Passive infrared motion detectors. The best infrared thermometers according to customer reviews Optical electronic passive surface detector

In security alarm systems, detectors with an optical-electronic operating principle are widely and willingly used by installers. Let's figure out how they work, and also consider the advantages, disadvantages and scope of these devices.

The key word in the name of such devices is “optiko” - that is, optical. True, the range in which they operate is invisible to the human eye, since it is shifted to the infrared (IR) region. All devices of the operating principle under consideration are divided into two groups:

• passive,
• active.

The former are more common due to ease of installation and configuration. They consist of a receiver, a special lens and an electronic signal processing unit (that’s the second part of the name). Among them there is also a division into:

• superficial,
• linear.

These names come from the type of detection zone - that is, the configuration of the part of the space in which the optical-electronic detector is capable of detecting an alarming event. This event is the movement of a body of a certain mass at a certain speed. These parameters are determined by its technical characteristics.

The range of detectable speeds usually starts from a value of 0.3 m/sec. As for the mass, much depends on the distance to the object and the height of the detector. In any case, a person is detected without problems, and pets, in most cases, too. Therefore, there are volumetric infrared detectors with “protection” from pets, weighing, say, up to 10 or 20 kg (registered in the passport).

A common disadvantage of all passive optical-electronic sensors is sensitivity to convection air flows, be it warm air from a heating device or a trivial draft. Therefore, when determining the installation locations of these detectors, such points must be taken into account. Also critical is the rigidity of the supporting structure (no vibration during operation) and protection from extraneous light.

AREA OF APPLICATION OF SECURITY IR DETECTORS

Infrared sensors are used in security alarm systems. as a rule, to organize the second line of defense, that is, to control the internal volume of premises by detecting the movement of a potential intruder in them. However, surface and linear devices can be used for perimeter security.

Passive surface detectors are used to detect intrusion through doors, windows, all kinds of hatches and ceilings. There is only one drawback to this method of using them - they will work when the intruder is already inside the room. That is, there is no talk of early detection of an intrusion attempt.

All passive devices have a relatively short detection distance of 10-20 meters. Volumetric - smaller, linear - larger. This property determines their installation inside small rooms. If you need to equip large areas with a security alarm, you can:

• install several passive sensors,
• use active infrared detectors.

By the way, the latter are, as a rule, intended to protect extended perimeters of open areas, and therefore have a linear detection zone. In addition, it is technically impossible to implement other types of zones for active devices. To increase the vertical monitoring area, multi-beam detectors are used.

Infrared sensors are critical to the optical density of the environment (rain, snow, fog), so this should be taken into account when installing them outdoors.

In conclusion, we can cite several of the most popular lines of models of optical-electronic detectors from domestic manufacturers. These are detectors of the following types:

• Aster,
• Photon,
• Icarus.

All of them are produced in different versions both according to the installation method and the parameters of the detection zone. For example, Astra 5A is a volumetric detector, 5B is a surface detector, 5B is a linear detector.

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People go to great lengths to secure their property. Special equipment is provided to quickly detect an intruder on the territory and take the necessary measures. You shouldn’t waste money on installing high-tech devices - the products are well worth their cost. You can purchase a linear optical-electronic detector, which has already proven itself on the positive side.

Features of the device

Such products can be installed both in residential premises and in large industrial facilities. The detection area depends on the power of the optical system. Typically, a linear optical-electronic detector signals when an object has already entered the territory. Many consider this a minus, but this is just the operating principle of this device.

For the device to function properly, it must be installed correctly. The instructions specify where and how exactly the linear optical-electronic detector should be mounted. There are a few simple tips to remember:

• do not install the device near heating devices;
• protect the product from direct sunlight;
• do not place objects within the range of the device that will create “dead” zones;
• Do not point a fan at the sensor.

Most of the limitations are related to temperature changes, since a linear optical-electronic detector can generate and send a false signal. In addition, negative external factors can affect the quality of the device. It is likely that it will fail much earlier than with proper operation.

Advantages of the device

A product such as a linear optical-electronic detector enjoys well-deserved popularity among customers. There are objective reasons for this. The main advantages of the device:

• prompt response;
• ease of installation;
• low price.

Buyers note that the cost of the equipment is quite affordable. And the scope of use of such detectors is quite wide. They are suitable for apartments, industrial facilities, warehouses, shopping centers and so on.

Before buying a device, it is better to consult with specialists. They will advise which model to choose and why. Professionals will also talk about installation features.

The last question remains - where to buy the product? Our company “Sintez Security” is engaged in the sale and installation of various types of security equipment. If you contact us, the craftsmen will quickly arrive at the specified address and do everything carefully and competently.

Why you should buy products from us

The well-known company “Sintez Security” has been working in this market segment for many years. Our clients include both enterprises and individuals. We try to ensure that everyone is satisfied with the service. We are sure that we can do it.

The Sintez Security company guarantees excellent product quality and low prices. Our products are much cheaper than many of our competitors. Consequently, you can save not only money, but also nerves. Contact us today!

