Written in a clear, understandable style, this new edition of Vibration Spectrum Analysis includes valuable information on using the latest techniques of spectrum . Vibration Spectrum Analysis helps teach the maintenance mechanic or engineer how to identify problem areas before extensive damage occurs. Every rotating. Frequency Analysis Vibration Spectrum Analysis Steve Goldman - Download as PDF File .pdf), Text File .txt) or read online.
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There are two possible problems in using the shock-pulse method of monitoring bearing condition.
One is the inability to differentiate between various sources of white noise. A bearing checker designed to measure the amplitude of white noise amplified by the natural frequency of its accelerometer may well yield high values due to a bearing fault. The problem, however, is that it will also yield high values due to small bubble cavitation, steam leaks near the accelerometer, turbulence, and so on. The presence of steam leaks near a bearing to be monitored is a common problem in the dryer section of paper mills, where this method, if blindly followed, will lead to the replacement of a great many perfectly good bearings.
Healing Bearings It has occasionally been found by people who regularly take white-noise-type bearing readings that a given bearing will show signs of deteriorating but, shortly before total failure, exhibit lower amplitude values.
Machinery monitoring personnel have been fooled into believing that the bearing was getting better by lower readings when it was actually on the verge of failure. A possible explanation of this phenomenon can be found in pulse theory.
Suppose the bearing was failing not simply by adding more tiny faults which would increase the white noise content , but because the existing fault was growing.
As the fault grew, the time duration of the pulse generated when the fault came in contact with other components of the bearing would grow.
The pulse would lose more and more of its white noise characteristics until there was no more energy in the frequency range necessary to excite the natural frequency of the accelerometer. The amplitude reading of the bearing-checking box would drop, implying that the bearing had healed see Figure B.
The above described possibility for a bearing to appear to heal puts an additional requirement on the work of machinery-monitoring personnel. When the reading of a bearing-checking device begins to drop for a particular bearing, careful consideration must be given to the possibility that the bearing is very near to failure.
It is wise, at this point, to look at the amplitudes of the classical discrete frequencies of that bearing in order to make a decision as to when it must be changed. The Walls of Jericho To demonstrate that pulse theory may be applied to a great many varied phenomena, one last case will be covered: Jericho is one of the oldest known cities on earth.
The people of Jericho were not very good wall builders. In fact, the walls of Jericho had fallen many times before the time of Joshua.
As can be seen by the background of the photo of some of the remains of the walls of Jericho in Figure B. Note that wet, fertile ground transmits low-frequency signals rather well. Stone walls, especially of the primitive kind shown in the photo, tend to have a large mass and a very little stiffness. Therefore, the natural frequency of the structure would be quite low. Joshua commanded his people to march around the city seven times, blowing ram's horns and shouting and the walls came tumbling down.
Pulse theory yields, an interesting insight into this historical event. The blowing ram's horns and shouting would cause pressure waves of rather high frequency, several hundred to several thousand Hertz.
It is extremely unlikely that these pressure waves, while certainly capable of scaring the wits out of the citizens of Jericho, would have been capable of causing the low natural frequency walls to collapse.
On the other hand, the stomping of a large number of feet on fertile ground would have caused long-time-duration pulses of rather high amplitude. Pulse theory tells us that long-time-duration pulses have most of their energy concentrated in the low-frequency range, near the natural frequency of the wall. We can surmise, therefore, that the walls of Jericho fell due to the marching of the Jews, not their shouting or blowing or ram's horns. The miracle was not that the walls fell, but that pulse theory was successfully employed by an ancient general at an ancient city to change history.
Something to Think About The effect of the shape of a pulse is something that is so well known and so widely taken for granted by many of us that its ramifications in vibration analysis are seldom considered. This is unfortunate because, as shown above, the due consideration of the relationship of pulse shape to frequency response can lead to a great many insights and hypotheses that may well provide a better understanding of the phenomena being studied.
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The second edition includes new information on current instrumentation, along with case studies and new practice questions.
Vibration analysts, predictive maintenance specialists, and field mechanics will find valuable information on using the latest techniques of spectrum analysis in solving problems and enhancing machine reliability in this key reference text. A book good for both engineers and non-engineers alike. From the Back Cover - The Second Edition of Vibration Spectrum Analysis includes vital new information on current instrumentation, along with case studies, additional appendixes, and new practice questions.
Engineers and non-engineers alike will find this clearly-written book an invaluable resource for understanding the latest tehniques of spectrum analysis for solving problems and enhancing machine reliability.