Electrochemical Noise Measurements in ZRA mode make simultaneous measurements of both current and voltage noise. Two identical corrosion specimens are held at the same potential and the current flow between them is measured. Simultaneously, the potential difference between the specimens and a reference electrode is measured.
ECN in ZRA mode is especially valuable in detecting localized corrosion. Uniform corrosion, by definition, should occur equally on both specimens. Therefore, there should be no net current flow between them.
Localized corrosion reactions cause fluctuating currents as pit or crevices become active and repassivate. At any given time, one specimen can have more active sites than the other. As a result, there is a fluctuating (noisy) current flow between the specimens.