Current Measurement
Current measurements explain how much protective current is being produced, where it is flowing, and whether the CP system is behaving as expected.
Potential readings tell part of the story. Current measurements connect those readings to rectifier output, anode-bed condition, bonds, current distribution, coating condition, and troubleshooting.
Common Current Measurements
| Current Type | Where Used | Interpretation Use |
|---|---|---|
| Rectifier DC output | Rectifier panel meters or calibrated field meter | Verifies power supply output and trends. |
| Shunt current | Rectifiers, bonds, anode leads, coupons | Converts millivolt drop across known resistance to current. |
| Clamp-on current | Accessible conductors where suitable signal exists | Useful for cable current checks but must match instrument capability. |
| Line current | Pipeline current spans or test stations | Supports interference and current-distribution evaluation. |
| Anode current | Individual anode leads or junction boxes | Identifies current imbalance, failed leads, or depleted anodes. |
Interpretation Priorities
- Compare current with voltage; a current change without voltage change means something different than both changing together.
- Check whether a zero-current condition is a true outage, open circuit, blown fuse, failed shunt, bad meter, or disconnected lead.
- Trend current over time rather than relying on one isolated inspection.
- Use current distribution data to explain why some test points polarize and others do not.