Calibration consistency of AC Voltage Standards developed at the Silesian University of Technology

In 2014 at the Silesian University of Technology (SUT) two calculable thermal AC voltage standards were developed. AC-DC differences of those standards were calculated from an appropriate mathematical model in 1 kHz – 1 MHz frequency range and determined experimentally in 10 Hz – 1 kHz frequency range. The correctness of determination of the AC-DC differences of the standards were verified by comparing them with a thermal converter calibrated in an external laboratory. That calibration confirmed the correctness of the determined AC-DC transfer differences. Lately, a comparison with a third laboratory has been performed. The paper presents results of these comparisons and a discovered inconsistency between the calculated AC-DC transfer differences of the SUT calculable thermal AC voltage standards and the AC-DC transfer difference of the AC voltage standard from the third laboratory.