Machinery Safety 101
12 July, 2021

Understanding Safety Functions: the Safety-related stop function

by Doug Nix
in Complementary Protective Measures, Control Functions, Emergency Stop, Functional Safety, Interlocks, Interlocks, ISO 13849
A stop sign - A red octagon with a white border, and white block text reading STOP.
This entry is part of 3 in the series Under­stand­ing Safety Functions

The most used safety func­tion on machinery is the safety-related stop func­tion. The require­ments dis­cussed in this post are not gen­er­ally applic­able to pro­­cess-related stop func­tions unless the pro­cess and… 

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2 June, 2021

Manual reset using an HMI

by Doug Nix
in Complementary Protective Measures, Control Functions, Control Reliability, Emergency Stop, Functional Safety, Inherently Safe Design, ISO 13849 /
1 Comment
A Siemens HMI displaying control functions and data.
This entry is part 2 of 3 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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19 May, 2021

Understanding safety functions: Manual Reset

by Doug Nix
in Control Functions, Functional Safety /
1 Comment
A reset button graphic
This entry is part 1 of 3 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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9 June, 2020

ISO/DIS 13849 – 1 Available for Public Review

by Doug Nix
in Canada, Control Functions, EU European Union, Functional Safety, International, Standards
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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28 October, 2019

Using Form C relays in safety circuits

by Doug Nix
in Control Functions, Control Reliability, Functional Safety /
2 Comments

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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