Vibrations occur naturally in machinery, caused by the rotation of its components. Each component has its own frequency or frequencies and this is dependant upon the running speed of the machine. This vibration can be used as an indicator of machinery condition. When the level of vibration increases or becomes excessive there is usually some mechanical reason. These vibrations are compounded into a resultant cacophony of noise.

• There are literally hundreds of specific problems that can cause a machine to exhibit excessive vibration. To locate the root cause of vibration an analysis of the vibration is required. The forces that cause vibration are usually generated through the rotating motion of the machine’s parts or electrical supply frequency. When a fault condition occurs the problem will exhibit characteristics that are directly related to these frequencies. The following is a list of common “forcing frequencies”.