Page 14 - Vibrations-2

There are limitations, not suitable for signals whose

frequencies vary over time – signals have to be stationary.

Another limitation of the FFT is that it cannot detect

transients or short spikes in the signal.

Transients are sudden events that last for a short time in a

signal and usually have low energy and a wide frequency

band.

When transients are

transformed into the

frequency domain,

their energy is spread

over a wide range of

frequencies.

Since transients have low energy, you might not be able

to recognise their existence in the frequency domain.

Special measures are needed to box-car the transient

signal in order to find it’s frequency content.

Order Analysis

When performing vibration analysis many sound and

vibration signal features are directly related to the

running speed of a motor or machine

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