5.
APPLICATIONS
5.1.
GENERAL
The Power
Amplifier
Type
2706
has
been designed
to
drive small vibra-
tion
exciters,
particularly
the
B & K
Vibration
Exciter 4809. When switched
to
the 1.8 A RMS
output
current
limit,
it
will
safely drive
theM
ini Shaker
Type
4810
at
full
rating. However, the 2706
can
be
used
for
general purpose
amplification
in
vibration
and acoustics applications.
Some
of
the devices
to
be
driven by the Power
Amplifier
could,
for
many
applications,
be
directly
driven
by
a signal generator
(for
example the B & K
Beat Frequency Oscillator Type 1022),
but
the low impedance
of
a shaker
or
a loudspeaker
will
cause
considerable
distortion
of
the generator
output,
which may
be
a problem when measuring a frequency response curve. Also,
it
may
be
difficult
to
get sufficient power.
These
problems
can
be
solved
easily
by
using
the
2706.
It
will
provide the desired power and reduce
distortion,
as
its
input
impedance (15
kQ)
will
have
no loading effect on the
generator.
Distortion
from
the
generator
will
therefore
be
reduced. Since
the Power
Amplifier
Type
2706 itself introduces very
little
distortion,
the
output
signal
will
exhibit
less
distortion
than when taken
directly
from
the
oscillator.
Measurements on
the
Mini
Shaker
Type
4810
directly
driven
from
a
generator have shown
that
the
third
harmonic
level
could
be
only
15 dB
below the fundamental.
For
the
same
vibration level
on
the
Mini
Shaker,
use
of
the Power
Amplifier
reduces the level
of
harmonics
by
at least
20
dB.
5.2.
USE
WITH THE B & K
VIBRATION
EXCITERS
The
Vibration
Exciters Type 4809
and
the Mini Shaker
Type
4810
are
small
vibration
exciters having a wide
range
of
applications,
with
force
ratings
of
10
lbf
(45 N) and 1.5
lbf
(7 N) respectively. The useable
frequency range
of
Type
4809
is
10Hz
to
20kHz
and the maximum
input
current
is
5 A RMS. The useable frequency
range
of
Type
4810
is
20Hz
to
18kHz
and the
maximum
input
current
is
1.8
ARMS.
14
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