The operation of transformer rectifiers (electrical units that place a voltage onto the pipeline to counteract the electrolytic corrosion reaction) is critical to cathodic protection. The voltage must be applied consistently and at the correct level:

Pipeline operators are recommended to check the correct functioning of their rectifiers at monthly intervals.

To be allowed to carry out functional rectifier checks, CP technicians must be trained on different electrical systems (AC supply and DC output) and many rectifier sites are remote and difficult to access.

Rectifier measurements are taken automatically by a MERLIN Transformer Rectifier Monitor installed at the rectifier. This checks that the electrical supply is still present, monitors the voltage and current output and (optionally) can take ON and OFF potential measurements at the rectifier drain point.