Infrared detectors are among the most common in systems. security alarm. This is explained by a very wide range of their use.
They are used:
In addition to climatic execution (street and internal 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 by the type of detection zone, namely:
Let us consider in order for what purposes these or other types are used.
Passive infrared detectors.
These sensors have a lens in their composition, a "cut" controlled area into separate sectors (Fig. 1). The triggering of the detector occurs when the temperature differences are detected between these zones. Thus, the view is that such a security sensor reacts purely onto the heat erroneously.
If a person who is in the detection zone will stand still, the detector will not work. In addition, the temperature of the object close to the background also affects its sensitivity towards the decrease.
The same applies to the cases when the speed of moving the object is lower or higher than the normalized value. As a rule, this value lies within 0.3-3 meters / second. For confident detection of the violator of this is quite enough.
Active infrared detectors.
The devices of this type have an emitter and receiver in their composition. They can be performed by separate blocks or combined in one case. In the latter case, when installing such a security device, an element reflecting IR rays is additionally used.
The active principle of operation is characteristic of linear sensors, which are triggered when crossing the infrared beam. The principles of action and features of the application of the main types of IR detectors are considered below.
These devices are passive (which is as follows) and are used, mainly to control the internal volume of rooms. The flow rate diagram of the volume sensor is characterized by:
Note - the range is indicated by the central petal of the chart, for the side it will be less.
What is characteristic of any infrared sensor, including volume - any obstacle for it is opaque, accordingly creates dead zones. On the one hand, this is a disadvantage, with the other - dignity, since there is a completely absent reaction to moving items outside the protected area.
Also, the disadvantages should include the possibility of false response from such factors as:
Thus, when installing the volume detector, these moments cannot be ignored. By the installation method, there are two versions of "volumetric".
Wall volumetric IR detectors.
Ideal for offices, apartments, private houses. In such premises, furniture and other interior items are located, as a rule, along the walls, therefore blind areas do not create. If we consider that the horizontal viewing angle of such sensors is about 90 degrees, then by setting it in the corner of the room, one device can be almost completely blocked by a small room.
Ceiling volumetric detectors.
For such objects as stores or warehouses, a characteristic feature is the installation of racks or showcases throughout the area of \u200b\u200bthe room. Installing the ceiling sensor in such cases is more efficient, of course, if the specified elements have a height below the ceiling.
Otherwise, you will have to block each compartment formed. For the sake of justice, it should be noted that this necessity does not always occur, but these are the subtleties of the alarm design for each specific object, taking into account all its individual characteristics.
According to its principle of operation, they are active and form one or more rays, tracking their intersection by a possible violator. Unlike bulk, linear sensors are resistant to different kind of air flow, and direct illumination, in most cases they will not hurt.
The principle of operation of the linear single-collar infrared emitter is illustrated in Figure 2.
The range of active linear devices is from tens to hundreds of meters. The most characteristic options for their application:
For perimeter protection, detectors have more than one beam (better if there are no less than three). This is quite obvious, because it reduces the probability of penetration under or over the control zone.
When installing and configuring infrared line detectors, an accurate adjustment of the receiver and a transmitter is required for double-block devices or a reflector and a combined block (for single-block). The fact is that the cross section (diameter) of the infrared beam is relatively small, therefore even a small angular displacement of the transmitter or receiver leads to its significant linear deviation at the reception point.
From the above, also follows the need to fasten all the elements of such detectors on rigid linear structures that completely eliminate possible vibrations.
I should notice that a good "scheduler" - the pleasure is quite expensive. If the cost of single-riga devices with a small range of action still lies 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 the 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 at the maximum range, they significantly inferior to their linear fellows.
It is quite obvious that the alarm detector of the street execution must have appropriate climatic execution. This applies primarily:
According to the generally accepted existing classification, the Street Detector Protection Class must be no lower than IP66. By and large, for most consumers it is not fundamentally - it is quite enough to indicate the "Street" in the description of the technical parameters of the device. At the temperature range, the attention is worth paying.
More importantly, the features of the use of such devices and factors affecting the reliability of protection are deserved.
By the nature of the detection zone, infrared security detectors intended for outdoor installation can be of any type (in descending order of popularity):
As already mentioned, street linear detectors are used to protect the perimeter of open areas. Surface sensors can be used for the same purposes.
Volumetric devices serve to control various kinds of squares. It is worth noting immediately that by the range of action they are inferior to linear sensors. It is quite natural that the prices for street detectors are significantly higher than on the device intended for the internal installation.
Now, with regard to the practical side of operation in the system of security alarm systems of infrared outdoor detectors. The main factors provoking false responses installed on the street of security sensors are:
The first point may seem non-attributed, since, at first glance, it is static and can be taken into account at the design stage. Do not, however, forget that trees, grass and bushes are growing and with time can be a hindrance for normal operation of security equipment.
The second factor manufacturers are trying to compensate for the use of the corresponding signal processing algorithms and the effect of this is. True, how not to twist, if the object, even with small linear dimensions, moves in close proximity to the detector, most likely, it will be identified as a violator.
As for the last item. It all depends on the change in the optical density of the medium. Speaking by simple language, rain, large snow or thick fog can make an infrared detector completely inoperable.
So, when making a decision on the use of street-security detectors in the alarm, consider everything that said. Thus, you can get rid of yourself from many unpleasant surprises during the operation of the outer security system.
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Movement detectors This is the basis of the security system, their type and technical characteristics determine the level of its efficiency and complexity of unauthorized penetration.
The most common detectors used in the alarm systems are passive infrared motion sensors.
Their main function is the bulk control of the protected space of the entire room.
The device registers the dynamics of changes in the thermal radiation of the object and the common background. Monitoring is carried out for a certain period of time.
Combination requires certain conditions. First, changing the position of the object in space controlled by the detector.
Secondly, the trajectory should be perpendicular to the direction of the IR radiation generated by the device.
Thirdly, the distance from the radiation source should be sufficient for its level of perception, that is, it must determine the temperature difference between the object (taking into account the clothing) and the surrounding background.
The main scanning element of the device is a pyropremist, has a dual structure, and therefore in the radiation plane there is a pair splitting of each beam.
Based on the characteristics of the structure of various models of infrared motion sensors, the sensitivity zones of various models can have a different configuration. These can be point rays directed in a small angular segment forming a remote detection point.
Several such rays of the arranged, horizontal or vertical plane form a "vertical barrier" or "scanning surface", it can be horizontal or have a slope.
A single wide beam emitted in a horizontal, or vertical plane forms the "scanning curtain".
