1Pew SMWF-0420A Hall Flow Sensor Micro Flow Meter #9

Sensor · Flow Meter · SMWF-0420A · Hall Effect · In stock

What Is the SMWF-0420A Hall Flow Sensor?

The SMWF-0420A Hall Flow Sensor is a micro flow meter that uses a Hall effect sensor to measure liquid flow rate. Inside the plastic body, a small turbine or rotor spins at a speed proportional to the liquid flow passing through it. Embedded in one blade of the rotor is a tiny magnet. Each time this magnet passes the Hall effect sensor chip mounted on the body, the sensor outputs an electrical pulse. By counting pulses per unit time (using a microcontroller, PLC high-speed counter, or frequency-to-voltage converter), you can calculate the instantaneous flow rate. By summing total pulses, you can measure total volume dispensed. The SMWF-0420A is designed for low flow rates and small diameter tubing — applications include coffee machines, beverage dispensers, medical dosing pumps, laboratory peristaltic pump calibration, and small-scale chemical metering.

In short: This is a small Hall effect flow sensor that outputs a pulse train proportional to liquid flow rate. If you need to measure or control the flow of water, coolant, or other non-aggressive liquid in a small-diameter tubing system, this sensor provides the feedback signal to a controller that does the counting and math.

How to Integrate a Hall Flow Sensor into Your System

Electrical Connection

A typical Hall flow sensor has three wires: VCC (power, often 5V to 24V DC — check the sensor label for the exact rating), GND (ground), and OUT (pulse output signal). The OUT line is typically an open-collector NPN output — when the magnet passes the Hall sensor, the output transistor pulls the OUT line to ground. You need a pull-up resistor (typically 4.7k to 10k ohms) from OUT to VCC for the signal to swing between ground (magnet detected) and VCC (no magnet detected). Connect this conditioned signal to a digital input pin on your microcontroller, a PLC high-speed counter input, or a frequency meter.

Calibration — Converting Pulses to Flow Rate

Each flow sensor model has a K-factor (pulses per liter or pulses per gallon) specified by the manufacturer. For example, a sensor with K=450 pulses/L will output approximately 450 pulses for every liter that passes through. The actual K-factor varies slightly from unit to unit and with fluid viscosity and temperature. For applications requiring high accuracy, calibrate your specific sensor by dispensing a precisely known volume of the actual fluid you will be measuring, counting the pulses, and calculating the K-factor for your specific setup. Store this calibration value in your controller's EEPROM or configuration file.

Key Specifications

Frequently Asked Questions

What liquids can this flow sensor handle?

The SMWF-0420A is designed for water and water-like liquids (low viscosity, non-corrosive, non-flammable). The wetted materials are typically a plastic body (nylon, polypropylene, or POM), a plastic rotor, and a stainless steel shaft. It is not suitable for: strong acids or bases, organic solvents (acetone, toluene, gasoline), high-viscosity fluids (oil, glycerol), or fluids containing particulates that could jam the rotor. If your application involves anything other than clean water, contact our team with the fluid specifications to verify chemical compatibility before ordering.

How do I connect this to an Arduino or Raspberry Pi?

For Arduino: connect VCC to 5V (or the sensor's rated voltage), GND to GND, and OUT to a digital pin (e.g., pin 2). Add a 10k pull-up resistor between OUT and VCC. Use attachInterrupt(digitalPinToInterrupt(2), pulseCounter, FALLING) to count pulses in an interrupt service routine. In your main loop, calculate flow rate = (pulse_count / K_factor) per time interval. For Raspberry Pi: use the GPIO library with edge detection (GPIO.add_event_detect(pin, GPIO.FALLING, callback=pulse_callback)). Be aware that the Pi's GPIO pins are 3.3V — if your sensor outputs a 5V signal, use a logic level converter or a voltage divider to avoid damaging the Pi.

The sensor outputs pulses but the reading is inconsistent — what could cause this?

Inconsistent flow readings commonly result from: (1) air bubbles in the liquid line — the rotor spins differently through air than liquid, causing erratic pulse counts; purge all air from the system, (2) pulsating flow from a diaphragm or peristaltic pump — use a pulse dampener or smooth the readings with a moving average filter in software, (3) electrical noise coupling onto the signal wire — use shielded cable with the shield grounded at the controller end only, keep signal wires away from motor and pump power cables, and add a small capacitor (0.1uF) between OUT and GND to filter high-frequency noise.

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