Every couple of months I get an email asking me if there is any reason why e‑stop functions can’t be used as the primary power control (on/off button) for machinery. Following a recent exchange, I thought I would share the reasons for why this is such a bad idea. The short answer The short answer is an unequivocal NO. Don’t…
Read MoreIntroduction to Functional Safety Seminars
If you are interested in functional safety, and I know many readers are based on the statistics I see for my other functional safety-related posts, I think you will be interested in this. I am collaborating with the IEEE Product Safety Engineering Society’s Virtual Chapter to provide a series of three 35 minute seminars discussing the fundamentals of functional safety. The…
Read MoreEmergency Stop Pull-Cords
This article was updated 2019-04-26, adding specific details related to IEC 60947 – 5‑5. When it comes to emergency stop devices there is no doubt that the red mushroom-head push button is the most common – they seem to be everywhere. The second most common emergency stop device is the pull-cord, and like the light-curtain in safeguarding…
Read MoreSafe Drive Control including Safe Torque Off (STO)
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…
Read MoreISO 13849 – 1 Analysis — Part 7: Safety-Related Software
Post updated 2019-07-24. Ed. Safety-Related Software Up to this point, I have been discussing the basic processes used for the design of safety-related parts of control systems. The underlying assumption is that these techniques apply to the design of hardware used for safety purposes. The remaining question focuses on the design and development of safety-related software…
Read MoreISO 13849 – 1 Analysis — Part 2: Safety Requirement Specification
This article was updated 2019-07-24. Ed. Developing the Safety Requirement Specification The Safety Requirement Specification sounds pretty heavy, but actually, it is just a big name for a way to organize the information you need to have to analyze and design the safety systems for your machinery. Note that I am assuming that you are doing this in…
Read MoreISO 13849 – 1 Analysis — Part 1: Start with Risk Assessment
This post was updated 2019-07-24 I often get questions from clients about how to get started on Functional Safety using ISO 13849. This article is the first in a series that will walk you through the basics of using ISO 13849. Keep in mind that you will need to hold a copy of the 3rd edition of ISO 13849 – 1 [1]…
Read MoreWhy you should stop using the term ‘Deadman’
The Deadman Control Do you use the phrase ‘deadman’ or ‘deadman switch’ when talking about safety-related controls on your machinery? I often run into this when I’m working with clients who use the terms to refer to ‘enabling devices’ – you know, those two or three-position switches that are found on robot teaching pendants and in…
Read MoreUnderstanding the Hierarchy of Controls
(Eds. note: This article was originally written in 2011 and was updated in Nov. 2018.) The “Hierarchy of Controls” is one approach to risk reduction that has become entrenched in the Occupational Health and Safety (OHS) sector. There are other approaches to risk reduction which are equally effective but are less rigidly structured. If you…
Read MoreEmergency Stop Categories
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 the control does – and…
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