The Siemens 3SK2942-2AA11 is a SIRIUS safety relay delivered as a PROFINET starter kit. It comprises the 3SK2122-2AA10 basic unit, the 3SK2511-2FA10 PROFINET interface module, the SIRIUS Safety Professional TIA configuration software, and all required cables — everything needed to commission a safety application on PROFINET out of one box.
The total current maximum of 7 A governs the load side — this is the aggregate current through the safety outputs, not per-channel. For a typical guard-door or two-hand control circuit with contactors and indicator loads, 7 A covers most single-zone safety cells. The 2 non-safety-related auxiliary contacts handle status feedback to a PLC without eating into the safety-rated current budget. Snap-mounted to DIN rail, or screw-mounted with an additional push-in lug. The 45 mm width and 124.5 mm depth mean it occupies a standard 45 mm slot on the rail — same footprint as a slimline contactor or a 4-pole relay base. IP20 on the enclosure and the terminal — finger-safe, not washdown. This is a panel-inside component; it needs an enclosure rated for the environment. Input delay time adjustable from 0 to 150 ms. This is the debounce or filter window for the safety input signals — set it short (0 ms) for fast-reacting light curtains, longer for mechanical interlock switches that bounce on closure. The readback time maximum of 400 ms governs how quickly the safety relay detects a feedback-loop fault from the downstream contactors. Valve monitoring is built in — the relay checks the state of a downstream valve (typically a pneumatic safety valve) before allowing the safety outputs to enable. Monitored start-up means the relay verifies that all inputs and feedback loops are in their safe state before it will start; this is standard for category 3 / PL d safety circuits.
Fieldbus and communication
PROFINET IO protocol is supported when using the included PN interface module, with 64-bit cyclic data. PROFIBUS DP is also an option with the DP interface module, also 64-bit cyclic. The starter kit ships with the PROFINET variant, so if your line runs PROFIBUS you need the DP interface module separately.