Vibration monitoring and analysis

 

Rotating machinery is well suited to vibration monitoring. The sensing devices are generally piezoelectric although piezo-resistive and variable capacitance methods have been used. Such transducers may be capable of indicating acceleration, displacement and velocity in the form of an electrical output. Vibration may also be measured by using laser interferometry principles, this technique being particularly successful on large turbines.

Analysis of the data usually yields a figure for the vibrational velocity which is a good indicator of a machine’s condition. Further processing, using frequency analysis, will yield a frequency spectrum that may be compared with that from the machine when in a healthy condition. Repeated testing will readily identify changes caused by faults as they develop. This technique has been used to successfully detect imbalance due to bent or poorly aligned shafts, defective bearings and loose housings. As experience is gained it will become apparent how much vibration may be tolerated and indeed when the condition of the machine becomes critical. It is therefore possible, using either periodic or continuous vibration monitoring, to either alert machinery operators of impending failure or to automatically shut down the machine if failure would be expensive or catastrophic.