BPFI, BPFO, BSF and FTF - the four characteristic vibration frequencies that appear in an envelope spectrum for a rolling-element bearing with a defect.
Formula
$$ \text{BPFI} = \tfrac{n f_r}{2}(1 + \tfrac{B_d}{P_d}\cos\alpha), \quad \text{BPFO} = \tfrac{n f_r}{2}(1 - \tfrac{B_d}{P_d}\cos\alpha) $$
Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| $f_r$ | Shaft frequency (rpm/60) | Hz | derived |
| $n$ | Number of rolling elements | - | bearing data |
| $B_d$ | Rolling-element diameter | mm | bearing data |
| $P_d$ | Pitch diameter | mm | bearing data |
| $α$ | Contact angle | ° | bearing data |
Sources
- ISO 10816 and ISO 20958.