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 degrees C and 500 degrees 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 degrees 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 degrees 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 degrees C and 500 degrees C was on average approximate to 1/3 compared to the CVD equation, approximate to 1/2 compared to the ITS-90 deviation function and approximate to 70% compared to the third-order polynomial. When the upper limit was 100 degrees 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 degrees C.