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The Coriolis flowmeter works using the Coriolis-effect. The Coriolis-effect is described in the law of conservation of momentum, something that is currently moving will resist against a change in that movement. In a Coriolis meter the tubing through which the substance moves are vibrated. The Coriolis-force of the moving medium causes the vibration in the incoming part to be left behind compared to that of the outgoing part. The time difference between the vibrations in the incoming and outgoing part is directly proportional to the mass-flow of the medium.
The eigen frequencies of the vibrating tubing is influenced by the mass of the medium. Because the volume of the tubing is calculated a comparable mass of the medium can be calculated, and with that also the volume flow.
Because the deformations of a straight tube initially weren’t reliably measurable, the first measurers were made as a U-shaped tube. Because a single tube quickly influences the measurer through external vibrations, the measurer is almost always made with a double U-shaped tube that is made to vibrate in the opposite phase. This way external influences cancel each other out. The most accurate Coriolis flowmeters even have four Coriolis tubes.
With the coming of digital signal processing, it is possible to get a reliable measurement signal from a straight tube. To help remove the external influences with a straight tube, the measurers often have a balance bar that vibrates in the opposite phase with the measuring tube. The newest Coriolis flowmeters therefore have no U-tubes at all.