We assemble a motion sensor to turn on the light. Operating principle of security alarm sensors Microwave detection method

Modern vehicles no longer measure speed using the outdated mechanical method - through a rotating cable. Nowadays special devices are used, the operation of which is based on the Hall effect. The sensor works in tandem with a controller that receives electromagnetic pulses from it and instantly calculates the current speed of the vehicle. The calculation process occurs according to the following scheme: for every kilometer traveled, the sensor sends the controller a strictly defined number of electromagnetic pulses - 6004.

The higher the current speed of the car, the more intense the impulses are transmitted to the controller, which allows the latter to accurately determine at what speed the vehicle is currently moving. In addition to determining speed, this sensor performs another important function. When the vehicle is coasting and its speed does not exceed, the pulse speed sensor does not block the flow of fuel, helping to save fuel. The principle of operation of the speed sensor is quite simple, but if malfunctions occur, this inevitably affects the operation of the engine as a whole.

How does the speed sensor affect engine performance?

A working speed sensor transmits a signal to the controller, which in turn sends data about the current speed to the electronic engine control unit. Based on these data, the fuel supply is calculated and, if the driver takes his foot off the gas pedal, the fuel supply is sharply reduced, which allows the engine to consume it quite rationally. Malfunctions that occur with the sensor lead to the control unit not receiving the necessary information.

At the same time, the ECU sets the current speed to 1500/min and deactivates the fuel cut-off mode. All this leads to significant excess fuel consumption, as well as to uneven operation of the engine itself, which operates jerkily. For reference, the operating fuel cut-off mode helps save up to 2 liters of fuel when driving in urban areas. In addition, the speed sensor affects the correct gear shifting of the automatic transmission. If it is faulty, cruise control will not work, and on some car models there will be interruptions in the operation of the electric power steering.

Advice! If the speedometer or tachometer needle suddenly begins to twitch, it is important to immediately check the condition of the cable, since delay may lead to the need to replace the device itself.

The main causes of car DS malfunction

The most common problems with this device include a broken electrical circuit, so it’s best to start self-diagnosis by checking the electrical contacts and the wires themselves. They are called by a tester and checked visually. You can often observe their breakage immediately after the plastic connector, as well as in the exhaust manifold area.

All contacts must be disconnected and checked. As a rule, moisture and salt contribute to the rapid oxidation of contacts, which leads to an interruption of the electrical circuit. If such a situation is detected, the contacts are cleaned and lubricated with grease. Be sure to check the speedometer cable - with prolonged use, breaks appear on it, preventing normal operation sensor To avoid problems with the cable, it must be periodically lubricated with engine oil. To independently suspect a speed sensor malfunction, you should pay attention to the following signs:

• failure or incorrect operation of the speedometer;
• lack of engine stability at idle speed;
• suddenly increased fuel consumption;
• the engine suddenly loses power.

Often, problems with the sensor may be indicated by the engine stopping on its own when idling while coasting, or when pressing the clutch pedal to change gear. As a rule, if the above problems are detected, the device must be replaced.

Self-test

Before checking the speed sensor, you should find out whether electrical voltage is supplied to the contacts. It should be understood that since the operation of the sensor is based on the Hall effect, the contact intended for transmitting pulses is checked only during torsion, and in its absence, no voltage will be supplied to the device. Its normal values, when tested with a multimeter, can range from 0.5 to 10 V. There are three ways to independently test the speed sensor.

1. This diagnostic method will require preliminary dismantling of the device. Using a digital multimeter, you should find among the contacts the one through which pulses are transmitted. The positive probe of the multimeter is connected to it, and the negative probe is connected to the car body. After this, the axis of the sensor itself must begin to rotate at a low speed - the multimeter will show a small voltage, which should increase in parallel with the increase in the speed of rotation of the axis.

Attention! Removing the sensor should only be done with the ignition off, otherwise the device may simply burn out when the contacts are disconnected.

When using the second and third methods, it makes sense to check the device drive as well. It is found by touch, and when the wheel rotates, the rotation stability of the drive is assessed.

How to replace the speed sensor yourself

Before starting the procedure for replacing the speed sensor, you should perform the above steps to diagnose it, and only after that it is advisable to carry out replacement. At the same time, you should pay attention to the quality of the newly purchased device - it is better to use European or domestic sensors, but not manufactured in China. In addition to the quality of the materials themselves, in domestic devices all contacts that may be affected by adverse environmental factors are varnished, which significantly extends their service life.

In addition, of all the options, you should prefer the device version not with a plastic shank, but with a metal one. The plastic shank wears out much faster, especially if the driver prefers an aggressive driving style and high speed. To facilitate the replacement process, it is better to drive the car into a pit or lift it with a lift. You can find out where the speed sensor is located in the owner's manual for your specific vehicle.

