The Siemens 6ES7131-4BF00-0AA0 is an ET 200S electronics module packing 8 digital inputs at 24 V DC into a 15 mm slice — the narrowest in the family, so it fits tight panel layouts where every millimeter counts. It accepts 2-wire sensors with a permissible quiescent current up to 1.5 mA, and the input thresholds are set for standard 24 V logic: signal "0" from -30 to +5 V, signal "1" from +15 to +30 V, with a typical draw of 5 mA at signal "1".
The 15 mm width means this module occupies exactly one slot on the ET 200S rail — no wasted space, but also no room for extra terminals or fuse holders inside the module itself. The 52 mm depth keeps it flush with the backplane, so it doesn't overhang into the wiring duct. Unshielded cable runs up to 600 m and shielded up to 1 000 m are allowed, so you can reach remote limit switches or proximity sensors across a large machine without a remote I/O drop. The backplane bus draws a maximum of 10 mA at 3.3 V DC, and total power loss is a typical 1.2 W — negligible for the power budget, but worth checking if you're loading a long rail near its current limit. Reverse polarity protection is built in on the supply side, and isolation between channels and the backplane bus is tested at 500 V DC. No diagnostics, no parameterization, no channel-to-channel isolation — this is a straight-through, non-configurable input block. The 3-byte parameter field exists in the firmware but is not accessible to the user, so don't expect any software filtering or debounce adjustment.