The Siemens 3SF7844-8BD13-0SS1 is a Type 4 safety light curtain receiver from the SIMATIC FS420I family, designed for finger and hand detection at 30 mm resolution across a 900 mm protected height. Blanking is supported, and the sensing range spans 0 to 18 m. Communication is via PROFIsafe bus connection, integrating directly into a SIMATIC safety controller without a separate safety relay.
What the ratings mean for fit
Type 4 per IEC 61496-1/2 is the highest safety integrity level for electro-sensitive protective equipment — it can detect a 30 mm object anywhere in the field and is rated for applications up to SIL 3 / PL e. The 30 mm resolution means it catches fingers reaching into the hazard zone, making it suitable for press, robot cell, and assembly station guarding. The 900 mm protected height covers a typical standing operator's reach zone; pair it with a matching transmitter (same series) for the full light curtain. Blanking allows fixed or floating objects (like a workpiece fixture) to break the beam without tripping the safety output, as long as the blanked zone stays within programmed limits. The 0 to 18 m range gives flexibility for long-reach guarding on conveyor lines or large machinery.
Integration context
The PROFIsafe bus connection eliminates a separate safety relay — the receiver's safety status is transmitted directly to a SIMATIC F-CPU over the PROFIBUS or PROFINET network. Mounting uses standard light curtain brackets; alignment aids and a visible LED indicator on the receiver simplify commissioning. The 30 mm resolution and blanking are configured via the FS420I software tool.