This standard provides safety requirements and guidance on the principles for the design of safety-related parts of control systems (SRP/CS). For these parts it specifies characteristics and categories required for carrying out related safety functions. It applies to SRP/CSs, regardless of the type of technology and energy used (e.g. electrical, hydraulic, pneumatic, mechanical) for all kinds of machinery. It does not specify which safety functions and which categories shall be used in a particular case. In the case of using electronic system(s), this standard is applicable if one or more of the following is satisfied: 1) the required performance level (PLr)is a or b, or 2) the safety function is carried out by hardware where the fault behaviour is clearly determined and assessable, or 3) the contribution of programmable electronic systems within the SRP/CS which carries out the safety function is low (e.g. for monitoring) and the (PLr)is from a to d, or 4) the safety function is carried out by diverse programmable electronic systems and the required performance level is from a to d. Depending on the application the diverse programmable electronic system consists of diverse application software and/or diverse operational systems and/or diverse hardware and the required performance level is from a to d, or 5) safety-related parts used (including the software) are designed to the requirements of appropriate standards. NOTE 1 For the definition of required performance level see 3.24. NOTE 2 The requirements provided in this standard for programmable electronic systems are compatible with the methodology for the design and development of safety-related electrical, electronic and programmable electronic control systems for machinery given in the horizontal application standard IEC 62061 (under preparation in IEC/TC44/WG7).