Abstract: This paper presents a comparison of results of coherent and incoherent sampling measurements of complex ratios of sinusoidal voltages, obtained with the use of an ellipse-fitting algorithm (EFA) and with the use of discrete Fourier transform (DFT). The EFA algorithm has not been yet used in the measurements of the complex voltage ratio. Known applications of EFA in impedance measurements were based on simultaneous sampling of two voltages by a two-channel aquisition card. Measurements presented in this paper were made with an automated measurement system consisting of Keysight 3458A multimeter operating in the DC voltage sampling mode. The internal 20-MHz clock generator of this multimeter was replaced with a custom-made clock module dividing the clock frequency by 2 and providing fiber optic 10-MHz synchronization signal. This signal was used as the reference frequency of the Keysight 33250A generator which served as a reference frequency clock for the dual-channel source of digitally synthesized sinusoidal voltage. Because the output frequency of the Keysight 33250A generator can be adjusted with very high resolution and accuracy, it was possible to perform coherent and incoherent sampling measurements with controlled frequency deviation.
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