Invited Article: Expanded and improved traceability of vibration measurements by laser interferometry

Abstract

Traceability to the International System of Units has been established for vibration and shock measurements as specified in international document standards, recommendations, and regulations to ensure product quality, health, and safety. New and upgraded laser methods and techniques developed by national metrology institutes and by leading manufacturers in the past two decades have been swiftly specified as standard methods in the ISO 16063 series of international document standards. In ISO 16063-11:1999, three interferometric methods are specified for the primary calibration of vibration transducers (reference standard accelerometers) in a frequency range from 1 Hz to 10 kHz. In order to specify the same (modified) methods for the calibration of laser vibrometers (ISO 16063-41:2011), their applicability in an expanded frequency range was investigated. Steady-state sinusoidal vibrations were generated by piezoelectric actuators at specific frequencies up to 347 kHz (acceleration amplitudes up to 376 km/s(2)). The displacement amplitude, adjusted by the special interferometric method of coincidence to 158.2 nm (quarter the wavelength of the He-Ne laser light), was measured by the standardized interferometric methods of fringe counting and sine-approximation. The deviations between the measurement results of the three interferometric methods applied simultaneously were smaller than 1%. The limits of measurement uncertainty specified in ISO 16063-11 between 1 Hz to 10 kHz were kept up to frequencies, which are orders of magnitude greater; the uncertainty limit 0.5% specified at the reference frequency 160 Hz was not exceeded at 160 kHz. The reported results were considered during the development of ISO 16063-41 by specifying the instrumentation and procedures for performing calibrations of rectilinear laser vibrometers in the frequency range typically between 0.4 Hz and 50 kHz--the interferometric methods may be applied within expanded frequency ranges using refined techniques and procedures. It is concluded that calibration frequencies up to 0.5 MHz are attainable in compliance with the first international document standard for the calibration of laser vibrometers.