Question:
Why do frequency inverters not switch to the Operational communication phase?
Answer:
In machines, in which frequency inverters are driven by a PLC, often only the frequency inverters are disconnected in case of emergency stop.
As normally frequency inverters are defined as system bus slave (Lenze factory default setting: C0352 = 0), after switching on the inverters are in the Pre-Operational phase. However, a process data communication is only possible in the Operational phase. Thus, the PLC must send a telegram to the frequency inverters in order to switch them to the Operational phase. Normally, this happens only when the PLC is switched on. In case of emergency stop the frequency inverters remain in the Pre-Operational phase.
Remedy:
At least one frequency inverter should be defined as system bus master (C0352 = 1) parallel to the PLC, so that after switching on of the frequency inverters it switches all other inverters to the Operational phase.
