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Submitted by
Sivaprasad K.S.MD1107
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A vibration exciter is a machine which produces a
mechanical motion to the test object Designed to produce a given
range of harmonic or
time dependent excitation force and/ or displacementthrough a
given range of frequencies
Can be mechanical , electro-dynamic,electrohydraulic, or
non-contact type(electro-magnetic) in nature.
Introduction
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Two types Direct drive and Rotating Unbalance
It uses rotating unbalance, usually a pair of contrarotating
eccentric masses, to generate a givenexcitation force or
reciprocating follower motionfrom an eccentric cam or otherwise to
generate a
given displacement Inexpensive, reliable and easy to operate
Mechanical Exciters
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The main limitation of mechanical exciters are
No control over the force or displacement
Limited frequency range
Mechanical Exciters
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It uses a piston-cylinder arrangement, the movement
of which is controlled by the fluid pressure A wide range of
excitation force can be obtained
Capable of producing large displacements upto 50cmand also
generate a very high force upto 50 tons or
more They can generate only very low frequencies
Ideally suited for testing civil engineering structures,but not
mechanical machines and their components
Hydraulic Exciters
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Most widely used vibration exciter today
It consists of a magnet which produces a desiredmagnetic field ,
the moving element which forma=sthe exciter table on which the test
object is mounted,a coil mounted on the moving element fed from
an
AC source, flexible supporting system holding the coiland the
moving element in position w.r.t. the magnet
Electro-dynamic Exciters
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Excitation force is determined by the magnet
strength, coil diameter, no. of coil turns and thecurrent
passing through the coil.
Electro-dynamic Exciters
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Electro-dynamic Exciters
An Electro-dynamic Vibration Exciter
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Used where a contact between test specimen and
exciter not desired It consists of a coil wound on a strong
permanent or a
DC electromagnet
The test specimen should be of magnet material and
is kept at a suitable distance away from the shaker sothat no
contact is made between them
Electro-magnetic Exciters
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The force exerted by the coil on the test specimen is
harmonic with the same frequency as that of thecurrent from the
oscillator
They are very expensive and are heavy and hard tomove from place
to place between tests
Stray magnetic fields creates problem
Electro-magnetic Exciters
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