody furnace maintained at 40°C was measured. The indicated temperature drift was less than ±0.9°C when the room temperature was varied in a range of ±6°C alternatively. The drift was improved to less than ±0.2°C with a compensation using the inner temperature of the radiation thermometer.
