PNP vs NPN
Side by side comparison: how they work, where each fits, and which to choose.
Quick answer: A PNP sensor switches the positive supply to the load (sourcing) and needs a sinking input; an NPN sensor switches the load to 0 V (sinking) and needs a sourcing input.
PNP vs NPN: Comparison Table
| Aspect | PNP | NPN |
|---|---|---|
| Output | Switches +24 V | Switches 0 V |
| Also called | Sourcing | Sinking |
| PLC input type | Sinking input | Sourcing input |
| Common in | Europe, India | Japan and some Asian equipment |
| On state voltage at output | About +24 V | About 0 V |
Choose PNP when
- Most European style PLC systems
Choose NPN when
- Equipment designed with NPN logic
Key Differences Explained
The two types are not interchangeable without changing the input type or using interface relays. Mixed sensors on one card cause confusing faults.
Some sensors are programmable for either output.
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Frequently Asked Questions
What is the difference between PNP and NPN?
A PNP sensor switches the positive supply to the load (sourcing) and needs a sinking input; an NPN sensor switches the load to 0 V (sinking) and needs a sourcing input.
How do I test which type I have?
Measure the output to 0 V when active: about 24 V means PNP.
Is PNP safer?
With PNP, a short to 0 V turns the input off rather than on, which is often preferred.
Can a relay solve a mismatch?
Yes, an interposing relay or converter can.
Learn more on the blog
Why 24 volts is used in PLC systems
A practical guide on instrumentationblog.in that goes deeper into this topic with field examples.
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