FIELD: protection of underground metal structures against corrosion, determination of degree of protection of any underground metal service line by method of auxiliary electrode in case of cathode protection by superimposed current. SUBSTANCE: according to invention device comes in the form of sonde placed in case with lid. Measurement part of device is made of comparison and auxiliary electrodes. Auxiliary electrode is fabricated from metal and has hole with capillary put into it. One end of capillary comes to working surface of electrode and is located at same level with it. Wires, one being connected to comparison electrode and two others being linked to auxiliary electrode, pass through lid. EFFECT: simplified measurement circuit and increased measurement accuracy. 3 dwg
