Impedance spectroscopy for diagnostics of magnetic flowmeter

We have developed and implemented advanced diagnostics features for magnetic flowmeters to measure the medium conductivity as an important process parameter and coating on electrodes or liner, which disturbs the flow measurement. The electrode-electrolyte interface (Helmholtz or double layer) is a major obstacle to determine the conductivity directly from the impedances between electrodes at low frequencies. The impedance matrix of the multi-electrode transducer was measured using impedance spectroscopy and different electrochemical components could be identified. The measurements were verified in numerical field simulations. The results have been used to derive a lumped model of the transducer. Coating is found to have an effect on the electrode-electrolyte interface, whereas conductivity can be determined from the bulk resistances. This served as the basis for a successful implementation of the diagnostics function in an embedded microcontroller system.