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.

This paper presents a modified sine-fitting algorithms which can be used for high-accuracy sampling measurements of complex voltage ratio of sinusoidal signals. The proposed algorithms provide a significant reduction in the measurement uncertainty of phase shift when synchronizing the sampler and signal source is impossible.

Issues related to measurements of the complex ratio of two sinusoidal voltages based on digital sampling are considered in this article. Several algorithms for determination of the complex voltage ratio are discussed. Results of five algorithms are compared and minimizing their errors related to differences between the two sampling channels is examined. For verification, a sampling system with National Instruments PXI 4461 data acquisition module (DAQm) was used.

This paper describes an improved version of a sampling-based bridge designed for impedance calibration. Based on the original concept of the new multiplexer, which constitutes a key element of the improved impedance bridge, we propose a new procedure for determining the complex voltage ratio using both successive and simultaneous sampling. The procedure significantly improves the accuracy of impedance comparisons by eliminating digitizer gain errors and reducing errors caused by instabilities in the excitation voltages supplied by the precision sources driving the bridge arms. An implementation of the new procedure, employing an innovative cross-multiplexer together with modified software, is presented. We also provide an analysis of selected error sources, including the effects of digitizer nonlinearity, which is crucial when applying the modified method for determining the impedance ratio. Finally, validation results are presented, demonstrating the performance and accuracy of the SUT sampling-based bridge in comparison with another validated bridge used at the Italian National Metrology Institute (INRIM) in Turin.