Types of metal detectors on the principle of work. Different types of metal detectors and their principle of operation. Scheme, description. Typical metal detector design

Modern metal detectors work on the principle of primer probe electromagnetic radiation. Moreover, the presence of a metallic subject changes this radiation, for example, its frequency. In the simplest metal detectors, only one operating frequency is used. More advanced devices simultaneously operate at several frequencies, and can also switch to work in various modes. The main characteristic of the metal detector is sensitivity. Also, the ability of the device to distinguish the types of metals is also important. Then they are more correct to refer to metal detectors. Several types of metal detectors share:

Simple ground metal detector

Such devices are widely used for the close search of small metal objects on the beach or under the forest addressed. They use one operating frequency (for soil optimally 100 kHz or less). The detection principle is based on the deviation of the frequency of the search generator. As a result, biodins occur - a difference signal that is tracked by the processor. Often such devices do not have the display and only serve sound signal. Sometimes they are built into the metal type analyzer: black / colored. Sensitivity allows you to detect a coin by 3 - 5 cm from the search coil. Sewer hatch - 60 cm. Metal type analyzer is often absent. However, it can be implemented with an indication on a numeric scale.

Metal detectors with one working frequency can be made by lovers. Simple metal detectors Recommended beginners. They are in the lowest price category of search devices.

Semi-professional metal detectors

From simple differ from a multi-frequency range. If in the usual metal detector only one sensing frequency emitter, then there may be several semi-professional. The same discovered metal object changes the field of several generators to varying degrees. Thus, it is possible to increase their sensitivity, especially to small objects. The coin they confidently detect from 10 to 15 cm.

The cost of semi-flowing metal detectors is two - three times taller than simple. They are recommended to those who have experience in operation of simple devices, see the options for such devices on the site - http://pro-spec.ru/catalog/sredstva-i-sistemy-bezopasnosti/poiskovozopasnosti/poiskovo-dosmotrovoe-oborudovanie/metallodetektory-i-metalloiskateli / gruntovye-metalloiskateli.

Professional metal detectors

Always work according to a multi-frequency principle. Have multiple switching modes. (At the same time, various sensing frequency combinations are included). This makes it possible to judge the contours of the found item. Calculate its mass and depth of location. Metal detector adjusts to the properties of the soil. The element base is made completely digital on microprocessors. Almost always there is a display and all other types of indication.

The operating frequency is selected depending on the nature of the search. For small items use high frequency. More depth search lead on more low frequenciesoh. The most advanced devices allow you to detect a coin from 20 - 25 cm. The lid from the hatch is 1 m. They simultaneously use 28 operating frequencies. For processing such a number of responses, a rather powerful microprocessor is required.

Sounding frequencies detect a subject according to various principles: beating (resonance breakdown), the induction balance of two generators and others. Especially promising technology using low search frequencies. They are known to have the highest permeability. Another direction is to register the change in phase characteristics of the search generator radiation.

The main drawback of professional metal detectors is a high price. Device S. good characteristics It costs almost as much as the car is economy class. Also, the instruments are required to adjust the soil, which is difficult for beginners.

Metal detectors for gold

Usually a specialized version of the professional metal detector is. Price category They have the same. This type It is recommended to search for items made of gold and non-ferrous metals in highly particulated metal household trash.

Depth metal detector

If all the previously discussed metal detectors work on the principle of change of sensing frequency (induction metal detectors), the depth devices have the principle of operation similar to the echolocator. The device uses an electromagnetic wave generator of sufficient power to test 5 - 6 meters to depth. The signal is perceived by a sensitive receiver. Such metal detectors allow to detect massive metal objects at the limiting depth. However, small objects, even if they are almost on the surface, do not fall into the field of view. Typically, the criterion of the minimum dimension of the object must be at least 10 x 10 cm.

In order to save battery energy and improve sensing efficiency, pulse generators are used.

Such devices are quite rarely used in amateur practice, as there is no need to look for large items at great depths. Basically, they enjoy to search for pipelines, cables and lifting facilities. Sometimes they are needed in archeology.

