Section 4 — Measurement Types and their Uses
68
Eccentric belt
pulley
General A high amplitude peak will appear at 1X
the running speed of the pulley. Look
for a phase change of either 0° or 180°
between the horizontal and vertical
readings. This indicates straight line
motion instead of the usual 90°
difference. This symptom is similar to
bearing resonance (described above).
However, in this case, the direction of
maximum vibration will be in line with
the two belts.
Mechanical
looseness
General High amplitude peaks will show up at
several multiples of the running speed
and sometimes even multiples of 0.5X
running speed (e.g. 1.5X, 2.5X), etc. Look
for fluctuating phase readings at a
location from one recording to the next.
Also compare the phase readings at 30°
increments around a bearing housing.
The phase will be significantly different
at each angle.
Soft foot A high amplitude peak will show up at
1X the running speed. Look for a 90° to
180° phase change between the
machine foot and its concrete base. The
soft foot may also have a different
phase measurement from the other
feet.
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