What it does — IQ-Sense sensor interface
The 6ES7338-7XF00-0AB0: The SM 338 connects up to eight IQ-Sense photoelectric proximity switches or ultrasonic sensors, reading their digital status on the S7-300 backplane. Cycle time runs 2.88 to 6 ms per channel — fast enough for part-present and level-detection loops on a conveyor or crusher feed, but not for high-speed counting. Each input is 24 V DC, and the module draws 120 mA typical from the 5 V backplane bus plus 2.5 W total power loss. That 2.5 W is the heat you need to vent in a sealed panel — it is not much, but in a densely packed S7-300 rack with multiple modules, the cumulative thermal load matters.
The module measures 120 mm deep, 40 mm wide, and 125 mm tall — standard S7-300 single-width format. It requires a 20-pin front connector (sold separately) for field wiring. The 40 mm width leaves room alongside other slices in the DIN-rail rack, but the depth means you need at least 130 mm clearance behind the mounting panel for the connector and wiring loom.
Status and diagnostics
Each channel has a green status LED for digital input indication. A red group-error SF LED flags a fault on any connected sensor or the module itself. Isolation between channels and the backplane bus is tested at 500 V DC — channel-to-channel isolation is not provided, so all inputs share a common reference.