Metal detectors are several types:

Initial-level detectors to search for ground
Semi-professional
Professional primer detectors.
Special devices for the detection of gold nuggets
Metal detectors for searching under water.
Deep Metal Detectors
Framework devices (arched), stationary metal detectors
Hand metal detector for inspection
Pinpo channels (devices for accurate object detection)

Ground-level ground metal dealers

The cost of such devices varies in the range of $ 100-500. Popularity is mostly popular with beginner seekers, since it is easy to use, have a minimum set of functions for search. To search for goals, one, sometimes two frequencies is used. They have a function of discrimination, in some devices there is a definition of the depth of the object. The available depth of metal detectors of this species is small, depends on the properties of the soil: minor coins 15-17 centuries. ("Scalys) - 3-5 cm, coins with a nominal five kopecks of Catherine II - 15-20 cm, objects with an ax - 20-30 cm, the lid from the hatch can be found at a depth of 70 cm.

There are masters who collect metal detectors themselves according to the schemes from books. However, the quality of such devices is not too high. At home, it is almost impossible to rebuild the metal detector from all sorts of electromagnetic influence, even having a special equipment at hand. The background from metal objects located around forms a variety of interference. As a result, when used in the field where there is no interfering background, such a metal detector begins to work incorrectly.

Alone, of course, you can make it possible to make the easiest metal detector with the sound indicator. However, due to its devices, a large piece of ferrous metal will give the same signal as "color" items. Disrupt the device from this interference without having a gadograph is extremely difficult.

The leader among initial level devices is due to a democratic price. good quality and indicators (as well as the possibilities of upgrading coils).

Semi-professional metal detectors

There are such devices about $ 500-800. These metalpeakers will use search engines with experience. The work of the metal detectors of this species is based on the use of several working frequencies at once. Such devices provide sound and visual information. Visual data is shown on the display where you can see the VDI subject found. If the VDI value is in the zone positive, that is, it goes with the "+" sign, then the device found from the non-ferrous metal, if the value is "-", then the found object from ferrous metal. Based on the value of VDI, with 70% probability, it is possible to find out which item from the non-ferrous metal is found.

Copper, and always silver coins create a VDI value close to the maximum mark. In metal detectors of different firms, the maximum and minimum values \u200b\u200bof VDI are different. There are devices with a scale -10 - +10, and there is a scale -30- + 50, etc. With this, these instruments are considered professional. Maximum possible depth efficient work Such instruments: "Scales" - 5-15cm, five kopecks of Catherine II - 25-30CM, items with an ax - 40-50 cm, covers from hatch - 100-150 cm.

P roffessionalmetal detectors

Such instruments can cost from $ 800 and up to several thousand. The high price of such metal detectors is explained by the fact that these devices are multifunction and designed for professional treasures. The devices of this type of multi-voiced discrimination, multiple frequencies for search are used, there is a whole set of manual, as well as automatic settings. Professional metal detectors can reveal under the ground "color" item located next to the "black" with a probability of about 80%. This greatly simplifies the search in the territories highly contaminated with metal garbage. If the target is detected, professional metal detectors issue a visual, digital and beep. After analyzing the received data, an experienced search engine can immediately determine what detected the device at what depth is the object, its dimensions.

In professional metal detectors, the signal is processed by a microprocessor.
Professional experience workers use complex multifunctional devices that can detect all the "color" items on the territory under study. The depth of detecting devices of this type: flakes - 15-25 cm, coins with a nominal five kopecks of Catherine II - 30-45 cm, the items with an ax - 50-80 cm, covers from the hatch can be found at a depth of 150-200 cm.

Effective search for various metal objects underground or hidden by other structures is of interest not only for clad hunters, but also for builders engaged in laying new and restoring damaged underground communications. For this, efficient devices are used - metal detectors. This article discusses the most popular models of metal detectors, the main characteristics and prices for them.

Garrett Ace 250.

It is characterized by simplicity of its use and high search accuracy, therefore it is often recommended for applications who do not have sufficient experience and qualifications. The Garrett ACE 250 metal detector does not have an inductance coil, which does not prevent him from being very effective. A double concentric coil is used as an indicator, which has a positive effect on the price of the device. Before testing, the entire scrap metal is carefully closed into the ground with non-metallic objects, and was located in the uncomfortable places to determine the places at a depth of at least 50 mm. Under such conditions, the percentage of items detected using the metal detector under consideration reached 98%.

