Description
The YF-S402 is a compact Hall-effect water flow sensor designed for inline measurement of liquid flow rate and total volume in plumbing, irrigation, coffee machines, and water dispenser applications. It features a 1/4-inch (DN8) threaded connection with a white plastic body and is specifically intended for small-diameter water lines where standard 1/2-inch sensors would be too large.
The sensor consists of a plastic valve body containing a magnetic pinwheel rotor and a Hall-effect sensor. As water flows through, the rotor spins at a rate proportional to flow velocity, and the Hall sensor outputs a digital pulse train. The pulse frequency is directly proportional to flow rate, allowing the microcontroller to calculate instantaneous flow (L/min) and cumulative volume (liters). The 1/4″ YF-S402 is rated for a flow range of 0.3–6 L/min, with a pulse characteristic of 4380 pulses per liter and a frequency relationship of f = 73 × Q (Hz, where Q is L/min) .
The sensor operates from 3.5V to 24V DC with a typical current draw of 15mA and outputs a pulse signal . Accuracy is specified at ±2% for volume measurement, making it more precise than the larger YF-S201 family . The maximum liquid pressure is 1.75 MPa, and the maximum liquid temperature is 120°C .
Critical limitations: This is a low-cost, non-certified sensor intended for educational, hobbyist, and light commercial use. For 3.3V microcontrollers (ESP32, ESP8266), the pulse output amplitude follows the supply voltage and may require a logic level shifter or voltage divider if powered from 5V. For revenue-grade metering or safety-critical systems, a certified flow meter should be used instead.
Features
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Compact 1/4″ (DN8) Connection: Designed for small-diameter water lines in coffee machines, water dispensers, and precision irrigation.
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Hall-Effect Pulse Output: Digital square wave proportional to flow rate, readable by any microcontroller with an interrupt-capable GPIO.
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Low-Flow Measurement Range (0.3–6 L/min): Suitable for applications where larger 1/2″ sensors cannot resolve low flow rates .
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4380 Pulses per Liter: High pulse density provides good resolution for volume tracking .
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Wide Voltage Range (3.5–24V DC): 5V typical for Arduino; flexible for different power supplies .
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Low Power Consumption: 15mA typical at 5V, suitable for embedded applications .
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Durable Construction: Plastic body with magnetic rotor and Hall sensor.
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High Precision (±2%): Better accuracy than the YF-S201 family for volume measurement .
Technical Specifications
| Parameter | Specification (1/4″ DN8 YF-S402) |
|---|---|
| Model | YF-S402 |
| Connection Size | 1/4″ (DN8) |
| Body Color | White |
| Operating Voltage | 3.5V – 24V DC |
| Operating Current | 15mA @ 5V |
| Output Signal | Pulse; amplitude tied to VCC |
| Flow Rate Range | 0.3 – 6 L/min |
| Accuracy | ±2% (volume measurement) |
| Pulse Characteristic | 4380 pulses per liter |
| Frequency Formula | f = 73 × Q (Hz, Q in L/min) |
| Max Liquid Pressure | 1.75 MPa |
| Max Liquid Temperature | 120°C |
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