Sources of measurement error in laser Doppler vibrometers and proposal for unified specifications

Abstract

The focus of this paper is to disclose sources of measurement error in laser Doppler vibrometers (LDV) and to suggest specifications, suitable to describe their impact on measurement uncertainty. Measurement errors may be caused by both the optics and electronics sections of an LDV, caused by non-ideal measurement conditions or imperfect technical realisation. While the contribution of the optics part can be neglected in most cases, the subsequent signal processing chain may cause significant errors. Measurement error due to non-ideal behaviour of the interferometer has been observed mainly at very low vibration amplitudes and depending on the optical arrangement. The paper is organized as follows: Electronic signal processing blocks, beginning with the photo detector, are analyzed with respect to their contribution to measurement uncertainty. A set of specifications is suggested, adopting vocabulary and definitions known from traditional vibration measurement equipment. Finally a measurement setup is introduced, suitable for determination of most specifications utilizing standard electronic measurement equipment.

Model assessment of a composite mock-up bladed rotor based on its vibration response and radial expansion

“…Optical measurement systems such as a coupled system of an optical derotator with an ESPI or a laser Doppler vibrometer provide non-invasive measurements, but are strongly affected by external noise and vibrations caused by imbalances [15].…”

The problem of calibrating Laser-Doppler Vibrometers at high frequencies

“…It is well-known from systems theory that in order for a signal to pass a linear, time-invariant (LTI) system undistorted -allowing only for attenuation and time delay -that system must have a flat amplitude response and a linear phase response [12,13]. Generally, this is not the case with real-world systems or their components.…”

Metrology of vibration measurements by laser techniques

“…The metrological base established for vibration measurements by laser techniques allows, among other things, traceable calibrations of laser vibrometers [ 28 ], [ 29 ], [ 30 ] in extended frequency and intensity parameter ranges to be performed, whereby the chain of calibrations providing traceability has its origin in adequate national measurement standards using laser techniques in accordance with the relevant ISO standards.…”