Abstract
An automatic two wavelength pyrometer without a drift was achieved by using zero method The application of zero method permits the use of photosensors whose stability in spectral responses is rather poor.
A feedback system including two variables was newly developed for this instrument. In order to detect the differences between object and reference lights at two wavelengths, the instrument is equipped with a rotating mirror which guides object and reference radiations alternately to a pair of photosensors, one for a short wavelength and the other for a long wavelength.
The output of the former photosensor is used to suit the color temperature of a reference radiator to that of the object, because the brightness at shorter wavelengths is generally sensitive to changes in the color temperature of radiators. On the other hand, the output of the latter photosensor controls an optical wedge adjusting the radiant energy from the reference radiator to that from the object.
A prototype pyrometer using PbS as photosensors was calibrated by a standard black body furnace, and it was proved that the operational range was between 400°C and 900°C with the reproducibility of as good as ±5 deg and the response time was 1.5 second.
