Our conveyor travel distance is measured by an inductive proximity sensor counting the conveyor gear wheel teeth. The gear wheel is about 4 inches in diameter. The prox is 24V NPN shielded. We had to replace the prox. Everything works great when we test it right after installing the prox. But always about a day later, the prox reading stays at 1 while the gear wheel turns ONLY IN ONE DIRECTION. 0 and 1 alternates as it is supposed to when the gear turns the other direction. We tried different proxes. We adjust the gap. Adjusted conveyor speed. But as always, the prox works at first and then a day after of running the machine the prox stops working (0 and 1 not changing) always in one direction. The other direction always works.