INTERNATIONAL TEMPERATURE SCALE : Temperature sensor

The first internationally recognized temperature scale was the international temperature scale of 1927 ITS-27. Its purpose was to define procedures by which specified, high quality yet practical thermometry could be calibrated such that the values of temperature obtained from them would be concise and consistent instrument-to-instrument and sensor-to-sensor, while simultaneously approximating to the appropriate thermodynamic values within the limits of the technology available. This goal remains intact today.

ITS-27 extended from just below the boiling point of oxygen, -200°C, to beyond the freezing point of gold, 1065°C. interpolation formulae were specified for platinum resistance thermometer calibrated at 0°C & at the boiling points of oxygen, water and sulphur (445°C). Above 660°C, the Pt-10% Rh vs. Pt thermocouple was specified for measurement. Above the gold point optical pyrometry was employed and the values of the fixed points were based on the best available gas thermometry data of the day.

ITS-27 was revised somewhat in 1948, and then more substantially in1968-with the adoption of the international practical temperature scale, IPTS-68. 1975 saw realignment with thermodynamic temperature through some numerical changes, and 1976 witnessed the introduction of the provisional 0.5 to 30Ktemperature scale EPT-76. The current scale, ITS-90, was adopted by the International Committee of Weights and Measures at its meeting in 1989, in th accordance with the request embodied in Resolution 7 of the 18 General Conference of Weights and Measures of 1987. This scale supersedes the International Practical Temperature Scale of 1968 (amended edition of 1975) and the 1976 Provisional 0.5 K to 30 K Temperature Scale.