Every time you make a sound when singing, speaking, or even whispering, you are making vibrations.
Vibration analysis is mostly a learned skill. It is based 70 percent on experience and 30 percent on classroom training and self study. It takes years to become a confident and competent vibration analyst. When the analysis is wrong, the recommendations for repair also will be incorrect. No vibration analyst wants to make the wrong call. In this business, credibility is gained in small steps and lost in large chunks.
A vibration sensor placed on a bearing housing and connected to a vibration analyzer provides time, frequency and amplitude information in the form of a waveform and a spectrum (Figure 1). This data is the foundation for vibration analysis. It contains the signatures of nearly all mechanical and electrical defects present on the machine.
The vibration analysis process involves determining the vibration severity, identifying frequencies and patterns, associating the peaks and patterns with mechanical or electrical components, forming conclusions and, if necessary, making recommendations for repair.
Everybody involved in vibration analysis knows that analyzing vibration is not easy nor automated. Have you ever wondered why? Here are a few reasons:
1) Machines Have Multiple Faults: The vibration patterns we learn in training and read about in books just don’t look the same in the real world. We learn how mechanical and electrical faults look in the purest form – as if there was always only that one problem on the machine causing vibration. Machines usually have more than one vibration-producing fault. At a minimum, all machines have some unbalance and misalignment. When other faults develop, the waveform and spectrum quickly become complicated and difficult to analyze. The data no longer matches the fault patterns we have learned.
2) Cause and Effect Vibration: For every action, there is a reaction. Some of the vibration we measure is the effect of other problems. For example, the force caused by rotor unbalance can make the machine look like it is out of alignment, loose or rubbing. Consider all of the things that shake and rattle on your car when one tire goes out of balance.
3) Many Fault Types Have Similar Patterns: Because machine rotors rotate at a particular speed, and vibration is a cyclical force, many mechanical and electrical faults exhibit similar frequency patterns that make it difficult to distinguish one fault from another.
Learning to analyze vibration just takes time. Training courses, technical publications and other resources such as online resources and commercial self teaching material are available that can improve analysis skills and shorten the learning curve.
There is one diagnostic technique which quickly gets to the source of most vibration problems. It is possibly the most powerful of all vibration diagnostic techniques. It has been around as long as vibration analysis itself yet hasn’t gotten a lot of attention, and it’s rare to find good information about the subject. What is this technique? It’s called phase analysis.