Evaluation of measurement uncertainty in calibrations of laser vibrometers

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The international standard for the calibration of laser vibrometers, ISO 16063-41:2011, specifies the instrumentation and procedures for performing primary and secondary calibrations of rectilinear laser vibrometers, as well as the requirements for reporting the calibration results including the uncertainty of measurement. The procedures of evaluation of the measurement uncertainty are reviewed to consider that interferometric standard methods specified in ISO 16063-11 for primary vibration calibrations of accelerometer standards in a frequency range up to 10 kHz, proved to be applicable to higher frequencies far beyond 100 kHz. The expanded uncertainty of measurement shall be given in accordance with the Guide to the expression of uncertainty in measurement (GUM). An adaptation of the GUM procedures to vibration measurements and calibrations is described. It is shown how a model function of simplified structure can be established for the complex relationship between the measurand Y of an indirect measurement (e.g. module of sensitivity of a laser vibrometer), the input quantities directly measured to calculate the output estimate y of the measurand Y (e.g. displacement or velocity amplitude, voltage amplitude and frequency) and various influence quantities which may affect the measurement result. Methodical means were introduced to facilitate the determination of standard uncertainties, the calculation of the uncertainty contributions to the measurement result, the calculation of the combined uncertainty and the determination of the expanded uncertainty for a given coverage probability. Specific uncertainty evaluations are demonstrated for interferometric vibration calibrations using standardized interferometric methods in a national metrology institute and in an accredited calibration laboratory.