Access control intercom system cable selection
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 on 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.
Access control intercom system cable selection
The connection cables used in building intercom systems currently on the market are mostly signal control lines (such as PVC sheathed cord RVV and shielded electric wire RVVP), coaxial SYV-75 series cables, and the requirements of the system for cables. It is the transmission of voice, data, video and other signals. At the same time, the requirements for cables are also reflected in the quality of voice transmission, the speed of data transmission, the quality and rate of video signal transmission, etc. In building video intercom systems, for connection The quality of the cable is quite high.
The cable that transmits voice signals and alarm signals mainly uses four-core or more PVC sheathed cords (RVV). In the video transmission, the coaxial line SYV-75-5 is adopted. 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.
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 connected directly 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 lines include video coaxial lines (SYV-75-3, SYV-75-5, etc.), and power lines ( 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 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.
How to monitor the quality of cables
The good and bad cable identification, the real test requires specialized equipment and instruments. These equipment and instruments are not available in design and engineering units.
1. PVC jacket: The surface can see the regular "unevenness" of the netting inside the net, which means that the processing technology is good, and no relative sliding will occur. It is a good cable. The appearance is smooth, can't see the "unevenness" of the compacted net, and the looseness of the sheath is caused by hand, which is a poor cable;
2, check the shielding layer network: the number is enough? Copper wire mesh, check the weldability, tinned copper computer wire scraping to see if it is copper wire, the hardness of aluminum-magnesium alloy wire is obviously greater than copper wire; the wire mesh is sparse, the distribution is uneven, and the insulation layer is not tightly wrapped. Poor cable;
3, check the core: diameter - SYV cable is 0.78-0.8mm, SYWV cable is 1.0mm; recently appeared a SYV75-5 core diameter is 1.0mm cable, the cable's characteristic impedance, certainly not 75 ohms Not applied to 75 ohm transmission systems;
4. Check the binding force between the core wire and the insulating layer: Cut the insulation layer obliquely, pull the core wire in the direction of peeling, and see if the core wire and the insulation layer are covered with the process material; good cable has a large binding force, poor The cable is not covered;
5. Longitudinal tensile test: Take one meter cable, peel the core wire, insulation layer, shielding layer, and outer cover in layers, leaving 10 cm long. The method is: two hands hold the adjacent two layers of the cable and pull in the opposite direction; the cable is generally unable to pull the power, so the cable can be easily pulled out without any effort.