Characteristic feature Garrett ACE 250 is a high accuracy of fixing the location, as well as a metal class. The device recognizes about 67% of non-ferrous metals, which is important for subsequent identification of objects. The accuracy of the depth indicator is about 56%, while the device is mistaken mainly towards the increase, especially if several heterogeneous metals are hidden in one place (for example, copper-nickel coins, covered with shallow steel grid).

Metal detector Garrett ACE 250 is easy to use. The device is equipped with an LCD display, on the screen of which there is a movable arrow. When the metal is detected, the arrow indicates its approximate type, and on the histogram located on the right side of the screen, you can set an exemplary depth of the detected item. The sequence of action is that the primary sound is heard first, which is enhanced by approaching the device to the metal. The limiting depth of determination by this metal detector is declared by the manufacturer within 200 ... 220 mm. Lack of instrument - a two-year warranty.

Fisher F4.

Structurally, the device from Fisher is considered constructively the most difficult, and, consequently, the most expensive. The metal detector is equipped with a double electromagnetic coil, which expands the technical capabilities of the device. Nevertheless, the percentage of object detection is only 72%, with the accuracy of fixing the location of the metal to 54%, and in depth - up to 35%. Such unrelated results are associated with relative complexity. pre-tuning The device that for inexperienced users is quite laborious. Nevertheless, with sufficient practice with the device, most difficulties disappear.

As in the previous case, there is a significant variation in the testimony of the location of the metal subject in depth: the actual testimony of the device is oversold in 2 ... 3 times. Such a feature of Fisher F4 is explained by the design and principle of action electromagnetic coil. It is great for differentiation between two closely located objects due to its wedge-shaped magnetic field, but to obtain accurate readings, a more professional touch of the search tip to the surface of the soil or material in which the object is located.

Unlike Garrett ACE 250 Metal Detector in the Fisher F4 device there is additional option Double control, which allows you to avoid a false signal. LCD settings can be constantly updated depending on the purpose of the search. In addition, the indicator of the address under consideration takes into account the unevenness of the soil in the search zone, which increases the accuracy of determining the metal hidden in the land. A qualitatively balanced hand can even take into account the character of the soil, which also contributes to the high accuracy of the search results. The coil in Fisher F4 has no concentric, and oval contour, and this increases the area of \u200b\u200bthe survey area.

Bounty Hunter Quick Draw Pro

According to test results, it is recognized as one of the best metal detectors, since it allows you to establish the fact of the presence of a metal in 86% of cases. At the same time, in 39% with the help of this device, you can accurately set the generation of metal, and its approximate dimensions.

Bounty Hunter Quick Draw Pro, as well as Fisher F4, is equipped with an elliptic concentric coil, which has an ellipse form. A convenient LCD screen shows target identifiers in the form and numbers, and conditional signs. The monitor interface is simple and easy to use, it is also equipped with quite advanced user functions, and this reduces the total number of metals detection attempts. When testing, the design was recognized as one of the best for the purposes of both the identification of the metal and to determine the depth of its occurrence. For the device of this type, a minimum variation of the show and actual depth of metal location is observed. At the same time, at a considerable depth (more than 250 mm), the accuracy of the instrument readings drops sharply.

The LCD screen has two target identifiers, which consistently indicate the type of metal and on the approximate depth of its occurrence. The testimony is purely qualitative, and do not show the distance, therefore the use of the Bounty Hunter Quick Draw Pro metal detector can be justified only for an approximate estimate. Warranty period The use of the device is five years.

The device is characterized by a good accuracy of fixing the result, which is important with difficulty search conditions. Minelab specializes in the development and production of metal bes, which can work under water, in the demining processes, so the Minelab X-Terra 305 metal detector is distinguished by the reliability of its scheme. At a high price for its products, its advantage of the art is considered almost complete insensitivity to all external search conditions. The fact of the presence of a metal under the ground is set in 90% of cases, the type of metal is 62%, the depth of occurrence is 57%.

