A method of protecting a control signal provided to a field device in a process control system, the method comprising: providing a host station (111, 202); communicatively coupling the host station (111, 202) to a plurality of input output I/O cards (116, 206) including a first card and a second card, wherein operation is selectively switched from the first card to the second card; communicatively coupling a control signal protection device to the input output I/O cards (116, 206) and to the field device via a control signal loop, wherein the control signal protection device comprises an input terminal (212,302) connecting the control signal protection device to the input output I/O cards, an output terminal (214,304) connecting the control signal protection device to the field device, and a power storing element (314,316); providing a control signal for the field device from the host station (111, 202) via the first card or the second card to the control signal protection device; in a first operational mode of the control signal protection device, accumulating electric energy, that is extracted from the control signal loop, in the power storing element (314, 316) at a controlled rate without interfering with communicating the control signal; and causing the control signal protection device to switch from the first operational mode to a second operational mode during a transition of operation from the first card to the second card, wherein the control signal protection device sustains the control signal at the output terminal (214, 304) of the signal protection device during a switchover operation between the first I/O card and the second I/O card by supplying electric energy stored in the power storing element (314, 316) to the output terminal (214, 304) of the control signal protection device in the second operational mode. providing a host station (111, 202); communicatively coupling the host station (111, 202) to a plurality of input output I/O cards (116, 206) including a first card and a second card, wherein operation is selectively switched from the first card to the second card; communicatively coupling a control signal protection device to the input output I/O cards (116, 206) and to the field device via a control signal loop, wherein the control signal protection device comprises an input terminal (212,302) connecting the control signal protection device to the input output I/O cards, an output terminal (214,304) connecting the control signal protection device to the field device, and a power storing element (314,316); providing a control signal for the field device from the host station (111, 202) via the first card or the second card to the control signal protection device; in a first operational mode of the control signal protection device, accumulating electric energy, that is extracted from the control signal loop, in the power storing element (314, 316) at a controlled rate without interfering with communicating the control signal; and causing the control signal protection device to switch from the first operational mode to a second operational mode during a transition of operation from the first card to the second card, wherein the control signal protection device sustains the control signal at the output terminal (214, 304) of the signal protection device during a switchover operation between the first I/O card and the second I/O card by supplying electric energy stored in the power storing element (314, 316) to the output terminal (214, 304) of the control signal protection device in the second operational mode.