Reducing the uncertainty in real-time impedance measurements

This paper arises from the exigency of enhancing the performance of a VXI-based digital meter designed for real-time tracking of impedance. Specifically, the metrological characterization of the meter has put into evidence that the experienced measurement uncertainty is mostly due to wide-band noise corrupting the acquired signals. With the aim of reducing its noise susceptibility without compromising the measurement rate, two digital signal-processing solutions are proposed. The first one pre-processes the acquired signals by means of predictive digital filtering for improving zero-crossing detection and, consequently, granting more reliable phase displacement measurements. The second solution evaluates the inner product of the signals of interest in order to average noise during the course of measurement, thus limiting its effect on the overall uncertainty. Many impedance measurements are carried out to draw a proper comparison between the proposed solutions.