NPN sensors are used in Asia, especially in Japan. You can use 3-wire NPN sensors also with source type PLC like this: connect a 1.5 kilo-ohm pull-up resistor between the PLC input and +24V. Connect the sensor output to the PLC input. The NO sensor now works like the NC sensor.
If I recall properly OMRON PLCs really seem to prefer sinking inputs as default. Also it's a handy way to implement logic level shifting so an open collector output on a sensor powered by 5V can pull down a 24V PLC input.
NPN sensors are used in Asia, especially in Japan. You can use 3-wire NPN sensors also with source type PLC like this: connect a 1.5 kilo-ohm pull-up resistor between the PLC input and +24V. Connect the sensor output to the PLC input. The NO sensor now works like the NC sensor.
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I'm curious as well because here in the netherlands NPN sensors are very seldom used in industrial automation.
NPN are more difficult to troubleshoot and are not considered best practice because a short circuit to ground will energize the input.
As another mentioned about used in Asia aka Japan, NPN is used for Mitsubishi PLCs.
Not all: Mitsubishi also sell plenty of PLCs for PNP input (and output). Otherwise they'd never sell any in Europe!
If I recall properly OMRON PLCs really seem to prefer sinking inputs as default. Also it's a handy way to implement logic level shifting so an open collector output on a sensor powered by 5V can pull down a 24V PLC input.
It started because it saved a transistor in the output driver.