Phase in the Time Domain
The concept of phase is interesting in that it can be considered a property of the time domain waveform or a property of the frequency domain spectrum. Phase is nothing more than the time difference between a reference time and a measured time. It usually is represented in units of milliseconds in the waveform, and as degrees of angle in the spectrum. One complete rotation corresponds to 160 degrees of phase angle.
As we will see later in this book when we look at diagnostics of machine problems, we will see that there are many different areas where phase gives us important diagnostic information, balancing being one of the most important.
Even though phase really is defined in the time domain, it is usually much easier to measure and display in the frequency domain. For this reason, we will not address it further here.
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