From Micro Ohm's description

YF-S201 Water Flow Measurement Sensor with 1-30Liter/min Flow Rate – Black This is YF-S201 Water Flow meter Measurement Sensor with 1-30Leter/min Flow Rate in black colour. This sensor sits in line with your water line and contains a pinwheel sensor to measure how much liquid has moved through it. There’s an integrated magnetic hall effect sensor that outputs an electrical pulse with every revolution. The hall effect sensor is sealed from the water pipe and allows the sensor to stay safe and dry. By counting the pulses from the output of the sensor, you can easily calculate water flow. Each pulse is approximately 2.25 millilitres. Note this isn’t a precision sensor, and the pulse rate does vary a bit depending on the flow rate, fluid pressure, and sensor orientation. It will need careful calibration if better than 10% precision is required. However, it’s great for basic measurement tasks! We have an example Arduino sketch(check the ATTACHMENTS tab) that is useful to quickly test the sensor; it will calculate the approximate flow of water in liters/hour. The pulse signal is a simple square wave so it’s quite easy to log and convert into liters per minute using the following formula. To know how to use water flow meter click here! Connection Red wire : +5V Black wire : GND Yellow wire : PWM output Features : The simple and compact module. Easy to Install. High Sealing Performance. High-Quality Hall Effect Sensor. Package Includes : 1 x YF-S201 Water Flow meter Measurement Sensor with 1-30Liter/min Flow Rate – Black. Model YF-S201 Working Voltage (V) 5 ~ 18 Max current draw 15mA @ 5V Working Flow Rate (Liters/Minute) 1 ~ 30 Operating Temperature range (℃) -25 ~ +80 Operating Humidity Range 35% – 80% RH Accuracy ±10% Maximum water pressure 2.0 MPa Output duty cycle 50% +-10% Output rise time (µsec) 0.04 Pulses per Liter 450 Output fall time (µsec) 0.18 Outer diameter (mm) 20 Intake diameter (mm) 11 Outlet diameter (mm) 11 Length (mm) 62.5 Width (mm) 36 Height (mm) 35 Weight (gm) 50 Shipment Weight 0.089 kg Shipment Dimensions 9 × 6 × 6 cm YF-S201 DATASHEET EXAMPLE ARDUINO CODE

From Makers Electronics's description

Description of the YF-S201 YF-S201 is a water flow measurement sensor with high-grade quality sealing property. It works on the Hall effect principle and with a flow rate range of 1~30L/min. The module has three pins: Power, Ground, and the Analog output. YF-S201 consumes very little current and can work with an allowing pressure of ≤1.75MPa. Features of YF – S201 Operating Voltage: 4.5V to 18V DC Output type: 5V TTL Maximum current draw: 15mA at 5V The sensor used: Hall Effect Working Flow rate: 1 to 30 Liters/Minute Accuracy: ±10% Pulses per Liter: 450 Output duty cycle: 50% +-10% Maximum water pressure: 2.0 MPa Flow rate pulse characteristics: Frequency (Hz) = 7.5 * Flow rate (L/min ) Outer diameter: 20mm Intake diameter: 9mm Outlet diameter: 12mm Pin configuration of YF-S201 YF – S201 has 3 Pins for power and the output. The table below explains the color, pin type, and function of the pin. Colour Pin type Function Red Power To provide power to the module Black Ground Connected to the ground terminal Yellow Signal Analog output from the sensor Applications of YF – S201 Agriculture Food processing Coffee/Tea makers Water Management Mining Industry

From Future Electronics Egypt's description

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. Can be used with ardduino How to Use? Reading water flow rate using flow sensor and Arduino Water flow rate on LCD Specifications: Working voltage 5V-24V Maximum current 15 mA(DC 5V) Weight 43 g Flow rate range 1~30 L/min FAQ Question1: What type of materials the sensor is made out of that contact the water? Answer: The water flow sensor is made of nylon with fiber. It should not be used with strong acid and strong base. Question2: Is it safe to be used for drinking water? Answer: Yes, it has been used on drinking machine.