Design and Experimental Validation of Multi-Frequency Impedance Measurement System

Commercially available impedance meters can only measure at one frequency at the time. In this paper, we propose and validate multi-frequency impedance meter capable of simultaneous impedance measurement for several frequencies, which is very advantageous in engineering practice. The proposed system is based on the conventional auto-balancing bridge method and adapted to cooperate with an inductive-loop sensor for impedance measurement simultaneously at 3 frequencies. The hardware of the proposed system consists of the measurement bridge and the PXI module equipped with a field programmable gate array (FPGA) card, and analogue-to-digital and digital-to-analogue converters. Multi-frequency excitation source, vector voltmeters, and measurement algorithms are implemented in the FPGA and PXI. The proposed impedance measurement system is validated by comparison with a commercial impedance analyzer. The results revealed that the proposed system has high speed (less than 10 ms per measurement) and high relative accuracy in the frequency range of 6-15 kHz.