The biggest problem with X-Terra 305 is the simplicity of its use. The device does not contain graphic identifiers, and, instead, the number appears on the screen that corresponds to the conductivity of the detected metal. Further, by this parameter, the user is proposed to determine the size and type of item. This process requires certain experience and qualifications. The Minelab X-Terra 305 metal detector is equipped with a circular concentric coil, and has a discrete tone identification signal, calculated on 12 sound shades (unlike the remaining technology, the tone of which determines only three levels of tone).

Metal detector "Pirate"

Domestic development designed to detect hidden metal of various configurations and sizes. The metal detector uses a combined magnetic inductive principle of recognition. The generator creates an alternating electromagnetic field in the coil, which interacts with a conductive object in the ground or inside another design. In the metal guys its alternating magnetic field, which is captured by the audio indicator.

Metal detector "Pirate" has no LCD display, so it is not able to determine the type of metal. His advantage is accessibility, simplicity of circulation and reliability. In addition, "pirate" is one of the few samples of the represented equipment that is capable of recognizing metal items at relatively long distances - up to 450 ... 500 mm, while the recognition time does not exceed 20 s.

Comparison of metal detectors, prices and characteristics:

"Pirate" - up to 5000 rubles.
Fisher F4 - up to 23,000 rubles.
Garrett Ace 250 - up to 15,000 rubles.
Bounty Hunter Quick Draw Pro - up to 16000 rubles.
Minelab X-Terra 305 - up to 14,000 rubles.

From the magnitude of the electrical resistance of the coil with the wire depends on the attenuation time of this electrical pulse. The complete absence of resistance, or opposite the very high value will make the pulse fluctuate. It looks like throwing a rubber ball on a very hard surface, on which he bounces many times before calming finally. With a sufficient electrical resistance, the attenuation time of the impulse is shortened and the reflected impulse "smoothes". This is similar to throwing the rubber ball in the pillow. The coil of the detector with pulse induction says that it is critically plugged when the reflected impulse quickly fades up to zero without hesitation. Excessive or insufficient suppression will make instability to work and mask signals from well-conductive metals such as gold and reduce detection depth. When the metal object is close to the search coil, it poins some part of the pulse energy, which leads to tightening the damping process of this pulse to zero. The change in the width of the reflected pulse is measured and signals the presence of a metal object. In order to highlight the signal of such an object, we must measure the part of the pulse where it falls to zero (tail). At the inlet of the coil receiver, there is a resistor and a limiting diode scheme, which clip the input pulse voltage to 1 volt in order not to overload the input of the circuit. The signal in the receiver consists of a pulse from the transmitter and the reflected impulse. Usually the receiver amplification is 60 decibels. This means that the area where the reflected signal falls to zero can be increased 1000 times.

Gate scheme.
Stressed signal The receiver enters the circuit that measures the voltage drop to zero. The reflected pulse is converted into a sequence of pulses. When the metal object is approaching the coil, the shape of the transmitter pulse will not change, but the reflected impulse will become a little longer. The increase in the duration of the "tail" of the pulse is only a few millionth fractions of a second (microsecond) sufficient to determine the presence of a metal under the coil. The impulses (gates) are superimposed on this reflected pulse, synchronized with the start of the transmitter pulse and the output electronic circuit A series of gates is obtained, the number of which is proportional to the length of the "tail" of the pulse. The most sensitive impulse is located as close as possible by the end of the tail where the voltage is completely close to zero. This is usually a temporary area of \u200b\u200babout 20 microseconds after turning off the transmitter and the beginning of the reflected impulse. Unfortunately, this is also the area where the operation of a metal detector with pulsed induction becomes unstable. For this reason, most models of metal detectors with pulsed induction continue to produce gating pulses of another 30-40 microseconds after complete attenuation of the reflected impulse.

