I quote TA:

"Key point of phase behavior at unbalance:Whatever is the phase difference bertween the OB and IB bearings horizontal phase measurement on a rotor, the vertical difference between OB and IB bearings must be the same (within +/-30*)".

I believe this is insufficient. What is missing here is a requirement that on the top of that the phase difference between H and V on EACH of the bearings should be close to 90* if unbalance is the predominant problem. Failure to meet this requirement indicates that other factors such as misalignment, looseness may be a significant part of the problem.

Any other opinions?

David,
You may also need to take into account the type of rotor you are looking at. For instance if it is an overhung rotor.