VA - ISO 13373 - The Traditional Approach

VA - Vibration Analysis (ISO 13373) - what is internally causing the vibration - monitor by transducer, analyse and interpret by a trained operator.

We do not try to dismiss VA as a valuable technique; it is and will continue to be a mainstream CM option in addition to any other techniques used.

The sophistication of VA enables an improvement in signal to noise ratio for repetitive defect signals. It does this by transforming signals into the frequency domain and homing in on pre-calculated frequencies for each defect type.

These defect repetition frequencies are critically dependent upon the machine component design and geometry as well as the precise running speed. Vibration can occur independently in X,Y or Z axis and so orientation of the sensor is as important as location. For a detailed interpretation it is also necessary to know internal machine geometries, shaft speeds, meshing frequencies etc and to analyse the data before making a diagnosis.

Example of vibration analysis - blade pass frequency - high vibration at running speed times number of blades (Source: Marinevibe)

What can be seen from vibration analysis is:

Rotational Imbalance - Characteristic of high one time vibration at rotational speed
Rotational Misalignment - High one time vibration at rotational speed
Looseness - Multiple odd orders of rotation
Defects in rotational elements - Bearings, gears
Resonance, from a single or multiple vibration sources
Synchronous Averaging

The main drawback in comparison to related techniques is the level of knowledge required to effect a good diagnosis.

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