Infrared detectors are among the most common in burglar alarm systems. This is explained by the very wide range of their applications.
They are used:
In addition to climatic performance (street and indoor installation) they are also subdivided according to the principle of action. There are two large groups: active and passive. In addition, infrared detectors are classified according to the type of detection area, namely:
Let's look in order for what purposes these or those types are used.
Passive infrared detectors.
These sensors include 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 still, the detector will not work. In addition, the temperature of the object, which is close to the background, also affects its sensitivity in the direction of decreasing.
The same applies to cases when the speed of movement of the object is lower or higher than the normalized value. As a rule, this value is in the range of 0.3-3 meters / second. This is quite enough for confident detection of the 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 a security device, an element that reflects IR rays is additionally used.
The active principle of operation is characteristic of linear sensors that are triggered when the infrared beam is crossed. The principles of operation and features of the application of the main types of infrared detectors are discussed below.
These devices are passive (see above for what it is) and are used mainly to control the internal volume of rooms. The directional pattern of the volumetric sensor is characterized by:
Please note that the range is indicated by the central lobe of the diagram; for lateral lobes it will be shorter.
What is typical for any infrared sensor, including a volumetric one - any obstacle for it is opaque, and accordingly creates dead zones. On the one hand, this is a disadvantage, on the other, an advantage, since there is no reaction to moving objects outside the protected premises.
Also, the disadvantages include the possibility of false positives from factors such as:
Thus, when installing a volumetric detector, these points cannot be ignored. According to the method of installation, there are two versions of "volumetric".
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 blind spots are not created. Considering 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-mounted volumetric detectors.
For objects such as shops or warehouses characteristic feature is the installation of shelves or showcases throughout the entire area of the room. Installation of 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 for each specific object, taking into account all its individual characteristics.
By their principle of action, they are active and form one or more rays, tracking their intersection by a possible intruder. Unlike volumetric, linear sensors are resistant to various kinds of air currents, and direct illumination, in most cases, will not harm them.
The principle of operation of a linear single-beam infrared emitter is illustrated in Figure 2.
The range of active linear devices is from tens to hundreds of meters. The most typical options for their use:
To protect the perimeter, detectors with more than one beam are used (it is better if there are at least three of them). This is fairly obvious as it reduces the likelihood of penetration under or over the control area.
When installing and configuring infrared line detectors, precise alignment of the receiver and transmitter is required for two-unit devices or reflector and combination unit (for single-unit ones). 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 point of reception.
It also follows from the above that it is necessary to mount all elements of such detectors on rigid linear structures that completely exclude possible vibrations.
I must say that a good "lineman" is a rather expensive pleasure. If the cost of single-beam devices with a short range of action still lies within a few thousand rubles, then with an increase in the controlled range and the number of infrared beams, the price rises to tens of thousands.
This is explained by the fact that security detectors of this type are rather complex electromechanical devices containing, in addition to electronics, high-precision optical devices.
By the way, passive linear detectors also exist, but in terms of the maximum range of action they are noticeably inferior to their linear counterparts.
It is quite obvious that a street burglar alarm detector must have an appropriate climatic design. This applies primarily to:
According to the generally accepted existing classification, the protection class of the outdoor detector must be at least IP66. By and large, for most consumers this is not a matter of principle - the indication "street" in the description is quite enough technical parameters device. It is worth paying attention to the temperature range.
The features of the use of such devices and the factors affecting the reliability of protection deserve more interest.
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, outdoor linear detectors are used for perimeter protection. open areas... Surface sensors can also be used for the same purposes.
Volumetric devices are used to control various types of areas. It should be noted right away that they are inferior to linear sensors in terms of range. It is quite natural that the prices for outdoor detectors are significantly higher than for devices intended for indoor installation.
Now, with regard to the practical side of the operation of outdoor infrared detectors in burglar alarm systems. The main factors provoking false alarms of security sensors installed on the street are:
The first point may seem unimportant, since, at first glance, it is static and can be taken into account at the design stage. Do not forget, however, that trees, grass and bushes grow and over time can interfere with the normal operation of security equipment.
