This basic flow meter is used to measure liquid/water flow in solar, computer cooling, or gardening projects. This sensor sits in line with your water line, and measures how much liquid has moved through it.
The sensor comes with three wires: red (5-12VDC power), black (ground) and yellow (Hall effect pulse output). By counting the pulses from the output of the sensor, you can easily track fluid movement: each pulse is approximately 2.2 mL. The pulse rate does vary a bit depending on the flow rate, fluid pressure and sensor orientation and needs careful calibration if higher precision is required