bsen61508-4-20xxfunctionalsafetyofelectricalelectronicprogrammableelectronicsafety-relatedsys

bsen61508-4-20xxfunctionalsafetyofelectricalelectronicprogrammableelectronicsafety-relatedsys内容摘要：

................................... 8 2 Programmable electronic system (PES): structure and terminology ............................ 14 3 Electrical/electronic/programmable electronic system (E/E/PES): structure and terminology .......................................................................................... 14 4 Failure model ........................................................................................................... . 20 Table 1 Abbreviations used in this standard .......................................................................... . 10 Page 5 EN 61508−4:2020 Licensed Copy: Institute Of Technology Tallaght, Institute of Technology, Mon Jun 11 16:24:19 GMT+00:00 2007, Uncontrolled Copy, (c) BSI INTRODUCTION Systems prised of electrical and/or electronic ponents have been used for many years to perform safety functions in most application sectors. Computerbased systems (generically referred to as programmable electronic systems (PESs)) are being used in all application sectors to perform nonsafety functions and, increasingly, to perform safety functions. If puter system technology is to be effectively and safely exploited, it is essential that those responsible for making decisions have sufficient guidance on the safety aspects on which to make those decisions. This International Standard sets out a generic approach for all safety lifecycle activities for systems prised of electrical and/or electronic and/or programmable electronic ponents (electrical/electronic/ programmable electronic systems (E/E/PESs)) that are used to perform safety functions. This unified approach has been adopted in order that a rational and consistent technical policy be developed for all electrically based safetyrelated systems. A major objective is to facilitate the development of application sector standards. In most situations, safety is achieved by a number of protective systems which rely on many technologies (for example mechanical, hydraulic, pneumatic, electrical, electronic, programmable electronic). Any safety strategy must therefore consider not only all the elements within an individual system (for example sensors, controlling devices and actuators) but also all the safetyrelated systems making up the total bination of safetyrelated systems. Therefore, while this International Standard is concerned with electrical/elec tronic/programmable electronic (E/E/PE) safetyrelated systems, it may also provide a framework within which safetyrelated systems based on other technologies may be considered. It is recognised that there is a great variety of E/E/PES applications in a variety of application sectors and covering a wide range of plexity, hazard and risk potentials. In any particular application, the required safety measures will be dependent on many factors specific to the application. This International Standard, by being generic, will enable such measures to be formulated in future application sector international standards. This International Standard – considers all relevant overall, E/E/PES and software safety lifecycle phases (for example, from initial concept, through design, implementation, operation and maintenance to demissioning) when E/E/PESs are used to perform safety functions。 – has been conceived with a rapidly developing technology in mind。 the framework is sufficiently robust and prehensive to cater for future developments。 – enables application sector international standards, dealing with safetyrelated E/E/PESs, to be developed。 the development of application sector international standards, within the framework of this International Standard, should lead to a high level of consistency (for example, of underlying principles, terminology, etc.) both within application sectors and across application sectors。 this will have both safety and economic benefits。 – provides a method for the development of the safety requirements specification necessary to achieve the required functional safety for E/E/PE safetyrelated systems。 Page 6 EN 61508−4:2020 Licensed Copy: Institute Of Technology Tallaght, Institute of Technology, Mon Jun 11 16:24:19 GMT+00:00 2007, Uncontrolled Copy, (c) BSI – uses safety integrity levels for specifying the target level of safety integrity for the safety functions to be implemented by the E/E/PE safetyrelated systems。 – adopts a riskbased approach for the determination of the safety integrity level requirements。 – sets numerical target failure measures for E/E/PE safetyrelated systems which are linked to the safety integrity levels。 – sets a lower limit on the target failure measures, in a dangerous mode of failure, that can be claimed for a single E/E/PE safetyrelated system。 for E/E/PE safetyrelated systems operating in – a low demand mode of operation, the lower limit is set at an average probability of failure of 105 to perform its design function on demand, – a high demand or continuous mode of operation, the lower limit is set at a probability of a dangerous failure of 10–9 per hour。 NOTE – A single E/E/PE safetyrelated system does not necessarily mean a singlechannel architecture. – adopts a broad range of principles, techniques and measures to achieve functional safety for E/E/PE safetyrelated systems, but does not use the concept of fail safe which may be of value when the failure modes are well defined and the level of plexity is relatively low。 the concept。