Sensor Basics: What is the difference between PNP and NPN sensor outputs? (Sourcing vs Sinking)

How do I choose PNP vs NPN? What does sourcing or sinking mean for a sensor? This basic discrete sensor output topic throws off experts and novices both. To start, the sensor output is always tied to a load. A load can be: a light or a LED or a valve or a relay or PLC input or I/O block. There’s a great automation-insights blog by Henry M. called “An Easy Way to Remember PNP & NPN Sensor Wiring.” Henry explains this in the simplest way as I’ve seen it: “Just remember the first letter tells you everything you need to know.” ✅ PNP = Switched Positive so P for Positive ✅ NPN = Switched Negative so N for Negative Sometimes you might hear someone say sourcing vs sinking: ✅ Sourcing (which is PNP) is bringing “power” to the load, sourcing power to it. ✅ Sinking (which is NPN) is bringing “common” to the load, sinking power away from it. This way you can always answer the question: “Is the sensor bringing positive or negative to the load/light/LED/valve/relay/plc/block?” So why pick one over the other when selecting a sensor? ✅ PNP sensor outputs tend to be easier to understand for technicians and engineers as the “positive output” indicates “on” and no power indicates “off”. This logically makes more sense. ✅ Another reason is that if an output wire from an NPN sensor got damaged and grounded, this would read to a controller as an “on” signal causing motion or create a hazard unintentionally. ✅ NPN sensors are more common in Asian manufactures. ✅ PNP is more common in...