The Siemens 3RK2402-2MG00-2AA2 is a Slimline AS-i SC22.5 compact I/O module built for control-cabinet mounting. It gives you 4 digital inputs (PNP Type 2) and 2 relay changeover outputs, all packed into a 22.5 mm wide housing that screws or snaps onto a DIN rail. The AS-Interface slave profile is S-7.A.0, and the slave type is A/B, so it works on either standard or extended addressing networks. Address setting happens through a front-facing socket, not DIP switches on the side — saves a little panel space. Inputs are 2- and 3-wire capable, and the relay outputs are rated for 1 A at 24 V, 0.2 A at 110 V, and 0.1 A at 230 V. The thermal current through the module is 5 A, so don't plan on paralleling those relay contacts for a bigger load — the limit is per-contact and package.
Power supply and sensor feed
This module can pull its power two ways: 200 mA from the AS-Interface bus itself, or 500 mA if you feed it an auxiliary 24 V supply (Uaux). The sensor supply follows the same split — run sensors off the AS-i bus and you need no extra power; switch to Uaux and you need a 20 to 30 V DC auxiliary feed to power the sensors. The AS-Interface bus voltage is 8.5 V from the bus, and the external auxiliary supply can deliver up to 4 A at 1 V minimum. For the 24 V AS-i Power24V variant, the maximum draw is 270 mA at 30 V.
At 22.5 mm wide, 100 mm tall, and 120 mm deep, this module fits the standard Slimline footprint — you can pack several next to each other on a DIN rail without losing much panel real estate. Fastening is screw or snap-on, so it goes in fast and stays put. Shock resistance is 15g / 11 ms for the module alone, 10g / 11 ms with the device connector attached.