I understand programming, and the human interface is all done, a LCD and a keyboard to input data its all set.
For a simple console to imput RPM to a motor, arduino is enough and dont need to get a expensive PLC console for such trivial task, and its a inhouse project its not for resell, the industrial VFD is used because it has safe-backs built-in such as emergency button, obstruction detector etc.
What iam not familiar is outputing to the VFD in the analog form, I read it is possible but I couldnt find any schematic avaible for such task, I found stuff but its all bits and pieces.
I will try to find more info on the VFD