Machinery Safety 101

Manual reset using an HMI

A Siemens HMI displaying control functions and data.
This entry is part 2 of 2 in the series Under­stand­ing Safety Functions

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… 

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Understanding safety functions: Manual Reset

A reset button graphic
This entry is part 1 of 2 in the series Under­stand­ing Safety Functions

Fol­low­ing the risk assess­ment, risk reduc­tion is the next step. Whenev­er the con­trol sys­tem is called upon to reduce the risk, a safety func­tion is needed. Safety func­tions are defined in… 

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ISO/DIS 13849 – 1 Available for Public Review

Decision tree used to determine PL based on risk parameters.

Update 2020-10-11: The next three-day ISO/TC 199/WG8 meet­ing runs Tues­day-Thursday this week. Our com­mit­tee mem­bers will be wad­ing into the next 1 600 com­ments along with expert mem­bers from around the… 

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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… 

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More E‑Stop Questions

This entry is part 17 of 16 in the series Emer­gency Stop

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… 

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Can Emergency Stop be used as an “on/off” control?

Emergency Stop Button
This entry is part 16 of 16 in the series Emer­gency Stop

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… 

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Introduction to Functional Safety Seminars

Man training a group of people, pointing to Functional Safety topics on the whiteboard

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.… 

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Emergency Stop Pull-Cords

This entry is part 15 of 16 in the series Emer­gency Stop

This art­icle was updated 2020-06-13, adding links to the Rock­well Auto­ma­tion and Schmersal pull-cord data, and on 2019-04-26, adding spe­cif­ic details related to IEC 60947 – 5‑5 [7]. Addi­tion­al vendor links and… 

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Trapped Key Interlocking

This is a trapped key interlock on the door of an electrical switchgear cabinet. To open the door the key must be inserted and turned to withdraw a bolt that holds the door closed. With the bolt withdrawn, the key is held in the lock. The upstream switching device is held open by another interlock using the same key; since the key can only be in one of the two locks, it prevents accidentally closing the upstream switch while the cabinet is open for maintenance. The interlock is attached to the door with one-way screws to discourage casual removal of the lock, which would defeat the system.
This entry is part 3 of 7 in the series Guards and Guarding

Many machine design­ers think of inter­locks as exclus­ively elec­tric­al devices; a switch is attached to a mov­able mech­an­ic­al guard, and the switch is con­nec­ted to the con­trol sys­tem. Trapped Key Inter­lock­ing is… 

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Q & A: Category 2 and Testing Intervals

Logical block diagram for ISO 13849-1 Category 2 architecture.
This entry is part 1 of 2 in the series Q&A

Dur­ing the Free Safety Talks that we did with Schmersal Canada and Frank­lin Empire, we had a “hot ques­tion” come up regard­ing Cat­egory 2 archi­tec­ture and the test­ing inter­val require­ment. The… 

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