Introduction, selection and development trend of anti-theft alarm detector

Infrared detector is the most critical component of the anti-theft alarm system, which directly determines the sensitivity and stability of the system, and is the guarantee of the quality of the entire system. Over the years, Chinese security manufacturers have improved significantly in terms of mastery of technology and production capacity. This is due to the continuous absorption of foreign product design and production technology by Chinese manufacturers, and their commitment to reduce costs and make Chinese security The products are beginning to be recognized by the engineering companies, and the low price has an important attraction for Party A, which makes domestic products grow rapidly in the market. Although the quality of domestic products still has a gap with imported products, China's security products still have a strong competitive advantage when users are not familiar with security products.

Many foreign manufacturers also admit that in the past, foreign companies relied heavily on technological advantages to cope with the cost advantages of Chinese national products. The ability to launch distinctive products has greatly improved the level of Chinese security products. This phenomenon mainly comes from the importance attached by many manufacturers to brand awareness and product quality, which has increased investment and R & D efforts.

Principles and characteristics of infrared detectors

The human body has a constant body temperature, generally around 37 degrees, and emits infrared rays with a specific wavelength of about 10 μm. The passive infrared detector works by detecting the infrared rays emitted by the human body about 10 μm. The infrared ray of about 10μm emitted by the human body is enhanced by the Fresnel filter and concentrated on the infrared induction source. Infrared induction sources usually use pyroelectric elements, which will lose the charge balance when the temperature of the infrared radiation of the human body is received and release the charge outward. The subsequent circuit can generate an alarm signal after detection and processing.

1. Passive infrared detectors are aimed at detecting human radiation, so pyroelectric elements must be very sensitive to infrared radiation with a wavelength of about 10 μm.

2. In order to be sensitive to the infrared radiation of the human body only, its radiation surface is usually covered with a special Fresnel filter, so that the interference of the environment is obviously controlled.

3. The sensor contains two pyroelectric elements connected in series or parallel. Moreover, the two polarized electrodes are made in the opposite direction. The environmental background radiation has almost the same effect on the two pyrolysis elements, causing the discharge effect to cancel each other, so the detector has no signal output.

4. Once a person intrudes into the detection area, the infrared radiation of the human body is focused through a part of the mirror surface and received by the pyroelectric element. However, the heat received by the two pyroelectric elements is different, and the pyroelectricity cannot be cancelled. The signal is processed to alarm.

    The advantages and disadvantages of passive infrared sounder:

Advantages: It does not emit any type of radiation itself, the power consumption of the device is very small, the concealment is good, and the price is low.

Disadvantages: easy to be interfered by various heat sources and sunlight sources; passive infrared penetration is poor, infrared radiation of the human body is easily blocked and not easily received by the detector; it is susceptible to interference from radio frequency radiation; when the ambient temperature and the human body temperature are close, detect and Sensitivity drops significantly, sometimes causing short-term failure.

How to properly install and use passive infrared detectors

Passive infrared detectors are a type of detectors that are very commonly used in security engineering. But for its normal use, it is necessary to prevent false negatives and reduce false positives, mainly to minimize false positives. To do this, we must first understand some basic concepts and technical characteristics of passive infrared detectors, so that according to these basic technical characteristics, from the installation, commissioning, use and other links, according to the basic technical characteristics of the detector, Only in this way can the maximum effect of the detector be maximized.

Then first we must understand the following information, which will be of great help to the correct use of passive infrared detectors.

Determine the installation height according to the instruction

The installation height of the detector is not arbitrary, it will directly affect the sensitivity of the detector and the effect of preventing small animals. The installation height of the general wall-mounted infrared detector is 2.0-2.2 meters.

Not suitable for facing glass doors and windows

There are two problems facing glass doors and windows: One is white light interference. Although the passive infrared detector (PIR) has a strong suppression function for white light, it is not 100% suppression after all. Do not face the glass doors and windows to avoid strong light. The second is to avoid complex environmental interference outside the doors and windows, such as direct sunlight, crowds, mobile vehicles, etc. 

Should not face the cold and hot vents or cold and heat sources

The induction effect of passive infrared detectors is closely related to temperature changes. Both cold and hot vents and cold and heat sources may cause false alarms. For some low-performance detectors, sometimes the air convection through the doors and windows will also be Cause false positives.

Should not face large objects that are easy to swing

Large swings of large objects can instantly cause sudden airflow changes in the detection area and may also cause false alarms; for example, outdoor detectors should avoid large trees and tall shrubs.

Reasonable location

There should be no screens, furniture, large bonsai or other partitions within the detection range; it is best not to install two wireless infrared detectors in the same space to avoid interference caused by simultaneous triggering; infrared detectors should be The walking line in the room is at a certain angle. The detector is least sensitive to radial movement, but most sensitive to tangential movement (ie, perpendicular to the radius). Choosing a suitable installation location on site is an extremely important part of avoiding false alarms of infrared detectors and obtaining the best detection sensitivity.