After finding it, you should clean it of dirt by first turning off the ignition or disconnecting the terminals from the battery, and try to unscrew it. If it doesn’t work out the first time, it is not recommended to use excessive force - it is better to treat the connection with WD-40 and wait a little. After successful dismantling, a new device is installed, the speed sensor connectors are connected and power is connected to the battery. About how to perform independent replacement explained in the video:

Advice! After installing a new speed sensor, you must manually reset the error in electronic unit engine control, otherwise the malfunction indicator will continue to light, and the ECU will assume that the sensor is faulty.

Is it possible to extend the life of the speed sensor?

Since the speed sensor device is not particularly complex, and the replacement procedure is complicated, many car owners do not pay any attention to this device, which to a certain extent contributes to its rapid failure. Especially at risk are those drivers who prefer to drive high speeds, and the installed sensor has a plastic shank, which is quickly broken by a cable.

A common cause of malfunction can be the cable itself. It is constantly negatively affected by factors such as moisture and reagents used to treat roads, as a result of which it loses its original elasticity and begins to delaminate. The cable braid also loses its elasticity. To prevent premature chafing of the cable, it makes sense to periodically treat it with machine oil, which is pumped under the braid through a syringe.

Special attention should be paid to the speed sensor shank in the place where the sensor itself and the cable are connected. If the shank is plastic, then the fastening is tight, because if it becomes loose during the operation of the car, the seat may be broken. Such a nuisance will lead to the fact that the sensor will stop working, and its shank cannot be repaired - the entire device will have to be replaced.

You should be aware that the speed sensor contacts also require periodic cleaning, since they are constantly exposed to moisture and reagents, leading to their oxidation. In addition to deteriorating the conductivity of electrical voltage, this can also lead to short circuit, which is guaranteed to damage the sensitive device.

Among the elements of radio electronics, automation, as well as measuring equipment, the Hall sensor, the operating principle of which is based on the effect of the same name, occupies a special place. The meaning of the mentioned effect is that when a conductor is placed in a magnetic field, electromotive force(EMF), the direction of which will be perpendicular to the field and current. How is this used in a car?

Hall sensor - operating principle and purpose

In modern conditions, there is a constant technological development of Hall sensors. They are distinguished by reliability, accuracy and consistency of data. These devices are widely used in cars and other vehicles. They have increased resistance to aggressive external influences. Hall sensors are an integral part of many devices with the help of which a certain state of equipment is monitored.

In many cases, this device is located in the distributor and is responsible for generating a spark, that is, it is used instead of contacts. This device is often used to monitor load current. With its help, a shutdown occurs when current overloads. If the sensor overheats, the temperature protection is triggered. A sudden change in voltage can have serious consequences for the device. Therefore, in the latest models, an internal diode is installed that prevents the voltage from turning back on.

Until now, the Hall effect sensor has not been able to replace conventional mechanical switches. However, in any case, it has a number of significant advantages. The main ones are the absence of contacts, contamination, and mechanical stress. Therefore, you can often find a Hall sensor on a scooter, used as a component.

Hall sensor - connection diagram and “physics” of the process

The classic Hall sensor device in practice is a thin semiconductor sheet material. When passing through it direct current A relatively low voltage is generated at the edges of the sheet. If a magnetic field passes at a right angle across the plate, then at the edges of the sheet a voltage increase occurs, which is directly proportional to the magnetic induction. A Hall effect sensor is a type of pulse sensor that produces low voltage electrical impulses. Due to its properties, this element is widely used in contactless ignition systems..

We looked at the operating principle of the Hall sensor; its diagram is not yet clear to us. She includes in her set permanent magnet, a semiconductor wafer with a microcircuit and a steel screen with slots. The steel screen allows passage through the slots magnetic field, due to which voltage begins to arise in the semiconductor wafer. The screen itself does not allow the magnetic field to pass through, so when the slots and the screen alternate, low voltage pulses are created.

When this sensor is structurally combined with the distributor, a single device is obtained - a distributor, which performs the functions of an ignition distributor-distributor.

Hall sensor and operating features

When a Hall sensor is actively used in the design of a car, its connection diagram requires regular checks and preventive maintenance. The main thing is not to cause any harm during such checks, so disconnecting the cable connector from the sensor must be done with the ignition off. Otherwise, the element may simply fail; there is no point in repairing it; replacement will be required.

You can check the correctness of the circuit as follows: when rotating and, accordingly, the distributor shaft, the control LED should alternately light up and go out, indicating the presence of a signal . Do not check the sensor using a conventional test lamp. Special attention During operation of the device, pay attention to the cleanliness and reliability of the connector and the contact of the plugs. It must be remembered that the Hall sensor cannot be used in a conventional ignition system.

Expert opinion

Ruslan Konstantinov

Automotive expert. Graduated from Izhevsk State Technical University named after M.T. Kalashnikov, specializing in “Operation of transport and technological machines and complexes.” More than 10 years of professional car repair experience.

