Metal detector in an educational institution. Metal detectors. Issues of regulation of requirements Are metal detectors classified as special means

Berezansky David Pavlovich, candidate of technical sciences

Metal detectors - screening devices.
Questions of regulation of requirements.

The article is reprinted from the magazine "Special Technique" No. 2, 1998.

For a wide range of readers of the journal, a number of problems are proposed for discussion on the regulation of requirements for metal detectors, as one of the important types of inspection equipment. In conditions when in the Russian Federation there is still no State Standard regulating the regulatory requirements for metal detectors as screening devices, the issues outlined in the article are relevant.

An important role in organizing the protection of buildings, structures, monitoring and regulating the movement of people is played by metal detectors - detectors of objects prohibited from being carried to these objects.

According to the classification adopted today, metal detectors are screening devices that are part of integrated security equipment or used autonomously. Structurally, such metal detectors can be built into the barrier devices of access control and management systems, autonomous stationary or autonomous portable.

Items prohibited from being carried by visitors to protected facilities and detected by a metal detector (hereinafter OP - search objects) primarily include:

Firearms;
- hand grenades;
- knives,

The functional purpose of metal detectors in the general case is quite wide: from the search for non-ferrous metals weighing ~ 1 g to the detection of objects made of ferromagnetic metals, significantly exceeding the OD in mass. The tasks that metal detectors solve in protection and security systems are narrower and have their own characteristics that determine the specific requirements for such devices. These include:

Reliable OP detection;
- ensuring selectivity in relation to metal objects allowed to be carried to a protected facility;
- ensuring noise immunity in working conditions at a protected facility;
- providing special security.

Until now, in Russia there is no state standard that regulates most of the requirements discussed above. As a result, consumers of metal detectors suffer. Having purchased a product, the documentation for which gives only qualitative assessments of its main characteristics (reliably detects weapons, does not react to small metal objects, is resistant to interference, etc.), the consumer, having discovered that the metal detector does not suit him in terms of actual capabilities, cannot bring claims against the manufacturer or seller. Often there is such a situation that the purchased universal metal detector has a variety of work programs. However, the operational documents do not indicate the characteristics provided by the product when using the programs implemented in it. And even references to setting the security level according to the international standard “NILECJ-SCD 0601-00 Security level 1...5” do not allow the domestic consumer to decide on the choice of mode.

It follows from the above that there is a need to develop a Russian standard for metal detectors - screening devices. Let us consider in more detail each of the requirements for such devices.

detection characteristics.

OP, discussed above, have different sizes, mass, shape, electrical conductivity, magnetic permeability. In a metal detector, the signal at the output of the receiving antenna depends both on these characteristics and on the location of the OP relative to the antennas. Accordingly, the detection characteristics of a metal detector should be evaluated taking into account the factors listed above.

The studies carried out made it possible to develop a number of test samples with design parameters generalized for the OP. The use of such test samples or real ODs makes it possible to estimate the probability of their detection by a metal detector at different spatial orientations of OPs in the most probable locations on a person.

selective characteristics.

Under the selective characteristics in relation to metal detectors - access devices, they consider the probability of passing objects smaller in size and mass than the OP allowed to be carried to a protected facility (hereinafter PLP - personal items), or the probability of a false alarm of the product.

These characteristics in a metal detector are directly related to the probability of detecting an OP. The electromagnetic field across the width of the passage of the metal detector is significantly inhomogeneous. Even the use of a special configuration of coils and special signal processing from the receiving antenna does not significantly improve this heterogeneity. Therefore, when carrying the same object under the same angle in the immediate vicinity of the coils and in the middle of the passage, these signals may differ by 2...4 times. Thus, the signal from the OP in the middle of the passage is commensurate with the signal from the PLP carried near the coils. In addition, most of the considered metal detectors have flat antenna systems and have sufficient sensitivity in one or, at best, in two directions. Therefore, to ensure reliable detection at any orientation of such objects as a gun or a knife, which have significantly different sizes in different directions, a low sensitivity threshold is required, which reduces the selective characteristics of the metal detector.

Selectivity also has a purely psychological significance for security guards at facilities equipped with metal detectors. From the practical observations of the author, it follows that frequent false alarms from the PLP reduce the attention of security workers to any alarm signal, including when triggered by the OP. The use of metal detectors with low selectivity is most often just an excuse for security personnel to screen visitors.

