The Siemens 3SF7844-8BB20-1SS1 is a Type 4 safety light curtain host receiver from the SIMATIC FS420I family, with 14 mm resolution across a 1350 mm protected height and a 0 to 6 m operating range. The 14 mm resolution means it detects finger-sized objects entering the field — finger-protection class per IEC 61496-1 — so it suits guarding around assembly stations, pick-and-place cells, and small-part handling lines where hand access must be caught without allowing a full hand through. Blanking capability is built in, letting you define fixed or floating zones in the curtain for workpiece pass-through or fixture clearance without disabling the entire field. Communication is over PROFIsafe bus, which integrates directly into a SIMATIC safety CPU without an external safety relay or interface module — one less component on the DIN rail and one less wiring loop to troubleshoot.
Deployment context
The receiver mounts in a standard safety light curtain column profile, aligned with its matching transmitter. PROFIsafe bus connection means the safety signals travel over the same network cable as standard I/O, so the wiring run from the curtain to the safety CPU is a single M12 or similar fieldbus cable rather than a bundle of individual OSSD wires. That simplifies panel wiring and reduces the number of terminals on the safety relay or input card. The 0 to 6 m range covers most machine-cell guarding distances; if your application needs a longer span, you would step up to a different resolution or a curtain with a higher range.