Type 4 safety light curtain, host receiver — 14 mm finger protection
The Siemens 3SF7844-8BB04-1SS1 is a Type 4 host receiver in the SIMATIC FS420I safety light curtain family, with 14 mm resolution and a 300 mm protective height. That 14 mm detection capability means it catches fingers reaching into the hazard zone — finger-protection class per IEC 61496-1 — so it's sized for point-of-operation guarding where hand access is the risk. The protective field spans 0 to 6 m, giving you flexibility to cover a reach-in station or a small robot cell without re-spacing the columns. Communication is over PROFIsafe, the safety-rated PROFIBUS/PROFINET profile, so it drops directly into a Siemens F-CPU safety program without a separate safety relay or interface module. The bus connection simplifies wiring and diagnostics — the light curtain's status, blanking configuration, and fault codes travel over the same cable as the safety signal.
What the specs mean for your application
The 14 mm resolution determines the smallest object the curtain reliably detects — a finger, not a hand. That makes it suitable for applications where the operator's fingers could reach the danger zone, such as press brakes, assembly stations, or packaging machinery with small openings. The 300 mm protective height defines the vertical area covered; pair it with a matching transmitter (same height, same resolution) for a complete guarding pair. The 0 to 6 m range gives you installation flexibility: at shorter distances the optical alignment is easier, but the system can still cover a 6 m gap if your machine layout requires it. Blanking capability is built in — you can disable specific beams to allow fixed objects (like a workpiece support) to pass through the field without tripping the safety output. This is configured via PROFIsafe, not DIP switches, so the setup lives in the safety program.