Objective
The aim of this experiment is to understand the working principles of an inductive proximity sensor, and demonstrate how it can detect metallic objects through changes in the magnetic field caused by inductive reactance.
Materials Needed
- Inductive proximity sensor (e.g., LJ12A3-4-Z/BX or similar)
- Power supply (typically 12V or 24V)
- Multimeter
- Metallic objects for detection (e.g., steel, iron)
- Breadboard and jumper wires
- LED (optional for indication)
- Resistor (appropriate for LED if used)
Theory
An inductive proximity sensor operates by generating a magnetic field using a coil. When a metallic object enters the sensor’s detection range, eddy currents are induced in the object, which changes the inductance of the coil. This change is detected and converted into an output signal indicating the presence of a nearby metallic object.
Inductive sensors are used extensively in automation, industrial applications, and robotics where contactless detection of metal objects is required. They have no moving parts, making them durable and reliable for harsh environments.
Steps
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Set Up the Circuit
Connect the inductive proximity sensor to the power supply according to the datasheet. Typically, the sensor has three wires: brown (VCC), blue (GND), and black (signal output). Connect the brown wire to the positive terminal of the power supply and the blue wire to the ground.
If you’re using an LED to indicate when the sensor is triggered, connect the black wire (output) to one leg of the LED through an appropriate current-limiting resistor (e.g., 220Ω), and connect the other leg of the LED to ground.
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Power On the Sensor
Power on the sensor by supplying the correct voltage (e.g., 12V or 24V). The sensor should now be active and ready to detect metallic objects.
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Test the Sensor Output
Place different metallic objects (e.g., steel, iron) near the sensor and observe the output signal. If you’re using an LED, it should light up when a metallic object is detected. If you're using a multimeter, set it to measure voltage and monitor the voltage level on the output pin (black wire). The voltage should change when a metallic object is detected.
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Measure Detection Range
Move the metallic object closer to and further away from the sensor to observe the detection range. You can measure this range by placing a ruler next to the sensor and noting the distance at which the sensor first detects the object. Repeat this test with different metallic objects to see how material type affects detection.
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Record Results
Document the detection range for different metals and note any differences in sensor behavior based on the material composition of the objects.
Example Data
In a typical experiment using an LJ12A3-4-Z/BX inductive proximity sensor:
- Steel object detection range: 4 mm
- Iron object detection range: 3.5 mm
- Brass object detection range: No detection (inductive sensors are typically used for ferrous materials)
Conclusion
This experiment demonstrates how an inductive proximity sensor can detect the presence of nearby metallic objects through changes in the sensor’s magnetic field. The sensor is particularly effective for detecting ferrous metals such as iron and steel, while non-ferrous metals (e.g., brass) may not be detected, depending on the sensor’s design.
The inductive proximity sensor is ideal for use in industrial environments where durability and contactless detection are required. Its reliable performance makes it a key component in automation and manufacturing systems.