Noise immunity.

A metal detector installed in a protected area is affected by a number of external conditions (interference) that make it difficult or impossible to perform its functions. Interference is divided into electromagnetic and caused by the presence of large masses of metal near the antennas, closed circuits, moving or stationary. The most common sources of electromagnetic interference are:

Power electrical networks and their switching equipment;
- working power electrical devices (electric motors, electric generators, transformers);
- fluorescent lamps;
- monitors;
- TVs, etc.

The presence of electromagnetic interference can lead to false alarms, which in some cases become continuous and make it practically impossible to use the metal detector. In addition, electromagnetic interference adversely affects selectivity.

False alarms are also caused by structures located near the metal detector and closed circuits moving according to their functional purpose (doors, elevator cabins, etc.) or moving due to the non-rigidity of structures, vibrations.

If the passage through the metal detector is not properly organized, false positives can be caused by moving metal objects (hand luggage, umbrellas, etc.) from visitors located near the antennas.

The noise immunity of a metal detector is determined by its ability to maintain its characteristics under the influence of the interferences discussed above. To ensure the noise immunity of metal detectors, a number of both constructive and organizational measures are used:

Special circuit solutions for electronic components;
- special processing of signals from receiving antennas;
- various types of synchronization with noise;
- removal of metal detectors from moving metal objects;
- exclusion of carrying hand luggage through the area controlled by the metal detector, and close to it.

To control hand luggage, X-ray machines or metal detectors for hand luggage can be used, located in close proximity to a metal detector designed for screening people. The listed devices are sources of additional electromagnetic interference, and to reduce their influence, the measures discussed above should be provided.

Special security.

Metal detectors generate an electromagnetic field that a person crosses when passing and near which security workers stay for a long time. Therefore, in addition to meeting the usual safety requirements for powered devices, they must provide:

Safety in relation to the human body;
- permissible level of influence on implantable pacemakers;
- permissible level of influence on magnetic storage media.

Thus, special requirements are imposed on metal detectors - screening devices. The analysis of the requirements for such devices, carried out in this article, allows us to formulate the main approaches to the development of the standard.

Proposals for standardization of requirements

The main characteristic of a metal detector - an inspection device can be the probability of detecting an OP. The requirements for the value of this characteristic may be different depending on the required degree of protection of the object. The author proposes to divide these requirements into four groups: reduced, normal, increased and high security, with the following numerical values of the Robn detection probability:

Downgraded from Robn. >= 0.95;
- normal with Robn. >= 0.97;
- increased with Robn. >= 0.98;
- high with Robn. >= 0.99.

The proposed values are chosen based on the need to ensure a sufficient level of selectivity and noise immunity, as well as taking into account the technical feasibility of these values in existing metal detectors. In addition, such a division will allow certifying the entire variety of Russian and imported products and having a certain margin for promising metal detectors.

A critical point in evaluating Robn. is the measurement technique. To create it you need:

Select the nomenclature of OP or their imitators with specific design characteristics;
- select and justify the measurement points in the controlled opening of the metal detector;
- select and justify the number of measurements based on the required confidence level;
- to develop and substantiate algorithms for processing measurements.

The second important characteristic of specific screening devices is selectivity. It also, depending on the value of the probability of detecting PLP (probability of false alarm Rlt.), Can be estimated in four groups:

Reduced from RLT.<= 0,1;
- normal with RLT.<= 0,05;
- increased with RLT.<= 0,02;
- high with RLT.<= 0,01.

Approach to RLT measurement methods. may be similar to the one discussed above.

Proposed for normalization Robn. are closely related to the time spent by the OP in the area controlled by the metal detector. Therefore, the maximum speed of carrying objects, at which certain probabilistic characteristics are provided, should also be normalized. Usually the speed of a calmly walking person is 0.5 ... 1.0 m / s. However, at the same time, the relative speeds of movement of individual parts of his body (arms, legs), and, accordingly, the OP, can reach 1.5 ... 2 m / s. Methods for measuring the maximum flow rate of the OP (or the throughput resulting from it) are quite obvious.

The requirements for noise immunity of metal detectors in relation to external electromagnetic interference are formulated in the developed standard. Normalization of requirements for noise immunity from moving metal masses is generally impossible.

