The standard function for a platinum resistance thermometer above the setting point of silver

Abstract

A method and apparatus are described for measuring the characteristics W(T) at 962– 1085 °C for a hightemperature platinum resistance thermometer. A special design has been used containing a radiating cavity of black-body type localized around the sensitive element. The measurements were made with a spectropyrometric comparator by brightness comparison at the Ag, Au, and Cu reference points, and also at temperatures representing multiple and fractional brightnesses. The results are compared with the W(T) obtained by interpolating measurements made by the contact method at the Zn, Al, and Cu reference points. The differences in the W(T) constituted the temperature equivalent of 0.16, − 0.14, and 0.04 at the reference points correspondingly for Ag, Au, and Cu. The over- all measurement error is estimated as 0.19°C. An interpolation formula is proposed that is based on the standard function W_ref(T₉₀) given in the definition of ITS- 90.