# Vibration Dose : Definitions, Terms, Units and Measurements

**Vibration Dose** is a parameter that combines the magnitude of vibration and the time for which it occurs.

**To see a range of Vibration Dose Meters** click here.

**Vibration Dose Value : VDV** :

When assessing intermittent vibration it is necessary to use the vibration dose value (VDV), 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/s^{1.75}

a(t) is the frequency weighted
Acceleration in m/s^{2}

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.**