FIXED-POINT TECHNIQUE FOR APPROXIMATING THE ITS-90 BETWEEN 420-DEGREES-C AND 1085-DEGREES-C WITH AN INFRARED THERMOMETER

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 (band-widths 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 ±0.05°C throughout the Zn-Cu interval when the thermometer in its 900 nm configuration is calibrated at the Zn, Al and Cu points.