What this SIRIUS starter kit does in a safety circuit
The Siemens 3RK3921-1AA10 is a SIRIUS modular safety system starter kit — the base building block for a configurable safety controller in a control panel. It carries 8 safety-related inputs, all 2-channel, meaning every input expects a dual-channel signal pair from an E-stop, guard switch, or light curtain. That 2-channel architecture gives you SIL CL 3 per IEC 61508 and SIL 3 per IEC 62061, which is the level you need for guarding a hazard zone where a single fault must not lead to loss of the safety function. Response time sits at 1 ms at 24 V DC, so the safety reaction is fast enough for most machine guarding — a light curtain break or E-stop press stops the hazardous motion within that window. The input delay is adjustable from 0 to 150 ms, which lets you filter out contact bounce on mechanical guard switches without slowing the safety response beyond what the risk assessment allows.
PROFIBUS DP and parameterization
The starter kit supports PROFIBUS DP when used with the DP interface module, carrying 32-bit cyclical data. That means it talks to a PLC over the fieldbus for diagnostics and parameterization — you can adjust input delays, muting configurations, and start-up behavior from the controller without opening the panel.
Wiring and environmental limits
Shock resistance is 15g for 11 ms, which covers most industrial vibration environments.