Proximity Induction Sensor NPN Normally Open Switch LJ12A3-4-Z/BX

  • Was  RM22.00 
  • RM18.00

  • Product Code: Proximity Sensor LJ12A3-4-Z/BX
  • Availability: In Stock

Inductive proximity sensors are used for non-contact detection of metallic objects. Their operating principle is based on a coil and oscillator that creates an electromagnetic field in the close surroundings of the sensing surface. The presence of a metallic object (actuator) in the operating area causes a dampening of the oscillation amplitude. The rise or fall of such oscillation is identified by a threshold circuit that changes the output of the sensor. The operating distance of the sensor depends on the actuator's shape and size and is strictly linked to the nature of the material:

 Sensitivity when different metals are present. Sn = operating distance.
 Fe37 (Iron)  1 x Sn
 Stainless steel  0.9 x Sn
 Brass - Bronze  0.5 x Sn
 Aluminum  0.4 x Sn
 Copper  0.4 x Sn


  • NPN NO (Normally Open)
  • To detect metal object
  • High precision of repeated location
  • Diversified exterior structures 
  • Wide voltage range
  • With short-circuit protection and inverted connecting protection 
  • Minimize interference by visible light
  • Easy to install



  • Working Voltage: DC 6V - 36V
  • Loaded Current: 300mA
  • Response Frequency: 500Hz
  • Detect Range: 0 - 4mm
  • Switch Appearance Type: Cylinder Type
  • Theory: Induction Sensor
  • Output Pin: NPN 3-wires Normally Open
  • Working Environment Temperature: -25°C ~ + 70°C
  • Wire Length: 1.2meter
  • Protection degree: IP 65
  • Body Material: Alloy & Plastic
  • Sensor: Iron 10.5 x 10.5 x 1mm
  • Dimensions : 2.2 x 6cm
  • Net Weight: 85g


  • Brown - VCC (+)
  • Blue - Ground (-)
  • Black - Trigger Signal


LJ12A3-4-Z Others Version

Current item



NPN Normally Open

PNP Normally Open

NPN Normally Closed



Connect Proximity Sensor NPN to an Arduino   (14core)

The metal proximity sensor will have three color wire. The blue should be in the ground, brown is on +VCC which should be giving to Arduino + 5v VCC and when you take metal near tot the sensor it induces more current which results in higher voltage. In this case you need to open your serial monitor to see the incoming signal from the analog pin then make a threshold to determine if metal is detected or not.

Generally speaking the Iron/Copper or Metal with good magnetic properties will induce more that 1v when brought nearer to the sensor you need to touch the surface it will start detecting from a distance about 3cm.

Arduino Sketch

Metal Detection with 3 wire sensor

float metalDetected;
int monitoring;
int metalDetection = 1;

void setup(){

void loop(){
  monitoring = analogRead(metalDetection);
  metalDetected = (float) monitoring*100/1024.0;
  Serial.print("14CORE METAL DETECTOR TEST");
  Serial.print("Initializing Proximity Sensor");
  Serial.print("Please wait...");
  Serial.print("Metal is Proximited = ");
  if (monitoring > 250)
    Serial.println("Metal is Detected");


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