Inline ‘axial’ turbine flowmeters are velocity measuring devices - they measure the average velocity of a fluid flowing through the body of the meter. Mounted within the body of a liquid turbine flowmeter is a vaned rotor. The rotor is centred on a shaft and allowed to rotate on bearings. The shaft is supported in the housing by tube bundles that also provide a measure of flow conditioning for the fluid stream.
The rotor is made from a ferromagnetic material or contains a magnet within the hub of the rotor. Liquid flowing through the meter body engages the rotor forcing it to rotate. The rotational velocity of the rotor is proportional to the average linear velocity of the liquid flow stream. This rotational velocity is transformed into an electrical frequency signal by means of a non-intrusive sensor or coil threaded partially into the body of the meter aligned with the rotational circumference of the rotor. Being in close proximity to the ferromagnetic or magnetic rotor creates an electromagnetic coupling with the coil. The output frequency of the coil then is directly proportional to the rotational velocity of the rotor. This frequency can then be converted to a flow rate indication or scaled signal by dividing the frequency by the meter’s scaling or K-factor (e. g. pulses per gallon or pulses/litre). The K-factor is established by factory calibration of the flowmeter at the time of manufacture.