Because of the importance of closed-circuit television monitoring system, it is widely used in banks, highways, airports, residential areas, buildings, schools, hospitals, families and other places. This paper focuses on the construction of closed-circuit television monitoring system in residential quarters and buildings.
2 system composition
Closed-circuit monitoring system generally consists of front-end equipment, transmission part and back-end equipment (including control equipment and real equipment).
2. 1 front-end equipment
Front-end equipment mainly includes camera, lens, protective cover, bracket, column, pan/tilt, decoder (also classified as back end), transformer, standby power supply (also classified as back end) and so on.
The reasonable selection of front-end equipment will directly affect the effect of the system, especially the reasonable configuration of the camera, which should be adapted to local conditions. It will be described in detail later.
2.2 transmission part
The transmission part mainly includes video line, audio line, control line and power line.
The video cable can be coaxial cable (within1000m) or optical cable (above1000m). If you choose coaxial cable, the distance is more than 350m (about), you need to add a video amplifier. If optical cable is selected, optical transmitter will be added to the front-end equipment and optical receiver will be added to the back-end equipment.
2.3 back-end equipment
The back-end equipment mainly includes matrix, picture processor, hard disk video recorder, ordinary video recorder, monitor, display, pan/tilt controller, large uninterrupted power supply, TV wall, console and other equipment.
The back-end image processing equipment can choose matrix, image processor, hard disk video recorder or mixed arrangement. See the following for details. The display device needs at least one TV wall, or it can be used in combination with the display. At present, there is a new display trend, that is, splicing large screens with DLP. At present, the application of hard disk video recorder in video recording equipment is more and more extensive, and the traditional video tape has been gradually replaced.
3 system design
This paper will discuss how to design according to the composition of CCTV monitoring system.
3. 1 front end
3. 1. 1 camera selection
CCD cameras can be roughly divided into the following categories:
1. Divided by imaging color
According to the imaging color is divided into:
Color camera: suitable for distinguishing scene details, such as distinguishing the color of clothes or scenery. Because of color, the amount of information increases, which is generally considered to be 10 times that of black and white cameras; and
Black-and-white camera: used in areas with poor light and areas where lighting equipment cannot be installed at night. When monitoring only the position or motion of the scene, you can choose a black-and-white camera with higher resolution than a color camera.
At present, the closed-circuit monitoring system gradually replaces black-and-white cameras with colors, especially in digital systems. The author suggests that if the funds are sufficient, the overall effect of color system is good, which is conducive to publicity and image recognition.
2. Divide by camera resolution
According to the resolution of the camera, it is divided into:
The image pixel is about 250,000 pixels, the color resolution is about 330 lines, and the black and white resolution is about 400 lines.
Image pixels are between 250,000 and 380,000, color resolution is 420 lines, and black and white resolution is below 500 lines. and
The image is above 380,000 points, the color resolution is greater than or equal to 480 lines, the black-and-white resolution is above 600 lines.
In the closed-circuit monitoring system, most systems use cameras with more than 420 lines. If you need clear and flicker-free image quality, it is recommended to use a camera with more than 480 lines.
3. According to the sensitivity of the camera
According to the sensitivity of the camera, it is divided into:
Ordinary type: the illumination required for normal operation is1~ 31x;
Moonlight type: the illumination required for normal operation is about 0.1x;
Starlight type: the illumination required for normal operation is below 0.0 1x; and
Infrared illumination type: in principle, it can be zero illumination, and it can be imaged by infrared light source.
The choice of lighting is very important for closed-circuit monitoring system. Ordinary cameras are used in daytime and places with high illumination, moonlight cameras are used in places with low illumination but good light (such as street lamps with high illumination at night), starlight cameras are used in places with street lamps or light sources but low light, and infrared cameras are used in places without light sources or with low illumination.
4. Adjust according to the size of the CCD target surface of the camera element.
Forest target size 12.7mmX 9.6mm high16mm; Diagonal line;
The size of 2/3 inch target surface is 8.8mmX 6.6 mm high, and the diagonal is11mm;
The size of target surface 1/2in is 6.4mmX wide, 4.8mm high and 8 mm diagonal;
1/3 inch target size is 4.8mmX wide, 3.6mm high and 6mm diagonal;
1/4in target size is 3.2mmX wide, 2.4mm high and 4 mm diagonal; and
1/5in is under development, and the official product has not yet been launched.
