NPN and PNP sensor types are two common configurations used in industrial automation for digital signal output, and they differ primarily in how they handle current flow and interface with control systems.
NPN - stands for negative, positive, negative.
PNP- stands for positive negative, positive
Essentially, it is how the current flows and is represented on the graph
It is important that devices getting data from NPN/PNP sensors are configured to the correct sensor type.