Safety relay base unit — what's in the box
The Siemens 3SK2112-2AA10 is a SIRIUS safety relay base unit — 10 fail-safe digital inputs (F-DI), 2 fail-safe digital outputs (F-DQ), and one standard digital output (DQ) in a 22.5 mm wide IP20 enclosure that snap-mounts to DIN rail or screws in with an optional push-in lug. Rated for 24 V DC control voltage, it handles PROFIBUS DP and PROFINET IO protocols when paired with the respective interface module, carrying 64-bit cyclic data. Input delay is adjustable from 0 to 150 ms, and it supports monitored start-up and valve monitoring — useful for press or hydraulic safety circuits where you need to confirm the valve spool actually shifted before the cycle starts.
Snap-mounts to DIN rail in any orientation — no derating for sideways or upside-down installs. The 22.5 mm width means it takes up one standard module slot in a panel. IP20 on both enclosure and terminals — panel-only use, no washdown rating. Shock rated at 15g for 11 ms.
Wiring and fieldbus
Terminals accept 1x or 2x solid or stranded wire from 20 to 16 AWG. Unshielded sensor cable runs up to 600 m; shielded runs up to 1000 m. The PROFIBUS DP and PROFINET IO capabilities are enabled via separate interface modules — the base unit itself is the I/O carrier, not the network node. Total current draw across all outputs is capped at 6.5 A maximum; readback time for the safety outputs is 400 ms max.