The Siemens 3RG4023-0KA00 is an inductive proximity switch with an 8 mm sensing range, rated for a supply of 20-265 VDC/AC, and a normally closed (NC) output. This is a wide-voltage-range sensor that can run on either DC or AC line power, which simplifies stocking for panels that mix control voltages.
The 8 mm sensing range is the maximum flush-mount distance for a standard metal target. The 20-265 VDC/AC supply range means it can be wired into a 24 VDC control circuit or a 120 VAC panel without a separate power supply — useful for retrofits where the control voltage is mixed. The NC output is fail-safe: if the sensor loses power or the target leaves the sensing zone, the output opens, which is typical for safety interlocks or conveyor presence detection.