Autotuning in VFD

http://en.wikipedia.org/wiki/PID_controller

Auto Tuning in a VFD usually refers to the setup of the VFD to the motor it is attached to, not the PID loop. Newer VFDs must be tuned to the motor to get maximum performance. if you know all of the details of the motor design, you can tune it manually, or guess, or if the VFD has Auto Tuning, it energizes the motor and runs through a procedure, which may or may not including turning it slowly, to detect the motor optimal performance parameters and enter the settings. Off-line and on-line likely refers to whether or not the drive must turn the motor with the load connected to the motor or not; off-line meaning no, on-line meaning yes.

Some of the higher end drives may also offer Auto Tuning of their internal PID loop controller as well, but because of the potential for confusion, they are usually very specific about describing that. No idea what off or on line would mean in that case.

Here is a good video explaining the auto tune process tuning the VFD to the motor, not a PID.

http://www.youtube.com/watch?v=q8pXKNrnR2g