When monitoring the structure to soil potential of a tank protected by an impressed current cathodic protection system, in what state should the rectifier be?

For monitoring the structure-to-soil potential of a tank that is protected by an impressed current cathodic protection system, the rectifier should be in the "turned on" state. This allows for accurate readings of the potential difference to be acquired while the cathodic protection system is actively supplying current.

When the rectifier is on, you can measure how effectively the cathodic protection system is functioning to prevent corrosion on the tank. The monitoring process reveals information about the protective currents and the overall effectiveness of the system in mitigating corrosion risks.

In contrast, if the rectifier were turned off, it would lead to misleading measurements, as no current would be flowing from the rectifier, resulting in a potential reading that does not reflect the real conditions during active protection. Similarly, if the rectifier were in standby mode or disconnected, the readings would also be inaccurate or unavailable, which would prevent proper assessment and maintenance of the tank protection measures. Thus, the best practice is to ensure that the rectifier is turned on during monitoring to obtain valid and useful data.