Coriolis flowmeters are instruments that, using the Coriolis principle, measure directly the mass flow rate of a process. The Coriolis force is the phenomenon that causes objects to appear to curve as they move across the surface of the earth.
A Coriolis meter artificially introduces a positive and negative Coriolis acceleration to the process. As illustrated in the diagram below, the entire process is split and re-directed through two curved tubes. The tubes are vibrated at a multiple of their natural resonant frequency. Miniature velocity transducers comprising of a coil & a magnet are each mounted on one of the tubes as shown. When no flow is present the tubes vibrate and the sine wave output of each velocity transducer is in phase. When flow is initiated the tubes will begin to twist due to the Coriolis acceleration induced by the moving mass. This causes the sine waves to shift in relation to one another (either lead or lag depending on the flows' direction) and a measurement is made.
An added benefit of Coriolis meters is their ability to perform multiple measurements. In addition to measuring mass flow directly, Coriolis mass flow meters also measure the density of the process by monitoring the period of the tube vibration and characterizing that as a density. Advanced digital signal processing enables Coriolis meter transmitters to calculate the concentrations of two component mixture and net volumes, etc. Variations on the split-tube design now includes straight-through tubes and double- looped single tubes.