Quantitative Estimation of the Influence of External Vibrations on the Measurement Error of a Coriolis Mass-flow Meter

In this paper the quantitative influence of external vibrations on the measurement value of a Coriolis Mass-Flow Meter for low flows is investigated, with the eventual goal to reduce the influence of vibrations. Model results are compared with experimental results to improve the knowledge on how external vibrations affect the measurement error. A Coriolis Mass-Flow Meter (CMFM) is an active device based on the Coriolis force principle for direct mass-flow measurements, independent of fluid properties, with a high accuracy, range-ability and repeatability. Besides the effect of the mass-flow on the mode shape of the tube, external vibrations can introduce motions that cannot be distinguished from the Coriolis force induced motion, thus introducing a measurement error. From a multi-axis flexible body model, the transfer function between external vibrations (e.g. floor vibrations) and the flow error, including the active filter characteristics, is derived. The floor vibrations are characterised with a PSD. Integrating the transfer function times the PSD over the whole frequency range results in an RMS flow error estimate. In an experiment predefined vibrations are applied on the casing of the CMFM (white noise spectra and VC norm spectra) and the error is determined. The experimental results corresponds with the model results. The agreement between model and measurements implies firstly that the influence of any floor vibration spectrum on the flow error, can be estimated and secondly that the performance of different CMFM designs can be compared and optimised by shaping their respective transfer functions.