From us you can buy IR linear optical-electronic ones at a low price - there are 15 pieces in the catalog, compare, study the characteristics.

Currently, passive electro-optical infrared (IR) detectors occupy a leading position when choosing to protect premises from unauthorized intrusion at security facilities. Aesthetic appearance, ease of installation, configuration and maintenance often give them priority over other detection means.

Passive optical-electronic infrared (IR) detectors (they are often called motion sensors) detect the fact of human penetration into the protected (controlled) part of the space, generate an alarm signal and, by opening the contacts of the executive relay (monitoring station relay), transmit an “alarm” signal to the warning equipment . Terminal devices (TD) of notification transmission systems (TPS) or a fire alarm control panel (PPKOP) can be used as warning means. In turn, the above-mentioned devices (CU or Control Panel) transmit the received alarm notification via various data transmission channels to the central monitoring station (CMS) or local security console.

The operating principle of passive optical-electronic IR detectors is based on the perception of changes in the level of infrared radiation of the temperature background, the sources of which are the human body or small animals, as well as all kinds of objects in their field of vision.

Infrared radiation is heat that is emitted by all heated bodies. In passive optical-electronic IR detectors, infrared radiation hits a Fresnel lens, after which it is focused on a sensitive pyroelectric element located on the optical axis of the lens (Fig. 1).

Passive IR detectors receive streams of infrared energy from objects and are converted by a pyroelectric receiver into an electrical signal, which is supplied through an amplifier and a signal processing circuit to the input of the alarm driver (Fig. 1)1.

In order for an intruder to be detected by a passive IR sensor, the following conditions must be met:

. the intruder must cross the beam of the sensor sensitivity zone in the transverse direction;
. the offender’s movement must occur within a certain speed range;
. The sensitivity of the sensor must be sufficient to register the difference in temperature between the surface of the intruder’s body (taking into account the influence of his clothing) and the background (walls, floor).

Passive IR sensors consist of three main elements:

. an optical system that forms the directional pattern of the sensor and determines the shape and type of the spatial sensitivity zone;
. a pyro receiver that registers human thermal radiation;
. signal processing unit of the pyro receiver, which separates signals caused by a moving person from the background of interference of natural and artificial origin.

Depending on the design of the Fresnel lens, passive optical-electronic IR detectors have different geometric dimensions of the controlled space and can be either with a volumetric detection zone, or with a surface or linear one. The range of action of such detectors lies in the range from 5 to 20 m. The appearance of these detectors is shown in Fig. 2.

Optical system

Modern IR sensors are characterized by a wide variety of possible radiation patterns. The sensitivity zone of IR sensors is a set of rays of various configurations diverging from the sensor in radial directions in one or more planes. Due to the fact that IR detectors use dual pyroelectric receivers, each beam in the horizontal plane is split into two:

The detector sensitivity zone can look like:

. one or several narrow beams concentrated in a small angle;
. several narrow beams in the vertical plane (radial barrier);
. one wide beam in the vertical plane (solid curtain) or in the form of a multi-fan curtain;
. several narrow beams in a horizontal or inclined plane (surface single-tier zone);
. several narrow beams in several inclined planes (volumetric multi-tiered zone).
. In this case, it is possible to change in a wide range the length of the sensitivity zone (from 1 m to 50 m), the viewing angle (from 30° to 180°, for ceiling sensors 360°), the angle of inclination of each beam (from 0° to 90°), the number rays (from 1 to several dozen).

The variety and complex configuration of the forms of the sensitivity zone are primarily due to the following factors:

. the desire of developers to ensure versatility when equipping rooms with different configurations - small rooms, long corridors, the formation of a specially shaped sensitivity zone, for example with a dead zone (alley) for pets near the floor, etc.;
. the need to ensure uniform sensitivity of the IR detector over the protected volume.

It is advisable to dwell on the requirement of uniform sensitivity in more detail. The signal at the output of the pyroelectric detector, all other things being equal, is greater, the greater the degree of overlap by the intruder in the detector's sensitivity zone and the smaller the beam width and distance to the detector. To detect an intruder at a large (10...20 m) distance, it is desirable that the beam width in the vertical plane does not exceed 5°...10°; in this case, the person almost completely blocks the beam, which ensures maximum sensitivity. At shorter distances, the sensitivity of the detector in this beam increases significantly, which can lead to false alarms, for example, from small animals. To reduce uneven sensitivity, optical systems are used that form several oblique beams, while the IR detector is installed at a height above human height. The total length of the sensitivity zone is thereby divided into several zones, and the beams “closest” to the detector are usually made wider to reduce sensitivity. This ensures almost constant sensitivity over distance, which on the one hand helps to reduce false alarms, and on the other hand increases detection ability by eliminating dead zones near the detector.

