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

Abstract

The standard platinum resistance thermometer is currently the most accurate contact temperature sensor. One of the most important characteristics of its error is the instability of resistance during the interval between calibrations. In this work, the task was set to analyze the data from periodic calibration of 27 thermometers performed at the D. I. Mendeleev Institute for metrology for several years. Based on the analysis, it was concluded that the instability of the resistance of thermometers at the triple point of water for most thermometers exceeds ±0.002 °C, sometimes reaching several hundredths of a degree. The work analyzes the reasons for the instability of resistance, as well as the instability of the relative resistance of thermometers. Based on data analysis of the thermometer error at the temperatures between calibration points and graphs of changes in the interpolation function during the interval between the calibrations in the entire measurement range, it was shown that the error associated with the instability of the thermometer can be reduced from hundredths to thousandths of a degree when used as a measured parameter relative resistance of the thermometer. It is proposed to include in the regulatory documents on the verification methods of Standard platinum resistance thermometers an additional periodic calibration of the thermometers at the triple point of water.