Selection guide of anti-theft alarm video monitoring system cable

Basic knowledge of cable selection

     The most commonly used in the wiring of the anti-theft system are signal transmission cables and power transmission cables. Due to the number of detection points, different detection methods, different transmission methods, different power requirements, etc., select the matching cable according to the actual situation Is the key to the overall system.

     The application of cables in the monitoring system has the most specifications of the models, different equipment, different quantities, different monitoring methods, different image quality requirements, etc., which requires different wiring methods and cable selection requirements. We need to design the system at the same time, Adhere to the premise of ensuring the overall quality of the system, select the economical and reliable transmission medium that meets the technical requirements.

     There are many types of security system subsystems, and the requirements for security cables are also diverse. Here, we elaborate on the selection of security cables in the security system from the cable selection of several subsystems of the current security system.

     Video surveillance system

     Good video transmission design is a very important part of CCTV monitoring system. If a well-established system uses cameras, lenses, monitors, and video recorders that can produce or process high-quality images, but without a good transmission system, the final image seen on the monitor will be unsatisfactory. According to the "barrel rule", the final image quality will depend on the worst link in the entire system; and the worst link is often the transmission system. System designers and installers must choose the appropriate transmission method, high-quality transmission cables and equipment according to actual needs, and install according to professional standards to achieve the desired transmission effect.

     Video signal transmission generally adopts direct modulation technology in the form of baseband frequency (about 8MHz bandwidth). The most commonly used transmission medium is coaxial cable. Coaxial cable is specially designed to transmit video signals. Its frequency loss, image distortion, and image attenuation are relatively small, and it can accomplish the task of transmitting video signals well. Generally, a dedicated SYV75 ohm series coaxial cable is used, and the commonly used model is SYV75-5 (its non-relay transmission distance for video signals is generally 300-500m); when the distance is longer, SYV75-7, SYV75-9 or even SYV75-12 coaxial cable (in actual projects, the thick cable's non-relay transmission distance can reach more than 1km); there are also video amplifiers to increase the brightness, chroma and synchronization signal of the video, but the interference signal in the line is also It will be amplified, so there can not be too many video amplifiers in series in the loop, otherwise saturation phenomenon will occur, resulting in distortion of the image; the farther distance uses the optical fiber transmission method, the optical fiber transmission has small attenuation, frequency bandwidth, and is not subject to electromagnetic wave interference. A series of advantages, such as light weight and good confidentiality, are mainly used in national, provincial and municipal backbone communication networks, cable TV networks and high-speed broadband computer networks. In closed-circuit television monitoring systems, optical fiber transmission has also become the preferred method for long-distance video and audio and control signal transmission.

     Video signals can also be transmitted using twisted-pair cable, which requires twisted-pair transmission equipment. In some special applications, twisted pair transmission equipment is essential. For example, when a large number of twisted pairs (called Category 3 or Category 5 in the standard) have been laid in the building according to the integrated wiring standard and the corresponding information interface (RJ45 or RJ11) is left in each relevant room, the new No additional wiring is required when adding CCTV monitoring equipment. Both video and audio signals and control signals can be transmitted through twisted-pair cables, where the transmission of video signals requires the use of twisted-pair cable transmission equipment. In addition, for applications where the twisted pair (or two-core sheathed wire) has been laid and the image of the front-end camera needs to be transmitted to the central control room equipment, the twisted pair transmission device is also required. The function of the twisted pair video transmission equipment is to convert the video signal suitable for unbalanced transmission (that is, suitable for 75Ω coaxial cable transmission) into the video signal suitable for balanced transmission (that is, suitable for twisted pair transmission) at the front end; The processing opposite to the front end converts the video signal transmitted through the twisted pair into an unbalanced video signal. Twisted pair transmission equipment itself has the function of video amplification, so it is also suitable for long-distance signal transmission.

