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Title: Gold Versus Platinum Thermocouples: A Highly Accurate Secondary Reference Thermometer
Author: Dean Ripple
Source: 1995 Measurement Science Conference
Year Published: 1995
Abstract: Gold versus platinum thermocouples are stable to 15 mC over 1000 hours of use at temperatures up to 1000C. Compared to high temperature standard platinum resistance thermometers, the thermocouples are more rugged and may have less long-term drift at temperatures above 960C. These factors make Au/Pt thermocouples ideal as a secondary standard for temperatures up to 1000C. Practical methods used at NIST for the preparation, calibration, and use of Au/Pt thermocouples are described in this talk. Special techniques are necessary to properly anneal the wire elements, to minimize contamination of the thermoelements by impurities, and to prevent wire strain caused by the different thermal expansion coefficients of platinum and gold. The assembled thermocouples are calibrated at the freezing points of In, Sn, Zn, Al, Ag, and Au, which arc defining fixed points of the International Temperature Scale of 1990. The deviations of the measured emf values from the reference values are fitted with a low-order polynomial to obtain a calibration function for the thermocouple.

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