Zero-voltage ammeters (ZVA) are required to measure the coupling currents from each electrode of the coupled multielectrode array sensor (CMAS) probe to the coupling joint to derive the corrosion current. All ZVAs, including the zero-resistance ammeter (ZRA) or the shut-resistance ammeter, impose a small voltage between each of the electrodes and the coupling joint. The Butler–Volmer Equation was used to assess the effect of the small voltage imposed by the ZVA on the measurement of the corrosion rate. The calculated results indicate that the effect of the ZVA that imposes less than a 0.2-mV voltage in the measuring circuit is less than 5% regardless of the type of the ZVA. The cases considered in the analysis include large ranges of the Tafel slopes in the anodic direction, βa, and in the cathodic direction, βc, (βa= 30 to 120 mV/Dec; βc=50 mV/Dec to infinity) and the lowest value between the coupling joint potential and the corrosion potential of the most anodic electrode reported in the literature (5 mV). If this value is 20 mV, instead of 5 mV, the effect of the ZVA that imposes a 0.5-mV or lower voltage in the measuring circuit is less than 5%, regardless of the type of the ZVA.

Subject
Circuits, Anode potential, Voltage, Corrosion currents, Anodic electrodes, Cathodic current, Couplings, Silicate deposits, Anodic current, Corrosion probes, Localized corrosion, Electrodes, Corrosion potential
Keywords:
Zero Resistance Ammeter, ZRA, Zero Voltage Ammeter, ZVA, electrochemical sensor, multielectrode sensor, corrosion monitoring, corrosion sensor, localized corrosion sensor, multielectrode array
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2016
Association for Materials Protection and Performance (AMPP)
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