Calculation of measurement uncertainty in a measuring system for electrical energy

A measuring system has to be verified at regular intervals with respect to the measuring uncertainty and a mathematical model of how to calculate this overall uncertainty has been developed by the SP Swedish National Testing and Research Institute, the National Metrology Institute of Sweden. The model is based on an ISO guide to the expression of uncertainty in measurement and the recent EA (European Accreditation) guide EAL-R2. According to the ISO and EA guide, a combined uncertainty should be stated at a confidence level of 95% and by the RSS (root sum square) of identified uncertainty contributions estimated at one sigma level. In the model used, the uncertainty contributions normally refer to relevant IEC and/or CENELEC standards for the meter and measuring transformers used. Measured values for uncertainty contributions from voltage drop, burden, etc., are also taken into account