Photometry of the Optical Pyrometer and Its Use below 800°C

The standard deviation of temperature measurements due to uncertainty in photometric matching has been determined for the disappearing filament optical pyrometer, with and without a red filter, for exit pupils of 0.7-mm and 1.4-mm diameter and for filament apparent angular widths of 10 min and 7 min. It is shown that the results are in quantitative agreement with the direct measurements of contrast limens reported by Blackwell. With a good commercial pyrometer in which the red filter has been removed it is possible to make measurements with a standard deviation for a single pair of observations of 6°C at 600°C.