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extra strong flexures, to
resist
large
applied
moments
.
Environmental
testi
ng
of
large de
vices, of
unbalanced
objects, and of objects
w
ith
severe
transverse resonances,
is
best
don
e with this
head.
The General Purpose Head Type 4812 has a 445 N (100 Ibf) force rating
.
The table is
larger than the
4
811
but smaller than 4813. The moving element weight, moment limit,
and resonant freq uency are intermediate in value between the 4811 and the 48
1
3
.
The
Exciter Head Type
4812
is tr
uly
a
"General
Purpose" head,
s
uit
able
for
a wide
r
ange
of
appl ications.
The Mode Study Head Type
48
14 has a
2
5
mm (1
in) peak-to-peak
di
splacement capabil
ity, co
mpl ia
nt springs
and
a light-weight mov ing
element
.
The t able
is
ro
u
nd
,
19
mm
(0,75 in) in diameter, with a centre insert.
Both metr
ic
and
inch inse
rt
s are
provided.
This head is intended
to
be used either sing ly or
in
m
ultiple
exciter arra
ys
as a
force gen
erator
. In
most
struct
ural vibration
testing
applications
, eit
her
a
pu
sh
rad
or a
t
ension
wire is connected betwee
n
the
exc
iter ta
bl
e
t
op
a nd
th
e
t est
object
to
m in imi
ze
th
e
cou
pling of
skew
force s from the test object to
t
he exciter.
Typical structural
testi
ng
applica
t
ians would in
cl
ude the
determ
ination
of
th
e
frequ
ency
and
da
m
ping
for
eac
h
of the
reso
nant modes of ai rcraft elements, suc
h
as co
ntroi
surfaces,
wi
ngs
,
or
la
ndin
g gear.
Hy
drodynamicists and ae
rodyn
a
m
icists may find
t
he Exc
iter Head
Type
4814 usef
u
l fo
r
cavi
tation or vortex
shedding
stu dies
.
Chemists
and
Chemical
Engineers may use t
h is h
ead
to vary the rate of
chemical
reactions or
to vibrat
e
plastic
extrusion
dies
.
The Ca libration Head Type
481
5 is
designed
for t
he
calibration
of
accele rometers.
A
Ref
erence Standard
Accelerometer
(included) is fi
xed to
a
mou nting block
in the
centre
of
the table
.
The accelerometer
to
be cali
brated
is
screwed into
the
top of t
he refe
ren
ce ac
celerometer
.
The skel
eton of
the
Exciter
Head
Type
481
5
is
st
iff
,
provid
ing
a
r eson
ant
frequency of
10kHz
w
ithout a
n
attached
accelerom eter
,
and more
th
an 8,5 kHz w
ith
most types of accele
ro
m
eters
.
Adequate
force is
pr
ovided
for cal ibration at
levels to
100
g
at fre quencies up
to
10
kHz
.
Calibr
ation
at levels
as
low
as
0 ,01 g
is
also
possi
bl
e, either
by
d
isco
nnecti
ng
the cooling
syste
m
in the
4801
or
by
using
a 480
5 Exciter
Body.
3.3.
MOUNTING AND REMOVAL OF EXCITER HEAD
3.3 .1
.
4801 Body
With the power to the Exciter Body turned off
,
place the Exciter Head on top
of
t
he Exci
ter Body with the connector
to
t
he rear (the cableto the Exciter Body is also to the rear).
The lower edge of the Head Protective Can w ill slip over the Upper Wheel of the Exc iter
Body
and the Head Alignment Pins will rest on the upper surface of th
e
Upper Wheel
.
Rotate the head until the Head Alignment Pins drop into the holes in the Upper Wheel
and
lower the head until it is fully engaged
.
The Spl it Hub of the Head will provide close
concentricity guidance
.
Engage and press down
the
Head
Latches
in any order
.
Attach
the cable from the Power Amplifier to the connector on the Head
.
The Exciter is now
ready for operation.
To
remove
an
Exciter
Head,
f irst turn off
the
power
switch
on
the Power Amplifier
,
w
hich
controls the
power
for
the magneti
c
fi
eld
of th
e Exciter
. Next
,
disconnect
the ca ble from
t he
Exc
iter
Head
, to eliminate
the
po ssi bility
of
burning
out
the
Driver Co
i
l
wh
en the Exc i
ter Head is
removed
from
the
Exciter
Body.
Lift the
Exciter
Head
evenly a
nd
smoot
hly
straight upward
,
being care
f
ul
not to lift one side before the other
.
tf
one side is
p
ulled up
before the other
,
it is possible to jam the head with two pins out of their holes and
one
pin cocked and jammed inside its hole
.
If
this happens
,
agentle tap upward with a
wooden block on the lower edge of the Head Protective Can or in a handle hole will re
lease the jammed pin
.
Place the head on a smooth clean surface with the table upward.
being sure that there is nothing on the surface that might damage the Driver Co il
.
15
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