Ⅰ. Selection of video monitoring cables
1. Video cable:
When the distance between the camera and the monitoring host is less than or equal to 200 meters, usually about 100 meters, you can use SYV-75-3 (ie RG59 line) video cable or SYV-75-5 (96 series).
When the distance between the camera and the monitoring host >200m and <350m, you can use SYV-75-5 (128 series) video cable.
When the distance between the camera and the monitoring host is about 500 meters, you can select the SYV-75-7 video cable. (Generally not commonly used)
When the distance between the camera and the monitoring host is 500 to 1000 meters, optical fiber transmission can be used.
(Note: The full name of SYV cable is solid polyethylene insulated radio frequency coaxial cable, which is a kind of coaxial cable. SYV-75-5: S stands for radio frequency, Y stands for polyethylene insulation, V stands for sheath, 75 stands for characteristic impedance, 5 stands for wire diameter. A: 64 series, B: 96 series, C: 128 series, "Series" represents the density of the shielding layer, that is, the dense copper wire on the outside.)
2. Pan-tilt control cable
When the distance between the pan-tilt and the controller is less than or equal to 100 meters, use RVV6×0.5 sheathed cable.
When the distance between the pan-tilt and the controller >100 meters, use RVV6×0.75 sheathed cable.
(Note: Introduction of sheathed cable: soft sheaths include RVV and BVV, v-polyvinyl chloride insulation, v-polyvinyl chloride sheath, R-soft, VV-polyvinyl chloride insulated PVC sheathed power cable RVV- PVC insulated PVC sheathed flexible cable (also called sheathed cable)
3. Lens control cable: RVV4×0.5 sheath cable is adopted.
4. Decoder communication cable: RVV2×1 sheathed cable should be used.
5. Camera power line
If the system has 20 ordinary cameras and the distance between the camera and the monitoring host is within 50 meters, BVV6M2 should be used.
Ⅱ. The laying of monitoring system line:
1. Cautions for laying the video cable:
If the distance between the camera and the monitoring host (image processor, matrix control host or digital video recorder) is less than 200 meters, you can use the RG59 (SYV-75-3) video cable; if it exceeds 200 meters, you should use the SWY-75-5 video cable to ensure the quality of monitoring images.
For the cameras installed in the elevator, the wiring in the elevator shaft should adopt the star iron trough and be grounded to reduce the interference to the video signal when the elevator motor starts.
If the camera is installed outdoors (such as the entrance of a compound or a parking lot, etc.), the line needs to be routed outdoors or through overhead steel cables. If conditions permit, video arresters should be installed (because the installation of lightning protection equipment will cause the increase in overall cost of the project). That is, the video arrester is installed on the camera side and the monitoring host side respectively, and each video arrester must be grounded (outdoor cameras must be grounded separately, and the video arresters in the monitoring room can be grounded uniformly) to prevent the inductive thunder from damaging the equipment.
2. Precautions for laying control lines:
In an analog monitoring system, if a PTZ zoom security camera is installed and controlled by a pan-tilt lens controller, the selection of the control line should be determined according to the distance between the camera and the pan-tilt lens controller. When the distance is less than 100 meters, the pan-tilt control line can use RVV6×0.5 sheathed cable; when the distance is greater than 100 meters, the pan-tilt control line should use RVV6×0.75 sheathed cable, and the lens control line uses RVV4×0.5 sheathed cable. If the analog monitoring system controls the pan-tilt and lens through a matrix control host, a decoder is generally needed. For the control line layout, please refer to the technical requirements of the matrix control host which is used.
In the digital monitoring system, if a camera equipped with a pan-tilt zoom lens is installed, the pan-tilt and lens need to be controlled through a decoder. The decoder is generally installed next to the camera, and the decoder and the digital video recorder use the RS485 bus for communication. RVVP2×1 shielded twisted-pair cable used for the wiring is first from the digital video recorder to the nearest decoder 1, and then from decoder 1 to decoder 2. The current 16-channel digital video recorder can be connected to a maximum of 16 decoders. The total length of the RS485 communication line can be as long as 1200 meters.
