A safety control device intended to process a control signal and generate a safety control order. The device has: a control input, a protection circuit, a coupler having an emitter circuit designed to emit a second signal and a receiver circuit for providing a third signal, a switch, a pulse generator designed to cyclically control opening and closure of the switch, and a processing circuit designed to execute a method for safely processing the third signal.

Also disclosed are a contactor having such a control device and to a method for safely processing a control signal.

An optocoupler based control circuit and a method thereof are disclosed. The control circuit comprises a first control branch, which includes a first control signal input terminal configured to receive a first OFF function control signal; a first optocoupler, wherein a primary side of the first optocoupler is coupled to the first control signal input terminal, and an output of a secondary side of the first optocoupler is configured to control a first power supplied to a motor driving circuit; a first primary side on/off control circuit connected to the primary side of the first optocoupler, and configured to periodically turn on and off the coupling of the primary side to the first control signal input terminal; and a first secondary side filter circuit connected to the secondary side of the first optocoupler, and configured to filter the output of the secondary side, and configured as a low pass filter having a cutoff frequency lower than an on/off frequency of the primary side. The control circuit further comprises a diagnostic circuit configured to diagnose an operating state of the control circuit based on the output of the secondary side of the first optocoupler and the first power. The control circuit may be a Safe Torque Off (STO) circuit.

A field device for a process plant, may include a power distributing data switch having an electrical primary connection to consume power at a first power level higher than 10W, and at least two electrical secondary connections for combined data communication and power transfer at a second power level of lower than 10W per secondary connection. The field device may also include a housing to accommodate electrical components safe from dust and/or water, which forms a first housing compartment fitted for pressure proof enclosure of electrical components in an environment with explosive or flammable atmosphere and which accommodates the primary connection. The secondary connections may be arranged outside a pressure proof enclosure and outside the first housing compartment. The device may include a protective bridge to isolate leads out of the first housing compartment to connect the primary connection to the secondary connections.

An optocoupler based control circuit and a method thereof are disclosed. The control circuit comprises a first control branch, which includes a first control signal input terminal configured to receive a first OFF function control signal; a first optocoupler, wherein a primary side of the first optocoupler is coupled to the first control signal input terminal, and an output of a secondary side of the first optocoupler is configured to control a first power supplied to a motor driving circuit; a first primary side on/off control circuit connected to the primary side of the first optocoupler, and configured to periodically turn on and off the coupling of the primary side to the first control signal input terminal; and a first secondary side filter circuit connected to the secondary side of the first optocoupler, and configured to filter the output of the secondary side, and configured as a low pass filter having a cutoff frequency lower than an on/off frequency of the primary side. The control circuit further comprises a diagnostic circuit configured to diagnose an operating state of the control circuit based on the output of the secondary side of the first optocoupler and the first power. The control circuit may be a Safe Torque Off (STO) circuit.