For roller bearing, the rolling, inner ring, outer ring of the irregular damage, such as peeling, pitting, cracks inevitably lead to shock.  The basic repetition rate shock and vibration repeat the same or similar frequency, but the impact caused by the initial failure is often far less than the magnitude of vibration. This is due to the vibration performance of long-lasting process, sustained release of energy accumulated value was greater than the impact of short process is abnormal, the amplitude of the energy may be great, but the accumulated energy is minimal. Frequency analysis method with failure because it is easy to accept, is today the development of more sophisticated methods. But because of the impact of short duration, the frequency of its energy to the vast areas of divergence, fall within the scope of rolling bearing vibration frequency components even smaller, not larger but with the energy field of the basic focus on the low-frequency vibration components compared. Thus, the direct impact of the vibration signal contains the fault spectrum analysis to diagnose faults and sometimes there will be damage to the bearing failure occurred on the spectrum but can not see the phenomenon.
Resonance is a common physical phenomenon of resonance characteristics can be used to extract the information buried in the normal vibration of the impact of information failure. As the vibration of non-normal frequency components, and bearings which have failed shocks, therefore, can set up a high frequency of normal vibration frequencies reach the resonant system, excluding the normal vibration, shock response to incentives, to achieve the impact of information the extraction.
Therefore, the resonance demodulation technique is a low frequency (number of kHz or less often) aroused by the impact of high frequency (10 times the number of impact frequency) resonance waveform envelope detector and low pass filter, that is demodulated to obtain corresponding low impact, but amplification and broadening of the resonance demodulation wave; by the amplitude of this wave resonance demodulation and spectrum analysis, to determine the value of failure and fault type.