Sourcing vs Sinking outputs and CE

[JFW1964]

I read somewhere that CE requires that PLC output logic be PNP (or sourcing)? Is this accurate? I believe that the applicable standard is IEC 61131-4, though I don't have a copy of it

 

[buzzp]

Hmmm, never heard of that before. Not to say its not a requirement but I can't imagine the reasoning if it is a requirement. It seems this standard is a guideline and is not really a requirement. Where is the PLC going to be used (what type of equipment or what will it be controlling)?
You might try this website to get some insight on this standard -

http://www.plcopen.org/

 

[JFW1964]

I may be wrong on the standard. The application is on a very large pick and place machine in the pharmaceutical industry. Our customer plans on shipping these machines to US customers to start, but wanted to make sure the machine was CE ready. I've visited the PLC open site before. Have you any opinion, in general, as to which output logic type is better/safer?

 

[denison]

Troubleshooting wise, I believe sourcing is much better, Really depends on the customer, what do their people like and already have in place? Mixing is the biggest problem I've seen.

 

[Skogsgurra]

The PNP is a requirement for machine-tools and safety related equipment. It is a preferred standard for most (all) PLCs in Europe. The reason is that an earth fault will not activate any connected load. And since ground faults are much more common than faults to +24 V (or whatever your supply voltage is), there is less risk for unwanted activation with the PNP output.

Also, inputs are fail-safe when using positive (PNP) logic. A loose wire will not start anything in such a system while it can be seen as a logic one in an NPN system where inputs are closed to ground.



Gunnar Englund

http://www.gke.org

 

[JFW1964]

I've always used sourcing outputs, if for no other reason than the troubleshooting simplicity. I agree that mixing is very poor design.

 

[jonesy29847]

We use a safety PLC (TUV certified) that has paired sinking sourcing solid state outputs, this allowed us to eliminate interposing relays and meets category 4 requirements. We also had a design where we used sinking inputs because they were faster, the cable didn't leave the enclosure so ground faults were no more likley than a fault to V+.

 

[denison]

I don't believe sourcing is a requirement for machine tools unless this is very recent. I have to many okumas and mazaks that are fairly new for this to be the case. Everyone of those machines I've worked on were sinking.

 

[Skogsgurra]

denison,

Are you sure about that?

And, are you in Europe or somewhere else?

Gunnar Englund

http://www.gke.org