Vibration testing equipment
Hydraulic actuator vibration testing
hydraulic actuators are used for high amplitude and low frequency testing. And cannot reach high frequencies as electrodynamic shakers. As they are limited to hydraulic fluid flow rates and servo valve capacity. To increase the frequency performance, use a three stage servo-valve configuration.
An example of hydraulic testing is tire burst testing on vehicles and plane. Where the frequencies are low and the displacements are high.
Electrodynamic / acoustic shakers
Electrodynamic shakers are used for high frequency low amplitude vibration testing. The shaker itself has a moving armature driven by an electric coil which induces a magnetic field. This moves the armature vertically up and down.
When and how to use electrodynamic shakers
Electro dynamic shakers have typical frequency ranges from 5Hz to 3000Hz.
Some limitations of electro dynamic shakers are:
displacement of the armature
the payload which is also dependent on
the vibration signal, i.e. high vibration levels need more acceleration and thus the payload reduces.
For large items there are other configuration, if you need more advice, please call.
For long test items, like actuators of several metres long, two shakers can operate in tandem at the same time, with ether ends of the actuator positioned on each shaker. There are shaker manufacturers in the UK that can help with the drive signal for tests like these.
Once again, if you have would like to take this approach, or you are having problems with this, please get in touch.
When is a slip table required?
An electro dynamic shaker is available as a stand-alone unit or with a slip table. The slip table is used to drive vibration into the test unit in its lateral and longitudinal axes.
vibration testing is usually performed in three main orthogonal axes, i.e. x, y and z axes. Where the z axis is the vertical axis in this explanation. These axes are all at right angles to each other.
When the controller controls the shaker movement, it uses feedback from the accelerometers. Whether it is the vertical axis, lateral or longitudinal axes, it controls the accelerometer on the shaker to the profile o nte controller, no matter what the direction.
Because of this, small items can be tested on shakers using in the vertical direction, and using a bookend fixture (A fixture to mount the test unit at right angles to the direction of excitation, avoiding the use of a slip table) for the other two orthogonal axes.
Except when the test unit contains fluids that must be representative of installation. Then a shaker with a slip table is required.