Integrator.
Next, the stroved signal must be converted to voltage direct current. This is done by the circuit - an integrator that averages the pulse sequence and converts them to the appropriate voltage, which increases when the object is close to the frame and decreases when the object is removed. The voltage is further enhanced and controls the audio control circuit.
The period of time during which the integrator collects incoming gates is called integrator time constant - (PVI). It determines how quickly the metal detector reacts to a metal object. Long-term PVI (order of seconds) has an advantage in reducing noise and simplify the setting of the detector, but it requires a very slow movement of the search coil, since the object can be missed by quick movement. A short PVI (about the tenths of a second) is faster reacting to the goal, which allows you to quickly move the coil, but the noise immunity and stability of work deteriorate.

Discrimination (recognition).
The metal detector with impulse induction is not capable of the same degree of discrimination as the SNC devices. Due to the measurement of an increasing period of time between the end of the transmitter pulse and a point in which the reflected pulse is absorbed to zero (delay time), objects consisting of certain metals can be filtered. In the first place for this characteristic there is an aluminum foil, then minor nickel coins, buttons and gold. Some coins can be calculated on a very long pulse tail, but iron is thus not determined.
A lot of attempts have been made to create a metal detector with a pulsed induction, capable of determining the iron, but all these attempts had a very limited success. Although iron and gives a long "tail", silver and copper have the same characteristics. Such a long delay does not affect the determination of the depth of the occurrence. The content of minerals in the soil will also extend the reflected impulse, changing the point in which the object is determined or rejected. If the integrator time constant is configured so that the gold ring is not determined in the air, the same ring can "light up" in the soil saturated with the salts. Thus, the soil saturated with salts changes everything to the delay time and the electoral ability of a metal detector with pulsed induction.

Adjusting from the Earth.
Definition from the Earth is very critical for SNC devices, but not for metal detectors with impulse induction. On average, the soil does not spare any significant amount of energy from the search coil and usually does not give any signal. Soil will not mask the signal from the object and even on the contrary, the soil mineralization slightly lengthens the signal in proportion to the increase in the depth of the object. In relation to MD with impulse induction, the term "automatic detuning from the Earth" is often used (Automatic Ground Balance), they usually do not react to excessive soil mineralization, do not require an external adjustment for different types Soil. An exception is one of the most unpleasant components of the soil - magnetite (Fe3O4), or magnetic iron oxide. It causes overloading of the input coils of the SCH type detectors, strongly reducing their sensitivity, the metal detectors with pulse induction will work, but can show false goals if you bring the coil too close to the ground. You can minimize this harmful effect, extending the delay time between the end of the transmitter pulse and the beginning of the gating. Configuring this time constant can be disturbed from the interference caused by the mineralization of the soil.

Automatic and manual adjustment.
Most of the metal detectors with pulse induction have manual setting. This means that the operator must turn the setup until the click or itching sound in the headphones is heard. If the soil in the search area varies from and to neutral sand or from dry soil to sea water, in this case the adjustment is necessary. If this is not done, you can lose in the depths of detection and skip some objects. Manual setting is very difficult when using a short time integrator time (PVI). Therefore, many devices with manual setting Have a long PVI and require slow search coil moving.
There are no problems using MD with pulse induction for underwater search, since the search coil is not moved quickly. When used in the surf band, the coil will be, it will be in water, then under water, and under such conditions, the use of manual adjustment devices can be very disappointed, because they will have to continuously adjust the trigger threshold. Some operators in this case immediately set up the device just below the trigger threshold. But this can lead to a decrease in detection depth, when the soil characteristics change.
Automatic setting The SAT-SELF Adjusting Threshold) gives a significant advantage when searching for and over salty water or on the soil with a high salt content. It allows you to use the detector on the maximum sensitivity without constant adjustment. This improves the stability of work, noise immunity and allows you to use a greater gain. MD with pulse induction does not emit strong negative signals as SNC devices. Therefore, they are not excavated by pits with minerals. You must continuously move the coil of the metal detector equipped with the auto-adjustment system, if you stop the coil, the setting is knocked down or the device stops reacting.

