The Output Circuit Solution of the Safety PLC for a Larger Number of Output Points

Safety PLCs (Programmable Logic Controllers) are commonly a part of the Safety Related Control System (SRCS), especially in industrial applications. In most cases, the controlled devices cannot be connected directly to the safety PLC outputs, but they require an output circuit consisting of relays or contactors. The paper deals with the solution of the output circuit for a larger number of controlled devices and analyzes the influence of selected factors (especially the switching frequency of the used relays) on the Safety Integrity Level (SIL) of the output circuit.