Reducing the uncertainty in real-time impedance measurements

This paper arises from the exigency of enhancing the performance of a VXI-b ased digital meter designed for real-time tracking of impedance. Specifical ly, the metrological characterization of the meter has put into evidence th at the experienced measurement uncertainty is mostly due to wide-band noise corrupting the acquired signals. With the aim of reducing its noise suscep tibility without compromising the measurement rate, two digital signal-proc essing solutions are proposed. The first one pre-processes the acquired sig nals by means of predictive digital filtering for improving zero-crossing d etection and, consequently, granting more reliable phase displacement measu rements. The second solution evaluates the inner product of the signals of interest in order to average noise during the course of measurement, thus l imiting its effect on the overall uncertainty. Many impedance measurements are carried out to draw a proper comparison between the proposed solutions. (C) 2001 Elsevier Science Ltd. All rights reserved.