In addition, the intensity of the generated radiation affects the length of the scanned triggering zone. The survey sector can be from 30 0 to 180 0 for wall detectors and circular - 360 0 for ceiling models. It is also possible to regulate the number of rays, and the angle of their inclination, up to 90 0.
Such a variety is due to the requirements for operation in different conditions and a high level of efficiency, which should ensure the uniform sensitivity of the detector throughout the overall timing.
The sensitivity of the detector depends on the percentage of overlapping the area of \u200b\u200bthe beam. Accordingly, at a distance of 15-20 m to detect an object with a person with a person, a ray width is needed.
But when approaching the device, the sensitivity level will increase, and from a distance of 5 m, an ordinary mouse can raise an alarm.
To distribute the uniformity of sensitive zones, optical elements form several radiation sectors with different widths and direction at different angles. The device itself is usually attached slightly above human growth.
Consequently, the entire volume of detection zone is divided into several sectors, with a different degree of sensitivity of rays, selected in such a way that the overall sensitivity of the device has not changed from removing or approaching it.
The problem of uniformity of the sensitivity of passive IR motion sensors is solved using optical diffusers.
Such a system can be configured more accurately, which makes it possible to increase its sensitivity at distant distances up to 60%. In addition, the segment structure makes it easier to set up the protection of the near "sabotage" zone.
The use of triplex technology in mirrors allows the use of infrared motion sensors in rooms, where there is pets.
Modern highly efficient models use a combination of both systems, where Fresnel lens controls the middle zone, and the devices of the mirror optics are long-range approaches and a sabotage zone.
The pyroelectric converter is a semiconductor device that can register the difference in temperatures and convert it to an electrical impulse.
In such sensors, pairs are used, and in some models there are two pairs of pyroelectric elements. This reduces the number of false positives, which cause a simple increase in the room temperature.
In paired pyriproducts, the trigger occurs only when one of the rays intersect, the processing occurs according to the differential algorithm, the subtraction of one pyroelement from the other signal.
The main types of interference that can cause false response of the embedded IR motion sensors:
Analog, digital or combined device, which ensures the processing of signals incoming from the adarcector to highlight the pulse caused by the intruder, from the total interference stream.
The processing algorithm is based on the analysis of the form, duration and signal value. The signal from the human figure is symmetric and bipolar, in contrast to noise asymmetric signals.
The value of the signal is the main parameter by which the incoming pulse analysis occurs.
In low-cost models, only it analyzes it, comparing with the threshold indicator and counting the number of responses. After exceeding a certain number per unit of time, the alarm is activated.
This method is imperfect and leads to a large number of false positives from vibrations or electromagnetic interference.
If you configure low sensitivity, then in sensors with a "single curtain type control zone" may not be triggered at all if only one beam is crossed.
In more expensive sensors, the polarity and symmetry of the form of the incoming signal are additionally analyzed.
A special light filter plastic of external lenses allows you to protect the pyroelegen from white light, to protect against insects between the pyropry element and the lens, the hermetic chamber is mounted.
Also almost all modern models Equipped with an autopsy relay that signals the hacking device.
NV500 company Paradox
Optics - hybrid cylinder-spherical lens with Fresnel lenses segments with a viewing angle of 1020.
The orientation diagram is designed to ensure uniform sensitivity through the entire control. Super Creep Zone is a sabotage zone control function. Digital blocking of animal detection up to 16 kg.
Two-level pulse count according to the APSP algorithm. Temperature autocompensation. Automatic digital adjustment of 5 level sensitivity. Opening protection is a solid-state relay.
Sensors of this type can be used not only in, but also in the automatic lighting device, and early warning systems, etc.
Among the large variety of security detectors, the infrared motion sensor is the most common device. Affordable price and effectiveness, here is the qualities that have contributed to them. And all due to the fact that at the beginning of the nineteenth century, infrared radiation was discovered.
It is abroad visible red light in the range of 0.74-2000 μm. The optical properties of substances differ greatly and depend on the type of irradiation. A small layer of water is opaque for IR radiation. Infrared radiation of the Sun is 50 percent of all radiated energy.
Infrared motion sensors for protection are used for a long time. They recorded the movement of warm objects in the rooms, and transmitted alarm to the control panel. They began to combine with video cameras and cameras. In violation there was a fixation of the incident. Then the scope expanded. Zoologists began to apply in photo gallets to control the studied animals.
Most IR sensors are used in the smart home system, where the role of the presence sensor is played. When a warm-blooded object is hit to the device area, it includes lighting indoors or on the street. Electricity saves and facilitates the lives of people.
In access control systems, motion detectors manage opening and closing the doors of social structures. According to experts, the IC Sensor market will grow by 20% annually the next 3-5 years.
The work of the IR Detector is to control the infrared radiation of a certain area, comparing it with the background level, and according to the results of the analysis of the issuance of the message.
IR Motion Sensors for protection use active and passive types of sensors. The first to control use their own transmitter, irradiating everything in the device area. The receiver receives a reflected part of the radiation IR and determines it, there was a violation of the protection zone or not. Active sensors are a combined type when accepting and transmitting blocks are separated, these are detectors controlling the perimeter of the object. Have a greater range compared to passive devices.
A passive infrared motion sensor has no emitter, it reacts to a change in the surrounding IR radiation. In general, the detector has two sensitive elements capable of fixing infrared radiation. The sensors are set to Fresnel lens, breaking the space for several tens of zones.
Little lens collects radiation from a specific area of \u200b\u200bspace and sends to its sensitive element. The adjacent lens controlling the adjacent section sends the radiation stream to the second sensor. The radiation of neighboring sites is about the same. If the balance is violated, exceeding some threshold value, the device announces the control panel of violation of the protection zone.
Each manufacturer has a unique principal scheme of an IR detector, but they are functionally different.
IR sensor has an optical system, a serving element, signal processing unit.
The work area of \u200b\u200bmodern motion sensors is very diverse due to various forms of the optical system. Rays dissolved from the device in the radial direction in various planes.
Since the detector has a dual sensor, then all rays are split.
The optical system is oriented in such a way that only one plane or several planes at different levels will be monitored. It can control the space lying or on the beam.
When building optics of IR sensors, Fresnel lenses are often used representing many prismatic facets on a convex plastic cup. Each lens collects an IR stream from its site of space and sends an element on the feast.
The design of the optical system is such that selectivity for all lenses is the same. To protect yourself from its own heat of elements, insects in the device are installed a hermetic chamber. Rarely used mirror optics. This significantly increases the range of the device and the price of the device.
