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 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,…

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Interlock Architectures Pt. 6 – Comparing North American and International Systems

industrial Control Console

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…

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Interlock 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 on 2020-05-11. – DN — The most reliable of the five system architectures, Category 4 is still considered to be single-fault tolerant and uses enhanced diagnostics (DC >= 99%) to help ensure that component…

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Interlock Architectures – Pt. 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 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…

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Interlock Architectures – Pt. 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 – Pt. 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 – Pt. 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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