I'm using Beckhoff's BK9000 (Ethernet TCP/IP Bus Couplers) with other KL blocks to connect the switch. I'd like to choose the switch which fits this bus coupler, but I noticed that there are two choices for the switch, NPN or PNP.
Many modern PLC input cards can be configured and wired to be either 'sinking' or 'sourcing' although it will usually necessitate all inputs on a particular input card being configured the same.
Which switch should I choose? Is BK9000 a sourcing or sinking device? Or doesn't it matter at all?
I'm sorry if I'm asking a silly question. I tried to find more information and tutorial, but couldn't find the practical explanation (most of them were just about the general explanation of PNP/NPN or sourcing/sinking).
The BK9000 is only the coupler and doesn't determine whether it is sinking or sourcing. It is the KL cards you choose that determine it. You can choose versions of the KL cards that are either sourcing (supplying the positive voltage), such as the KL2408 or sinking, such as the KL2488