Daily exposure may consist of several activities with different vibration magnitudes. This can be
the case if there are longer interruptions in the work process, if the work equipment or its way
of use is changed. Resulting daily exposure is calculated:
A
8
=
1
T
0
∑
i
=
1
n
a
wi
2
T
i
Equation 2
where
a
wi
is the energy equivalent mean value of the frequency weighted acceleration of activity i
n
is the number of activities
T
i
is the duration of activity i
T
0
is the reference duration of 8 hours
For
hand-arm vibration
the energy equivalent mean value a
we
is calculated to ISO 5349. It is
the square root of the sum of the squares (vector sum) of the interval rms values a
wx
, a
wy
and a
wz.
The interval rms values are measured as the accelerations in three orthogonal directions with
the weighting filter W
h
.
This vector sum is often called
Total Vibration Value
a
hv
:
a
we
=
a
hv
=
a
wx
2
a
wy
2
a
wz
2
Equation 3
In the case of machines which need to be held with both hands, measurements must be made on
each hand. The exposure is determined by reference to the higher value of the two.
For
whole-body vibration
the energy equivalent mean value of acceleration a
we
(interval rms) is
measured separately on three orthogonal axes to ISO 2631-1. For seated persons the following
weighting filters and multiplying factors are applied:
X axis: Filter W
d
Multiplying factor k
x
= 1.4
Y axis: Filter W
d
Multiplying factor k
y
= 1.4
Z axis:
Filter W
k
Multiplying factor k
y
= 1
The highest one of the three values is inserted as a
we
in the calculation of A(8).
If no dominant axis of vibration exists,
the energy equivalent mean value of acceleration a
we
may also be calculated as vibration total value a
hv
, where the multiplying factors k
x
, k
y
and k
z
are
to be used:
a
we
=
a
hv
=
k
x
2
a
wx
2
k
y
2
a
wy
2
k
z
2
a
wz
2
Equation 4
6