CCTV is the abbreviation of Closed Circuit Television, which means closed circuit television system. It uses electrical principles to convert the image light energy captured through the optical lens into electrical energy through the chip (CCD) or camera tube (tube) in the camera, and then transmits it to the monitor through the cable and some auxiliary equipment with different purposes , So that the electrical energy returned to the light can be displayed on the screen.
In most modern systems, except for special applications, CCD cameras are used. This trend will become more common in the future. The so-called CCD (charge coupled device) is a camera device. This device can turn light into electric charge, and can store and transfer the electric charge, and can take out the stored electric charge to change the voltage.
â— Compared with CCD camera and camera tube camera, it has the following advantages:
(1) Small size and light weight.
(2) Low afterimage.
(3) The magnetic field will not affect the screen.
(4) Anti-vibration and anti-impact.
(5) Long life.
â–¼ The CCD used by CCD size cameras can be divided into 2/3 ", 1/2", 1/3 "and other size categories. As the image surface becomes smaller, the number of pixels and sensitivity (sensiTIvity) decrease accordingly. To solve this problem, in order to save costs, manufacturers often use 1/3 "CCD.
â–¼ Power
(1) AC mains
(2) 24V AC power supply (24V AC) This type of camera needs an additional 24V AC adapter.
(3) One cable The DC power of this kind of camera comes from coaxial cable (need to install a controller), this cable is used for video signal output.
â–¼ Resolution (resoluTIon)
Usually refers to horizontal resolution, unless "vertical" is specified.
(1) Horizontal resolution (horizontal resoluTIon) The number is obtained by multiplying the maximum number of obvious vertical interactive black and white lines by 0.75.
It is generally determined by the number of pixels of the CCD and the electronic characteristics of the camera.
(2) The vertical resolution (verTIcal resolusion) The number is derived from the maximum number of horizontally alternating black and white lines.
Generally obtained by the number of scanning lines and scanning method.
â–¼ Black and white / color When monitoring the position or movement of a scene, it is recommended to use a black and white camera. The color camera is suitable for real-time monitoring of scene details. Generally, black-and-white cameras are more sensitive than color cameras, so black-and-white cameras are suitable for areas with insufficient light or where lighting equipment cannot be installed at night. â–¼ Illumination (illumination) Select the camera according to the brightness of the installation site. If the brightness of the location exceeds the minimum object brightness by more than 10 times, the picture must be clear.
â– Synchronization system (synchronization system)
When synchronizing the transmitter and receiver, the signal synchronization must be completed. The horizontal synchronization signal controls horizontal scanning, and the vertical synchronization signal controls vertical scanning.
The synchronization system is divided into the following four types:
â–¼ Internal synchronization (internal synchronization) completes the operation by the synchronization signal of the camera's internal synchronization signal generating circuit.
â–¼ external synchronization (external synchronization) by an external synchronization signal generator, the synchronization signal is distributed to the external synchronization input of the camera to complete the synchronization.
â–¼ Power (line-lock) synchronization (power (line-lock) synchronization) uses the camera's AC power cycle to complete vertical drive (VD) synchronization.
â– Function â–¼ Electronic shutter (electronic shutter) The charge accumulation time of solid-state imaging elements, which controls the exposure time according to the variability of electrons. This feature allows the camera to capture fast-moving objects. â–¼ White balance (white balance) is a function for color cameras to adjust color reproduction to match the light source. (1) Automatic white balance (AWB) Automatically store the preset white balance of the object. Suitable for fixed light source. (2) Automatic tracking white balance (ATW) can often track and detect the color temperature change of an object, and automatically adjust the white balance. It is suitable for places where the light source changes regularly, such as places where fluorescent lights are used to replace natural light at night. â–¼ Iris (1) Manual Iris When the brightness changes, the iris needs to be adjusted manually, so it is suitable for places where the brightness does not change. (2) The auto iris can be automatically adjusted when the brightness is changed, so it is suitable for the place where the light source will change every day. â— Video input type lens has a circuit to detect the light entering the lens. â— There is no photometric detection circuit in the DC input type lens. On the contrary, some cameras have a photometric detection circuit inside, so the lens itself is cheaper.
