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Modes of Operations to Install Exciter for Structural Testing Operations


While manufacturing a structure or equipment, modal testing is performed on the structure to test its dynamic characteristics. It is specifically done to verify the structural stability and endurance of the structure under stress and its physical properties. In the process, the relationships between frequency response functions and their individual modal parameters are analysed, which leads to more accuracy during the measurement phase. 

A common practice is to attach the exciter to the structure under test and transmit signals to the structure. This generates a reaction excitation force within the structure by a controlled acceleration of a mass, which is then measured to analysed the capacity of dynamic forces that can be exerted on the structure. 

A modal excitation setup generally comprises an Exciter, Controller, Sensor and a software for structural testing. Various optional accessories allow different modes of operation and facilitate the handling of the equipment. APS has been a supplier of modal exciter for years to ensure the structural stability and endurance of your equipment under stress.

Fixed Body Mode

This mode allows the shaker to be fixed along with an armature attached to the test structure, so that the shaker force is directly delivered to the test structure. A force transducer is inserted between the armature and test structure to measure the force delivered to the structure. 

One can also remove the armature band and use the shaker current as a measure to the generated force.

Free Body Mode

In applications where test structures lie at a considerable distance above ground level, the above approach cannot work. Such setups are costlier to apply in such cases. 

Free body mode can be employed in such applications, in which the shaker body is used as the reaction mass by suspending the shaker from an overhead support. The load force can be either measured by the force transducer or the axial acceleration of the shaker body. 

Reaction Pass Mode

Large structures having floors need to be tested for horizontal and vertical forces applied to generate resonant modes of vibration. 

The shaker can be used in a reaction pass mode where it can be rested on the horizontal surface on the shaker body. A moving armature provides a reaction mass that allows for delivery of the shaker force via the shaker body to the surface. The force is measured by a force transducer or by measuring the acceleration of the moving masses. 

Shaker Table Mode

The shaker table mode allows users to operate in both horizontal and vertical modes with armature guidance and suspension systems to provide long stroke tables for the excitation of test loads. 

These tables have inserts to mount the test load directly or a fixture on the table. Generally, accelerometers are used in this set up to record the response of the structure due to varying input impedance at the base of a test load.

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