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Russell Bull
08/25/05 03:06
Read: 865 times

#100051 - IEC 61508
Responding to: Steve M. Taylor's previous message

Could also be EN61508 -there's a few parts to this and a dead boring read at that.

Therac 25 is what can happen when you get it wrong. There were no safety interlocks and dodgy software. As I mentioned in the other thread you started that you cannot rely on the microprocessor alone for safety. I also mentioned that the emergency stop was to cut power directly - not via the microprocessor. So for a 'simple' device like a numerically controlled lathe the requirements could be as simple as:
1/electrical wiring safety
3/an emergency stop switch and maybe a safety cover with an interlock switch.
4/ labelling and a user manual pointing out safe operating procedures

In most safety systems the rules are pretty simple:

1/ You're allowed one failure
2/ The failure must be detected
3/ One failure cannot create a dangerous situation

The EN standards don't tell you exactly how to do it - they generally give guidelines and recommendations. Its up to you to prove that you comply. If you're unsure, you'll have to employ the services of a company that specialises in this type of work to advise and certify your equipment. You probably want to do this anyhow - if something does go wrong and you get sued - you have to demonstrate 'due diligence' in your design.

As Steve said - its a 'bag of worms'. How did I learn (not that I would call myself an expert)? Read the standards, look at other similar equipment, speak to suppliers. If you don't want to purchase the standards - go to the local public university library. They will most likely have them.

List of 12 messages in thread
EU legislations      J Cena      08/24/05 07:37      
   What an how..      José Félix Díaz Ivorra      08/24/05 08:18      
   Saferty critical      Steve M. Taylor      08/24/05 09:43      
   Indutrial machinary      J Cena      08/24/05 09:55      
      BSI      Andy Neil      08/24/05 11:01      
      bag of worms      Steve M. Taylor      08/24/05 11:03      
         IEC 61508      Russell Bull      08/25/05 03:06      
            safety systems      Steve M. Taylor      08/25/05 06:14      
               I recall      Erik Malund      08/25/05 07:03      
                  simce nobody ventured a guess, here it i      Erik Malund      08/26/05 12:53      
                     Only in America?      Andy Neil      08/26/05 13:32      
                        Here ?      Steve M. Taylor      08/26/05 14:54      

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