# DEPENDENCE OF THE PYROMETRIC MEASURING TEMPERATURE ON THE EMISSIVITY FACTOR OF OBJECTS

2019;
: pp. 34-40
Authors:
1
Lviv Polytechnic National University, Ukraine
2
Lviv Polytechnic National University, Ukraine

Study  of  the  dependence  of  the  temperature  determination  error  on  the  emissivity  factor  of  materials  is conducted  in  the  paper.  The  mathematical  models,  which  describe  the  ratio  of  thermodynamic  temperature  and  measured imaginary temperatures, taking into account the emissivity factor, are analyzed. The constructions of the full radiation, brightness radiation, and spectral ratio radiation pyrometers are underpinned by the considered models. Analyzing the mathematical models of radiation thermometers (or pyrometers), one can observe a fundamental circumstance that interferes with the wide application of pyrometry, namely,  lack of knowledge or  even  the mere  absence of  information on  the  true numerical values of  the  emissivity factor of the objects. When measuring the temperature of objects that fall under the classification of “real body”, there arise serious problems with the reliability of its determination. The vast majority of modern pyrometers, which are calibrated by a blackbody, compute the data received from sensitive element of the pyrometer into temperature values, not taking into account the real value of the object’s emissivity factor. Thus, if the latter is 0.1, and the pyrometer is graded by the blackbody, then, only ~10 % of its radiation energy  is perceived by sensitive element of  the pyrometer. As  result,  the determined temperature value is substantially lower  than  the  actual  one.  It  can  be  argued  that  the  lack  of  information  about  a  real  numeric  value  of  the monitored  object’s emissivity factor is the determining source of distortion of the measurement result. The problem is further complicated by the fact that the mentioned factor is the parameter that depends on many factors, and in particular on the temperature, which is exactly to define.

The  paper  presents  the  results  of  the  study  of  the  dependence  of  the  absolute  measurement  error  of  temperature  on emissivity factor for different types of pyrometers. The accuracy of measuring the temperature with pyrometric means is minimal only for measuring the black body or gray body by the spectral ratio pyrometers. The error of measuring the temperature of real object differs significantly from the error of the black body. This is due to the ignorance of the true value of the emissivity factor of the real object. Therefore, presetting of this factor in pyrometers that is recommended by most pyrometers guidelines is completely incorrect.

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