The Siemens 3SF7844-8MD22-0SS1 is a Type 4 safety light curtain receiver from the SIMATIC FS420i family, designed for finger and hand protection on access points and hazardous zones. With 30 mm resolution and a 1500 mm protective height, it detects objects as small as 30 mm across the full height — suitable for guarding robot cells, assembly stations, and palletizers where personnel access must be detected without physical barriers. The 0 to 18 m operating range gives flexibility for wide openings or long conveyor in-feed zones. Type 4 per IEC 61496-1 means the receiver is rated for the highest safety integrity level for electro-sensitive protective equipment, capable of withstanding a single fault without losing the safety function. The PROFIsafe bus connection integrates directly into a SIMATIC safety PLC or F-capable controller over the standard PROFINET network, eliminating the need for a separate safety relay or interface module — the safety signal travels over the same cable as standard I/O. The muting function allows the light curtain to be temporarily overridden during material transport (e.g., a pallet passing through the protected zone) while still maintaining safety for personnel. This is a configurable feature typically set during commissioning via the FS420i software or the controller's safety program.
Integration notes
The receiver mounts to a standard extruded-aluminum profile or bracket system common to the FS420i family. Alignment with the matching transmitter (typically a 3SF7844-8MD22-0SS0 or similar) requires the supplied alignment tool and a clear line of sight. The PROFIsafe connection uses a standard M12 connector (D-coded) for the bus interface; the power supply is typically 24 VDC drawn from the same bus cable or a separate M12 L-coded connector depending on the variant. Commissioning involves configuring the muting sensors (typically two through-beam sensors per muting zone) and setting the blanking or reduced-resolution parameters in the safety program. The receiver's diagnostic LEDs indicate alignment quality, muting status, and bus communication health — useful during FAT and on-site startup.