Abstract: The sensor according to the invention has at least one metal electrode of the same material as the measured structure and a permanent reference electrode. The measuring surface area of the metal electrode satisfies the relation 2.0m.sup.2 .gtoreq.S.gtoreq.0.1cm.sup.2, where S is the measuring surface of the electrode. The sensor is buried in the ground at a distance L from the measured structure, said distance L satisfying the relations 20m.gtoreq.L.gtoreq.0.1m and L.gtoreq.6R, where R is the radius of a hypothetical sphere having the same surface area as the measured non-linear structure, or the radius of a cylindrical linear structure such as a pipeline.

Abstract: A parallel galvano-electrolytic current path is provided to conduct a current comprising (i) a portion of the interfering current and (ii) currents arising due to varying degrees of polarization of metal surfaces. The current is measured and a variable resistor inserted in the galvanic path is reduced in value until zero current flows through the parallel galvano-electrolytic current path in the direction of the electrolytic portion of said galvano-electrolytic path. Also disclosed is a circuit for applying said method.

Abstract: A parallel galvano-electrolytic current path is provided to conduct a current comprising (i) a portion of the interfering current and (ii) currents arising due to varying degrees of polarization of metal surfaces. The current is measured and a variable resistor inserted in the galvanic path is reduced in value until zero current flows through the parallel galvano-electrolytic current path in the direction of the electrolytic portion of said galvano-electrolytic path. Also disclosed is a circuit for applying said method.

Abstract: A portable sensor for measuring the corrosion endangering and electrochemical protection of a metal structure buried in an electrolyte in a current field. An elongated carrier made of an electrically nonconductive material, whose longer dimension is at least double its shorter dimension, said carrier having two extremities, is provided with a reference electrode on one of its extremities, and the carrier is fitted with at least one other electrode, e.g., an auxiliary metal electrode.

Abstract: A method and apparatus for measuring the polarization potential of anodically protected metal structures in moist soil in a current field utilizes auxiliary electrodes and a reference electrode immersed adjacent the metal structure in the same soil. The auxiliary electrodes are connected to the metal structure, then disconnected, and the electrical potential between the auxiliary electrodes and reference electrode is measured immediately after the disconnection.