Fail-safe NAMUR input module for Ex zones
The Siemens 6AG1326-1RF01-4AB0 is a SIPLUS SM 326F digital input module for the S7-300 system, purpose-built for fail-safe applications in potentially explosive atmospheres. It packs 8 NAMUR inputs and 8 fail-safe outputs into an 80 x 125 x 120 mm housing, drawing 4.5 W typical from the backplane. Rated SIL 2 in single-channel configuration and SIL 3 in two-channel, with a corresponding Performance Level of PLe per ISO 13849-1. That means it can serve as the safety I/O slice in a SIL 3-rated safety loop — think emergency stop chains, light curtain monitoring, or two-hand control circuits — without needing an external safety relay.
Intrinsic safety and sensor wiring
The module is certified for Ex(i) protection, meaning the input circuits are intrinsically safe. The open-circuit voltage Uo is capped at 10 V, short-circuit current Io at 13.9 mA, and the maximum permissible external capacitance Co is 3 µF with inductance Lo of 80 mH. These limits let you wire directly to NAMUR proximity sensors in Zone 1/Zone 2 gas groups without an isolating barrier. Each input draws 2.1 to 7 mA for a signal "1" and switches with a 1.2 to 3 ms delay in either direction. The 8.2 V DC output voltage powers the sensor loop; total available power Po is 33.1 mW, which comfortably drives a standard NAMUR sensor at 8.2 V.
Cable length and isolation
Unshielded sensor cables can run up to 100 m; shielded runs stretch to 200 m. Channel-to-channel isolation is provided, as is isolation between the channels and the backplane bus — no ground-loop coupling when mixing sensors on different field supplies. The module requires a 40-pin front connector (sold separately) and draws up to 90 mA from the 5 V DC backplane bus plus up to 160 mA from the load voltage L+. Reverse polarity protection is built in on the load voltage side.