At present, 1/3 "in CCD cameras is mostly used for cameras with optional lenses. Some integrated hemispheres, high-speed balls and some cameras use other CCD sizes.
5. According to the system division
According to the system is divided into:
PAL system: Most European countries, Australia and some Central and South American countries adopt the line-by-line phase inversion (PAL) standard, with 25 frames and 625 lines per second. China adopts this standard; and
NTSC system: When the National Television System Committee (NTSC) of the United States formulated the commercial television broadcasting standards in the United States, Canada, Japan and parts of Central and South America, it stipulated that there were 30 pictures per second and 525 lines were displayed.
PAL system is adopted in China, but most cameras on the market support PAL/NTSL system, so you can choose it at will.
3. 1.2 lens selection
1. lens type
The lens is divided into:
Wide-angle lens: the viewing angle is greater than 90 degrees, the nearby image is distorted, and the observation range is large;
Standard lens: the viewing angle is about 30 degrees, and the use range is wide;
Telephoto lens: the viewing angle is less than 20 degrees, and the focal length can reach tens or hundreds of millimeters;
Zoom lens: the focal length of the lens is continuously variable, and the focal length can be changed from wide angle to telephoto, and the longer the focal length, the greater the imaging; and
Pinhole lens: used for hidden observation, often installed on the ceiling or wall.
Generally speaking, the standard lens is selected, and other lenses are selected according to the actual situation in special occasions. A camera equipped with a tripod head is equipped with a zoom lens, and a pinhole lens is used in the elevator.
2. The relationship between the size, distance and focal length of an object.
Suppose the width and height of the subject are w and h respectively, the distance between the subject and the lens is l, and the focal length of the lens is f.
3. Relative aperture
In order to control the luminous flux passing through the lens, an aperture is set behind the lens. Assuming that the effective aperture of the aperture is D, the actual effective aperture of mirror light is D, which is greater than D. The ratio of D to focal length F is defined as the relative aperture A, that is, A = D/F. The relative aperture of the lens determines the illumination of shooting, and the reciprocal of the illumination of the image and the relative aperture of the lens represents the size of the lens aperture. The smaller the f value, the larger the aperture and the greater the luminous flux reaching the CCD chip. Therefore, in the case of the same focal length f, the smaller the value of f, the better the lens.
4. The focal length of the lens
Fixed focal length: the focal length is fixed and can be divided into two types: aperture and non-aperture.
Aperture: The aperture of the lens can be adjusted. According to the change of environment, the aperture should be adjusted accordingly. The aperture can be adjusted manually or automatically. If you adjust the aperture manually, it is called manual aperture. If the lens comes with a micro-motor to automatically adjust the aperture, it is called automatic aperture; and
No aperture: that is, fixed aperture, and its luminous flux is fixed. It is mainly used when the light source is constant or the camera has its own electronic shutter.
Zoom: you can adjust the focal length as needed to enlarge or reduce the image of the subject.
Commonly used zoom lenses include six-fold zoom and ten-fold zoom.
Trivariate and bivariate lenses
Three variable lenses: adjustable focal length, adjustable focal length and adjustable aperture.
Variable lens: adjustable focal length, adjustable focal length, automatic aperture.
5. The principle of matching lenses first
In order to obtain the expected camera effect, we should pay attention to six basic elements when choosing a lens:
The size of the subject;
Detailed dimensions of the main body;
Object distance;
Focal length;
Size of CCD camera target surface; and
Resolution of lens and camera system.
3. 1.3 camera cover
Shielding cover is an important part in monitoring system. It is a protective device, which can make the camera work normally under the conditions of dust, rain, high and low temperature, etc.
Protective covers are usually divided into two categories:
Indoor protective cover: This protective cover has simple structure and low price. Its main function is to prevent the camera from falling off, and it has certain safety protection functions, such as anti-theft and anti-destruction; and
Outdoor protective cover is generally an all-weather protective cover, which means that the camera installed in the protective cover can work normally under severe conditions such as wind, rain, snow, high temperature and low temperature. Therefore, this kind of protective cover has the functions of cooling, heating and rain and snow protection. At the same time, in order to make the camera shoot images normally in rainy and snowy weather, a controllable wiper is usually installed in front of the glass window of the all-weather protective cover. At present, the better all-weather protective cover is the protective cover with semiconductor device heating and refrigeration. This kind of protective cover is equipped with semiconductor components, which can automatically heat up and cool down, with low power consumption.
