The Siemens 3RG7211-3DK42 is a SIMATIC PXO620 K80 retro reflective sensor with a polarization filter, built for surplus light detection in industrial automation. It runs on DC 10-36V, outputs PNP at 200 mA, and includes a programmable light/dark-on switch plus an adjustable timer from 0.01 to 1 second. The M12 4-pole connector and IP67 rating make it a straightforward swap on a machine line where the original unit has failed.
The 6-meter sensing range with polarization filter handles shiny targets that would fool a standard retro. The 200 mA PNP output drives a PLC input directly. The timer (0.01-1 s) is useful for ignoring brief interruptions on a conveyor — set it and forget it. IP67 means it survives washdown without a secondary enclosure.