Answer: Abnormal vibration often indicates a fault. To identify the fault based on the extracted vibration signal characteristics, it is necessary to analyze the parameters such as time, frequency (speed), period, phase, amplitude (energy).
Most of the signals encountered in engineering are dynamic signals, whose amplitude changes with time. Dynamic signals can be divided into deterministic periodic signals (simple harmonic signals, complex periodic signals) and non-periodic signals (quasi-periodic signals, transient signals), non-deterministic stationary random signals (variable state ergodic signals, non-variable state ergodic signals) and non-stationary random signals. These signals correspond to vibrations one by one and are closely related to faults.
There are four classification methods for vibration. The first is the dynamic classification method based on the essence of vibration, which can be divided into forced vibration, transient vibration, self-excited vibration, and parametric vibration; the second is the classification method based on the high and low vibration frequency to roughly estimate the fault location; the third is the classification method that distinguishes various vibration characteristics based on the characteristics of the signal and can make a theoretical explanation of the characteristics of the spectrum; the fourth is the classification method based on the characteristics of the vibration system (linear vibration, nonlinear vibration). For example, rotor imbalance and misalignment faults produce simple harmonic vibrations, which are forced vibrations under the action of centrifugal force; when there are several rotor imbalance or misalignment faults in the gearbox or unit at the same time, complex periodic vibrations are generated; the attenuated vibration caused by the excitation of the rolling bearing component damage fault is a quasi-periodic vibration; gear tooth breakage, rotor friction and other faults produce impact transient vibrations.
If there is a simple diagnostic instrument that can only display the vibration amplitude (or energy), the optimal installation method should be selected according to the frequency response range of the sensor, and the measuring points should be selected and marked. It is necessary to identify which parameter (acceleration, velocity, displacement) the vibration amplitude displayed on the instrument is, whether there is a graded range (low pass, high pass, band pass) and its purpose, whether it can display dimensioned (or dimensionless) diagnostic parameter values or decibel values, etc. With this type of instrument, diagnostic methods such as amplitude value, trend chart, waveform factor, crest factor, dimensionless parameter, and impact pulse can be selected to make a qualitative and simple diagnosis of the unit.
