Measurement of the Difference between IPTS-68 and Thermodynamic Temperature in the Range 457 °C to 630 °C

This paper describes the measurement of the difference between the International Practical Temperature Scale (IPTS-68) and thermodynamic temperature in the range 457 °C-630 °C using the NPL photon-counting pyrometer. This instrument operates at sufficiently low radiance temperatures to allow the gas thermometry results of Guildner and Edsinger, which cover the range from 0 °C to 457 °C, to be extended upwards. The results agree well with the recent measurements of Jung (1984). Their implications with respect to the differences at still higher temperatures are discussed briefly.