ELECTRICAL IMPEDANCE MEASUREMENT USING VOLTAGE/CURRENT PULSE EXCITATION

Electrical impedance measurements based on pulse excitation are fast and simple to implement, which makes them attractive for low-power measurement systems such as remote water conductivity monitoring based on two-electrode cells. Pulse measurements also allow us to estimate electrode parameters but measurement errors increase when the electrode resistance is very different from that of the electrolyte. We propose a dual pulse excitation technique to minimize errors in estimating electrode parameters: a voltage pulse is followed by a current pulse whose amplitude is set according to the results for the first ( voltage) pulse. Experimental results for impedance networks that emulate water resistivity from 100 Omega cm to 10 k Omega cm ( corresponding to surface waters) measured with two stainless-steel electrodes, yield relative errors below 0,2 % even for ( emulated) corroded electrodes. For actual electrodes, relative errors are below 2 % for the resistance and 4 % for the capacitance that model its impedance. Conductivity measurements for surface waters yield relative errors about 0,1 %, which is quite acceptable for low-cost autonomous sensors. Electrode impedance estimates differ from the first to the second pulse, presumably due to the different effective current density injected by each pulse. Nevertheless, experimental results can still be used to detect corrosion in stainless steel electrodes.