—Standards for safety in control systemsBuilding a protection system that works in practice and provides sufficient safety requires expertise in several areas. The design of the safety functions in the protection system in order to ensure they provide sufficient reliability is a key ingredient. As help for this there is, for example, the EN ISO 13849-1 standard. The purpose of this text is to provide an introduction to the standard and its application in conjunction with our products. Please note that outside of the European Union there are often other standards that are used in place of EN ISO 13849.Introducing the standardThe generation change for standards on safety in control systems introduced new concepts and calculations for machine builders and machine users. The EN 954-1 standard has been phased out and is replaced by EN ISO 13849-1 (PL, Performance Level) and EN 62061 (SIL, Safety Integrity Level).PL or SIL? What should I use?The standard you should use depends on the choice of tech-nology, experience and customer requirements. Choice of technology– PL (Performance Level) is a technology-neutral concept that can be used for electrical, mechanical, pneumatic and hydraulic safety solutions. – SIL (Safety Integrity Level) can, however, only be used for electrical, electronic or programmable safety solutions.ExperienceEN ISO 13849-1 uses categories from EN 954-1 for defin-ing the system structure, and therefore the step to the new calculations is not so big if you have previous experience of the categories. EN 62061 defines the structures slightly differently.Customer requirements If you or your end customer comes from an industry that is accustomed to using SIL (e.g. the process industry), require-ments can also include safety functions for machine safety being SIL rated.We notice that most of our customers prefer PL as it is tech-nology-neutral and that they can use their previous knowl-edge in the categories. In this text we show some examples of how to build safety solutions in accordance with EN ISO 13849-1 and calculate the reliability of the safety functions to be used for a particular machine. The examples in this text are simplified in order to provide an understanding of the principles. The values used in the examples can change. What is PL (Performance Level)?PL is a measure of the reliability of a safety function. PL is divided into five levels (a-e). PL e gives the best reliability and is equivalent to that required at the highest level of risk. To calculate which PL level the system achieves you need to know the following:– The system’s structure (categories B, 1-4)– The Mean Time To dangerous Failure of the component (MTTFd)– The system’s Diagnostic Coverage (DC)You will also need to:– protect the system against simultaneous failure of both channels (CCF)– protect the system from systematic errors built into the design– follow certain rules to ensure software can be developed and validated in the right wayThe five PL-levels (a-e) correspond to certain ranges of PFHD-values (probability of dangerous failure per hour). These indicate how likely it is that a dangerous failure could occur over a period of one hour. In the calculation, it is ben-eficial to use PFHD-values directly as the PL is a simplifica-tion that does not provide equally accurate results.What is the easiest way of complying with the standard?1. Use pre-calculated components.As far as it is possible, use components with pre-calculated PL and PFHD-values. You then minimise the number of calcu-lations to be performed. All ABB Jokab Safety products have pre-calculated PFHD-values.2. Use a calculation tool.With the calculation softwares FSDT or SISTEMA you avoid making calculations by hand. You also get help to structure your safety solutions and provide the necessary documenta-tion.3. Use Pluto or Vital Use the Pluto programmable safety controller or Vital safety controller. Not only is it easier to make calculations and changes in the future, but above all it is easier to ensure a higher level of safety.1INTRODUCTION1– 11
