I’ve had a number of questions from readers regarding testing of emergency stop systems, and particularly with the frequency of testing. I addressed the types of tests that might be needed in another article covering Checking Emergency Stop Systems. This article will focus on the frequency of testing rather than the types of tests. The Problem Emergency…
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 MoreEmergency Stop Failures
I am always looking for interesting examples of machinery safety problems to share on MS101. Recently I was scrolling Reddit/r/OSHA and found these three real-world examples. Broken Emergency Stop Buttons The first and most obvious kinds of failures are those resulting from either wear out or damage to emergency stop devices like e‑stop buttons or pull…
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 MoreCan Emergency Stop be used as an “on/off” control?
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 MoreMore E‑Stop Questions
Here are some more questions I’ve been asked regarding emergency stop requirements. These ones came to me through the IEEE PSES EMC-PSTC Product Compliance Forum mailing list. Primary Sources There are three primary sources for the requirements for emergency stop devices: [1] Safety of machinery — Emergency stop — Principles for design, 3rd Edition. ISO 13850. 2015. [2] Safety of…
Read More