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In addition to the above discussion, for the camera part, in some cases, especially in the case of outdoor applications, for the dustproof, rainproof, high temperature resistant, corrosion resistant, etc., the camera and its lens are also Special protective covers should be installed, and even protective measures should be taken for the gimbal. These will also be discussed in the relevant sections that follow.
The transmission part <br> The transmission part is the image signal path of the system. In general, the transmission part refers to the transmission of image signals. However, in some systems, in addition to images, sound signals are transmitted. At the same time, because the control center needs to control the camera, the lens, the pan/tilt, the shield, etc. through the console, the transmission system also includes control. The transmission of signals, so the transmission part we are talking about here usually refers to the sum of the transmission systems formed by all the signals to be transmitted.
As mentioned before, the main transmission content of the transmission part is an image signal. Therefore, it is very important to focus on the transmission of image signals and related issues in transmission. For the transmission of image signals, the key requirement is that after the image signal passes through the transmission system, no obvious noise or distortion is generated (the chrominance signal and the luminance signal do not produce significant distortion), and the original image signal (image signal output from the camera) is guaranteed. The clarity and gray level of the ) are not significantly reduced and so on. This requires the transmission system to have good performance in terms of attenuation, introduction of noise, amplitude-frequency characteristics, and phase-frequency characteristics.
In terms of transmission mode, most of the current TV monitoring systems use video baseband transmission. If the camera is far away from the control center, there are also RF transmission methods or fiber transmission methods. For these different transmission methods, the transmission components and transmission lines used are quite different.
Control Section <br> The control section is the "heart" and "brain" of the entire system and is the command center for the function of the entire system. The control part consists mainly of the main console (some systems also have a sub-console). The main functions in the main console are: video signal amplification and distribution, image signal correction and compensation, image signal switching, image signal (or sound signal) recording, camera and its accessories (such as lens, pan/tilt, Control of the protective cover, etc. (Remote Control), etc. Among the above-mentioned parts, the most important influence on image quality is the three parts of amplification and distribution, correction and compensation, and switching of image signals. In some cases where the camera is close to the control center or the overall system requirements are not high, there is often no correction and compensation part in the total console. However, correction and compensation are very important for some distances or for transmission requirements. Because the image signal is transmitted after transmission, its amplitude and frequency characteristics (because the different frequency components reach the total console, the attenuation is different, resulting in different amplitudes of different frequency components of the image signal, which is called amplitude-frequency characteristic), phase-frequency characteristics. (The phase shift generated by the image signal of different frequencies after passing through the transmission part is different, this is called phase-frequency characteristic). The requirement of the index cannot be absolutely guaranteed. Therefore, the amplitude and phase frequency of the transmitted image signal should be corrected on the console. With compensation. The corrected and compensated image signal is then distributed and amplified, enters the video switching section, and is sent to the monitor. Another important aspect of the main console is the ability to remotely control cameras, lenses, pan/tilts, shields, etc., to complete a comprehensive, detailed monitoring or tracking of the monitored location. The video recorder provided on the main console can record the image of the monitored location at any time for later reference or as an important basis. At present, some consoles are equipped with one or two "long-delay video recorders". This type of video recorder can record image signals of several days with a 60-minute long video Tape, which can be very important for some. The images of the monitored places are continuously recorded without having to use a large number of video tapes. There are also "multi-screen splitters" on the main console, such as four-picture, nine-picture, sixteen pictures and so on. That is to say, with this device, it is possible to simultaneously display the images of the monitored places sent by four, nine or sixteen cameras on one monitor, and record them with a conventional video recorder or long delay video recorder. . The settings of these functions are determined according to the requirements of the system and may not be used.
At present, the total console is produced in the control function, and the number of control cameras is often made into a building block. Can be combined as required. In addition, there is a character generator with time and address on the main console. Through this device, the year, month, day, hour, minute and second can be displayed, and the address and name of the monitored place are displayed. It can be recorded on the recorder, which makes it convenient for future reference.
The total console controls the camera and its auxiliary equipment (such as lens, pan/tilt, protective cover, etc.) in a bus mode. The control signal is sent to the "terminal decoding box" near each camera, and the total control is performed on the terminal decoding box. The coded control signal sent from the station is solved, and becomes a command signal for controlling the action, and then controls various actions of the camera and its auxiliary equipment (such as zooming of the lens, rotation of the pan/tilt, etc.). In the case that some cameras are close to the control center, in order to save money, the command signal that directly sends out the control action by the console can be used, that is, the "on, off" signal. In short, according to the situation and requirements of the system composition, comprehensive consideration can be made to complete the design requirements or ordering requirements for the main console.
What are the structural characteristics of the TV monitoring system?
[ Huaqiang Security Network News ] Detailed TV monitoring system is mainly composed of two parts: front-end equipment and back-end equipment. The back-end equipment can be further divided into central control equipment and sub-control equipment. Front and back devices are available in a variety of ways, and the connections between them (also known as transmission systems) can be achieved in a variety of ways, including cable, fiber, or microwave. The television monitoring system consists of four parts: a camera part (sometimes a microphone), a transmission part, a control part, and a display and recording part. In each section, more specific equipment or components are included. Camera section <br> The camera section is the front edge of the TV surveillance system and is the "eye" of the entire system. It is placed at a location on the monitored site so that its field of view can cover the entire monitored area. Sometimes, the area to be monitored is large. In order to save the number of cameras used, simplify the transmission system and control and display system, an electric (remote-controllable) variable focal length (magnification) lens can be added to the camera to enable the camera to The distance of observation is farther and clearer. Sometimes the camera is mounted on the electric pan/tilt. Through the control of the console, the pan/tilt can be used to drive the camera to rotate horizontally and vertically, so that the angle and area of ​​the camera can be covered. Big. In short, the camera, like the eyes of the entire system, turns the content it monitors into an image signal that is transmitted to the monitor on the control center. Since the camera portion is the foremost end of the system, and the situation of the monitored site is transmitted from the image signal to the monitor of the control center, the camera portion is the original signal source of the system from the entire system. Therefore, the quality of the camera section and the quality of the image signal it produces will affect the quality of the overall system. From the perspective of system noise calculation theory, the biggest factor affecting system noise is the signal-to-noise ratio of the first-stage output (here, the image signal output of the camera) in the system. Therefore, it is crucial to carefully select and process the camera section. If the image signal output by the camera passes through the transmission part and the control part and reaches the monitor, the signal-to-noise ratio of the image signal reaching the monitor will decrease, which is due to the introduction of the line, amplifier, switcher, etc. of the transmission and control part. The reason for the noise.