Virtual instrument using bilinear transformation for parameter identification ofhigh impedance objects

Abstract

This paper presents a virtual instrument for measuring the impedance parametersof high impedance objects (|Zx | ≤ 10 GΩ).A method of component identification of multi-element two-terminal networks hasbeen developed on the basis of bilinear transformation. The method is dedicatedto parameter identification of different kinds of anticorrosion coatings. During theidentification, the vector measurement of the object impedance is necessary at afew selected frequencies, equal to the number of elements under identification. Theanalysis of optimal frequencies selection is presented ensuring minimalidentification error. The test results from the implemented algorithm are shown.The results proved the possibility of shortening the anticorrosion coatingperformance testing time by several orders in relation to the traditionalimpedance spectroscopy technique. A digital signal processing technique hasbeen used in the virtual instrument for determination of the orthogonalparts of the measurement signals. It allows us to achieve a wide range ofmeasurement frequencies, especially very low, from 1 MHz to 100 µHz. In orderto measure impedance in the range 100Ω ≤ |Zx | ≤ 10 GΩwith an error not exceeding 2.5%, an input circuit based on a current-to-voltageconverter has been used. The use of modern electronic components combined withdigital signal processing techniques resulted in a low-cost instrument formeasurement parameters allowing widespread use in impedance spectroscopy formany technical objects.