The requirements for the safety of the electromagnetic field of a metal detector in relation to the human body are determined by: SanPiN 2.2.4 / 2.1.8.055-96 “Electromagnetic radiation of the radio frequency range”, MSanPiN 001-96 “Sanitary standards for permissible levels of physical factors when using consumer goods in a domestic environment” .

With regard to implantable pacemakers, according to the information available to the author, neither in Russia nor in other countries have established standardized requirements for the permissible characteristics of the surrounding electromagnetic fields. Therefore, the requirements for the safety of the electromagnetic field of the metal detector

can be formulated in relation to a certain (fixed) pacemaker, for example, the most sensitive to the considered influence. In particular, a number of imported metal detectors available on the Russian market have been tested for safety in relation to specific models of pacemakers.

When developing a standard, it is necessary to determine the requirements for the safety of the electromagnetic field of a metal detector in relation to magnetic media (magnetic tape, disks, etc.), which is most likely important for metal detectors for screening hand luggage.

Methods for measuring in most areas of safety of the electromagnetic field emitted by a metal detector consist in measuring field strength levels in certain frequency ranges with conventional measuring instruments and comparing them with acceptable standards.

General safety requirements for metal detectors are set out in GOST 12.1.004, GOST 12.1006, GOST 12.2.003, GOST 12.2.004, GOST 12.2.006.

International Standards

The best known are two international standards that define the requirements for metal detectors used to detect weapons on a person.

Consider the ratio of the main requirements proposed in this article for standardization with the corresponding requirements according to the standard of the US Federal Aviation Administration. In the standard of the Federal Aviation Administration of the United States, the lower limit of Robn is normalized. for three specific types of firearms. The samples are made of different materials (steel, stainless steel, special alloys), have a fairly small weight and dimensions. The tests are carried out at three fixed points on the human body. There are no requirements for the probabilities of detecting grenades and knives in the standard. In addition, there is no gradation in terms of Robn., which does not allow comparing metal detectors with each other. According to the author, in the developed Russian standard, a number of provisions set forth in, for example, the choice of similar or the same OP, the use of similar locations of weapons on the human body and in the same spatial orientation can be used. However, the nomenclature of the OPs used in the tests, the number of points at which the probabilities of their detection are estimated, the scope of tests (confidence probabilities) in the Russian standard should be higher. This will make it possible to more reliably estimate the parameters of metal detectors in relation to the problems considered above.

The author failed to analyze the requirements of the standard within the framework of this article, because he did not have the text of the standard at the time of writing. Therefore, the issues of comparison with the accepted classification and permissible values of the characteristics of metal detectors according to this international standard require additional consideration.

1 - Draft GOST R XXXXX-98, “System of standards for technical means of protection and protection, Means and systems for access control and management. Blocking devices, General technical requirements and test methods”.

2 - NILECJ-SCD 0601-00 Security level 1...5 - international standard, security levels 1...5.

3 - Test samples according to the standards of the US Federal Aviation Administration 3-GUN-TEST, Z-GUN-TEST ENHANCED.

The topic of special means for security firms and security departments of companies and enterprises is not at all new, but it has not lost its relevance. The list of these special equipment, of course, is not limited to rubber truncheons. A self-respecting company must be solidly equipped, including various special technical means.

One of the main and basic special equipment is a metal detector. This tool should be in the arsenal of security personnel without fail. If you need to continuously monitor a significant flow of passing employees and visitors, you can buy a frame-type metal detector, similar to those that check passengers for the presence of prohibited items in airport terminals. When it comes to security, metal detectors will become your effective ally.

Another mandatory technical special tool that should be available in the security department of every corporation or company is an anti-bug. This word is semi-slang, it would be more correct to call this device a bug detector. Bug Detector makes it possible to improve information security in your organization, and prevent the leakage of trade secret information.

But if attackers use wired lines - how to proceed? Or other eavesdropping devices are involved, say, small digital voice recorders. Such devices are turned on by an audio signal - in other words, this bug is in standby mode, while the room is quiet and no one is talking. In this case, devices called field indicators come to the aid of the security service. The field indicator, generally speaking, is a completely peaceful device that electricians use to find electrical wires in walls. However, it is easy to see that it can also serve to ensure security. During the operation of any electronic and electrical device, disturbances of the magnetic field necessarily occur, which the field indicator is designed to reveal. And these include the above devices that criminals can use to obtain important commercial information. The field indicator should help you calculate the location of eavesdropping devices, even if they do not use radio to transmit the intercepted audio stream.

