Furnace Effect for the Re-C Fixed Point

Abstract The furnace effect of the rhenium–carbon (Re–C) high-temperature fixed point was experimentally estimated by comparing the point-of-inflection temperature of the melting plateau demonstrated by the same Re–C cell in three furnaces of different dimensions. Two cells with the same outer size but different blackbody cavity designs were used. After corrections of the measured temperature for the size-of-source effect and the pyrometer stability, the furnace effect, estimated as the maximum change of the Re–C temperature from furnace to furnace, was found to be 0.094 K for the ‘best’ realisation of the fixed point. For the ‘normal’ realisation, additional components of the furnace effect, associated with non-optimal use of the fixed-point cell and furnace, were considered. The uncertainty components of the Re–C fixed point realisation associated with the furnace effect were estimated to be 0.060 K and 0.110 K for the best and normal cases, respectively.