Audio control.
Schemes of sound alarm systems with pulse induction are disintegrated into two categories: with a changing frequency and changing volume. Schemes with a variable frequency, built on the basis of a voltage controlled generator, are good for registration of small items, since the change in frequency is easier to catch on a rumor than change in volume, especially with a small volume level, especially for instruments with manual adjustment of the threshold. However, the sound like a fire siren quickly tires, and some people are not able to distinguish high tones. One of the good options is a mechanical vibration that was originally used for underwater vehicles. Such a device makes sounds and vibration that increases to buzz when the object is detected. Signals of this mechanical device Easy to recognize and they do not muffle the air supply system.
Many people prefer a more traditional sound tone with increasing volume, not frequencies. Such sound control systems work well in devices, with a rapid movement of the frame, those in devices with automatic adjustment, and they sound like instruments with SNC.

Conclusions on MD with impulse induction.
These are specialized tools. They are little suitable for searching coins in urban conditions, since they cannot filter the iron and ferro-containing garbage. They can be used for archaeological searches in the countryside, where there is no iron garbage in large quantities, the search for gold nuggets and to search at the maximum depth in extreme conditions, such as the coast of the seas or the place where the land is strongly mineralized. Such metal detectors show excellent results in such conditions and in general are comparable to SNC devices, especially by their abilities to be removed from such soils and "punch" them to maximize depth.

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Introduction

In the modern world, security plays a huge role in all areas of activity, whether economy or politics, science or military industry. In the conditions of the actions of criminal and radical groups, intensifying terrorist activities in the territory of the Russian Federation, the relevance of the detection of firearms, garnet, cold weapons disguised under clothing or in baggage is determined by the need to solve the security task of the population. Quite often, we are watching a picture of the search by employees of the security authorities of citizens of their things to search for items that are a source of increased danger to the public. For inspection, various technical devices. One of the most common intended to carry out inspections in the field of mass accumulation of people is passing metal detectors.

The purpose of the abstract - familiarization with the description, common characteristics, device and principles of work of metal detectors as well as the scope of their application.

1. General

The first metal detector was invented at the beginning of the 20th century in the United States, these devices were too high and uncomfortable for mass use, but at the beginning of the 60s more compact models were developed. Initially, the device was developed to prevent theft of metal parts from the plants, but subsequently, the benefits of metal detectors were seen in other industries, both industrial and military.

1.1 Terms and Definitions

Metal detector (metal engineer) - a technical means of detecting forbidden to unauthorized rig for metal objects hidden under the clothing of people or in their hand-made bags.

Metal detector (metal detector) is a device that allows you to register forbidden and dangerous metal objects in the non-conductive medium.

The detection control zone (hereinafter referred to as the zone, characterized by a height, width and depth of the free space, in which the metal detector is detected by the detection of a given object or the selective non-peculiar to the specified item.

The detection object is metal-containing items prohibited to unauthorized rig.

OP - search object.

PPP is a subject of personal use.

Selective detection - the ability to establish the fact of the presence of OP on the background of the simultaneous presence of PLP and not give false alarms from the PLP in the absence of search objects.

The response signal is the reaction of the metal detector of the light and / or sound indication (and / or as an image on the display screen) on the application of the detection object in its KZ.

The false response is the reaction of the metal detector of the response signal in the absence of an object of detection object in its KZ or when an admissible subject of non-yield is introduced into its shortcut.

1.2 Scope

Metal detectors are used in the following areas:

Warfare;

Control systems;

Security services;

Defectoscopy;

Search meteorites;

Poppers and search for relics, archeology.

Search for minerals;

Food sphere;

Building;

1.3 Purpose

Metal detectors are induction-electronic devices designed to detect metal items in various environments: water, soil, wood, etc.

So in the military industry, metal detectors (ministraders) are intended mainly to search for min.

In the field of security and controlling access control, metal detectors play the role of a detecting weapon transfer device, explosive devices and prohibited objects by intruders and terrorists, as well as to control the flow of people, for example, in the buildings of banks, airports, metro and railway stations;

In the food industry, metal detectors are used as a means of detecting unwanted items, randomly or deliberately falling into the food product;

The use of metal detectors to search for minerals, valuable non-ferrous metals, important historical relics, valuable treasures, etc is widespread.;

In the field of construction, the metal detector performs the same search role. With it, it is detected by the detection of hidden cables in the ground or walls in the reconstruction of buildings.

2. Classification of metal detectors

According to GOST R 53705-2009, metal detectors are classified by:

Functional purpose;

Conditions of application;

Designs;

The dimensions of the control zone.

