What it is and what it does
The Siemens 6AG1991-1AF00-7AA0 is a SIPLUS NET SCALANCE X SFP991-1LD SFP module. It gives a SCALANCE X managed switch a single 100 Mbps LC port on single-mode fiber at 1310 nm, supporting links up to 26 km. Built on the standard 6GK5991-1AF00-8AA0 with conformal coating, this version is rated for continuous operation from -40 °C to +85 °C — though the spec allows +85 °C for a maximum of 16 hours, with the rest of the range being continuous. MTBF is listed at 490 years, a reliability figure appropriate for the extended-temperature industrial network segment. Dimensions are 14 mm wide, 57 mm deep, 9 mm high — it latches into a standard SFP cage. Protection class is IP20.
Optical and EMC specifications
The LC port uses a single-mode optical interface at 1310 nm, with transmitter output rated -8 dB maximum and -15 dB minimum, and receiver input maximum -8 dB. The module can span up to 26 km. CE marked. Emitted interference conforms to EN 61000-6-4:2007 Class A; immunity per EN 61000-6-2:2005. Temperature range during storage and transport is the same -40 to +85 °C as operation.