In addition, there are hemispherical and spherical protective covers with built-in universal adjustable brackets, which are beautiful in appearance.
3. 1.4 Yuntai
Pan/tilt is the supporting equipment for installing fixed cameras, which can be divided into fixed and electric pan/tilt:
Fixed pan/tilt is suitable for occasions with small monitoring range. After the camera is installed on the fixed pan/tilt, the horizontal and pitching angles of the camera can be adjusted, and the adjustment mechanism can only be locked after reaching the best working posture. and
The electric pan-tilt is suitable for large-area scanning and monitoring, which can expand the monitoring range of the camera. The high-speed attitude of the electric pan-tilt is realized by two executive motors, which receive the signals from the controller for accurate operation and positioning. Under the action of the control signal, the camera on the tripod head can not only automatically scan the monitoring area, but also track the monitored object under the control of the personnel on duty in the monitoring center.
According to the rotation characteristics of the tripod head, the tripod head can be divided into a horizontal tripod head that can only rotate left and right and an omnidirectional tripod head that can rotate left and right and up and down. Generally speaking, the horizontal rotation angle is 0? ~350? , the vertical rotation angle is +90? . The horizontal rotation speed of constant-speed pan/tilt is generally 3? ~ 10? /s, the vertical speed is 4? /s or so, the horizontal rotation speed of the variable-speed pan/tilt is generally 0? ~32? /s, the vertical rotation speed is 0? ~ 16? /s In some high-speed camera systems, the horizontal rotation speed of the pan/tilt is as high as 480? /s, and the vertical rotation speed is 120? /s or more.
If you use a high-speed spherical camera, you don't need a pan/tilt. At present, there are a large number of spherical ptz, built-in decoder and ptz in China. Most of them are spherical, close to the high-speed ball but not the high-speed ball, which is cheap and good, and gradually replaces the traditional Yuntai.
3.2 transmission part
The construction of transmission part of closed-circuit monitoring system is directly related to the whole system. The transmission part mainly includes video line, audio line (not included in most projects, which will not be discussed in this paper), control line and power line. Of course, the pipeline is also an important part, and the weak current pipeline system is generally built by professional companies.
Transmission lines should be far away from strong current. If parallelism or crossing is really unavoidable, keep a distance of at least 30cm and use shielded wires.
1. video line
The reasonable selection of video lines directly affects the display effect of the back end. Generally, the distance is less than 500m, and SYV 75-5 coaxial cable can be used. If the interference is serious, you can use the coaxial cable of SYV 75-7 or SYV 75-9. If the distance exceeds 500m and does not exceed 1000m (empirical value), it is recommended to increase the video amplifier. If the distance exceeds 1000m, it is recommended to use optical fiber transmission. Of course, it is also possible to combine several signals into one signal for transmission through a modem. The use of optical fiber transmission requires the addition of special optical transmitters and receivers (widely used in remote closed-circuit monitoring systems such as highways).
Generally speaking, the monitoring distance between residential areas and buildings does not exceed 1000m, so 75 ohm coaxial cable is used. The selection and installation of coaxial cable are described here.
It is very important to choose the right cable for the equipment to achieve the best performance. Generally speaking, the impedance of coaxial cable is 75 ohms.
Materials:
Only pure copper conductor cables can be used. Don't use copper-plated copper-core cable or aluminum-core cable, because they can't effectively transmit signals in the whole frequency band used by closed-circuit monitoring system.
Solid bare copper wire is most suitable for video applications without bending. If bending cannot be avoided in normal use, stranded wires should be used.
The insulating material is preferably porous (foamed) polyethylene. It has better electrical characteristics than solid polyethylene, but it is easily affected by moisture. Therefore, cables with solid polyethylene insulation and thick external insulation should be used in humid environment.
The shielding layer must be a copper wire editing layer covering more than 95%.
Installation skills
Do not overstretch or bend the cable.
Avoid cable contact with heating pipes and other heat sources. Even if the heat is insufficient to cause obvious damage to the cable, the transmission characteristics will be affected.