The role of the sensor in the IR sensor plays a pyroelectric converter on sensitive semiconductor elements. It consists of two sensors. Each of them from two adjacent rays flows the radiation stream. With the same uniform background, the sensor is silent. If an imbalance occurs, an additional heat source appears in the same zone, and there is no sensor, the sensor works.
To increase the reliability and reduction of false positives, the quad feast elements have become applied lately. This increased the sensitivity and observance of the device. But reduced the distance of confident impairment recognition. To solve this, you have to use precision optics.
The main task of the block is reliable human recognition on the background of interference.
They are the most diverse:
The analysis processing unit uses amplitude, shape and duration of the output of the pyroelectric converter. The impact of the intruder causes a symmetric bipolar signal. Interference issues asymmetric values \u200b\u200bon the machining module. In the simplest embodiment, the amplitude of the signal with the threshold value is compared.
If the threshold is exceeded, the detector reports this by submitting a specific signal to the control panel. In more complex sensors, the duration of the threshold exceeding the number of these extests is measured. Automatic thermocomponation is used to increase the observance of the device. It provides permanent sensitivity in the entire temperature range.
The signal processing is performed by analog and digital devices. The newest devices began to use digital signal processing algorithms, which made it possible to improve the selectivity of the device.
From the correctness of the selection of the type of sensor, its efficiency depends on the object of protection largely. Passive IR Motion Sensors Street and internal application React to moving warm compared to the background of objects at certain speeds of movement. With a small speed of movement, changes in the flow of infrared radiation in the adjacent sectors are so insignificant that it is perceived as a background drift, and does not respond to a violation of the protection zone.
If the violator donates a protective suit with excellent thermal insulation, then the IR motion sensor will not respond, there will be no disruption of the radiation balance in adjacent zones. A person is somewhat with background radiation.
The violator moves along the rays of the motion detector at low speed, in this case it is often silent.
Flow changes are insufficient to trigger the device. Especially characterized by detectors with animal protection function. They reduce sensitivity to avoid reactions to the appearance of pets.
It is important to correctly install an infrared sensor. Required by building configuration apply a device such as a "curtain" type, you should do so. The manufacturer recommends the installation of the device at a certain height, must be observed.
To improve the efficiency of infrared sensors, they are used in conjunction with sensors operating on other principles.
Usually, it is additionally attached to a radio wave detector with high sensitivity, which reduces the percentage of false positives and increases the reliability of the security alarm. When protection of windows from penetration, an ultrasonic detector reacting to the breakdown of glass is additionally installed.
Gradually, IR sensors are complicated, their sensitivity increases, selectivity improves. Sensors are widespread in "Smart Home" systems, video surveillance, access control. Sharing with various devices raised the consumer properties of the sensors. He is prepared a long life.
Principle of action of passive Ikso.The principle of operation of passive ICSO is based on the registration of signals generated by a heat flux emitted by the detection object. The useful signal at the output of the idleness of the unintelligent radiation receiver is determined by the expression:
where S u is the volt sensitivity of the radiation receiver, - changing the magnitude heat fluxFalling on the optical system input window and caused by the movement of an object in the detection zone.
The maximum value value is the case when the object is fully falling in the field of view of ICSO. Denote this value as
Considering that losses in the optical system are so small that they can be neglected, expressing the parameters of the object and the background. Let within the background, the surface of which has an absolute temperature T f and radiative ability E. f. , the object appears, the absolute temperature of which TOB,and radiative ability Eov.. The area of \u200b\u200bprojection of the object to the plane, perpendicular to the direction of observation, denote Soe,and the area of \u200b\u200bprojection of the background in the field of view - B f. Then the magnitude of the heat flux falling on the optical system input window until the object appears is determined by the expression:
where the distance from the input window to the background surface; 1. Frochuriness background; S BX is the area of \u200b\u200bthe optical system input window.
The magnitude of the heat flux created by the object is determined in the same way:
where t. - distance from Ikso to the object; - Brightness of the object.
In the presence of an object, the heat flux falling to the input window is created by the object and that part of the background surface, which is not shielded by the object, from where the total thermal flow
Then the change in the thermal flux of AF is recorded as:
Considering that the Lambert law is valid for the object and the background, express brightness LO6and φ through radiative abilities and absolute temperatures:
where is the constant Stefan Boltzmann.
Substituting and in, we obtain the expression for AF through absolute temperatures and the emitting abilities of the object and the background:
Under the specified parameters of the optical system and the radiation receiver, the signal value in accordance with fully determined by the change in the exposure De.
The radiative ability of a person's skin is very high, on average it is 0.99 with respect to absolutely black body at wavelengths more than 4 microns. In the IR region of the spectrum, the optical properties of the skin are close to the characteristics of the black body. Leather temperature depends on heat exchange between leather and the environment. Measurements carried out using the AGA-750 thermal imager showed that at air temperature + 25 ° C, the temperature over the surface of the palm of the person changes within +32 ... + 34 ° C, and at air temperature + 19 ° C - limits +28 ... + 30 ° С. The presence of clothes reduces the brightness of the object, as the temperature of the clothes is lower than the temperature of the nude skin. At ambient temperature + 25 ° C, the measured average temperature of the body of the body dressed in a person's costume was + 26 ° C. Emitting clothes can also be different than that of naked skin.
Other parameters included in the expression can take different values \u200b\u200bdepending on the specific situation and / or operational task.
Consider the process of signaling and basic types of interference affecting the false response of passive ICSO.
Signal formation.For a better understanding of methods and algorithms for increasing the noiselessness of ICSO, it is necessary to have an idea of \u200b\u200bthe basic parameters of the signal - form, amplitude, duration, dependence on the speed of the person and the temperature of the background
Consider one radiation zone of detection with a length of 10 m with a ray diameter at the base of the cone 0.3 m. It is believed that the person crosses the zone on the normal to it with the maximum and minimum speeds at a distance from the receiver Yu, 5 and 1 m. Signal form when crossing the beam At a distance of 10 m, there is a triangle view with a maximum with full overlap of the zone. In fig. 4.8.6 shows the spectrum of this signal. When crossing the beam at a smaller distance, the signal acquires the shape of a trapezoid with steep fronts and the spectrum of this signal acquires the view shown in Fig. 4.9.6.
It is obvious that the duration of the signal is inversely proportional to the speed of movement and the distance to the receiver.
