Potential probes for applications in cathodic protection: accuracy of the measurement of the IR-free potential

Potential probes are sensors consisting of a reference electrode and a metal plate close to the electrode used for measuring the protection potential of underground metal structures in cathodic protection. They allow the reading of the potential purified from the contribution of ohmic drop, the so-called IR-free potential, a useful parameter for assessing the effectiveness of a cathodic protection system. Aim of this work is to compare the accuracy of the potential measurements of three commercial probes, which differ in geometry, extension of the porous septum and position of the metal coupon. Measurements of reference electrode potential stability in the presence of cathodic protection and ability of the probes to compensate the ohmic drop were performed. The results show that not all three probes are able to effectively measure the IR-free potential, as the measurement contains an ohmic drop contribution, greater for more negative cathodic polarization values.