Coriolis: special issue [flow meter]

The Coriolis meter is without question the most accurate general purpose flow meter used in industry. Its ability to measure mass flow directly is important where commodity value is related to mass rather than volume, for example in food and beverage applications. The high turn-down and ability to deal with non-Newtonian fluids are also valued. Its more widespread use has been limited by its high cost, and need for a separate power supply, but the most serious drawback is the inability to deal with aerated or two-phase flow. A Coriolis meter consists of a flowtube, which is caused to vibrate sinusoidally at a resonant frequency by one or more drivers, while two sensors monitor the vibration. The flowtube geometry and sensor placement are arranged so that the frequency of oscillation (which may vary from 80Hz to 800Hz for different flowtube designs) gives the density of the process fluid, while the phase difference between the two sensor signals provides the mass flow rate. An electronic transmitter maintains flowtube operation by generating the required drive signal(s) and carries out measurement calculations.