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How is Machine Vibration Data Collected?

Fig 63

In most factories there are usually numerous critical machines that need to be monitored. Furthermore, to enable thorough analysis, each machine usually needs to be monitored at various points. Each point in turn often requires monitoring using different accelerometer orientations, and occasionally, using different measurement parameters as well. Thus, on every round of data collection a large number of recordings usually need to be taken.

Fig 64

To avoid having to repeatedly travel between the office and machines, recordings are usually taken of all machines before the recordings are brought to the office for analysis.

Fig 65

It is important that recordings be taken both accurately and systematically. When you have an organized method of taking recordings there is less chance of confusing the spectra of different machines. If recorded spectra get mixed up they would most likely lead to wrong conclusions and perhaps to very costly consequences as well.

Fig 66

In view of the large matrix of recordings that need to be taken, how do we ensure that recordings are always taken of the locations intended, that the recordings that are taken are not confused with one another, and that no recordings are left out? A recording list is used.A recording list shows all the recordings that need to be taken on a given round of data collection. It is like a detailed shopping list that shows us exactly what to buy during a shopping mission. From a recording list, we can see which recordings need to be taken on which machines, at which points on the machines, in which orientations, and using which measurement parameters.

Fig 67

Although a recording list in the vb instrument does not appear exactly like that shown in the last page, it has the same information structure.In the example shown, 'Motor A1', 'Gearbox B2', 'Rotor B2' are machines for which data is to be collected. 'Front end', 'back end', 'input end', and so forth are the measurement points on the various machines. 'horizontal', 'vertical', 'axial', and 'radial' are the orientations in which measurements are to be taken, and in brackets are the measurement parameters that are to be used. Note that for 'Gearbox B2', two recordings are to be taken, each using a different set of parameters. More information regarding recording lists may be found in the vbSeries Instrument Reference Guide.

To avoid confusion, you must give machines and measurement points unique and meaningful names in the recording list. To rule out misidentifications, you must clearly label machines and measurement points with names that match those adopted in the recording list. When taking recordings, you must take care to ensure that the mounting orientation of the accelerometer matches that described in the recording list.

Fig 68

Not all machines on the recording list may be equally critical. Less critical machines can be monitored less frequently. If only certain machines or measurement points from the recording list need to be monitored during a particular round of data collection, you can tag those machines that need to be monitored so that recordings are only taken for items that are tagged. The tagging of items in a recording list is further explained in the vbSeries Instrument Reference Guide.

To help ensure data collection is done regularly, you should create a schedule showing when data collection will be carried out.

Fig 69

For most machines, data should be collected every month. For critical machines, data may need to be collected every week, and for less important machines, every alternate month. We advise you to begin with a rigorous schedule then adjust it later as more experience is gained.

Imagine going shopping with a shopping list but without enough money to buy what is needed, and without the means to transport things bought back home. We would expect such a shopping mission to fail.

Fig 70

Similarly, with machine vibration monitoring, we need sufficient battery and memory capacity in the vb instrument to complete a round of data collection. Before beginning to collect data, you must ensure that there is sufficient battery and memory capacity in the instrument (see the vbSeries Instrument Reference Guide for further details).Most kinds of vibration problems are detected while the machine is running steadily and exhibiting a steady vibration pattern.

If a machine has just started up, or if its operating speed has just been changed, you need to ensure that the machine is given time to settle into a steady state before taking spectrum recordings, otherwise, the recorded spectra will not reflect the true steady-state behavior of the vibrating machine.

Fig 71

When a round of data collection is complete, you should transfer the recorded data to a computer with AscentTM software for analysis and archiving. Once the recorded data has been archived, you can erase the data from the vb instrument, thus freeing up memory space on the instrument for another round of data collection.

Fig 72

From the Beginner's Guide to Machine Vibration, copyright © Commtest 1999, 2006.

Revised 28/06/06

To find out how to set up your own machine vibration monitoring program, contact Commtest Instruments Ltd or one of our representatives for a demonstration of a vbSeries vibration monitoring system. For the address of your nearest representative please visit our website at

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