Wireless security alarm products do not need wiring, and installation is convenient and fast. In addition, the wireless alarm technology has been continuously improved. The occupancy rate in the security alarm market, especially the home alarm market and network alarm operation market, is getting higher and higher. Compared with the performance of wired alarm system products, due to the working principle and technical characteristics of wireless alarm products, their higher requirements for installation and use environments are determined, and different installation methods and use environments are used for wireless alarm systems. (The main reason for false positives is the false negative rate.) If the technical principles of the wireless alarm system and its installation methods are not well understood, it will inevitably result in excessively high false positives and false negatives, so some system engineering firms are The project is not willing to use the wireless alarm system. This article analyzes the application of the technical principles of wireless alarm system and its related technologies, prompts readers what issues to be aware of when selecting and installing wireless alarm products, in order to maximize the performance advantages of wireless alarm products, improve the stability of the system, and reduce The maintenance of the project allows users to use it with confidence.
First, the definition of wireless technology in the way of non-wire, through the establishment of electromagnetic wave carrier space communication, called wireless transmission, the vast majority of wireless alarm products use specific radio frequency or band to transmit information. From this concept, it can be seen that the influence of space electromagnetic environment and the shielding effect of different obstacles are the most important factors for the quality of signal transmission of wireless alarm products.
Second, the wireless alarm system works understand the working principle of wireless alarm can be judged from the system structure, which affects the wireless alarm system performance of the links, the occurrence of fault or transmission interference is which part, and then effectively improve the system application effect.
A wireless alarm system has at least one transmitter (Tx) (for example, various wireless infrared detectors) and one receiver (Rx) (for example, various wireless alarm controllers or wireless receiver modules). When a transmitting current flows through the transmitting antenna The electromagnetic radiation generated becomes the carrier body of the wireless signal and realizes space broadcasting and communication (ie, the transmission and reception of wireless alarm signals). For example: When a wireless motion detector triggers a zone to trigger how this message is sent to the receiver, the workflow is as follows.
First, the detector converts the signal to a binary code; secondly, after the converted signal passes through a 433 MHz frequency carrier, the current is conducted to the antenna through the power amplifier; again, the receiver receives the wireless signal and restores the original signal. Alarm information; Finally, the receiver then sends the processed alert to the control panel.
Third, wireless alarm system application main interference source analysis The main concern of wireless alarm system application is to avoid or reduce a variety of interference factors, the types of interference, from the following examples to see what is the interference:
For example, in a large room, you are among 100 people who speak at the same time. You try to hear what a particular person in the crowd says. At this point, a police car whispered and there was a dog calling. Then each person, siren, and barking dog represented different signals at different frequencies. The noisy crowd, siren and barking dog are the sources of interference. The frequency of talking to people is close to becoming the biggest source of interference.
In the actual wireless alarm system installation process, many interference factors are easier to eliminate. It is possible to suppress or reduce various interference sources through the installation location of mobile devices and the addition of wireless signal enhancers (repeaters).
The types of interference are mainly electric wave interference; phase shift or harmonic interference of multiple conducting paths; electrical interference; interference of the same frequency; reflection and attenuation of electric waves. Explained in detail as follows:
1. The radio waves interfere with other non-set signals to physically superimpose the radio waves of the set signal; other non-set devices emit valid set signals; other transmit signals near the set frequency have an effect on the notch of the receive filter. Other possible sources of interference are: AM/FM/short-wave broadcasting stations, television transmitters; amateur radio equipment, walkie-talkies; remote controls; cordless phones; mobile handsets; vehicle radios, police and aeronautical radio communications; microwave ovens; Detectors; radar systems; medical radiography instruments and other industrial equipment.
2. Multiple propagation path interference This is a typical wireless interference. Although the same source transmits the same signal, the receiver receives many signals from different paths at the same time.
When signals from many different paths are received by the same antenna system, a composite signal is obtained, which is vastly different from the original signal and difficult to identify. In some extreme cases, if the signals from the different paths A and B are just opposite to each other, the signal is completely canceled and disappears. Therefore, to reduce the interference, the transmitter (wireless infrared detector) or receiver (wireless) can be slightly moved. Alarm host) for the best integrated conduction path.