When constructing optical systems of IR sensors, the following can be used:

. Fresnel lenses - faceted (segmented) lenses, which are a plastic plate with several prismatic lens segments stamped on it;
. mirror optics - several specially shaped mirrors are installed in the sensor, focusing thermal radiation onto the pyroelectric detector;
. combined optics using both mirrors and Fresnel lenses.
. Most PIR sensors use Fresnel lenses. The advantages of Fresnel lenses include:
. simplicity of the design of a detector based on them;
. low price;
. the ability to use one sensor in various applications using interchangeable lenses.

Typically, each segment of the Fresnel lens forms its own beam of the radiation pattern. The use of modern lens manufacturing technologies makes it possible to ensure almost constant sensitivity of the detector for all beams due to the selection and optimization of the parameters of each lens segment: segment area, angle of inclination and distance to the pyro receiver, transparency, reflectivity, degree of defocusing. Recently, the technology for manufacturing Fresnel lenses with complex precise geometry has been mastered, which gives a 30% increase in the collected energy compared to standard lenses and, accordingly, an increase in the level of useful signal from a person at long distances. The material from which modern lenses are made provides protection for the pyroelectric receiver from white light. Unsatisfactory operation of the IR sensor can be caused by such effects as heat flows resulting from heating of the electrical components of the sensor, insects falling on sensitive pyroelectric detectors, and possible re-reflections of infrared radiation from the internal parts of the detector. To eliminate these effects, the latest generation of IR sensors use a special sealed chamber between the lens and the pyro-receiver (sealed optics), for example, in the new IR sensors from PYRONIX and C&K. According to experts, modern high-tech Fresnel lenses are practically not inferior in their optical characteristics to mirror optics.

Mirror optics as the only element of an optical system are used quite rarely. IR sensors with mirror optics are produced, for example, by SENTROL and ARITECH. The advantages of mirror optics are the ability to focus more accurately and, as a result, increase sensitivity, which allows you to detect an intruder at long distances. The use of several specially shaped mirrors, including multi-segment ones, makes it possible to provide almost constant distance sensitivity, and this sensitivity at long distances is approximately 60% higher than for simple Fresnel lenses. Using mirror optics, it is easier to protect the near zone located directly under the sensor installation site (the so-called anti-tamper zone). By analogy with replaceable Fresnel lenses, IR sensors with mirror optics are equipped with replaceable detachable mirror masks, the use of which allows you to select the required shape of the sensitivity zone and makes it possible to adapt the sensor to various configurations of the protected premises.

Modern high-quality IR detectors use a combination of Fresnel lenses and mirror optics. In this case, Fresnel lenses are used to form a sensitivity zone at medium distances, and mirror optics are used to form an anti-tamper zone under the sensor and to provide a very long detection distance.

Pyro receiver:

The optical system focuses IR radiation on a pyroelectric receiver, which in IR sensors uses an ultra-sensitive semiconductor pyroelectric converter capable of recording a difference of several tenths of a degree between the temperature of a person’s body and the background. The temperature change is converted into an electrical signal, which, after appropriate processing, triggers an alarm. IR sensors usually use dual (differential, DUAL) pyroelements. This is due to the fact that a single pyroelement reacts in the same way to any temperature change, regardless of what it is caused by - the human body or, for example, heating a room, which leads to an increase in the frequency of false alarms. In a differential circuit, the signal of one pyroelement is subtracted from another, which makes it possible to significantly suppress interference associated with changes in background temperature, as well as significantly reduce the influence of light and electromagnetic interference. The signal from a moving person appears at the output of the double pyroelectric element only when the person crosses the beam of the sensitivity zone and is an almost symmetrical bipolar signal, close in shape to the period of a sinusoid. For this reason, the beam itself for a double pyroelectric element is split into two in the horizontal plane. In the latest models of IR sensors, in order to further reduce the frequency of false alarms, quadruple pyroelements (QUAD or DOUBLE DUAL) are used - these are two dual pyroelectric sensors located in one sensor (usually placed one above the other). The observation radii of these pyro receivers are made different, and therefore the local thermal source of false alarms will not be observed in both pyro receivers at the same time. In this case, the geometry of the placement of pyro receivers and their connection circuit is selected in such a way that signals from a person are of opposite polarity, and electromagnetic interference causes signals in two channels of the same polarity, which leads to the suppression of this type of interference. For quadruple pyroelements, each beam is split into four (see Fig. 2), and therefore the maximum detection distance when using the same optics is approximately halved, since for reliable detection a person must, with his height, block both beams from two pyroelectric detectors. The detection distance for quadruple pyroelements can be increased by using precision optics that form a narrower beam. Another way to correct this situation to some extent is the use of pyroelements with complex intertwined geometry, which is what PARADOX uses in its sensors.

Signal processing block

The signal processing unit of the pyro receiver must ensure reliable recognition of a useful signal from a moving person against a background of interference. For IR sensors, the main types and sources of interference that can cause false alarms are:

. heat sources, air conditioning and refrigeration units;
. conventional air movement;
. solar radiation and artificial light sources;
. electromagnetic and radio interference (vehicles with electric motors, electric welding, power lines, powerful radio transmitters, electrostatic discharges);
. shocks and vibrations;
. thermal stress of lenses;
. insects and small animals.

