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Bearing Defect Frequencies

BPFI, BPFO, BSF and FTF - the four characteristic vibration frequencies that appear in an envelope spectrum for a rolling-element bearing with a defect.

MaintenanceVibration

Shaft speedrpmNumber of rolling elements - Rolling-element diameter BdmmPitch diameter PdmmContact angle α°

BPFI (inner race)

180.00Hz

BPFO (outer race)

120.00Hz

BSF (ball spin)

72.00Hz

FTF (cage)

12.00Hz

Formula, assumptions, and limits

Envelope demodulation on a broadband accelerometer signal reveals the defect frequency even when its amplitude is dwarfed by running-speed harmonics. Matching a peak to the expected BPFI/BPFO identifies the defective bearing element.

Symbol legend

Meaning	Unit	Source
Shaft frequency (rpm/60)	Hz	derived
Number of rolling elements	-	bearing data
Rolling-element diameter	mm	bearing data
Pitch diameter	mm	bearing data
Contact angle	°	bearing data