This article lists only some of the devices that are absolutely mandatory for any organization concerned about their safety - metal detectors, field indicators and anti-bug.

Handheld Metal Detector (inspection metal detector) - a wearable device used during the search, with which you can determine the presence of hidden metal objects from the searched.

It is used to search for metal objects hidden under clothing or in luggage. Hand-held detectors are usually used in two cases: to localize an object detected using a stationary device, and in situations where an inspection is necessary, but the use of a stationary system is impossible for a number of reasons.

First of all, you need to pay attention to the following characteristics:

1. sensitivity;
2. selectivity;
3. indication;
4. determination of the parameters of the object;
5. nutrition;
6. design

Operating principle metal detector, is based on the intersection of two electromagnetic fields: the one that the device creates, and the one that radiates a metal object under the influence of someone else's electromagnetic field.

This interaction sends information to the circuits, which is already converted into a sound or light signal emitted by handheld metal detector. For this interaction to occur, it is necessary to hold the device in the immediate vicinity of the desired object.

The device of hand-held metal detectors

Hand held metal detectors are made from plastic. In more advanced models, the material is shockproof and waterproof. These improvements allow you to use the device outdoors during rain, as well as in difficult conditions.

Weight varies between 200-500 gr. The handle on some models is rubberized for a better grip. On many devices, there are fasteners for carrying the device on a belt in a protective case.

A safety strap is attached to the handle, for comfortable and safe carrying in the hand. The power button, target indicator lights, speakers and battery compartment may be located differently depending on the model of the device.

You can get acquainted with the full range of metal detectors: arched, manual and specialized - by clicking on the link. Also, you can order the metal detector you are interested in at an attractive price, and our experts will advise on the issue of interest.

Functions

Previously, metal detectors were limited in range and could only detect an object at close range. In a modern device, the sensitivity to a large object the size of a pistol is 20-25 cm. A knife will find such a detector at a distance of 12-15 cm, a bunch of keys from 8-10 cm.

An experienced user determines the size of the found object by sound. Different tonality, depending on the distance of the center of the electromagnetic field, makes it possible to make such calculations. The headphones that come with many hand-held metal detectors make this much easier.

To work in conditions with insufficient lighting, many devices have a backlight function.

In some cases, it becomes necessary to eliminate small targets from the search, and focus on large ones. To do this, you can use the sensitivity reduction function. With its help, small objects like coins, buttons, rings are cut off, and the signal goes only to sufficiently large objects. Such selectivity will be especially useful in the course of antiterrorist measures.

Advantages

The advantages of the inspection detector in the first place include compactness. Not everywhere it is possible to install arched metal detectors, but you can put a person with a device in his hand almost anywhere.

Ease of use, according to the principle: "plug and play", makes their use ubiquitous, and does not require special knowledge from a person.

Application

They are usually used in conjunction with turnstiles during personal searches at checkpoints in public places, at enterprises, and customs posts.

They are used by housing and communal services and maintenance personnel for repair work related to the search for metal objects in walls and floor coverings. They are used by special services to check correspondence and luggage.

A high-quality hand-held metal detector in the hands of the security service is a guarantee of the security of the protected facility. In addition, when working with a good device, the inspection process is accelerated, which increases throughput.

This fact is important when organizing public events with a large crowd of people (football matches, concerts, elections).

Special mention should be made of handheld metal detector with the function of searching for radioactive substances. Such a device will be indispensable at the enterprises of the nuclear-industrial complex and at military facilities. A security officer equipped with such a device will not allow the removal of hazardous substances outside the enterprise.

Exploitation

Inspection detectors absolutely safe, and contrary to popular belief, they do not emit any harmful rays. Such devices operate in the low-frequency range and do not harm people, including pregnant women and people who have a pacemaker installed.

But at the same time, the main thing is not to overdo it and not attach any metal objects to the sensitive element that can cause an alarm. This will cause it to become unbalanced and reduce detection efficiency.

