Security cable requirements for use in access control systems
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In the construction of the entire weak current project, the cable is the most basic facility, and the cable industry will also rise accordingly. Let's talk about the selection of cables in the access control system.
Since the middle of the 20th century, with the continuous advancement and rapid development of science and technology, the content of human economic and social activities has risen from depth to breadth, and the booming and rapid development of the information industry has resulted in an increasing demand for wire and cable products. Increasing, a variety of models of wire and cable products have been used in communications, networking, security, fire and other emerging high-tech industries.
According to incomplete statistics, the cable market is increasing at an annual rate of 8% to 12%, and the security cable is rapidly growing at a rate of 15% to 20%. Compared with electric power, telecommunications, radio and television and other industries, the security cable industry has started late and is lagging behind in technology and equipment. After more than 30 years of vigorous development, the security industry in China has continuously expanded its scope of application, and industry segments have touched all aspects of society. In the construction of the entire weak current project, the cable is the most basic facility, and the cable industry will also rise accordingly. Let's talk about the selection of cables in the access control system.
Domestic security usher in the peak of development
In China, with the rapid development of the national economy and informatization technology, the country’s investment in power grid construction has increased, coupled with the rapid development of the domestic security industry, which requires a lot of wire and cable, which has promoted the domestic wire and cable industry. Great development.
Compared with electric power, telecommunications, radio and television and other industries, the security cable industry has objective conditions such as late start-up, backward technology and equipment, and small industrial scale. The major manufacturers of domestic cables mainly focus on the Yangtze River Delta and the Pearl River Delta. According to the scale of the company and its characteristics, the company is generally divided into foreign-funded enterprises, domestic professional companies, and general small-scale enterprises.
Foreign-funded enterprises also look at the tremendous potential of China's wire and cable industry. They have set up factories in China in order to enter the Chinese cable market, and domestic security cables usher in the peak of development.
1. Cable application requirements in access control
In building video intercom systems, the quality requirements for connecting cables are quite high. Cables for transmitting voice signals and alarm signals mainly use 4-core or more PVC sheathed cords (RVV). The SYV-75-5 coaxial cable is used for video transmission. Nowadays, some networks are also used. Twisted-pair transmission includes new techniques for signal transmission, including video, and does not use coaxial lines. If the system is to prevent external interference or not grounded, the cable used in the system must be a shielded cable (RVVP) type shielded cable.
1. rs-232-c is a serial physical interface standard developed by the Electronic Industry Association (eia) of the American Electronics Industry Association. Rs is an abbreviation for "recommended standard" in English, 232 is an identification number, and c is the number of modifications. The rs-232-c bus standard has 25 signal lines, including a main channel and an auxiliary channel. In most cases, the main channel is used. For general duplex communication, only a few signal lines are required, such as a Send line, a receiving line, and a ground line. The rs-232-c standard specifies data rates of 50, 75, 100, 150, 300, 600, 1200, 2400, 4800, 9600, and 19200 baud per second. The rs-232-c standard stipulates that the driver is allowed to have a capacitance load of 2500 pf and the communication distance will be limited by this capacitance. For example, when using a communication cable of 150 pf/m, the maximum communication distance is 15 m; if the capacitance per meter of cable is reduced The communication distance can be increased. Another reason why the transmission distance is short is that rs-232 is a single-end signal transmission, there is a common ground noise and can not suppress common-mode interference and other issues, it is generally used for communication within 20m.
2, access control intercom system cable selection
The rs-485 bus has widely used the rs-485 serial bus standard when the communication distance is required to be several tens of meters to several kilometers. Rs-485 uses balanced transmission and differential reception, so it has the ability to suppress common-mode interference. Coupled with the high sensitivity of the bus transceiver, it can detect voltages as low as 200mv, so the transmitted signal can be recovered beyond a few kilometers. Rs-485 uses a half-duplex mode of operation. Only one point can be in a transmission state at any time. Therefore, the transmission circuit must be controlled by the enable signal. Rs-485 is very convenient for multi-point interconnection and can save many signal lines. Application rs-485 can be networked to form a distributed system that allows up to 32 drives in parallel and 32 receivers.
In the past, communication between pc and smart devices mostly depended on rs232, rs485, Ethernet, etc., depending on the interface specifications of the device. However, rs232 and rs485 can only represent the physical media layer and the link layer of the communication. If you want to achieve two-way data access, you must write your own communication application program. However, most of these programs cannot conform to the iso/osi specifications. The single function is applicable to a single device type, and the program does not have versatility.
In the equipment network of rs232 or rs485 equipment, if the number of equipment exceeds 2, it is necessary to use rs485 as the communication medium. The equipment of rs485 network must exchange information only through the “master†equipment to realize the communication. The master device is usually a pc, and only one master device is allowed in this device network, and the rest is all "slave devices". The fieldbus technology is based on the iso/osi model and has a complete software support system that can solve issues such as bus control, collision detection, and link maintenance.
All kinds of access control intercom system requirements for cables
The standard of the line-to-line videophone system is that the video, two-way audio and remote unlocking of each indoor unit are connected in parallel with the door machine by bus, but the call lines are directly connected to the door machine. Therefore, there are many cables used in this type of multi-residential video intercom system: video coaxial cable SYV-75-3 or SYV-75-5, microphone/speaker/unlocking line with a 4-core non-shielded PVC RVV or RVVP, power cords generally use 2-core PVC sheathed cords (RVV), and call lines use 2-core shielded wires (RVVP).
Digital coded push-button video intercom systems are generally used in multi-residential applications in high-rise residential buildings. According to different vendors' equipment systems, the standards for connecting cables are also different, but generally speaking, the basic wiring of the system is: the main line includes the video coaxial cable (SYV-75-3, SYV-75-5, etc.) and the power cable ( 2-core PVC sheathed cord RVV), audio/data control cable (4-core shielded wire RVVP), household signal wire (6-core shielded wire RVVP), etc.
Most of the residential buildings where the building's video intercom system is installed have a management center machine, and a community wall machine is installed at the entrance of the community wall to enable residents, management centers and visitors to implement the so-called “three-way call†of technical defense. The wiring of such a networked system adds the interconnection lines between the cell door machine, the cell door machine and the management center machine, generally including the video coaxial line (SYV-75-3, SYV-75-5, SYV-75 -7, etc.) Transmission of video image signals, 4-core shielded wires (RVVP) for transmission of audio and control signals, etc.
The above mentioned is to select different cables for different wiring according to the transmission of different signals. With the enhancement of the cable manufacturers' R&D capabilities, there are also some comprehensive functions available in the market for the use of the access control video intercom system. The cable adopts a specific process structure, so that the cable core assembly includes a coaxial line for transmitting video signals, a signal line for transmitting audio signals, a signal line for transmitting control signals, a power line for transmitting power signals, and the like, so that the primary wiring can be achieved. The required effect can save a large amount of work, but it depends on the specific requirements of various visual intercom systems to produce cables.