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Operating Voltage : DC 6-24V range within Universal
Output Type : PNP or NPN normally open three-line
Detection object : metal objects

Detection distance : 4 mm
Output Current : 300 mA
Response Frequency : 0.5KH

Working temperature : Temperature range -30 ° - = 60 °, + 23 °,  within+ (-) 15% detection distance
Temperature range : -25℃ to + 60℃ within + (-) 10% detection distance
Dimensions : 12 mm or 18mm screw diameter
Cable length : about 115 cm
Material : Metal

NPN  - Output Logic Low    ,PNP  - Output Logic High

Sensors are epoxy filled for shock and vibration resistance.
Sensors are designed for maximum heat tolerance to survive demanding industrial applications.
Sensors are built with high-quality stainless steel housings for reliable performance.

This metal sensor is INDUCTIVE sensor , which means that it induces current when metal is near to it.
This sensor is a non-contact electronic sensor that is used detect positions of a metal objects.
The sensing sensing range depend on the type of metal being detected. Ferrous Metal, such as iron and steel, allow for a longer sensing range, while nonferrous metal objects such as aluminum, copper, can reduce the sensing range by 60 percent. Since the output of an induction sensor has two possible states, an inductive sensor sometimes referred to as an inductive proximity switch.
This sensor consist an induction loop, electric current generates a magnetic field, which collapses generating a current that falls toward zero from its initial trans when the input electricity stops.
The inductance of the loop changes according to the material inside it and since metals are much more effective conductors that other materials the presence of metal increases the current flowing through the loop. This change can be detected by sensing circuitry which signal pass true to some other device whenever metal is detected.
This device is commonly used in traffic lights, car washes, manufacturing machinery, automated industrial machinery, elevators and building automatons this device is mostly used because can adopt in a rugged and dirt environment.

Connecting to Arduino

The metal proximity sensor has three wires. 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 to 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 code
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(" METAL DETECTOR TEST");
Serial.print("Please wait...");
Serial.print("Metal is Proximited = ");
if (monitoring > 250)
Serial.println("Metal is Detected");

Operating Principle

The sensor incorporates an electromagnetic coil which is used to detect the presence of a conductive metal object. The sensor  ignores the presence of an object if it is not metal.
Inductive proximity sensors are operated using an Eddy Current Killed Oscillator (ECKO) principle. This type of sensor consists of four elements: coil, oscillator, trigger circuit, and an output.
The oscillator is an inductive capacitive tuned circuit that creates a radio frequency. The electromagnetic field produced by the oscillator is emitted from the coil away from the
face of the sensor. The circuit has just enough feedback from the field to keep the oscillator going.

When a metal target enters the field, eddy currents circulate within the target. This causes a load on the sensor, decreasing the amplitude of the electromagnetic field.
As the target approaches the sensor the eddy currents increase, increasing the load on the oscillator and further decreasing the amplitude of the field.
The trigger circuit monitors the oscillator’s amplitude and at a predetermined level switches the output state of the sensor from its normal condition (on or off).
As the target moves away from the sensor, the oscillator’s amplitude increases. At a predetermined level the trigger switches the output state of the sensor
back to its normal condition (on or off).

Output Configurations
Three-wire, DC proximity sensor can either be PNP (sourcing) or NPN (sinking). This refers to the type of transistor used in the output switching of the transistor.

The following drawing illustrates the output stage of a PNP sensor.
The load is connected between the output (A) and the negative side of the power supply (L-).
A PNP transistor switches the load to the positive side of the power supply (L+). When the transistor switches on, a complete path of current flow exists from L- through the load to L+.
This is also referred to as current sourcing since in this configuration conventional current is (+ to -) sourced to the load.
This terminology is often confusing to new users of sensors since electron current flow (-to +) is from the load into the sensor when the PNP transistor turns on.

The following drawing illustrates the output of an NPN sensor. The load is connected between the output (A) and the positive side of the power supply (L+). An NPN transistor switches the load to the negative side of the power supply (L-). This is also referred to as current sinking since the direction of conventional current is into the sensor when the transistor turns on. Again, the flow of electron current is in the opposite direction.

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