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

Abstract

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.