Reference Electrode Placement — Close vs Remote (IR Error) (Diagram #005)
Shows how reference electrode placement affects ON readings due to soil voltage gradients and why instant-OFF reduces IR error regardless of placement.
What this visual explains
This diagram shows how reference electrode placement affects ON pipe-to-soil readings due to soil voltage gradients. The farther the electrode is from the structure (or the gradient center), the more the ON reading can be distorted by IR error.
Diagram
How to read it
- Close placement: electrode nearer the structure reduces the amount of gradient included in the reading (often).
- Remote placement: electrode farther away may include more gradient and distort ON.
- OFF readings: interruption collapses most gradient, reducing placement sensitivity.
Field interpretation
- If ON values vary significantly with electrode position, suspect strong gradients (high current, poor coating, close anodes).
- Place the electrode where it best represents the surface of interest (often “over the structure” for localized checks).
- Use instant-off when the goal is polarization rather than “system voltage + soil gradient.”
Common mistakes
- Chasing ON criteria without recognizing the reading is dominated by IR error.
- Assuming “remote earth” is always better for ON readings (it can be worse if it captures more gradient).
- Not controlling electrode contact/stability (mud contact, dry soil contact, drift).
CP 3 relevance
CP 3 field interpretation frequently depends on distinguishing real polarization from measurement artifacts. Electrode placement is one of the quickest ways to confirm whether ON values are gradient-dominated.