The combined expanded uncertainty for calibrations according to NT FIRE 050 performed in the furnace at SP is calculated and presented. The result is presented in tables so that the parameters that contributes most to combined uncertainty is easily recognized.
An example is also given for how to include the uncertainty in the regression analysis performed after the calibration. Calculations are performed for two temperature levels, i.e. 400°C and 1000°C and for the case with and without fitting piece.
The results show that with the furnace used today at SP the combined expanded uncertainty lies within of ±3% for the 1000°C case but not for the 400°C case. The limit of ±3% is defined by ISO for methods to be used as a primary calibration standard.
However, if the distribution of the wall temperature inside the furnace can be made more even, then the calibrations are well within the limit for all temperature ranges.