3.2. Passive infrared motion detectors

For interior security greatest distribution received passive IR motion detectors. They differ from each other mainly in the size of the detection zone and noise immunity.

The operating principle of passive IR detectors is based on recording changes in the intensity of IR radiation that occurs when a thermal object, such as a person or dog, moves in the detection zone of the device. The sensitive element of such a device is a pyroelectric element (pyroelectric detector), on the surface of which an electric charge arises under the influence of IR radiation from any thermal object. To register the fact of movement of a thermal object in the detector, a multi-beam radiation pattern is formed using a multi-segment mirror, consisting of many detection beams directed at different angles and in different directions. The intersection of these rays with a thermal object causes IR radiation pulses to hit the pyroelement and, as a consequence, the latter generates electrical pulses. These pulses are amplified and processed by a detector, which counts their number and the time interval between them. The values ​​of these parameters determine

noise immunity of the device and the range of detectable speeds of a moving thermal object (from 3 m/s for a fast running person to 0.3 m/s for a very slow movement). The detection beams form a detection zone, which determines the sensitivity of the device, i.e. maximum distance, on which a moving object is still reliably detected. Precise geometric characteristics (configuration) of the detection zone are provided by multi-segment mirrors and an optical system based on Fresnel lenses. Usage various types lenses allows you to change the configuration of the detection zone depending on the situation. Thanks to this, motion detectors have universal application and are used to protect the volume of premises, places of concentration of valuables (museum exhibits, office equipment, etc.) and approaches to them, corridors, internal perimeters, passages between shelving, window and door openings, floors, etc. Optical system depending depending on the type of lenses used, it allows you to obtain detection zones of the following types: volumetric, superficial and narrowly focused.

The volumetric zone (standard) is formed when using wide-angle lenses and is a sector of 90-110° in size with detection beams forming several discrete detection zones: far, intermediate, near and lower. The number of detection beams in these zones is different.

When using horizontal curtain lenses, a surface detection zone is formed. Such a zone has a “dead” area (zone of uncertain detection) up to a height of 1 - 1.2 m from the floor level, which allows the use of detectors with a “horizontal curtain” lens in rooms where there are pets.

The narrowly focused zone formed by the vertical curtain lens allows the detectors to be used to protect narrow corridors.

To increase detection ability, some detectors use sensors based on two or four pyroelements. In this case, the detection beam consists of two (four) elementary beams, and the special circuit for switching on the sensitive areas of the pyro receiver and the signal processing method provide increased resistance of the device to flare caused by the radiation of lighting devices (white lamps) and the sun, perceived as interference.

The detectors are well protected from electrical discharges and electromagnetic radiation Microwave range, durable metal case, acting as a screen. LED indication is used to visually monitor the performance of the device and the level of interference at its installation location. Some types of detectors have the ability to remotely turn on/off LED indicators via an alarm loop.

When motion, interference is detected, or when the device is opened, an alarm notification can be generated in two ways: a short circuit (by increasing the current consumption) or a break (by decreasing the current consumption) of the alarm loop. An alarm is issued by closing/opening the contacts of the alarm, intrusion and fault output relays. An alarm notification is issued within a few seconds, because the detector remembers the alarm signal.

Sometimes an IR motion detector is placed in the same housing with other types of detectors, for example, a broken glass detector. This is possible thanks to the use of passive infrared detection in motion detectors, which does not create interference or affect the operation of other devices.

3.2.1. XJ series motion detectors.

3.2.1. XJ Series Motion Detectors

Motion detector XJ660T

Fig.3.5 XJ660T motion detector

The passive infrared detector XJ660T from S&K Sysytem (IntelliSense) is a compact, attractive and easy-to-install device (Fig. 3. 5). It is used to protect residential and industrial premises.

The XJ660T is a passive infrared detector with a detection area measuring 18x15 m. The detector is manufactured using patented technology that virtually eliminates possible sabotage of the device.

Features of the XJ660T detector:

> automatic pulse counting;

> combination of a multi-segment mirror and a Fresnel lens;

> adjusting the characteristics of the detection zone depending on the installation height;

> temperature compensation;

> resistance to white light;

> possibility of using different types of lenses.

The device is equipped with a wide lens

angle" (Fig. 3. 6) or a lens type "vertical

curtain". It is possible to install a lens that provides protection from pets; it prevents the device from triggering when an object with a height of less than 1 m moves.

Main technical characteristics of the XJ660T device

Passive infrared sensor.................................dual pyroelectric element

with adjustable sensitivity Detection zone size, m.................................................... ............... 18x15

Rice. 3. 6. XJ660T detector detection zones

Operating voltage range, V................................................... ..... 6-14

Output relays:

alarm relay, mA/V................................................... ............... 100/30

intervention relay, mA/V................................................... .......... 25 / 30

Resistance to white light at a distance of 2.4 m, not less than cd........ 20000

Operating temperature range, °C.................................... from -18 to + 65

Overall dimensions, mm.............................................. .......... 130x70x60

To increase the detection area of ​​the detector, an additional swivel bracket type DT4SW is used. Thanks to its excellent design, the device fits well into the interior of an apartment or office. The detector is certified by the Russian Ministry of Internal Affairs.

Motion detector XJ413T

Reliable detection, adjustable sensitivity, compact modern design - all these characteristics are inherent in the XJ413T passive infrared motion detector from S&K Systems (Fig. 3. 7). The detector is intended for use inside residential premises and offices. It can be easily installed on a wall or in a corner of a room (see section 1.4).

Fig.3.7.Motion detector XJ413T

Features of the XJ413T detector:

> detection zone size 13x13 m;

> adjustable pulse counter;

> control of the lower zone;

> ease of installation;

> additional lenses;

> small dimensions;

> tampering sensor;

> resistant to white light;

> resistant to radio interference.

