Proximity Sensor 101: NPN vs PNP
NPN Sensors
Working Mechanism:-
NPN sensors are also called “sinking” sensors. When triggered, they provide a path to ground for the load.
Wiring: Typically wired with the load connected to the positive voltage (+V), the sensor switches the ground (-).
Applications: Commonly used in systems where the controller or PLC inputs are designed for sinking connections.
Diagram:Power (+V) —-Load —->—- Sensor —- Ground
PNP Sensors
Working Mechanism:- PNP sensors are referred to as “sourcing” sensors. When activated, they provide the load with a positive voltage.
Wiring: The load is connected to the ground (-), and the sensor switches the positive voltage (+V).
Applications: Preferred in systems with sourcing input requirements, like many modern PLCs.
Diagram:Ground—- Load —->—- Sensor —- Power (+V)
Choosing Between NPN and PNP
Input Compatibility: Check the compatibility of your control system. European systems often favor PNP, while some legacy or Asian systems may use NPN.
Wiring Preferences: PNP sensors are generally more intuitive for wiring, as they source current to the load.
Safety: PNP systems may be slightly safer because accidental grounding of a wire in a PNP setup won’t falsely trigger the sensor.
Key Differences at a Glance
Feature:-
NPN (Sinking)
PNP (Sourcing)
Current Flow From load to sensor
From sensor to load Typical Application
Older systems, sinking inputs Modern systems, sourcing inputs Wiring Logic
Switch to ground Switch to positive voltage.