Current state and trends of ensuring traceability for vibration and shock measurements

Abstract

Recent and current activities at the level of national metrology institutes (NMIs) towards ensuring traceability of vibration and shock measurements to the International System of Units are mainly twofold: (i) initiating and contributing to new international standardization projects, within the International Organization for Standardization, ISO TC 108, to specify upgraded or new standard methods for the vibration and shock calibration of transducers; and (ii) improving the metrological base by developing upgraded or new standard equipment (e.g. national measurement standards) in compliance with up-to-date standard methods. Laser interferometry, which is the preferred primary vibration calibration method at NMI level, has been further developed at the Physikalisch-Technische Bundesanstalt (PTB) in recent years as a uniform methodology and technique for the primary measurement of translational motion quantities (e.g. acceleration) and rotational motion quantities (e.g. angular acceleration) at sinusoidal, shock-shaped and other, user-defined time histories. A traceability chain has been defined and developed which realizes and disseminates the units of the respective physical quantities at such time-dependencies which reproduce as closely as possible, during calibration of any transducer (e.g. accelerometer) or measuring instrument (e.g. laser vibrometer), the conditions of use after calibration (i.e. shock measurement in the peak acceleration range 1000 m/s2 to 50000 m/s2). A general account is given of the state of the art in transducer calibration, and an ensemble is presented of six national measurement standards (example from the PTB) with comparison results verifying the lowest measurement uncertainty achieved so far. From a survey of past comparisons, conclusions are drawn for key comparisons in the field of vibration and shock. Recommendations for future work areas are made.