Practical experiences in primary vibration calibration using laser vibrometry - measurement uncertainties in wide frequency range applications

摘要

SPEKTRA is a leading manufacturer of primary calibration systems for vibration calibration. They are the first DKD calibration laboratory that applies for having a primary calibration system certified and accredited. It means that they have to carry out all the calculations, measurements and verification procedures - well known from their secondary calibration systems - one more time for the new primary calibration system. Some of the investigations carried out for their secondary calibration systems had been very helpful in primary calibration, too. But the methods applied and the measurement procedures involved in particular tracing the vibration quantity back to the wavelength of the laser vibrometer, had been completely different which means that completely new investigations had to be carried out. In the accreditation procedure, SPEKTRA had to draw up a Measurement uncertainty budget (MUB)that is based on GUM (Guide to the expression of uncertainty in measurement, ISO 1993, revised edition 1995, in German: DIN V ENV 133005). In this paper, some of the results of theoretical considerations and practical measurements and investigations will be presented and discussed. Because of the wide frequency range between 0.4 Hz and 20 kHz, a wide range of components and several modified system configurations had to be designed. Measuring results of complex sensitivity (magnitude and phase shift of transfer coefficient) obtained on different accelerometers in a wide frequency range will be presented and discussed. Our paper comes to the conclusion that for primary calibration, high quality components alone will not be enough. It is necessary to integrate these components in an optimised system that takes into consideration all requirements and influences and therefore allows reducing the uncertainties of the calibration procedure to the lowest possible values. The influence of components as well as relevant questions of mechanical adaptation, vbration isolation, AD conversion, and digital signal processing are discussed.