According to the functional purpose, metal detectors are divided into intended for inspection:

Man;

Hand luggage.

Under the conditions of application, metal detectors are divided into both stationary and portable / mobile.

By constructive execution, metal detectors are divided into:

Arched;

Rack (with mechanically non-associated detection panels made in the form of vertical racks or columns);

Having one pass through the control zone;

Having two passages and more through the control zone.

By the size of the control zone, metal detectors for the inspection of a person are divided into:

With a complete control zone;

With limited control zone.

Classification of metal detectors of other free sources

Soil: Designed to scan the soil for the presence of metal-containing items, scanning walls of buildings;

Arched metal detector (happening stationary and mobile): Designed to provide public order (scans people);

Compact manual metal detector: Used to check people and their hand baggage or luggage.

The soil metal detector (as the most popular among the treasures) in turn can be divided into budget value into three groups:

Budget models: possess minimum adjustments and settings. Used newcomers for learning and to search for any metal objects.

Middle class: equipped with an electronic unit with a wide range of settings and advanced programs. Such metal detectors acquire already advanced operators, professionals and amateurs in order to find interesting items at depth.

Professional equipment: It is intended for use on professional purposes, because a set of computer functions can hit the imagination of a novice and scare away an amateur. The price of such devices from $ 1000 to infinity.

3. Device and principles of metal detector

3.1 Metal detector device

Currently, there are many different types of metal detectors: from large and inappropriate, to relatively small and barely noticeable. On the example of a compact manual and soil metal detectors, consider them "architecture".

Compact manual metal detector.

Figure 3.1 - Manual metal detector device

Standard soil metal detector

Figure 3.2 - The structure of the ground metal detector

1. "Coil". This part of the instrument includes two antennas (transmitter and signal receiver), structurally connected in one case. Usually the coil is a round or elliptical lattice design made of plastic. The signal from the coil to the instrument control unit is transmitted through the cable, made at the same time with the coil. At the end of the cable there is a threaded electrical connector for connecting to the control unit. The coil is mounted with screws to the bottom of the device with the help of lylish on the housing. The coil and its connection with the cable are performed hermetic to avoid moisture and dirt on the instrument antenna. There is a leakage cable connection with a control unit (except appliances for underwater, less often - for beach search). Be careful when working in heavy rain or on the beach! Almost each device allows you to replace the coil, which allows the operator to adapt to specific search conditions. Differences in coil species We will consider in the article "Types of Search Coils".

2. Lower rod. The rod is a hollow plastic or metal tube. The Lower MD bar is designed to fix the search coil and allows the user to adjust the coil angle for more accurate wiring over the ground. In most instrument models, the rod has a device for adjusting the height of the device and telescopic connection with the next bar.

3. Middle rod. For example, in the metal detector Garrett ACE 250, the middle rod is an intermediate link between the bottom bar, which is located search coil, and the top bar with the control unit. There are also MD designs that consist of two rods. The middle rod also has fixtures for fastening and changing the height of the instrument.

4. Upper rod. Usually has an S-shaped form for the convenience of working with the device. On the top of the device, the device is usually located - armrest, control unit, handle.

5. Armrest. Used to stop the elbow of the user. It is usually performed from plastic and has a tape with "velcro" to fix the elbow joint during a long work. Also the armrest is based on the land in order to avoid dirt from digging finds.

6. Control unit. The control unit is designed for processing information coming from the coil, converting it to a user-friendly view, as well as to configure the instrument modes. The control unit can be both removable and strictly fixed to the device. A cable from the search coil is connected to the control unit using a quick-release threaded connector. In some (especially professional requiring high energy for nutrition), the battery compartment (6a) can be placed separately from the control unit. The control unit is considered in more detail in the article "Getting Started".

7. Handle. Located on the upper rod, it is performed from porous material and serves to conveniently hold the device to the user.

3.2 Principles of work

On the principle of operation, the following types of metal detectors are distinguished:

Devices with a dependent generator (BFO - emitting generator detector);

Metal detectors operating on the induction balance (balanced induction);

Metal detectors with a pulse-inductive search method;

Metal detectors working on the principle of disorder;

Magnetometers;

Reception-transmission type devices;

Devices - frequency meters;

Induction metal detectors;

Devices fixing the change in the voluntary of the oscillatory circuit part in the LC generator;

Pulse metal detectors.