â– Lens selection Lens selection is as important as camera selection. Choose the type of lens according to the size of the object to be observed (observation range), the brightness change of the object and the size of the CCD during monitoring. Generally there are the following selection conditions: â–¼ focal length (focal length) must pay attention to the distance between the object and the camera and the observation size. â–¼ Lens types can be divided into wide angle, telephoto, standard, motorized, pin-hole, and prism. â–¼ The mount is divided into C mount and CS mount. â–¼ Aperture ratio (aperture ratio) Aperture ratio can indicate the brightness of the lens, that is, the F-stop number we have seen in the specifications. This ratio is the ratio of the aperture diameter (D) of the lens to the focal length (f) of the lens; the smaller the value, the larger the aperture and the more light transmitted. F = f / D â– The choice of monitor is based on black and white or color and screen size. â– Peripheral equipment must be installed with many peripheral equipment such as turntable, protective cover, platform jumper, or even matrix controller due to the requirements of installation location environment and comprehensive and convenient monitoring operation.
â— Brightness required by surveillance camera â– The minimum subject illumination is within the recognizable range of the camera. The subject needs a certain brightness before the camera can output the image of the subject. Body illuminance>. The brightness required for each type of camera to capture images is different, so brightness becomes the standard for camera sensitivity.
<Minimum illuminance of the subject> will vary with different conditions such as the F value (maximum aperture ratio) of the lens, the color temperature of the light source, the reflectance of the subject, and the maximum gain.
Lens F-number (Maximum aperture ratio) Numerical brightness of lens Numeral color temperature of light source is not identifiable by human naked eye. Reflectance of the subject The ratio of the incident light to the reflected light of the subject The maximum gain of the camera sensitivity Maximum value â– Brightness of lens (F value)
The F value refers to the brightness of the lens. The <1.2> of the <maximum aperture ratio 1: 1.2> shown in the lens specifications is the F value. The smaller the F value, the higher the brightness of the lens. Each time the F value is reduced by one step, the brightness increases twice. The amount of light incident on the lens is proportional to the cross-sectional area of ​​the light beam [the effective aperture of the lens [D] squared], so the image brightness is inversely proportional to the square of the F value. It is estimated from this that each time the F value is reduced by one step, the brightness increases twice.
â– Conversion method of the minimum subject illuminance The minimum subject illuminance recorded in the camera specifications is the value measured using the F1.4 lens. In actual use, the minimum illuminance of the subject varies according to the F value of the combined lens.
When C-CC350 camera <minimum subject illumination: 3Lx (50IRE) (F1.4)> is equipped with CT-0312G (F1.2) lens, the converted minimum subject illumination is:
(3Lx) × (1.2 × 1.2) / (1.4 × 1.4) = 2.2Lx
When using a lens with higher brightness than F1.4 (aspheric lens, etc.), the minimum illumination of the subject also decreases. Even if it is a dark object, the camera can clearly output the image of the subject.
CCTV CCTV monitoring system equipment introduction 2
The CCTV monitoring system is to set up front-end cameras in the main channels, important public buildings and perimeters of the community, and transmit the images to the intelligent management center. The center monitors and records the entire community in real time, so that the center management personnel fully understand the dynamics of the community. At the same time, the multimedia control platform is used in conjunction with the perimeter anti-overpass alarm system and the residential indoor alarm system. When an alarm occurs, the central monitor will automatically pop up the screen of the area where the alarm occurred and record it.
The main purpose of the community CCTV monitoring system is to transmit the detected images of important observation points (mainly distributed in the main roads and entrances of the community, other key parts and other key areas) to the control room of the property management center It can remotely control the controlled camera point, and can record the on-site situation with time, place and other information content superimposed in time when an emergency occurs, so that it can be analyzed and investigated during replay and serve as important evidence with legal effect. This not only improves the accuracy of the security personnel handling the police, but also provides strong evidence for the public security personnel to quickly solve the case.
