What it is and what it does
The Siemens 6ES7138-4FA01-0AB0 is a PROFIsafe fail-safe digital input module for the ET200S distributed I/O system. It provides 8 single-channel or 4 two-channel inputs rated at 24 V DC, with a 30 mm width that fits the standard ET200S rail. The module is parameterizable and carries diagnostics, including a group error SF (red) LED and per-channel green status indicators.
Safety ratings that matter for your BOM
This module is rated for SIL 2 (single-channel) and SIL 3 (two-channel) per IEC 61508, and Category 3 (single-channel) or Category 4 (two-channel) per EN 954-1. It also meets AK 4 (one channel) and AK 6 (two channel) per DIN VDE 0801. For a safety loop, the two-channel wiring is what gets you to SIL 3 / Cat. 4 — plan the field wiring accordingly.
Electrical and timing constraints
Input signal thresholds: a logic '0' is -30 to +5 V, and a logic '1' is +15 to +30 V. Typical current draw at signal '1' is 3.7 mA. The module draws 300 mA from the backplane bus and dissipates 4 W typ. Switching times range from 0.3 ms to 17 ms for both 0→1 and 1→0 transitions. The output voltage sits at min. L+ (-1.5 V). Short-circuit protection is electronic with a response threshold between 0.7 A and 1.8 A. Note: reverse polarity protection is not provided, so check your 24 V DC supply polarity.