A fixed-point technique for calibrating infrared thermometers between the Zn (420°C) and Cu (1085 "C) points was analyzed. To do this, a precision silicon detector thermometer working at 900 nm and 950 nm (bandwidths of 70 nm and 40 nm, respectively) and a set of four fixed-point black-body cavities (Zn, Al, Ag and Cu) were used. The best results showed that the ITS-90 can be approximated to within k0.05 "C throughout the Zn-Cu interval when the thermometer in its 900 nm configuration is calibrated at the Zn, A1 and Cu points.

The design of a compact blackbody furnace that allows temperature fixed points to be realized to a high degree of accuracy is described. Using this apparatus, the standard uncertainty in the calibration of a precision infrared thermometer at the fixed-point temperatures of indium, tin and zinc was estimated to be about C. This furnace can be used as a travelling standard for intercomparisons as well as laboratory apparatus for the calibration of precision infrared thermometers.

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Round-robin measurements with a transfer standard radiation thermometer were organized by the NRLM in the framework of a three-year joint research agreement with the NIST, the IMGC and the PTB: the NPL also took part in this exercise. The aim of the study was to assess the mutual traceability of the ITS-90 temperature scales established by the different laboratories in the high-temperature range (above 1000 °C). The thermometer was a monochromatic (0,65 µm) silicon-detector thermometer belonging to the NRLM. It was circulated in the period from May to July 1993 and was calibrated by all the participants against their local reference thermometers. The temperature interval from 1000 °C to 2000 °C was covered by all the participants, but some extended the range down to 800 °C or up to 2700 °C. The results indicate that all the calibrations agree to within 0,5 °C at 1000 °C and to within 2 °C at 2000 °C.

The primary purpose of the comparison was to establish the equivalence of the calibration of infrared radiation thermometers within Europe in the temperature range 800 °C to 2000 °C. Seven EU national metrological institutes (NMIs) participated. The equivalence of calibrations was determined by circulating a transfer standard infrared radiation thermometer between the participating laboratories. The calibrations obtained were compared with the reference calibration performed by the co-ordinating laboratory (National Physical Laboratory). It was found that, after correction for the size-of-source effect, the calibrations of the participating laboratories nearly all agree to better than 0,1 % of temperature.