Turbine flow meters for use with liquids have a relatively simple theory of operation, as a fluid flows through the tube of the flow meter it impacts upon turbine blades. The turbine blades on the rotor are angled to transform energy from the flowing liquid into rotational energy.
The shaft of the rotor spins on bearings, as the fluid velocity increases the rotor spins proportionally faster. Revolutions per minute or RPM of the rotor is directly proportional to the mean flow velocity within the flow tube diameter and this relates to the volume over a wide range.
As the rotor moves so do the turbine blades, movement of the blades is often detected either by a magnetic or modulated carrier (RF) pickoff. The pickoff is commonly mounted to the outside of the flow tube and it senses each rotor blade passing. The pickoff sensor will then generate a frequency output, the frequency is directly proportional to the volume of the liquid.
Turbine flow meters will often be supplied with calibration certificates, the certificate will also state the meter K-factor. The K-factor is defined as the number of pulses (detected by the pickoff) per unit of volume (litres) at a stated flow rate (10 litres per minute). The calibration certificate will often state multiple flow rates within the turbine meters specifications, each flow rate will have a corresponding K factor. An average of these flow rates is then calculated so that a turbine has a meter K-factor. As turbines are mechanical devices and due to manufacturing tolerances two turbine flow meters will have differing k factors.
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