When a 4-20mA speed reference is wired in series from one drive to another using AI2 and COM terminals, the speed reference is not passed to the second drive when the first drive has faulted or is powered off.
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AI2 on the ATV61 and ATV71 is selectable between voltage and current. When power is removed a resistor is switched in the circuit of AI2 which will not allow the 4-20mA to pass to the next drive.
Use a 4-20mA loss set to Spd maintain or fallback spd. See the Fault Management menu, then 4-20mA Loss for these and other options on a 4-20mA signal loss. Fallback Speed is also in the Fault Management menu.
Use a separately mounted signal splitter instead of wiring the drives in series.