The processing unit's identification of a useful signal against a background of interference is based on an analysis of the signal parameters at the output of the pyroelectric detector. These parameters are the signal size, its shape and duration. The signal from a person crossing the beam of the IR sensor sensitivity zone is an almost symmetrical bipolar signal, the duration of which depends on the speed of movement of the intruder, the distance to the sensor, the width of the beam, and can be approximately 0.02...10 s with a recorded range of movement speeds of 0 ,1…7 m/s. Interference signals are mostly asymmetrical or have a different duration from the useful signals (see Fig. 3). The signals shown in the figure are very approximate; in reality, everything is much more complicated.

The main parameter analyzed by all sensors is the signal magnitude. In the simplest sensors, this recorded parameter is the only one, and its analysis is carried out by comparing the signal with a certain threshold, which determines the sensitivity of the sensor and affects the frequency of false alarms. In order to increase resistance to false alarms, simple sensors use a pulse counting method, which counts how many times the signal exceeded the threshold (that is, in essence, how many times the intruder crossed the beam or how many beams he crossed). In this case, an alarm is not issued the first time the threshold is exceeded, but only if, within a certain time, the number of exceedances becomes greater than a specified value (usually 2...4). The disadvantage of the pulse counting method is the deterioration of sensitivity, which is especially noticeable for sensors with a sensitivity zone such as a single curtain and the like, when an intruder can only cross one beam. On the other hand, when counting pulses, false alarms are possible due to repeated interference (for example, electromagnetic or vibration).

In more complex sensors, the processing unit analyzes the bipolarity and symmetry of the signal shape from the output of the differential pyroelectric receiver. The specific implementation of such processing and the terminology used to refer to it1 may vary from manufacturer to manufacturer. The essence of the processing is to compare a signal with two thresholds (positive and negative) and, in some cases, to compare the magnitude and duration of signals of different polarities. A combination of this method with separate counting of excesses of positive and negative thresholds is also possible.

Analysis of the duration of signals can be carried out either by a direct method of measuring the time during which the signal exceeds a certain threshold, or in the frequency domain by filtering the signal from the output of the pyro receiver, including using a “floating” threshold, depending on the range of frequency analysis.

Another type of processing designed to improve the performance of IR sensors is automatic thermal compensation. In the ambient temperature range of 25°C...35°C, the sensitivity of the pyroelectric receiver decreases due to a decrease in the thermal contrast between the human body and the background; with a further increase in temperature, the sensitivity increases again, but “with the opposite sign.” In so-called “conventional” thermal compensation circuits, the temperature is measured, and when it increases, the gain is automatically increased. “True” or “two-way” compensation takes into account the increase in thermal contrast for temperatures above 25°C...35°C. The use of automatic temperature compensation ensures almost constant sensitivity of the IR sensor over a wide temperature range.

The listed types of processing can be carried out by analogue, digital or combined means. Modern IR sensors are increasingly beginning to use digital processing methods using specialized microcontrollers with ADCs and signal processors, which allows detailed processing of the fine structure of the signal to better distinguish it from the background noise. Recently, there have been reports of the development of completely digital IR sensors that do not use analog elements at all.
As is known, due to the random nature of useful and interfering signals, the best processing algorithms are those based on the theory of statistical solutions.

Other protection elements for IR detectors

IR sensors intended for professional use use so-called anti-masking circuits. The essence of the problem is that conventional IR sensors can be disabled by an intruder by first (when the system is not armed) taping or painting over the input window of the sensor. To combat this method of bypassing IR sensors, anti-masking schemes are used. The method is based on the use of a special IR radiation channel, which is triggered when a mask or reflective obstacle appears at a short distance from the sensor (from 3 to 30 cm). The anti-masking circuit operates continuously while the system is disarmed. When the fact of masking is detected by a special detector, a signal about this is sent from the sensor to the control panel, which, however, does not issue an alarm until the time comes to arm the system. It is at this moment that the operator will be given information about masking. Moreover, if this masking was accidental (a large insect, the appearance of a large object for some time near the sensor, etc.) and by the time the alarm was set it had cleared itself, the alarm signal is not issued.

Another security element that almost all modern IR detectors are equipped with is a contact tamper sensor, which signals an attempt to open or break into the sensor housing. The tamper and masking sensor relays are connected to a separate security loop.

To eliminate IR sensor triggering from small animals, either special lenses with a dead zone (Pet Alley) from floor level to a height of about 1 m are used, or special signal processing methods are used. It should be taken into account that special signal processing allows animals to be ignored only if their total weight does not exceed 7...15 kg, and they can approach the sensor no closer than 2 m. So if there is a jumping cat in a protected area, then such protection will not will help.

To protect against electromagnetic and radio interference, dense surface mounting and metal shielding are used.

