Electrodynamic vibration exciters are widely used for different purposes. One of their important applications is usage as a vibration generating chain in absolute calibrations of vibration pick-ups. Main requirements for the vibration-generating devices are described in relevant ISO standard. These requirements are the total harmonic distortion of the acceleration, transverse, bending and rocking motion, hum and noise level, and the acceleration amplitude stability. The bending, rocking and transverse accelerations are the properties that belonging entirely to the vibration exciter. Contribution of these effects to the overall calibration uncertainty is not as small as to be assumed negligible. Investigation of the motional behavior of some of the commercial electrodynamic exciters by self-mixing interferometry has been carried out at Turkish National Metrology Institute (UME). Interferometer in configuration of the external cavity diodes laser (ECDL) constructed at UME was used for the characterization of the exciters' surface displacement in the medium frequency range.
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