The turbine fl owmeter model DOT consists of a helically shaped turbine rotor supported in two tungsten carbide bear-ings, the rotor being solid ferritic stainless steel of a grade compatible with the metered liquid, all contained within a housing of non-magnetic stainless steel. A pick off coil having a permanent magnet core is mounted in the housing adjacent to the rotor blade tips such that a magnetic circuit is set up via the rotor blades (fi g.1).
Rotation of the rotor varies the reluctance of this magnetic circuit and the fl ux changes induce a small voltage in the coil, the frequency of which is directly proportional to the rotor speed and therefore proportional to the volumetric fl ow rate.
The effects of increasing viscosity reduce the linear fl ow-range, the lower end fl ow rate is to be raised as the viscosity increases with a maximum viscosity of 10 mm²/s To calculate the low end accurate fl ow rate limit use: 0.7 x the square root of the metered liquid viscosity in mm²/s x normal minimum fl ow rate. Eg. If normal fl ow range is 10~100 l/min then for viscosity of 5 mm²/s time minimum accurate fl ow rate would be 15.65 l/min.