What this Type 4 receiver does on the line
The Siemens 3SF7844-8MD20-0SS1 is a Type 4 safety light curtain receiver from the SIMATIC FS420I series, paired with a matching emitter to form a finger- and hand-protection zone. Its 30 mm resolution detects objects as small as 30 mm — that catches individual fingers reaching into a hazard zone, meeting the finger-protection class per IEC 61496-1. The 1350 mm protected height covers a typical machine access opening; the 0 to 18 m range gives flexibility for longer guarding spans on conveyor or robotic cells. PROFIsafe bus connection means it integrates directly into a safety-rated fieldbus network without a separate safety relay — the safety signals travel over the same PROFIBUS or PROFINET cable as standard I/O, simplifying wiring and diagnostics.
Muting and integration context
Muting capability is built in — the receiver handles muting sensors that temporarily suspend the light curtain during material pass-through (e.g., a pallet entering a guarded zone) without stopping the machine. This is a standard feature on the FS420I series, not an add-on module. The receiver mounts to the machine frame or guarding structure using the standard FS420I brackets; alignment aids and a visible LED status bar on the receiver simplify commissioning. PROFIsafe addressing is set via the bus connector or the FS420I configuration tool — no DIP switches on the receiver itself.