The Sick WF2‑B 4150 is a compact infrared photoelectric slot sensor (2 mm slot) with dual PNP/NPN outputs and a 500 Hz switching rate, commonly used for fork detection or small object sensing in industrial conveyors. Common failure modes include optical contamination or misalignment of the LED/photodiode pair, power‑supply ripple exceeding ±10 % causing output instability, and wiring faults such as broken or shorted pins on the M8 connector. First‑check diagnostics: verify 24 V DC supply voltage and current draw against spec; inspect the optical window for dirt or damage and clean with a lint‑free cloth; test each pin with a multimeter for continuity and correct output polarity under load, then review any error codes from the host controller.[oss-gpt-20b]