Interface circuit for impedance sensors using two specialized single-chip microsystems

The paper presents an interface circuit designed for the measurement of impedance parameters of sensors or measurement cells installed on technical objects. The interface circuit allows measurement of the modulus and argument of impedance in the range of 10 Ω ≤ |Zx| ≤ 10 GΩ at a measurement frequency in the range of 0.01 Hz to 100 kHz. The new solution based on two specialized SoC AD5933 microsystems has been used. This has allowed to obtain miniaturization, low power consumption and low-cost of the circuit of the impedance interface. During tests of the realized prototype using the reference object, the object impedance measurement errors have been determined and they do not exceed ±1.6% (for relative error of impedance modulus) and ±0.6° (for absolute error of impedance argument). The obtained accuracy is fully acceptable in case of impedance measurement of anticorrosion coating in the field. The comparison measurements performed with the aid of Solartron set of instruments showed that the impedance measurement accuracy of the proposed module is comparable to laboratory set of instruments. The important advantage of the used solution based on AD5933 microsystems is lowering the power consumption down to ca. 0.7 W, which makes possible powering the measurement module from a PC using +5 V from the USB. It is a very profitable feature for a module designed to work directly in the field.