This article is part of a guided learning series on building our understanding of the Siemens S7-1200 PLC.
Canonical Article: Navigating Siemens S7-1200 PLC model numbers
Learning Companion (Q&A): Learning Companion Navigating Siemens S7-1200 PLC model numbers
You are reading: Question 4
Does the S7-1200 support NPN (sinking outputs)?
Clarification
The S7-1200 CPU supports relay and solid-state (transistor) outputs.
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The terms sinking and sourcing are also applicable to PLCs with relay outputs. They describe how the PLC will be configured to the load.
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Sourcing: The load is connected to between the PLC and return. Internally, the PLC connects a load to the source.
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Sinking: The load is connected between the source and the PLC. Internally, the PLC connects the load to the return line.
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The terms NPN (sinking) and PNP (sourcing) are typically associated with the solid-state outputs.
Answer
There are two ways to answer this question depending on your perspective:
CPU-centric answer
The built-in outputs are either relay or solid-state with PNP transistors (sourcing).
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Relay can be connected as either sinking or sourcing
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Solid-state outputs are connected as sourcing. The connections for PNP (sourcing) loads are shown in this image derived from the S7-1200 Easy Book.
System answer
The S7-1200 is expandable. Sinking NPN output are supported via the SM 1222 module which provides 16 NPN outputs. This image from the TIA selection tool shows the SM 1222 module installed next to a CPU 1214C DC/DC/RLY.
Article by Aaron Dahlen, LCDR USCG (Ret.), Application Engineer at DigiKey