Manufacturers and Models of Handheld Metal Detectors

Garrett

Garrett was founded in the USA in 1964 by a married couple named Garrett. The company's priority was to create a metal detector that is affordable and easy to use.

In 1980, the company already produced the entire range of search and inspection equipment, as well as light and sound detectors. In addition to ground metal detectors, the production of arched and hand-held metal detectors was put on the conveyor.

To this day, Garrett is one of the world leaders in this industry. And the fact that the special services of many countries of the world are equipped with hand-held metal detectors speaks of the quality of the products. And

Sphinx

CJSC Sphinx was founded in 1992 in Moscow. Specializing in production manual screening metal detectors. During the existence of CJSC Sphinx, the company cooperated with both state security services and private security companies.

According to statistics, every second employee of law enforcement agencies of the Russian Federation is equipped with a Sphinx detector. Manufacturers position the Sphinx metal detector as the best on the market today, in terms of price and quality. And, when compared with foreign competitors, "Sphinx" is significantly inferior to them in price.

Another feature that manufacturers endow the product with is the use of a detector for self-defense purposes. The design and material of the detector is so strong that it can withstand strong impacts. Metal detectors of this company have a light, sound signal and vibration signal.

e-sun

E-sun products are manufactured by the Eastern Company, an international corporation headquartered in the United States and manufacturing plants in China. A clear advantage of hand-held metal detectors produced under this brand is an acceptable price and quality confirmed in practice.

The range of models includes detectors with extended battery life without recharging. The light weight and style of the instrument is another advantage.

Main advantage hand-held metal detectors E-Sun is, first of all, in a low price. Thanks to a convenient carrying case and low weight of the devices, security personnel can always carry E-Sun metal detectors with them and use them at any time.

checkpoint

Manual metal detector Checkpoint and.

CEIA

Italian manufacturer, one of the recognized leaders in the market. The product is of European quality. And

detection characteristics.

OP, discussed above, have different sizes, mass, shape, electrical conductivity, magnetic permeability. Their detection depends both on these characteristics and on the location of the OP relative to the DM antennas. Accordingly, the detection characteristics of a metal detector should be evaluated taking into account the factors listed above.

The main detection parameter (characteristic) of a metal detector, as an inspection device, is probability of detecting an OP. The requirements for the value of this characteristic may be different depending on the required degree of protection of the object. Often in the technical literature, these requirements are divided into four groups: reduced, normal, increased and high security, with the following numerical values of the Robn detection probability:

Downgraded from Robn. >= 0.95;
- normal with Robn. >= 0.97;
- elevated with Robn. >= 0.98;
- high with robn. >= 0.99.

The probability of correct detection is the ratio of the number of correct detections to the total number of detection procedures for the same object or standard, made under the same conditions while meeting the requirements specified for the sensitivity of a given metal detector. For example, if a hundred detection procedures (Ntot = 100) were performed sequentially, an object or standard was detected 99 times (N pr = 99), then the probability of correct detection Pdet = 0.99.

selective characteristics.

The metal detector should solve the problem of selective (selective) detection of certain metal or metal-containing search objects against the background of metal items for personal use (PLP) that visitors usually have. Selective detection - the ability to establish the fact of the presence of an OP against the background of the simultaneous presence of PLP and not give false alarms from PLP in the absence of search objects. Selective detection can be carried out only if the OP has characteristic features. These features are understood to be any of their constant properties that are revealed in one or another physical method implemented in a metal detector, according to which there are the greatest differences between the OP and the main part of the set of PLPs.

Selectivity is assessed false alarm probability(Rlt.) and is also divided by some authors into four groups:

Reduced from RLT.<= 0,1;
- normal with RLT.<= 0,05;
- increased with RLT.<= 0,02;
- high with RLT.<= 0,01.

Approach to RLT measurement methods. may be similar to the one discussed above.

Selectivity also has a purely psychological significance for security guards at facilities equipped with metal detectors. From practical observations, it follows that frequent false alarms from PLP reduce the attention of security workers to any alarm signal, including when triggered by OP. The use of metal detectors with low selectivity is most often just an excuse for security personnel to screen visitors.

Noise immunity.

Power electrical networks and their switching equipment;
- working power electrical devices (electric motors, electric generators, transformers);
- fluorescent lamps;
- monitors;
- TVs, etc.

