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4. Bearing Status Assessment
When the rolling elements move inside a bearing, broadband noise and vibration is
generated. This increases if the bearing is not properly lubricated, or is overloaded sue to
misalignment or damaged surfaces.
The bearing vibration Bg or Bv measured by the meter is the RMS value of all high frequency
bearing vibrations between 1kHz and 12kHz.
The vibrations below 1kHz are suppressed in the Bg and Bv modes to eliminate the
measurement vibrations caused by imbalance or misalignment. A practical problem arises
in gearboxes, and other machines where steel meets steel, in which vibrations are produced
in the same frequency range as bearing vibrations. For this reason bearings should not
normally be exchanged on the basis of a high bearing value only. A high bearing condition
value is an indication that further analysis is required, and an FFT analyser will indicate if
there are frequencies corresponding to the calculated bearing frequencies.
4.1 Bg Value
Bg Value is vibration acceleration within 1-12kHz in units of g RMS. The reason for using
acceleration is that it gives larger values at higher frequency than velocity measurements.
The rule-of-thumb assessment of Bg is shown in the chart on page 10.
QM014 Issue 5
- 10 -
HS-620/630 User Guide
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