In the field of security, for inspection, identification of objects, devices that react to metal have been used for a long time. Modifications with an expanded set of basic and additional functions have been created.

An example of such a device is an arched metal detector. It is improved for the specific conditions of the objects on which it is used.

Arched metal detectors are stationary devices (prefabricated or ready-made) that detect metal objects carried through them.

They are made with an arch (frame) and are able to scan a person completely or overall objects. They detect alloys in dielectric and weakly conductive substances (wood, plastic, clothing).

The operation of the device is based on the use of radio waves. One wall sends a specially generated radio signal to the other, which receives and sends it back. Materials are resistant to electromagnetic and radio waves, so the signal passing through them loses its strength or does not pass at all.

When they meet an object on the body of a person moving through the detector frame, the radio waves are reflected from it and return faster than other signals. The device records the reflection time, if the reflection speed indicates a metal barrier-a light and sound alarm is triggered.

After analyzing the radio waves involved, the device detects the object and displays the localization on its monitor. Modern equipment of this type is equipped with digital control, special microprocessors, programs. The sensitivity of the device is adjusted according to several parameters.

The coils of the side walls of the device create a scanning electromagnetic field, the quality of which is changed by the control unit. The area under the arch is divided into programmable zones: one or more.

A separate group is represented by particularly sensitive scanners. The principle of operation is the same, but the scanning procedure is different: the signal of a passing person is compared with the data entered in the computer database about the signal of the same person, but absolutely clean.

Types of arched metal detectors

The following two types of detectors are used:

• passive. Only products made of ferrous alloys are detected;
• active. Use extended range parameters. Capable of detecting all ferrous and non-ferrous metals, alloys under clothing, inside luggage, on people's bodies.

Products are distinguished by the following parameters:

• sensitivity threshold;
• external design;
• network operation of the device;
• purpose, a set of functions;
• light indication.

Types of arch-type devices by functionality:

• weakly sensitive for general use-detection of weapons, large objects;
• hypersensitivity. Detect small objects;
• hypersensitive. Detect objects made of non-ferrous metals weighing from units of grams.

There are single-, multi-zone, mobile (prefabricated), and stationary arch detectors.

According to the type of generated radiation, there are devices with a field:

• pulsed. Generated by an intermittent signal;
• harmonious. Constant, continuous radiation.

The first ones are more resistant to vibrations, they are more reliable, these are the majority of products on the market. Harmonic detectors are better protected from interference, but the quality is worse.

Functions and features

The device performs the following tasks:

• single - or multi-zone object detection algorithm;
• search under clothing, inside carry-on luggage, other materials;
• detection of metals from 1 g;
• detection of objects of specified shapes (guns, knives) in certain places.

Opportunities:

The pros and cons of walk-through metal detectors

The advantage of arch detectors is high throughput (from 20 to hundreds of people per minute), extended range (limited to the arch).

A key role in the creation of this equipment is played by the method of distribution of magnetic radiation.

The advantage of high-quality products: they generate a continuous, uniform electromagnetic field.

Low-quality devices create an uneven field with blind (dead) areas, they miss small objects.

The detector winding affects the field coverage of the zones and the activation levels of the alarm signal. Large coils guarantee increased accuracy, but they are more affected by complex electrical characteristics.

An incorrectly installed winding reduces the reliability of the device while increasing the power consumption. This is a typical problem for all such devices, so some manufacturers use high-precision robotic equipment for winding.

Fully digital control by means of a microprocessor control panel gives the device a better sensitivity, an expanded range of values, additional ranges of sensitivity adjustment, and trigger limits appear.

The more printed circuit boards, contacts between sensors, the more likely the risk of their failure.

Equipment with an outdated design is prone to false positives, failures due to interference. Against this background, devices created with digital control units are more reliable.

Obsolete arched equipment, like new ones, consists of transmitting, receiving, and controlling segments. But the control unit in the old one is made on boards in metal cases.

Such devices are cumbersome, time-consuming to install, move. Working with them is more difficult. It is recommended to choose modern microprocessor panels with the control of breakdowns, failures, and interference protection.

The high-quality product has a strong, moisture-proof housing that meets the IP20 standard (for indoor use), IP55 (for outdoor use), with protection against electric shock, specially treated coils inside the panels.

Application

Detectors with very high sensitivity are used for special purposes: as equipment for preventing thefts from enterprises mining or processing precious metals, checking visitors to prisons, nuclear magnetic resonance facilities in hospitals. They are complex to set up, equipped with an integrated secure access system.

Most metal detectors on the market are general – purpose. They have an average quality, sufficient for everyday work. They are used in stores and supermarkets.

Devices in the form of columns are used in places without special safety requirements, with a low-intensity flow of visitors.

For higher requirements, detectors with coils in the form of panels are used.

The devices are used in the inspection points of enterprises, warehouses, jewelry factories, airports, train stations. As well as at security facilities, in places where people gather, to prevent terrorist attacks and detect weapons. They are equipped with law enforcement buildings, military units, prisons, stadiums.

Operation

Usually, the sensitivity level of the detector is set so that it does not react to too small metal objects. Otherwise, it sends signals after detecting rivets, zippers on clothes, metal dental fillings, hairpins in the hair.

If you need to find small objects, the sensitivity of the device is increased. The detector is used with an open inspection point with visual inspection of identified metal objects. Personnel are advised to wear clothing and shoes with a minimum of metal in a satisfactory electromagnetic environment.

Metal detectors have factory and custom programs for selective detection (detection) of weapons, metal objects, as well as programs created for a variety of standard threats. The device is also programmed to detect non-standard objects.

To get started, assemble the product according to the instructions. The panels are positioned exactly according to the instructions – each has its own place relative to the central unit. The central unit is installed in the connectors of the panels. The structure is secured with the bolts supplied with it. The power cord is connected to one of the side panels, and the power cord is connected to the same panel. For convenience, each panel has connectors for the power supply.

If the detector is installed close to a reinforced concrete wall, adjust the sensitivity, as the reinforcement creates interference.

The device is turned on by turning the key, after which the self-diagnosis function is activated, and the device is ready for operation.

Safety precautions

Arched metal detectors are highly sensitive equipment that uses the laws of electromagnetic fields. When operating, it is advisable to adhere to several rules.

The space within two to three meters near the device is cleared of large metal objects. External interference is minimized by placing the device as far as possible from the cables of power networks, communications, and radio devices. Do not place the device near electric motors, transformers, electrical panels. Moving metal masses — gates, elevators, turnstiles-are a possible cause of interference.

Arched metal detectors standing next to each other are separated by a certain distance. They are configured so that they do not interfere with each other's work. The mounting location of the device affects the sensitivity. If it is too sharp, it increases the number of false positives, and too low leads to failure.

You should check that the equipment meets the standards. The electromagnetic fields of a high-quality device are safe for people with electrostimulators of the heart, pregnant women, do not damage magnetic media, tapes, cards with a magnetized strip.

Stability, vibration exclusion — the main requirement for the installation site. The socket is equipped with a ground connection. It is recommended to use power stabilizers.

It is strictly forbidden to work with the inside of the product (disassemble, disconnect elements) when the power is turned on. Electric welding manipulations, working radios, electric shock devices are prohibited when the device is turned on.