A faulty Hall sensor is almost impossible to determine visually, except perhaps for obvious mechanical damage and broken electrical wiring or contacts. To carry out an accurate diagnosis, you cannot do without the services qualified specialists having necessary equipment. Any car service center has an oscilloscope that can be used to determine any malfunctions of sensors, including the Hall sensor. The following reasons may be the reason for such a diagnosis:

1. difficulty starting the engine, and in some cases it is impossible to start it at all;
2. unstable idling (speeds fluctuate);
3. while driving, when the speed increases, sharp jerks are felt;
4. The engine can stall at any time for no apparent reason.

Despite the complexity of the Hall sensor testing procedure, anyone can carry out the test on their own, although the objectivity of the testing will be lower. For example, you can use a multimeter, set the device to voltmeter mode and measure the output voltage, which should be in the range from 0.4 to 11 V. Well, the easiest way to check is to install a known-good sensor; if changes are obvious, this is a reason go to the store for a new sensor.

How does the tilt-displacement sensor work inside...
A tilt and displacement sensor was used to write this article.
What's inside?

Figure 1. Key components of the sensor.

The heart of the sensor is a 3-axis acceleration sensor (accelerometer). It is marked with the letter "A" in the photograph.
Accelerometers are produced by several companies that are the pillars of world microelectronics. The Spider® tilt sensor uses a MEMS sensor from Freescale.
Inside it contains micromechanical capacitive assemblies that are sensitive to acceleration (the so-called g-cell) and an integrated chip that provides primary signal processing, thermal compensation and output for further processing by a microcontroller.

The sensing element (g-cell) is a mechanical structure formed from semiconductor materials (polysilicon) using technological processes masking and etching. They can be thought of as a set of electrodes attached to a mass that is movable relative to the rigidly fixed electrodes. Under the influence of acceleration, the mass deviates from the neutral position, changing the ratio of the distances between the moving and stationary electrodes.

Figure 2. Simplified sketch of acceleration-sensitive cell (g-cell)

The mass with movable electrodes moves under the influence of applied acceleration. In this case, the capacitance of the capacitors formed by the electrodes changes proportionally (for one capacitor it increases, and for the other it decreases). An integrated circuit built into the accelerometer measures capacitances and calculates acceleration based on their difference. The integrated circuit also amplifies the signal and normalizes it so that it is proportional to the acceleration.

The accelerometer has three sensing elements, oriented according to axes X,Y and Z and three channels, the signals in which correspond to the acceleration acting on the sensor.
The sensing element is sealed during the production of the accelerometer.

All objects around us are affected by gravity. In other words, all of them, even when at rest, experience acceleration due to gravity (g).
It is this acceleration that is “laid out along the axes” of the accelerometer.

Outdated car tilt sensors were built on 2-axis accelerometers (just a few years ago, a 3-axis sensor was considered an unaffordable luxury due to the greater complexity of manufacturing and price) and required installation in a position as horizontal as possible. Otherwise, they simply stopped “seeing” the slope.

How a modern tilt sensor works: it already has a 3-coordinate sensor inside. that is, the same Spider TMS2 or Spider STMS, having the ability to navigate in all three coordinates of our three-dimensional space, works equally well regardless of the position of its installation.

The accelerometer signal is processed by a highly integrated microcontroller (marked “M” in Figure 1). An analog-to-digital converter (ADC) digitizes the signals. When the vehicle is impacted, the resulting “distribution” of acceleration along the axes changes.

The microcontroller and its built-in program also perform additional processing to filter out false positives. And they, as you can guess from the principle of operation, can be triggered by shock, vibration, rocking, and even just a large change in temperature.
In general it looks like this:
- signals with frequencies above 30-60 Hz are impacts
- signals with frequencies of 0.1-10 Hz are movements (naturally, rocking and pulling the car are different)
- changes in the constant component - this is the rise of the body
- etc.
When they try to remove the wheels from the car or drag it somewhere, or try to roll away a motorcycle or moped, the microcontroller of the tilt sensor (in accordance with the sensitivity settings) will trigger warning and alarm zones.

Algorithms that make it possible to reliably distinguish what is happening to the machine based on signal changes are the “know-how” of the tilt sensor manufacturer. But it is in attention to the “little things” that the secret lies combination of high sensitivity and immunity to false positives sensor

High reliability of the Spider TMS2 and Spider STMS tilt-displacement sensors is ensured by:
— using intelligent signal processing algorithms
— using the best element base from global manufacturers
- uncompromising attitude to build quality

PASSIVE IR SECURITY ALARM SENSORS

Sensors are one of the main elements of the alarm system and largely determine its effectiveness. An analysis of the range of sensors offered by the largest manufacturers of security alarm systems shows that in the class of sensors for the protection of premises, the most popular are infrared (IR) passive, combined (mainly IR + microwave), various modifications of contact (primarily magnetic contact) and acoustic sensors breaking glass. Microwave, ultrasonic active and inertial shock sensors are less commonly used.
Below we discuss the principles of operation, nomenclature and features of the use of the most popular security alarm sensors - passive IR. These sensors are designed primarily to protect the volume of the protected premises.

