Which flow meter type measures flow by using a mechanical rotor?

Turbine flow meters measure flow by using a mechanical rotor, which is central to their operating principle. In these devices, the fluid passes through a chamber that contains a turbine. As the fluid flows, it causes the turbine blades to rotate. The speed of this rotation is directly proportional to the flow rate of the fluid. This movement is then translated into a flow measurement, making turbine flow meters effective for various applications where accurate flow measurement is required.

Paddle wheel flow meters, while also mechanical, operate differently by using a paddle that pivots in response to the flow, rather than a rotor. Mass flow meters typically measure the mass of the fluid instead of the volume, and vortex flow meters work on the principle of vortex shedding caused by an obstruction in the flow. Thus, the unique mechanism of a rotor in turbine flow meters distinguishes them as the correct answer for this question.