Manufacturers are trying to compensate for the second factor by applying appropriate signal processing algorithms, and there is an effect from this. 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.
As for the last point. It all depends on the change in the optical density of the medium. In simple terms, heavy rain, heavy snow or heavy fog can render the infrared detector completely inoperative.
So, when deciding on the use of outdoor security detectors in signaling, consider all of the above. Thus, you can save yourself from many unpleasant surprises when operating an outdoor security system.
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One of the most demanded elements of security systems is a volumetric passive infrared detector. This is explained by the very wide range of applications of such devices. They can be used both to control the internal volume of premises and to organize perimeter security. The Sintez Security company invites you to buy such equipment from us. We guarantee high quality, as well as the fact that the price of the products will be quite affordable.
The functioning of such devices is based on the registration of changes in the infrared temperature background emanating from a variety of heated objects and, first of all, living bodies. Depending on the principle of operation, the sensors are divided into active and passive. In the latter, fluxes of infrared energy enter a sensitive pyroelectric element through the lens.
Passive infrared detectors are triggered if temperature differences are detected during the inspection of the sectors of the monitored area. They indicate the presence of movement in the area of the sensor. There are several types of such equipment, differing in their ability to fix a certain speed of movement.
After the built-in microprocessor has analyzed the received data, the contact network is opened or closed. This leads to the formation of an alarm message arriving at the security console. Depending on the type of detection zone, there are:
This equipment is considered one of the most efficient and has a number of advantages over surface and linear models. The reason for this is that when scanning rooms, the device studies them not only in the vertical direction (from floor to ceiling), but also in the horizontal plane. As a result, the reliability of the system is significantly increased.
Volumetric sensors are passive devices. They are most often used for indoor safety. When designing systems using such equipment, it is necessary to take into account the fact that for devices of this type, any obstacle is opaque. As a result, a kind of "dead" zones appear. This feature is not necessarily considered a disadvantage. Thanks to it, you can avoid a reaction to a moving object outside the protected area.
If you choose such devices, the company "Synthesis Security" recommends that you take into account a number of parameters. These include:
Moreover, it should be taken into account that the parameter of the equipment range is indicated along the main axis. This figure will be lower along the lateral axes. In addition, when setting up the system, you must also specify the temperature range correctly. It differs significantly in heated and unheated premises, For example. The Sintez Security company will help you make the right choice. Contact us, state your wishes, and we will take care of the rest.
You can buy passive IRs from us at a low price - there are 40 pieces in the catalog, compare, study the characteristics.
One of the innovations that have come into our lives, the scope of its application is wide, so it ceased to be a "curiosity" and began to be applied everywhere. Naturally, people are interested in this device. I managed to find the publication of the author, who covered this topic in great detail, as they say, will not add, not subtract.
I present to your attention article from the magazine "Radioamator" by N.P. Vlasyuk, Kiev.
The passive infrared motion sensor powered by ~ 220 V is produced in a set with a halogen floodlight and is designed as a single device. It is called passive because it does not illuminate the controlled area with infrared radiation, but uses its background infrared radiation, therefore it is absolutely harmless.
The sensor is designed to automatically turn on the load, for example, a searchlight, when a moving object enters its control zone and turns it off after the object leaves the zone. It is used to illuminate the facades of houses, household yards, construction sites, etc.
The supply voltage of the sensor and the entire device is ~ 220 V, the current consumption of the sensor itself in the security mode is 0.021 A, which corresponds to the power consumption of 4.62 W. Naturally, when a halogen lamp with a power of 150 or 500 W is turned on, the power consumption increases accordingly. The maximum detection radius of a moving object (in front of the sensor) is 12 m, the sensitivity zone in the horizontal plane is 120 ... 180 0, an adjustable illumination delay (after the object leaves the control zone) from 5 ... 10 s to 10 ... 15 minutes. The admissible operating temperature range is -10 ... + 40 ° С. Permissible humidity up to 93%.