The decoder has two power supply types: AC220V and AC24V. If an AC24V decoder is selected, it is generally supplied by an AC24V transformer. It is particularly important to note that because the DC12V power supply output by some decoders has interference, and it will have a certain impact on the image when used for camera power supply, so it is necessary to uniformly supply power to the camera (12V).
3. Precautions for laying the power line of the camera:
The working current of ordinary cameras on the market that use DC12V power supply is about 200 to 300mA, and that of integrated cameras is 350 to 400mA. If the number of cameras is small (less than 5) and the distance between the camera and the monitoring host is relatively close (less than 50 meters), each camera can be separately wired with RVV2×0.5 power line to the monitoring room and powered by a small transformer. If the number of cameras is large, a high-power 12V DC stabilized power supply should be used for centralized power supply.
In the program design and construction process, it is necessary to consider the total power of all cameras and the voltage drop caused by the transmission line (commonly known as "line loss", the resistance of a 1m2 copper wire per 100m is 1.8Ω). For the monitoring of a building, two 2.5 to 6m2 copper core double plastic wires are generally used as the main power supply which will be led from the monitoring room to the line well, and from the line well to the line well on the floor where each camera is located. For the power supply of each camera on the floor, one RVV2×1 or RVV2×1.5 (if the number of cameras on the floor exceeds 6) power lines can be drawn from the line well to supply power to the cameras. Or use RVV2×0.5 sheath cables for one-to-one correspondent power supply.
Ⅲ. The types and differences of commonly used monitoring cables
Cables include video cables, RF cables, shielded and unshielded cables, signal cables, control cables, etc. These various models are often confused by beginners. The following is the distinction between several commonly used models: RVV and KVV, RVVP and KVVP: The wire used in RVV and RVVP is a flexible wire composed of multiple strands of thin copper wires, that is, RV wire. The wire used in KVV and KVVP is a hard wire composed of a single thick copper wire, that is, a BV wire. The difference between AVVR and RVVP: materials are the same, except that when the internal cross-section is less than 0.75 square millimeters, the name is AVVR, and when it is greater than or equal to 0.75 square millimeters, the name is RVVP.
Ⅳ. Distinguish good from bad
To distinguish the quality of the cable, the real testing requires special equipment and instruments. But these equipment and instruments are not available in the design and engineering units. In engineering practice, how can we distinguish the quality of the video cable?
1. PVC sheath: from the surface we can see the regular "unevenness" of the compressed netting, indicating that the processing technology is good, and there will be no relative sliding, so it is a good cable. If the appearance is smooth, there is no "unevenness" of the compressed netting, and the sheath is loose when pinched by hand, it is a bad cable;
2. Check the netting in the shielding layer: is the number of netting enough? The weldability of copper netting should be checked. The tinned copper wire can be scratched to see if it is the real copper wire inside. The hardness of the aluminum-magnesium alloy wire is obviously greater than that of the copper wire; If the netting is sparse, unevenly distributed, and is not tightly wrapped with the insulating layer, it is a bad cable;
3. Check the core wire: in terms of diameter, SYV cable is 0.78 to 0.8mm, and SYWV cable is 1.0mm; recently there has been a SYV75-5 cable with a core wire diameter of 1.0mm. The characteristic impedance of this cable is definitely not 75Ohm, and cannot applied to 75Ohm transmission system;
4. Check the adhesion force between the core wire and the insulating layer: cut the insulating layer diagonally, and pull the core wire in the peeling direction to see if the core wire and the insulating layer are bonded with the adhesive craft materials; good cables have great adhesion strength, but poor cables have not;
5. Longitudinal tensile test: Take one meter of cable, strip the core wire, insulation layer, shielding layer, and outer jacket in layers, leaving 10cm long each. The method is: hold the two adjacent layers of the cable with two hands and pull them in opposite directions; a good cable can't be pulled with strength, and a bad cable can be pulled out easily without much effort-for the elevator cable, this point is very important, because many so-called "elevator cables" all have problems in the respect.