The anti-theft alarm system in the perimeter of the community can also be linked with the closed-circuit television monitoring system. Once the alarm occurs, the image related to the alarm point will immediately appear on the image monitoring screen of the monitoring center, and the video will be automatically recorded in high density. The security personnel on duty can monitor all the conditions in the alarm area through the gimbal and zoom lens, so as to send out the alarm information in time.
The basic structure of the TV monitoring system system composition: camera transmission control display (recording)
System functions:
The camera part is installed at the scene. It includes a camera, lens, protective cover, bracket and motorized gimbal. Its task is to take a picture of the subject and convert it into an electrical signal.
The task of the transmission part is to transmit the electrical signals sent by the on-site camera to the control center. It generally includes cables, modulation and demodulation equipment, and line drive equipment.
The display and recording part converts the electrical signal transmitted from the scene into an image and displays it on the monitoring device. If necessary, it is recorded with a video recorder, so the main equipment it contains is a monitor and a video recorder.
The control part is responsible for the control of all equipment and the processing of image signals.
System size:
The number of cameras in a small TV monitoring system is generally less than 10. The number of cameras in a medium-sized TV monitoring system is generally in the range of 10 to 100. The monitoring system can set up several levels of control keyboards and corresponding monitors according to management needs. Large-scale TV monitoring systems generally have more than 100 cameras. It is a combination of medium-sized monitoring systems. The system is equipped with a main controller and sub-controller for monitoring and management.
Television monitoring system equipment camera transmission cable control equipment display terminal recorder
1. The cameras are classified as follows according to the camera's performance, functions, usage environment, structure color, etc.
(1) Classification according to performance â‘ Ordinary cameras: work in normal indoor lighting or outdoor daytime.
â‘¡Dark light camera: work in an environment without normal lighting indoors.
â‘¢ Low-light camera: work under outdoor moonlight or starlight.
â‘£Infrared camera: work in indoor and outdoor places without lighting.
2) Classification by function â‘ Video alarm camera: if the target is moving within the monitoring range, it can send an alarm signal to the controller.
â‘¡Wide-angle camera: used to monitor a wide range of places.
â‘¢Pinhole vibration camera: used to covertly monitor the local area.
(3) Classification according to the use environment â‘ Indoor camera: There is no protective device outside the camera, and the use environment has requirements.
â‘¡ Outdoor camera: Install a protective cover outside the camera. There are cooling fan, sunshade, heater, wiper, etc. inside. Adapt to changes in outdoor temperature and humidity.
(4) Classification by structure composition â‘ Fixed camera: monitor fixed targets.
â‘¡Rotating type: with rotating pan / tilt camera, can do up, down, left, right, rotation.
③Spherical camera: 360 ° horizontal rotation, 90 ° vertical rotation, preset rotation position.
â‘£Semi-spherical camera: Ceiling mounted, can rotate up, down, left and right.
(5) Classification by image color â‘ Black and white cameras: high sensitivity and sharpness, but cannot display image color.
â‘¡Color camera: It can display the image color, and the sensitivity and clarity are lower than the black and white camera under the same conditions.
2. Transmission cable
(1) The coaxial cable is used to transmit short-distance video signals. When transmitting black and white video signals, when the unevenness at 5.5MHz is greater than 6dB, an equalization amplifier needs to be added.
(2) When the optical cable needs to transmit video and control signals over a long distance, the optical cable is used for transmission. There is no need to add a repeater within a transmission distance of tens of kilometers.
3. Control device (1) The video switcher has functions such as screen switching output and fixed screen output.
(2) Multi-screen split controller has the functions of sequential switching, picture-in-picture, multi-screen output display playback image, interconnected camera alarm display, touch pause screen, alarm record playback, time, date, title display and other functions.
(3) Matrix switching system ①Partition control function: authorize keyboard, monitor and camera. • Keyboard to monitor: Set which keyboards can control which monitors. • Monitor to camera partition: set which monitors can display which camera images. • Keyboard to camera partition: set which keyboard can call which camera images. • Keyboard to camera control partition: set which keyboard can control which camera actions.
