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Vibration testing extended with low-frequency test rig

07 June 2010

TRaC, the environmental and standards-compliance test house, has extended its capabilities in low-frequency mechanical vibration testing by commissioning a new low-frequency test rig at its Warwick laboratory. The rig is one of the few commercially available systems that can apply a wide range of vibration tests, such as the demanding European Naval specifications, to large and/or heavy products and systems.

Vibration testing extended with low-frequency test rig
Vibration testing extended with low-frequency test rig

The test system comprises a vibration platform measuring 1.3 x 1.3m, that can carry a test-piece load of up to 2 tonnes. The system is single-axis; that is, the platform’s actuator moves it back-and-forth in one plane or direction, subjecting a unit-under-test (UUT) to vibration over a calibrated frequency range that extends as low as 0.1Hz, and up to 150Hz. UUTs can be subjected to a maximum acceleration of 5g at a frequency of 150Hz, and maximum displacement is 150 mm full-scale.

Movement of the table is under the control of a closed-loop system that employs electro-hydraulic actuators to generate the motion, and a combination of displacement transducers and capacitance-type accelerometers to give high-accuracy feedback in position and acceleration, respectively. The level of precision of which the control system is capable means that it can apply either sinusoidal or random vibration, or pre-defined profiles of shock and vibration over specified intervals. These scenarios include the marine and sub-sea low-frequency environments that the original specification set out to meet.

Existing test facilities that generate low-frequency mechanical vibration use electromagnetic actuation ("electrodynamic" systems) which creates stray magnetic fields, meaning that UUTs sensitive to such fields cannot be tested. TRaC’s electro-hydraulic system completely avoids this limitation, as well as going far beyond the lower frequency limit of electrodynamic systems.

Robust construction also means that TRaC’s test platform can carry loads with a high centre of gravity, accommodating equipment such as large valves for under-sea installations; however, the versatile specification now allows TRaC to offer precision low-frequency shock and vibration test services for a very wide range of other products and systems.

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