The size of the detection zone of the detector is determined by the “wide angle” lens (Fig. 3. 8) and is 13x13 m. The lower zone is controlled due to the greater density of beams directed downwards. Dual PIR element with additional horizontal curtain lens

allows you to avoid false alarms of the device in rooms with pets. By changing the number of counting pulses, the detector can be adjusted to suit the environment. The device body contains an intrusion sensor (relay with normally open contacts), which generates an alarm signal when the detector body is opened.

Main technical characteristics of the XJ413T device:

Detection zone size, m................................................... ............ 13x13

Current consumption (at supply voltage + 12 V), mA....................... 20

Output relays:

alarm relay, mA/V................................................... ............... 100/24

Resistance to white light at a distance of 3 m, not less, cd............ 20000

10-1000 MHz, V/m............................................... ................................. thirty

Overall dimensions, mm.............................................. ............ 73x57x40

The sensitivity of the device, normal or high, is set by a jumper on the board. The detection zone consists of double beams and has a far (22 beams), intermediate (7 beams) and near (4 beams), as well as a lower zone (2 beams). The device is mounted on a wall or in a corner of the room; it can be installed on the SMB-10 universal mounting hinge.

Rice. 3. 8. XJ413T detector detection zones

Motion detector XJ-450T

Rice. 3.9. Passive IR motion detector XJ450T

The passive infrared detector XJ450T from S&K Systems is made in a durable white plastic case (Fig. 3. 9). It provides reliable detection of moving objects that emit heat. Adjustable sensitivity and range allow you to quickly configure the sensor for specific application conditions. The device is intended for use in residential premises, offices and small businesses.

Features of the XJ450T detector:

> adjustable detection range;

> control of the lower zone;

> adjustable sensitivity;

> protection from insects;

> additional lenses;

> LED indication of operation

A double passive infrared element with an additional “horizontal curtain” lens (Fig. 3. 10) allows you to get rid of false alarms of the detector when moving pets in a protected area. Using a special signal processing algorithm, potential sources of false signals are eliminated.

Rice. 3. 10. XJ450T detection zones

alarms, such as insects. The lower zone is controlled thanks to the dense multi-beam structure of the radiation pattern. The ability to adjust the position of the detector sensor vertically allows you to adjust the size of the detection zone of the device, which makes its use more flexible. Depending on the adjustment, the size of the detection zone can be 15x12 m or 10x12 m. The sensitivity of the detector is set by a jumper and has two levels: normal and high.

Main technical characteristics of the XJ450T device:

Detection zone size, m................................... 15x12 or 10x12

Supply voltage, V................................................... ................ 10-14

Current consumption (at supply voltage + 12 V), mA....................... 20

Output relays:

intervention relay, mA/V................................................... .......... 25 / 24

alarm relay, mA/V................................................... ............... 100 / 24

Resistance to white light at a distance of 2.4 m no more than cd.......... 20000

Immunity to radio interference in the frequency range

10-1000 MHz, V/m............................................... .................................thirty

Operating temperature range, C.................................... from 0 to + 49

The detector can be easily installed on a wall or in a corner of a room. The detection zone consists of double beams and has a far (22 beams), intermediate (6 beams), near (3 beams), and lower (2 beams) zones.

By changing the number of pulses counted, the sensitivity of the detector can be adjusted to suit the environment. To install and configure the device, you can use the SMB-10 mounting hinge.

The detector has a quality certificate for use in Russia.

Motion detectors MS-550/MS-550T

Passive IR detectors MS-550/MS-550T from S&K (IntelliSense) are intended for use in enclosed spaces. These are devices with a high degree of reliability achieved through the use of a microprocessor. The detectors have a self-diagnosis mode and are also equipped with an operating mode indicator. The appearance of the devices is shown in Fig. 3. 9. It is the same as XJ405T detector.

Features of MS-550/MS-550T detectors:

> use of double pyroelements;

> dense radiation pattern;

> microprocessor signal processing system;

> automatic temperature compensation;

> self-diagnosis;

> sensitivity adjustment;

> protection from insects;

> mode for checking the configuration of the protected zone.

A double pyroelectric element and an optical system make it possible to obtain a detection zone measuring 15x12 m (Fig. 3. 10) with double the density of detection beams. The detector is resistant to false alarms in the presence of any number of cats or other small animals of the same size with a total weight of no more than 7 kg, as well as any number of birds flying at random or in cages. Mice and rats also do not affect the operation of the detector.

An automatic check of the detector's performance is performed hourly. If a malfunction is detected, testing is repeated every 5 minutes. Errors during test execution are indicated by a flashing LED. od. Upon successful completion of the self-test carried out automatically after power is applied, or when the user starts the self-diagnosis mode, the detector goes into a 10-minute mode for checking the configuration of the protected zone. In this mode, you can determine the exact configuration of the protected area by performing a test pass - each time the edge of one of the detection beams is crossed, the LED will turn on.

Main technical characteristics of MS-550/MS-550T devices:

Supply voltage, V................................................... ............ 10-14

Current consumption (at supply voltage + 12 V), mA....................... 20

Output relays:

intervention relay, mA/V................................................... .......... 25/24

Alarm relay, mA/V................................................... ............... 100/24

Resistance to white light, lux................................................... ......... 6500

Immunity to radio interference in the range

frequencies 10-1000 MHz, V/m.................................... ........................ thirty

Operating temperature range, C.................................... from 0 to + 40

Overall dimensions, mm.............................................. ............ 90x44x45

Weight, g................................................... ............................................... 85

The detector allows you to adjust the sensitivity using jumpers on the circuit board of the device. Three sensitivity levels are possible: high, normal and low.

The detector can be installed on a wall or in a corner of a room at a height of 1, 2, 2, 3 or 3 m from the floor. It should be remembered that the protected area must be within the direct line of sight of the detector.

Rice. 3.10. XJ450T detection zones

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Rice. 3.6. XJ660T detector detection zones

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Rice. 3.8. XJ413T detector detection zones

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Fig.3.5 XJ660T motion detector

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Fig.3.7. Motion detector XJ413T

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3.2.2. Motion detector PIR700E.

