What are safety-related parts of a control?
A safety-related part of a control (SRP/CS) is one which reacts to safety-related input signals and generates safety-related output signals. EN ISO 13849-1:2007, Safety-related parts of control systems, Part 1: General principles for design, stipulates the following: “Parts of machine control systems that are assigned to provide safety functions are called safety-related parts of control systems (SRP/CS), and these can either consist of hardware and software and can either be separate from the machine control system or an integral part of it. In addition to providing safety functions, SRP/CS can also provide operational functions (e.g. two-handed controls as a means of process initiation). The ability of safety-related parts of control systems to perform a safety function under foreseeable conditions is allocated one of five levels, called the “performance level” (PL). These performance levels are defined in terms of probability of dangerous failure per hour.
