Vibration spectra provides important
clues to machine problems. There are tools provided in all software packages
that help with this analysis. The most important are:
-
Moveable Cursor
- A "base" cursor that can be moved to any frequency and identifies
the amplitude at that frequency.
-
Harmonic Cursors
- Activating this tool creates additional cursors (as many as are required)
that appear at integer multiples of the base cursor. If the base cursor
is located at 1x rpm, harmonics will appear at 2x, 3x, 4x, etc. This is
the most important analysis tool available. All harmonic cursors
are at higher frequencies than the base cursor.
-
Sideband Cursors
- Activating this tool creates additional cursors at frequencies to either
side of the base cursor. If the 1st (closest) sideband cursors are located
50 cpm to either side of the base cursor, additional sideband cursors (as
many as required) will each be located an additional 50 cpm away. For instance,
the 2nd sideband cursors will be 100 cpm away from the base cursor, the
3rd will be 150 cpm away, etc.
These three tools are sufficient for
the beginner and for 99% of most analyses. There are, of course, other
useful tools such as " "labels" and frequency groups but that is more vendor
specific and should be learned in a software class and through experience.
-
Remember, ALL spectral analysis
is limited in its use and accuracy by the spectrum resolution.
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