Page 16 - Vibrations-2

To monitor the health of the bearings - follow the

th
4 harmonic.

th
As the speed changes downward to 50 Hz, the 4 harmonic

of the power spectrum shifts downward.

The peaks in a power spectrum of a rotating device are all

related to the fundamental rotational speed of that device.

So, even if the FFT is able to clearly analyse the data and

show the power spectrum for the machine, it is not

capable of easily tracking speed driven harmonics.

In order analysis, instead of taking the FFT of the time

domain data, the signal is first resampled into the angular

domain.

Resampling combines the speed measurements taken from

a tachometer on the machine with the vibration

measurements and interpolates the vibration

measurements into a data point per fraction of angular

rotation.

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