Metal Detectors • Prepared By: Ravi Kumar (210114014)

NATIONAL INSTITUTE OF TECHNOLOGYTIRUCHIRAPPALLI

• Introduction• Principle of operation• Circuit diagram• BFO detector design• Advantages and Disadvantages of circuit

• Application• Conclusion• Bibliography

TABLE OF CONTENTS

• Metal detector is a device that can detect metal, the basics can make a sound when it is near some metal.• Metal detectors work on the principle of transmitting a magnetic field and

analysing a return signal from the target and environment.• when some metals are coming close to the coil the amplitude of the reflective

pulse is getting little lower and a duration of the pulse a little longer.

• The need for detection is very clear to protect our self from any kind of danger.

INTRODUCTION

• The operation of a metal detector is based on the principle of electromagnetic induction.

• Metal detectors contain one or more inductor coils. When metal is placed in a close proximity to a varying magnetic field (generated by the coil or coils), currents are induced in the metallic part;

• These current are called eddy Currents. The eddy Currents, in turn, induce their own magnetic field ( called eddy field).

• These fields act in such a direction as to oppose that generated by the coils. The resultant field and using a specially designed electronic circuit can indicate the type of material being magnetized.

• Here in our metal detector circuit transistor is used as a colpitts oscillator.• If we increase L1’s inductance it will cause the decrease in frequency and if we

decrease this L1’s inductance it will cause the increase in frequency.

PRINCIPLE OF OPERATION

CIRCUIT DIAGRAM

1) Beat-frequency oscillator (BFO) 2) Pulse induction detector (PI),

3) Very Low Frequency (VLF).

Types of Metal detectors

The basic way the beat frequency oscillator (BFO) works, when a detector coil is above some metal, it will change the frequency in the detector oscillator, which has the detector coil in the frequency dependent circuit. This relative simple metal detector is not a real BFO, but it is the closest group of detectors. When the metal is near the detector coil the signal is send to a timer pin. Internally the calculation is made, and showed on the LED and some different sounds are made.

“BFO” DETCTOR DESIGN

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Advantages- 1) Circuit diagram is very simple.2) We can easily measure the oscillation frequency of this circuit.3) It has some sensitivity through which it can sense the metal easily.

Disadvantages-1) It has less sensitivity. 3) Instead of variable capacitor we cannot use any other capacitor for tuning purposes.

ADVANTAGES AND DISADVANTAGES

Airport and Building SecurityMetal detectors are used for airport and building security to determine whether

guns, knives, or other weapons are being transported onto aircraft or into public buildings.

APPLICATIONs…

• Construction Industry Metal detectors are also used in the construction industry to locate steel reinforcement bars embedded in concrete, and to pinpoint metal pipes and wires in floors and walls. This is useful in avoiding unnecessary damage when replacing plumbing or wiring in a building or house.

• Civil Engineering In Civil Engineering, metal detector are used to locate rebar (strengthen steel used as rod in concrete) .Rebar detectors are less sophisticated. Detectors can only locate metallic objects below the surface.

• Land Mine Detection Land mine detector can sense as little as 0.5 grams of metal. So, now-a-days militaries are using land mine detector to identify the land mine. Military has used metal detector to pinpoint buried land mines since world war1.

• Archaeological exploration,• Geological research &• Item recovery.

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• The equipment is compact, simple in design and can be used practically anywhere needs.

• This circuit may also be constructed by using chip and the chip is CS209A.• • Even the detectors with good coil compensation could not always detect the smaller target

to the required depth in all lanes.

• The metal detector gives a respectable range for beat frequency operation (BFO) up to 90mm.

conclusion

(1)http://www.freesimpleelectroniccircuitdiagram.com(2) http://www.simplemetaldetectorcircuitdiagram.com (3) http://www.wikipedia.com(4) http://slideshare.net

BIBLIOGRAPHY

THANK YOU