Vibration Dose is a parameter that combines the magnitude of vibration and the time for which it occurs.
Vibration Dose Value (VDV), when assessing intermittent vibration it is necessary to use the vibration dose value, a cumulative measurement of the vibration level received over an 8-hour or 16-hour period.
Measurement is the preferred method as the vibration may vary and in many cases be intermittent
If the vibration level is 'steady' then shorter measurements of the acceleration may be used in the following formulae.
The VDV formulae uses the RMS acceleration raised to the fourth power and is known as the root-mean-quad method. This technique ensures the VDV is more sensitive to the peaks in the acceleration levels.
VDV is the vibration dose value in m/s1.75
a(t) is the frequency weighted acceleration in m/s2
T is the total measurement period in seconds.
Estimated Vibration Dose Value (eVDV), it is possible to estimate the vibration dose value using an alternative formulae.eVDV = k·a (rms)·t 0.25
where k is nominally 1.4 for crest factors below 6 **
a (RMS) = weighted RMS acceleration (m/s2)
t = total cumulative time (seconds) of the vibration events(s) or period(s) of vibration.
** For Crest Factors above 6, the eVDV equation may be inaccurate, and this estimate should not be used.