Timewaveform 101
Timewaveform 101
(OP)
Being admittedly poor in timewaveform analysis skills, I have a question concerning flattened/truncated waveforms.
If waveform is "clipped" through full cycle (+ to -) is this rotor rub, data taken on overhung belt driven fan, inboard bearing vertical.If motor bearing is bad could this transfer to fan shaft in the form of rotor rub.What is full cycle flattening telling me?
If waveform is "clipped" through full cycle (+ to -) is this rotor rub, data taken on overhung belt driven fan, inboard bearing vertical.If motor bearing is bad could this transfer to fan shaft in the form of rotor rub.What is full cycle flattening telling me?





RE: Timewaveform 101
RE: Timewaveform 101
I see the clipped pattern on the Diagnostic chart indicating rub as mentioned above. However, imho by physical reasoning one would expect this pattern for sleeve bearing machine monitored by prox probe, but not for rolling element machine monitored by housing accelerometer (rub on rolling element machine monitored by housing accelerometer would look like impacts, would it not?).
I will be glad to understand if someone thinks I am mistaken on the above opinion.
Sorry I don't have any constructive suggestions. I have not seen that pattern.
RE: Timewaveform 101
cause subharmonic multiples of 1/2 or 1/3 times RPM...[and]will often allow excessive vibration for relatively small unbalance or misalignment."
Continuous or intermittent rubbing between bearing, shaft, impeller components would seem to be one possible manifestation of mechanical looseness as suggested by electricpete. Constraint of any periodic motion whether rotational or linear seems to be the key to time-amplitude waveform truncation which may or may not entail physical contact or rubbing. For instance, in fluid film bearings, truncation of transient rotor displacement by an impenetrable bearing fluid squeeze-film might truncate the 1X waveform without allowing any physical contact between the shaft journal and the bearing wear surface.
A paper by F.F.Ehrich (not presently onhand) discusses "beat-frequency truncation" of vibration waveforms and mentions some interactions to produce other spectral peaks that are not represented in Berry's Type B mechanical looseness spectrum.
looseness spectrum
RE: Timewaveform 101
The components that have been ck'd are - brg' loose on shaft,sheave loose/concentric, and motor supports with all checking out o.k. The phase is unsteady. My data is limited to two permanently mtd. transducers, vertical on pillowblock roller bearings.
RE: Timewaveform 101