LJ12A3-4-Z/BX NPN Inductive Proximity Sensor

LJ12A3-4-Z/BX is an inductive proximity sensor with an NPN normally open (NO) output, designed for non-contact detection of metal objects. Commonly used in automation systems, CNC machines, and 3D printers.

✅ Main Specifications

• Model: LJ12A3-4-Z/BX
• Sensor Type: Inductive, proximity
• Output Type: NPN, normally open (NO)
• Detection Distance: 4 mm
• Operating Voltage: DC 6–36 V
• Max Output Current: 300 mA
• Response Frequency: ~500 Hz
• Target Material: Metal
• Housing Material: Nickel-plated brass
• Thread Size: M12 x 1
• Length: ~60 mm
• Wiring:
  • Brown: +V (power supply)
  • Blue: GND (ground)
  • Black: Signal (output)
• Operating Temperature: –25 °C to +55 °C
• Protection Rating: IP67

⚙️ Wiring Diagram

    +V (6–36 V DC)
        │
     [Brown]
        │
     ┌────────┐
     │        │
  [Sensor]────[Black]──→ Output signal (connect to controller input, e.g., Arduino)
     │        │
    [Blue]
        │
       GND

Note: This is an NPN sensor, meaning the output goes LOW (connected to GND) when a metal object is detected.

📦 Applications

• ✅ 3D Printers: used as a Z-axis endstop or auto bed leveling probe
• ✅ CNC Machines: detect workpiece position or axis limits
• ✅ Industrial Automation: object counting, conveyor position detection
• ✅ Gate/Door Systems: position monitoring
• ✅ Robotics/Mechatronics: metal object detection and positioning

🧪 Example: Arduino Integration

const int sensorPin = 2;   // Input from black (signal) wire
const int ledPin = 13;     // Arduino onboard LED

void setup() {
  pinMode(sensorPin, INPUT);
  pinMode(ledPin, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  int state = digitalRead(sensorPin);
  if (state == LOW) {  // Metal detected
    digitalWrite(ledPin, HIGH);
    Serial.println("Object detected!");
  } else {
    digitalWrite(ledPin, LOW);
  }
  delay(100);
}

This example turns on the Arduino’s LED when a metal object is detected by the sensor.