The Siemens 3RG4012-3JB00 is an inductive proximity switch with a 2 mm sensing range, operating on 10–30 VDC and providing a normally open (NO) output. This is a standard cylindrical prox for detecting ferrous targets at short range — typical for end-of-stroke or presence sensing on small actuators and grippers.
The 2 mm sensing range is the flush-mounted rated distance to a standard steel target — derate for aluminum or stainless. The 10–30 VDC supply covers 24 VDC control systems common in panel wiring; the NO output pulls high when a target enters the field. No load current or housing style is listed, so verify the barrel diameter and thread from the full datasheet before panel layout.