interlock Archives | Machinery Safety 101

3 July, 2018

Trapped Key Interlocking

in Control Functions, Functional Safety, Hazardous Energy Control Procedures, Interlocks, Interlocks /

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 With the bolt withdrawn, the key is held in the lock.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…

16 May, 2018

Q & A: Category 2 and Testing Intervals

by Doug Nix

in Control Functions, Functional Safety, Interlocks, ISO 13849, Q & A /

2 Comments

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…

15 May, 2018

Five reasons you should attend our Free Safety Talks

by Doug Nix

in Events, Free Talks, Functional Safety, Hazardous Energy Control Procedures, Interlocks, Interlocks, ISO 13849, Lockout, News, Ontario, Pre-Start Health and Safety Reviews, Standards /

No Comments

Reason #1 – Free Safety Talks You can’t argue with Free Stuff! Last week we partnered with Schmersal Canada and Franklin Empire to put on three days of Free Safety…

27 January, 2014

CSA Z432 Safeguarding of Machinery – 3^rd Edition

by Doug Nix

in Canada, Control Functions, Control Reliability, Emergency Stop, Functional Safety, Guards and Guarding, Hazards, Hierarchy of Controls, Interlocks, Risk Assessment, Standards /

No Comments

If you build machinery for the Canadian market, or if you modify equipment in Canadian workplaces, you will be familiar with CSA Z432, Safeguarding of Machinery. This standard has been…

1 June, 2012

Interlocking Devices: The Good, The Bad and the Ugly

by Doug Nix

in Canada, CE Mark, Components, Control Functions, Control Reliability, EU European Union, EU Robotics, Guards and Guarding, Hierarchy of Controls, Interlocks, Interlocks, International, International Robotics, ISO 13849, North American Robotics, Ontario, Robotics, USA /

7 Comments

This entry is part 1 of 7 in the series Guards and Guarding

Note: A shorter version of this article was published in the May-2012 edition of Manufacturing Automation Magazine. When designing safeguarding systems for machines, one of the basic building blocks is the…

17 July, 2010

Interlocked gate testing

by Doug Nix

in Asides, Guards and Guarding, Interlocks /

5 Comments

Did you know that interlocked gates require stopping performance testing?

Machinery needs to be able to stop in the time it takes a person to open the guard and reach the hazard. If the distance from the guard opening to the hazard is short enough that a person can reach the danger point before the hazard can be controlled, the guard is useless. The resulting situation may be worse

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