This article deals with the correlation between active corrosion of steel in concrete electrode potential measurements obtained by both classical method and bi-electrode method. In a first part, this paper deals with a relative value interpretation method which leaves aside the degree of ambiant hygrometry and the moisture of concrete. This relative value interpretation exhibits a good correlation between the corroded areas of concrete reinforcing rebars extracted from laboratory beams and the potential measurement. In a second part, this paper deals with an improved potential measurement using two reference electrodes. Two kinds of bi-electrode device are presented. In the first place, one reference electrode is fixed and takes the place of the electrical connection to reinforcement. Secondly, the two reference electrodes are moving simultaneously. With the relative value method, it is possible to make direct use of the values measured with both types of bi-electrode device. The results presented show a good correlation between potential mesurement obtained by bi-electrode devices and corrosion of rebars.