Machinery Safety 101

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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Updates to Popular Articles

We’ve recently updated a couple of our popular articles! Check them out! Busting Emergency Stop Myths Reader Question: Multiple E-Stops and Resets

Reader Question: Multiple E-Stops and Resets

I had an interesting question come in from a reader today that is relevant to many situations: “When you have multiple E-Stop buttons I have often gotten into an argument that says you can have a reset beside each one. I was taught that you were required to have a single point of reset. Who…

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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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Emergency Stop Categories

Emergency Stop on machine console

I’ve noticed a lot of people looking for information on Emergency Stop categories recently; this article is aimed at those readers who want to understand this topic in more depth. First, a clarification: Emergency stop categories DO NOT EXIST, but stop categories do. A stop category is a description of a control function – what…

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