Assignment of \(T_{90}\) Temperature to a Vertical Co–C Cell for Thermocouple Calibration

Noble metal thermocouples are often required to be calibrated up to \(1400\,^{\circ }\hbox {C}\) in fixed points in order to get the lowest uncertainties. The International Temperature Scale of 1990 (ITS-90) defines the temperature of fixed points until the copper point (\(1084.62\,^{\circ }\hbox {C}\)). At higher temperatures, the metal carbon fixed points can be used, and the needed traceability to the ITS-90 is given by means of a standard radiation thermometer. This paper presents the method developed by the Centro Espanol de Metrologia to give traceability to the ITS-90 to the Co–C cell used to calibrate thermocouples by means of a mirror and a standard radiation thermometer with an expanded uncertainty (\(k =2\)) of \(0.5\,^{\circ }\hbox {C}\).