Four electrode conductivity meters

As mentioned before, soil is a physically, chemically, and biologically complex system. Factors that affect corrosion in soil, in addition to specific ions, are resistivity of soil, oxygen content, and acidity. Field measurements of soil resistivity are covered in ASTM G 57, Method for Field Measurement of Soil Resistivity Using the Wenner Four-Electrode Method, which is the most widely used test, and using the proper meter produces accurate and reproducible results. Conducting field measurements of soil pH is covered in ASTM G 51, Test Method for pH of SoU for Use in Corrosion Testing. The corrosion resistance of lead and its alloys depends mainly upon the presence of silicate, carbonate, and to a lesser extent sulfates, in contributing to the passive film formation. 

Soil resistivity measmements are frequently conducted with a resistivity meter connected in a Wenner array, as illustrated in Figure 27.13. Four electrodes are driven into the ground along a straight Kne, with an equal spacing, d, between each electrode. Cmrent, I, is passed between the two outer electrodes (called cmrent electrodes) Cj and C2, and the resulting voltage, V, is measured... 

The electrical conductivity of the plated electrodes is estimated fi om their sheet resistances, which are measured using a low-resistivity meter with a four-pin probe (measurement range of 10 to 10 f2). 

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