In Gear Flow Meters, enclosed, medium-filled cavities are created between the teeth and the housing. The flowing measured medium causes the gear pair to rotate freely and without braking. Turbine Flow Meters measure with the aid of a high-precision turbine wheel. The medium flows against the turbine wheel in the axial direction and causes it to rotate. In Helical Flow Meters, the volumetric flow of the fluid is measured by the screw wheel principle. Two screw spindles, which overlap, are located in the housing. Enclosed media-filled cavities are created between the spindle flanks and the housing. The speed of the respective type of measurement is proportional to the flow rate and is picked up by transducers through the housing wall without contact.