A new method to detect zero drift and sensitivity of a Coriolis Mass Flow Meter (CMFM) by using phasor control

Abstract

Coriolis Mass Flow Meters (CMFM) are directly measuring mass flow, by analyzing the induced oscillation of the measuring pipe. The accuracy is high and the sensitivity regarding other features of the flow to be measured like heat conductivity, heat capacity and viscosity is rather small. CMFM available at the marketplace often show changes in zero point and sensitivity during normal operation. The well known procedure for online determination of zero and sensitivity [3,4] is very sensitive regarding the compensation forces to be calculated and deserves a cyclic state transition of the meter which is rather time consuming (about 2 to 3 seconds). The new approach using a phasor model of the meter together with an observer for the phasor variables is a major contribution to enhance the performance of the control system, as the cyclic stimuli applied to the meter are now interpreted as disturbances acting on the control loop. The phasor controller, mainly a nonlinear controller for phase and amplitude, is able to compensate the disturbances much faster than in the previous approach.