3. Electrical interference mainly consists of electrical discharges and arcs generated by the discharge of internal circuits; wires near the vicinity of the arc act as radio waves emitted by the antenna. In general, electrical appliances that usually have surge or oscillating circuits may often become interference sources.
Three typical types of electrical interference: radio clutter from radioactive instruments; electric waves from electrical circuit operations; other natural phenomena such as lightning or cosmic rays. Possible electrical interference objects: Cathode ray tube display elements such as televisions and computers; Electrowelding; Air-conditioning motors; Brush AC and DC motors; Relays and high-powered knifes; High-voltage power line insulator discharges; Phosphor starters or neon arcs; Silicon dimmer.
4. Co-channel interference When a strong signal (such as that generated by a communication base station) that is not close to the receiver's frequency overloads some of the receiver's circuitry, interference occurs, resulting in strong signal harmonics, which then combine to form a new frequency. The newly generated frequency, the intermodulation frequency, interferes with the system product as well as other interference sources.
5. Reflecting and attenuating radio waves experience reflections on the surface of obstacles such as walls or floors. When radio waves encounter obstacles, some of the signals will pass through. This process will always consume a portion of energy. Therefore, this is the attenuation of the conduction process, and the degree of attenuation is related to the material and structure of the obstacle.
In practice, installing a wireless system in a building will always have various obstacles that will affect the transmission of wireless signals. Signals such as walls, doors, floors, elevators, people, and others will cause signal reflection and attenuation. These factors will cause wireless transmission coverage and The uncertainty of the angle.
When radio waves encounter obstacles, you may encounter the following three phenomena:
Reflections, such as walls, ceilings, and floors, reflect waves that cause transmission of multiple propagation paths. For example, when an electric wave passes through a room and encounters a wall, the direction of conduction changes, such as when an electric wave encounters a window or the edge of a wall. At the same time, objects that are subject to diffraction due to reflection and attenuation include: metal objects (reinforced concrete, electric water pipes); furniture containing metal structures; flooring; strong electric control boxes; The greater the absorption, the larger the wall: the inner light partition will not cause large attenuation of the signal, but the attenuation of the load-bearing wall (with reinforced concrete) will be particularly large; the floor: the wood floor will not cause large attenuation of the signal. However, the attenuation of the ground covered with steel plates is particularly large; the mirror walls have a particularly large attenuation of signals.
First, the definition of wireless technology in the way of non-wire, through the establishment of electromagnetic wave carrier space communication, called wireless transmission, the vast majority of wireless alarm products use specific radio frequency or band to transmit information. From this concept, it can be seen that the influence of space electromagnetic environment and the shielding effect of different obstacles are the most important factors for the quality of signal transmission of wireless alarm products.
Second, the wireless alarm system works understand the working principle of wireless alarm can be judged from the system structure, which affects the wireless alarm system performance of the links, the occurrence of fault or transmission interference is which part, and then effectively improve the system application effect.
A wireless alarm system has at least one transmitter (Tx) (for example, various wireless infrared detectors) and one receiver (Rx) (for example, various wireless alarm controllers or wireless receiver modules). When a transmitting current flows through the transmitting antenna The electromagnetic radiation generated becomes the carrier body of the wireless signal and realizes space broadcasting and communication (ie, the transmission and reception of wireless alarm signals). For example: When a wireless motion detector triggers a zone to trigger how this message is sent to the receiver, the workflow is as follows.
First, the detector converts the signal to a binary code; secondly, after the converted signal passes through a 433 MHz frequency carrier, the current is conducted to the antenna through the power amplifier; again, the receiver receives the wireless signal and restores the original signal. Alarm information; Finally, the receiver then sends the processed alert to the control panel.
