The synchronous synthesis and synchronous measurement of sinusoidal signals using a single internal clock frequency of a high-resolution digitizer allow the determination of alternating current (AC) quantities with unprecedented low uncertainties. A fully digital system based on this technique was developed at the Physikalisch-Technische Bundesanstalt - PTB to calibrate measuring instruments for complex AC voltage and current ratios, phase angle, effective value of AC voltages and currents, active, reactive, and apparent power with very low uncertainties. It allows the measurement of the ratio of AC voltages and AC power with uncertainties at the µV/V and µW/W levels respectively. Measurement methods and models for estimating the measurement uncertainties are presented.weiterlesen