The IR sensor can be in one of the following modes. "Security mode", in which he "vigilantly" monitors the monitored zone and is ready to turn on the executive relay (load) at any time. "Alarm mode", in which the sensor switched on the load with the help of the executive relay, since a moving object got into its controlled area. "Sleep mode", in which the sensor, being switched on (energized), in the daytime, does not react to external stimuli, and with the onset of twilight (darkness) automatically switches to the "Security mode". This mode is provided in order not to turn on the lighting in the daytime. After energizing, the detector starts from the "Alarm mode", and then switches to the "Security mode".
These sensors are also sold separately. They are used much wider than a set (a floodlight with a sensor), and according to the power supply mode, they can be designed for a voltage of ~ 220 V or = 12 V.
How a passive infrared sensor works
The infrared background radiation of the monitored area is focused by the front glass (lens) onto a phototransistor that is sensitive to infrared rays. The low voltage coming from it is amplified with the help of operational amplifiers (OA) of the microcircuit included in the sensor circuit. Under normal conditions, the electromechanical load switch is de-energized. As soon as a moving object appears in the controlled area, the illumination of the phototransistor changes, it outputs a changed voltage to the input of the op-amp. The amplified signal throws the circuit out of balance, the relay is triggered, which turns on the load, for example, a lighting lamp. As soon as the object leaves the zone, the lamp continues to glow for a while, depending on the set time of the electronic time relay, and then switches to the initial state - "Security mode".
A schematic diagram of a passive IR sensor model 1VY7015 is shown in Fig. 1.
Compared to similar 1 2V IR sensors, the circuitry of this model is simple. It is drawn according to wiring diagram... Since the manufacturers did not indicate all the radio elements on the wiring diagram, the author had to do it himself. On the board with dimensions of 80 × 68 mm there are mounted radioelements without the use of CHIP-elements.
1. The sensor power supply unit is transformerless, made using a quenching capacitor C2 with a capacity of 0.33 μF × 400 V. After the rectifier bridge, the Zener diode ZD (1 N4749) sets a voltage of 25 V, which is used to power the relay coil K1, and the stabilizer DA1 (78L08 ) of 25 V stabilizes 8 V, which is used to power the LM324 microcircuit and, in general, the entire circuit. Capacitor C4 is a smoothing capacitor, and SZ protects the sensor from high-frequency interference.
2. Three-output infrared phototransistor PIR D203C is the "keen eye" of the sensor, its main element, it is he who issues the "command" to turn on the executive relay when the infrared background of the monitored area changes rapidly. It is powered by +8 V through a resistor R15. Capacitor C13 is a smoothing capacitor, and C12 protects the phototransistor from high-frequency interference.
3. Microcircuit LM324N (market value $ 0.1) - the main amplifier of the sensor. It includes 4 op-amps, which are connected in series (4-3-2-1) by a sensor circuit (radioelements R7, C6; D1, D2; R21, D3), which ensures high amplification of the signal produced by the IR phototransistor and high sensitivity the whole sensor. It is powered by 8 V ("plus" - pin 4, "minus" - pin 11).
4. The purpose of the electromechanical relay K1 model LS-T73 SHD-24VDC-F-A is to turn on the load, or rather, to supply it with ~ 220 V. The voltage of +25 V to the relay coil is supplied by the transistor VT1. The rated operating voltage of the relay winding is 24 V, and its contacts, according to the inscription on the case, allow a current of 10 A at ~ 240 V, which raises doubts about the ability of such a small-sized relay to switch a load of 2400 W. Foreign manufacturers often overestimate the parameters of their radioelements.
5. Transistor VT1 type SS9014 or 2SC511. Main limiting parameters: Ukemax = 45 V, lkmax = 0.1 A. Provides switching on / off relay K1 depending on the voltage ratios (pin 1 of LM324N and collector VT2) on its base.
6. Bridge (R5, R6, R7, VR2, photoresistor CDS) transistor VT2 (SS9014, 2SC511) are designed to establish one of two modes of operation of the sensor: "Security mode" or "Sleep mode". The required mode is provided by the illumination of the CDS photoresistor (it is he who, with its changing resistance C "illumination, indicates to the sensor whether it is day or night by the position of the variable resistor VR2 (DAY LIGHT). Thus, when the variable resistor slider is in the" Day "position, the sensor works as day and night, and in the "Night" position - only at night, and during the day it is in "sleep" mode.
