Virtual instrument using bilinear transformation for parameter identification of high impedance objects

Abstract

This paper presents a virtual instrument for measuring the impedance parameters of high impedance objects (|Zx | ≤ 10 GΩ). A method of component identification of multi-element two-terminal networks has been developed on the basis of bilinear transformation. The method is dedicated to parameter identification of different kinds of anticorrosion coatings. During the identification, the vector measurement of the object impedance is necessary at a few selected frequencies, equal to the number of elements under identification. The analysis of optimal frequencies selection is presented ensuring minimal identification error. The test results from the implemented algorithm are shown. The results proved the possibility of shortening the anticorrosion coating performance testing time by several orders in relation to the traditional impedance spectroscopy technique. A digital signal processing technique has been used in the virtual instrument for determination of the orthogonal parts of the measurement signals. It allows us to achieve a wide range of measurement frequencies, especially very low, from 1 MHz to 100 µHz. In order to measure impedance in the range 100Ω ≤ |Zx | ≤ 10 GΩ with an error not exceeding 2.5%, an input circuit based on a current-to-voltage converter has been used.