AiVibeSourcing and Sinking I/O (PNP and NPN)
Sourcing and sinking describe the direction of conventional current flow between a DC field device and a controller I/O channel; PNP sensors source current to the load, NPN sensors sink it, and inputs and outputs must be paired accordingly.
A sourcing device supplies current from the positive side of the DC supply to the load, while a sinking device provides the path from the load to the negative side, or common. A PNP sensor output switches the positive supply and is therefore sourcing, so it must connect to a sinking input. An NPN sensor output switches to common and is sinking, so it needs a sourcing input. The same terminology applies to transistor output modules driving solenoids, relays and lamps.
Correct pairing matters whenever sensors, valve terminals or I/O modules from different suppliers are combined. Conventions differ between regions, suppliers and machine builders, so each machine's documentation should be followed. Some input modules accept either configuration, selected by connecting the input common to the positive or negative supply.
A mismatched pairing leaves an input permanently off or an output unable to switch its load, and wiring errors can damage equipment. Behaviour under fault conditions, such as whether a broken wire reads as off, also depends on the chosen convention and on whether the sensor is normally open or normally closed. Wiring work must follow OEM documentation and applicable electrical standards and be carried out by qualified personnel.
Key points
- Sourcing devices supply current from the positive rail; sinking devices return it to common
- PNP sensor outputs are sourcing; NPN sensor outputs are sinking
- A sourcing device must be paired with a sinking input, and vice versa
- Conventions vary by region, supplier and machine builder
- Mismatched pairing leaves signals stuck and can damage equipment
Where AiVibe comes in
AiVibe designs and manufactures the AiAmbA AI Factory, whose edge devices and AI agents let people talk to PLC, CNC and robot controllers in plain language. Agents only propose changes, a trained operator confirms each one, and the AI Factory never replaces a machine's control or safety systems.