3.2.2. Motion detector PIR700E

The PIR700E passive infrared detector is designed for installation in rooms up to 200 m2. It can be installed on the wall or in the corner of the room. The operation of the detector is based on the use of a double pyroelectric element. Design features detector allow it to be used in residential areas where there are pets. Features of the PIR700E detector:

> effective protection from false alarms caused by radio interference;

> adjusting the size of the detection zone in vertical and horizontal planes;

> double pyroelectric element;

> tamper evident;

> high sensitivity;

> small dimensions;

> filtering the supply voltage from network noise;

> Possibility of installation in the corner of the room.

It is recommended to use an uninterruptible power supply to operate the detector. When using a “wide angle” lens (Fig. 3. 11) and installed at a height of 1.8 m, the detector allows monitoring an area measuring 15x15 m. The use of additional lenses allows you to adjust the directional pattern of the sensor (Fig. 3. 11). Using the Lens Lens 817 The “horizontal curtain” type makes sense only when the detector is installed in a room where there are pets. Using the Lens Lens 818 The “vertical curtain” type is justified when the device is installed in a narrow corridor.

Rice. 3. 11. PIR700E detection zones

Main technical characteristics of the PIR700E detector:

Dimensions of detection zone, m................................................... ..... 15, 2x15, 2

Supply voltage, V................................................... .............. 10, 6-16

Current consumption (at supply voltage + 12 V), mA.................................... 23

Maximum installation height, m................................................... ....... 3, 6

Alarm relay, mA/V................................................... ........................... 100/24

Detector output...................................normally closed relay contacts

Relay activation time no more than, s................................................... ............. 3

Operating temperature range, C.................................... from -10 to + 50

Overall dimensions, mm.............................................. .......... 114x64x43

Weight, g................................................... ........................................... 198

The detector is installed on a wall or in a corner of the room, the maximum installation height is 3.6 m. The sensor goes into security mode no earlier than 3 minutes after power is applied. This mode is indicated by the LED indicator of the device lighting up. To turn off the LED, you must remove the jumper on the device board. When installing the detector, it is not recommended to place it near heat sources such as radiators, heater, incandescent lamps and etc..

Rice. 3.11. PIR700E detection zones

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3.2.3. Outdoor motion detector LX-2AU.

3. 2. 3. Outdoor motion detector LX-2AU

The Optex LX-2AU Passive Infrared Detector is a device specifically designed for outdoor use. The detector ensures stability of the size of the detection zone in the most severe climatic conditions such as snow, rain, fog, etc.

Features of the LX-2AU detector:

> automatic stabilization of the size of the detection zone in any conditions environment;

> high sensitivity double pyroelectric sensor;

> balanced temperature compensation;

> three sensitivity levels;

> sensitivity adjustment;

> built-in LED operating mode indicator;

> the ability to adjust the position of the sensor in the vertical and horizontal plane;

> rapid change in the size of the detection zone.

The sensor is resistant to direct sun rays and car headlights. A special signal processing algorithm allows it to adapt to changing environmental conditions. Main technical characteristics of the LX-2AU device:

Detection zone size, m................................................... ............ 12x14

Viewing angle, degrees................................................... ........................... 120

Registered speed of movement, m/s........................ from 0.3 to 1.0

Adjustment:

in the vertical plane, deg................................................... ....... ±45

in the horizontal plane, deg................................................... 0 - 20

Output relay, mA/V................................................... ................... 100/24

Number of sensitivity levels......................................................... ... 3

Operating temperature range, °C.................................... from -20 to + 50

The built-in photodiode allows automatic shutdown sensor at a certain level of illumination, usually during daylight hours. The light level at which this shutdown occurs is adjustable.

The sensor is easy to use and install. Ceiling and wall brackets allow you to adjust the position of the sensor in the vertical and horizontal plane.

3.2.4. Motion detectors "Photon".

3. 2. 4. Motion detectors "Photon"

Passive infrared detectors "Foton-6" and "Foton-8"

Security passive infrared detectors "Foton-6" and "Foton-8" developed and manufactured in Russia. They are designed to work as part of control panels, such as " Signal- 37A", "Signal-40", "Signal-45"", as well as in the systems "Phobos", "Neva-10M", "Comet-K".

The devices are powered via an alarm loop. A double pyroelectric element is used as a sensor. Thanks to the use of three types

lens detectors have three detection zones. The body of the devices has a modern design (Fig. 3. 12), which allows them to fit well into the interior of any room.

Features of “Photon” type detectors:

> high detecting ability;

> high resistance to electromagnetic, thermal and light interference;

> two ways to generate an alarm notification;

> quick access to operating mode;

> visual control of the device’s performance;

> supply voltage control;

> power supply via alarm loop;

> wide installation options.

The high detecting ability of the detectors is ensured through the use of three detection zones: volumetric, surface and linear (Fig. 3: 13). This allows them to be used to protect premises of almost any configuration.

Rice. 3. 13. Detector detection zones "Foton-6"

Main technical characteristics of detectors "Photon":

Controlled area with volumetric detection zone, m2............... 120

Recorded movement speed, m/s.................................... 0, 3-3, 0

Current consumption:

"Foton-6" mA................................................... ............................ 15

« Foton-8", mA................................................... ............................. 1

Operating temperature range:

"Foton-6"°C................................................... ............. from -30 to + 50

"Foton-8",°C................................................... ............. from -10 to + 50

Overall dimensions, mm.............................................. ......... 107x107x64

Weight, kg................................................... ........................................ 0.25

Motion Detector "Foton-SK"

Security volumetric optical-electronic motion detector "Foton-SK"(Fig. 3. 14) is produced in Russia. It was developed jointly with the American company S&K Systems by order of the Main Directorate of Private Security of the Ministry of Internal Affairs of Russia. The sensor is recommended for installation in residential premises, offices and small businesses.

