Manual reset using an HMI

A Siemens HMI displaying control functions and data.

Update: Things have changed a bit since this post was first published in 2021. There are now some safety-rated HMIs available from big controls companies like Siemens, so if you are considering this approach, consult with your controls vendor to see if their HMIs can meet the requirements of ISO 13849-1. Ed. – 2022-05-10 Question: Can…

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What exactly is PELV?

Photo of the interior of an electrical control cabinet showing the components and wireways on the backplane.

What exactly is Protected Extra-Low Voltage (PELV)? Electrical designers run into lots of specialized terminology as part of their work. IEC is notorious for creating specialized terms unfamiliar to North American designers. PELV is a definition of a limited range of system voltage and current and is related to some other terms you may run…

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Force and injury — How hard is too hard? ISO/TR 21260 will help

ISO/TS 15066 body model

Force represents the mechanical energy that causes injury to the human body. ISO/TC 199 has been working on answering that question since 2012.

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ISO 13849-1 Analysis — The 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.

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ISO 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…

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