Multiple shaker systems are typically used for vibration testing when the unit under test (UUT) is too long or too heavy to test with a single shaker. This approach overcomes the limitations of high drive requirements with a single shaker test. Multiple shaker systems also allow the UUT to be tested in various configurations and directions in the horizontal and vertical orientations.
Sentek Dynamics recently conducted an interesting test for an end-user consisting of two 50 kN shakers with a horizontally orientated set up configured with rails, slip table and driving bars. A dual shaker test was executed with the shakers in a push-push arrangement. A dummy test specimen is mounted in the following figure to illustrate the system capabilities.
Uni-axial accelerometers are mounted onto the slip table in the direction of the shakers to control the vibration test. Since the shakers are facing each other, the control sensors are attached opposite to each other. A phase difference of 180 degrees is used between the controls to allow the shakers to move in-phase (and avoid any physical damage to the system).
EDM MESA Vibration Control software by Crystal Instruments was used to execute the multi-shaker random and sine vibration tests.
The MESA vibration test can easily overcome the resonances and anti-resonances of the complete system. The test was executed from 5-1200 Hz on this large system.