Sometimes control logic belongs inside the drive — at drive cycle times, microseconds from the current controller. DCC is Siemens’ answer: a graphical block language (logic, arithmetic, filters, ramp generators, technology blocks) compiled into the SINAMICS runtime.
Where DCC earns its place
- Fast corrections that a PLC cycle would arrive late for: tension trim loops, cut-to-length corrections, load-share balancing between coupled motors.
- Autonomy: a drive that must behave sensibly even when the PLC is down or the machine is in local mode.
- Retrofit archaeology: replacing analog technology cards from DC-drive eras — their summing amplifiers and function generators map naturally onto DCC charts.
The free blocks (BICO interconnections on steroids) wire into the drive’s parameter world, so a DCC output can feed the torque setpoint channel directly.
The maintainability rules
DCC’s danger is invisibility: logic hiding in a drive that the PLC programmer five years later does not suspect exists. Our rules: every DCC chart is documented in the machine’s software architecture page; a “DCC present” marker lives in the PLC code comments at the interface tags; charts stay small and single-purpose (a trim loop, not a machine sequence — sequences belong in the PLC); and the chart source is archived with the drive backup, always.
FAQ
DCC or a faster PLC? If the loop needs sub-millisecond reaction tied to drive-internal signals, DCC. If it is machine coordination at normal cycle times, PLC — resist the temptation.
Does DCC cost performance? Charts consume control-unit computing time budgeted per execution group — the engineering shows the load; heavy charts on a busy multi-axis CU need checking, not guessing.
Zone Otomasyon has replaced whole analog control cabinets with S120+DCC. Legacy drive retrofits.