FREQUENCY DOMAIN
Figure 23.10 illustrates a three-dimensional graph of the signal shown in Fig. 23.9. The frequency domain permits separation of the components in the waveform. The frequency domain illustrates the same time domain that was shown in Fig. 23.9. It is the summation of two sine waves, which cannot be recognized in the time domain.
Each frequency component appears as a vertical line in the frequency domain. The height represents the amplitude of the vibration. The representation of the signal in the frequency domain is called the spectrum of the signal. The frequency domain is powerful because any real signal can be generated by adding up sine waves (Fourier’s law). Therefore, the fre- quency domain can separate the sine wave components of any vibration signal.
The frequency spectrum of a vibration signal defines the vibration completely. There is no loss of information by converting to the frequency domain, provided that the phase information is included.
