The 6ES7138-4FA04-0AB0: Out here in the grease, that SIL 3 two-channel rating means you can use it on safety circuits up to the highest performance level without a separate safety relay — just watch the wiring. The module also carries electronic short-circuit protection with a trip threshold between 0.7 and 1.8 A, so a crushed cable won't take out the backplane bus.
Fit and wiring
The module sits on an ET 200SP base unit (BusAdapter required). It occupies 30 mm width on the DIN rail and extends 52 mm deep — that leaves room for fingers and wiring ducts in a crowded cabinet. Input voltage is 24 V DC, and the module draws 300 mA from the backplane plus 4 W typical. Isolation between channels and the backplane bus is tested at 500 V DC, so it shrugs off the kind of noise you get from a VFD or motor starter sharing the same panel. The green status indicator on each input lets you walk the route and spot a dead sensor without dragging out a meter. The group error LED (red) and diagnostic alarm tell the PLC something's wrong before the line stops.