The SINAMICS G115D is a wall-mount drive meant to live beside the conveyor it drives — no cabinet, no long motor cables, just a motor-mounted neighbor on the string. That placement changes the control question: with the drive distributed along hundreds of meters of conveyor, the network you choose for commands and diagnostics decides whether the system is maintainable or a rodent-chewed mystery.
Three wiring philosophies
AS-Interface is the minimal bus: two wires carry power and every command bit along the conveyor. A 7.5 kW G115D with AS-Interface or the 1.5 kW AS-Interface unit joins the string with a single flat cable — fast to install, trivial to extend, and diagnostic depth limited to what AS-i carries.
PROFINET is the full-featured choice: an 0.37 kW PROFINET G115D reports currents, temperatures and faults into the PLC's regular diagnostics, and ride-through behavior can be configured centrally. For new plants standardized on PROFINET, this is the default.
Plain I/O remains legitimate: a 5.5 kW I/O-control G115D takes run/stop/speed from a few cores and reports a digital health bit. Where a conveyor is short, standalone, and controlled from a local panel, hardwired I/O is the cheapest honest answer.
The choice mirrors how the plant treats its PLC estate: bus-rich plants pick PROFINET, sensor-level strings pick AS-i, islands stay hardwired.
Can I mix the three on one conveyor?
Yes, and it is common in brownfield extensions — new string sections on PROFINET, legacy ends on AS-i or I/O. Each drive's control interface is part of its order code, so plan the mix before ordering, not after.
Which option gives the best fault diagnosis?
PROFINET by a wide margin: per-drive fault codes and live currents reach the controller. AS-i reports presence and a fault bit; plain I/O reports what you wired. If MTTR matters more than cable cost, PROFINET pays for itself at the first midnight stoppage.
