Manual reset using an HMI

A Siemens HMI displaying control functions and data.

Update: Since this post was first published in 2021, things have changed a bit. 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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Using Form C relays in safety circuits

I recently had a discussion with a colleague who wanted to know if it was OK for a design to include a form C relay in an e-stop circuit. You might recall that e-stop functions are required to meet at least PLc/SIL1 requirements [1], [2]. It’s important to remember that PLc/SIL1 can be met using…

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Safe Drive Control including Safe Torque Off (STO)

Graph illustrating STO Function

Safe Drive Control including STO Motor drives are everywhere. From DC variable speed drives and indexing drives, through AC Variable Frequency drives, servo drives and stepper motor drives, the capabilities and the flexibility of these electronic systems have given machine designers unprecedented capabilities when compared to basic relay or contactor-based motor starters. We now have…

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ISO 13849-1 Analysis: Complete Series 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. Copyright secured by Digiprove © 2017-2020Acknowledgements: As cited.Some Rights ReservedOriginal content here is published under these license terms: X License Type:Non-commercial,…

ISO 13849-1 Analysis — Part 8: Fault Exclusion

Post updated 2019-07-24. Ed. Fault Consideration & Fault Exclusion ISO 13849-1, Chapter 7 [1, 7] discusses the need for fault consideration and fault exclusion. Fault consideration is the process of examining the components and sub-systems used in the safety-related part of the control system (SRP/CS) and making a list of all the faults that could…

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