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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.

According to the website,

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).

Matteo Italia
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kangaroo
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1 Answers1

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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

Archie
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  • Thank you for your comment. So, let's say I choose KL2408. In that case, which switch device should I connect, PNP or NPN? – kangaroo Sep 19 '17 at 19:38
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    The KL2408 is an output card. Maybe the answer you are looking for is with a KL1408 input card which is a sinking card. With the KL1408, since it is sinking, you need a switch that would source. Think of the sourcing device as the one that supplied a positive current flow. The device it connects to will need to be the opposite (sinking) in order to accept the positive current flow. The PNP will supply a positive. The way I tell people to remember this is by the one with the more P's(positives) supplies positive. To clarify, PNP switch goes into a sinking input card. – Archie Sep 19 '17 at 23:21
  • Very helpful. How did you know KL1408 is the sinking card? – kangaroo Sep 20 '17 at 00:44
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    On web page it says the reference for all inputs is 0V, therefore +24V would be the required signal to activate the input. Therefore the current flow would sink into the card to the 0V common. The KL1488 is the "negative switching" or the input that works with NPN switches. – Archie Sep 20 '17 at 02:48