Photoelectric pyrometer

In the regions below 4000°K., the disappearing-filament optical pyrometer, the two-color pyrometer, or the photoelectric pyrometer can be used to measure International Scale Temperatures. Since optical pyro-metry has been well covered in the literature (F5, Rl), further discussion here would serve no purpose. 

Radiation thermometers were developed for measuring temperatures higher than 1064°C they have the advantage that they are noncontact thermometers. Optical pyrometers measure apparent temperatures of objects by comparing the radiation from the objects over a narrow wavelength band with that of a standard, preferably using a photoelectric detector for the comparison. Corrections for the emissivity of the source must be made to determine the temperature the preceived temperature may be, and usually is, lower because all of the heat is not radiated. Total-radiation pyrometers measure the whole spectrum of energy radiated by the source. They are less accurate than optical pyrometers but can measure much lower temperatures (of the order of 100°C). This type of pyrometer also requires emissivity corrections. 

The disappearing filament optical pyrometer is slow and manual. However, other pyrometers such as the photoelectric optical pyrometer can be automated. 

The values of (dCjdx) were measured photoelectrically, and of T a, function of x with an optical pyrometer. The results obtained by this method were comparable with those obtained by the other two methods. 

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