ArticleAn Introduction To Steady State Data Analysis For Sleeve Bearing Machinery
by William T. Pryor III
This excellent paper provides a brief, yet surprisingly thorough introduction to the various steady-state vibration analysis techniques as applied to sleeve-bearing machinery. The paper begins with a discussion of basic machinery convention such as proper view direction, proper orientation of the X and Y probes, etc. along with a brief discussion of proximity probes. Data acquisition considerations to obtain adequate frequency and time resolution are discussed. The five steady state vibration analysis tools of overall level, frequency (spectral) analysis, phase analysis, waveform analysis and orbital (shape) analysis are described in detail with examples provided for each technique. This paper should be on the required reading list for anyone wanting to learn about vibration analysis of sleeve bearing machinery.
“Introduction: When sleeve bearing analysis is discussed in our industry it is typically inferred that proximity transducers are being utilized to directly measure shaft displacement within the bearing. Unlike casing mounted transducers used for routine data collection proximity transducers are usually permanently mounted on the machinery close to the bearing. These transducers are non-contacting devices which can directly measure the Peak-to-Peak displacement of the shaft as it rotates within its bearing support. In most cases, 2 proximity transducers are installed at a bearing location as an XY pair mounted at 90° to each other. This configuration thus allows for the analyst to determine planes of maximum and minimum motion along with the shape of the shaft motion within the bearing.
As we will see, the shape of the shaft motion along with procession will be important elements in determining machine condition in sleeve bearings. In many cases these parameters may be more important than the amplitude and frequency of the vibration. To correctly evaluate the shape and procession, it is very important that correct transducer convention be followed. As a result it is always a good idea to review the transducer installation prior to collecting any data. A mistake here can result in incorrectly evaluating the machine or the condition. While the rules are simple many incorrect evaluations have been made by not following the rules. Along with convention it is equally important to ensure that the data acquisition equipment is correctly set up to handle the expected amplitude and frequencies. Taking a few extra minutes to evaluate data collection setup on the front end can save a lot of time and perhaps agony in the review process. Always remember that the analysis can only be as good as the data collected.
Once the data has been successfully collected, the condition assessment and diagnostic evaluation of steady state shaft data can be performed using 1 or more of the 5 key areas listed on the following page.
Key areas for assessment and condition of Sleeve Bearing Machinery
1. Overall Vibration Level
2. Frequency Analysis
3. Phase Analysis
4. Waveform Analysis
5. Shape Analysis
The first two areas, vibration amplitude level and frequency are those most commonly used by all vibration analysts to assess machinery condition. While these are also important in sleeve bearing analysis, exclusive use of these measurement techniques can result in incorrect evaluation of the equipment. To avoid an incorrect assessment, sleeve bearing analysis requires that additional diagnostic tools be used as part of normal evaluation process.”
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