Question about selection of NPN or PNP sensor component for PLC?

Thread Starter


Joined Jun 6, 2008
I have a pressure sensor that I want to integrate into a PLC.

The pressure sensor has a programmable alarm out that I can wire into a PLC input.

The pressure sensor is available in NPN or PNP. What does this mean and how do I know which type to get?

Thank you,



Joined Apr 20, 2004
Ordinarily, I would think that it had to do with the output from the sensor. It would be a positive voltage from the NPN and negative from the PNP. That is just guesswork without looking at a data sheet. Can you provide the part numbers for the sensors?


Joined May 28, 2008
PNP gives positive voltage when active,

NPN gives negative(ground) when active,
most PLCs accept both Positive and Ground as input,
but in industry Negative is generated because of noise,
so I recommend u to use PNP, if the distance bitween sensor and PLC is far,