The Siemens 3RG7201-6HC42 is a SIMATIC PXO620 K80 retro reflective sensor with a built-in polarisation filter, sized at 83x61x25 mm and rated IP67. It operates on DC 10-36 V, delivers a 6 m sensing range via an NPN antivalent output (two complementary NPN transistors, normally-open and normally-closed), and can switch up to 200 mA. The connection is a 4-pole PG11 cable gland.
The polarisation filter lets this sensor ignore reflections from shiny targets — it sees the retro reflector, not the glossy stainless tank next to it. That matters in a wet well or washdown area where water droplets or metal surfaces can fool an unfiltered retro. The IP67 rating means it survives hose-down and temporary submersion, which is the real test in a lift station or clarifier environment. The antivalent output gives you both a dark-on and light-on signal from one sensor, so you can wire it fail-safe without a separate logic inversion.