Turbine flow meter
When gas flows through a turbine flow
meter it makes a vane turn; flow through the tube is proportional
to the number of revolutions per unit of time. The latter
is measured from the electrical impulses generated by interrupting
light directed at a photocell at each turn of the vane.
An advantage of this system is that it is insensitive to turbulent flow, gas composition, and water vapor and gas temperature. A disadvantage of the system is its inertia, which needs to be minimized by using a very lightweight vane and applying a deflector.
Example of a turbine flow meter.