text: Lorentz force flowmeters are usually classified in several main conceptual setups. Some of them designed as static flowmeters where the magnet system is at rest and one measures the force acting on it. Alternatively, they can be designed as rotary flowmeters where the magnets are arranged on a rotating wheel and the spinning velocity is a measure of the flow velocity. Obviously, the force acting on a Lorentz force flowmeter depends both on the velocity distribution and on the shape of the magnet system. This classification depends on the relative direction of the magnetic field that is being applied respect to the direction of the flow. In Figure 3 one can distinguish diagrams of the longitudinal and the transverse Lorentz force flowmeters.
  It is important to mention that even that in figures only a coil or a magnet are sketched, the principle holds for both.
  Rotary LFF consists of a freely rotating permanent magnet (or an array of magnets mounted on a flywheel as shown in figure 4), which is magnetized perpendicularly to the axle it is mounted on. When such a system is placed close to a duct carrying an electrically conducting fluid flow, it rotates so that the driving torque due to the eddy currents induced by the flow is balanced by the braking torque induced by the rotation itself. The equilibrium rotation rate  varies directly with the flow velocity and inversely with the distance between the magnet and the duct. In this case it is possible to measure either the torque on the magnet system or the angular velocity at which the wheel spins.