The Siemens 3RK3923-1AC00 is a SIRIUS Modular Safety System (MSS) starter kit — the central unit plus the software and cabling needed to commission a safety application on the ASIsafe bus. It ships with the MSS central unit, the Safety ES V1.0 Premium software, and a USB PC cable, all terminated through screw-type terminals. The kit is rated SIL CL 3 per IEC 61508 and PL e per ISO 13849-1, with a PFHD of 0.000000007 1/h under high demand rate, meaning it meets the highest integrity level for guarding a hazard zone where a failure could cause serious injury.
SIL CL 3 (IEC 61508) and PL e (ISO 13849-1) are the top performance levels for safety-related control systems. A SIL CL 3 circuit has a probability of dangerous failure per hour between 10⁻⁷ and 10⁻⁸ — this kit's PFHD of 7 × 10⁻⁹ 1/h sits at the low end of that band, giving you margin if the rest of the safety loop adds failure contributions. The diagnostic test interval is capped at 1000 s, which governs how often the internal self-test cycles; for a high-demand application running at the maximum 1000 operations per hour, the test completes well within one operating cycle. The input delay at the digital input maxes out at 150 ms, with an ingress acquisition time of 60 ms. That means a signal from a safety light curtain or e-stop must be present for at least 60 ms to be reliably captured, and the total response through the input stage is bounded at 150 ms. For a typical guard-locking application, that's fast enough — but if you're coordinating with a high-speed press or a robot cell cycle under 200 ms, factor that delay into your safety distance calculation.
That is the cleanest procurement posture for a BOM line: no risk of a sudden EOL forcing a redesign.
What's in the box and how it connects
The starter package includes the MSS central unit with ASIsafe basic connection, the Safety ES V1.0 Premium configuration software, and a USB PC cable. Screw-type terminals handle the field wiring — no spring-cage, so expect a screwdriver for each termination. The central unit draws 4.5 W operating power; the dark period of the common drivers is 1 ms at 24 V, which governs how long the safety outputs can be off during a test pulse without dropping the load.