Detector Features "Foton-SK":

> disabling the LED indicator in security mode;

> protection against unauthorized opening;

> high noise immunity;

> protection from pets;

> minimal amount components;

> Possibility of installation on the wall or in the corner of the room.

Currently the device "Foton-SK" is one of the cheapest motion detectors on the Russian market. In the production of the device, modern technological equipment for surface mounting from Universal Instruments Corporation, which makes it possible to obtain very high characteristics of the device.

The detector has five detection zones and covers an area measuring 15x12 m

(Fig. 3.15). Digital signal processing makes it possible to exclude the sensor from triggering by flying insects. An additional lens allows you to limit the detection zone from below to a certain height, thereby providing protection from pets.

Rice. 3. 15. Device detection zones "Foton-SK"

Main technical characteristics of the device "Foton-SK":

Detection zone size, m................................................... ............ 15x12

Supply voltage, V................................................... ............ 10-14

Current consumption, mA................................................... ......................... 20

Operating temperature range, °C.................................... from -18 to + 49

Overall dimensions, mm.............................................. ............ 90x64x41

Weight, g................................................... ............................................... 85

"Foton-SK" - This is one of the best detectors produced by the domestic industry. It has the highest quality/price ratio.

Rice. 3.12. Motion detector "Foton-SK"

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Rice. 3.12. Motion detectors "Photon-6" and "Photon-8"

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Rice. 3.13. Detection zones of the Foton-6 detector

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Rice. 3.15. Detection zones of the Foton-SK device

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3.2.5. Motion detector MRS 4040T.

3. 2. 5. Motion detector MRS 4040T

The MPC 4040T passive infrared detector with a dual sensitive sensor manufactured by IntelliSense is an economical device with a detection zone size of 12x15 m (Fig. 3. 16). It uses patented technology S&K, as well as a combination of a segment mirror and a Fresnel lens, which virtually eliminates possible sabotage of the device.

Features of the MRS 4040T detector:

> temperature compensation;

> sensitivity adjustment;

> adjustment of the detection zone depending on the installation height;

> resistance to white light;

> additional swivel bracket.

Rice. 3. 17. Detection zones of the MRS4040T device

The device uses a double pyroelectric element with adjustable sensitivity. When using a “wide angle” lens (Fig. 3. 17), the area controlled by the device will be 144 m2 (12x12 m). It is possible to install a “vertical curtain” lens, which provides a narrow protected area up to 18 m long. The “horizontal curtain” lens for protection from pets prevents the detector from triggering when movement occurs in an area whose height is below 1.2 m. This is ensured as when using wide and narrow radiation patterns.

Main technical characteristics of the MRS4040T device:

Detection zone size, m................................................... ............ 12x 12

Radio interference immunity at a distance of 3 m

in the range of 20-100 MHz, W.................................................... ................. 100

Resistance to white light at a distance of 2.4 m, not less than cd......... 20000

Supply voltage, V................................................... ................. 8-14

Current consumption (at supply voltage + 12 V), mA....................... 20

Output relays:

alarm relay, mA, V................................................... ............... 100/30

Operating temperature range, C.................................... from -18 to + 65

Overall dimensions, mm.............................................. ............ 92x60x50

Weight, g................................................... ........................................... 71

The sensor is installed on a wall or in a corner of the room. An additional swivel bracket type DT4SW can be used for installation. The detector is designed to protect enclosed spaces. The high quality and reasonable price of the device is exactly what makes it competitive in the domestic market of technical security equipment.

IntelliSense's IQ200 Series passive infrared motion detectors use a combination of four pyroelements with adjustable sensitivity. The devices (Fig. 3.18) are intended for organizing security and installation in residential premises, offices and small enterprises. The IQ220T detector has a range of 12 m, and the IQ260T detector has a range of 18 m. Features of the 10200 series detectors:

> the ability to adjust the size of the detection zone;

> LED indication of operating mode;

> resistance to radio interference;

> resistance to white light;

> temperature compensation.

The IQ220T features patented technology S&K, thanks to which false alarms of the system are almost completely eliminated. The multi-segment mirror and Fresnel lens provide a detection area of ​​approximately 200 m2. Using a set of lenses, you can obtain the required radiation pattern of the detector (Fig. 3.19). The device can be equipped with a “horizontal curtain” lens to protect against false alarms caused by pets. The detector contains two double pyroelements with adjustable sensitivity.

Main technical characteristics of IQ200 series devices:

Detection area size:

IQ220T,M................................................... ................................ 12x12

IQ260T, m................................................... ................................ 18x15

Radio interference immunity at a distance of 3 m

in the range 27-1000 MHz, W.................................................... ................ 100

Resistance to white light at a distance of 2.4 m, cd....................... 20000

Supply voltage, V................................................... ............ 10-14

Current consumption (at supply voltage +12 V), mA.................................30

Output relays:

alarm relay, mA/V................................................... ............... 100/30

intervention relay, mA/V................................................... .......... 25/30

Operating temperature range, °C.................................... from -18 to +65

Overall dimensions, mm.............................................. .......... 130x70x60

Weight, g................................................... ........................................... 227

3.2.7. Ceiling detector FIR5030.

3. 2. 7. Ceiling detector FIR5030

The FIR5030 motion detector from S&K (IntelliSense) is two independent devices in one housing: a passive infrared detector and a broken glass detector. FIR5030 has a circular radiation pattern and is designed for installation on the ceiling of a protected area. It has a modern design (Fig. 3. 20) and high performance characteristics, which makes it an excellent means for protecting premises, such as small shops with a glass facade or offices. Features of the FIR5030 detector:

> Possibility of installation flush with the ceiling surface and on suspended ceiling;

> two output relays in one housing (one for each detector);

> adjustable installation height;

> sensitivity adjustment;

> LED operating mode indicator;

>memorizing the alarm.