The real signal differs from the perfect picture by distortion made by the gain path and the imposition of chaotic noise created by temperature fluctuations of the background. Records of real signals obtained using the PM2D domestic pyroprifier are shown in Fig. 4.10. Here are its spectral characteristics obtained by transmitting rebuilt signals through the company's spectrum analyzer
Analysis of records Allows you to determine the spectral "window" required to pass signals formed when crossing the zone anywhere in the entire speed range from 0.1 to 15 Hz. At the same time, at the edges of the range it is possible to weaken the signal, since the pyrribronic has an amplitude-frequency characteristic with a decline in the region of 5 ... 10 Hz. To compensate, it is necessary to introduce a special corrective amplifier signal to the signal processing path, which provides a frequency lift in 5 ... 20 Hz.
Temperature contrast.The amplitude of the signal, as already mentioned, is determined by the temperature contrast between the human body and the background to which the beam is directed. Since the background temperature changes after changing the temperature in the room, the signal, proportional to their difference, also changes.
At a point where the temperature of the person and the background coincide, the output signal value is zero. In the area of \u200b\u200bhigher temperatures, the signal changes the sign.
The temperature of the background indoors reflects the condition outside the room with some delay due to the thermal inertia of the construction materials of the building.
Temperature contrast depends on the temperature of the outer surface of the person, i.e. Mainly from his clothes. Moreover, it turns out to be a significant investigation. If a person enters the room where Ikso is installed, outside, for example, from the street, where the temperature can differ significantly from the temperature in the room, then at the first moment the thermal contrast can be significant. Then, as "adaptation" of the temperature of the clothing to the room temperature, the signal decreases. But even after a long stay in the room, the signal value depends on the type of clothing. In fig. 4.11 The experimental dependences of the temperature contrast of a person from ambient temperature are given. The stroke line shows the extrapolation of experimental data for temperature above 40 ° C.
Shaded area 1 is a range of contrasts depending on the shape of the clothing, type of background, the size of the person and the speed of its movement.
It is important to note that the transition of the magnitude of the temperature contrast through zero occurred only if in the temperature range of 30 ... 39.5 ° C was carried out after the adaptation of the person in the heated room during 15 minutes. In the case of an invasion of the sensitivity zone from a person who was in a room with a temperature below 30 ° C or outdoors with a temperature of 44 ° C, signal levels in the temperature range of 30 ... 39.5 ° C lie in the region 2 and not Reach zero value.
The temperature distribution over the surface of the person is not evenly. It is closest to 36 ° C at the open parts of the body -lice and arms, and the surface temperature of the clothing closer to the background of the room. Therefore, the signal at the inlet of the pyropria depends on which part of the body is overlap the radiation zone of sensitivity.
Consideration of the signaling process allows you to draw the following conclusions:
The amplitude of the signal is determined by the temperature contrast of the surface of the person and the background, which can be from the fraction of degree to decades of degrees;
The waveform has a triangular or trapezoidal form, the duration of the signal is determined by the place of intersection of the radial zone and when moving along the normal to the beam can be from 0.05 to 10 s. When driving at an angle to normal, the signal duration increases. Maximum spectral signal density lies in the range from 0.15 to 5 Hz;
When a person moves along the beam, the signal is minimal and is determined only by the difference in temperatures of individual sections of the human surface and is the fraction of degrees;
When a person moves between the rays, the signal is practically absent;
At a room in a room close to the surface temperature of a human body, the signal is minimal, i.e. The temperature difference is a fraction of degrees;
The amplitudes of the signals in different rays of detection zone can differ significantly from each other, as they are determined by the temperature contrast of the human body and the background area on which this ray is directed. The difference can reach ten degrees.
Interference in Passive Ikso.We turn to the analysis of interference influences that cause false response of passive ICSO. Under noise, we will understand any effect of the external environment or the inner noises of the receiving device that are not associated with the movement of a person in the sensitivity zone of CO.
There is the following interference classification:
Thermal, due to the heating of the background when exposed to solar radiation, convection flows of air from the operation of radiators, air conditioners, drafts;
Electric, caused by tips from sources of electro and radio emissions to individual elements of the electronic part of CO;
Own, due to the noise of the pyrribronyon and the signal amplification path;
Strying associated with moving in the sensitivity zone from small animals or insects on the surface of the input optical window CO.
The most significant and "dangerous" interference is the thermal, caused by a change in temperature of the area of \u200b\u200bthe background, on which the radial zones of sensitivity are directed. The effect of solar radiation leads to a local increase in the temperature of individual sections of the wall or floor of the room. In this case, the gradual change in temperature does not pass through the filtering schemes of the device, however, relatively sharp and "unexpected" its oscillations associated, for example, with the shading of the Sun passing clouds or the passage of transport, cause interference, similar to a signal from human passage. The amplitude of interference depends on the inertia of the background, to which the beam is directed. For example, temperature change is bare concrete Wall Much more than wooden or floating wallpaper.
In fig. A record of typical solar interference is given at the outlet of the pyropraliary during the passage of the cloud, as well as its spectrum.
In this case, the change in temperature during solar interference reaches 1.0 ... 1.5 ° C, especially in cases where the beam is directed to a minority background, for example, on a wooden wall or a tissue from a tissue. The duration of such interference depends on the rate of shading and can fall into the range of velocities characteristic of human movement. It is necessary to note one significant circumstance that allows you to deal with such interference. If the two beams are aimed at adjacent areas of the background, the appearance and amplitude of the interference signal from the effects of the Sun is almost the same in each ray, i.e. There is a strong correlation of interference. This allows the appropriate construction of the scheme to suppress them by subtracting signals,
Convective interference caused by the impact of moving air flows, such as drafts with open-windows, slots in the window, as well as household heating devices -adiators and air conditioners. Air flows cause a chaotic fluctuation change in the background temperature, amplitude and frequency range of which depend on the flow rate of the air and the characteristics of the background surface.
In contrast to the solar illumination of convective interferences from various areas of the background, acting even at a distance of 0.2 ... 0.3 m, weakly correlated between themselves and their subtraction does not give effect.
Electrical interference occurs when you turn on any sources of electrical and radio emission, measuring and household equipment, lighting, electric motors, radio devices, as well as when current oscillations in the cable network and power lines. Significant level of interference also create lightning discharges.
The sensitivity of the pyrribronic is very high - when the temperature is changed by 1 ° C, the output signal directly from the crystal is the shares of the microvolt, so the tip from the sources of interference in a somewhat volt on the meter can cause an interference pulse, thousands of times more than a beneficial signal. However, most of the electrical interference has a small duration or a steep front, which allows you to distinguish them from a useful signal.
The own noise of the pyrosemifer is determined by the highest border of the sensitivity of ICSO and have the kind of white noise. In this regard, the filtering methods cannot be used here. The intensity of the interference increases with increasing the temperature of the crystal approximately twice for every ten degrees. Modern pyriproducts have the level of their own noise corresponding to the change in temperature by 0.05 ... 0.15 ° C.
