Thank you for your question regarding Direct-Current (DC) versus Alternating-Current (AC) measurements for earth readings. It is our pleasure to help.
When measuring resistance, you technically can only use a Direct-Current (DC) signal. When you use an Alternating-Current (AC) signal you are actually measuring impedance.
Now to your soil measurement question. We have never heard that the “ionic recombination of salts” presents a special issue for Direct-Current(DC) measurements. But, the resistance that the salts present would be something that we would want to measure. While we are not Geologists, I can tell you that every single manufacturer of ground measuring equipment advertises Direct-Current (DC) gear for a reason. Even when their gear actually uses AC signals.
Often you will see lower-cost ground measurement meters that claim to use 128 Hz “pulsed DC” signals. “Pulsed DC” is a less-than-honest way of saying that the meter uses a Square-Wave AC Signal. The reason for the misrepresentation is clear, the manufacturers of this gear want you to think that they use the better Direct-Current (DC) measurement method.
E&S Grounding Solutions does NOT recommend the use of Alternating-Current (AC) for earth measurements.
We hope you find this information useful. If you should have any further questions, please feel free to call us at 310-318-7151 to further discuss how we can assist you.
The Engineering Team at E&S Grounding Solutions