If the passage through the metal detector is not properly organized, false positives can be caused by moving metal objects (hand luggage, umbrellas, etc.) from visitors located near the antennas.

So, noise immunity of the metal detector - this is its ability to maintain its characteristics under the influence of the interference discussed above.

To ensure the noise immunity of metal detectors, a number of both constructive and organizational measures are used:

Special circuit solutions for electronic components;
- special processing of signals from receiving antennas;
- various types of synchronization with noise;
- removal of metal detectors from moving metal objects;
- exclusion of carrying hand luggage through the area controlled by the metal detector, and close to it.

Special security.

Safety in relation to the human body;
- permissible level of influence on implantable pacemakers;
- permissible level of influence on magnetic storage media.

Other features used in practice include:

Sensitivity;

Resolution;

Supply voltage, power consumption.

Sensitivity.

Sensitivity is defined as the smallest value of an item that can be detected with a given probability.

For mobile (manual) metal detectors, it is characterized by the maximum distance between the search element and the reference test object for this type of metal detector (an object made of ferrous or non-ferrous metal). In this case, depending on the type of sensor, a certain interval can be specified for the speed of movement (scanning) of the search element relative to the object of inspection.

For stationary metal detectors, a certain area of \u200b\u200bspace is indicated near the transmitting coils and sensors, in which the sensitivity is maximum.

Resolution.

It is characterized by the minimum distance between two reference objects for this type of metal detector, which are detected separately at the specified maximum distance from them to the search element. At the same time, for some types of sensors, the interval of the allowable speed of movement of the search element is indicated.

To study (measure) the characteristics of metal detectors, a number of test samples (object-tests) have been developed that have design parameters generalized for the OP. The use of such test samples or real ODs makes it possible to estimate the probability of their detection by a metal detector at different spatial orientations of OPs in the most probable locations on a person.

Samples of object-tests are made of different materials (steel, stainless steel, special alloys), have a fairly small weight and dimensions. The tests are carried out at three fixed points on the human body. There are no requirements for the probabilities of detecting grenades and knives in the standard.

The state standard of the Russian Federation requires:

......should provide the issuance of sound and light alarms when objects made of ferrous and non-ferrous metals weighing 150 g or more and / or with dimensions of 20 × 20 × 20 mm or more are carried through the control zone at a speed of carrying through the control zone from 0.3 to 2.5 m/s

- 189.00 Kb

Introduction

The relevance of this topic lies in the fact that in our time the threat of terrorist acts, as well as the commission of crimes using firearms and knives is quite high. To minimize this threat, devices such as metal detectors have been created that allow you to track all metal objects that are both in luggage and on the body of a person or animal. These devices can not only prevent crime, they can also be used in the military field, in the food industry. Metal detectors are indispensable in construction and repair work, in timber processing, in mining, as well as in archeology and even in processing garbage. In a word, we can say that metal detectors play an important role in our life.

The purpose of this course work is to study metal detectors, their types and characteristics. To achieve this goal, I set the following tasks:

To study the history of the creation of metal detectors;

Formulate the basic requirements for metal detectors;

Learn the types of devices;

Analyze the characteristics of hand-held metal detectors.

The object of the study is the currently existing metal detectors and their types.

The structure of the course work is as follows:

The first chapter contains the history of the creation of metal detectors, as well as the basic requirements for these devices.

The second chapter includes types of metal detectors, as well as an analysis of the characteristics of hand-held metal detectors.

1 History of metal detectors and their basic requirements

1.1 History of metal detectors

For the first time, metal detectors are mentioned in ancient Chinese treatises of the 2nd century BC. BC. In them, the entrance to the imperial chambers is described in the form of an arch, which is made of natural magnetite. The arch is in the shape of a horseshoe. Such a magnet arch attracted all metal objects, including weapons. Therefore, it was impossible to secretly carry, for example, a knife into the imperial chambers.

