Interpolating equation of industrial platinum resistance thermometers in the temperature range between 0 °C and 500 °C

This paper compares four interpolation equations?for the calibration of 18 industrial platinum resistance thermometers (IPRTs) in the temperature range between 0??C and 500??C. They are the quadratic Callendar?van Dusen (CVD) equation, the deviation function specified in the International Temperature Scale of 1990 (ITS-90), and the third- and fourth-order polynomials of resistance as a function of temperature. It was found that when the upper limit of the calibration range was higher than 240??C, the third- and fourth-order polynomials resulted in a smaller standard error-of-fit than either the CVD equation?or ITS-90 deviation function did, and of the latter two functions, the ITS-90 deviation function worked better. When the upper limit of the temperature range was 500??C, the fourth-order polynomials showed distinctly better performance than the others. The standard error-of-fit for the fourth-order polynomial in the temperature range between 0??C and 500??C was on average??1/3 compared to the CVD equation,??1/2 compared to the ITS-90 deviation function and??70% compared to the third-order polynomial. When the upper limit was 100??C, the difference among the four equations?was insignificant. Consideration is briefly given to using interpolation as specified in the ITS-90 but with additional check points, and also to the use of the CVD equation?below?0??C.