When cables must be continuously bent, special cables (such as scanners or horizontal tilt heads) should be used. The core wire of the cable shall be multi-strand glued wire.
Use only crimp BNC connectors.
2. Control line
At present, most of the domestic pan-tilt and high-speed spherical cameras on the market support RS485 transmission mode, and the requirements for cable specifications are not strict. Generally speaking, shielded twisted pair can be used, and RVVP 2× 1.0 is the majority. Some imported high-end high-speed spherical cameras have higher requirements for cables, and most of them design the control line and the power line together. Some high-speed spherical cameras also consider the grounding line together, so they need a 5-core shielded control line. In the engineering example, American Belden 8723(4-core shielded wire) is selected as the control cable, and the power cord does not need to be considered separately.
3. Power cord
Most fixed cameras in the market use DC 12V power supply (DC 12), high-speed spherical cameras use 24V AC power supply (AC24), and pan/tilt also use 24V AC power supply, so the power supply is low. Generally, two-core power cord, RVV 2× 1.0, can be used. Of course, many cameras are compatible with DC 12 and AC24, and some cameras are directly connected to the AC 220V power supply. If the power supply is 220V, the power cord should be separated from other cables with a distance of not less than 30cm. This must be noted.
3.3 back-end equipment
3.3. 1 image processing system
In a TV monitoring system composed of multiple cameras, a video switcher is usually used to display multiple images on one monitor in turn. But sometimes, in order to let the monitoring personnel see all the monitoring points at the same time, they often use a multi-picture splitter to display multiple pictures on one monitor at the same time. When multiple multi-picture splitters are used, multiple pictures transmitted by all cameras can be displayed simultaneously with the same number of monitors as the multi-picture splitters. This not only reduces the number of monitoring personnel, but also enables the monitoring personnel to see the situation of each part at a glance. Commonly used picture splitters include four pictures, nine pictures and sixteen pictures.
The basic working principle of the picture splitter: By means of image compression and digital processing, several pictures are compressed on the screen of a monitor in the same proportion. Some also have built-in sequence switcher function, which can output and display the full-screen images input by each camera in sequence and interval on the display (just like switching the host to switch the images in sequence), and can be recorded by the video recorder in the above sequence and interval. This interval is usually adjustable.
Main performance:
Color/black-and-white image splitter for fully compressed image and digital processing;
Video input of four channels (or nine or sixteen channels) and loop output of four channels (or nine or sixteen channels);
Built-in timing switch, adjustable time, independent switch output. According to the camera number, the full-screen images are displayed in turn, and the display time of sensitive road images can be optimized and programmed by users themselves;
High resolution and real-time update rate. The picture index is 5 12×5 12 pixels, and the update rate is 25-30 fields/second;
During video playback, you can zoom from 1/4 (or 1/9,116) to full screen (back to real-time full screen).
Compatible with standard SUPER-VHS video recorder (some also have S-VHS interface);
With alarm input/output interface, it can be connected with alarm system. When giving an alarm, you can call a full-screen screen to generate an alarm output signal and start a video recorder or other related equipment. That is to say, when the alarm signal is generated, the scene in the area related to the alarm will be displayed in full screen and can be recorded automatically. Users can set their own alarm and video duration. The number of alarm input interfaces is the same as that of screen input;
Eight-character camera name. Users can write their own names for each camera, with a maximum of 8 characters;
Alarm picture superposition and video signal loss index. This function can facilitate users to quickly check the reasons for loss;
Set the on-screen menu programming/calling. Simple programming, convenient operation and friendly man-machine interface; and
Electronic safety lock. Users can set their own passwords, and only allowed operators can operate the system.
Image processor plays a very important role in the back end of closed-circuit monitoring system;
Generally, a picture processor has a main port (such as 2 1 ") connected to a large display and a fixed-point monitoring port (such as 14") connected to a small display. Most picture processors have loop-through function, which can output all input signals through loop-through, which is convenient for single channel monitoring and video recording respectively; The picture processor also has the function of motion detection and alarm linkage, which is actually a small matrix. It is precisely because of these advantages that a picture processor is needed where TV wall monitoring is needed, as shown in Figure 1 and Figure 2.
