Vibration Exciters 5cj3d

VIBRATION EXCITERS Submitted by Sivaprasad K.S. MD1107

Introduction  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 displacement through a given range of frequencies  Can be mechanical , electro-dynamic, electrohydraulic, or non- type(electromagnetic) in nature.

Mechanical Exciters  Two types – Direct drive and Rotating Unbalance  It uses rotating unbalance, usually a pair of contra rotating eccentric masses, to generate a given excitation force or reciprocating follower motion from an eccentric cam or otherwise to generate a given displacement  Inexpensive, reliable and easy to operate

Mechanical Exciters  The main limitation of mechanical exciters are  No control over the force or displacement  Limited frequency range

Hydraulic Exciters  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 50cm and 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

Electro-dynamic Exciters  Most widely used vibration exciter today  It consists of a magnet which produces a desired magnetic field , the moving element which forma=s the exciter table on which the test object is mounted, a coil mounted on the moving element fed from an AC source, flexible ing system holding the coil and the moving element in position w.r.t. the magnet

Electro-dynamic Exciters  Excitation force is determined by the magnet strength, coil diameter, no. of coil turns and the current ing through the coil.

Electro-dynamic Exciters

An Electro-dynamic Vibration Exciter

Electro-magnetic Exciters  Used where a 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 so that no is made between them

Electro-magnetic Exciters  The force exerted by the coil on the test specimen is harmonic with the same frequency as that of the current from the oscillator  They are very expensive and are heavy and hard to move from place to place between tests  Stray magnetic fields creates problem