â‘¡Group synchronization switching. All or part of the cameras in the system are divided into several groups, and each group of cameras can be switched to a group of monitors synchronously.
â‘¢ Switch arbitrarily. Refers to any combination of cameras, and the display time of any camera picture is independently adjustable. The picture of the same camera can appear multiple times in the same group of switches, and any group of switches can be transferred to any monitor at any time.
â‘£Automatically start at any switching timing. Any group of universal switches can be programmed to be executed automatically and regularly on any monitor.
⑤Alarm switch automatically. With alarm signal input interface and output interface, when the system receives the alarm signal, it will automatically switch to the alarm screen and start the recorder device, and output the alarm status to the designated monitor.
â‘¥Automatic output system for alarm status. The alarm status can be automatically output to the printer and monitor.
⑦Alarm processing. Alarm display: • Time sequence display mode: time sequence display multiple alarm points, the display time of each point is independently adjustable. • Fixed display mode: display the first alarm point until it is confirmed. • Dual monitor display mode: multiple alarm points are grouped and displayed on a group of monitors. • Alarm reset: manual reset, automatic reset after delay, automatic reset when the alarm signal disappears.
⑧Multiple control keyboard input interface.
⑨RS-485 output interface and control output interface.
(4) Other controls â‘ Control of electric zoom lens. A zoom lens is a lens that can continuously adjust the focal length when the imaging surface is fixed. It can be used in combination with an electric pan-tilt head to monitor a very wide range, and it can also close-up any part of the range. The control of it is three functions of zoom, focus and iris, each of which has two kinds of control: length, distance, or opening and closing, a total of six kinds of control.
â‘¡ PTZ control. The electric pan-tilt head needs four types of control: left, right and up and down. Some pan-tilt heads also have an automatic patrol function, so the automatic control of the pan-tilt head should be added.
â‘¢ Switch the control of the device. The control of switching generally requires synchronization with the control of the gimbal and the lens, that is, the device of which channel is controlled as soon as the image is switched to. The TV monitoring system also has many advanced controls. For example, some integrated cameras that package the gimbal, zoom lens and camera are equipped with an advanced servo system. The gimbal can have a high rotation speed and can also preset monitoring points and patrol paths. It can be automatically patrolled according to the set route. Once an alarm occurs, it can quickly point to the alarm point for fixed-point monitoring and recording. One camera can play the role of several cameras.
4. Display terminal and video recorder
(1) Display terminal (monitor) The video signal transmitted from the front-end camera to the terminal is reproduced as an image by the monitor. According to different functions, it can be divided into image monitor and TV monitor.
①Image monitor. Compared with TV receivers, it does not contain circuits such as high frequency tuning, intermediate frequency amplification, detection, and audio amplification. Its characteristics are: the video bandwidth can reach 7 ～ 8MHz, and the horizontal resolution can reach more than 500 ～ 600 lines. The size of the picture in the picture tube frame in the horizontal and vertical directions can be adjusted freely, so as to check all the pictures of the picture.
â‘¡ TV monitor. This monitor combines the functions of an image monitor and a television receiver. Its characteristics are: it can be used as a monitoring receiver of a video recorder, convert broadcast TV signals into video signals, and send it to the video recorder for recording while displaying on the screen. As an image display device when the video signal of the video recorder is played back. You can input video and audio signals directly from the camera for monitoring and monitoring, and send them to recording equipment for recording and recording at the same time.
(2) The working principle of the video recorder is to record the video and audio signals on the magnetic tape by magnetic information through the role of the magnetic head and the magnetic tape coated with strong magnetic material, and can restore the magnetic information on the magnetic tape to audio and video electric signal. Long-time video recorders are generally used in TV surveillance systems. In addition to recording and playback at standard speeds, they also have the following functions:
â‘ Images recorded at standard speed can be played back in slow speed or still image mode.
â‘¡Images recorded for a long time can be played back in quick or still mode.
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