Reasonable selection

There are many types of passive infrared detectors, from indoor to outdoor, from wired to wireless, from single infrared to three infrared, from wall-mounted to ceiling-mounted, then the detector to be installed must consider the size of the guard space , The surrounding environment, the characteristics of the entrance and other actual conditions.

After installing the detector, commissioning the detector is the last thing to do. The debugging of passive infrared detectors is generally a walk test, that is, the debugger walks the S-shaped line in the warning area to perceive the length and width of the warning range to test whether the entire alarm system meets the requirements. You can refer to the instruction manual to adjust the sensitivity of the detector appropriately. Too high or too low sensitivity will affect the prevention effect.

Factors and solutions of false alarms of detectors

The ideal intrusion detector responds only to the presence of people, not to the activities of animals such as dogs, cats and mice, nor to changes in the indoor environment, such as changes in temperature and humidity and wind, rain sounds and vibrations. It is not easy to do this. Most devices not only respond to human existence, but also respond to some unrelated factors.

The alarm issued when there is no intrusion is called a false alarm. False alarms may be caused by component failures or some external influences. The bad consequences it produces are unimaginable. The lightest consequence is that it adds a lot of unnecessary troubles that annoys people, which greatly reduces the possibility of the alarm. Reliability. The worst consequence is that it makes the police or security personnel rush to the scene unnecessarily, so that their own safety and the safety of the people around them will be jeopardized. Therefore, false alarm is the fatal weakness of the alarm.

Let's analyze the main reasons that infrared detection alarms will cause false alarms. At present, there are mainly the following reasons for the false alarms in the alarm system: the poor anti-interference ability of wireless detectors is manifested as the same frequency interference is easy to cause false alarms; the infrared detectors are not accurate enough to judge the intrusion behavior; False alarms are generated due to the influence of environmental factors such as temperature and light; because the host and the detector are both set using wireless encoding, the encoding is repeated, which causes the host and the detector to repeat the code, resulting in false alarms; and the quality of some alarms is too poor, such as components Damages and poor production processes cause false alarms; they are also related to the selected equipment, installation method, angle, and location; there are also human factors under the influence of the environment, such as air flow, pet actions, etc., and human factors Misreports can be generated by user improper operation, accidentally triggering an alarm, accidentally breaking into, or entering a fortified visiting area.

The causes of false positives are many and complex. Therefore, to reduce the false alarms of anti-theft alarms, the most important thing is to consider from various factors, such as the selection of detectors from the technical and performance aspects, including the selection of sensor detectors, the shape design of Fresnel lens, and micro processing Program, multi-scan technology, rolling code technology with automatic code skipping, production process, use method, temperature compensation, sensitivity detection distance adjustment, etc. These comprehensive factors all determine the performance and false alarm rate of the detector.

A new generation of infrared detectors designed for the above deterrent uses some unique technologies to solve such problems. First of all, on the focus of the infrared lens, two photothermal sensors connected by different circuits are applied. The special lens divides the coverage area into multiple trapezoidal protection zones with sensitivity, and ensures the signal strength within the protection zone. The unique lens can also serve as an infrared filter. The specially treated black lens allows visible light and short-wave infrared light (which exists in most places with white light sources) to enter, and then is absorbed by its black base. The black infrared lens only reflects infrared rays whose wavelength matches the movement of the human body, and reflects them onto the photothermal sensor. Through the white light filter, the detector can prevent white light interference. If someone enters or leaves one or several areas covered by the detector, the detector should be able to detect the change in infrared radiation energy. After the A / D converter digitizes the signal sent by the sensor, the processor will analyze it. Then the alarm signal is sent out.

This process involves all the criteria in detection, such as signal amplitude, time, format, energy, and spectrum, plus the statistical information actually extracted from the scene. These standards must be combined to judge the rationality of detecting them, and the detector will only issue an alarm after the result meets the criteria for forced intrusion. Digitizing the signal of the photothermal sensor can eliminate signal transients and electromagnetic wave interference.

At present, the dual-detector detector occupies a certain share in the market, and microwaves are not sensitive to changes in temperature and light. Through the combined detection of two detection units, the intelligent dual-detector passive infrared detector of the deterrent detector has greatly reduced the error Report the possibility.

The sensitivity and reliability of the alarm detector affect each other. Reasonable selection of the detection sensitivity of the alarm detector and the use of different measures against external interference can improve the performance of the alarm detector. The use of different anti-interference measures determines the performance of the alarm detector in different environments. Understanding the performance and characteristics of various alarm detectors, according to different use environments, reasonable configuration of different alarm detectors is the key link of the anti-theft alarm system. Various detectors have different working principles, and they have their own advantages and disadvantages. To make the detectors function effectively in any occasion, they should be carefully selected and installed carefully.

