A control signal protection device having a first operational mode and a second operational mode includes a first terminal pair that connects the signal protection device to a control system and a second terminal pair that connects the converter to a field device. The control system provided a control signal to the control system protection device. The control signal device further includes a power storing element for temporary accumulation of electric energy and a switching circuit for controlling operational mode of the signal protection device. Electric energy is stored in the power storing element in the first operational mode. Electric energy stored in the power storing element is supplied to a positive terminal in the second terminal pair in the second operational mode.