The Siemens 3SF7844-8MS51-0SS1 is a Type 4 standard receiver for a safety light grid, part of the SIMATIC FS420i family. It provides a 500 mm protective height and a detection range from 6 to 70 m, with integrated muting capability. The PROFIsafe bus connection allows direct integration into a safety-rated PROFINET network without a separate safety relay.
Type 4 per IEC 61496-1/2 means this receiver is rated for the highest level of fault tolerance in optoelectronic protective devices — it can detect a single component failure and still maintain a safe state. The 500 mm protective height defines the vertical zone it monitors; paired with a matching transmitter, it creates a curtain that guards access to a hazard area. The 6 to 70 m range covers most conveyor, press, and robotic cell applications; the lower end (6 m) is the minimum separation between transmitter and receiver, not a resolution figure. Muting built into the receiver means it can temporarily bypass the light grid for material transport (e.g., a pallet passing through) without external muting sensors or a separate controller — the logic is handled inside the FS420i system over PROFIsafe. This simplifies wiring and reduces the component count in the safety circuit.
Deployment context
Mounts in a standard industrial enclosure with the transmitter opposite, aligned within the manufacturer's specified beam angle. The PROFIsafe connection means it communicates safety status directly to a failsafe PLC (e.g., SIMATIC S7-1200/1500 F-CPU) over the same Ethernet cable as standard I/O — no dedicated safety bus coupler needed. The 500 mm height suits guarding of a typical conveyor infeed or machine access point where a full-height light curtain would be overkill.