In the back-end video recording system using the matrix, the matrix can only output signals, but can't monitor (only display 1 channel through a third-party computer) and record. The output port can't be connected with the monitor and video recorder at the same time, and only one of them can be selected. Even if the video distributor can connect video recorders and monitors at the same time, the number is very large and uneconomical, so connecting one or more picture processors at the output end of the matrix can effectively deal with this problem.
In the system using hard disk video recording, the human eye can't monitor more than three monitors at the same time in a short distance, so the monitoring function can only be realized through the TV wall, while the general hard disk video recorder does not have the function of directly connecting the monitors, so it needs a picture processor, and then the monitoring function can be realized through the picture processor and the monitor.
3.3.2 hard disk video recording system
The basic function of hard disk video recorder is to convert analog audio and video signals into JPGE MPEG digital signals and store them on hard disk (HDD), providing functions corresponding to recording, playing and managing programs.
Its outstanding features are reflected in the following aspects:
The digital high-fidelity storage of analog programs is realized, and the analog audio and video programs widely disseminated and collected by individuals can be recorded and stored in an advanced digital way, recorded once and played repeatedly, and the quality will not decrease;
Integrated input and output interface: provide antenna/TV cable, AV terminal, S terminal input interface, AV terminal and S terminal output interface. Can record almost all TV programs and signals output by other players and cameras, and can be easily connected with other audio-visual equipment;
Multiple optional image recording levels: For the same program source, three image quality recording levels are provided: high, medium and low. When the highest level is selected, the recorded image quality is close to DVD.
Large-capacity long-term program storage, strong scalability, users can choose 20GB, 40GB or more hard disks for program storage;
It has advanced time-shift function: when the TV program must be interrupted, the user only needs to press the time-shift key, and the program from the interruption time will be automatically saved, and the user can continue to watch the program from the interrupted position after handling the transaction without any sense of pause;
Perfect reservation recording/playing program function: users can freely set the start time and duration of recording/playing programs. By editing and combining the reserved programs, we can systematically record various intermittent TV programs, including TV dramas;
Powerful network information home appliance center: users can use DVR-tailored web browser through network communication interface, and be equipped with corresponding network resources to enjoy rich online information;
Provide convenient management methods for recorded programs: users can sort and classify recorded programs according to recording time and program type, and set bookmarks at their favorite positions at will; and
Because of the fast and random storage of hard disk, you can enjoy recorded and recorded programs in a more flexible way than the current DVD player, with smoother images at fast speed and higher detail resolution at slow speed.
It is precisely because of these outstanding performances of hard disk video recorders that more and more people are replacing the traditional ways to record and display videos. According to the author's experience, at present, the closed-circuit monitoring system of residential areas and buildings mostly adopts hard disk video recorders, which can be conveniently displayed, recorded and controlled remotely through local area networks and even the Internet. It is very convenient to build multiple monitoring centers in residential areas or buildings to meet the actual needs.
Because there are about 100 cameras in the general monitoring system of residential areas and buildings, generally 6-9 16 hard disk video recorders are used. However, in view of the fact that not all monitors are used to display images, but also many operation buttons and menus, and the images displayed by the monitors are very small, only a close distance can have a good monitoring effect; At the same time, people's naked eyes can't monitor more than three monitors at the same time, even if they can see, they can't monitor all the pictures at the same time. Therefore, the closed-circuit monitoring system of hard disk video recording is generally used, and most of them use image processors to connect to the monitoring wall through ring communication, and the effect is good.
.3.3 matrix
Matrix is a powerful system device for video switching and control. Generally, it is a modular microcomputer with high-density matrix design, which can connect up to thousands of cameras and hundreds of monitors.
General matrix system has the following characteristics:
Pre-assembly system;
Menu comprehensive setting;
Keyboard password input;
Priority operation;
The system can be divided;
Parallel/packet switching;
Universal patrol/display sequence;
Automatically call patrol sequence and contact fortification table;
Screen display (camera number and title, adjustable date/time format, monitor number and its shape);
The system can be graded and multi-controlled: camera field of view control: control constant speed or variable speed pan/tilt;
Automatic alarm telephone;
Internal video loss detection: synchronous detection;
Programmable alarm contact table;
Five different alarm display modes;
Three methods to eliminate alarm state;
Alarm status output;
Backup battery protection for all programming data; and
8 RS-232 communication ports.