Industrial Engineer · phase 2 of 16
NPN Sensor
Three-wire DC sensor whose output sinks current to DC common when active.
The Explain card
- Plain English
- An NPN sensor connects its output wire to DC common when it detects something. It sinks current, so the load sits between the positive supply and the output.
- Example
- An NPN photo eye from an Asian machine builder lands on an input card set up for PNP. The light on the sensor blinks happily and the PLC never sees it.
- Why it matters
- NPN sensors need sourcing input cards or a card that can be wired either way. Knowing the difference saves the afternoon spent swapping a sensor that was never broken.
- Hook
- NPN pulls to negative.
Where it sits in the deck
Phase 2: PLC I/O and Field Signals
Where the controller meets the machine: discrete and analog signals, the wiring conventions behind them, and the field devices that send them.
