The Vibrator (Shaker)
Shakers (Vibrators) for stress screening applications are electromagnetic devices, very similar in principle to loudspeakers. Instead of reproducing sound, as in the case of a loudspeaker, they are designed to produce a force applying vibration to test items and structures. They operate in conjunction with a power amplifier a computer based control system and vibration sensors (accelerometers) to generate, measure and control precise vibration conditions.
A shaker is in concept a very simple device. A large electromagnet generates a field and an armature within the field acts in the same way as a linear motor. At the top of the armature is a table for mounting test items. See figure 1.
In an environmental stress screening application, the shaker generates a controlled vibration environment designed to stress the product uder test in such a way that latent defects are exposed in the lab. Shakers for stress screening need not be any different from those used in R & D testing or product qualification, however there are certain attributes which are likely to be required.
- The shaker table is frequently called upon to hold a great many products at one time. Therefore large table sizes are often preferred.
- Testing is often carried out in combination with thermal testing, which means that the form factor of the shaker should be suitable for working underneath a chamber. See figure 2.
