On the Measurement of the Temperatures of Unenclosed Objects by Radiation Methods

The functional relationships between apparent temperature and true tem-perature for the total radiation pyrometer, the optical pyrometer, the two-color pyrometer, and the two-temperature pyrometer are developed and discussed. It is shown that it is impossible to measure the temperature of an unenclosed object in the range 2000~176 with accuracy greater than about 10 % with-out prior knowledge of the emissivity. If the emissivity is known within 20%, the temperature can be determined within 1 or 2 % by means of an optical pyrometer, particularly if the instrument is operated at the blue end of the spectrum. The accuracy obtainable with the other instruments under equivalent conditions i significantly lower. Since the last war there has been a growing need to operate various devices at h igher and higher temperatures in order, for example, to obtain more efficient rocket motors or faster airplanes. As a re-