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BRUEL & KJAER System V - Callbratio NHEAD TYPE 4815; Frequency Response of the Head

BRUEL & KJAER System V
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__
frequency
Instead,
it is
more
49
Fig. 7.
10.
Frequency
response
of
a
typical
Mode
Study
Head
1000
200
500
100
/..
Velocity
hf-
-
-t-,
f---/-
-+~
'--
*-~
'--t----f--
-
/
2
f--
--,
r-
-W-
-
/---/-
+--
r-."+
---+----f---
/ Displa
ce
ment
/1.0
in. 25.4
c
o
50
~
Z
"
E
100
20
50
10
Limit
-'"
ro
40
in/s. 1.0 1 mls peak _
~
20
c
"
<ii
~
10
Limit
<;
u.
mm
peak
to
peak
5
1LL
_
L-~
_~~~
-L
_~
__
_J
__
_ _
~
_ _
~
__
~
_
__
_L
__
~
10
2
5
10 Hz
20
50 100 200
500
Hz
Fr
equency
17
1072
Fig.
7.11.
Loading
limits
for
the
Mode
Study
Head
7.3.
CALlBRATION
HEAD
TYPE
4815
7.
3.1
. Frequ
ency
Response
of
the
Head
Fig. 7 .
12
shows
a
plot
of
the
frequency
response
of
the
Type
4815
Calibration
Head.
There
are
three
curves
shown,
each
for
a
different
loading.
They
all
have
the
same
gen-
eral
shape
,
with
a
levelling
off
at
about
500
Hz, a
constant
level
to 3 kHz,
and
final
ly
, a
climb
to
a
resonance
peak.
As
the
moving
mass
increases,
the
resonance
drops
.
This,
in
turn,
narrows
the
frequency
limits
of
the
flat
part
of
the
curve.
From
this
it
can
be
seen
that
it
is
not
practical
to
operate
the
exciter
from
a
constant
volt-
age
source
if
the
full
possibilities
of
its
range
are
to
be
exploited
.
common,
especially
in
the
case
of
accelerometer
calibration,
to
operate
with
a
compres-
sor
circuit.
In a
compressor
circuit
(automatic
gain
controi
circuit).
the
signal
from
the
ac-
celerometer
is
fed
back
to
the
generator,
where
it
is
used
to
regulate
a
voltage
controlled
amplifier
. In
the
lower
frequencies,
where
the
level
drops
off,
the
gain
of
the
amplifier
is
increased
and
more
power
is
supplied
to
the
exciter.
In
the
higher
frequencies,
as
the
res-
onance
is
reached,
the
gain
is
decreased
. In
this
way,
a
constant
level
of
acceleration
is
maintained
throughout
the
frequency
range
which
can
be
accommodated
by
the
dynamic
range
of
the
compressor
circuit.
""dO
"r"
1
00
Meot.url"9
Dbj
.;
Constant
~2010t=.10
~
~
~;";;-,,
--
o
o~
1
20
H,
Multipl1
Fr~r
Sc.o
l.
by
50
H'O
1
200
bro
1.-':_l
i9_·
500 1000 2000 5000
10000
16
12/
2112 A B C
lin
.
2'0000
<&0000
D A B C lin.
dO""
660
.
.,
,
JO
2
15
o o

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