At the beginning of the twentieth century, the development of metal detectors was carried out mainly to detect minerals, including electrically conductive ores in America and England. The devices of that time were very heavy, had large dimensions and were mounted on a car. They consisted of a powerful generator and a large radiating coil, which created a strong electromagnetic field. Such detectors could explore territories as far as meters deep, the signal from metal ores and other electrically conductive objects was picked up by a receiving coil. Changing the parameters of the secondary field made it possible to understand which object was detected by the device. Later, installations of such high power were banned in the member countries of the Convention on the Maximum Permissible Levels of Electromagnetic Waves. one

The first arch type detectors were designed in Germany in 1925. With their help, it was possible to detect metal objects that workers tried to take out of a plant or factory. At the same time, a researcher from Germany, S. Herr, discovered the magnetic induction balance; on the basis of this phenomenon, the scientist designed a metal detector. The prototype of S. Guerra was so successful that soon the idea of creating metal detectors of this kind was picked up by all leading companies, especially in the USA. The American private company "Radio Metal Locating Company" was the first to start producing hand-held metal detectors already in the late 20s. XX century. The detector coils were fixed on a wooden frame and were separated from each other at a distance of two meters, due to this, an induction balance was maintained between the receiving and transmitting coils, because mutual electronic interference was excluded. All metal objects that fell into the electromagnetic field of the transmitting coil violated the inductive balance, thus, a voltage appeared in the receiving coil, amplified by the device, it was transmitted in the form of sound to the operator. The device worked on 6 radio tubes, it was very bulky, but with its help it was easy to find pipes at a depth of three meters. Despite initial success, by the beginning of the 30s. the company went bankrupt. The economic depression in America ended with active developments, the construction industry was rapidly gaining momentum, so again there was a demand for devices for detecting cables and pipes. In 1923, the American Gerhard Fischer began to develop devices of this type. In 1937, he first patented his model of a metal detector, calling it the "metaloscope". In the same year, Fisher opens his own metal detector manufacturing company. G. Fischer's metalloscope already used 9 lamps, and the device circuit itself was much more complicated. G. Fischer lowered the operating frequency of the device to 1 kHz, which ensured the operation of the device at a greater depth. The scheme of G. Fisher's device was described in detail in several popular science publications, so radio amateurs were able to assemble such detectors on their own at home. Along with the company of G. Fisher, another company from the USA, the "Goldak Company", is engaged in the development of metal detectors. In the 30s. for the first time it produces its own detectors, very similar to those of G. Fischer. The Goldak Company's detectors were called "radioscopes". Their distinctive feature is that for the first time in radioscopes the issue of detuning from the ground was solved. This company owns the first patent for metal detectors with a round search coil, which is used in most modern devices. In the 30s. detectors were made of wood, worked with radio tubes, and weighed 15-25 kg. 2

Since the late 1930s, metal detectors have been developed, mostly with a round search coil and an electronic unit mounted on a rod. Devices of this design were easier to use, with their help it was possible to find both small objects and large treasures. Beat detectors were massively used to detect pipes, over time they began to be used to search for mines.

At the end of the 40s. mine detectors began to be used to detect treasures. For the first time, such an experiment was carried out in the United States, when obsolete equipment began to be sold from military warehouses. Mine detectors were then used mainly to search for gold nuggets and treasures. The devices were quite heavy and uncomfortable, so they were used only by amateur enthusiasts.

Everywhere in the United States they began to search for treasures from the end of the 50s, when models of light compact metal detectors operating on transistors appeared on sale. In the same period, many companies were opened that manufactured and sold various metal detectors that worked on beats or on induction balance. The sensitivity of the devices at that time was not too high (for coins 10-15 cm), there was no discrimination and balance from the ground, however, these devices were much more convenient than mine detectors, they could be used to detect coins, rings, and other small jewelry. In the 60s. the main manufacturers of detectors in America are: G. Fisher, C. Garrett, W. Megan, E. Reis.

In the 70s. gold prices skyrocketed, after which a huge number of people rushed to look for gold nuggets. From 1933 to 1974, the US government artificially lowered the price of gold ($35 per ounce), while private individuals were prohibited from owning gold. With the lifting of this ban, the price of gold immediately rose. At the end of the 70s. 1 ounce of gold was already worth $800. Such a sharp price jump stimulated interest in the search for gold and in metal detecting in general. Sales of metal detectors in the US have skyrocketed. The number of firms producing devices for finding gold has also increased dramatically. True, in the face of fierce competition, only a few managed to take their rightful place in the metal detector market: Fisher Research Laboratory, Garrett Electronics, White's Electronics and the English company Inc. and C-Scoop.

