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I am confused with the amplitude at 1x, 2x, 3x frequency. The 1x, 2x and 3x is the harmonic (or mutiples) of the original frequency, meaning that if the shaft is turning at 1500rpm, then 2x will be the amplitude at 3000rpm and 3x will be the amplitude at 4500rpm right? But how will the amplitudes at 3000 and 4500rpm be measured as the shaft is only turning at 1500rpm?

And how does one interpret this kind of graph, for e.g.: why does an unbalanced shaft wil have high amplitude at 1x frequency, while misalignments will have high amplitude at both 1x, 2x and sometimes even at 3x frequency?

Thanks.

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# Reading a spectrum graph for vibration analysis

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