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Reply to "Vibration Analysis Level 1 (or 2) Practice Question Q 45"

Jake,

Thanks for the chart. I've comments that might be useful for some readers.

There is a fundamental difference between the two waveforms (in Jake's post) which is physics. To explain this, let us use a third illustration.

2: A sinusoidal wave generated in a string[see, Wikipedia) [18]

[source: https://www.researchgate.net/f...ia-18_fig1_262450664]

Jake's upper plot is the amplitude (elevation of a point of the string) in the y-axis versus the location of points (examples are A, B, C, etc) along the length of the string on the x-axis. So here we look at the entire string as its points positioned up and down at a fixed point of time. This presentation is a sort of operating deflection shape (ODS).

Now, focus only on Point A, for example, and let the string wave continuously with time. If I trace the elevation of Point A (amplitude) over a time window, the second plot in Jake's post is generated. This plot itself does not let us anything about the location of the measurement point on the string. This data presentation is a typical vibration signal we know as a waveform from which we can find a period in time units.

So, if I have only a string plot without information about time, can I find the period?

Regards- Ali M. Al-Shurafa

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  • Vibration Analysis using string waveform: Vibration Analysis using string waveform
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