R. Rybski

Impedance Measurement With the D-Optimum Experimental Conditions

A computer-based automatic alternating current (ac) bridge for impedance measurement is proposed. The problem of impedance measurement is formulated as a linear-in-parameter estimation one, and a suitable algorithm is proposed that ensures high measurement accuracy under a high convergence rate. In particular, the optimum experimental conditions regarding the reference resistance and the sampling time are developed. These conditions guarantee that the estimation is performed with possibly high accuracy. This paper also shows how to use the proposed approach for fault detection, which is very important from the point of view of modern control and fault diagnosis. The final part of this paper shows a number of illustrative experiments that justify the effectiveness of the proposed approach.

Characterization of a digitizer for a low value resistor calibration system in the audio-frequency band

The paper characterizes selected properties of a dual-channel digitizer designed for a low value resistor calibration system working in the frequency range from 40 Hz to 10 kHz. There are presented the experimentally determined frequency characteristics of magnitude and phase of the complex voltage ratio, as well as the research results of the digitizer linearity and the phase measurement accuracy.

Impedance Comparison Using Unbalanced Bridge With Digital Sine Wave Voltage Sources

This paper presents a digital automatic unbalanced bridge designed for comparing the impedances of R-R, R-C, and C-C. The measurement principle uses initial balancing of the bridge using two digital sine wave sources, then measuring the ratio of voltage drops on the compared impedances as well as the finite bridge unbalance voltage. The present method is novel because it is not necessary to obtain a complete voltage nulling and also because it is readily implemented with a commercial data acquisition (DAQ) card. An NI USB6281 DAQ card was used to obtain the results; this card combines the two 16-bit digital-to-analog converters with one multiplexed 18-bit analog-to-digital converter. Such a measurement system, which is relatively simple and inexpensive, can compare impedances with an error below 10 ppm. Some considerations concerning the relationship between the measurement accuracy of unbalanced voltage and the level of the bridge unbalance are given.