The difference and application of active infrared and passive infrared detectors

The active infrared intrusion detector is composed of a transmitter and a receiver. The transmitter is composed of a power supply, a light emitting source and an optical system. The receiver is composed of an optical system, a photoelectric sensor, an amplifier, a signal processor and other parts. The active infrared detector is an infrared beam blocking alarm. The infrared light-emitting diode in the transmitter emits a modulated infrared beam (the wavelength of this beam is between 0.8 and 0.95 microns) under the excitation of the power supply. After the function of the optical system becomes parallel light emitted. This beam is received by the receiver, and the infrared photoelectric sensor in the receiver converts the light signal into a signal, which is processed by the circuit and passed to the alarm controller. The infrared rays emitted by the transmitter pass through the defense zone and reach the receiver, forming a warning line. Under normal circumstances, the receiver receives a stable optical signal. When someone invades the cordon, the infrared beam is blocked, and the infrared signal received by the receiver changes. Extract this change, and then amplify and properly process it. The alarm signal from the controller. At present, such detectors have two-beam, three-beam and multi-beam infrared fences. Generally used in the perimeter defense, the biggest advantage is that the prevention distance is far, and it can reach more than ten times the detection distance of passive infrared.

Passive infrared detectors mainly determine whether someone is moving according to changes in the outside infrared energy. The infrared energy of the human body is different from the environment. When a person passes through the detection area, the position of the different infrared energy collected by the detector changes, and then an alarm is issued through analysis.

But the external environment is: not only the human body emits infrared energy, many objects emit infrared energy under certain conditions, and this energy is particularly prominent in visible light, so the anti-white light interference of any passive infrared detector has become an important index. In the case of stable indoor light and relatively constant infrared energy, this detection method performs very well. But the outdoor situation is different. For a long time, only a few manufacturers can do passive infrared infrared detection outdoors. As the so-called indoor and outdoor one-step, three-step technology content, SAFESTNET, with its strong R & D team, did not take the lead in launching a variety of highly stable wired and wireless outdoor detectors in the early 1990s. Civilian product detector series, such as window guard radar, super bodyguard, iron guard, laser fighter and other products.

Active infrared detector device selection

1. According to the minimum and maximum temperature of the scene and its duration, choose an active infrared intrusion detector with a suitable working temperature; if the ambient temperature is too low, a special heater can be used to ensure the normal operation of the detector.

2. Active infrared intrusion detectors are seriously affected by fog. When using outdoors, equipment with automatic gain function should be selected (the sensitivity of such equipment will be automatically adjusted when the climate changes); In addition, the detection distance of the selected equipment is 20% away from the actual warning distance More than% margin to reduce false alarms caused by climate change.

3. When using it outdoors, a dual-beam or 3-beam active infrared intrusion detector must be selected to reduce false alarms caused by birds and fallen leaves.

4. The wavelengths of infrared light-emitting diodes used in active infrared intrusion detectors are around 0.85 μm and 0.95 μm, respectively. The former is caused by red exposure, and its concealment is not as good as the latter.

5. Active infrared intrusion detectors should not be used outdoors in foggy areas and in areas with large, dirty, and sandy areas.

6. When using active infrared intrusion detectors in open areas or on fences and roofs, equipment with lightning protection should be selected.

7. In case of folding walls, and the distance is closer, reflective devices can be used to reduce the number of detectors.

8. The maximum beam distance of the active infrared intrusion detector used outdoors should be more than 6 times the detection distance specified by the manufacturer.

The development trend and market prospect of intrusion detector

With the development of security technology, the maturity of the security market, and the improvement of policies and regulations, it can be summarized as digital, wireless, and integrated technology development trends of anti-theft alarm systems:

1. More stable / reliable: if the detector needs to be resistant to RFI / EMI, lightning protection, etc., to adapt to the harsh climate;
2. More diverse functions: such as adjustable frequency of the detector, anti-blocking, anti-spray cover, anti-damage, etc .;
3. More exquisite and compact appearance: to meet the increasing taste of interior decoration;
4. More intelligent design: convenient setting / disarming, humanized operation interface;
5. More powerful networking function;
6. More convenient scalability.

Product technology will strive for breakthroughs under the premise of digitalization, wirelessization and integration. In the application market, it will move towards a more refined direction --- launching different products for different markets. Taking the fastest growing residential community application as an example, some manufacturers indicated that the directional curtain + pet-proof detector designed for residential communities has low cost and simple installation. It is suitable for home-use wireless networked alarm systems, as well as residential intelligent security. ＋ Alarm integrated system products will be the highlights. In addition to the indoor / outdoor applications of residential quarters and commercial buildings, outdoor applications such as airports, docks, farms, mines, and oil fields are still areas for manufacturers to vigorously expand.

In view of the above situation, after continuous adjustment, adaptation and improvement, China's security products industry will certainly develop more healthily and orderly, and its prospects are optimistic.