More often than not, the levels of complexity achieved when defining monitoring parameters for any machine type have been excessive to achieve the minimum level of “sensitivity” we seek within a detection context. The previous should also bring to mind the historical aspects of machine asset CM management: this complexity extends to the collection sequence (whether it is visible or not), the programming of the sequence, the handheld instrument processing, and it also spreads to data review.
A simple trend of one parameter or another typically fails to adequately paint a picture of machine health. Neither velocity nor acceleration will succeed in that respect. Changing units from peak to RMS or the reverse will also fail in providing an efficient detection net. What kind of SIMPLE safety net will mostly be up to the task? Do note the caveat: “mostly”, as some problems would still likely escape our notice…
Imagine a system delivering the following simultaneous trends:
Velocity pk (time waveform derived or true peak)
Acceleration pk (time waveform derived or true peak)
Crest Factor for either of the previous
High-Frequency / Ultrasonic “Estimator” (meaning Spike Energy, PeakVue or similar; these last are trademarks of their respective owners).
Such a system would not function for ALL machines and configurations, but on most common configurations, it would adequately cover the detection function for most problems occurring within the machine park. It still would not be perfect. We can find a number of cases for electric motors where the previous system would leave gaps. Certain machines would also benefit from a trend of displacement and/or a correlate to measurements off proximity probes.
For many years now, single parameter pen-like mini-instruments have been a popular item. While the intent was likely to quick check a machine just worked on, some pre CM “entry level” shops or plants may partly or wholly rely on such overly simplistic single-parameter trends. Vendors might provide a better “view” through the inclusion within their ”simplest” tool of multi-parameter trending as suggested above. It would come closer to adequate monitoring. This being said, the detection safety net based on correlated trends of multiple parameters provides helpful coverage in a “wide” net: this applies to a large number of machine assets such as what is found in a paper mill, and not so much to a power generation station where the assets are few, usually complex, and allow for wider man-hour resources in terms of analytical exploration.
© 2007 by François Gagnon