I am dealing with a medium sized direct coupled overhung fan unit. 85KW motor.
The unit is roughly 7 years old (PDM program is new here, I have 6 years experience). Unit was checked for the first time on 3/30/2017 with an overall amplitude of 0.08 in/sec (0-peak) at 1200 RPM on the Motor non drive end horizontal.
Unit checked again on 5/12/2017 had an amplitude of 1.14 in/sec (0-peak) at 1500 RPM on the motor non drive end horizontal. Velocity spectrum showed a very high 1X RPM peak. A natural resonant frequency problem was suspected.
Today I was able to run a Coast down peak and phase test with my CSI 2140 on the unit. The results are:
The orbital plot is very odd, and the phase changes aren't as apparent as what I've normally seen.
This is the same test run on the fan unit directly next to the one in question. The orbital plot looks normal, and the phase shifts are very definite.
I am now questioning my original diagnosis of the unit. Any help and further insight into possible problems is greatly appreciated!