New aspects concerning the comparison tests between the STL reference current shunt and an ICMET standard shunt, regarded in interference with the issues of the “CMC” concept

This paper provides an overview of the comparison tests on two current shunts performed on March 2012 in ICMET Craiova as well as the consequences of this comparison for the demonstration of the traceability of the calibrations carried out by the ICMET Calibration Laboratory “C.L. - High Currents”, and other issues about the measurement uncertainties. The two current shunts which underwent the comparison program are the STL reference standard shunt for Europe and Africa and the coaxial shunt type 200kA manufactured by IPH Berlin which stands for the C.L. - ICMET standard shunt. Both of the shunts are of the same manufactory type with similar technical characteristics, thus providing the ability of comparison. The comparison results, proving little errors (in comparison with the magnitude order of the CMC having been stated for the C.L. for this kind of tests) related to the scale factor of the IPH-ICMET shunt, are consistent with the results of all its Calibration Certificates, so this is a witness of the traceability of the measurement results in C.L. On the other side, the IPH shunt and the HBM digitizers are the main error component sources of the Current Reference Measuring System belonging to C.L.-ICMET. By two different checking undertakings and by the calibration certificates, we conclude that the errors introduced by the digitizers are also very small. The results here-above showed that the uncertainties associated to the scale factor of the Reference Measuring System are much smaller than the “CMC” having been stated for it under accredited regime.