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Building intercom system layout control cable purchase and use recommendations
Release time:
2018-06-21
At present, the connecting cables used in building intercom systems on the market are mostly signal control lines (such as PVC sheathed flexible wire RVV and shielded wire RVVP) and coaxial SYV-75 series cables. The requirements of the system for cables are to transmit signals such as voice, data and video. At the same time, the requirements for cables are also reflected in the quality of voice transmission, the rate of data transmission, the quality and rate of video signal transmission, etc. In building visual intercom systems, the quality requirements for connecting cables are quite high. The cables for transmitting voice signals and alarm signals mainly use 4-core PVC sheathed flexible cords (RVV).
At present, the connecting cables used in building intercom systems on the market are mostly signal control lines (such as PVC sheathed flexible wire RVV and shielded wire RVVP) and coaxial SYV-75 series cables. The requirements of the system for cables are to transmit signals such as voice, data and video. At the same time, the requirements for cables are also reflected in the quality of voice transmission, the rate of data transmission, the quality and rate of video signal transmission, etc. In building visual intercom systems, the quality requirements for connecting cables are quite high.
The cables for transmitting voice signals and alarm signals mainly use more than 4-core polyvinyl chloride sheathed flexible cords (RVV), and coaxial SYV-75-5 are mainly used for video transmission. Nowadays, there are also some new technologies for signal transmission including video transmission through network twisted wires, without coaxial lines. If the system is to prevent external interference or grounding, the connecting wire used in the system must be shielded wire (RVVP) type shielded cable.
Cable for video intercom system connection
Line standard for direct key-type building visual intercom system: the video, two-way audio and remote unlocking terminals of each indoor unit are connected in parallel with the door machine by bus, but each call line is directly connected with the door machine separately. Therefore, the multi-household video intercom system of this structure uses more cables: video coaxial cable SYV-75-3 or SYV-75-5, microphone/speaker/unlocking line uses a 4-core unshielded polyvinyl chloride sheathed flexible wire (RVV) or shielded wire (RVVP), power connection line generally uses 2-core polyvinyl chloride sheathed flexible wire (RVV), and calling line uses 2-core shielded wire (RVVP).
Digital coding push-button visual intercom system is generally used in high-rise residential buildings and multi-household occasions. According to the equipment system configuration and connection cable standards of different manufacturers, but generally speaking, the basic wiring of the system is not to say that the main line includes video coaxial line (SYV-75-3, SYV-75-5, etc.), power line (2-core PVC sheathed flexible line RVV), audio/data control line (4-core shielded wire RVVP), household signal line (6-core shielded wire RVVP), etc.
Most residential buildings equipped with visual intercom systems are equipped with management center machines, and residential wall machines are installed at the gate of residential walls, so that residents, management centers and visitors can realize the so-called "three-way communication" of technical defense ". The wiring of such a networked system increases the network cable between the unit gate machine, the cell gate machine and the management center machine, which generally includes video coaxial line (SYV-75-3, SYV-75-5, SYV-75-7, etc.) transmitting video image signals, 4-core shielded wire (RVVP) transmitting audio and control signals, etc.
What is said above is that different cables are selected for separate wiring according to different signals. With the enhancement of the research and development strength of cable manufacturers, there are also some comprehensive cables with complete functions suitable for access control visual intercom systems on the market, using specific process structures, 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, etc., so that a wiring can achieve the required effect and save a lot of engineering. However, it is necessary to produce cables according to the specific requirements of various video intercom system equipment.
Access control, video intercom system backbone cable
1. RS-232-C is a serial physical interface standard developed by the American Electronics Industry Association EIA(ElectronicIndustryAssociation). RS is an abbreviation of "recommend standard" in English, 232 is an identification number, and C represents 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 mainly used. For general duplex communication, only a few signal lines can be realized, such as a sending line, a receiving line and a ground line. RS-232-C standards specify data transfer rates of 50, 75, 100, 150, 300, 600, 1200, 2400, 4800, 9600, 19200 baud per second.
The RS-232-C standard stipulates that the driver is allowed to have a 2500pF capacitive load, and the communication distance will be limited by this capacitance. For example, when a 150pF/m communication cable is used, the maximum communication distance is 15m; If the capacitance of the cable per meter is reduced, the communication distance can be increased. Another reason for the short transmission distance is that the RS-232 belongs to single-ended signal transmission, which has problems such as common ground noise and inability to suppress common mode interference. Therefore, it is generally used for communication within 20m.
2. RS-485 bus, when the communication distance is required to be tens of meters to thousands of meters, the RS-485 serial bus standard is widely used. RS-485 uses balanced transmission and differential reception, it has the ability to suppress common mode interference. In addition, the bus transceiver has high sensitivity and can detect voltages as low as 200mV, so the transmission signal can be recovered beyond kilometers. RS-485 the half-duplex mode of operation is adopted, only one point can be transmitted 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. The application RS-485 can be networked to form a distributed system that allows up to 32 drivers and 32 receivers to be connected in parallel.
In the past, the communication between PC and intelligent equipment mostly relied on RS232, RS485, Ethernet and other methods, which mainly depended on the interface specification of the equipment. However, RS232 and RS485 can only represent the physical media layer and link layer of communication. If you want to realize two-way access to data, you must write your own communication application program. However, most of these programs cannot meet the ISO/OSI specifications and can only achieve a single function. They are suitable for a single device type and do not have versatility. In the equipment network of RS232 or RS485 devices, if the number of devices exceeds 2, RS485 must be used as the communication medium. In order to communicate information between devices of RS485 network, it can only be realized through the transfer of "master (Master)" devices. This master device is usually a PC, and only one master device is allowed in this equipment network, and the rest are all "slave (Slave) devices". The fieldbus technology is based on the ISO/OSI model, with a complete software support system, can solve the bus control, conflict detection, link maintenance and other issues.
According to this requirement, cable manufacturers have developed a series of twisted-pair shielded wires for RS-485 transmission (the core adopts twisted-pair structure to enhance its anti-interference performance). If the above system indicates that the wiring is suitable for RS-485 transmission, it is recommended to use such cables for connection to ensure that the performance of the system meets the standard.
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