The EN 13849 standard “Safety of Machinery – Safety Related Parts of Control Systems” is applicable for the design of machinery and has been for some years now. It is the go-to standard when ensuring the safety of machinery that requires active measures, as is the case from laser cutting machines to stone crushers. The problems facing designers are varied, but in this blog, I will discuss some challenges that we at Huld have seen more than others.
A very typical problem is that for some component no reliability data is available. The situation has gotten better in the last years, but there are still components for which the manufacturer does not provide any reliable data. In this case there are two main recourses: applying Appendix C of the standard or using generic failure data provided in guides such as MIL-HDBK 217. There are also software packages which combine the databases from many such guides. When you use the data from these guides it is important that you check that environmental factors such temperature match your application and make the appropriate conservative adjustments.
Although the EN 13849 standard addresses software, the requirements are quite difficult to interpret. This has left many machinery designers vary of using software in safety functions. The EN 13849 is actually quite flexible in the use of software for safety functions, and in many cases there is a cost effective software-based solution which is simpler to implement and maintain rather than a hardware–only solution. Naturally, the required performance level has a big impact on the considerations, but dismissing a software-based solution out-of-hand does not always result in the best solution.
The EN 13849 categories are captured by the reference architectures presented in the standard. However, we are regularly asked whether a specific design meets a certain category when it does not trivially map into the reference architectures of the standard. The way the approach this question is asking whether the design meets the key requirements of the category. Usually, this requires understanding the safety principles of the design, the behaviour of the design under failures and how diagnostics have been implemented in the design. If these are understood, determining whether the system meets the requirements for a specific category is achievable.
I hope you found some of the questions relevant to your work on machinery safety. A good resource for inspiration is the Sistema cookbooks. If you have questions which you would like us to address in a future blog, please be in contact.