78
leads directly to the differential operator
dt
, which may be approximated by
t
Δ
in a digital
realization of the weighting if the sampling interval
t
Δ
is small enough.
NOTE 2. Frequency weighting
b
W
is considered to be the appropriate weighting curve for
z
direction comfort in rail vehicles.
b
W
is defined in BS6841:1987, and is equivalent to :
( )
( )
( )
( )
( )
1.024
h
l
t
s
H s
H
s
H s
H s
H
s
=
⋅
⋅
⋅
⋅
Where the parameter values
1
f
to
6
f
and
4
Q
to
6
Q
for
( )
h
H
p
,
( )
l
H p
,
( )
t
H p
and
( )
s
H
p
are :
1
0.4
f
Hz
=
;
2
100
f
Hz
=
;
3
4
16
f
f
Hz
=
=
;
4
0.55
Q
=
;
5
2.5
f
Hz
=
;
5
0.9
Q
=
;
6
4.0
f
Hz
=
;
6
0.95
Q
=
NOTE 3. Parameter values in [Table 1] define exactly the frequency weighting
k
W
,
d
W
,
t
W
,
c
W
,
e
W
and
i
W
according to ISO2631-1:1997.
NOTE 4. Frequency weighting W.B.Combined and
h
W
,(formerly H.A) are unchanged by this
amendment. The parameter values in Table 1 are chosen to reproduce the weighting curves of ISO
8041:1990 using formulae of ISO2631:1997.
Above analog frequency response function is transferred to digital frequency response function by
bilinear transformation method which is below :
1
1
1
2
1
s
z
s
F
z
−
−
⎛
⎞
−
=
⎜
⎟
+
⎝
⎠
<Fig. 1 Highpass Filter with 0.7943Hz Cutoff>
Summary of Contents for SLA-PA201
Page 64: ...64 Appendix 1 The Theory for calculating RMS by ISO2631 and ISO8041 ...
Page 67: ...67 Appendix 2 Frequency Response of Filter in the Vibration Level Meter ...
Page 75: ...75 Appendix 3 Theory of WBCombined Filter and Frequency Response ISO6954 Filter ...
Page 79: ...79 Fig 2 Lowpass Filter with 100Hz Cutoff Fig 3 a v transition Frequency Response ...
Page 88: ...88 Fig 12 Error between theoretical value and measured value ...
