scope:

1.1 General This Part of IEC 61131 specifies requirements for programmable controllers and their associated peripherals, as defined in Part 1, which are intended to be used as the logic subsystem of an electrical/electronic/programmable electronic (E/E/PE) safety-related system. A programmable controller and its associated peripherals complying with the requirements of this Part is considered suitable for use in an E/E/PE safety-related system and is identified as a functional safety PLC (FS-PLC). An FS-PLC is generally a hardware (HW) / software (SW) subsystem. An FS-PLC may also include software elements, for example predefined function blocks. An E/E/PE safety-related system generally consists of sensors, actuators, software and a logic subsystem. This Part is a product specific implementation of the requirements of IEC 61508 and conformity to this Part fulfils all of the applicable requirements of IEC 61508 related to FS-PLCs. While IEC 61508 is a system standard, this part provides product specific requirements with more precise information for the application of the principles of 61508 to FS-PLC. This Part of IEC 61131 addresses only the functional safety and safety integrity requirements of an FS-PLC when used as part of an E/E/PE safety-related system. The definition of the functional safety requirements of the overall E/E/PE safety-related system and the functional safety requirements of the ultimate application of the E/E/PE safety-related system are outside the scope of this Part, but they are inputs for this Part. For application specific requirements the reader is referred to standards such as IEC 61511, IEC 62061, and ISO 13849. This Part does not cover general safety requirements for an FS-PLC such as requirements related to electric shock and fire hazards specified in 61131-2. This Part applies to an FS-PLC with a Safety Integrity Level (SIL) capability not greater than SIL 3. For FS-PLC with SIL 4 capability this Part is to be used as a part of its safety life-cycle process with additional requirements according to IEC 61508 and/or sector functional safety standards.