The Problems Related to Realization of Safety Function with SIL4 Using PLC

Safety PLCs are currently a common tool for realizing safety functions in industrial applications. Commercially available safety PLCs enables the realization of safety functions with a maximum of SIL (Safety Integrity Level) 3 without additional measures. However, the guaranteed safety features of safety PLCs create the preconditions for their usage even in applications where the use of safety PLC has not been common. This paper aims to point out the problems related to the use of safety PLC to realize safety functions with SIL 4.