Shakers, transducers and similar vibration- and shock-testing equipment generate force in order to produce vibrations
shock or modal excitation for testing and analysis. Using shakers, test
- determine product or component performance under vibration or shock
- measure structural fatigue of a system or material
- detect flaws through modal analysis
- verify product designs
- simulate the shock or vibration conditions encountered in aerospace,
defense, transportation, etc.
Shakers may operate using several different physical principles:
-- these shakers use a motor with an eccentric on the shaft to generate
- Electrodynamic -- these shaker-amplifier
systems use an electromagnet to create force and vibration.
- Hydraulic -- these systems use pressurized fluid and hydraulic "motors"
to generate vibration. Hydraulic shakers are used when large-force amplitudes
are needed (e.g. testing large aerospace or marine structures or when
the magnetic fields of electrodynamic generators are a problem).
- Pneumatic systems (or: air-hammer tables)
-- use pressurized (compressed) air to drive a table.
- Piezoelectric shakers -- operate via application of an electrical
charge and voltage to a sensitive piezoelectric crystal or ceramic element.
This phenomenon deforms the crystal resulting in vibration.
Features common to most shakers are:
- active suspension -- compensates for environmental or floating platform
- an integral slip table -- allows horizontal or both horizontal and vertical testing of samples. The slip table is a large flat plate that
rests on an oil film placed on a granite slab or other stable base.
Important specifications for shakers include:
- peak sinusoidal force
- frequency range
- peak acceleration and peak velocity
Note: These rating specs may be without a load, since shaker
manufacturers may not always be able to predict how their shakers will
The three main test modes shakers
can have are:
- random vibration-- force and velocity of the table and test sample
will vary randomly over time
- sine wave vibration -- sinusoidally varies the force and velocity
of the table and test sample over time
- shock or pulse mode -- test sample is subject to high-amplitude pulses
Typical specifications of shakers:
- Sine Force -- may range from 4.5 lbs force peak (20 N) up to 500 lbs
force peak (2,220 N) for large systems
- Random Force -- may range from 3.0 lbf rms random (13 N) to 350 lbf
rms random (1,550 N) for large systems
- Shock Force -- may range from 9.5 lbf peak shock (42 N) to 1,000
lbf peak shock (4,440 N) for large systems
- Frequency Range -- may range from (DC to 11,000 Hz) to (DC to 4,500
Hz) for large systems
If you can only run one test, either sine or random,
which should it be -- which is the most severe?
Some general assumptions:
- failures due to vibration are caused at the peak G level seen by the
- most products have resonances at one or more frequencies
- at these resonances the vibration levels applied to the product are
amplified by the Q factor of the resonance
The relative severity of a sine test and a random test will vary depending
on a product's resonant frequencies and Qs (amplification factor). In
general, when sine and random tests have the same peak vibration levels
at the control point, the product will see higher vibration levels
with a sine test than with a random test due to the resonances in the
Nevertheless, one must remember that a sine test only excites a single
product resonance at a time; hence, a sine test will not test the interaction
between two resonances in a product or component. Because a random test
excites the full frequency spectrum all at once, it can be used to find
problems resulting from the interaction between two resonances.
Shakers and Shaker-Amplifier Systems
RELATED: Shock Test Systems and Shock Testers, Shaker