Installation of detectors

Passive optical-electronic IR detectors have one remarkable advantage over other types of detection devices. It is easy to install, configure and maintain. Detectors of this type can be installed either on a flat surface of a load-bearing wall or in the corner of a room. There are detectors that are placed on the ceiling.

A competent choice and tactically correct use of such detectors are the key to reliable operation of the device, and the entire security system as a whole!

When choosing the types and number of sensors to ensure the protection of a particular object, one should take into account the possible routes and methods of penetration of an intruder, the required level of detection reliability; costs for the acquisition, installation and operation of sensors; features of the object; tactical and technical characteristics of sensors. A feature of IR passive sensors is their versatility - with their use it is possible to block a wide variety of rooms, structures and objects from approaching and entering: windows, showcases, counters, doors, walls, ceilings, partitions, safes and individual objects, corridors, room volumes. Moreover, in some cases, a large number of sensors will not be required to protect each structure; it may be sufficient to use one or several sensors with the required sensitivity zone configuration. Let's take a look at some of the features of using IR sensors.

The general principle of using IR sensors is that the rays of the sensitivity zone should be perpendicular to the intended direction of movement of the intruder. The sensor installation location should be chosen in such a way as to minimize dead zones caused by the presence of large objects in the protected area that block the beams (for example, furniture, indoor plants). If the doors in a room open inward, you should consider the possibility of masking an intruder with open doors. If dead spots cannot be eliminated, multiple sensors should be used. When blocking individual objects, the sensor or sensors must be installed so that the rays of the sensitivity zone block all possible approaches to the protected objects.

The range of permissible suspension heights specified in the documentation (minimum and maximum heights) must be observed. This especially applies to radiation patterns with inclined beams: if the suspension height exceeds the maximum permissible, this will lead to a decrease in the signal from the far zone and an increase in the dead zone in front of the sensor, but if the suspension height is less than the minimum permissible, this will lead to a decrease in range detection while simultaneously reducing the dead zone under the sensor.

1. Detectors with a volumetric detection zone (Fig. 3, a, b), as a rule, are installed in the corner of the room at a height of 2.2-2.5 m. In this case, they evenly cover the volume of the protected room.

2. Placing detectors on the ceiling is preferable in rooms with high ceilings from 2.4 to 3.6 m. These detectors have a denser detection zone (Fig. 3, c), and their operation is less affected by existing furniture.

3. Detectors with a surface detection zone (Fig. 4) are used to protect the perimeter, for example, non-permanent walls, door or window openings, and can also be used to limit access to any valuables. The detection zone of such devices should be directed, as an option, along a wall with openings. Some detectors can be installed directly above the opening.

4. Detectors with a linear detection zone (Fig. 5) are used to protect long and narrow corridors.

Interference and false alarms

When using passive optical-electronic IR detectors, it is necessary to keep in mind the possibility of false alarms that occur due to various types of interference.

Interference of a thermal, light, electromagnetic, or vibration nature can lead to false alarms of IR sensors. Despite the fact that modern IR sensors have a high degree of protection from these influences, it is still advisable to adhere to the following recommendations:

. To protect against air flows and dust, it is not recommended to place the sensor in close proximity to sources of air flows (ventilation, open window);
. Avoid direct exposure of the sensor to sunlight and bright light; when choosing an installation location, the possibility of exposure to light for a short time early in the morning or at sunset, when the sun is low above the horizon, or exposure to the headlights of vehicles passing outside, should be taken into account;
. During arming, it is advisable to turn off possible sources of powerful electromagnetic interference, in particular light sources not based on incandescent lamps: fluorescent, neon, mercury, sodium lamps;
. to reduce the influence of vibrations, it is advisable to install the sensor on permanent or supporting structures;
. It is not recommended to point the sensor at heat sources (radiator, stove) and moving objects (plants, curtains), towards the presence of pets.

Thermal interference - caused by heating of the temperature background when exposed to solar radiation, convective air flows from the operation of radiators of heating systems, air conditioners, and drafts.
Electromagnetic interference - caused by interference from sources of electrical and radio emissions to individual elements of the electronic part of the detector.
Extraneous interference - associated with the movement of small animals (dogs, cats, birds) in the detector detection zone. Let us consider in more detail all the factors affecting the normal operation of passive optical-electronic IR detectors.

Thermal interference

This is the most dangerous factor, which is characterized by changes in the ambient temperature background. Exposure to solar radiation causes a local increase in the temperature of individual sections of the walls of the room.

Convective interference is caused by the influence of moving air flows, for example from drafts with an open window, cracks in window openings, as well as during the operation of household heating devices - radiators and air conditioners.

Electromagnetic interference

They occur when any sources of electrical and radio radiation are turned on, such as measuring and household equipment, lighting, electric motors, and radio transmitting devices. Strong interference can also be caused by lightning strikes.

Extraneous interference

Small insects such as cockroaches, flies, and wasps can be a unique source of interference in passive optical-electronic IR detectors. If they move directly along the Fresnel lens, a false alarm of this type of detector may occur. The so-called house ants, which can get inside the detector and crawl directly on the pyroelectric element, also pose a danger.

