BPFI – Ball pass frequency Inner
The spectrum shows several harmonic peaks of the inner ring failure frequency (typically between 8 and 10 harmonic multiples of BPFI) modulated by sidebands at 1x revolutions per minute (RPM).
E.g. for the SKF 22228 bearing, the frequencies are calculated for 1500 revolutions:
![SKF-bearing-fault-fgrequency](https://vibroguard.cz/wp-content/uploads/2023/05/SKF-bearing-fault-fgrequency.jpg)
So in the spectrum we would see 1x BPFI peak at 269.7Hz and harmonics 2x, 3x, … and then side bands of speed around them, in our case 1500 RPM / 60 = 25Hz, i.e. 1xBPFI = 269.7 +25Hz -25Hz
![Bearing_fault_BPFI](https://vibroguard.cz/wp-content/uploads/2024/04/Bearing_fault_BPFI.png)
Examples of inner ring damage:
Real-world example, time, spectrum and envelope, inner ring damage:
![porucha-ložiska-amplituda-spektrum](https://vibroguard.cz/wp-content/uploads/2023/06/porucha-loziska-amplituda-spektrum.jpg)
![porucha-ložiska-obálka](https://vibroguard.cz/wp-content/uploads/2023/06/porucha-loziska-obalka.jpg)