Ohmic drop soil resistivity measurements

The measured potential contains, besides the true object/soil potential, an ohmic voltage drop that is proportional to the specific soil resistivity and the current density. 

Potential measurements of protected structure, especially in soil, are comprised with an error resulting from the voltage drop between the structure and the reference electrode. This error depends on the resistance of layers of corrosion products and insulation, and the resistance of the electrolytic environment. Equation (1) shows the amount of ohmic potential drop in the measurement of the potential of a... 

A critical paper on these potential criteria was published by Gummow [25], who described the effect of placement of a reference electrode during measurement on the IR ohmic voltage drop, the importance of the resistivity of the soil, the presence of bacteria, and the temperature. He has also warned against overprotection of the structure and recommended maintaining the CP potential of steel in the range —0.85 V to —1.1 V versus SCE. 

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