Flow sensor is a water flow sensor commonly used in fish pond water pumps, mini pumps, hot water pumps, etc. The sensor operates based on the water impeller and the Hall sensor inside. When the water flows through, it makes the water impeller rotate, which in turn triggers the Hall sensor to generate square wave pulses (NPN).
The 3-wire output functions are as follows:
Red wire: power supply: 5 – 24V
Black wire: GND (ground).
Yellow wire: signal.