Machinery Safety 101

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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Understanding Risk Assessment

A group surrounding a computer discussing a problem.

When people discuss ‘Risk’ there are a lot of different assumptions made about what that means. For me, the study of risk and risk assessment techniques started in 1995. As a technologist and controls designer, I had to somehow wrap my head around the whole concept in ways I’d never considered. If you’re trying to…

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IEC/TR 62061-1 Reviewed

Why You Need to Spend More Cash on Yet Another Document Standards organizations publish documents in a fairly continuous stream, so for those of us tasked with staying current with a large number of standards (say, more than 10), the publication of another new standard or Technical Report isn’t news – it’s business as usual.…

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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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