7. Adjustable electronic time relay (C14, R22 VR1) provides a time delay for turning off the luminous lamp from 5 ... 10 s to 10 ... 15 minutes after the object leaves the controlled area. Adjustment is provided
variable resistor TIME VR1.
8. Variable resistor SENS VR3 is used to adjust the sensor sensitivity by changing the depth of negative feedback in op-amp # 3.
9. Damping circuit R1C1 absorbs voltage surges that occur when the halogen lamp is turned on / off.
10. Other radioelements (for example, R16-R20 R11, R12, etc.) ensure the normal operation of the op-amp of the LM324N microcircuit.
When starting to repair an IR sensor, you should remember that all its radio elements are under phase voltage, which is life-threatening. When repairing such devices, it is recommended to turn them on through an isolation transformer. The sensor works reliably and rarely gets repaired, but if it is damaged, then the repair begins with an external examination of its circuit board. If no damage is found, then the output voltages of the power supply device (25 and 8V) should be checked. The power supply device, and any other element of the circuit (microcircuit, transistors, stabilizer, capacitors, resistors), can fail due to voltage surges in the supply network or lightning strikes, and, unfortunately, protection against them is not provided in the sensor circuit ... The tester can check the serviceability of all these elements, except for the microcircuit. The microcircuit, if suspected of inoperability, can be replaced. The weak link in the sensor may be the contacts of the relay K1, since they switch significant inrush currents of the halogen lamp, their performance is checked with a tester.
Setting up the IR sensor is correct installation three adjusting resistors located at the bottom of the sensor (Fig. 2).
What do these resistors regulate?
TIME - adjusts the delay time for turning off the halogen lamp after the object that caused it to turn on has left the controlled area. The adjustment range is from 5 ... 10 s to 10 ... 15 min.
DAY LIGHT- sets the detector to "Armed" or "Sleep mode" in the daytime. From a physical point of view, the position of the variable resistor slider allows or prohibits the sensor to work under a certain illumination. Adjustable illumination range 30 lux. So, if the regulator is turned counterclockwise (set to the “crescent” sign), then the sensor works only in the dark, and during the day it “sleeps”. If you turn it to the extreme position counterclockwise ("little sun" sign), then the sensor works both in the daytime and at night, i.e. all day long. In an intermediate position between these values, the sensor can switch to the "armed mode" already at dusk. The sensor switches to one of the above modes automatically.
SENS - adjusts the sensitivity of the sensor, i.e. sets a larger or smaller area (or range) of the controlled area.
The disadvantages of the ~ 220 V IR sensor are its false positives. This happens when the branches of trees or bushes are in the controlled area; from a passing car, more precisely, from the heat of its engine; from a changing heat source if located under the sensor; from a sudden change in temperature during gusts of wind; from lightning and flashing of car headlights from the passage of animals (dogs, cats); from the blinking of the mains, the sensor is triggered and the lamp continues to shine for some time. The disadvantages of the above-described sensor should also include its inoperative state in the absence of a voltage of ~ 220 V. It is possible to reduce the number of false alarms by changing the position of the sensor.
The purpose of the front glass is the lens of the IR sensor. To expand the monitored area up to Control 120 ° and even 180 °, the sensor lens is made semicircular or spherical. During its manufacture (casting), numerous rectangular lenses are provided on its inner side. They divide the controlled sector into small sections. Each lens, from its section, focuses infrared radiation into the center of the phototransistor. The division of the controlled area into sections leads to the fact that the controlled area becomes fan-shaped (Fig. 3).
As a result, the sensor “sees” the intruder only in the black zone, and in the white one he is “blind”. These zones, depending on the number and size of the lenses, have a configuration set by the designers. The use of microprocessors makes it possible to eliminate a number of the above-described disadvantages of these sensors. The lens is the most important element of the IR sensor. It depends on how widely the sensor "sees" horizontally and vertically. Some IR sensors have interchangeable lenses that create a controlled area for a specific task. The lens glass must be intact (not broken), otherwise the configuration of its controlled area is unpredictable.
