from the Automation department...
Compliance with EN-954-1 Category 3
PLCs and related questions. topic
Posted by Adel Abdellatif on 17 June, 2003 - 1:54 pm
How can one acheive compliance with EN-954-1 category 3, without using a safety module in the PLC? Is there is any other way to acheive such compliance for connecting Emergency stop, and critical signals to a PLC system?


Posted by Daniel Chartier on 19 June, 2003 - 4:47 pm
Hello Adel;

Of course there are ways to achieve compliance to cat 3, even cat 4, without safety PLCs. Cat 3 basically means that a single failure of the control element shall not impede the safety funcvtion of that element (therefore 1oo2 technology) and that the single fault should be detected within a single safety function cycle (therefore monitoring of the safety cycle). Safety relays (such as Pilz and others manufacture)are a common electromechanical technology used to achieve compliance.

Follow the following link to HVGB's pdf on "Safety-related control Systems in accoedance with EN 954-1". It is a precious ressource.

Hope this helps,
Daniel Chartier

Posted by BobB on 19 June, 2003 - 5:00 pm
Use an external safety relay that disconnects the power to the PLC output lines.

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