Device-transmission type devices. They are based on two inductance coils - a receiving and transmitting, located so that the signal emitted by the transmitting coil does not succeed in the receiving coil. When a metal object appears near the device, the signal of the transmitting coil reserves them in all directions and enters the receiving coil, it is enhanced and fed to the indication unit.

The frequency metering instruments is based on the LC generator. When the metal approaches the contour, its frequency changes. This change is fixed by various methods:

Mixing the frequency of the generator with the reference and measurement of the frequency of the beats;

Signal supply from the generator to the FAPC system and measurement of the voltage in the feedback circuit.

Induction metal detectors are a type of receiving-transmission type devices, but unlike the latter, not two, but only one coil, which is simultaneously transmitting and receiving.

When the metallic object approaches the coil, the voltage of the circuit decreases and the oscillation amplitude at the output of the LC generator is also reduced.

The principle of operation of impulse metal detectors is based on excitation in the zone of the metal object of pulsed vortex currents and measuring the secondary electromagnetic field that these currents lead. In this case, the exciting signal is transmitted to the sensor coil is not constantly, but periodically, in the form of pulses. In conducting objects, fading vortex currents are fed, which excite the decaying electromagnetic field. The field, in turn, leads the flowing current in the sensor coil. Accordingly, depending on the conducting properties and size of the object, the signal changes its shape and duration.

4. Industrial Samples

Arched metal detector general purpose Ceia Classic

Classic is a stationary arched metal detector designed for use in public institutions such as airports, schools, hotels, entertainment centers and government agencies.

Metal detector Classic allows you to ensure the maximum level of security in combination with high performance efficiency.

The use of advanced technologies makes it possible to achieve high speed of people pass through a metal detector with a minimum number of false alarms from personal items, such as coins, keys and belt buckles.

Characteristics.

Compliance with the requirements of all international security standards in combination with high efficiency;

Ease and speed installation;

Ease of operation;

Lack of requirements for special maintenance;

Passage width up to 820 mm;

The presence of a special moisture-proof version for installation outdoors;

Figure 4.1 - Arched Metal Detector Ceia Classic

Features.

Digital sensitivity adjustment in a wide range;

Microprocessor management of all functions;

Automatic synchronization between two or more metal detectors installed at a distance of up to 5 cm from each other, without the use of additional cables;

High degree of integration and reliability of electronic components;

The electronic unit is integrated directly into the design of the metal detector antenna;

It does not require initial and periodic calibration;

Easy to maintain and repair;

Color: light gray RAL 7040;

Installation data.

Power supply: ~ 230 V +10% / - 20%, 45 ... 60 Hz, Max. 20a.

Range of operating temperatures: -20 ° С ... + 70 ° С.

Storage temperature: from -35 ° C to + 70 ° C.

Relative humidity: from 0 to 95% (without condensation).

Anxiety alarm modes.

Visual alarm:

High-contrast display;

Green and red zone to display the signal level, proportional mass of metals;

Conclusion

metal detector Induction dangerous

As part of this abstract, a goal was to get acquainted with theoretical information, characteristics, descriptions, classifications and functions of metal detectors; Get acquainted with the device of metal detectors and analyze the principles of their action. This goal is achieved.

Studies in the work on this abstract showed how many areas of activity covers metal detectors and how important they are. Also, analysis of the mechanisms of operation of these devices showed that they are an important element in creating access control systems.

Bibliography

1. GOST R 53705-2009 Complex security systems. Metal manufacturers stationary for premises.

2. Zaitsev A.P., Suspendanov A.A. Technical protection of information. Studies. benefit. - M.: Hotline Telecom, 2007

3. Scherbakov G.N. Detection of hidden objects - for humanitarian demining, forensic, archeology, construction and struggle against terrorism. - M.: Arbat-Inform, 2004

4. Koryakin-Chernyak S.L., Familyan A.P. Metal detectors do it yourself.: NIT, 2009

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