Published in MATERIALS PERFORMANCE, Vol. 33, No. 11, pp. 14-17 (1994) November
	Published by NACE International, Houston, TX www.nace.org © NACE, 1994

Factors Affecting the Accuracy of Reference Electrodes

Frank J. Ansuini
Electrochemical Devices, Inc.
PO Box 31
Albion, RI 02802

James R. Dimond
Dimondale Co., Inc.
PO Box 838
Middlefield, OH 44062

ABSTRACT

This article discusses several factors that affect the reference potential established by silver/silver chloride and copper/copper sulfate reference electrodes. Data is presented on the effects of temperature, light, contaminants, and solute concentration. More information is available in CORROSION/94 paper no. 323, presented in Baltimore Maryland.

When measuring corrosion potential, a voltmeter is used to measure the potential (voltage) between the structure and a reference electrode placed in the same electrolyte. The entire circuit, structure plus reference, can be thought of as a single cell. Because a reference electrode comprises one half of this cell, it is commonly referred to as a "half-cell". Measured potentials are actually the difference in potential between that of the reference and that of the structure. It is frequently assumed that the potential established by a reference electrode is absolutely invariant; therefore, any observed potential changes must be occurring on the structure. This is not always the case. The observed changes could also be caused by a change in the reference while the structure remains steady. To ensure accurate potential measurements, it is important to understand those factors that affect the potential of a reference electrode.

CONCLUSIONS

• Accurate readings with portable references require that the ambient temperature be recorded and a temperature correction be applied.
• Light striking the element of a portable Cu/CuSO₄ reference through the clear-view window can induce significant photo-errors. This window should be covered with dark tape.
• Portable references should be cleaned and the electrolyte replaced on a regular basis for them to maintain accuracy.
• Dry electrodes should be used only in electrolytes known to have a consistent composition and that contain nothing that can adversely react with the element metal.
• Permanently installed references are usually not affected by photo-errors, and their ambient temperature range is much narrower (not including concrete bridge deck applications). For this reason, they are more accurate than a portable reference.

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