The Siemens SIMATIC 3RK1908-0AP00-0KP0 is a BaseUnit — the DIN-rail-mounted backplane that carries one fail-safe digital input (F-DI), with no AC/DC infeed onboard. It feeds the input from a 24 V DC supply rail (20.4 to 28.8 V permissible) and handles up to 7 A total ampacity. The single input is Type 1 per EN 61131-2, meaning it's designed for standard industrial proximity switches and pushbuttons, not the higher-threshold Type 2/3 variants used on some 2-wire sensors. 75 mm deep, 30 mm wide, 215 mm tall — it slots into a standard DIN-rail panel alongside other SIMATIC safety modules.
Push-in spring terminals on both the main current circuit and the auxiliary/control circuit. Standard slot screwdriver, 0.6 mm x 3.5 mm tip, for release. Strip length is not given here, but 8 mm is typical for this terminal family — verify against the terminal marking on the unit. Spring-cage holds firm under vibration; the unit is rated for 6g shock at 11 ms and 2g vibration up to 500 Hz.
Mounts vertically or horizontally on DIN rail. Pollution degree 2 (non-conductive dust only). Relative humidity 10 to 95%, non-condensing. Air pressure range 900 to 1060 hPa — fine for altitudes up to about 1000 m without derating.