31-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…

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Inconsistencies in ISO 13849-1:2006

I’ve written quite a bit recently on circuit architectures under ISO 13849-1, and one of my readers noticed an inconsistency between the standard text and Figure 5. This diagram shows how the categories can span one or more Performance Levels. If you look at Category 2 in Figure 5, you will notice that there are…

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Interlock Architectures — Part 6: Comparing North American and International Systems

industrial Control Console

Note: This article references now-obsolete versions of standards. Please use the current editions in your work! — DN 2022-08-18 I’ve now written six posts on circuit architectures for the safety-related parts of control systems, including this one. In this post, I will compare the International and North American systems. Comparing the requirements is not intended…

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Interlock Architectures — Part 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 on 2020-05-11. – DN The most reliable of the five system architectures, Category 4 is still considered single-fault tolerant and uses enhanced diagnostics (DC ≥ 99%) to help ensure that component failure does not…

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Interlock Architectures — Part 4: Category 3 – Control Reliable

Category 3 Architecture Logic Block Diagram

This post was updated on 2020-03-28. Category 3 system architecture is the first category that could be considered to have similarities to “Control Reliable” circuits or systems as 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,…

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Interlock Architectures — Part 3: Category 2

ISO 13849-1 Figure 10

This article explores the requirements for safety related control systems meeting ISO 13849-1 Category 2 requirements. “Gotcha!” points in the definition are highlighted to help designers avoid this common pitfalls.

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Interlock Architectures — Part 2: Category 1

This article expands on the first in the series “Interlock Architectures ? Pt. 1: What do those categories really mean?”. Learn about the basic circuit architectures that underlie all safety interlock systems under ISO 13849-1, and CSA Z432 and ANSI RIA R15.06.

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Interlock Architectures — Part 1: What do those categories really mean?

Basic Stop/Start Circuit

In 1995 CEN published an important standard for machine builders – EN 954-1, Safety of Machinery – Safety Related Parts of Control Systems – Part 1: General Principles for Design. This standard set the stage for defining control reliability in machinery safeguarding systems, introducing the Reliability categories that have become ubiquitous. So what do these categories mean, and how are they applied under the latest machinery standard, ISO 13849-1?

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