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Sum Frequency And Difference Frequency - Rolling Bearing

You must have a different understanding of the knowledge of sum-frequency and difference frequency. Now we will explain the contents of sum-frequency and difference frequency of rolling bearing.


A component fault → fault deterioration → knowledge causing it, it is component fault → fault frequency of other components. The addition and subtraction of frequencies will not only produce the fundamental frequency of a fault frequency. When there is a fault, the fault frequency is likely to exist in the form of sidebands of other existing frequencies. For example, bearing cage fault frequency FTF generally does not appear at the fundamental frequency of about 0.35x ~ 0.45X speed frequency, but the sideband of BSF, bpor and bpir fault frequency, and can even be modulated into a new frequency with other vibration sources.

Sum Frequency And Difference Frequency - Rolling Bearing

What are the effects of bearing faults?

If there is a single fault on the bearing outer ring or bearing inner ring, there will only be a single bearing outer ring or bearing inner ring fault frequency (bpor or bpir). When there are multiple faults around him, there will be many harmonic frequencies of the bearing outer ring or bearing inner ring fault frequency (bpor or bpir). With the expansion of bearing inner ring and outer ring faults, the better indicators of fault deterioration are the number of harmonic frequencies of bearing fault frequency and the sideband of 1x speed frequency on both sides of bearing outer ring or bearing inner ring fault frequency.

In the fault frequency analysis of rolling bearing, the emphasis is not the amplitude, but the frequency component in the frequency spectrum. Especially when the defects of the bearing inner ring or bearing outer ring begin to expand. Pay attention to the number of harmonic frequencies of bearing fault frequency, accompanied by 1x sideband. The bearing fault continues to worsen, the modulation continues, and the impact becomes greater and greater until the spectrum becomes the harmonic frequency of 1x speed frequency.

How to diagnose bearing faults?

For self-aligning double row bearings with oscillating rolling elements, two groups of bearing fault frequencies can be generated: (a) only one side of the inner ring or outer ring, calculate the fault frequency with a single row of rollers; (b) if the defect occurs on both sides of the outer ring or inner ring of the bearing, calculate the fault frequency with the total number of rolling elements.

It is difficult to diagnose a single fault of a rolling element on the bearing inner ring only from the spectrum, because its amplitude is often very small, and there is no discrete spectrum line at the calculated fault frequency. Therefore, in addition to the vibration spectrum itself, the time domain waveform should also be studied. In rolling bearings, when there are speed harmonic frequencies, they may be signals of bearing Looseness on the shaft or in the bearing seat, or more importantly, they may be signals of bearing rotation on the shaft or in the bearing seat.