Water flow sensor consists of a plastic valve body, a water rotor, and a hall-effect sensor. When water flows through the rotor, rotor rolls. Its speed changes with different rate of flow. The hall-effect sensor outputs the corresponding pulse Signal.
Flow gauges typically output a series of pulses proportional to the instantaneous flow rate .This means that to interpret them it's necessary to implement a simple frequency counter. This is actually the same way many car speedometers work: a wheel sensor outputs a pulse for each rotation of a wheel which means the pulse frequency varies proportionally to the vehicle speed. The speedo then displays a scaled version of the current pulse frequency to show instantaneous speed while the odometer displays a scaled cumulative pulse count to show distance traveled - both pieces of information are based on the same underlying data but they are recorded and displayed in different ways.
This water flow sensor outputs approx. 4.5 pulses per second per litre of flow per minute.It means , at 10 litres per minute , the sensor will output 45 pulses per second.By measuring the pulse frequecy and dividing by 4.5 (or multiplying by 0.22) we can determine the current flow rate in litres per minute.
The flow sensor is made from a strong reinforced plastic material & has a 0.5 inch thread on each end so it can be screwed into standard plumbing fittings.