| Temperature is one of the most widely required parameter.In modern industrial production,the percentage of temperature measurement in the whole monitoring parameter is about 50%.According to the measured object,it can be divided into inner temperature measurement and surface temperature measurement.Surface temperature is mainly measured by the non-contact radiation thermometry at above 400?.Surface temperature measurement plays an important role in aerospace,material,energy and metallurgy industry.With the rapid development of industrial technology,the measurement of surface temperature is required more and more accurate.For example,in the steel making process,the maximum error of surface temperature measurement of the oriented silicon steel in annealing process is expected to be within 830 ± 5?,temperature exceeds the limit would result in the decreasing of the magnetism.The expected temperature range in annealing for the TRIP steel is 670 ± 5?,temperature exceeds the limit would result in the crack.However,the error of widely used single and two-color pyrometers can be 6?30? as the result of the indetermination of emissivity,which do not meet the demand of quality promotion and energy saving.The indetermination of emissivity is the reason of inaccuracy of surface temperature measurement.Pyrometers needs to set the emissivity parameter before use,which influenced by the material,roughness and degree of oxidation and cannot be determined properly.The measurement error caused by the indetermination of emissivity restricts the development of infrared thermometry.As it does not meet the increasing demand of industry,the problem of inaccuracy of surface temperature measurement gained much attention by authoritative NMIs world widely.In 2013,a program called High Temperature Metrology for Industrial Applications(HiTeMS)organized by EURAMET was held.The participants are 15 authoritative NMIs including National Physical Laboratory(NPL)and Die Physikalisch-Technische Bundesanstalt(PTB).One of the research contents is about surface temperature measurement,which is treated as one of the contents in the roadmap for thermometry.How to decrease or eliminate the influence of emissivity is vital for precise measurement of surface temperature.In this paper,a novel blackbody converting-type method for measuring surface temperature is proposed to solve the emissivity problem.The instrument is developed and the experiment is conducted(The research domain of the paper concerns about the measurement of medium-high(>600?)opaque solid surface temperature).The research approach is stated as follows.Surface temperature and emissivity are high correlated,measurement of a single one needs the other.So the best way for eliminating the influence of emissivity is to measure it.Measurement of surface temperature in association with the emissivity is the key process.To measure the emissivity,according to its definition,two measurements are required,which include measuring the intrinsic radiation of the tested sample and the blackbody radiation in the same temperature.Emissivity is obtained by division of the two measurements.However,it is difficult to form isothermal condition required by the Kirchhoff blackbody model.So how to realize blackbody condition online is the key to measure surface temperature in association with emissivity.The model of secondary blackbody source removes the isothermal constraint of the model of Kirchhoff blackbody source,which can realize blackbody radiation in situ condition.Putting a gold plated reflector against the measured surface can be an approximate model of secondary blackbody,which the effective emissivity approaches to 1.In this paper,the blackbody converting-type measurement method based on secondary blackbody model was proposed,which correlatively measures the surface temperature as well as emissivity to eliminate the influence of the emissivity.The two wavelengths method was proposed to eliminate the systematic uncertainty caused by the imperfectness of the reflector.At last,precise measurement of surface temperature is realized by combining together the blackbody converting-type measurement method and the two wavelengths method.Two problems have been put a brake for the application of the secondary blackbody.First is the radiation characteristic of secondary blackbody is influenced by various factors,so the effective emissivity cannot be determined accurately.Second is the reflector would disturb the measured surface temperature.So the contents of the paper also concern how to solve the two problems discussed above.The main content and innovations of this paper is listed below:(1)Study on the characteristic of the focused spherical reflector and the mechanism of surface temperature disturbance.The focused spherical reflector was proposed to reduce the influence of the fluctuation of the gap between the reflector and the measured surface and the non-isothermal distributed surface,and the expression of the effective emissivity was deduced.Research shows that the uncertainty component from the non-isothermal distributed surface can be deduced though measuring the energy of the target radiated from right at the focal point of the reflector.For studying on the influence of the unfocused reflector,a Monte Carlo Method was used to build the model to analyze the characteristic of the reflector,and the influence of the deviation of the focal point and the measured surface to the effective emissivity is analyzed,which counted into the measurement uncertainty components.The mechanism of the temperature disturbance by the reflector was analyzed,the expression of temperature rise of the measured surface made by the reflector was deduced,and the compensation method was proposed,which counted into the measurement uncertainty components.(2)The blackbody converting-type method for simultaneously measuring surface temperature and emissivity has been proposed.The method of two-color pyrometer placed with a reflector can reduce but not eliminate the influence of the emissivity.A novel blackbody converting-type method was proposed to measure the intrinsic and reflective radiation in the two wavebands,the surface temperature and emissivities can be solved out simultaneously to eliminate the influence of the undetermined emissivity.In addition,as an important physical parameter,emissivity can be measured online in situ condition by the method.To meet integrative design thought,the instrument is developed,including the structure,reflector,blackbody-converter,optical component and moving component.The measurement uncertainty was evaluated by a Monte Carlo Method,the standard uncertainty is 1.4? at 750?.(3)The apparatus for surface temperature measurement has been developed.The apparatus for accuracy verification was developed,the instrument is driven by a servo motor along with a linear guideway to realize high precision locating and fast measurement.As a result,the uncertainty components from unfocused and temperature disturbing were reduced and controlled.As to verification,the standard uncertainties of temperature comparison error between the instrument and the thermocouple at a range from 600? to 900? are within 2?.To verify the accuracy of emissivity measurement,the measurement results of emissivities of the oxidized Incone1600 sample were compared with that of the NIST,the descrepancies of the two were 0.024(2.9%)and 0.006(0.7%).The research results have shown that the proposed method solves the problem that the surface temperature measurement error caused by the indetermination of emissivity which restricts the development of infrared thermometry.The instrument can be applied to the industry process where precise measurement of surface temperature is required. |
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