ER Probe measures the corrosion rate as an increase in electrical resistance over time for a steel probe element exposed to the corrosive environment.

The increase in electrical resistance is proportional to the accumulated corrosion in period exposure. The main benefit of this method is that it can be utilized in continuous on -line process monitoring anf optimize the injection of corrosion inhibitor.

LPR probe measures the direct current throught the metal or fluid interface when  the electrodes are polarized by a small electrical potential . As this current is related to the corrosion current that in turn is directly proportional to corrosion rate, the method provides an instantaneous measurement of corrosion rate