Parasitic capacitance influence of potential-sensing electrodes on four-electrode liquid impedance measurements

摘要

Four-electrode techniques are used to minimize the effects of electrode polarization on measurements of the frequency-dependent impedance of conductive solutions. Basic circuit analysis confirms that an ideal Schwan-type four-electrode measurement can theoretically determine the polarization-free impedance of a sample. However, circuit analysis including parasitic effects indicates that the input impedance of the potential-sensing electrodes will be a significant influence on the measurement. This is verified in experiments on conductive solutions employing measurements of the gain and phase between potential-sensing electrodes in a four-electrode arrangement. The electrode impedance is varied by adding capacitors in parallel with the probes. The combined theory and experimental data indicate that parasitic capacitance of the potential-sensing electrodes is non-negligible and will alter the measured capacitance at all frequencies and even distort conductivity measurements at high-frequencies. This result has significant implications for the feasibility of broadband measurements of liquids based on four-electrode impedance methods.