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.

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This calculator requires JavaScript to compute its result. The formula, symbols, and regulatory sources are shown in the Formula section below.

Formula, assumptions, and limits

\text{BPFI} = \tfrac{n f_r}{2}(1 + \tfrac{B_d}{P_d}\cos\alpha), \quad \text{BPFO} = \tfrac{n f_r}{2}(1 - \tfrac{B_d}{P_d}\cos\alpha)

Symbol	Meaning	Unit
$f_r$	Shaft frequency (rpm/60)	Hz
$n$	Number of rolling elements
$B_d$	Rolling-element diameter	mm
$P_d$	Pitch diameter	mm
$α$	Contact angle	°

Source: ISO 10816 and ISO 20958

In short

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

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