Safety-rated inputs for SIL 3 / PLe circuits
This is a Siemens ET 200SP fail-safe digital input module, order code 6AG1138-4FA05-2AB0, HF (high-feature) variant. It gives you 8 digital inputs at 24 VDC, configurable as 8 one-channel or 4 two-channel — the two-channel wiring is what gets you to SIL 3 (IEC 61508) and PLe (ISO 13849-1). That means a single module can cover an emergency-stop string or a light-curtain pair without needing a separate safety relay. The inputs are parameterisable — you set the filter time (0.3 ms to 17 ms) and the sensor type (2-wire or 3-wire) in the safety program. The module draws 300 mA from the backplane bus and dissipates 4 W typical, which matters for the thermal budget in a dense ET 200SP station.
That -25 °C floor means it starts and runs in a cold mine drift or an unheated outdoor cabinet in a northern winter. The 60 °C ceiling handles the heat inside a sealed panel next to drives or transformers — no derating needed at the top end.
Diagnostics that tell you which channel failed
This module has a diagnostic alarm and a group error LED (red SF). It reads out diagnostic information over the backplane — which channel shorted, which sensor lost power, whether the load voltage L+ dropped. That saves a technician from meter-probing every input when a fault trips the safety chain. Short-circuit protection is electronic with a response threshold between 0.7 A and 1.8 A per channel. It protects the module and the field wiring without needing an external fuse per input — the module shuts down the affected channel and reports it.