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BRUEL & KJAER System V - Exciter Lamp Indication; Operation in High Ambient Temperatures; 4801 Body; Reduction of Residual Motion

BRUEL & KJAER System V
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3.11.
"EXCITER"
lAMP
INDICATION
A
lamp
labelled
EXCITER is
mounted
on
the
front
panel
of
the
Power
Amplifier
Type
2707
.
Lighting
of
this
lamp
indicates
that
something
is
wrong
at
the
Exciter.
Drive
to
the
Exciter
Head is
removed
when
this
lamp
is
lit.
a)
Make
sure
that
the
Exciter
Head is
properly
mounted
on
the
Exciter
Body.
b)
Make
certain
that
the
Exciter
Cable is
connected
both
to
the
Power
Amplifier
and
to
the
Exciter
Head .
c)
Check
if
dirt
or a
piece
of
paper
blocks
the
Field
Supply
Air
Inlet
Screen.
If
so,
clean,
allow
20
minutes
for
the
Exciter
to
cool,
and
turn
on
again
.
d) Check
the
MOTOR
fuses
(see Fig .
2.5).
If
any
of
these
are
blown,
turn
off
the
POWER
switch
on
the
Power
Amplifier,
clean
the
Field
Supply
Air
Inlet
Screen,
re-
place
the
fuse,
wait
20
minutes
for
the
motor
to
cool
down
and
turn
on.
If
the
fuse
blows
again
see
"Care
and
Maintenance",
Chapter
8.
3.
12.
OPERATION
IN
HIGH
AMBIENT
TEMPERATURES
3.12.1.
4801
Body
The
cooling
system
for
the
4801
is
designed
to
limit
component
temperatures
to
normal
values
for
ambient
temperatures
as
high
as
104
°F
(40
°
C).
Operation
with
ambient
tem-
peratures
as
high
as
122
°F
(50°C)
is
possible
if
input
power
to
the
Driver
Coil is
reduced
by
limiting
Driver
Coil
currents
slightly
.
For
ambient
temperatures
of
104
°F
to
122
°F
(40°C
to
50
°
C)
reduce
the
setting
of
the
CURREI\JT
LIMIT
controi
by
1 %
for
each
2°F above
104°F
(1
%
for
each
1° C above
40
°
C)
.
The
available
force
is
reduced
in
proportion
to
the
reduction
in
current.
3.12.2.4805
Body
The
above
rules
also
apply
to
the
Type
4805
when
adequate
cooling
is
provided
(see sec-
tion
2 .3) .
However,
if
there
is
no
cooling,
then
the
CURRENT
LIMIT
should
be
set
to
half
of
the
value
shown
on
the
back
of
the
Head
and
reduced
proportionately
for
increased
ambient
temperatures
.
3.13.
REDUCTION
OF
RESIDUAl
MOTION
The
residual
motion
is
the
motion
of
the
moving
element
when
the
input
signal
to
the
Power
Amplifier
is zero.
The
residua
I
motion
of
the
system
consisting
of
the
Power
Am-
plifier
Type
2707,
the
Exciter
Body
Type
4801,
and
a
matching
Exciter
Head is
typically
about
0,05
mms-
2
.
This
low
leve I
of
background
motion
is
insignificant
for
most
appli-
cations
.
It is
traceable
to
Amplifier
noise
and
fan
motor
residua
I
unbalance.
The
proportion
of
the
latter
depends
on
whether
the
Amplifier
OUTPUT
IMPEDANCE
is
set
to
"
Low"
or
"
High".
This
is
because
the
suspension
provides
some
isolation
of
the
table
from
vibra-
tions
of
the
Exciter
Body, and
the
amount
of
vibration
isolation
is
influenced
by
the
im-
pedance
in
the
drive
coil
electrical
circuit.
25

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