impeller turbine mass flow meter.
The impeller, turbine-type mass flow meter uses two rotating elements in the fluid stream, an impeller and a turbine. Both elements contain channels through which the fluid flows. The impeller is driven at a constant speed by a synchronous motor through a magnetic coupling and imparts an angular velocity to the fluid as it flows through the meter.
The turbine located downstream of the impeller removes all angular momentum from the fluid and thus receives a torque proportional to the angular momentum. This turbine is restrained by a spring which deflects through an angle which is proportional to the torque exerted upon it by the fluid, thus giving a measure of mass flow.