The effect of ultra-high pressure on the emf of thermocouples

The effect of ultra-high pressure on the thermal emf of a chromelialumel thermocouple is investigated using an indirect method which does not require a direct knowledge of the temperature of the pressurized junction. The unknown temperature is written parametrically as a function of a directly measured quantity, the electrical power delivered to the internal furnace. The emf of the pressurized thermocouple is then written as a function of the temperature and a set of unknown coefficients. Combining the two functions to eliminate the unknown junction temperature, the pressurized emf is given as a function of the furnace power. The coefficients of both the temperature-versus-power function and the pressure-corrected emfver sus -temperature function are then obtained simultaneously by per forming a nonlinear least-squares fit to the directly measured emfversus -furnace power data. Results for the temperature correction due to pressure are compared with estimates obtained by other methods for pressures between 25.0 kbar and 60.6 kbar and temperatures up to approximately 900°C