Human perception of vibration varies considerably depending on the frequency of the vibration f.

 

If 1G (9.8m/s²) is expressed in terms of the displacement X,

 

mm

 

Displacement at 100Hz is 0.025mm, and 2.5mm at 10Hz – a large difference.

 

A vibration level meter is used to measure perception of ground and floor vibrations. The factor is expressed in dB (logarithmic scale) relative to a reference value of 10-5 m/s²,

 

and thus, at 1G, the value becomes

 

Humans are able to perceive vibrations between approximately 1Hz and 100Hz, however the perceived strength of these vibrations depends on frequency. This referred to as the ‘vibration sensation characteristic’, whereby vibrations between approximately 4Hz and 8Hz are readily perceived, and perceived less and less outside this range.

 

The above vibration values are generally expressed as a vibration level in dB compensated for the vibration sensation characteristic.

 

Earthquakes are ranked as the seismic intensity 0 - VII (although Magnitude is currently used). The relationship between acceleration and Magnitude is as follows.

 

1G = 980cm/s² = 980gal (1gal = 1cm/s²)

 

 

Since frequency is an important factor when vibration affecting to floor in machinery installations is measured, a frequency analysis is conducted.

 

1 kine = 1cm/second is used as a unit of velocity.