Installation errors

A special place in the incorrect or incorrect operation of passive optical-electronic IR detectors is occupied by installation errors when performing work on installing these types of devices. Let us pay attention to striking examples of incorrect placement of IR detectors in order to avoid this in practice.

In Fig. 6 a; 7 a and 8 a show the correct, correct installation of detectors. You only need to install them this way and no other way!

In Figures 6 b, c; 7 b, c and 8 b, c present options for incorrect installation of passive optical-electronic IR detectors. With this installation, real intrusions into protected premises may be missed without issuing an “Alarm” signal.

Do not install passive optical-electronic detectors in such a way that they are exposed to direct or reflected rays of sunlight, as well as the headlights of passing vehicles.
Do not direct the detector detection zone at the heating elements of heating and air conditioning systems, at curtains and curtains that may sway due to drafts.
Do not place passive optical-electronic detectors near sources of electromagnetic radiation.
Seal all openings of the passive optical-electronic IR detector with the sealant supplied with the product.
Destroy insects that are present in the protected area.

Currently, there is a huge variety of detection tools, differing in operating principle, scope, design and performance characteristics.

The correct choice of a passive optical-electronic IR detector and its installation location is the key to reliable operation of the security alarm system.

When writing the article, materials were used, among other things, from the magazine “Security Systems” No. 4, 2013

Lecture 6

Active optical-electronic detectors

Active optical-electronic detectors are used to protect internal and external perimeters, windows, shop windows, and individual objects. They generate an alarm when there is a change in the reflected flow (single-position detectors) or a cessation (change) in the received flow (two-position detectors) of optical radiation energy caused by the movement of the intruder in the detection zone. The operating principle of the detectors is based on the directional propagation, reception and analysis of received infrared radiation.

The detection zone of the detector has the form of an invisible beam barrier between the emitter and the receiver, formed by one or more parallel narrowly directed beams located in the vertical plane; it differs from detector to detector, usually in range and number of beams.

Install the emitter and receiver on durable, non-deformable structures;

Avoid exposing the receiver to sunlight and car headlights, as well as direct sunlight, as this can lead to overheating and premature failure of photodiodes and LEDs.

The influence of these factors can be eliminated by using lightproof screens; do not allow foreign objects to be located closer than 0.5 m from the space through which the beam passes.

Typical representatives of this class of products are domestically produced detectors “Vector” and “SPEK”.

Passive optical-electronic detectors

Passive optical-electronic infrared detectors are the most widely used. This is due to the fact that with the help of optical systems specially developed for them, it is possible to quite simply and quickly obtain detection zones of various shapes and sizes and use them to protect objects of almost any configuration: residential, industrial, commercial and administrative premises; building structures: shop windows, windows, doors, walls, ceilings; open areas, internal and external perimeters; individual items: museum exhibits, computers, office equipment, etc.

The operating principle of the detectors is based on recording the difference between the intensity of infrared radiation emanating from an intruder penetrating into the controlled area and the background temperature at the protected object. All bodies with a temperature above absolute zero are sources of infrared radiation. This also applies to a person whose various parts of the body have a temperature of 25...36°C. Obviously, the intensity of IR radiation from a person will depend on many factors, for example, his clothing. However, if a person appears at an object that does not have sources of IR radiation with varying temperatures, the overall flow of IR radiation from the controlled area also changes. These changes are recorded by a passive electro-optical infrared detector.

The sensitive element of the detector is a pyroelectric converter, on which infrared rays are focused using a mirror or lens optical system (the latter are currently the most widely used). Modern detectors use a double pyroelectric converter (pyroelement). Two pyroelements are connected back-to-back and connected to a source follower mounted in the same housing. Thus, this is no longer just a pyroelectric element, but a pyroelectric receiver that converts the input signal - thermal IR radiation into an electrical signal and pre-processes it. The back-to-back connection of pyroelements makes it possible to implement the following algorithm for their operation. If the IR radiation incident on both pyroelements is the same, then the current generated by them is equal in magnitude and opposite in direction. Therefore, the input signal at the amplifier input will be zero. If the pyroelements are illuminated asymmetrically, their signals will differ and a current will appear at the amplifier input. Signals from the pyro receiver are processed by a logical block, which controls the output element of the detector circuit, which issues an alarm message to the alarm loop of the control panel.

The use of a pyro receiver with two sensitive areas can significantly reduce the likelihood of false alarms under the influence of external factors, such as convective air flows, light interference, etc.

The detection zone of the detector is a spatial discrete system consisting of elementary sensitive zones in the form of rays located in one or several tiers or in the form of thin wide plates located in a vertical plane. Since the detector's pyro receiver has two sensitive areas, each elementary sensitive zone of the detector consists of two beams. A typical volumetric detection zone of a detector is shown in Fig. 7.1.

