STANDARDIZATION OF PLATINUM RESISTANCE THERMOMETERS AT TEMPERATURE FIXED-POINTS IN THE RANGE 273.16 TO 693 K

Standardization of some foregin make standard platinum resistance thermometers (SPRTs) has been undertaken at the indigeneously developed and fabricated temperature fixed points, i.e. at triple point of water (TPW), melting point of gallium and freezing points of tin and zinc. The uncertainty in temperature measurement with these SPRTs has been evaluated and found to be +/-0.2 mK at TPW and +/-0.5 mK at gallium, tin and zinc points. The values of constants of SPRTs calculated from the resistance ratios at the above fixed points are well consistent with the values given in the International Temperature Scale of 1990 (ITS-90). The results of these measurements show that the temperature fixed points established at the National Physical Laboratory, New Delhi are reproducible within +/-0.2 mK and are comparable to the fixed points of any other standard laboratory in the world.