Passive IR sensors, also called optical-electronic sensors, belong to the class of motion detectors and respond to thermal radiation from a moving person. The operating principle of these sensors is based on recording the time difference between the intensity of infrared radiation from a person and background thermal radiation. Currently, passive IR sensors are the most popular, they account for integral element security system of almost every facility.
In order for an intruder to be detected by a passive IR sensor, it is necessary to perform following conditions:

• the intruder must cross the beam of the sensor sensitivity zone in the transverse direction;
• the offender’s movement must occur within a certain speed range;
• The sensitivity of the sensor must be sufficient to register the difference in temperature between the surface of the intruder’s body (taking into account the influence of his clothing) and the background (walls, floor).
• Passive IR sensors consist of three main elements:
• an optical system that forms the directional pattern of the sensor and determines the shape and type of the spatial sensitivity zone;
• a pyro receiver that registers human thermal radiation;
• signal processing unit of the pyro receiver, which separates signals caused by a moving person from the background of interference of natural and artificial origin.

OPTICAL SYSTEM

Modern IR sensors are characterized by a wide variety of possible radiation patterns. The sensitivity zone of IR sensors is a set of rays of various configurations diverging from the sensor in radial directions in one or several planes. Due to the fact that IR detectors use dual pyroelectric receivers, each beam in the horizontal plane is split into two (see Fig. 1).

The detector sensitivity zone can look like:

• one or several narrow beams concentrated in a small angle;
• several narrow beams in the vertical plane (radial barrier);
• one wide beam in the vertical plane (solid curtain) or in the form of a multi-fan curtain;
• several narrow beams in a horizontal or inclined plane (surface single-tier zone);
• several narrow beams in several inclined planes (volumetric multi-tiered zone).
• In this case, it is possible to change in a wide range the length of the sensitivity zone (from 1 m to 50 m), the viewing angle (from 30° to 180°, for ceiling sensors 360°), the angle of inclination of each beam (from 0° to 90°), the number rays (from 1 to several dozen). The variety and complex configuration of the forms of the sensitivity zone are primarily due to the following factors:
• the desire of developers to ensure versatility when equipping rooms with different configurations - small rooms, long corridors, the formation of a specially shaped sensitivity zone, for example with a dead zone (alley) for pets near the floor, etc.;
• the need to ensure uniform sensitivity of the IR detector over the protected volume.

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

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

Typically, each segment of the Fresnel lens forms its own beam of the radiation pattern. The use of modern lens manufacturing technologies makes it possible to ensure almost constant sensitivity of the detector for all beams due to the selection and optimization of the parameters of each lens segment: segment area, angle of inclination and distance to the pyro receiver, transparency, reflectivity, degree of defocusing. IN Lately The technology for manufacturing Fresnel lenses with complex precise geometry has been mastered, which gives a 30% increase in the collected energy compared to standard lenses and, accordingly, an increase in the level of useful signal from a person at long distances. The material from which modern lenses are made provides protection for the pyro receiver from white light. Unsatisfactory operation of the IR sensor can be caused by such effects as heat flows resulting from heating of the electrical components of the sensor, insects falling on sensitive pyroelectric detectors, possible re-reflections of infrared radiation from internal parts detector. To eliminate these effects, the latest generation of IR sensors use a special sealed chamber between the lens and the pyro-receiver (sealed optics), for example, in the new IR sensors from PYRONIX and C&K. According to experts, modern high-tech Fresnel lenses are practically not inferior in their optical characteristics to mirror optics.
Mirror optics as the only element of an optical system are used quite rarely. IR sensors with mirror optics are produced, for example, by SENTROL and ARITECH. The advantages of mirror optics are the ability to focus more accurately and, as a result, increase sensitivity, which allows you to detect an intruder at long distances. The use of several specially shaped mirrors, including multi-segment ones, makes it possible to provide almost constant distance sensitivity, and this sensitivity at long distances is approximately 60% higher than for simple Fresnel lenses. Using mirror optics, it is easier to protect the near zone located directly below the sensor installation site (the so-called anti-sabotage zone). By analogy with replaceable Fresnel lenses, IR sensors with mirror optics are equipped with replaceable detachable mirror masks, the use of which allows you to select the required shape of the sensitivity zone and makes it possible to adapt the sensor to various configurations of the protected premises.