Third, wireless alarm system application main interference source analysis The main concern of wireless alarm system application is to avoid or reduce a variety of interference factors, the types of interference, from the following examples to see what is the interference:
For example, in a large room, you are among 100 people who speak at the same time. You try to hear what a particular person in the crowd says. At this point, a police car whispered and there was a dog calling. Then each person, siren, and barking dog represented different signals at different frequencies. The noisy crowd, siren and barking dog are the sources of interference. The frequency of talking to people is close to becoming the biggest source of interference.
In the actual wireless alarm system installation process, many interference factors are easier to eliminate. It is possible to suppress or reduce various interference sources through the installation location of mobile devices and the addition of wireless signal enhancers (repeaters).
The types of interference are mainly electric wave interference; phase shift or harmonic interference of multiple conducting paths; electrical interference; interference of the same frequency; reflection and attenuation of electric waves. Explained in detail as follows:
1. The radio waves interfere with other non-set signals to physically superimpose the radio waves of the set signal; other non-set devices emit valid set signals; other transmit signals near the set frequency have an effect on the notch of the receive filter. Other possible sources of interference are: AM/FM/short-wave broadcasting stations, television transmitters; amateur radio equipment, walkie-talkies; remote controls; cordless phones; mobile handsets; vehicle radios, police and aeronautical radio communications; microwave ovens; Detectors; radar systems; medical radiography instruments and other industrial equipment.
2. Multiple propagation path interference This is a typical wireless interference. Although the same source transmits the same signal, the receiver receives many signals from different paths at the same time.
When signals from many different paths are received by the same antenna system, a composite signal is obtained, which is vastly different from the original signal and difficult to identify. In some extreme cases, if the signals from the different paths A and B are just opposite to each other, the signal is completely canceled and disappears. Therefore, to reduce the interference, the transmitter (wireless infrared detector) or receiver (wireless) can be slightly moved. Alarm host) for the best integrated conduction path.
3. Electrical interference mainly consists of electrical discharges and arcs generated by the discharge of internal circuits; wires near the vicinity of the arc act as radio waves emitted by the antenna. In general, electrical appliances that usually have surge or oscillating circuits may often become interference sources.
Three typical types of electrical interference: radio clutter from radioactive instruments; electric waves from electrical circuit operations; other natural phenomena such as lightning or cosmic rays. Possible electrical interference objects: Cathode ray tube display elements such as televisions and computers; Electrowelding; Air-conditioning motors; Brush AC and DC motors; Relays and high-powered knifes; High-voltage power line insulator discharges; Phosphor starters or neon arcs; Silicon dimmer.
4. Co-channel interference When a strong signal (such as that generated by a communication base station) that is not close to the receiver's frequency overloads some of the receiver's circuitry, interference occurs, resulting in strong signal harmonics, which then combine to form a new frequency. The newly generated frequency, the intermodulation frequency, interferes with the system product as well as other interference sources.
5. Reflecting and attenuating radio waves experience reflections on the surface of obstacles such as walls or floors. When radio waves encounter obstacles, some of the signals will pass through. This process will always consume a portion of energy. Therefore, this is the attenuation of the conduction process, and the degree of attenuation is related to the material and structure of the obstacle.
In practice, installing a wireless system in a building will always have various obstacles that will affect the transmission of wireless signals. Signals such as walls, doors, floors, elevators, people, and others will cause signal reflection and attenuation. These factors will cause wireless transmission coverage and The uncertainty of the angle.
When radio waves encounter obstacles, you may encounter the following three phenomena:
Reflections, such as walls, ceilings, and floors, reflect waves that cause transmission of multiple propagation paths. For example, when an electric wave passes through a room and encounters a wall, the direction of conduction changes, such as when an electric wave encounters a window or the edge of a wall. At the same time, objects that are subject to diffraction due to reflection and attenuation include: metal objects (reinforced concrete, electric water pipes); furniture containing metal structures; flooring; strong electric control boxes; The greater the absorption, the larger the wall: the inner light partition will not cause large attenuation of the signal, but the attenuation of the load-bearing wall (with reinforced concrete) will be particularly large; the floor: the wood floor will not cause large attenuation of the signal. However, the attenuation of the ground covered with steel plates is particularly large; the mirror walls have a particularly large attenuation of signals.
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