1.Lighting various premises, i.e. automatic switching on / off lighting in entrances, warehouses, apartments (houses), household yards and farms. For this, depending on the situation, you can use both the above-described sets of IR sensors with spotlights, or separately sold sensors. The set is installed on stationary objects at a height of 2.5 ... 4.5 m (Fig. 4).
Separately sold passive IR sensors can be designed for a power supply voltage of either ~ 220 V or +12 V. For lighting, it is better to use sensors for ~ 220 V, they are relatively cheap and also provide ~ 220 V to the load, so it is easy to connect light bulbs to them ...
One of the variants of such a sensor, model USA 1009, is shown in Fig. 6.
It has only two adjusting resistors: Time Delay, which regulates the time when the load is disconnected after the object leaves the monitored area, and Light Control, which enables or disables the operation of the sensor in the daytime. Maximum permissible load 1200 watts The viewing angle of the controlled area is 180 °, and its maximum length 12 m.
Three colored wires come out of the sensor, intended for connecting the network and the load. Figure 7
shows a circuit for switching on such a sensor to a separate ~ 220 V lamp, which can be used as a table lamp.
When connecting the sensor to the existing electrical wiring of the house (apartment), i.e. to the already installed light bulbs and switches, it is important to correctly find the common wire of the sensor and combine it with the wiring. Fig. 8, a, b shows the diagrams of the wiring section before turning on the sensor and after turning on.
If you use the sensor to illuminate the porch of the house, then it is better to install the sensor itself near the light bulb.
The use of IR sensors in lighting schemes significantly saves energy and creates convenience when they are automatically turned on / off.
2. Automatic switching on of lighting in apartments and houses. In such a situation, it is better to adapt the sensor to table lamp, so that if unnecessary, you can easily turn it off.
3. Notification of the owner of the house about the arrival of guests. In this case, the sensor must be directed to the fence gate or the space around it, and for sound notification, use a bell or other sound detector powered by ~ 220 V.
4. Security for the utility yard, garage, farm, office, apartment. For this purpose, you can use the above-described cheap IR sensors powered by ~ 220 V. However, such sensors have a big drawback: when the network is lost, they do not work, therefore they are used only to protect insignificant objects. + 12V-powered IR sensors do not have these drawbacks, as they are easily provided backup power supply from batteries. For this, a small control panel (PKP) has been developed, which is mounted on the wall. It houses the power supply, 12 V batteries for 4 Ah or 7 Ah and electronic filling. All sensors of the protected object are connected to one control panel, which provides them with reliable power supply, receives alarms from them and transmits them to the guard. In the absence of security, a powerful sound siren can be connected to the control panel, which will scare off intruders. Thus, for the protection of important facilities, control panel sets with 12 V IR sensors should be used, a standard 4-wire cable should be pulled between them (two wires for 12 V power supply, two for an alarm signal). External regulating resistors are not installed on the +12 V IR sensors, since some of their functions are transferred to the "electronic stuffing" of the control panel control panel.
To protect your household yard, infrared sensors must be installed so that they are not visible, otherwise they can be damaged. For this, infrared sensors can be installed near the windows inside the house, directing their lens to the protected objects. For the protection of apartments and offices IR sensors They are installed in the corner of rooms, and to protect garages and farms, their lenses are directed to the entrance gate.
As already noted, cheap IR sensors for ~ 220 V and 12 V have a number of disadvantages, such as sensor triggering when dogs, cats, mice pass. To eliminate this phenomenon, it is necessary to install an IR sensor inside the house on the window sill, direct it to the courtyard and place a protective screen in front of it (Fig. 9).
In this case, a "blind zone" is formed between the ground and the capture zone of the IR sensor, in which the sensor does not respond to minor offenders, but it will react to a passing person, since the person is higher in height than this zone.
In the new 12 V sensors, the designers, by complicating the circuit and the sensor design, eliminated this drawback. So, in the Israeli Crow SRX-1100 infrared sensor, a microprocessor is added and a microwave radio emitter is installed, which determines the size of the intruder, compares it with the established thresholds and decides whether or not to give an alarm command.
