Abstract: To protect a structure immersed in an electrolyte, at least two protection units are located adjacent to different regions of the protected structure. In a preferred embodiment, each of these protection units includes a circuit for applying rectified alternating current voltage between the structure and electrodes immersed in the electrolyte adjacent to the different regions of the structure. Also, each of the protection units includes reference cells to produce direct current voltage between the reference cells and the structure, a measuring circuit coupled to the reference cells for measuring the potential between the reference cells and the structure, and a control circuit for controlling the level of the rectified alternating current voltage at the different regions of the structure in accordance with the measured potential levels.

Abstract: In making measurements of the potential of a structure immersed in an electrolyte, which structure is being protected from corrosion by a cathodic or anodic protection system, serious errors are often introduced by the IR drop component induced by current flowing between the cathode and anode of the protection system on a reference cell which is used for measurement. To overcome this, a system is provided of the type including means for applying a rectified alternating current voltage between the structure and an electrode which is immersed in the electrolyte and spaced apart from the structure. A direct current reference source is coupled to the structure. A reference cell is located in the electrolyte and spaced apart from the structure.