Calculation of Unknown Bearing Types in your Equipment

December 7, 2011

Knowing the exact bearing information for your equipment can make bearing defect analysis much easier.  However, it may not always be possible to acquire the bearing information for your equipment.  This can make it difficult to determine the bearing fault frequencies for correct analysis.

It is possible to remember easy formulas to calculate the approximate bearing fault frequencies for rolling element bearings.  The following formulas are easy to remember and can help you when the bearing information is not known:

FTF = 0.43 × RPM
BPFO = 0.43 × N × RPM
BPFI = 0.57 × N × RPM

Where:
FTF = Fundamental Train Frequency
RPM = Revolutions per minute
BPFO = Bearing Pass Frequency Outer Race
N = The number of rollers
BPFI = Bearing Pass Frequency Inner Race

The values derived from these formulas should be within 10% – 15% percent of the actual bearing fault frequencies.
Other formulas are available that will more accurately estimate bearing fault frequencies than the ones listed above.  LUDECA will be happy to provide those to you upon request.

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