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En ISO 13849-1 Safety performance level

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Safety performance level EN ISO 13849-1 issued by Rockwell
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      E    N     I    S    O     1    3    8    4    9  󰀭    1 Safety Performance Levels  Transition fromEN954-1 to EN ISO 13849-1  FUNCTIONAL SAFETY  Transition from EN 954-1 to EN ISO 13849-1 1 INTRODUCTION This publication is intended to shed some light on the recent and upcoming changesin the legislation and standards that apply to the safety of machinery. It is focusedon the EU requirements but, due to the increasing globalisation of machinery safetystandards, much of the content is relevant worldwide. Machinery and processes continue to become faster, more flexible and morepowerful. In order to offer the continued safety of operators and techniciansprotective measures have, in turn, evolved to keep pace with the increasingcomplexity of automation. Traditionally, safety systems have been implementedseparately to automation systems, operating independently and often in parallel tothe automation system. There is good reason for this; the safety system mustalways be available. A fault or unexpected occurrence in the normal operation of the machine must not degrade or compromise the safety protective measures. However it is an inescapable fact that as automation systems become moreintelligent then so must the safety system. What is required for safer functionalityincreasingly depends on what the machine is doing or what mode it is in. Thismeans that safety has, in some way, to communicate with the normal controlsystem. That means that we need to reconsider how we achieve theindependence and integrity of the safety system. One of the most significantmanifestations of this is a new generation of standards commonly referred to asFunctional Safety Standards. In this publication we will consider one of the mostsignificant of them: EN ISO 13849-1. In addition to this, there is a new MachineryDirective in the EU that looks to keep the legislative landscape relevant to thecontemporary industrial environment.For anyone supplying machines or using them it is important to keep informed of therelevant standards and regulatory requirements. This publication is intended toassist in that task especially with regard to control system aspects. It is not asubstitute for a detailed study of the specific provisions detailed in the standards andlegislation. It is intended to give an overview and hopefully it will help to give someclarity on what is required.  2 The migration from EN 954-1 to EN ISO 13849-1 For many years the most common way of classifying safety related systems hasbeen to use the Categories of EN 954-1 [or its counterpart ISO 13849-1:1999]. Atthe end of December 2009 EN 954-1 will be withdrawn [its counterpart ISO 13849-1:1999 has already been withdrawn] The main implication of this is the fact thatafter that date this standard can no longer be used to show conformity with theMachinery Directive. A new standard to replace EN 954-1 has already been published. It is EN ISO13849-1:2008. “Safety of machinery - Safety related parts of control systems . Thereis also an alternative standard that can be used: EN/IEC 62061 Safety of machinery - Functional safety of electrical, electronic and programmable electriccontrol systems. Either of these standards can be used to show conformity with theMachinery Directive. In this publication we will consider the relationship between thetwo standards where relevant. The choice of which one to use is left to the user butwe will concentrate on EN ISO 13849-1:2008. It has been specifically drafted toprovide a transition path for system designers who have been using Categories andtherefore it is likely to become the most commonly used standard for machine safetysystems. It can be used either for a complete system or for a subsystem. Basic differences between EN 954-1 and EN ISO 13849-1 Firstly let's have look at what are the basic differences between the old EN 954-1and the new EN ISO 13849-1. The outputs of the old standard were Categories [B,1, 2, 3 or 4]. The outputs of the new standard are Performance Levels [PL a, b, c, dor e]. The Category concept is retained but there are additional requirements to besatisfied before a PL can be claimed for a system.The requirements can be listed in basic form as follows:ãThe architecture of the system. Essentially this captures what we havebecome used to as the Categories.ãReliability data is required for the constituent parts of the system.ãThe Diagnostic Coverage [DC] of the system is required. This effectivelyrepresents the amount of fault monitoring in the system.ãProtection against common cause failure.ãProtection against systematic faultsãWhere relevant, specific requirements for software.  FUNCTIONAL SAFETY  Transition from EN 954-1 to EN ISO 13849-1 3 Later we will take a closer look at these factors but before we do it will be useful toconsider the basic intent and principle of the whole standard. It is clear at this stagethat there are new things to learn but the detail will make more sense once we haveunderstood what it is trying to achieve and why.First of all why do we need the new standard? It is obvious that the technology usedin machine safety systems has progressed and changed considerably over the lastten years. Until relatively recently safety systems have depended on simple equipment with very foreseeable and predictable failure modes. More recently wehave seen an increasing use of more complex electronic and programmable devicesin safety systems. This has given us advantages in terms of cost, flexibility andcompatibility but it has also meant that the pre-existing standards are no longer adequate. In order to know whether a safety system is good enough we need toknow more about it. This is why the new standard asks for more information. Assafety systems start to use a more black box approach we start to rely moreheavily on their conformity to standards. Therefore those standards need to becapable of properly interrogating the technology. In order to fulfil this they mustspeak to the basic factors of reliability, fault detection, architectural and systematicintegrity. This is the intent of EN ISO 13849-1.In order to plot a logical course through the standard it is important to realise that ithas two fundamentally different user types: the designer of safety relatedsubsystems and the designers of safety related systems. In general the subsystemdesigner [typically a safety component manufacturer] will be subjected to a higher level of complexity. They will need to provide the required data in order that thesystem designer can ensure that it is of adequate integrity for the system. This willusually require some testing, analysis and calculation. The results will be expressedin the form of the data required by the standard.The system designer [typically a machine designer or integrator] will use this data toperform some relatively straightforward calculations to determine the overallPerformance Level [PL] of the system.In order to determine what PL is required [PLr] the standard provides risk graph intowhich the application factors of severity of injury, frequency of exposure andpossibility of avoidance are input.The output is the PLr. Users of the old EN 954-1 will be familiar with this approachbut take note that the S1 line now subdivides whereas the old risk graph did not.Note that this means a possible reconsideration of the integrity of safety measuresrequired at lower risk levels.

VF AS1 Manual En

Jul 23, 2017
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