The Raytheon Emissitometer

The measurement of radiation (ultra-violet, visible, or infrared) from a surface as a means of knowing the surface temperature has been found useful in many applications. One of the simpler types of instruments which uses this principle is a brightness pyrometer. The brightness pyrometer relates radiation to temperature on the basis of radiation magnitude, which is a function of temperature, but the output of the brightness pyrometer is also a function of a material property known as emissivity. While many brightness pyrometers have compensation control for different values of emissivity, knowing the emissivity constant is left for the user to find through such aids as handbooks of materials and physics texts. Even then, the emissivity may vary as a function of the particular chemical content and environment to which the material is subjected. Hence, Raytheon felt there was a need for a device to measure emissivity simultaneously with other radiation measurements and within a fraction of the time span used by the heating process.