The detector detection zone is formed using a special optical system. The most widely used optical systems are those with a Fresnel lens. This is a structure made of a special material (polyethylene) that has the required optical properties. The lens consists of separate segments, each of which forms a corresponding beam of the detector detection zone. Standard detection zones

can be corrected by gluing individual segments of the Fresnel lens. In this case, individual rays are excluded from the detection zone.

Conventionally, detector detection zones can be divided into three main types:

Surface type “fan”, “curtain”, “blind” or “radial barrier”;

Linear type “corridor”;

Volumetric, including “cone” type and ceiling detectors.

Typical detection zones of passive electro-optical infrared detectors are presented in Fig. 7.2.

To ensure stable operation of the detector, it is recommended to adhere to the following rules:

Do not install the detector above heating appliances;

Do not point the detector at air conditioners, radiators, warm air fans, spotlights, incandescent lamps and other sources that cause rapid temperature changes;

Do not expose the detector to direct sunlight;

Do not allow animals and objects (curtains, partitions, cabinets, etc.) that can create “dead” zones to be in the detection zone.

Modern passive optical-electronic infrared detectors use digital signal processing, carry out constant self-monitoring, have increased resistance to various destabilizing factors and an optimal price-quality ratio. All this makes them the most common class of security alarm detectors. The variety of their types, produced by the world's leading companies engaged in the production of security equipment, creates constant competition in the consumer market. Basically, detectors from different companies have approximately the same tactical and technical characteristics in their classes.

Typical representatives of this class of products are domestically produced detectors of the “Photon”, “Ikar”, “Astra” series.

Radio wave detectors

Radio wave detectors can be used to protect the volumes of enclosed spaces, internal and external perimeters, individual objects and building structures, and open areas. They generate an intrusion notification when the field of electromagnetic waves of ultra-high frequency (microwave) is disturbed, caused by the movement of the intruder in the detection zone. Radio wave detectors are single-position and two-position. In single-position detectors, the receiver and transmitter are combined in one housing, and in two-position detectors they are structurally designed as two separate blocks.

The detection zone of the detector (as with ultrasonic detectors) has the shape of an ellipsoid of rotation or drop-shaped and differs from detector to detector, as a rule, only in size. A typical detection zone of a single-position detector is shown in Fig. 7.3.

The operating principle of single-position radio wave detectors, like ultrasonic ones, is based on the Doppler effect, which consists in changing the frequency of the signal reflected from a moving object. Single-position radio wave detectors are used to protect the volume of premises, open areas, and individual objects. The principle of operation of two-position detectors is based on the creation of an electromagnetic field in the space between the transmitter and the receiver, forming a detection zone in the form of an elongated ellipsoid of rotation and recording changes in this field when an intruder crosses the detection zone. They are used for perimeter protection.

In radio wave detectors, as already noted, electromagnetic waves of ultra-high frequency are used. Length

waves are usually about 3 cm (10.5... 10.7 GHz). The main advantage of centimeter waves, compared to light and acoustic waves, is their almost complete insensitivity to changes and heterogeneity of the air environment.

Microwave radio waves travel in a straight line. Objects whose dielectric constant differs from air are an obstacle for centimeter waves, but most often the obstacle is translucent. Objects with solid metal surfaces are opaque reflective obstacles.

To ensure stable operation of radio wave detectors, it is recommended to adhere to the following rules:

Do not install detectors on conductive structures (metal beams, damp brickwork, etc.), since a double ground loop appears between the detector and the power source, which can cause false alarms of the detector;

Move oscillating or moving objects that have a significant reflective surface, as well as large objects that can create “dead” zones, outside the detection zone, or form the detection zone in such a way that these objects do not fall into it.

If there are “dead” zones, it is necessary to ensure that they do not create a continuous path for the violator to material values; during the security period, lock doors, windows, vents, transoms, hatches, and also turn off ventilation and power switching installations; Do not allow plastic pipes and window glass through which water may move into the detection zone.

Effective methods for reducing the influence of these factors are the following:

Securing objects that can move;

Selecting the appropriate direction of radiation from the detector, as well as the use of radio-proof screens, for example in the form of metal mesh, in front of objects whose vibration or movement cannot be eliminated;

Eliminating the possibility of the detector triggering when small animals and insects appear in the detection zone by selecting the height of the detector suspension and orienting the direction of its radiation parallel to the floor;

Selecting an appropriate delay for the detector response time and treating the detector installation site with special chemicals;

Turning off fluorescent lighting sources for the security period.

If this is not possible, it is necessary to ensure that there are no vibrations in the fixtures, blinking or other transient processes in the lamps themselves, which usually occur before the lamp fails; do not point the detector at window openings, thin walls and partitions, behind which movement of large objects is possible during the security period; Do not use detectors on objects near which powerful radio transmitting equipment is located.

Typical representatives of this class of products are domestically produced detectors of the Argus, Volna, Fon, Radium, and Linar series.

The most common motion detectors used in fire and security alarms are optical-electronic detectors.

Based on the principle of motion detection, they are divided into two groups: passive object detectors and active ones - they produce their own radiation and, by its change, determine the presence of a moving object.

