When you look at the various causes of oscillations, it becomes clear that they primarily come from 2 sources:
当你看一下引起振荡的各种原因时，就会发现它们主要来自两个方面：
1. Imbalance and misalignment
1. 不平衡和不对中
Imbalance and problems with alignment lead to predominantly harmonic, sinusoidal oscillations.
不平衡和对中问题导致了以谐波为主的正弦波振荡。
Fig.: Imbalance - Harmonic oscillation
图: 不平衡 - 谐波振荡
2. Impacts
2. 冲击
Many types of machine damage can result in oscillations that cause the structure of the machine or adjacent machine parts to vibrate at their natural frequency. Impact-related causes of this are a result of corrosion, a rotor brushing up against the machine housing or roller bearing/gearing damage to the gears.
In the case of roller bearing damage, impact occurs when either the rolling elements roll over damage on the inner or outer track or when one of the rolling elements themselves is damaged.
许多类型的损坏可能导致振荡，从而导致机器或相邻机器部件的结构以其固有频率振动。造成这种情况的与冲击有关的原因是腐蚀、转子擦到机器外壳或滚柱轴承/齿轮损坏。
在滚子轴承损坏的情况下，当滚动体在内轨或外轨上滚动损坏时，或者当其中一个滚动体本身损坏时，就会发生冲击。
Fig.: Bearing damage - FFT of envelope signal
图: 轴承损坏--包络信号的FFT
This kind of impact can be compared to a clapper hitting a bell. If the bell is struck 2x per second, it vibrates at its natural frequency and not 2 Hz. The natural frequency is determined by the constructive design and material properties. As with any sound boxes, mounting also factors into this.
If the damage is to the roller bearing track, every shock pulse will lead to a corresponding reaction in the vibrating system. It is only practical to measure the sum of all pulses, i.e. the total signal.
In the case of damage to roller bearings, the bearing rings are the first to start vibrating.
这种冲击可以比喻为拍子敲打铃铛。如果铃铛每秒被敲击2次，它的振动频率是其固有频率，而不是2Hz。固有频率由结构设计和材料特性决定。与任何音箱一样，安装也是其中的一个因素。
如果损坏的是滚子轴承轨道，则每个冲击脉冲都会在振动系统中导致相应的反应。测量所有脉冲的总和，即总信号，才是实用的。
在滚子轴承损坏的情况下，轴承套是第一个开始振动的。
Analyzing oscillations
分析振荡
Oscillations are transmitted in the machine as waves and can be measured on the machine's surface. A prerequisite, of course, is that a path is available for the sound transport, i.e. there are no sound-absorbing border crossings such as air, rubber, etc. between the roller bearing and sensor.
This signal can be measured on the surfaces of the machine by means of an accelerometer. The signal is made up of a variety of oscillations and impacts that overlap each other. When considering the time signal in this way, it is easy to see that allocating individual frequencies is difficult, if not impossible.
Using a Fast Fourier transform, this time signal can be converted to give the natural frequency of the system. These are in the high-frequency range. The rotor frequency and its harmonic frequency are clearly identifiable as the dominant frequency portion.
The rollover frequencies of the roller bearings are between 15 and 70 Hz at a speed of approximately 600 rpm, depending on the bearing.
In particular, shock pulses of a lower intensity, as they are when damage first begins, can barely be noticed or assessed. It is only when there is advanced damage to bearings that signal peaks can be clearly observed.
振荡在机器中以波的形式传输，并且可以在机器表面上测量。当然，一个先决条件是有一条声音传输的路径，即在滚动轴承和传感器之间没有空气、橡胶等吸音边界。
该信号可以通过加速度计在机器表面上进行测量。信号由各种相互重叠的振荡和冲击组成。当以这种方式考虑时域信号时，很容易看到指定单个频率是困难的，甚至是不可能的。
使用快速傅立叶变换，可以将该时域信号转换为系统的固有频率。转子频率和它的谐波频率可以清楚地识别为主导的频率部分。
滚子轴承的滚动频率在大约600 rpm 的速度下是 15 到 70 Hz，这取决于轴承。
特别是强度较低的冲击脉冲，就像它们在刚开始损坏时一样，几乎不能被注意到或评估。只有当轴承出现晚期损坏时，才可以清楚地观察到信号峰值。
Fig.: Advanced bearing damage at 600 rpm
图: 600 rpm 时轴承损坏的严重情况
To make the actual result, or shock sequence, clearly visible, it is obviously not enough to simply provide the amplitude spectrum. It is much more important that the process of convolution that took place when the signal occurred be appropriately reversed so as to separate the excitation function from the natural frequency. This is what envelope analysis provides.
An amplitude-modulated signal is made up of a high-frequency carrier signal and a low-frequency wanted signal. The amplitude of the carrier signal changes depending on the wanted signal. In the receiver, the wanted signal is extracted from the carrier signal by the formation of the envelope curve (demodulation).
In the case of machine resonances caused by periodic impacts, the machine resonances can be viewed as the carrier signal and the low-pass-filtered shock pulses can be viewed as the low-frequency modulation signal. Demodulation results in the shock pulses being extracted from the resonance frequencies.
为了使实际结果或冲击清晰可见，仅仅提供振幅谱显然是不够的。更重要的是，在信号发生时发生的卷积过程要适当地反转，以便将激励函数与固有频率分开。这就是包络分析所提供的功能。
一个振幅调制的信号是由一个高频载波信号和一个需要的低频信号组成的。载波信号的振幅根据需要的信号而变化。在接收器中，通过形成包络曲线（解调），从载波信号中提取出想要的信号。
在周期性冲击引起机器谐振的情况下，机器谐振可以被看作是载波信号，低通滤波的冲击脉冲可以被看作是低频调制信号。解调的结果是将冲击脉冲从谐振频率中提取出来。