Machinery Safety 101

Manual reset using an HMI

A Siemens HMI displaying control functions and data.

Question: Can a safety-related stop function, for example, be reset via a graphical object representing a reset button on an HMI? The short answer: No, with an exception. Read on if you’d like to know more. If you’re interested in knowing more about the manual reset function, see our previous post on the manual reset…

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

Ed. Note: This article was revised 25-Jul-17 to include information on safe standstill. 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 has given machine designers unprecedented…

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How to do a 13849-1 analysis: 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. 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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