Interpolating Equation of Precision Platinum Resistance Thermometers in the Temperature Range between -80°C and 300 °C

Abstract

This paper compares two interpolation equations for the calibration of precision platinum resistance thermometers (PPRTs) in the temperature range between -80°C and 300°C. They are the deviation function specified in the International Temperature Scale of 1990 (ITS-90), and the quadratic Callendar–van Dusen (CVD) equation. It was found that when the calibration range was between -80°C and 300 °C, ITS-90 deviation function resulted in a measurement error-of-fit of ±23mK, and the CVD equation resulted in ±24mK. In the temperature range of (-80∼0)°C, ITS-90 deviation function showed distinctly better performance than the CVD equation. When the temperature range was between 0°C and 100°C, the difference among the two equations was insignificant. In the temperature range of (100∼300)°C, the measurement error-of-fit of ITS-90 deviation function increased with temperature, and the maximum error-of fit under the CVD equation appeared at 200°C. If the temperature range is wider, the ITS-90 deviation function had better calibration effect. While the CVD equation worked better in a narrow temperature range.