How to choose the access control intercom cable

[ Huaqiang Security Network News ] People's security awareness has been sublimated in recent years, and the community has been continuously improved. When installing the access control intercom system, the requirements for cables are getting higher and higher. We have to choose different signals for different signals. Transmission cable. First, the building intercom system currently used in the building intercom system on the cable is mostly signal control lines (such as PVC sheathed cord RVV and shielded wire RVVP), coaxial line SYV-75 series cable, The cable requirements of the system are to transmit voice, data, video and other signals. At the same time, the requirements for the cable are also reflected in the quality of voice transmission, the rate of data transmission, the quality and speed of video signal transmission, etc. In the system, the quality requirements for the connecting cable are quite high. Cables for transmitting voice signals and alarm signals mainly use 4-core or more PVC sheathed flexible cords (RVV), and coaxial transmission lines SYV-75-5 are mainly used for video transmission. Nowadays, some network pairs have appeared. The twisted-line transmission includes a new technology for video signal transmission, and does not use coaxial lines. If the system is to prevent external interference or grounding, the cable used in the system must be shielded cable (RVVP) type shielded cable.
Second, the video intercom system connection cable direct button type building video intercom system line standard: each indoor unit video, two-way audio and remote unlocking and other terminals are connected by bus and door machine, but each The call line is directly connected to the door machine. Therefore, the multi-residential video intercom system of this structure uses more cables: video coaxial cable SYV-75-3 or SYV-75-5, and a 4-core unshielded PVC protector for the microphone/speaker/lock line RVV or shielded wire (RVVP), the power cable usually uses a 2-core PVC sheathed cord (RVV), and the call line uses a 2-core shielded cable (RVVP).
The digital coded button-type video intercom system is generally used in multi-dwelling applications in high-rise residential buildings. According to the equipment system configuration of different manufacturers, the standard of connecting cables is different, but generally speaking, the basic wiring of the system is: the main line includes video coaxial cable (SYV-75-3, SYV-75-5, etc.) and power cable ( 2-core PVC sheathed flexible cable RVV), audio/data control cable (4-core shielded cable RVVP), and household signal cable (6-core shielded cable RVVP).
Most of the residential buildings that install the building video intercom system have a management center machine, and a community wall machine is installed at the door of the community wall to enable the residents, management centers and visitors to realize the "three-way call" of the so-called technical defense. The wiring of such a networked system increases the networking line between the unit door machine, the cell door machine and the management center machine, generally including video coaxial lines (SYV-75-3, SYV-75-5, SYV-75). -7, etc.) transmits video image signals, and 4-core shielded wires (RVVP) transmit audio and control signals.
The above mentioned is to use different cables to transmit different cables according to different signals. With the enhancement of the R&D strength of the cable manufacturers, some comprehensive functions for access control video intercom systems have appeared on the market. The cable adopts a specific process structure, so that the cable core assembly includes a coaxial line for transmitting a video signal, a signal line for transmitting an audio signal, a signal line for transmitting a control signal, and a power line for transmitting a power signal, so that the primary wiring reaches the position. The required effect can save a lot of engineering quantities, but the cable needs to be produced according to the specific requirements of various video intercom system equipment.
Third, the access control, video intercom system backbone cable 1, RS-232-C is a serial physical interface standard developed by the Electronic Industry Association EIA (Electronic Industry Association). RS is an abbreviation of the English "recommendation standard", 232 is the identification number, and C is the number of revisions. The RS-232-C bus standard has 25 signal lines, including one main channel and one auxiliary channel. In most cases, the main channel is mainly used. For general duplex communication, only a few signal lines are needed, such as a strip. Send line, one receive line, and one ground line. The data transmission rate specified by the RS-232-C standard is 50, 75, 100, 150, 300, 600, 1200, 2400, 4800, 9600, 19200 baud per second. According to the RS-232-C standard, the driver is allowed to have a capacitive load of 2500pF, and the communication distance will be limited by this capacitor. For example, when using a 150pF/m communication cable, the maximum communication distance is 15m; if the capacitance per meter is reduced The communication distance can be increased. Another reason for the short transmission distance is that RS-232 is a single-ended signal transmission, which has common ground noise and cannot suppress common mode interference. Therefore, it is generally used for communication within 20m.
2. RS-485 bus, RS-485 serial bus standard is widely used when the communication distance is required to be tens of meters to kilometer. RS-485 uses balanced transmit and differential receive, so it has the ability to reject common-mode interference. In addition to the high sensitivity of the bus transceiver, it can detect voltages as low as 200mV, so the transmitted signal can be recovered beyond the kilometer. RS-485 uses a half-duplex mode of operation, and only one point can be sent at any time. Therefore, the transmitting circuit must be controlled by an enable signal. RS-485 is very convenient for multi-point interconnection and can save many signal lines. Applications RS-485 can be networked to form a distributed system that allows up to 32 drives and 32 receivers to be connected in parallel.
In the past, PC and smart device communication mostly relied on RS232, RS485, Ethernet, etc., mainly depending on the interface specification of the device. However, RS232 and RS485 can only represent the physical media layer and link layer of communication. If you want to achieve bidirectional access to data, you must write your own communication application. However, most of these programs cannot conform to the ISO/OSI specification and can only be implemented. A single feature that works with a single device type and the program is not versatile. In the equipment network of RS232 or RS485 equipment, if the number of equipment exceeds 2, RS485 must be used as the communication medium. The communication between the RS485 network equipments can only be realized through the "master" equipment transfer. The master device is usually a PC, and only one master device is allowed in the device network, and the rest are all "slave devices". The fieldbus technology is based on the ISO/OSI model and has a complete software support system that can solve problems such as bus control, collision detection, and link maintenance.
According to this requirement, cable manufacturers have also developed a series of twisted-type shielded wires for RS-485 transmission (the cores are twisted to enhance their anti-jamming performance). If the above system indicates that the wiring is suitable for RS-485 transmission, it is recommended to use such cables to ensure the performance of the system is up to standard.
Summary: According to the characteristics of the access control system to select the appropriate transmission cable, in order to allow the access control intercom system to play the functional level of the application.