Vibration Analysis

What it is ... 

Vibration monitoring is the oldest type of machine monitoring technique and is the detection of the oscillation of a surface or structure up to a frequency of approximately 25 kHz. Vibration is detected and measured by using transducers to convert vibration energy into an electrical signal. The parameters measured are displacement, velocity and acceleration. Potentially all reciprocating and rotating machinery with moving parts can generate vibration and hence can benefit from vibration monitoring.

Vibration monitoring and analysis generally requires the identification of two quantities:
  1. The magnitude (overall level) of the vibration
  2. The frequency content via the frequency spectrum (and/or time waveform)
The magnitude is used to establish the severity of the vibration and the frequency content (and/or time waveform) is used to establish the cause or the origin of the vibration.

Vibration analysis, applied in an industrial or maintenance environment, aims to reduce maintenance costs and equipment downtime by detecting equipment faults. Vibration analysis is a key component in most condition monitoring programmes and is most commonly used to detect faults in rotating equipment (for example fans, motors, pumps gearboxes, compressors, generator sets and so on), such as unbalance, misalignment, rolling element bearing faults and resonance conditions.

Three important analysis techniques can be performed:

Certification
Vibration data is obtained on new or re-built machinery to ensure that it is operating within acceptable tolerances. If excessive vibration is discovered, then the cause can be remedied before the machinery is put into service.

Potential fault analysis
This is also called ‘predictive maintenance’ and is used to determine the health of machine components. A good assessment of machine health allows one to predict which component is likely to fail first and approximately how long the component will last before fault conditions begin to occur.

Diagnostic analysis
Whereas potential fault analysis is proactive, diagnostic analysis is reactive. It is only performed once a problem has occurred. Once the vibration data has been collected a comparison is made between the calculated fault frequencies and their harmonics and the actual frequencies that dominate the vibration signature. The cause of each fault frequency is determined and corrective measures are taken to correct the problem.