Mass flowmeters measure actual mass flow. While it is possible to calculate mass flow from a velocity or inferential measurement and other variables like temperature for known fluids, only one meter type commonly measures liquid mass directly, the Coriolis meter. This meter used to be applied only for when highly accurate, mass flow was required. Now with lower prices, a wider range of configurations and easier installation, it is being applied more routinely.

The heart of a Coriolis meter is a tube(s) that is vibrated at resonant frequency by magnetic drive coils. When fluid flows into the tube during the tube's upward movement, the fluid is forced to take on the vertical momentum of the vibrating tube. Therefore, as the tube moves upwards in the first half of the vibration cycle, the fluid entering the tube resists the motion of the tube and exerts a downward force. Fluid in the discharge end of the meter has momentum in the opposite direction, and the difference in forces causes the tube to twist. This tube twist is sensed as a phase difference by sensors located on each end of the tube arrangement, and twist is directly proportional to mass flow rate.

In addition to having high accuracy and a true mass flow measurement, Coriolis meters have no upstream and downstream straight run requirements, are independent of fluid properties, are low maintenance, and have a turndown ratio of as much as one hundred. While the meters originally were only available in...