     For the above different transmission methods, the transmission components and transmission lines used are quite different. Communication cables are generally used in camera devices equipped with motorized pan-tilt heads and motorized lenses. A remote control decoder must be installed on site when in use. The communication transmission cable between the on-site decoder and the video matrix switching host of the control center generally adopts 2-core shielded communication cable (RVVP) or category 3 twisted pair UTP, and the cross-sectional area of ​​each core is 0.3mm2 ~ 0.5mm2. The basic principle for selecting communication cables is that the longer the distance, the larger the wire diameter. For example: RS-485 communication stipulates that the basic communication distance is 1200m, but in actual projects, the use of RVV2-1.5 sheath line can extend the communication length to more than 2000m. When the communication distance is too long, RS-485 communication repeater is required.

     The control cable usually refers to the multi-core cable used to control the gimbal and the electric variable lens. It is connected to the gimbal of the controller or decoder, the control terminal of the electric lens, and the other end is directly connected to the gimbal and electric On the corresponding terminal of the lens. Because the control cable provides DC or AC voltage, and the distance is generally short (sometimes less than 1m), there is basically no interference problem, so there is no need to use shielded wire. Most commonly used control cables use 6-core or 10-core cables, such as RVV6-0.2, RVV10-0.12, etc. Among them, the 6-core cable is connected to the upper, lower, left, right, automatic, and common 6 terminals of the gimbal, and the 10-core cable includes the zoom, focus, and aperture of the motorized lens in addition to the 6 terminals of the gimbal. , Common 4 terminals. In the CCTV monitoring system, the control cable from the decoder to the gimbal and lens is generally not required due to the short distance; the distance from the controller in the central control room to the gimbal and motorized lens is tens of meters, For several hundred meters, there are certain requirements for the control cable, that is, the wire diameter should be thick, such as RVV10-0.5, RVV10-0.75 and so on.

     The sound monitoring cable generally adopts 4-core shielded communication cable (RVVP) or category 3 twisted pair UTP, and the cross-sectional area of ​​each core is 0.5mm2. In the environment without interference, it can also be selected as unshielded twisted pair, such as the type 5 twisted pair commonly used in integrated wiring (4 pairs of 8 cores); because the audio signal of the monitoring head in the monitoring system is transmitted to the central control room is The adopted point-to-point wiring method uses high voltage and small current transmission, so it is enough to use unshielded 2-core cable, such as RVV2-0.5.

Anti-theft alarm system

     The alarm system based on the professional bus form is currently the most widely used, and the application of the cable is also the most complicated, so we will focus on the discussion here.

     RVV2 * 0.3 (signal line) and RVV4 * 0.3 (2-core signal + 2-core power supply) cables are generally used between the front-end detector and the alarm controller, and 2 is generally used between the alarm controller and the terminal security center. The core signal wire, as for shielded wire or twisted pair or ordinary sheathed wire, needs to be determined according to the requirements of various brand products. The rough details of the wire diameter are determined according to the distance and quality of the alarm controller and the center, but First, we must determine the location of the security center and the distance of each alarm controller. The maximum distance cannot exceed the length specified by various brands, otherwise it will not meet the requirements of the bus; the entire alarm area is relatively large, and the bus must not meet the requirements. Under the conditions, the alarm can be divided into several areas, and the installation location of the sub-control center is determined in each area to ensure that the bus in this area meets the requirements, and the location of the general management center and the sub-administration center is determined, and the sub-control center to the general management Is the center's communication method using RS232-RS485 conversion transmission or RS232? TCP / IP using the community's integrated wiring system transmission or branch management center Management software uses to forward TCP / IP network to a total management center.

     The power supply of the alarm controller generally adopts local power supply instead of centralized power supply in the control room, and the line is short. Generally, the specifications of RVV 2 × 0.5 ”or more are sufficient. It is configured according to the actual line loss. Generally, the centralized power supply mode is adopted, and the line is longer. Generally, the specifications above RVV2 * 1.0 ”are adopted, and the configuration is based on the actual line loss. The grounding of all power supplies needs to be unified.