We present an emf-temperature reference function for platinum versus palladium (Pt/Pd) thermocouples in air for the range 0 EC to 1500 EC. The reference function is based on the International Temperature Scale of 1990 (ITS-90) and has an expanded uncertainty (coverage factor of two) of less than the equivalent of 11 mK for temperatures up to 1050 EC and rising smoothly to approximately 0.3 K at 1500 EC. The reference function is based on a set of Pt/Pd thermocouples of exceptional stability and homogeneity constructed from Pt and Pd wire of very high purity (99.999% mass fraction and 99.997% mass fraction, respectively). Experimental results are presented on the thermoelectric stability of Pt/Pd thermocouples at high temperatures and on the calibration of Pt/Pd thermocouples based on this reference function.
Reference tables for several thermoelements versus platinum (Pt-67) are given with values of the thermoelectric voltage as a function of temperature in degrees Fahrenheit. Only tables for standard letter-designated thermoelements are included: Types BP, BN, JP, JN, KP (same as EP), KN, TP, and TN (same as EN). These tables supplement those given in NBS Monograph 125 and were calculated from the power series expansions presented in that Monograph. They are based upon the absolute electrical units and the International Practical Temperature Scale of 1968 (IPTS-68).
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