Which instruments are categorized as mass flow meters?

Mass flow meters are designed to measure the mass flow rate of a fluid, and they operate based on different principles. Among the options provided, thermal and Coriolis meters are both recognized as mass flow meters.

Coriolis flow meters operate by detecting changes in the vibration of a flow-conducive tube. As fluid flows through the tube, it causes a change in frequency of the tube's vibrations. This change is directly related to the mass flow rate of the fluid, allowing for precise measurement without being affected by changes in temperature or pressure.

Thermal mass flow meters, on the other hand, assess mass flow by relating the heat transfer from a heated element to the fluid. The amount of heat removed by the flow is proportional to the mass flow rate, enabling accurate measurement of the mass flow in gases or liquids.

Both types interpret flow based on mass rather than volume, distinguishing them as true mass flow meters. In contrast, the other instruments listed do not directly measure mass flow but rather infer volume flow rates or employ different measurement techniques.