Electrolyte ir voltage compensator for cathodic protection systems or

Abstract

There is disclosed a cathodic protection system current control apparatus incorporating an IR compensator circuit wherein the electric potential between a reference cell such as a copper-sulfate half-cell and the wall of a tank or other structure being corrosion protected is measured in such a way that nearly all of the potential due to IR voltage drop through the electrolyte is compensated for and eliminated leaving only a voltage measurement representing the true electrolytic potential at the cathodically protected object. This true electrolytic potential is utilized to act as a control input for a conventional current controller to maintain the desired electrolytic potential by changing the current passing through the electrolyte. The compensator circuit includes a rectifier device and a capacitor charged by a constant current source, and thus has a much longer response time for rising voltage values than it does for falling voltage values. This substantially eliminates the effect of IR voltage drop in the electrolyte which rises and falls 120 times per second. A preferred circuit includes an operational amplifier having a semi-conductor diode connecting with the output and then to a junction of conductors from a constant current source and a capacitor connected to ground; feedback from the diode to an amplifier input eliminates the effect of diode forward voltage drop.