Sinking or sourcing safety issues?

[Nora]

allen bradley sinking sourcing opposite

Are there safety reasons why a board’s inputs would be designed as sourcing rather than sinking.
If a PLC had both options, would there be a reason to choose one rather than the other (besides that the inputting device goes in only one direction).
Thanks!
Nora

 

[KMoffett]

sinking and sourcing inputs allen bradley

Nora,

I think it's more a matter of the type of output the sensor you're using has, rather than a safety issue. As a side note, from another forum:

"Attention everybody.
The Mitsubishi definition of Sink/Source input is directly opposite to the Allen-Bradley's.
Mitsubishi defines input by being sinked or sourced by the sensor or contact.
AB defines input by being itself sinking or sourcing for connected external device.
As a result, our company just built a machine with sensors opposite to customers specification.
Our standard is Mitsubishi but this one was built on AB by cutomer's request.
Conclusion: always ask to specify NPN/PNP, not Sink/Source inputs.
By the way, Omron and Aromat do exactly this."

Ken