The device includes a passive infrared (PIR) detector with a circular radiation pattern based on a pyroelectric element with adjustable sensitivity. It is designed to detect unauthorized entry into the premises. It can use one of two interchangeable mirrors, the use of which is determined by the installation height of the device and the required number of detection beams (Fig. 3. 21).

When installing a mirror. No. 1, the installation height should be from 2.5 to 3.5 m from the floor. In this case, the radiation pattern will consist of 77 detection beams of various lengths.

When installing mirror No. 2, the installation height should be 3.5-4.9 m. The number of detection beams is reduced to 61.

The second detector of the device is the broken glass detector (GDS) Flex Guard

with a range of up to 9 m, designed to register the fact of glass breaking and generate an alarm signal. The operating principle of the detector is based

on the analysis of the spectrum of the sound signal generated when hitting glass

and when it breaks. To generate an alarm signal, the device must

register the impact on the glass and the sound of breaking glass, and the interval

There should be no more than 150 ms between both sounds. This eliminates the possibility of false positives. The range of the broken glass detector depends on the type, thickness and size of the glass. Therefore, to set up the device it is necessary to use a special glass breaking simulator FlexGuard 700..

Technical characteristics of the FIR5030 detector:

Radius of detection zone of PIR detector, m....................................................15

The number of detection beams is not less than................................................... .............61

Installation height, m................................................... ............. from 2.5 to 4.9

DBS detection radius no more than, m.................................................... ....... 9

Type of glass................................................... metallized, layered

tempered, reinforced Glass thickness, mm.................................................... ........................ 4 - 7

Glass size not less than, mm................................................... .......... 270x270

Supply voltage, V................................................... ............... 8.5-1.6

Current consumption (at supply voltage +12 V), mA.................................40

Output relays:

alarm relay PIC detector, mA/V..................................... 500/30

DBS alarm relay, mA/V.................................................... ............ 500/30

intervention relay, mA/V................................................... .......... 25 /30

Rice. 3. 21. Detection zones of the FIR5030 detector

The device can be installed on the ceiling surface or flush with it. The mounting height is adjustable using an additional mirror. The device provides the ability to adjust the sensitivity of the PIR detector and DBS and store the alarm signal.

– they open doors at airports and stores when you approach the door. They also detect movement and sound an alarm. burglar alarm. How they work: The sensor, sensitive to infrared radiation in the range of 5-15 microns, detects thermal radiation from the human body. If anyone has forgotten physics, let me remind you: it is in this range that the maximum radiation from bodies falls at a temperature of 20–40 degrees Celsius. The hotter an object is, the more it emits. For comparison: infrared illuminators for video cameras, beam (two-position) “cross-beam” detectors and TV control panels operate in the wavelength range shorter than 1 micron, visible to humans the spectral region is in the region of 0.45–0.65 µm.
Sensors of this type are called passive because they themselves do not emit anything, they only perceive thermal radiation from the human body. The problem is that any object at a temperature of even 0º C emits quite a lot in the IR range. Even worse, the detector itself emits radiation – its body and even the material of the sensitive element. Therefore, the first such detectors worked if only the detector itself was cooled, say, to liquid nitrogen (-196º C). Such detectors are not very practical in everyday life. Modern mass detectors all work on the differential principle - they are not able to accurately measure the actual amount of infrared radiation flux from a moving person (against the background of parasitic fluxes from much closer objects), but (also, in fact, on the verge of sensitivity) are capable detect a CHANGE in the DIFFERENCE in IR radiation fluxes incident on two neighboring sites. That is, it is important that radiation from a person is focused only on one of the sites, and moreover, it changes. The detector works most reliably if the image of a person first hits one site, the signal from it becomes greater than from the second, and then the person moves, so that his image now hits the second site and the signal from the second increases, and from the first decreases. Such fairly rapid changes in the signal difference can be easily detected even against the background of a huge and variable signal caused by all other surrounding objects (and especially sunlight).

How to fool an IR detector
The initial disadvantage of the IR passive motion detection method is that the person must be clearly different in temperature from the surrounding objects. At a room temperature of 36.6º, no detector will distinguish a person from the walls and furniture. Even worse: the closer the room temperature is to 36.6º, the worse the sensitivity of the detector. Most modern devices partially compensate for this effect by increasing the gain at temperatures from 30º to 45º (yes, the detectors also work successfully at the reverse temperature difference - if the room is +60º, the detector will easily detect a person, thanks to the thermoregulation system human body will keep the temperature around 37º). So, when the outside temperature is about 36º (which is often found in southern countries), the detectors open doors very poorly, or, on the contrary, due to extremely high sensitivity, they react to the slightest breath of wind.
Moreover, the IR detector can be easily blocked by any object room temperature(sheet of cardboard) or wear a thick fur coat and hat so that your arms and face do not stick out, and if you walk slowly enough, the IR detector will not notice such small and slow disturbances.
There are also more exotic recommendations on the Internet, such as a powerful IR lamp, which, if turned on slowly (with a regular dimmer), will drive the IR detector off scale, after which you can walk in front of it even without a fur coat. Here, however, it should be noted that good IR detectors in this case will give a malfunction signal.
Finally, the most well-known problem with IR detectors is masking. When the system is disarmed, during business hours during the day, you, as a visitor, come to the desired premises (a store, for example) and, seizing the moment while no one is looking, block the IR detector with a piece of paper, cover it with an opaque self-adhesive film, or fill it with spray paint. This is especially convenient for a person who works there himself. The storekeeper carefully blocked the detector during the day, climbed through the window at night, took everything out, and then removed everything and called the police - horror, they robbed, but the alarm did not work.
To protect against such masking, the following technical techniques exist.
1. In combined (IR + microwave) sensors, it is possible to issue a fault signal if the microwave sensor detects a large reflected radio signal (someone came very close or reached out directly to the detector), and the IR sensor stopped producing signals. In most cases in real life this does not mean the malicious intent of the criminal, but the negligence of the staff - for example, a high stack of boxes blocked the detector. However, regardless of malicious intent, if the detector is blocked, this is a disorder, and such a “malfunction” signal is very appropriate.
2. Some control panels have a control algorithm when, after disarming the detector, it detects movement. That is, the absence of a signal is considered a malfunction until someone passes in front of the sensor and it issues a normal “there is movement” signal. This function is not very convenient, because often all premises are disarmed, even those that no one is going to enter today, but it turns out that in the evening, in order to arm the premises again, you will have to go into all the rooms where no one was there during the day, and wave your hands in front of the sensors - the control panel will make sure that the sensors are operational and will graciously allow you to arm the system.
3. Finally, there is a function called “near zone”, which was once included in the requirements of the Russian GOST and which is often mistakenly called “anti-masking”. The essence of the idea: the detector should have an additional sensor looking straight down, under the detector, or a separate mirror, or a special tricky lens, in general, so that there is no dead zone below. (Most detectors have a limited viewing angle and generally face forward and 60 degrees downward, so there is a small dead zone directly below the detector, at floor level about a meter from the wall.) It is believed that a cunning enemy will somehow be able to get into this dead zone and from there block (mask) the lens of the IR sensor, and then brazenly walk around the entire room. In reality, the detector is usually installed so that there is no way to get into this dead zone without bypassing the sensor's sensitivity areas. Well, perhaps through the wall, but additional lenses will not help against criminals penetrating through the wall.