Conclusions:
1. The spectral range of noise overlaps the range of signals and lies in the region from the share to dozens of hertz.
2. The most dangerous type of interference is the solar illumination of the background, the effect of which increases the temperature of the background by 3 ... 5 ° C.
3. Interference from the solar illumination for close areas of the background is rigidly correlated between themselves and can be weakened when using a two-beam scheme for constructing CO.
4. Convective interference from thermal household appliances have the form of fluctuation random fluctuations of the temperature reaching 2 ... 3 ° C in the frequency range from 1 to 20 Hz with a weak correlation between the rays.
5. Electrical interferences have a form of short pulses or stepped effects with a steep front, the induced voltage can hundreds of times exceed the signal.
6. The intrinsic noise of the pyrosemifer corresponding to the signal when the temperature is changed by 0.05 ... 0.15 ° C, lie in the frequency range, overlapping the range of the signal, and increase in proportion to the temperature is approximately twice by every 10 ° C.
Methods for increasing the noise immunity of passive ICSO.Differential method of receptionRho radiation was quite widespread. The essence of this method is as follows: with the help of a two-proper receiver, two spatially separated sensitivity zones are formed. Signals that are formed in both channels are mutually deducted:
It is clear that the two spatially separated sensitivity zones cannot be crossed by a moving object at the same time. In this case, the signals in the channels occur alternately, therefore, the amplitude of them does not decrease. It follows from the formula that the interference at the output of the differential receiver is zero with the joint implementation of the following conditions:
1. Molds of interference in the channels coincide.
2. Amplitude interference is the same.
3. Interference has the same temporary position.
In the case of solar interference, conditions 1 and 3. Condition 2 is performed only when the same material or angles of solar energy drops are served as a background in both channels on the background in both channels or in both channels the solar radiation stream falls on The entire area of \u200b\u200bthe background that limits the sensitivity zone. In fig. The dependence of the amplitude of interference at the outlet of the differential cascade from the amplitude of interference at its entrance is shown.
The parameter is the ratio of amplitudes of interference effects in the channels. In this case, it is meant that conditions 1 and 3 are performed.
From fig. It can be seen that with a sufficiently good coincidence, the amplitudes of noise effects in the channels are achieved 5 ... 10 multiple suppression of these interference. At u b xi / u B. x2 \u003e 1.2 Interference Suppression decreases and the characteristic of the listed \u003d / tends to the similar characteristic of a single receiver.
When applied by convective interference, the degree of it is determined by a differential receiver determines its degree of correlation in the spatially separated points of the background surface. Evaluation of the degree of spatial correlation of convective interference can be carried out by measuring its intensity with differential and conventional methods of reception. The results of some measurements are shown in Fig. 4.14.
Optimal frequency filtering.Effective suppression of interference by this method is possible with a significant difference in frequency spectra of signals and interference. From the above data it follows that there is no such difference in our case. Therefore, the use of this method to complete interference suppressions is not possible.
The main view of the noise that determines the sensitivity of ICSO is its own noise of the receiver. Therefore, optimizing the bandwidth of the amplifier, depending on the spectrum of the signal and the character of the noise of the receiver, allows you to implement the limit features of the receiving system.
Optical spectral filtering.The essence of the optical spectral filtering method is the same as in the case of optimal frequency filtering. When spectral filtering, the interference is suppressed by differences in the optical spectra of signals and interference. These differences are practically absent for convective interference and for the component of solar interference arising from the change in the temperature of the background under the action of solar radiation, however, the spectrum reflected from the background of the component of the solar interference is largely different from the signal spectrum. The spectral density of the energy luminosity of absolutely black body is determined by the plank formula:
where- the length of the waves; K - Boltzmann's constant; T - body temperature; h - constant plank; C is the speed of light.
The graphic image of the function, crighted by software, for the contrast radiation of the object and solar radiation is shown in Fig. 4.15.
According to the classical theory of linear optimal filtering to ensure maximum signal / interference ratio, the optical filter bandwidth must be consistent with the spectrum of the contrast radiation of the object and have the view shown in Fig. 4.15.
The most fully of this condition from serially produced materials satisfies oxygen-free glass of X-33.
The degree of suppression of solar interference with the specified filters for different backgrounds is shown in Table. 4.1. From the table, it can be seen that the greatest suppression of solar interference is achieved by the X-33 filter. Black polyethylene film is somewhat inferior to X-33.
Thus, even when using the X-33 filter, solar interference is suppressed by only 3.3 times, which cannot lead to a radical improvement in the noise immunity of the passive optical detection tool.
Optimal spatial frequency filtering.It is known that the detection characteristics under optimal linear filtering conditions are uniquely connected with the value of the signal / interference ratio. For their assessment and comparison it is convenient to use the value
where U is the amplitude of the signal; - the spectral density of the signal power; - the spectral density of the interference power.
Table 1. The degree of suppression of solar interference with various filters for different backgrounds
In physical sense, the value is the ratio of the signal energy to the spectral density of the interference power. It is obvious that when the bodily angle of the elementary zone of sensitivity changes the intensity of the interference emitted by the background and falling into the receiving channel. At the same time, the amplitude of the signal depends on the geometric shape of the elementary sensitivity zone. Thusll, with what configuration of the elementary sensitivity zone, the value of C reaches the maximum value, for which we consider the simplest detection model. Let the zone of the sensitivity of the ICSO stationary relative to the background, and the detectable object moves with an angular speed VO6.regarding the observation point. The sensitivity zone and the object in normal to the optical axis of the plane are rectangles, and the angular dimensions of the field objects are very small, that with a sufficient degree of accuracy can be considered
where-solid angle under which the object is visible; - the body angle of the sensitivity zone; - the corner size of the object is
harmoniously in horizontal and vertical planes; angular size of the sensitivity zone, respectively, in horizontal and vertical planes;
The energy brightness of the object in about the same through its entire surface, and the spectral density of the energy brightness of the background shumaodynakov over the entire surface of the background. The signal and background is additive. The object movement occurs evenly in the plane of the angle A. Energy power receiver, quadratic. The signal from the receiver is fed to the rebuilt optimal filter. Then the spectral power density of the background interference at the output of the receiver will be determined by the expression:
where Copt- the transmission coefficient of the optical system; TO t. - the transfer coefficient of signal propagation track; TO p - The sensitivity of the receiver.
