LJ18A3-8-Z-BX 8mm Inductive Proximity Sensor
🔧 LJ18A3-8-Z-BX (8mm) Inductive Proximity Sensor — Detailed Explanation
🧠 What is it?
The LJ18A3-8-Z-BX Inductive Proximity Sensor is a non-contact sensor used to detect metal objects without physically touching them.
👉 It is widely used in automation, CNC machines, and robotics as a replacement for mechanical switches.
⚙️ How It Works
This sensor works based on electromagnetic induction:
The sensor generates a high-frequency electromagnetic field
When a metal object comes near:
Eddy currents are induced in the metal
This changes the sensor’s internal signal
The sensor detects this change and switches its output
👉 No physical contact needed → no wear & tear
🔌 Wiring (3-Wire Sensor)
| Wire Color | Function |
|---|---|
| Brown / Red | VCC (+6V to 36V DC) |
| Blue / Green | GND |
| Black / Yellow | Output (Signal) |
🔄 Output Type (Important)
Type: NPN (Normally Open - NO)
Behavior:
No metal → Output HIGH (or floating)
Metal detected → Output LOW (connected to ground)
👉 This is critical when interfacing with Arduino or PLC
📊 Key Specifications
Detection distance: 8 mm
Operating voltage: 6V – 36V DC
Output current: up to 200–300 mA
Type: Inductive (metal only)
Thread size: M18 (18mm diameter)
Protection: IP67 (water/dust resistant)
Response frequency: ~500 Hz
🧠 Important Notes
1. Detects Only Metal
Works with:
Iron
Steel
Aluminum (reduced range)
Does NOT detect:
Plastic
Wood
Glass
2. Sensing Distance
Rated: 8 mm
Real-world:
Iron → full range
Aluminum → less distance
3. Output Voltage Warning ⚠️
Output voltage = supply voltage
If powered with 12V/24V → output is also 12V/24V
👉 You must use a voltage divider for microcontrollers like Arduino (5V/3.3V safe)
🔄 Working Example
Metal Object Approaches
↓
Electromagnetic Field Disturbed
↓
Sensor Detects Change
↓
Output Switches (LOW)
↓
Controller Receives Signal
🚀 Applications
🤖 Robotics (object detection)
🖨️ 3D printers (auto bed leveling / endstop)
🏭 Industrial automation
🔩 CNC machines
🚪 Position sensing (metal parts)
👉 Commonly used as a limit switch replacement
✅ Advantages
No physical contact
Long life (no wear)
Works in dusty/oily environments
Fast switching
⚠️ Limitations
Only detects metal
Requires DC power (6–36V)
Needs level shifting for microcontrollers
Detection distance varies with material
💡 Practical Example (Arduino Use)
Power sensor with 12V
Use voltage divider on output
When metal comes near:
Arduino reads LOW
Trigger event (stop motor, count object, etc.)
🔍 Pro Tip
👉 If you see variants like:
BX → NPN NO (this one)
BY → PNP NO
Choose based on your circuit type (NPN = sinking, PNP = sourcing).
