The Siemens 3SF7844-8BD26-1SS1 is a Type 4 safety light curtain host receiver from the SIMATIC FS420I family, specified at 30 mm resolution across an 1800 mm protected height with a sensing range of 0 to 18 m. The 30 mm resolution means it reliably detects a 30 mm opaque object — typically a hand or finger — entering the guarded area, which is the standard for finger-protection applications per IEC 61496-1. The 1800 mm height covers a full access zone for a standing operator, and the 0 to 18 m range lets you set the curtain across a wide machine cell without needing a separate long-range variant. The PROFIsafe bus connection integrates directly into a safety-rated PROFINET network, so the safety signals travel over the same cable as standard I/O, cutting down on dedicated safety wiring and the associated terminal blocks.
This is the host receiver unit in a Type 4 pair — it talks to a separate transmitter (typically a 3SF7844-8BD26-1SS2 or similar) and handles the PROFIsafe communication back to the safety PLC. The blanking capability (noted in the description as BLANKING 0 TO 18 M) means you can program fixed or floating blanking zones to ignore small objects like workpiece carriers or chips that pass through the curtain without stopping the machine, as long as they don't exceed the blanking window size. The SIMATIC FS420I series is built for integration into Siemens safety systems, so the PROFIsafe GSDML file is available for TIA Portal configuration. Mounting brackets and alignment aids are part of the system; the receiver and transmitter must be aligned within the specified angular tolerance for reliable operation.
The 3SF7844-8BD26-1SS1 is a host receiver, so it contains the safety logic evaluation and PROFIsafe interface. In a typical deployment, the transmitter is mounted on one side of the hazard zone, the receiver on the opposite side, and the PROFIsafe connection runs back to an F-CPU (fail-safe CPU) over a standard PROFINET switch or port. The 30 mm resolution is the standard for finger detection; if your application only needs hand detection (40 mm or coarser), a lower-resolution curtain might be cheaper, but the 30 mm gives you the higher safety level without over-specifying. The 0 to 18 m range covers most machine cells; if you need longer, the FS420I family has extended-range variants.