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THE ACCURATE MEASUREMENT OF HIGH TEMPERATURES 1
Author(s) -
Forsythe W. E.
Publication year - 1929
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1929.tb17058.x
Subject(s) - pyrometer , thermocouple , optics , temperature measurement , monochromatic color , work (physics) , measuring instrument , acoustics , calibration , range (aeronautics) , computer science , materials science , mechanical engineering , physics , engineering , mathematics , statistics , thermodynamics , composite material
The standard temperature scale is defined and methods of realizing it both in laboratory and in factory practice are outlined. Methods of measuring temperature from very low values to the highest obtainable are described. The use of thermocouples, the errors encountered in the use of both base metal and rare metal thermocouples, and the methods used to avoid these errors are discussed. Thermocouples are useful in measuring temperatures up to about 1000 to 1500°C. Beyond the range of thermocouples and sometimes even in this range it is necessary to use some means of measuring temperature that depends on the energy radiated from the source under consideration. For this class of work the optical pyrometer is recommended as one very good method. Different forms of optical pyrometers are discussed and the advantages and disadvantages of these types are pointed out. The conclusion is reached that for many types of work the disappearing‐filament type of optical pyrometer has certain advantages over other forms. Some of these advantages are pointed out and reasons given for the selection of this pyrometer. The necessity for the use of a monochromatic screen with a pyrometer is discussed and a list of the various screens available are given. Reasons are given for the general choice of a red screen for this work. In the use of an optical pyrometer it is at times necessary to know something concerning the wave‐length of the light used. This brings up the question of the effective wave‐length of the screen used. The effective wave‐length is defined and methods given for determining and using this effective wave‐length in optical pyrometry. It is shown that with a well‐calibrated screen just as definite results can be obtained as with a spectrometer for determining wavelength, and the advantages of the screen over the spectrometer are set forth. Methods of calibrating optical pyrometers are discussed which bring in the idea of a black body. Methods of realizing the theoretical black body are given together with some experimental results along this line. The use of absorbing screens in extending the scale of an optical pyrometer is outlined and methods are given of obtaining the transmission of the absorbing screens so that it is easy to calculate the extension of the temperature scale with a particular screen. The kind of an absorbing screen needed for this work is shown and the advantages and disadvantages of the absorbing screens are given. Accuracy tests are included in which it is shown that very good agreement can be obtained in the use of a disappearing‐filament optical pyrometer by untrained or slightly trained observers. Results are also given to show what accuracy may be expected from experienced observers from this form of pyrometer.