ArticleTime Waveform Analysis
by William T. Pryor III
The basic concepts necessary to begin using the time waveform for analysis will be presented. This presentation will be directed toward the analyst who is just beginning to use the time waveform as a diagnostic tool. This paper will present basic waveform terminology, data acquisition considerations, and introduction to diagnostics utilizing the waveform. Diagnostics will include measurement of level, frequency, shape, phase, and comparative measurements. Waveform data will be presented along with spectral data where appropriate.
How is the time waveform used for analysis? How do I interpret the time waveform? Where can I go to get information on waveform analysis? Are there any courses on time waveform analysis? These questions continue to be some of the most commonly asked in the vibration analysis community and not just from individuals who are new to the field. There are many experienced analysts who do not use the time waveform as part of their day to day analysis and there are those who do not even collect it as part of their PdM program. Some analysts only consider collecting the waveform as part of “advanced troubleshooting”. This is especially interesting considering that everything we use for machinery analysis starts with the time waveform.
Overall level, spectrum, and phase are all derived from waveform processing, so why is it that the waveform is not one of our primary diagnostic tools? The most likely answer is that the analyst cannot go directly to a chart, table, cheat sheet, or use some rule of thumb to get an answer in 10 seconds or less. But is the quick answer always right? Do we have all the information we need to fully assess the situation and condition? If we are paying attention, we soon find out that we are not seeing a complete picture if we are only using these tools. As a result it becomes apparent that we need something else to help answer our questions or at least improve on our best guess. In many cases this missing piece of information can be found in time waveform evaluation.
As in every aspect of vibration analysis we find that we cannot use just one tool to measure, analyze, and solve every machinery malfunction. We need to utilize different transducers, different data collection devices, different analysis techniques, and presentations based on the malfunction or condition being evaluated. For this paper we will concentrate on steady state analysis utilizing a hand held data collection device. However the techniques discussed can be applied to other digital collection devices as well.
For steady state analysis the 4 primary diagnostic tools we have using a data collector are:
1) Overall Level
2) Frequency Analysis
3) Waveform Analysis
What happens in many cases is that the beginning analyst gets their initial (sometimes final) vibration analysis training as part of the PdM software and data collector purchase. In most cases this introduction deals with level and frequency of common machinery malfunctions. Phase may be discussed as part of balancing but not discussed as a diagnostic tool.”
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