In the 80s. New American detector manufacturers are actively developing: Tehnetics, Tesoro Electronics and the Australian company Minelab. In the same period, detectors of small sizes with a high degree of sensitivity appeared. Over time, new functions appear in the devices: detuning from mineralized soils and metal debris. True, until the end of the 70s. two of these processes could not be carried out at the same time. The operating frequency of the detectors has decreased from the initial 100 kHz to 1-5 kHz.

Over time, metal detectors began to automatically adjust to the ground during the search, and the production of inexpensive impulse devices with discrimination was launched. From year to year, metal detectors became more and more perfect, but with the advent of new functions and capabilities, the weight of the devices also increased. Therefore, in the 80s. G. Fischer presented to the public a completely new detector (1260-X), equipped with automatic ground balancing and automatic discrimination. Thanks to fundamentally new technologies, G. Fischer's device turned out to be light, easy to operate and quite efficient in operation. Very quickly, devices of this type began to be produced by other manufacturers.

Year by year, the signal from the detected target became more and more accurate. This function was significantly improved in the mid-90s. during the advent of computer technology. The representatives of Garrett Electronics were the first to patent a computerized metal detector. Although White's Electronics was the first to launch the production of computerized devices. Today, all metal detector manufacturers produce devices equipped with microprocessors.

Modern models of metal detectors are capable of performing such useful functions as detecting metal, determining which group it belongs to, determining the size of the find, its depth, exact location, screening out soil minerals and metal debris. Nevertheless, even today the capabilities of metal detectors are limited: not even the best device can find a coin at a depth of more than 70 cm, show the chemical composition of the find, and show its outline on the screen. In the future, metal detectors will certainly be endowed with similar functions. 3

1.2 Basic requirements for metal detectors

A metal detector is an electronic device that allows you to detect metal objects in a neutral or slightly conductive environment due to their conductivity. The metal detector detects metal in soil, water, walls, wood, under clothing and luggage, food, human and animal bodies, etc.

Items prohibited from being carried by visitors to protected facilities and detected by a metal detector primarily include:

Firearms;

Hand grenades;

The functional purpose of metal detectors in the general case is quite wide: from the search for non-ferrous metals weighing ~ 1 g to the detection of objects made of ferromagnetic metals, significantly exceeding the mass of the search object. The tasks that metal detectors solve in protection and security systems are narrower and have their own characteristics that determine the specific requirements for such devices. These include:

Reliable detection of the search object;

Ensuring selectivity in relation to metal objects allowed to be carried to a protected facility;

Ensuring noise immunity in working conditions at a protected facility;

Ensuring special security.

There is a need to develop a Russian standard for metal detectors - screening devices. Let us consider in more detail each of the requirements for such devices. 4

The first thing that will be considered in this paper is the detection characteristics.

The search objects discussed above have different sizes, weights, shapes, electrical conductivity, and magnetic permeability. In a metal detector, the signal at the output of the receiving antenna depends both on these characteristics and on the location of the search object relative to the antennas. Accordingly, the detection characteristics of a metal detector should be evaluated taking into account the factors listed above.

The foreseen researches allowed to develop a number of test samples having design parameters generalized for search objects. The use of such test samples or real search objects makes it possible to estimate the probability of their detection by a metal detector at different spatial orientations of search objects in the most probable locations on a person.

Consider Selective Characteristics. Under the selective characteristics in relation to metal detectors, they consider the probability of passing objects smaller in size and mass than the search objects allowed to be carried to the protected object, or the probability of a false alarm of the product. five

These characteristics in a metal detector are directly related to the probability of detecting a search object. The electromagnetic field across the width of the passage of the metal detector is significantly inhomogeneous. Even the use of a special configuration of coils and special signal processing from the receiving antenna does not significantly improve this heterogeneity. Therefore, when carrying the same object under the same angle in the immediate vicinity of the coils and in the middle of the passage, these signals may differ by 2-4 times. Thus, the signal from the search object in the middle of the aisle is commensurate with the signal from personal items carried near the coils. In addition, most of the considered metal detectors have flat antenna systems and have sufficient sensitivity in one or, at best, in two directions. Therefore, to ensure reliable detection at any orientation of such search objects as a gun or a knife, which have significantly different sizes in different directions, a low sensitivity threshold is required, which reduces the selective characteristics of the metal detector.