One more post about NPN vs PNP

I have never had a problem with NPN or PNP but then I do not ground my 24VDC either. There are reasons for and against grounding 24VDC - plenty in other posts.

Thanks everyone for the input. It makes me feel a bit better about my confusion knowing that there doesn't really seem to be any reason for the difference other than initially the price of production. I work at a Japanese international, so many of the MEs here are Japanese. That would explain why there are some butting heads between the state side and the Asian schools of thought, NPN vs PNP.

I hate NPN devices

I have some older machines with NPN input devices, and I hate them.

We just had a short to ground on a cable and it disabled the door interlocks on a machine so when a guard was opened it did not inhibit the machine from starting. If this was PNP it would of blown the control fuse/breaker.

Back to the OP I was taught that NPN has a faster on/off time, and if you look at response times on prox or eyes you will see a slight differance between PNP and NPN, same with input cards.