Ball Pass Frequency

The frequency corresponding to the rate at which balls or rollers in a bearing pass a particular location on one or other of the races. The inner race and outer race ball pass frequencies are different from each other, and are dependent on the geometry of the bearing and the rotation speed of the bearing. They are generally not harmonics of the turning speed, and are difficult to predict exactly due to variations in bearing geometry, contact angle, and load. The two frequencies are abbreviated BPFI for inner race and BPFO for outer race. Ball pass frequencies are some of the fault frequencies which are noted in the spectra of machine vibration.