Zero shifts due to non-proportional damping

A Coriolis flowmeter produces a signal directly proportional to the mass flow rate of a fluid. A zero shift is defined as the signal produced by the flowmeter at a mass flow rate of zero. This paper explores the effects of non-proportional damping on zero shifts in Coriolis flowmeters. An idealized finite element model of a Coriolis flowmeter is perturbed to explore the effects of localized damping changes, which result in a non-proportional damping matrix. A non-proportional damping matrix is not diagonalized by the modal transformation, which results in coupled modal domain equations of motion. This paper shows how the presence of the small off-diagonal terms in the transformed damping matrix can lead to modal responses in modes that are not excited by the modal force vector. The modal superposition of undesirable modes has been shown to be responsible for zero shifts in Coriolis sensors. This paper shows how these very slight damping changes can result in significant zero shifts.