3 wire npn prox sensor with inverted output?

We have a stamping press with some prox sensors on the die for slug detection and we just ran into a problem where the output from one of the sensors seems to be reversed. We replaced the sensor itself, the cable coming from the sensor, checked other connection points but havent found anything obviously wrong. Does anyone hve any ideas on what could be causing this?

Solved. This problem started before my shift, so I didnt watch the other electrician replace the sensor. When i got there to continue troubleshooting I double checked the model numbers and realized they grabbed a normally closed prox instead of a normally open. After a few minutes tracking down the right sensor, everything was fine.

Lesson: check the full model numbers, not just whether its npn or pnp...