A photoelectric sensor watches parts go by on a conveyor. It sees one part, misses the next. The lens is clean. The bracket is flexing. The sensor-to-part distance is bouncing in and out of range with every cycle.
Rated distance is not a working distance
An inductive proximity switch rated for 4 mm detects 4 mm under ideal conditions. Install it at 3 mm to leave margin. Don’t run it at the rated gap; temperature swings, voltage drop, and bracket vibration eat that margin fast.
Mount the sensor on a rigid bracket. The flex the sensor sees over thousands of cycles adds up. If the bracket wobbles, the switch drops out halfway through a count.
The target material matters
Inductive switches see steel at full rated distance. Stainless, aluminum, and copper reduce it. Stainless might give you 60 percent. Non-ferrous metal drops to 30 percent of the nameplate number.
Size for the actual target. A 4 mm switch on aluminum might only detect 1.5 mm, so you have to mount it closer than the catalog suggests.
What kills photoelectric sensors
Dirty lenses. Mist from coolant, dust, and oil film build up until the signal fades. In wet or dusty areas, add an air purge or use an ultrasonic sensor.
Through-beam beats reflective every time, but you need space on both sides of the part. Reflective panels have to be square; angle the reflector a few degrees and the signal drops.
Cabling next to VFDs
Sensor signal wire zip-tied to a VFD power cable picks up noise. The PLC counts phantom pulses. Use shielded cable, ground the shield at one end, and run signal and power in separate trays. When they have to cross, cross them at 90 degrees.
