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APS 420

Ball-bearing Long-Stroke vibration exciter

Our strongest ELECTRO-SEIS® modal shaker - maximum force of 900 N and up to 150 mm stroke

 

The APS 420 is used for vibration tests of airplanes and large structures. Its maximum force of 900 N and up to 150 mm stroke of the shaker unlocks new performance levels.

APPLICATIONS

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APS 420

Key Features

Applications

 Applications
  • seismic simulation for components 
  • test and calibration for seismic instruments
  • geological services, science, physics and seismic applications

Features 1

 Features
  • can be used to generate sine wave, swept sine wave, random or impulse force waveforms, fully adjustable at source
  • test set-up fl exibility with fi xed body, free body and free armature modes of operation

Features 2

 
  • optimized to deliver power to resonant load with minimum shaker weight and drive power
  • adjustable zero position of armature

Product details

  • Max. Force: 900 N
  • Max. Displacement pk-pk: 150 mm
  • Frequency Range: DC…200 Hz

Modes of Operation

Free Body Mode

Key Features
  • Suitable if the test object is in high altitude
  • Accelerated shaker body inserts reaction force in the test structure
  • Measurement of inserted force by a force transducer or the acceleration of the shaker body

The desired force input points on many test structures lie at a considerable distance above ground level. For tests on such items, it becomes difficult and expensive to use Fixed Body Mode support structures. For such applications, the Free Body Mode can be employed. In this mode the shaker body is used as the reaction mass by suspending the shaker from an overhead support. Besides using a force transducer a very convenient measure of the load force is the axial acceleration of the shaker body. This allows simplification of the test system instrumentation, in that force can be measured with an accelerometer system which is identical to that used to measure the structural response.

Fixed Body Mode

Key Features
  • (Generated) shaker force applied directly to structure
  • Low influence on structure due to low armature mass
  • Measurement of delivered force by force transducer or shaker current

In the Fixed Body Mode, the shaker body is fixed and the armature is attached to the test structure. So shaker force is delivered directly in the test structure. In this mode, force delivered to the test structure can be measured by inserting a force transducer in the thrust linkage between the armature and test structure. Alternatively, with the armature/body suspension bands removed, shaker current can be used as a direct measure of the generated force. The generated force is approximately equal to the force delivered to a resonant test structure, because the armature mass is typically small compared to the modal mass of most large test structures.

Shaker Table Mode

Key Features
  • Horizontal and vertical long stroke tables
  • Rugged design for harsh environment
  • High payload – up to 20 kg

Auxiliary table accessory units for both horizontal and vertical use employ the high load capability of the APS 113 armature guidance and suspension systems to provide long stroke tables for excitation of test loads. Each auxiliary table has a pattern of threads with helical inserts to mount the test load directly or a fi xture on the table. The mechanical input impedance at the base of a test load that is resonant in the operating frequency range can vary
signifi cantly. Thus, the acceleration response of the table and test item base will exhibit the familiar „peaks“ and „notches“ as frequency is varied. So it is recommended to observe the response of the structure using accelerometers.

Reaction Mass Mode

Key Features
  • Inertial vibration exciter
  • Vertical or horizontal operation
  • Easy to install reaction mass

Many large test structures having horizontal surfaces such as fl oors require vertical or horizontal force applied to these surfaces to generate resonant modes of vibration. The APS shakers may be used in a vertical or horizontal Free Armature Mode by resting the shaker body on the horizontal surface. The moving armature provides a reaction mass that allows for delivery of the shaker force via the shaker body to the surface (inertial shaker). Below a certain cross-frequency the shaker stroke limits the acceleration of the armature and thus the maximum force. Additional masses, e.g. APS 0112 or 4001, lower this frequency. The force applied to the structure can be measured by a force transducer or by measuring the acceleration of the moving masses.

Performance

The primary purpose of the APS  42  ELECTROSEIS® vibration exciter is to determine the dynamic charac teristics of mechanical structures. At resonance, a large amount of energy is contained in the structure, and the shaker must accommodate the resulting motion. However, it needs only supply the real mechanical power dissipated by damping mechanisms within the structure. If a drive point on a structure in resonance is vibrating with a velocity of 1 000 mm/s (39 in/s) peak and a force of 900 N (202 lbf) peak is required to sustain the vibration level, then the shaker will be delivering approximately 450 W RMS to the structure. Such a load on the shaker is termed a matched resonant load, and it is purely resistive since the force is in a phase with the velocity. If the resonant load input is other than 900 N × 1 000 mm/s, the full 450 W of mechanical power cannot be delivered to the structure, the system being either force or velocity limited. If the resulting maximum response level is not great enough, the user may have the option of moving the shaker to a drive point having an impedance closer to the matched value, or adding more shakers to the array driving the structure. Within the limitations of maximum force and velocity, the actual power delivered to a structure is a function of the input mechanical impedance at the drive point. In typical modal testing, this input impedance varies widely in magnitude and phase angle. At different frequencies, the input impedance of the drive point may appear predominately spring-like, mass-like, or resistive. Since the object of the tests is to establish resonant modes, at which the input mechanical impedance of all drive points are resistive, the shaker’s maximum performance capability is most meaningful stated in terms of the force and velocity that can be obtained when driving a matched resistive load. Therefore, performance is given in the form of graphs which present the envelopes of maximum force and velocity delivered to a resonant structure as functions of the resonance frequency of the structure. Another application is the excitation for sensor calibration. Acceleration envelopes of the APS 420  ELECTRO-SEIS® vibration exciter with various payloads are shown in the graph below for the 900 N force rating.

Force envelopes

Details

Velocity envelope - resonant load

Details

Acceleration with various mass loads

Details

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Frank Schulz
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+49 (0) 351 400 24 0

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