The Time Waveform
Introduction
The Time Waveform is the complex sum of all the individual frequencies that exist on a
machine. That statement in itself is cause for confusion and not very helpful to the
vibration analyst.
In order to correctly analyse the Time Waveform we must first understand what it is and
then decide whether it will be of use to us when trying to analyse problems in our
machines and systems.
We must understand that there are certain faults that can only be seen in the Time
Waveform and lack of use of the TWF measurement will mean we may miss the
development of a fault. We must then learn to interpret the waveform in the simplest
possible way.
The aim should always be to detect change in machinery condition at the earliest
opportunity using the simplest method possible.
What is the Time Waveform?
The most basic description of the Time Waveform is that it is the raw unprocessed signal
that we get from the vibration sensor when we display it on an oscilloscope. This would
normally be in an analogue format and would typically appear as shown below.
As the development of portable data collectors progresses, the opportunity to collect
digitised Time Waveform data is enhanced and made more user friendly. The challenge is
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to use the power of these systems to enhance machine condition monitoring systems.
There is also the requirement to ensure that we do not collect Mbytes of useless data.
Digital systems up to now have only replicated the same information in a format that can
be easily collected and stored.
Summary
1. Time Waveform analysis should be used strictly in conjunction with spectral
analysis as an additional, valuable tool for the analyst.
It may make the difference between vibration data and information
2. Ensure that when you use the Time Waveform that you think in the Time Domain
i.e. how long will the problem take to propagate or extend.
3. Use all available features of your analyser to help you with the diagnosis.
4. Do not rely solely on the Time Waveform or the spectrum, use both.
