Investigation of primary vibration calibration at high frequencies using the homodyne quadrature sine-approximation method: problems and solutions

Abstract

When homodyne quadrature techniques are used for primary vibration calibration at high frequencies the problem of low displacement amplitudes arises, which inhibits the accurate measurement of acceleration amplitude and initial phase. By exploiting the effect of disturbing motion caused e.g. by hum of the power amplifier or environmental vibrations, it is possible to still recover the displacement time history by phase unwrapping. However, it is then necessary to deal with the superimposed drift-like motion components. This contribution proposes two techniques to either include these components in the sine approximation or to apply a wavelet-based detrending technique. The performance and consistency of both methods are demonstrated by simulation tests, taking into account all significant influences known from real acceleration measurements, and by comparison of accordingly performed real calibrations with the respective calibration results with validated heterodyne techniques.