Designers from Japan and other countries have solved this problem in a different way. They provided for the displacement (inside the IR sensor) of the electronic board with the phototransistor up or down in relation to the focal point of the glass lenses. As a result, the black sensitive segments closest to the ground are cut off, and a "blind zone" is established near the ground, in which the sensor "does not see" small animals. The height of the "blind spot" can be adjusted with the same offset of the electronic board. There are other ways to exclude the reaction of infrared sensors to the passage of small animals. The problem of the IR sensor triggering when it is illuminated by lightning or car headlights has been resolved. Naturally, all these improvements cause a rise in the cost of passive infrared sensors, but they increase the reliability of protection.
How to trick an IR detector
The initial disadvantage of the IR passive method of motion detection: a person must clearly differ in temperature from the surrounding objects. At a room temperature of 36.6º, no detector can distinguish a person from walls and furniture. Worse, the closer the room temperature is to 36.6º, the worse the detector's sensitivity. Most modern devices partially compensate for this effect by increasing the gain at temperatures from 30º to 45º (yes, the detectors work successfully even with a reverse differential - if the room is + 60º, the detector can easily detect a person, thanks to the thermoregulation system, the human body will maintain a temperature of about 37º). So, when the temperature outside is about 36º (which is often found in southern countries), the detectors do not open doors very well, or, on the contrary, because of the extremely raised sensitivity, they react to the slightest breath of wind.
Moreover, it is easy to obstruct the IR detector with any object at room temperature (a sheet of cardboard) or put on 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 more exotic recommendations on the Internet, such as a powerful IR lamp, which, if you turn it on slowly (with an ordinary 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 out a fault signal.
Finally, the most famous problem with IR detectors is masking. When the system is disarmed, in the afternoon during working hours, you, as a visitor, come to the desired room (in a store, for example) and, catching 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 paint from a spray can. This is especially convenient for a person who works there himself. The storekeeper neatly blocked the detector during the day, climbed into the window at night, took out everything, and then removed everything and called the police - horror, they robbed, but the alarm did not work.
To protect against such masking, there are the following techniques.
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 stretched out his hand directly to the detector), and the IR sensor stopped emitting signals. In most cases, in real life, this does not mean at all 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 the malicious intent, if the detector is blocked, this is a mess, and such a "malfunction" signal is very appropriate.
2. In some control panels there is 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 gives a normal signal "there is movement". This function is not very convenient, because often all premises are disarmed, even those into which 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 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 national GOST and which is often mistakenly called "anti-masking". The essence of the idea: the detector should have an additional sensor that looks straight down under the detector, or a separate mirror, or a special cunning lens, in general, so that there is no dead zone at the bottom. (Most detectors have a limited viewing angle and mostly look 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 can somehow get into this dead zone and from there block (mask) the lens of the IR sensor, and then brazenly walk around the room. In reality, the detector is usually installed so that there is no way to get into this dead zone, bypassing the sensor's sensitivity areas. Well, perhaps through a wall, but additional lenses will not help against criminals penetrating through the wall.
Radio and other interference
As I said before, the IR sensor works close to the sensitivity limit, especially when the room temperature approaches 35 ° C. Of course, it is also very susceptible to interference. Most infrared detectors can give a false alarm if you put a cell phone next to them and call it. At the stage of establishing a connection, 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). Several watts of radio emission are quite comparable to microwatts of human thermal radiation.
In addition to radio emission, there may 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 adjacent spectral range, again, may well give 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 affects both sensitive elements of the IR sensor in the same way, thus, the detector can detect the interference and not generate a false alarm.
Ways to improve infrared sensors
For ten years now, almost all security infrared detectors contain a sufficiently powerful microprocessor and therefore are less susceptible to random interference. The detectors can analyze the repeatability and characteristic parameters of the signal, the long-term stability of the background signal level, which has significantly improved the immunity to interference.
Infrared sensors, in principle, are defenseless against criminals behind opaque screens, but they are susceptible to heat flows from climate equipment and extraneous light (through a window). Microwave (radio) motion sensors, on the contrary, are capable of giving false signals, detecting movement behind radio-transparent walls, outside the protected area. 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 particularly critical premises, which practically excludes the possibility of overcoming them.
