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 ther mometers (SPRTs) has been undertaken at the indigeneously developed an d fabricated temperature fixed points, i.e. at triple point of water ( TPW), melting point of gallium and freezing points of tin and zinc. Th e uncertainty in temperature measurement with these SPRTs has been eva luated 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 t he values given in the International Temperature Scale of 1990 (ITS-90 ). The results of these measurements show that the temperature fixed p oints established at the National Physical Laboratory, New Delhi are r eproducible within +/-0.2 mK and are comparable to the fixed points of any other standard laboratory in the world.