Doug Nix will be giving the third session in the three-part Introduction to Functional Safety seminar series at the IEEE Product Safety Engineering Society Virtual Chapter meeting.’ In this third of three sessions, Doug will be introducing key functional safety concepts MTTFD, DCavg, and CCF, and will be discussing Safety-related Software Development and Verification and…
Read MoreHow to do a 13849 – 1 analysis: Complete Reference List
Post updated 2019-07-24. Ed. As promised in previous posts, here is the complete reference list for the series “How to do a 13849 – 1 analysis”! If you have any additional resources you think readers would find helpful, please add them in the comments. Copyright secured by Digiprove © 2017 – 2018Acknowledgements: As cited.Some Rights ReservedOriginal content here is published under these license terms: X License Type:Non-commercial, Attribution,…
ISO 13849 – 1 Analysis — Part 8: Fault Exclusion
Post updated 2019-07-24. Ed. Fault Consideration & Fault Exclusion ISO 13849 – 1, Chapter 7 [1, 7] discusses the need for fault consideration and fault exclusion. Fault consideration is the process of examining the components and sub-systems used in the safety-related part of the control system (SRP/CS) and making a list of all the faults that could occur in each…
ISO 13849 – 1 Analysis — Part 7: Safety-Related Software
Post updated 2019-07-24. Ed. Safety-Related Software Up to this point, I have been discussing the basic processes used for the design of safety-related parts of control systems. The underlying assumption is that these techniques apply to the design of hardware used for safety purposes. The remaining question focuses on the design and development of safety-related software…
Read MoreISO 13849 – 1 Analysis — Part 6: CCF — Common Cause Failures
Post updated 2019-07-24. Ed. What is a “Common Cause Failure”? There are two similar-sounding terms that people often get confused: Common Cause Failure (CCF) and Common Mode Failure. While these two types of failures sound similar, they are different. A Common Cause Failure is a failure in a system where two or more portions of the system fail at…
Read More31-Dec-2011 – Are YOU ready?
31-December-2011 marks a key milestone for machine builders marketing their products in the European Union, the EEA and many of the Candidate States. Functional Safety takes a positive step forward with the mandatory application of EN ISO 13849 – 1 and ‑2. As of 1‑January-2012, the safety-related parts of the control systems on all machinery bearing a CE Mark will be…
Read MoreInconsistencies in ISO 13849 – 1:2006
I’ve written quite a bit recently on the topic of circuit architectures under ISO 13849 – 1, and one of my readers noticed an inconsistency between the text of the standard and Figure 5, the diagram that shows how the categories can span one or more Performance Levels. If you look at Category 2 in Figure 5, you will notice…
Read MoreInterlock Architectures Pt. 6 – Comparing North American and International Systems
I’ve now written six posts, including this one, on the topic of circuit architectures for the safety-related parts of control systems. In this post, we’ll compare the International and North American systems. This comparison is not intended to draw conclusions about which is “better”, but rather to compare and contrast the two systems so that…
Read MoreInterlock Architectures – Pt. 5: Category 4 — Control Reliable
Ed. note: I’ve made a few updates to this article since it was first published in 2011, with the most recent today, 6‑Dec-18. – DN – The most reliable of the five system architectures, Category 4 is the only architecture that uses multiple-fault tolerant techniques to help ensure that component failures do not result in an unacceptable…
Read MoreInterlock Architectures – Pt. 4: Category 3 – Control Reliable
This post was updated on 2020-03-28. Category 3 system architecture is the first category that could be considered to have similarity to “Control Reliable” circuits or systems as was defined in some North American standards, now obsolete (notably CSA Z432-04, CSA Z434-03, and ANSI/RIA R15.06 – 1999). ISO 13849 – 1 Category 3 is NOT the same as Control Reliable, but we’ll…
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