Safety relay for guarding circuits
The Siemens 3SK1120-1AB40 is a SIRIUS solid-state safety relay designed for monitoring safety functions like emergency stops, light curtains, and two-hand controls. It's rated SIL 3 per IEC 61508 and PL e per ISO 13849-1, so it's suited for the highest risk-reduction levels in machine guarding. The 24 V DC coil is standard for control panels, and the 17.5 mm width means it takes a single DIN-rail slot — easy to retrofit into existing cabinets without re-spacing the rail.
Safety Integrity Level (SIL) 3 and Performance Level (PL) e are the top categories for machinery safety — this relay can handle applications where a failure could cause serious injury. The 99% safe failure fraction (SFF) tells you the system can detect nearly all dangerous faults and switch to a safe state. The relay also monitors floating sensors (like guard-door switches) directly, so you don't need extra interface modules.
The 121.6 mm depth fits most standard cabinets; the 100 mm height is typical for this form factor.