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BRUEL & KJAER System V - Acceleration Vs. Load

BRUEL & KJAER System V
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.
7.12.
Frequency
response
of
the
Type
4815
7,3
.2 ,
Frequen
cy
Resp
onse
of
the
St
anda
rd
Acc
elerom
e
te
r
Ty
pe 8 3
05
If
the
Standard
Ac
celerometer
were
removed
from
its
case
and
inverted,
as
shown
in
Fig. 7
.13
it
would
showa
typical
accelerometer
response,
with
a
35
dB
peak
at
35kHz
,
which
is
the
natural
frequency
of
the
spring-mass
system
of
the
accelerometer
. In
the
calibration
procedure
of
an
unknown
accelerometer
using
4815
and
8305,
the
accelera-
tion
level
of
the
Standard
Accelerometer
is
held
constant
. In
this
case,
the
Exciter
char-
acteristics
and
the
resonance
of
the
steel
case
have
no
influence
.
However
the
screw
which
connects
the
two
accelerometers
is
effectively
a
spring
whose
influence
IS
particu-
larly
felt
at
high
frequencies.
This
spring
,
with
the
mass
of
an
accelerometer
above
i1.
has
a
resonance
at
about
20
kHz,
opposite
in
direction
to
that
of
the
mass-spring
system
of
the
Type
8305
.
The
two
effects
just
about
cancel
out
,
and
the
result
is
an
almost
flat
frequency
response
(see ca
libration
chart
for
Type
8305,
Fig .
7.14)
.
The
larger
the
accel-
erometer
being
calibrated,
the
more
the
resonance
curve
flattens
out.
272099
Fig. 7. 13.
Accelerometer
8305
removed
from
its
ca
se
and
inverted
7 .3 .3 .
Ac
c
eler
a
ti
on
vs.
Load
.'
Fig.
7.15
shows
the
relationship
of
the
possible
acceleration
level
to
the
mass
of
the
ac-
celerometer
being
calirated
.
Accelerometers
weighing
up
to
60
g
present
no
problem.
However,
it
should
be
noted
that
addition
of
mass
on
top
of
the
reference
accelerometer
in
creases
the
cross-motion
and
testing
of
large
transducers
(200
+
grams)
could
cause
base
bending
of
the
accelerometer
and
subsequent
error
in
its
output.
~
i
f*:
~
Bruel.&
Kjcer
Pot
....
t~.rl\~
,
~
c18
~~
Cop.oho~
..
..,
100 g
Meo~rino
Ob
i
.:
F
requency
.
:
rs
~seea~f
- Je
I.
~
3' ,6 g
with
d iff
er
en
t'
accelerometers
mo
u
nt
ed. -
1:::::-
.
Con
stan
t 20
10
lOg
'
vo
hage
.
throu
ghoul
. measurement
s.
;:
;=
="
t-
,
t::.
3,16 g
o.u....
~7
2
~~.i
;
7A
O
o'"
1
00
,
200
LtroLe-..l
'
_'g
L_U
.....
~
.
,.
_
19
-H1
'W
r.
~
_ _
~teC_
~
500 1
000"2000
8305
8305
+ 4339
(
16
gm)
305 + 4338
(60g.m)
5000
10000
16
1'2
/'2l!2 A B C
li
n.
2
11'
03
'20000 40000 D
A.
8 C
li
n.
WR
6
60
6 ' 5
.JIJ
2 "
o o
50
-'
-

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