Traditionally, non-destructive testing was concerned with material defects (for example cracks and voids) with the use of X-ray, ultrasonic and similar techniques. Gradually, computerised signal processing, data interpretation and processing has started to play an increasingly important role. The result is that non-destructive techniques such as infrared thermography (IT), vibration analysis (VA) and acoustic emission (AE) originally used as final inspection of products, are now used for periodic check-ups during the lifespan of a component or a machine with associated diagnostics and prognostics. This is condition monitoring.
Condition monitoring originally used mainly vibration and tribology analysis techniques but now encompasses new fields such as thermal imaging, acoustic emission and other non-destructive techniques. The diagnostic and prognostic elements, in addition to more and more sophisticated signal processing, is using trends from repeated measurements in time intervals of days and weeks.
There are new concepts such as smart systems which incorporate measuring elements directly into structures. The techniques are certainly non-destructive but are used for condition monitoring. It can be said that there is a considerable overlap of interest and both disciplines can only benefit from close collaboration.