NPN vs PNP Sensors: Understanding Output Types for Your PLC

The Basics

PNP (Sourcing): When the sensor detects an object, it connects the output to the positive supply (+V). The load is connected between the sensor output and 0V (ground).

NPN (Sinking): When the sensor detects an object, it connects the output to ground (0V). The load is connected between the sensor output and +V.

Which One for Your PLC?

• Siemens, Allen-Bradley, Mitsubishi (most modern PLCs): Use PNP sensors — their inputs are designed for sourcing signals
• Omron, older Japanese PLCs: Often use NPN sensors
• Universal inputs: Some PLCs accept both — check your PLC manual

NO vs NC

• NO (Normally Open): Output is OFF when no object is detected, turns ON when object is present
• NC (Normally Closed): Output is ON when no object is detected, turns OFF when object is present

Sri Vaarii Offers Both

All our proximity sensors are available in both NPN and PNP variants with NO/NC or NO+NC combined outputs. Custom wire lengths and connector types available on request.