The present invention relates to measuring electrical impedance and particularly to measuring impedance of electrodes used to acquire physiological signals. The measurement of electrode impedance is typically performed to ensure proper electrode to skin contact and thus verify the quality of the acquired signals. Electrode to skin contact impedance has also clinical utility for monitoring diagnosis prognosis or treatment as it can be used to measure skin conductivity which is function of physiological processes. The present invention relates in particular to a substantially continuous method for performing such measurement. The measurement is performed in such a way that it does not affect the bioband the range (or ranges) of frequencies that contains components used for diagnostic prognostic triage and/or treatment purposes. The present invention therefore performs this impedance measurement without affecting the physiological signal while allowing for uninterrupted monitoring of said signal.
