An experimental study of zero-shift in a straight-tube Coriolis meter

Abstract

In Coriolis meter terminology, zero-shift is a general term describing the change in time-lag at zero-flow (zero-point) in response to any of a number of external factors. Zero-shift of a straight single-tube Coriolis meter has been investigated experimentally. The meter-tube was stainless-steel (2.66/2 × 300 mm) and has been tested across a range of flow rates (0–1 lpm, Red<104), pressures (1–4 barg) and pretensions (0 & 22 N). Zero-shift was shown to be principally dependent on the vibration-frequency. This was confirmed by operating the meter in both free and force-vibration modes. For zero-point to become a function of frequency the system must possess asymmetry, which may arise from the fluid or solid component. It was hypothesized that an asymmetric deformation field (i.e. a deviation from straightness) was the principal source of system asymmetry in this particular case. The deformation field was shown to be dynamic and therefore capable of modifying the zero-point even in fixed-frequency operation. The relationship between zero-point and frequency is complex owing to the many interconnected factors which can create asymmetry. However, it was shown that sensitivity of zero-point to frequency depends on the degree of asymmetry and particularly asymmetry of deformation-gradient (w0′).