Measuring or Working Principle of Variable area flow meter HD

Do you know the measuring principle of Variable area flow meter? These flowmeters are suitable for the measuring of clean liquids and gases. They consist of upright conical tube made of metal, glass or plastic. in which a sophisticated float moves freely up and down. The flow goes through the tube. which is applied from the bottom to top, causes the float to rise until the forces are in equilibrium. Three forces are acting on the float: The buoyancy force B, which depends on the density of the medium and the volume of the float. The gravity force G, which depends on the mass of the float. The flow force F which depends on the float shape and the flow velocity through the variable area between float and tube. So the, Gravity Force(G)= Buoyancy Force(B) + Flow Force(F). Every flow rate corresponds to a defined variable area resulting from the conical shape of the measuring tube and the specific position of the float. With glass cones, the flow value can be read directly from a scale at the level of the float. With metal cones. the float position is transmitted to an indicator by magnetic means. There is no need for auxiliary power. Different measuring ranges are realised through variations in cone sizes and shapes and in selecting different float shapes and materials. This method of measurement offers the following advantages, first one, is the Pressure drop which is constant. Second one, there is No special fuel or external energy is required to pump. third one, it is Very easy to construct and we can use a wide variety of materials to construct.