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Title: Dynamical Effects In Expanding Volume Flow Calibrators
Author: Thomas O. Maginnis
Source: 2002 International Symposium on Fluid Flow Measurement
Year Published: 2002
Abstract: Standard flow calibrators using the constant pressure expanding volume method employ a circular cylinder as the collection volume, with the volume expansion occurring parallel to the axis. The volume of gas collected in a given time is related to the measured axial displacement through a meter Kfactor, (with dimensions of volume per unit axial displacement), that corresponds geometrically to the average interior cross-sectional area of the cylinder. These instruments as used rarely take advantage of the displacement flexibility arising from the translational symmetry, but typically operate between geometrically fixed start and stop points. It is usually assumed that the motion occurs with constant velocity between these points, i.e. that any startup transients rapidly die out. Any residual acceleration of the movable mass that seals the collected gas in this range will degrade the desired uniform linear expansion of the collection volume at constant flow and limit accuracy. A simple dynamical analysis shows that such systems are vulnerable to sustained oscillation in the absence of adequate damping.

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