IR sensors cannot tell a small person from a large dog. There are a number of sensors in which the sensitivity to the movements of small objects is significantly reduced due to the use of 4-area sensors and special lenses. Signal from tall man and from a short dog, in this case, it is possible to distinguish with some probability. It must be well understood that it is, in principle, impossible to completely distinguish a bent teenager from a Rottweiler standing on its hind legs. Nevertheless, the probability of a false alarm can be significantly reduced.
Several years ago, even more sophisticated sensors appeared - with 64 sensitive areas. In fact, this is a simple thermal imager with an 8 x 8 matrix. Equipped with a powerful processor, such (to call them "detector" does not turn at all) are able to determine the size and distance to a moving warm target, the speed and direction of its movement - even 10 years ago, such sensors were considered the pinnacle of technology for homing missiles, and now they are used for protection from commonplace thieves. Apparently, soon we will get used to calling the small robots with the IR sensor that will wake you up at night 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 and take your revolver? "
Infrared sensors are becoming more widespread every day. Whether you realize it or not, you've probably used an infrared (IR) sensor more than once in your life. Most of us switch TV channels with a remote control that emits IR light, and many of us go through security sensors that detect movement through infrared light.
Manufacturers use IR sensors extensively, and you've probably seen them at work in automated garage doors Oh. Today, there are two types of infrared sensors - active and passive. V this material We will cover the differences between active and passive infrared sensors and their applications.
The principle of operation of the IR sensor is simple. In a standard IR sensor, an emitter sends invisible light to a receiver at some distance. If the receiver does not receive a signal, the sensor indicates that an object is in between. But what exactly is the difference between passive and active sensors?
You might assume that passive IR sensors are less sophisticated than their active counterparts, but you are wrong. The functionality of a PIR sensor can be tricky to understand. First, everyone (people, animals, even inanimate objects) emit a certain amount of IR radiation. The infrared radiation they emit is related to the heat and material composition of a body or object. Humans cannot see IR, but humans have developed electronic detection devices to detect these invisible signals.
Passive IR (PIR) sensors use a pair of pyroelectric sensors to detect thermal energy in environment... These two sensors are installed next to each other, and when the signal difference between them changes (for example, if a person enters a room), the sensor turns on. IR radiation is focused on each of the two pyroelectric sensors using a series of lenses designed as a sensor body. These lenses expand the device's viewing area.
While lens mounting and sensor electronics are complex technology, these devices are easy to use in practical applications. You only need a power supply and a ground line for the sensor to produce a discrete output that is strong enough for the microcontroller to use. Typical tweaks include adding potentiometers to adjust sensitivity and adjusting how long the PIR stays on after it is triggered.
You will usually find PIR sensors in burglar alarms and automatic lighting systems. These applications do not require the sensor to detect a specific location of an object, it simply detects moving objects or people in a specific area.
While PIR sensors are excellent for their application if you want to detect motion in general, they won't give you more information about the subject. To find out more, you will need an active IR sensor. Both an emitter and a receiver are required to tune an active IR sensor, but this measurement method is simpler than its passive counterpart. This is how active IR works at a basic level. The IR emitter emits a beam of light towards the built-in receiver. If nothing is in the way, the receiver sees the signal. If the receiver does not see the infrared beam, it detects that the object is between the emitter and the receiver and, therefore, it is present in the monitored area.
One variation of a standard active IR sensor uses the emitter and receiver facing the same direction. Both are mounted very close to each other so that the receiver can detect the reflection of radiation from an object as it enters the area. The fixed reflector sends the signal back. This method replicates the installation of separate emitter and receiver units, but without the need to install a remote electrical component. Each method has advantages and disadvantages based on the material the sensor will detect and other specific circumstances.
Active infrared sensors are very common in industrial environments. In these applications, a pair of emitters and receivers can accurately mark whether an object is, for example, in a specific position on a conveyor. You can also find active infrared sensors in garage door security systems that prevent injury or mechanical failure due to obstacles in the door's path. Whatever your application, there are many infrared sensors available in passive and active configurations to suit your needs.
