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Chapter 1
Introduction
Designed for demanding modal testing applications, Modal Exciters Types 4825 and
4826 provide precise, reliable, stable and long-lasting operation. Highest quality ma-
terials, stringent quality control and rugged construction assure a versatile means of
modal excitation for any modal test requiring attached excitation.
Based on unique rare-earth neodymium magnet technology, Modal Exciters Types
4825 and 4826 feature extremely small physical dimensions relative to the 200 N and
400 N force ratings along with low total weight and a low mass, high-rigidity, spring-
suspended armature.
The low weight armature helps to ensure high-quality force measurements by mini-
mising force drop-offs at resonance frequencies of the test specimen. Four upper and
four lower radial flexures, the latter providing an additional guide for best stabilisa-
tion, form a strong rectilinear guidance system which keeps the driver coil perfectly
centered in the magnetic assembly's air gap. In the transverse directions and in
torsion, the flexure system provides very high stiffness to counteract rotational
movement of the test specimen. Also, through this configuration, the modal exciter
can absorb high lateral forces without damage to the internal construction of the
exciter.
The "hole-through" design of Modal Exciters Types 4825 and 4826 makes it possible
to use tension wire stingers as well as traditional push/pull stingers. Easy and rapid
attachment of both types of stingers is achieved by use of a chuck nut assembly.
In lateral setups of Modal Exciters Types 4825 and 4826, tension wire stingers can
easily be pre-tensioned when one of the optional Lateral Modal Exciter Stands
UA 1607 and UA 1608 is used. For electrical pre-tensioning, especially useful in verti-
cal, skewed excitation setups and for excitation in confined spaces, the optional DC
Static Centering Unit Type 1056 can be used. Modal Exciters Types 4825 and 4826
are delivered with a Video HR-10 connector that outputs the signal from the built-in
optical sensor, providing necessary feedback to the optional DC Static Centering
Unit Type 1056. Traditional push/pull stingers require no pre-tensioning.
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