In addition, such detectors classify the configurations of the scanned area, they are:

• Volumetric;
• Surface (curtain);
• Linear (beam).

The devices are used to organize security indoors, that is, as a second line of defense. However, devices with linear and surface detection methods can also be used to monitor perimeter crossings.

The main disadvantage of passive surface optical-electronic detectors is that they are triggered when the intruder has already entered the premises. That is, they cannot perform early intrusion detection.

Passive devices, both volumetric and linear, are characterized by a short distance of the controlled zone, depending on the power of the model, 10-25 m. Therefore, they are usually used to protect small and medium-sized premises in a set of several pieces per loop. To organize the security of buildings with large areas, it is recommended to use active optical-electronic devices.

Sensitivity The sensor of the optical-electronic detector is a pyroelectric detector. This is a device that senses infrared radiation. Depending on its intensity, the pyroelectric receiver produces a different number of electrical impulses, which are processed by an electronic logic unit. Most modern models are equipped with two sensitive sensors, which has significantly reduced the number of false alarms.

Active optical-electronic security detectors

The scope of application of these devices is quite diverse. They can be used to monitor windows and doorways, storefronts or external perimeters. Depending on the type of construction, two types of active detectors are distinguished:

1. Single-position - both the emitter and the receiver of reflected radiation are placed in the body of one device. Triggering occurs when the intensity or frequency of the reflected radiation flux changes.
2. Two-position - consist of two modules, one of which is an emitter, the second a radiation receiver. Triggering occurs due to an interruption in the reception of the stream being studied.

As a rule, the detection zone has the appearance of a barrier - a “curtain”, which is formed by one or several beams located in a vertical or horizontal plane. Different models may have different numbers of beam children, their sizes and configurations. In this case, the relative position of the rays may not necessarily be parallel. However, the receiver and emitter of each specific beam must be configured so that they do not intersect.

To ensure highly efficient uninterrupted operation of active optical-electronic detectors, it is necessary to adhere to certain rules during their installation and operation:

• Devices, both single-position and two-module, must be installed on non-deformable, durable building structures that exclude the possibility of excessive vibrations;
• The receiver of two-position devices must be placed in such a way as to exclude the possibility of influence of intense artificial and natural lighting on the photocells. Constant exposure to visible light on the receiver lens can lead to premature burnout of LEDs or photodiodes and, as a result, the device's speakers. This problem can be partially solved by using special light filters that do not transmit radiation in the visible and ultraviolet spectrum. However, in addition to the high cost of these devices, they somewhat reduce the sensitivity of the device.
• When installing both sources and receivers of IR radiation, it is necessary to exclude the possibility of various foreign objects passing less than 0.5 m from the passing beam.

Devices based on passive perception of IR radiation have become more widespread, since they are cheaper devices, and thanks to a wide selection (of Fresnel lens systems), the user quickly receives various forms of scanning zones, which makes it easier to create reliable security systems in buildings with complex layouts interior spaces. Passive IR motion detectors are used in alarm systems and access control systems for security:

• Industrial and public buildings, apartments and private households;
• Certain elements of structures that are most vulnerable to penetration: window openings and external doors, as well as walls, shop windows, ceilings and floors;
• Perimeters of land plots and fences;
• Individual material assets - expensive objects of art or unique devices.

A passive optical-electronic detector forms a scanning area consisting of narrow alternating sensitive and inactive zones in the shape of a fan, multidirectional in one plane. The relative position of the beams in space can be different: horizontal, vertical, in several rows or collected in one narrow beam. The shape of scanning zones is conventionally divided into 5 main types:

1. A wide-angle surface with one tier of rays emanating from one source - a “fan”;
2. Wide-angle surface with narrow beams oriented in one plane - “Curtain”;
3. A narrow beam is a “beam barrier”;
4. Single-tier surface panorama;
5. Multi-tiered volumetric.

When installing passive optical-electronic detectors, the following recommendations must be observed:

• Do not install the IR detector above convection heat sources;
• Do not point the sensitive area of ​​the device at spotlights, fan heaters, powerful incandescent lamps and other devices that can cause a rapid increase in the local temperature background;
• Protect the device from excessive exposure to solar radiation;
• Refrain from being in the responsible area to detect cabinets, curtains and other types of partitions that can create a “dead” controlled zone.

Brief overview of popular models

Surface security detector optical-electronic photon-sh— forms a curtain-type detection zone. Used to control entry into a room through window and door openings. Detection range 5m, curtain width 6.8m, viewing angle 70°.

Optical-electronic security detector Piron 4 B— equipped with a two-sensor pyro receiver. Detection zone type “curtain”, range 10m, viewing angle 70°. It has fine sensitivity adjustment, is resistant to radio interference and external light.

AX-100TF active dual beam detector— used to control extended sections of the external perimeter. Typically used in pairs, the devices are stacked on top of each other to form a barrier of four limiting beams. It is possible to select from four channels of carrier frequencies of the generated beams.