When the field of view is interacted by an object at the receiver output, a signal impulse is formed, the shape of which and spectrum, in the case of events, are determined by expressions:
where U0 is a signal impulse of a single amplitude; - Spectrum of the signal impulse of a single amplitude.
For the background emitting the interference, the spectral density of the power of which has the form, the value of the output of an uncontrolled receiver in accordance with the expression is defined as
The nature of the dependence of the magnitude of the form shown in Fig. 4.16. From the foregoing it follows that to ensure the maximum signal / background interference, the form of the sensitivity zone must be conjugate with the form of the object.
For the case of fluctuation background interference, the maximum value of the signal / background noise ratio is achieved by coincides the geometric shape of the elementary sensitivity zone with the form of the object. This conclusion is applicable for the case of impulse solar interference. This is a confirmation of this is the obvious fact that, with an increase in the corner angle of the sensitivity zone from a value equal to the bodily corner, under which the object is visible, the amplitude of the signal does not change, and the amplitude of the solar interference grows in proportion to the corporal corner of the sensitivity zone. That is, the optimal spatial-frequency filtering method allows to increase the noise immunity of the passive optical means of detection to both convective and solar interference.
Dual-band method for receiving IR radiation.The essence of this method is to introduce a second channel in the ICO, which provides an intraference to IR in visible or neighboring IR ranges, in order to obtain additional information that distinguishes a signal from interference. The use of such a channel in combination with the main channel in the conditions of one room is ineffective, since both the signal and interference in the presence of illumination are formed in both spectral ranges. It is much more effective to use the visible range channel when it is installed outside the protected premises, in places inaccessible to block this channel with artificial light sources. In this case, when changing solar illumination, the channel generates a signal that prohibits the possible response of ICSO under the influence of solar interference. With such an organization, the dual-band method allows you to completely eliminate the false responses of the ICSO, possible by the occurrence of solar interference. The possibility of blocking the heat channel during the actions of the interference is obvious.
Parametric methods for increasing the noise immunity of ICSO.The basis of parametric methods for increasing the noiselessness of the ICSO is the identification of useful signals according to one or the set of parameters characteristic for the appearance of these signals of objects. As such parameters, the speed of the object, its dimensions, distance to the object can be used. In practice, as a rule, the specific values \u200b\u200bof the parameters are not known in advance. However, there is some area of \u200b\u200btheir definition. So, the speed of a person moving on foot, less than 7 m / s. A combination of such restrictions can significantly narrow the field of determining the useful signal and, therefore, reduce the likelihood of false response.
Consider some ways to determine the object parameters when it is passive optical detection. To determine the speed of the object, its linear size in the direction of movement and distance to it, it is necessary to organize two parallel zones of sensitivity, separated in the plane of moving an object to some base distance L. Then it is easy to determine that the speed of the object is normal to the sensitivity zones
where the delay time between signals in the receiving channels.
Linear size object Bobin normal plane sensitivity zones is defined as
where Tio. .5 - the duration of the signal pulse at the level U \u003d 0.5U MAX.
When condition is conditioned to the object is determined by the expression
where the corner size of the elementary zone of sensitivity in radians; - the duration of the front of the signal impulse.
The obtained parameter values OB,b ^, D O6 is compared with the areas of their definition, after which the decision is made to detect the object. In the case when the organization of the two parallel sensitivity zones is not possible, the parameters of the signal pulse can be the identifying parameters: the duration of the front, the pulse duration, etc. The main condition for implementing this method is a wide bandwidth of the receiving path required to receive a signal without distorting its shape, i.e. In this case, the use of the optimal filtering method is excluded. In the process of optimal filtering, the parameter is the delay duration between the signals arising in space-spaced channels. Therefore, the identification according to this parameter can be done without expanding the bandwidth of the receiving path. To implement the identification of the useful signal in the ICCO with a multipath zone of sensitivity by parameter T 3, it is necessary that it is formed in the plane of moving an object using independent receivers.
For example, we consider the area of \u200b\u200bdetermining the parameters of the signal pulse and the value of T 3 for one-position ICSO with a multipath zone of sensitivity in the real values \u200b\u200bof the angular divergence of the elementary zone of sensitivity A n \u003d 0.015 rad, the size of the input pupil d \u003d 0.05 m and the angle between the sensitivity zones A P \u003d 0.3 happy.
The pulse duration by zero level is determined by the expression
The scope of determination of the pulse duration for the velocity range V O. 6 \u003d 0.1.7.0 m / s, amounts to io \u003d 0.036 ... 4.0 s. Dynamic range
The region of determining the pulse duration in terms of 0.5U max is already 0.036 ... 2.0 s, and the dynamic range
The duration of the front of the signal impulse is determined by the expression
Where is the area of \u200b\u200bdefinition, and dynamic
range
The delay duration between pulses arising in adjacent channels can be determined by the formula:
The area of \u200b\u200bdetermination of the delay 0 ... 30 s. For the received value d \u003d 0.05 m and the range of D O6 \u003d 1 ... 10 m, the definition region of 4.5 ... 14.0, and the dynamic range3.1.
When d \u003d 0 dynamic range of all range values DO6.\u003d 0 ... 10 m.
Thus, the most stable identifying parameter is the value of T 3 / TF.
Due to the synchronicity of the appearance of solar interference in spatially separated channels marked in section. 4.3, it is possible to complete detuning from it using the parameter.
The use of independent channels allows you to increase the resistance of the device and to convective interference, since end solution The detection is received only in the case of signal detection at least in two channels for a certain time interval, determined by the maximum possible delay of the signal pulse between the channels. In this case, the probability of a false alarm is determined by the expression
where RLS1. RLSG - probability of false alarm in separate channels.
Comparative analysis of ICSO noise immunity methods.The methods of increasing disabilities considered above are rather diverse in both its physical entity and the complexity of implementation. Each of them individually possesses both definite advantages and disadvantages. For the convenience of comparing these methods, the aggregate of positive and negative qualities will make a morphological tab. 4.2.
From the table, it can be seen that no method separately allows you to completely suppress all interference. However, the simultaneous use of several methods can significantly increase the noise immunity of ICSO with a minor complication of the device as a whole. By the aggregate of positive and negative qualities, the most preferred is a combination: spectral filtering + spatial-frequency filtering + parametric method.
Consider the main methods and means implemented in practice in modern ICSO, allowing to provide a sufficiently high probability of detection at the minimum frequency of false alarms.
