Temperature discrimination in optical and radiation pyrometers using photoelectric detectors is discussed and analyzed for the two cases where the discrimination is limited by noise in the detector and by the fundamental fluctuations in the radiation stream reaching the detector, respectively. The design of amplifiers consistent with these limits and the limits imposed by reference source instability is also discussed briefly. Graphical data are given for the calculation of detection limits for each of the two cases for both broad-spectral-bandwidth pyrometers with various long-wavelength cutoffs and for narrow-bandwidth pyrometers at various wavelengths.
The data are especially relevant to pyrometer design when the measurement of transients, small sources, or low temperatures is involved, and also in the design of narrow-spectral-bandwidth pyrometers for realizing temperature scales. For this last case an analysis is given for estimating the optimum spectral bandwidth required to obtain the maximum scale accuracy. It is shown that it should be possible to realize the International Practical Temperature Scale (IPTS) with an accuracy of about 0.01°C near 1063°C and 0.1°C near 1769°C by using a special trialkali photosurface photomultiplier or a silicon photodiode at a 1.0-μ wavelength. The accuracy of realization of a radiation scale of temperature below 1063°C is also discussed.
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