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

PIRE RECEIVER

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

SIGNAL PROCESSING BLOCK

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

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

The processing unit's identification of a useful signal against a background of interference is based on an analysis of the signal parameters at the output of the pyroelectric detector. These parameters are the signal size, its shape and duration. The signal from a person crossing the beam of the IR sensor sensitivity zone is an almost symmetrical bipolar signal, the duration of which depends on the speed of movement of the intruder, the distance to the sensor, the width of the beam, and can be approximately 0.02...10 s over the recorded speed range movements 0.1...7 m/s. Interference signals are mostly asymmetrical or have a different duration from the useful signals (see Fig. 3). The signals shown in the figure are very approximate; in reality, everything is much more complicated.
The main parameter analyzed by all sensors is the signal magnitude. In the simplest sensors, this recorded parameter is the only one, and its analysis is carried out by comparing the signal with a certain threshold, which determines the sensitivity of the sensor and affects the frequency of false alarms. In order to increase resistance to false alarms, simple sensors use a pulse counting method, which counts how many times the signal exceeded the threshold (that is, in essence, how many times the intruder crossed the beam or how many beams he crossed). In this case, an alarm is not issued the first time the threshold is exceeded, but only if, within a certain time, the number of exceedances becomes greater than a specified value (usually 2...4). The disadvantage of the pulse counting method is the deterioration of sensitivity, which is especially noticeable for sensors with a sensitivity zone such as a single curtain and the like, when an intruder can only cross one beam. On the other hand, when counting pulses, false alarms are possible due to repeated interference (for example, electromagnetic or vibration).
In more complex sensors, the processing unit analyzes the bipolarity and symmetry of the signal shape from the output of the differential pyroelectric receiver. The specific implementation of such processing and the terminology used to refer to it1 may vary from manufacturer to manufacturer. The essence of the processing is to compare a signal with two thresholds (positive and negative) and, in some cases, to compare the magnitude and duration of signals of different polarities. A combination of this method with separate counting of excesses of positive and negative thresholds is also possible.
Analysis of the duration of signals can be carried out either by a direct method of measuring the time during which the signal exceeds a certain threshold, or in the frequency domain by filtering the signal from the output of the pyro receiver, including using a “floating” threshold, depending on the range of frequency analysis.
Another type of processing designed to improve the performance of IR sensors is automatic thermal compensation. In the ambient temperature range of 25°C...35°C, the sensitivity of the pyro receiver decreases due to a decrease in the thermal contrast between the human body and the background; with a further increase in temperature, the sensitivity increases again, but with the opposite sign. In so-called "conventional" thermal compensation circuits, the temperature is measured and the gain is automatically increased as it rises. With "true" or "two-way" compensation, the increase in thermal contrast for temperatures above 25°C...35°C is taken into account. The use of automatic temperature compensation ensures almost constant sensitivity of the IR sensor over a wide temperature range.
The listed types of processing can be carried out by analogue, digital or combined means. Modern IR sensors are increasingly beginning to use digital processing methods using specialized microcontrollers with ADCs and signal processors, which allows detailed processing of the fine structure of the signal to better distinguish it from the background noise. Recently, there have been reports of the development of completely digital IR sensors that do not use analog elements at all.
As is known, due to the random nature of useful and interfering signals, the best processing algorithms are those based on the theory of statistical solutions. Judging by the statements of the developers, these methods are beginning to be used in the latest models of sensors from C&K. Simpler (but perhaps not much less efficient) processing methods are used in the most advanced microprocessor sensors of other leading companies. Generally speaking, it is quite difficult to objectively judge the quality of the processing used, based only on the data of the manufacturer. Indirect signs of a good modern sensor may be the presence of an ADC, a microprocessor and, as manufacturers have recently begun to report, the volume of the processing program used, which is several thousand bytes. The fact is that sometimes advertising information about the presence of digital processing in the sensor turns out to be only the ability to switch the usual pulse counting.

OTHER IR SENSOR PROTECTION ELEMENTS

IR sensors intended for professional use use so-called anti-masking circuits. The essence of the problem is that conventional IR sensors can be disabled by an intruder by first (when the system is not armed) taping or painting over the input window of the sensor. To combat this method of bypassing IR sensors, anti-masking schemes are used. The method is based on the use of a special IR radiation channel, which is triggered when a mask or reflective obstacle appears at a short distance from the sensor (from 3 to 30 cm). The anti-masking circuit operates continuously while the system is disarmed. When the fact of masking is detected by a special detector, a signal about this is sent from the sensor to the control panel, which, however, does not issue an alarm until the time comes to arm the system. It is at this moment that the operator will be given information about masking. Moreover, if this masking was accidental (a large insect, the appearance of a large object for some time near the sensor, etc.) and by the time the alarm was set it had cleared itself, the alarm signal is not issued.
Another security element that almost all modern IR detectors are equipped with is a contact tamper sensor, which signals an attempt to open or break into the sensor housing. The tamper and masking sensor relays are connected to a separate security loop.
To eliminate IR sensor triggering from small animals, either special lenses with a dead zone (Pet Alley) from floor level to a height of about 1 m are used, or special methods signal processing (IP series sensors from SENTROL, MC-550T sensor from C&K). It should be taken into account that special signal processing allows animals to be ignored only if their total weight does not exceed 7...15 kg, and they can approach the sensor no closer than 2 m. So if there is a jumping cat in a protected area, then such protection won't help.
To protect against electromagnetic and radio interference, dense surface mounting and metal shielding are used.
Let's take a closer look at the capabilities and characteristics of IR sensors using the example of products from well-known companies.
Let's start with Russian-made IR sensors, which are represented by the FOTON series. The sensors use Fresnel lenses (in FOTON-4 - a multi-segment mirror) and dual pyroelectric receivers. The configuration of sensitivity zones is as follows:

• FOTON-4, FOTON-6, FOTON-8 - volumetric three-tier zone up to 12 m long, 90° in the horizontal plane;
• FOTON-5, FOTON-6B, FOTON-8B - continuous curtain 10 m long, 5° in the horizontal plane;
• FOTON-6A, FOTON-8A - beam barrier 20 m long, 5° in the horizontal plane;
• FOTON-SK is a volumetric three-tier zone up to 10 m long with two anti-sabotage zones or a surface single-tier zone (protection from animals) up to 10 m long.

Photo 1. Sensor FOTON-8 Detectable speed range 0.3...3 m/s. The sensors are intended for use in indoor heated and unheated rooms in the temperature range from 0°C (FOTON-SK), -10°C (FOTON-8), -30°C (FOTON-4, FOTON-6), -40° C (FOTON-5) up to +50°C.
CROW Electronic Engineering Ltd. (Israel) produces a wide range of relatively cheap, but reliable and well-proven models of passive IR detectors. CROW sensors are manufactured using ASIC technology - using special-purpose pulse chips. The sensors use both traditional and unique solutions.
IR detectors use high-quality dust-proof replaceable lenses that form protection zones such as a vertical barrier 22 m long, a multi-tiered volumetric zone 88° measuring 18x22 m, a corridor zone 30x6 m, a single-tier zone 100° measuring 15x18 m with a passage for animals. Double and quadruple pyroelements are used, providing a high degree of protection from direct light, electromagnetic and radio frequency radiation (up to 30 V/m in the range of 10...1000 MHz). Automatic temperature compensation is provided to ensure constant sensitivity over the operating temperature range.
The GENIUS IR sensor uses dual optics that simulate three-dimensional stereo vision; during processing, pulses are counted with the ability to switch counting limits to 2 or 4. This sensor allows you to ignore signals from small animals. The D&D IR detector is an analogue of GENIUS in an outdoor version - it provides moisture protection and adaptation to changes in temperature, wind and background noise. The sensors are designed for difficult conditions.
For simpler conditions, the LYNX and LYNX-100 IR sensors are designed. The LYNX-100 detector provides the ability to adjust sensitivity and switch the processing mode: counting up to 2 or automatically selecting counting limits.
The new SRP series uses a combination of Fresnel lens and mirror optics to protect the area directly below the sensor. Used during processing spectral analysis and filtering of signals from the pyro receiver, as well as “real” two-way thermal compensation. It is also possible to count up to 1, 2, 3. The SRP-600 and SRP-700 sensors can be equipped with black lenses to increase protection from light pollution.
Photo 2. Sensor SRP-600/700 The main characteristics of IR sensors from CROW are shown in Table 1.

Company PYRONIX Ltd. (Great Britain) produces passive IR sensors that use sealed optics, dual and quadruple pyroelectric receivers, and detectors made using surface-mount technology. Replaceable Fresnel lens provides various configurations sensitivity zones: three-tier volumetric zone 90° (34 or 54 beams of 15 m each), single-tier surface zone of 142° (24 beams of 30 m each), vertical beam barrier 10° (24 beams of 30 m each). For ceiling sensors (OCTOPUS series), the sensitivity zone is 172 beams in four planes, the coverage angle is 360°. The speed of human movement recorded by the sensors is 0.3...3 m/s. When processing signals from pyro receivers, the following patented algorithms are used:

• IFT (independent floating thresholds) - the response threshold is set at a low level within the frequency range of the useful signal (0.6...10 Hz) and at a higher level outside this frequency range;
• SPP (alternating sign algorithm) - pulses are counted only for signals with alternating signs (opposite polarity);
• SGP3 (Group Sequence Counter) - only groups of pulses having opposite polarity are counted and an alarm condition occurs when three such groups occur within a set time

Some PYRONIX sensors use the registration of background thermal radiation of the surrounding space and indication of its level by the glow of an LED. This function helps, when installing a sensor at an object, to choose its rational placement and the optimal signal processing method for specific conditions. The main functions of the sensors are shown in Table 2.

