Vibration Measurement Types

According to different vibration issues, different vibration measurements types have to be used. The two main classes of vibration measurements are measurements in the time domain and measurements in the frequency domain.

Time domain measurements are useful for the analysis of transient vibration phenomenon and for long term vibration inspection. Transient vibration problems are often related to impacts and other non deterministic impulse type sources. As a result of the impact the vibration amplitude strongly depends on the time, e.g. the decay process until the mechanical system comes to rest again. The long term vibration inspection is used to investigate the presence of vibration sources over a specified time period. The time period varies between several minutes up to days or weeks. The target of long term inspection is to predict the presence or absence of vibration sources in order to optimize the use of sensitive equipment, like SEM.

Frequency domain measurements are useful for steady state vibration. To obtain the frequency domain the measured time signal (displacement, velocity, acceleration) has to be transformed by the Fast Fourier Transformation (FFT).  The resulting data are showing the vibration amplitude with respect to the frequency.