Radio interference and other interference
As I said, the IR sensor operates close to its sensitivity limit, especially with room temperatures approaching 35º C. Of course, it is also very susceptible to interference. Most IR detectors can give a false alarm if placed near them. cellular telephone and call it. At the connection establishment stage, the phone emits powerful periodic signals with a period close to 1 Hz (it is in this range that typical signals from a person walking in front of the IR sensor lie). A few watts of radio radiation are quite comparable to microwatts of human thermal radiation.
In addition to radio emissions, there may also be optical interference, although the lens of the IR sensor is usually opaque in the visible range, but powerful lamps or 100 W car headlights in the neighboring spectral range can again quite produce a signal comparable to microwatts from a person in the desired range. The main hope is that extraneous optical interference, as a rule, is poorly focused and therefore equally affects both sensitive elements of the IR sensor, thus the detector can detect the interference and not issue a false alarm.

Ways to improve IR sensors
For ten years now, almost all IR security detectors contain a fairly powerful microprocessor and therefore have become less susceptible to random interference. Detectors can analyze the repeatability and characteristic parameters of the signal, long-term stability of the background signal level, which has significantly increased immunity to interference.
IR sensors, in principle, are defenseless against criminals behind opaque screens, but are susceptible to the influence of heat flows from climate control equipment and extraneous illumination (through a window). Microwave (radio) motion sensors, on the contrary, are capable of producing false signals, detecting movement behind radio-transparent walls, outside the protected premises. They are also more susceptible to radio interference. Combined IR + microwave detectors can be used both according to the “AND” scheme, which significantly reduces the likelihood of false alarms, and according to the “OR” scheme for especially critical premises, which practically eliminates the possibility of overcoming them.
IR sensors cannot distinguish a small person from big dog. There are a number of sensors in which sensitivity to the movements of small objects is significantly reduced through the use of 4-area sensors and special lenses. In this case, the signal from a tall person and from a short dog can be distinguished with some probability. You need to understand well that it is, in principle, impossible to completely distinguish a crouched teenager from a Rottweiler standing on its hind legs. Nevertheless, the likelihood of a false alarm can be significantly reduced.
A few years ago, even more complex sensors appeared - with 64 sensitive areas. In fact, this is a simple thermal imager with an 8 x 8 element matrix. Equipped with a powerful processor, such IR sensors (calling them a “detector” is too much for me) are capable of determining the size and distance to a moving warm target, the speed and direction of its movement - 10 years ago such sensors were considered the pinnacle of technology for homing missiles, but now they are used for protection against common thieves. Apparently, we will soon get used to calling small robots that wake you up at night with the words “IR sensor” with the words: “Sorry, sir, but thieves, sir, they want tea. Should I serve them tea now or ask them to wait while you wash up and take your revolver?”

Infrared detectors are one of the most common in security alarm systems. This is explained by a very wide range of their applications.

They are used:

• to control the internal volume of premises;
• organization of perimeter security;
• blocking various building structures"on the way."

In addition to the climatic version (outdoor and indoor installation) they are also divided according to the principle of action. There are two large groups: active and passive. In addition, infrared detectors are divided according to the type of detection zone, namely:

• volumetric;
• linear;
• superficial.

Let's look in order for what purposes these or those types are used.

Passive infrared detectors.

These sensors incorporate a lens that “cuts” the monitored area into separate sectors (Fig. 1). The detector is triggered when temperature differences between these zones are detected. Thus, the opinion that such a security sensor reacts purely to heat is erroneous.

If a person in the detection zone stands motionless, the detector will not work. In addition, the temperature of an object close to the background also affects its sensitivity downwards.

The same applies to cases when the speed of movement of an object is lower or higher than the normalized value. As a rule, this value lies in the range of 0.3-3 meters/second. This is quite enough to confidently detect an intruder.

Active infrared detectors.

Devices of this type include an emitter and a receiver. They can be made in separate blocks or combined in one housing. In the latter case, when installing such security device An element that reflects IR rays is additionally used.

The active principle of operation is typical for linear sensors that are triggered when an infrared beam crosses. Below we discuss the principles of operation and application features of the main types of IR detectors.

VOLUMETRIC INFRARED DETECTORS

These devices are passive (see what they are above) and are used mainly to control the internal volume of premises. The directional pattern of the volumetric sensor is characterized by:

• opening angle in vertical and horizontal planes;
• range of the detector.

Please note that the range of action is indicated by the central lobe of the diagram; for the side lobes it will be less.