To protect the receiving device from the effects of emissions lying outside the spectral range of the signal, the following measures are being taken:
The peyrodul inlet window is closed with a plate of germanium that does not transmit radiation with a wavelength of less than 2 microns;
The input window of the total C is made of high density polyethylene, providing sufficient rigidity to maintain geometric dimensions and at the same time non-transmitting radiation in the wavelength range from 1 to 3 microns;
Table 2. Methods of increasing the noise immunity of ICSO
|
Positive traits |
Negative qualities |
|
|
Differential |
Low noise immunity to uncorrelated interference |
|
|
Frequency filtration |
Partial suppression of solar and convective interference |
The complexity of the implementation for multichannel systems |
|
Spectral filtering |
Easy to implement. Partial suppression of solar interference. |
Convective interference is not suppressed |
|
Dual-band |
Full suppression of solar interference, simplicity of the processing path |
The ability to lock the means by external light sources. Convective interference is not suppressed. The need for an additional optical channel |
|
Optimal Space-Venno-Fast Filtering |
Partial suppression of background and solar interference. Easy sales |
The need to apply receiver with a special form of sensitive platform |
|
Parametric methods |
Partial suppression of background interference. Significant solar interference suppression |
The complexity of the processing path |
Frenelle lenses are made in the form of concentric circles with a focal length of polyethylene eased on the surface of the inlet window, corresponding to the maximum level of radiation characteristic of the human body temperature. Radiation of other wavelengths will be "blurred", passing through this lens and, thus, weakened.
These measures can be able to weaken the effect of interference from the sources outside the spectral range of thousands of times and to ensure the possibility of functioning of ICSO under conditions of severe sunlight, the use of lighting lamps, etc.
The powerful means of protection against thermal interference is the use of a two-proper pyrribronic with the formation of a two-beam sensitivity zone. The signal during the passage of a person occurs sequentially in each of the two rays, and thermal interference is largely correlated and can be loosened when using the simplest subtraction scheme. Two-platforms are applied in all modern passive Ikso, and quadruple pyroelements are used in the latest models.
At the beginning of consideration of signal processing algorithms, you need to make the following remark. For the designation of the algorithm, various terminology can be used for different manufacturers, since the manufacturer often gives a unique name to some processing algorithm and uses it under its trademark, although in fact it can be used any traditional method Analysis of signals used by other firms.
Algorithm optimal filtrationit assumes the use of not only the amplitude of the signal, but all its energy, i.e., the product of amplitude per duration. An additional informative feature of the signal is the presence of two fronts - at the entrance to the "beam" and at its output, which allows you to relocate from many interference with the kind of "steps". For example, in an IKSO Vision-510, the processing unit analyzes the two-polarity and symmetry of the shape of the signals from the output of the differential pyrribrife. The essence of processing consists in comparing the signal with two thresholds and in some cases - in comparing the amplitude and duration of signals of different polarity. There is also a combination of this method with a separate calculation of exceeding the positive and negative thresholds. Paradox has given this algorithm name Entry / Exit Analysis.
Due to the fact that electrical interference has or a small durability, or a steep front, to increase the noise immunity, the use of the adjustment algorithm is the most efficient, and block the output device at the time of their action. Thus, a stable operation is achieved with even in conditions of intensive electrical and radio domain in the range from hundreds of kilohertz to one gigahertz at the field strength to the SE / m. In passports, the modern Ikso indicates resistance to electromagnetic and radio frequency interference with the field strength of up to 20 ... 30 V / m.
The following effective method of increasing noise immunity is the use of the scheme "Impulse accounts".The sensitivity diagram for the most common "volumetric" CO has a multipath structure. This means that when moving, a person crosses sequentially a few rays. At the same time, their number is directly proportional to the amount of rays forming the co and distance detection zone overcame. The implementation of this algorithm is different depending on the modification of CO. Most often used manual installation Switch at the expense of a certain number of pulses. Obviously, in connection with this, with an increase in the number of pulses, the noise immunity of the ICSO increases. To respond to the device, a person should cross several rays, but at the same time the detective ability of the device may decrease due to the presence of "dead zones". In Ikso, the Paradox company uses a patented APSP pyrose signal processing algorithm, which provides automatic switching of pulse accounts, depending on the level of signals. For high-level signals, the detector immediately develops alarm, while working as a threshold, and for low-level signals automatically switches to pulse counting mode. This reduces the likelihood of false alarms while maintaining unchanged detectivity.
In Ikso Enforcer-QX applied the following pulse account algorithms:
SPP - pulse counting is carried out only for signals with alternating signs;
SGP3 - Under-read only groups of pulses, having the opposite polarity. Here, the alarm state occurs when three such groups appear for the set time.
In the latest ISO modifications to increase noise immunity, a scheme applies "Adapted reception".Here the trigger threshold automatically tracks the noise level, and it also increases. However, this method is not free from flaws. In the multipath chart of sensitivity, it is very likely that one or more rays will be directed to the area of \u200b\u200bintense interference. This establishes the minimum sensitivity of the entire device, including those rays where the intensity of the interference is insignificant. Thereby decreases the overall probability of detection of the entire device. To eliminate this disadvantage, it is proposed before turning on the device "detect" rays with a maximum level of noise and shadow them with special opaque screens. In some modifications, they are supplied.
Analysis of the duration of signals can be carried out as a direct method for measuring the time during which the signal exceeds some threshold and in the frequency domain by filtering the signal from the yield of the pyrribrium, including using "Floating" threshold,depending on the range of frequency analysis. The trigger threshold is installed at a low level inside the frequency range of the beneficial signal and at a higher level outside of this frequency range. This method is laid in an Enforcer-QX Ikso and was patented called ift.
Another type of processing designed to improve the characteristics of ICSO is automatic thermocompensation.In the range of ambient temperatures, 25 ... 35 ° C, the sensitivity of the piroparium is reduced by reducing the thermal contrast between the human body and the background, and with further increase in temperature, the sensitivity rises again, but "with the opposite sign". In the so-called "ordinary" thermocomption schemes, the temperature is measured and is automatically increasing when it is increased. For "real",or "double-sided"compensation, the increase in thermal contrast for temperatures is higher than 25 ... 35 ° C. The use of automatic thermocomption provides almost constant sensitivity of ICSO in a wide range of temperatures. Such thermocomption is applied to Paradox and C & & to Systems.
