Analysis of the instability of the characteristics of a reference platinum thermometer in the interval between verifications and a method for reducing the thermometer error

Reference platinum resistance thermometers are described—currently the most accurate contact sensors for measuring temperature. One of the most important characteristics of the error of a reference platinum thermometer is considered—resistance instability in the interval between verifications. For several years we analyzed the instability of 27 standard platinum thermometers received for verification at the All-Russian Research Institute of Metrology named after. D.I. Mendeleev. It has been established that the instability of resistance in the equivalent temperature of most thermometers at the triple point of water exceeds \(\pm 0.002^{\circ}\mathrm{C}\) $\pm 0.002\mathrm{°C}$ , and sometimes reaches several hundredths of a degree. The reasons for the resistance instability, as well as the instability of the relative resistance of thermometers, are analyzed. The error caused by the instability of the thermometer can be reduced from hundredths to thousandths of a degree if the relative resistance of the thermometer is used as the measured parameter. This conclusion was made based on an analysis of changes in the interpolation function of the thermometer in the interval between calibrations and calculation of the thermometer error in the temperature range between calibration points. It is proposed in the regulatory documents on the verification methodology to provide for additional periodic verification of standard thermometers at the triple point of water. Additional verification will improve the accuracy of temperature measurements. The results obtained will be useful to users of reference platinum thermometers and specialists of verification centers.