What is typical for any infrared sensor, including volumetric, is that any obstacle for it is opaque, and accordingly creates dead zones. On the one hand, this is a disadvantage, on the other, it is an advantage, since there is a complete lack of reaction to moving objects outside the protected premises.

Disadvantages also include the possibility of false positives from factors such as:

• convection heat flows, for example, from heating systems of different operating principles;
• illumination from moving light sources - most often car headlights through a window.

Thus, when installing a volumetric detector, these points cannot be ignored. According to the installation method, there are two versions of “volumetrics”.

Wall-mounted volumetric IR detectors.

Ideal for offices, apartments, private houses. In such rooms, furniture and other interior items are usually located along the walls, so they do not create blind spots. If we take into account that the horizontal viewing angle of such sensors is about 90 degrees, then by installing it in the corner of the room, one device can almost completely block a small room.

Ceiling volumetric detectors.

For objects such as shops or warehouses, a characteristic feature is the installation of shelving or display cases throughout the entire area of ​​the premises. Installing a ceiling sensor in such cases is more effective, of course, if the specified elements have a height below the ceiling.

Otherwise, you will have to block each resulting compartment. In fairness, it should be noted that such a need does not always arise, but these are the subtleties of designing an alarm system for each specific object, taking into account all its individual characteristics.

LINEAR INFRARED DETECTORS

By their operating principle, they are active and form one or more beams, tracking their intersection by a possible intruder. Unlike volumetric sensors, linear sensors are resistant to various types of air flows, and direct illumination, in most cases, will not harm them.

The operating principle of a linear single-beam infrared emitter is illustrated in Figure 2.

The range of active linear devices ranges from tens to hundreds of meters. The most typical options for their use:

• blocking corridors;
• protection of open and fenced perimeters of the territory.

To protect the perimeter, detectors with more than one beam are used (it is better if there are at least three). This is fairly obvious as it reduces the likelihood of penetration under or above the control zone.

When installing and configuring infrared linear detectors, precise alignment of the receiver and transmitter for two-block devices or the reflector and combined block (for single-block devices) is required. The fact is that the cross-section (diameter) of the infrared beam is relatively small, so even a small angular displacement of the transmitter or receiver leads to its significant linear deviation at the reception point.

The above also implies the need to mount all elements of such detectors on rigid linear structures that completely eliminate possible vibrations.

I must note that a good “linear” is quite an expensive pleasure. If the cost of single-beam devices with a short range is still within a few thousand rubles, then with an increase in the controlled range and the number of IR rays, the price increases to tens of thousands.

This is explained by the fact that security detectors of this type are quite complex electromechanical devices containing, in addition to electronics, high-precision optical devices.

By the way, passive linear detectors also exist, but in terms of maximum range they are noticeably inferior to their linear counterparts.

OUTDOOR INFRARED DETECTORS

It is quite obvious that a street burglar alarm detector must have an appropriate climatic design. This applies primarily to:

• operating temperature range;
• degree of dust and moisture protection.

According to the generally accepted existing classification, the protection class of a street detector must be at least IP66. By by and large, for most consumers this is not important - the indication “street” in the description is quite enough technical parameters device. It is worth paying attention to the temperature range.

Of greater interest are the features of the use of such devices and the factors influencing the reliability of security.

Based on the nature of the detection zone, infrared security detectors intended for outdoor installation can be of any type (in descending order of popularity):

• linear;
• volumetric;
• superficial.

As already mentioned, street linear detectors are used to protect the perimeter of open areas. Surface sensors can also be used for the same purposes.

Volumetric devices are used to control various types of areas. It is worth immediately noting that in terms of range they are inferior to linear sensors. It is quite natural that prices for outdoor detectors are much higher than for devices intended for indoor installation.

Now, as for the practical side of using infrared outdoor detectors in security alarm systems. The main factors that provoke false alarms of security sensors installed on the street are:

• the presence of various vegetation in the protected area;
• movement of animals and birds;
• natural phenomena in the form of rain, snow, fog, etc.

The first point may seem unprincipled, since, at first glance, it is static and can be taken into account at the design stage. However, you should not forget that trees, grass and bushes grow and over time can become an obstacle to the normal operation of security equipment.

Manufacturers try to compensate for the second factor by using appropriate signal processing algorithms, and this has an effect. True, whatever one may say, if an object, even with small linear dimensions, moves in the immediate vicinity of the detector, it will most likely be identified as an intruder.

Regarding the last point. Here everything depends on changes in the optical density of the medium. Speaking in simple language, heavy rain, heavy snow or thick fog can render the infrared detector completely inoperable.

So, when deciding to use street security detectors in the alarm system, consider everything that has been said. This way you can save yourself from many unpleasant surprises when using an external security system.

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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 devices. 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 sent 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 offender’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 several 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, 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. Usage modern technologies lens manufacturing makes it possible to ensure almost constant sensitivity of the detector for all rays 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 pyro 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-sabotage 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 a 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 the PARADOX company 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 pyro 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.

One more protective element, which 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 methods signal processing. It should be taken into account that special processing signals allows you to ignore animals 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 the protected area, then such protection will not 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 Maintenance. Detectors of this type can be installed either on a flat surface load-bearing wall, and in the corner of the room. There are detectors that are placed on the ceiling.

Competent selection and tactically correct use of such detectors are the key to reliable operation devices, 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. However, in some cases it will not be necessary large quantity sensors to protect each structure - it may be sufficient to use one or more sensors with the desired sensitivity zone configuration. Let's take a look at some of the features of using IR sensors.

General principle using IR sensors - the rays of the sensitivity zone must 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 doors in a room open inwards, the possibility of masking an intruder should be taken into account 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 height). 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 pieces of 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 against 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 capital or load-bearing 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 it solar radiation, convective air flows from the operation of radiators of heating systems, air conditioners, 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 a change 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 point the detector detection area at heating elements heating and air conditioning systems, on curtains and curtains, which can fluctuate due to drafts.
Do not place passive optical-electronic detectors near sources of electromagnetic radiation.
Seal all holes 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.

