The Siemens 3RG7421-0AB00 is a SIMATIC PXO320 K21R retro reflective sensor with a built-in polarisation filter. It operates on DC 10-30V, outputs PNP light-on switching at 150mA, and detects reflective targets up to 3m away. The housing is 31x20x12 mm with an M18 threaded optics front, and the connection is a 2m PUR cable (3x0.14 mm²). Rated IP68, it handles washdown and wet environments without issue.
The polarisation filter rejects false triggers from shiny targets — a real help on conveyors with wrapped or reflective product. The 3m sensing range is for a standard reflector; real-world range drops with target size and ambient light. PNP light-on means the output goes high when the beam is made; if your PLC input expects dark-on (NPN or NO), you need a different variant or a converter. The 2m PUR cable is oil-resistant and flexible down to -40°C, so it runs cold and stays cold in a freezer application. IP68 lets you hose it down without worry.