Evaluation of uncertainties of the temperature measurement by standard platinum resistance thermometer calibrated at the defining fixed points according to ITS-90 is a problem that can be solved in different ways. The paper presents a procedure based on the propagation of distributions using the Monte Carlo method. The procedure employs generation of pseudo-random numbers for the input variables of resistances at the defining fixed points, supposing the multivariate Gaussian distribution for input quantities. This allows taking into account the correlations among resistances at the defining fixed points. Assumption of Gaussian probability density function is acceptable, with respect to the several sources of uncertainties of resistances. In the case of uncorrelated resistances at the defining fixed points, the method is applicable to any probability density function. Validation of the law of propagation of uncertainty using the Monte Carlo method is presented on the example of specific data for 25 Ω standard platinum resistance thermometer in the temperature range from 0 to 660 °C. Using this example, we demonstrate suitability of the method by validation of its results.
Atmospheric air temperature values are fundamental in meteorology and climate studies. To achieve high accuracy in the measurements, the features, characteristics and performances of instruments are of high importance. This study focuses on the most commonly used temperature sensors within automatic weather stations, with a specific focus on evaluating the self‐heating effect. Self‐heating in automatic weather stations originates not only from the temperature sensor itself but also from the electrical components housed together within. This effect introduces extra heating in the system, causing biases and errors in temperature records. The conducted measurements show the temperature change in the close vicinity of the thermometers over a time period of more than 66 hr with electric current and voltage supply values recommended by the respective sensor manufacturers. Furthermore, the temperature changes after increasing the voltage supply levels up to 80% of the maximum voltage recommended by the manufacturer are presented as well. The results of overall self‐heating indicated a +0.07°C increase in temperature for the tested sensors when using the manufacturers’ recommended electric current and voltage supply. However, the use of elevated voltage levels shows a considerably higher temperature increase in the vicinity of the temperature sensors. In the present study, the measured difference from the initial measured temperature can be as high as +0.32°C.
Au/Pt thermocouples are considered as an alternative to High Temperature Platinum Resistance Thermometers and are one of the prime candidates to replace them as the interpolating instrument of the International Temperature Scale of 1990 (ITS-90) in the temperature range between about 660 °C and 962 °C. This work presents the results of investigation of two Au/Pt thermocouples that used exclusively quartz glass (SiO2) as insulation material. Measurements in fixed points of Zn, Al, and Ag were realized on these thermocouples as well with interchanged inner insulation made of high purity aluminium oxide (Al2O3). The conducted experiments tested the performance of Au/Pt thermocouples with the use of different insulation materials. The measured electromotive forces were found to be sensitive to the replacement of the quartz glass by aluminium oxide as an insulation material of the Au/Pt thermocouples. This change of insulation has resulted in a temperature increase up to about 0.5 K measured at the freezing point of silver. The decreasing insulation resistance of quartz glass at higher temperatures is believed to be the source of thermoelectric instability.
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