Signal recovery system for mass flowmeter

Abstract

A mass flowmeter of the Coriolis-type having a primary wherein fluid being metered is conducted through a flow tube in the form of a double loop whose loops are excited by a driver to vibrate in phase opposition at the resonance frequency of the tuning fork. Because fluid passing through the flow tube is subjected to Coriolis forces, the vibrating loops are caused to torsionally oscillate in accordance with the mass flow of the fluid. A pair of sensors mounted on the respective loops sensor signals which are applied to a differential amplifier in a signal recovery system forming the secondary of the meter to produce an output voltage that is a function of mass flow. This output voltage is applied to the input of a microcontroller coupled to an indicator providing a reading of mass flow. The meter is calibrated so that at the resonance frequency under normal operating conditions it produces a reading proportional to mass flow. Because of changes in the density of the fluid and other variables encountered under actual operating conditions which bring about deviations in the resonance frequency and in the amplitude of the torsional oscillations, also applied to the microcontroller are frequency and amplitude signals which reflect these deviations. The microcontroller, in response to these signals, acts to correct the mass flow indication to provide an accurate mass flow reading.