SENTROL (USA), which produces a wide range of IR sensors both under its own brand and under the ARITECH Europe brand (the latter have the EV prefix in their name). The most interesting are the following sensors.
The AP series (for ARITECH - EV-200, EV-600) uses precision mirror optics with replaceable mirror masks, forming single or multi-fan curtain-type sensitivity zones with uniform sensitivity throughout the entire protected area. Curtain length is up to 25 m, the record holder is AP643 (ARITECH has EV-635) with a beam length of up to 60 m. Microprocessor “4D processing” is used, taking into account bipolarity, symmetry and duration of signals, as well as an adaptive threshold, supplemented by 2 or 4-pulse counting. The AP950AM (EV-289) sensors use an anti-masking circuit. Operating temperature range from -17°C to +50°C.
The Sharpshooter 6100 series of sensors uses interchangeable Fresnel lenses that form a variety of sensitivity zones: a single long beam, a beam barrier, three-four-tier volumetric zones with a number of beams up to 25, opening angles in the horizontal plane from 6° to 140°, maximum length beam from 6 m to 27 m. Dual and quadruple pyro receivers and digital signal processing are used. Temperature sensitivity 1°C...1.25°C. Operating temperature range from -40°С to +50°С. There are modifications in dust and moisture protection, including high-strength aluminum housing. Indoor and outdoor installation is allowed. Recommended by the manufacturer for any application - from schools to military installations. The PI series of sensors use special signal processing techniques to suppress triggers from small animals (weighing up to 14 kg for PI6000 and up to 32 kg for PI735).
C&K Systems, Inc. (USA) is one of the trendsetters in the development of IR detectors. Its latest achievements in this area are the new generation sensors MC-550T and MC-760T. The sensors are equipped with interchangeable Fresnel lenses that form various options for the sensitivity zone: a four-tier volumetric (33 beams) and a radiation barrier with additional anti-sabotage zones, a surface one with an alley for animals (the maximum range is 15 m for the MC-550T and 18 m for the MC-760T). The design of the sensors uses special protection against the penetration of insects into the pyroelectric element. These sensors use microcontrollers with built-in analog-to-digital converters, which allow not only to register the presence of a signal, but also to analyze such parameters as amplitude, duration of the signals themselves and intervals between pulses, and the constancy of the signal value from pulse to pulse. The volume of the signal processing program embedded in the microcontroller memory exceeds 2000 bytes. Digital processing significantly increases detection reliability while reducing false positives. The MC-760T sensor uses an advanced algorithm that uses elements of statistical detection and recognition. The features of these IR detectors are:

• ignoring small animals at a distance of more than 1.9 m from the sensor (animal weight no more than 7 kg for MC-550T and no more than 11 kg for MC-760T) due to digital processing;
• use of precision optics (for MC-760T), providing uniform sensitivity across the entire radiation pattern;
• “true” two-way temperature compensation;
• wide range of operating temperatures (0°С...+55°С for the MC-550T sensor and -10°С...+55°С for the MC-760T);
• dynamic self-diagnosis, which is automatically carried out once a day, testing both the information processing circuits (RAM, ROM, thresholds, power) and the detection channel itself, including the pyroelectric element; Self-diagnosis mode can also be activated from the control panel;
• improved noise immunity (light 6500 lux, electromagnetic and radio interference 30 V/m for MC-550T and 40 V/m for MC-760T);
• a special search mode for radiation pattern zones, which allows you to significantly simplify the connection and configuration of the sensor during installation;
• presence of a relay for opening the sensor housing.

Photo 3. MS-760T sensor PARADOX SECURITY SYSTEMS (Canada) produces two series of IR passive sensors: analog and microprocessor. These series are presented as traditional technical solutions, as well as new developments of the company. IR sensor lenses have complex, precise geometries, resulting in a 30% increase in collected energy compared to standard lenses. The use of 12 interchangeable lenses allows you to select the required sensitivity zone configuration. Double or quadruple pyro receivers with intertwined geometry are used. IR sensors use automatic temperature compensation, which ensures constant sensor performance in the temperature range from -25°C to +50°C. The recorded movement speed is 0.2...7 m/s.
PARADOX IR sensors use a patented APSP signal processing algorithm that provides automatic switching of pulse counting depending on the signal level: for high-level signals, the detector immediately generates an alarm, working as a threshold one, and for low-level signals it automatically switches to pulse counting mode (from 2 to 25 depending on the level), which significantly reduces the likelihood of false alarms. In its latest developments, PARADOX began to use an improved processing algorithm, which introduced signal symmetry analysis with separate counting of positive and negative polarity (Entry/Exit Analysis). These processing methods are implemented in the AVANTAGE analog IR sensor, which uses a quad pyroelectric element and until recently was the most efficient of the entire PARADOX analog series. The new ParadoxPro analog sensor additionally features a special lens for zero dead spots and increased white light protection, as well as metal shielding and tight surface mounting for EMI and RFI suppression.
The VISION-510 detector, which belongs to the microprocessor series, has the same basic characteristics and almost identical processing algorithm (quadruple pyroelement, APSP, Entry/Exit Anaysis) as AVANTAGE, the only difference is in the technical implementation - in VISION-510 processing is carried out with using a RISC processor. Photo 4. VISION-510 sensor The latest development from PARADOX is the Digigard series of detectors. These are completely digital IR sensors and have no analogue elements. The signal from the output of the pyro receiver (dual for Digigard-50, quadruple for Digigard-60) is directly fed to an ADC with a high dynamic range, and all processing is done digitally. The use of completely digital processing allows you to get rid of such “analog effects” as possible signal distortions, phase shifts, and excess noise. Digigard sensors use the patented SHIELD signal processing algorithm, which includes APSP, as well as analysis of all signal parameters: level, duration, polarity, energy, rise time, shape, time of appearance and signal sequence. Each sequence of signals is compared with patterns corresponding to movement and interference, even the type of movement (from slow to running) is recognized, and if the alarm criteria are not met, the data is stored in memory for analysis of the next sequence or the entire sequence is suppressed. The combined use of metal shielding and software noise suppression made it possible to increase the resistance of the Digigard-60 sensor to electromagnetic and radio frequency interference to 30...60 V/m in the frequency range from 10 MHz to 1 GHz (for comparison without the SHIELD algorithm, this figure averages 20 V/m).

