Safety-rated central unit for modular guarding
The Siemens SIRIUS 3RK3131-2AC10 is a modular safety system central unit, configured as 4/8 fail-safe digital inputs, 1 fail-safe relay output, and 1 fail-safe digital output. Its SIL CL 3 rating per IEC 61508 means it is qualified for safety functions up to that integrity level — suitable for EMERGENCY STOP circuits and valve monitoring in a guarded zone. Snap-mounted onto a DIN rail or screw-mounted with an additional push-in lug, the unit sits inside a standard IP20 enclosure — typical for a control cabinet where the safety logic lives separate from the field I/O. Input delay is parameterizable from 0 to 150 ms, allowing the designer to filter out contact bounce on safety gates without adding external timers.
PROFIBUS DP integration and data width
When paired with the DP interface module, the central unit communicates over PROFIBUS DP with 64-bit cyclical data. This allows the safety CPU to read all input states and output commands in a single bus cycle, keeping the safety reaction time predictable. The unit supports parameterizable inputs and outputs, so the safety logic can be tuned per machine zone without firmware changes.
Rated for operation from -20 to +60 °C and storage from -40 to +85 °C, with a shock resistance of 15g / 11 ms. Mounting position is vertical only — horizontal installation is not supported per the spec.