Paddlewheel and turbine flow sensors are similar in operation as they rely on the energy in the flow stream to spin the rotor. The spinning rotor generates either a sinusoidal or square wave output.

Most paddlewheel and turbine flow sensors use rotors with magnets embedded in each blade. The magnets are used together with a coil to produce the sinusoidal output (Hall effect sensors), or trigger an electronic switch to produce a square wave output (NPN or PNP transister output sensors). The resultant frequency is directly proportional to the flow rate.

45_Flow Rate and Total Flow Measurement