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Metal detector circuit using inductive proximity sensor

Metal detectors are utilized to dig or locate metal objects on a variety of surfaces. Popularly, this form of the circuit makes use of inductors and their inductive ability to detect metal. In this circuit, however, we use a specific proximity inductive sensor to identify ferrous items and a buzzer to sound an alarm when a ferrous object is detected.

What is an Inductive Proximity Sensor?

An Inductive proximity sensor can detect metal targets approaching the sensor, without physical contact with the target. Inductive Proximity Sensors are classified into the following three types based on the operating principle: the high-frequency oscillation type using electromagnetic induction, the magnetic type using a magnet, and the capacitance type using the change in capacitance.

This sensor operates under the electrical principle of inductance where a fluctuating current induces an electromotive force(EMF) in a target object. These non-contact proximity sensors detect ferrous targets, preferably mild steel with a thickness of less than one mm. 

Working of metal detector circuit:

Working of an inductive sensor:

We will utilize a proximity inductive sensor PL-05P for this circuit. Within its 5mm range, this inductive sensor can detect metals. It has an input voltage range between 10 and 30V. The internal oscillator of the inductive sensor generates a sequence of pulses. These pulses will generate a magnetic field surrounding their surface that reaches as far as their detection range. Therefore, when a metal object enters the detecting area (i.e., within its 5mm range), the magnetic field will be disrupted. Depending on this, the output state will change.

This Inductive sensor is available in multiple variations. As depicted in the diagram above, we choose the component with PNP output type. When there are no metal objects within the sensor’s range of detection, the base voltage of the transistor will be greater than 0.7V. This causes the Black wire to output 0 volts ( output ).

When a metal object reaches the sensor range, however, the base voltage will decrease by 0.7 Volts. This activates the transistor, and 11.3V (12V) will be displayed over the Black wire. We will use the output voltage from the black wire in conjunction with a comparator to create a metal detector.

Buzzer:

The output of the inductive sensor may drive up to 200mA of current. In our circuit, the sounding element is a 5-12V buzzer. This buzzer’s maximum current consumption is approximately 30 mA, which is well within the capabilities of our inductive sensor.

When the sensor’s output is high, the buzzer is activated and an alarm is raised for detection. When there is nothing inside the sensor’s range, the sensor’s output will be low, and the buzzer will be deactivated.

Current consumption:

The sensor consumes approximately 2.2mA whereas the buzzer requires approximately 30mA. It is therefore safe to assume that this circuit draws around 35 mA of current when operational. Therefore, it is mobile and can be powered by a 12V battery.

Conclusion

Hope this blog helps you to understand how to design a Metal detector circuit using an inductive proximity sensor. We, MATHA ELECTRONICS  will come back with more informative blogs.

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