The galvanic insulation, ensured by control opto-couplers, is made without transfer of energy nor conversion into frequency between the primary loop and the secondary loop. The input supplies on the primary loop of current. The output, supplied by a continuous tension (generally provided by the acquisition unit) recreates the image of the primary current of loop. A luminous indicator on the output loop makes it possible to control the presence of the signals. The system is protected from the inverted polarity and overvoltages. The value of the secondary current of loop is limited in the event of input overcurrent.