ZJ-B7 Brass Hall-Effect Water Flow Sensor — G1/2" for Arduino, ESP32 & Raspberry Pi
R225.22
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ZJ-B7 Brass Hall-Effect Water Flow Sensor — G1/2" for Arduino, ESP32 & Raspberry Pi
Product Details
| Spec | – Value |
|---|---|
| Model | – ZJ-B7 |
| Body Material | – Brass |
| Detection Method | – Hall-Effect (magnetic rotor / impeller) |
| Thread Size | – G1/2" (approx. 20mm OD, standard 4-point interface) |
| Operating Voltage | – 5V–15V DC (minimum startup 4.5V) |
| Flow Rate Range | – 1–25 L/min |
| Output Signal | – NPN open-drain pulse, square wave (~50% duty cycle) |
| Output High Level | – ≥4.7V (at 5V input) |
| Output Low Level | – ≤0.5V |
| Flow Pulse Formula | – F = 11 × Q (F = Hz, Q = L/min, ±3–5% accuracy) |
| Maximum Pressure | – ≤1.75 MPa (≈253 PSI) |
| Maximum Fluid Temp | – 120°C structural / 80°C recommended for electronics |
| Connector | – 3-pin or 4-pin JST-SM |
| Wire Colours | – Red = VCC, Black = GND, Yellow = Signal |
| Compatible With | – Arduino, ESP32, Raspberry Pi, PLC |
| Applications | – Water dispensers, coffee machines, irrigation, purifiers, industrial monitoring |
Handy Tips
- Use the formula to calculate flow rate — The sensor outputs pulses at F = 11 × Q, where F is frequency in Hz and Q is flow rate in litres per minute. Divide your measured pulse frequency by 11 to get flow rate directly, or count total pulses and divide by 11 to calculate total volume passed — no lookup table required.
- Pull-up resistor is mandatory — The yellow signal wire is NPN open-drain and produces no usable signal without a pull-up resistor (typically 10kΩ) between the signal wire and VCC. The majority of erratic or zero readings reported in the field are caused by this single omission.
- Use hardware interrupts for accuracy — Connect the yellow signal wire to a hardware interrupt-capable GPIO pin and count pulses in an ISR (Interrupt Service Routine) rather than polling in your main loop. At maximum flow of 25 L/min the output reaches 275Hz — polling will miss pulses and consistently underreport flow volume.
- Observe the flow direction arrow — The brass body has a unidirectional flow arrow cast directly into it. Fluid must enter the tail side and exit in the arrow direction for the impeller to rotate correctly and generate pulses. Reverse installation gives a zero reading but will not damage the sensor.
- Always install a filter upstream — Fit a screen mesh strainer before the sensor inlet before commissioning. Rust particles, pipe sediment, or organic matter will jam the internal impeller causing inaccurate readings or permanent mechanical failure — particularly important on older copper or galvanised iron installations.
- Keep away from magnetic interference — The internal Hall-effect element is sensitive to strong external magnetic fields. Maintain at least 100mm clearance from high-power transformers, large motors, solenoid valves, and permanent magnet assemblies to avoid signal disruption or drift.
- High temperature caution — The brass body handles fluid temperatures up to 120°C, but the internal Hall-effect electronics perform best below 80°C continuous. For hot water or steam-adjacent applications, insulate the sensor body from ambient heat sources and monitor for signal drift at sustained elevated temperatures.
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