The listed types of processing can be carried out with analog, digital or combined means. In modern Ikso, digital processing methods using specialized microcontrollers with ADC and signal processors are becoming increasingly widely used, which allows you to carry out a detailed processing of the "fine" signal structure for better allocation of it on the background of interference. Recently, there have been messages about the development of fully digital ICSO, not using analog elements at all. In this ISO, the signal from the pressing of the pyrosemaker directly enters the analog-to-digital converter with a high dynamic range and all processing is produced in digital form. The use of fully digital processing allows you to get rid of such "analog effects" as possible distortions of signals, phase shifts, excess noise. Digital 404 uses a patented SHIELD signal processing algorithm, which includes APSP, as well as analysis the following parameters Signals: amplitudes, duration, polarity, energy, increase time, form, time of appearance and order of signals. Each sequence of signals is compared with samples corresponding to movement and interference, and even the type of movement is recognized and if the alarm criteria are not satisfied, the data are stored in memory to analyze the following sequence or the entire sequence is suppressed. The joint use of metallic shielding and software suppression of interference allowed the stability of Digital 404 to electromagnetic and radio frequency interference to 30 ... 60 V / m in the frequency range from 10 MHz to 1 GHz.
It is known that due to the random nature of useful and interference signals, the processing algorithms based on the theory of statistical solutions are the best. Judging by the statements of developers, these methods begin to be used in the latest models of X & & to Systems firms.
Generally speaking, objectively judge the quality of the processing used, based only on the manufacturer's data from the manufacturer, is quite difficult. Cosnal signs of possession with high tactical and technical characteristics may be the presence of an analog-digital converter, microprocessor and a large amount of processing program used.
Currently passive Opto-electronic infrared ( IK) detectors occupy a leading position when choosing premises from an unauthorized invasion of protection. Aesthetic appearance, ease of installation, settings and maintenance provide them with a priority value compared to other detection tools.
k.T., Associate Professor V.E. Short
Passive optical-electronic infrared (IR) detectors (in the people they are often called motion sensors) detect a person's penetration fact to the protected (controlled) part of the space, form an alarm notification signal and by opening the contacts of the actuator relay (PCO relay) transmit alarm signal to Alert tools. The devices of the alerts can be used terminal (UN) notification systems (SP), or the device receiving-control security and fire (PPKOP). In turn, the above-mentioned devices (UO or PPKOP) on various data transmission channels translate the resulting alarmed notice to the centralized observation remote control (PCN) or local security console.
The principle of operation of passive optical electronic IR detectors is based on the perception of the change in the level of infrared radiation of the temperature background, the sources of which are human or small animals, as well as all sorts of objects in the field of their vision.
Infrared radiation is a heat that is radiated by all heated bodies. In passive optical-electronic IR detectors, infrared radiation falls on the Fresnel lens, after which it focuses on a sensitive pyroelement located on the optical axis of the lens (Fig. 1).
Passive IR detectors Take the streams of infrared energy from objects and are converted by a pinchief in an electrical signal that enters the amplifier and the signal processing scheme to the input of the alarm notification formator (Fig. 1).
Fig. 1. The main elements that are part of passive infrared detectors
With more detailed information on the principle of the action of passive optical-electronic infrared detectors can be found in the electronic 3D book«
Technical means of security alarm " ,
And you can buy it.
Depending on the execution of Fresnel lens, passive optical-electronic IR detectors have different geometric sizes of the controlled space and can be both with a bulk zone of detection and superficial or linear. The range of such detectors lies within the range from 5 to 20 m. Appearance These detectors are presented in Fig. 2.
Fig. 2. Appearance of passive infrared detectors
Passive optical-electronic IR detectors have one wonderful advantage compared to other types of detection tools. This is simplicity of installation, settings and maintenance. Detectors of this type can be installed both on a flat surface of the carrier wall and in the corner of the room. There are detectors that are installed on the ceiling.
Competent selection and tactically correct use of such detectors are the key to the reliable operation of the device, and the entire protection system as a whole!
Detectors with a volumetric detection zone (Fig. 3, a, b) are usually installed in the angle of the room at an altitude of 2.2 - 2.5 m. In this case, they evenly cover the volume of the protected room.
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| but) | b) | in) |
Fig. 3. Charts of passive IR detectors with volumetric zonesdetection
The installation of detectors on the ceiling is preferable in rooms with high ceilings from 2.4 to 3.6 m. Such detectors have a denser detection zone (Fig. 3, B), and their work to a lesser extent are affected by the available furniture items.
Detectors with a surface detection zone (Fig. 4) are used to protect the perimeter, for example, non-vacant walls, door or window openings, and can also be used to limit the approach to any values. The detection zone of such devices should be directed as an option, along the walls with openings. Some detectors can be installed directly above the opening.
Fig. 4. Chart passive IR detectors with surface zonedetection
Detectors with a linear detection zone (Fig. 5) are used to protect long and narrow corridors.
Fig. 5. Diagram passive IR detectors with a linear zonedetection
When using passive optical-electronic IR detectors, it is necessary to keep in mind the possibility of false positives that occur due to interference of various types.
Heat interference due to the heating of the temperature background when exposed to solar radiation, convective air flows from the operation of radiators of heating systems, air conditioners, drafts.
Electromagnetic interference They are caused by pressures from sources of electro and radio emissions to individual elements of the electronic part of the detector.
Outsunted interference related to moving in the detection zone of small animalsx (dogs, cats, birds).
Let us consider in more detail all the factors affecting the normal performance of passive optical electronic IR detectors.
This is the most dangerous factor that is characterized by changing the temperature background of the environment. The effects of solar radiation causes a local increase in the temperature of the individual sections of the walls of the room.
Convective interference is due to the impact of moving air flows, for example, from drafts with open-window, cracks in window openings, as well as when working with household heating devices - radiators and air conditioners.
There are in the inclusion of any sources of electro and radio emission, such as measuring and household equipment, lighting, electric motors, radio transmission devices. Strong interference can be created from lightning discharges.
A peculiar source of interference in passive optical electronic IR detectors may be small insects, such as cockroaches, flies, wasps. If they are moving directly on the Fresnel lens, a false response of the detector of this type may occur. Also, the danger represents the so-called home ants that can get inside the detector and crawl directly on the pyroelement.
A special place in the incorrect or incorrect work of passive optical-electronic IR detectors occupy installation errors when installing data type data setup. Pay attention to the bright examples of improper placement of IR detectors to avoid this in practice.
In Figures 6, a; 7, a and 8, and the correct, correct installation of the detectors is displayed. And they only need to install them and in any way!
In Figures 6, B, B; 7, B, B, and 8, B, in presented the option of improper installation of passive optical electronic IR detectors. With such an installation, there are transmissions of real invasions into protected premises without issuing "Alarm" signals.
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| but) | b) | in) |
Fig. 6. Optionscorrect and ne.right Installation of IR detectors
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Fig. 7. Optionscorrect and ne.right Installation of IR detectors
