2.
DESCRIPTION
AND
OPERATION
2.1. PRINCIPLE OF OPERATION
The forces generated in
an
electrodynamic exciter are due
to
the inter-
action between
an
electrical current
in
a coil and a magnetic field. This
is
illustrated in Fig.2.1.
Signal
Source
Power
Amplifier
r---;;:;::~
Test
Object
'
I
I F
I
Fig.2.
1.
Principle
of
operation
of
a 8 & K
Exciter
I
is
the
current in the coil, B the
flux
density
of
the magnetic field and F
the force generated
by
the coil. The magnitude
of
the force
is
given
by
F
where F
B
I
L
BIL
Force in Newtons
Magnetic
flux,
in
Gauss
Current in coil, Amperes
Length
of
conductor
in magnetic field, meters
The current
for
the exciter
is
provided by a power amplifier. A signal
source, such
as
a sine-wave oscillator
or
random generator
is
connected
to
the
input
of
the amplifier. As the signal
is
fed
to
the coil, a
fluctuating
force
and hence a
vibratory
motion
is
imparted
to
the test object.
Of
course
the
4
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