INSTALLING AND USING IR SENSORS

When choosing the types and number of sensors to ensure the protection of a particular object, one should take into account possible ways and methods of penetration of the intruder, the required level of detection reliability; costs for the acquisition, installation and operation of sensors; features of the object; tactical and technical characteristics of sensors. A feature of IR passive sensors is their versatility - with their use it is possible to block a wide variety of rooms, structures and objects from approaching and entering: windows, showcases, counters, doors, walls, ceilings, partitions, safes and individual items, corridors, room volumes. However, in some cases it will not be necessary large quantity sensors to protect each structure - it may be sufficient to use one or more sensors with the desired sensitivity zone configuration. Let's take a look at some of the features of using IR sensors.
General principle using IR sensors - the rays of the sensitivity zone must be perpendicular to the intended direction of movement of the intruder. The sensor installation location should be chosen so as to minimize dead zones caused by the presence of large objects in the protected area that block the beams (for example, furniture, houseplants). If the doors in the room open inward, you should consider the possibility of masking the intruder with open doors. If dead spots cannot be eliminated, multiple sensors should be used. When blocking individual objects, the sensor or sensors must be installed so that the rays of the sensitivity zone block all possible approaches to the protected objects.
The range of permissible suspension heights specified in the documentation (minimum and maximum heights) must be observed. This especially applies to radiation patterns with inclined beams: if the suspension height exceeds the maximum permissible, this will lead to a decrease in the signal from the far zone and an increase in the dead zone in front of the sensor, but if the suspension height is less than the minimum permissible, this will lead to a decrease in range detection while simultaneously reducing the dead zone under the sensor.
Interference of a thermal, light, electromagnetic, or vibration nature can lead to false alarms of IR sensors. Despite the fact that modern IR sensors have a high degree of protection from these influences, it is still advisable to adhere to the following recommendations:

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

Motion sensors are based on the analysis of waves of various types coming from the environment. Depending on the type of wave used, motion sensors are infrared, radio wave, ultrasonic and combined.

Principle of operation infrared sensor movement is based on determining the temperature of the object, which differs from the ambient temperature. Infrared or thermal radiation is focused by a special optical system - a Fresnel lens - and directed to a sensitive semiconductor element - a pyroelectric. This causes a change in the electrical potential of the pyroelectric, which is processed using a special algorithm and leads to the activation of an alarm signal. To prevent the sensor from reacting to heated but stationary objects, the lenses divide the sensor's sensitivity zone into several separate beams. The sensor will work if the object sequentially crosses several rays. In this case, movement at a very low speed may not be recorded by the system.

The operating principle of an ultrasonic motion sensor is based on sound location. The basis of such a sensor is a sound generator that produces oscillations with a frequency of 25-40 kHz. They are not audible to the human ear, but, like any sound waves, they are reflected from obstacles and return back to the source. The motion sensor has an vibration emitter and a microphone that perceives the reflected signal. According to the Doppler effect, any body crossing the radiation stream changes the interference pattern. Therefore, the frequency of the reflected signal will be different from the emitted frequency. Piezoceramic elements are used as emitter and receiver.


A radio wave motion sensor works on the same principle as an ultrasonic one, only instead of an audio frequency, the microchip generates microwave radiation with a frequency of 2.5 GHz. If a moving object appears in the wave propagation zone, the wavelength and frequency change, which is immediately detected by the receiver. Radio waves can pass through non-metallic barriers, such as walls and wooden furniture, and they are also quite expensive. Therefore, they are usually used to monitor large commercial areas, such as storage facilities.


To avoid false alarms, combined sensors are used. Typically, infrared and radio wave sensors are combined into one device. This circuit is characterized by high noise immunity, reliability and the absence of false alarms.