Right choice A passive optical-electronic IR detector and its installation location are the key to reliable operation of the security alarm system.

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

In the 21st century, everyone is familiar with IR sensors - they open doors in airports and stores when you approach the door. They also detect movement and sound an alarm in the security alarm system. 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 devices. 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.

How does a PIR motion sensor work?

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.

In passive optical-electronic IR detectors, infrared thermal 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 sent 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 offender’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 several 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 are 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 pyro 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-sabotage 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 whether 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 a 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 frequency analysis range.

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 pyro 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 the gain is automatically increased as it rises. With “true” or “two-way” compensation, the increase in thermal contrast for temperatures above 25°C...35°C is taken into account. 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 the room open inward, you should consider the possibility of masking the 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.

How to fool an IR detector

The initial disadvantage of the IR passive motion detection method is that the person must be clearly different in temperature from the surrounding objects. At a room temperature of 36.6º, no detector will distinguish a person from the walls and furniture. Even worse: the closer the room temperature is to 36.6º, the worse the sensitivity of the detector. Most modern devices partially compensate for this effect by increasing the gain at temperatures from 30º to 45º (yes, detectors also work successfully at the opposite temperature difference - if the room is +60º, the detector will easily detect a person; thanks to the thermoregulation system, the human body will maintain a temperature of about 37º). So, when the outside temperature is about 36º (which is often found in southern countries), the detectors open doors very poorly, or, on the contrary, due to extremely high sensitivity, they react to the slightest breath of wind.

Moreover, it is easy to shield yourself from the IR detector with any object at room temperature (a sheet of cardboard) or wear a thick fur coat and hat so that your hands and face do not stick out, and if you walk slowly enough, the IR detector will not notice such small and slow disturbances.

There are also more exotic recommendations on the Internet, such as a powerful IR lamp, which, if turned on slowly (with a regular dimmer), will drive the IR detector off scale, after which you can walk in front of it even without a fur coat. Here, however, it should be noted that good IR detectors in this case will give a malfunction signal.

Finally, the most well-known problem with IR detectors is masking. When the system is disarmed, during business hours during the day, you, as a visitor, come to the desired premises (a store, for example) and, seizing the moment while no one is looking, block the IR detector with a piece of paper, cover it with an opaque self-adhesive film, or fill it with spray paint. This is especially convenient for a person who works there himself. The storekeeper carefully blocked the detector during the day, climbed through the window at night, took everything out, and then removed everything and called the police - horror, they robbed, but the alarm did not work.

To protect against such masking, the following technical techniques exist.

1. In combined (IR + microwave) sensors, it is possible to issue a fault signal if the microwave sensor detects a large reflected radio signal (someone came very close or reached out directly to the detector), and the IR sensor stopped producing signals. In most cases in real life, this does not mean the malicious intent of the criminal, but the negligence of the staff - for example, a high stack of boxes blocked the detector. However, regardless of malicious intent, if the detector is blocked, this is a disorder, and such a “malfunction” signal is very appropriate.

2. Some control panels have a control algorithm when, after disarming the detector, it detects movement. That is, the absence of a signal is considered a malfunction until someone passes in front of the sensor and it issues a normal “there is movement” signal. This function is not very convenient, because often all premises are disarmed, even those that no one is going to enter today, but it turns out that in the evening, in order to arm the premises again, you will have to go into all the rooms where no one was there during the day, and wave your hands in front of the sensors - the control panel will make sure that the sensors are operational and will graciously allow you to arm the system.

3. Finally, there is a function called “near zone”, which was once included in the requirements of the Russian GOST and which is often mistakenly called “anti-masking”. The essence of the idea: the detector should have an additional sensor looking straight down, under the detector, or a separate mirror, or a special tricky lens, in general, so that there is no dead zone below. (Most detectors have a limited viewing angle and generally face forward and 60 degrees downward, so there is a small dead zone directly below the detector, at floor level about a meter from the wall.) It is believed that a cunning enemy will somehow be able to get into this dead zone and from there block (mask) the lens of the IR sensor, and then brazenly walk around the entire room. In reality, the detector is usually installed so that there is no way to get into this dead zone without bypassing the sensor's sensitivity areas. Well, perhaps through the wall, but additional lenses will not help against criminals penetrating through the wall.

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 capital 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 is 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 is 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.

Ways to improve IR sensors

For ten years now, almost all IR security detectors contain a fairly powerful microprocessor and therefore have become less susceptible to random interference. Detectors can analyze the repeatability and characteristic parameters of the signal, long-term stability of the background signal level, which has significantly increased immunity to interference.

IR sensors, in principle, are defenseless against criminals behind opaque screens, but are susceptible to the influence of heat flows from climate control equipment and extraneous illumination (through a window). Microwave (radio) motion sensors, on the contrary, are capable of producing false signals, detecting movement behind radio-transparent walls, outside the protected premises. They are also more susceptible to radio interference. Combined IR + microwave detectors can be used both according to the “AND” scheme, which significantly reduces the likelihood of false alarms, and according to the “OR” scheme for especially critical premises, which practically eliminates the possibility of overcoming them.

IR sensors cannot distinguish between a small person and a large dog. There are a number of sensors in which sensitivity to the movements of small objects is significantly reduced through the use of 4-area sensors and special lenses. In this case, the signal from a tall person and from a short dog can be distinguished with some probability. You need to understand well that it is, in principle, impossible to completely distinguish a crouched teenager from a Rottweiler standing on its hind legs. Nevertheless, the likelihood of a false alarm can be significantly reduced.

A few years ago, even more complex sensors appeared - with 64 sensitive areas. In fact, this is a simple thermal imager with an 8 x 8 element matrix. Equipped with a powerful processor, such IR sensors are capable of determining the size and distance to a moving warm target, the speed and direction of its movement - 10 years ago such sensors were considered the pinnacle of technology for homing missiles, and now they are used to protect against common thieves.

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 holes 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.

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