One of the systems that are used today to control and monitor the living and working environment as well as to create more security and comfort is CCTV systems or CCTV systems. These systems are also referred to as video surveillance systems or sometimes CCTV equipment. Due to the settings that can be made on cameras and other equipment, these systems have good performance in different weather conditions and day and night. Some of the places where these systems are used are as follows:
Banks, offices, schools and universities, factories, department stores, department stores of expensive goods such as gold shops, supermarkets – on the roads and streets to control traffic – parking lots – public places such as airport lounges, railway stations and city trains, etc.
Therefore, the use of CCTV systems is growing day by day, and according to the technology of manufacturing its equipment, which is based on the electronics and computer industry,
The production of equipment for these systems is constantly evolving and progressing, and in this brief we have tried to provide the general principles and general facilities of these systems for the information and familiarity of dear students.
Principles of operation of CCTV systems The general principles of operation of CCTV systems are that first the images are prepared by the cameras and then transferred to the monitor or TV for display and playback.
There is also equipment and facilities for recording or changing the way of displaying on the monitor and simultaneously playing the images of the cameras on the monitor and the remote control of the cameras. Due to the possibilities available on CCTV recorders that are able to detect movement in the area under the supervision of the system and warn or be stimulated by special sensors and start recording video from the place. To control the entry and exit of people to a place And for controlling large areas by multiple cameras and simultaneously displaying their image and audio-visual monitoring from a distance via local area network (LAN) or telephone lines without the need for physical presence of the controller on site and in devices that could not be visually controlled by humans Or CCTV systems can be divided into the following types based on how the image captured by the camera is sent to the control center:
Systems that transmit the image by coaxial wire (coaxial cable). These systems are the least expensive type in terms of equipment cost, but in their implementation, there are wiring problems and the problem of image quality loss at long distances (more than 300 meters) and as a result, the transmission distance is limited. The following figure shows an example of these systems:
Example of a system that transmits images by coaxial wire (coaxial cable) Systems that transmit images wirelessly. The cost of implementing these systems is higher due to the use of antennas and radio transceiver equipment, but the problems of the previous type of systems up to Some of them have been fixed. In the following figure, in some parts of the system, wireless equipment is used:
CCTV systems can be designed and implemented as a combination of wireless and wired systems. Surveillance system equipment The following equipment is commonly used in CCTV systems:
Image display (TV or monitor)
Camera stand (Mount- Bracket- BASE)
Image Selector (Switcher)
We now turn to a detailed description of each of the above sections:
The cameras used in CCTV systems are made in different types and with different features and are commonly known as CCTV Cameras. The main function of the camera is to produce a video signal from a controlled location to send or display a monitor or TV.
Types of cameras
The types of cameras used in CCTV systems in terms of application and facilities are as follows:
* Pinhole cameras
These cameras shoot through a small aperture on the front of the camera on the lens. Because of their small size and the possibility of hiding them, they are mostly used as hidden cameras or for espionage purposes. These cameras are also available wirelessly. An example of this camera can be seen below:
* Mini cameras
They are small and inexpensive cameras, mostly in CCTV systems
Small are used. Most have fixed lenses and their image output is used. One
Examples of these cameras can be seen below::
* Industrial cameras:
In these cameras, features such as interchangeable lenses and the possibility of adjusting the lens and light aperture and
There are image quality adjustment keys. You can see the image of the industrial camera below:
Some industrial cameras have the ability to adjust the lens in terms of magnification (zoom) and image resolution (focus) by a controller, which are shown in some examples of this type of camera:
* Night vision cameras:
These cameras have an optical sensor (photocell) to detect ambient light, and when it gets dark, the LED lamps that emit infrared light emit infrared rays themselves, and also provide the camera with the ability to shoot at night. The following figure shows these two parts on the camera:
It is usually not possible to change the lens on these cameras, but it is possible to apply adjustments on the lens and image quality on some models. The building of these cameras is protected against the penetration of water, moisture and dust and they can be installed outdoors. These cameras are mounted on the ceiling and wall. In the following figure, you can see an example of these cameras:
* Fixed ceiling cameras (DOM) and fast (Speed Dom)
These cameras are mounted on the ceiling or on a hanging base. If they have a controllable base that allows the camera to move quickly in all directions 360 degrees, they are called fast ceilings. It is possible to adjust the lens in terms of distance and amount of ambient light in these cameras. Control of these cameras by the device The controller or recorder or using special software on the computer.
* Wireless cameras:
These cameras have a transmitter (TX) inside the camera and a separate receiver (RX) that can send the image without the need for wiring depending on the power of the transmitter in a certain range. The image below shows a type of these cameras with the receiver Gives:
Motion Detection Cameras (MAD)
These cameras are designed to start filming when moving in the environment. The following figure shows the two types of motion detection eyes with the camera that start when the camera moves and record the image to the recorder. The sender sends:
Other types of cameras also capture images in their internal memory. It is also possible to transfer the image from the camera with a mobile phone SIM card via MMS. An example of this type of camera can be seen below:
* Nested cameras:
These cameras are installed inside the front door of apartments, suites and private homes.
It should be noted that a camera may have several types of features, for example, both night vision and wireless or industrial camera features. Different parts of the camera
The camera consists of 4 main parts:
2- Image sensor
3- Electronic circuit
We will now describe the above sections:
1- Camera lens
In the camera, the passage of light into the camera and its features affect the image quality
This part includes the lens and the light passage valve and to this set
The so-called camera lens. Depending on the type of camera and the facilities required and the location
Installation Different lenses are used on the cameras. Lenses are available at focal lengths
2.5, 8.2, 3.5, 4, 6, 8, 12, 16, 25, 35, 50 and 75 mm are made. The greater the focal length of the lens, the greater its magnification. Telephoto lens
This lens shows distant objects closer and better, but instead offers a smaller viewing angle. Conversely, the smaller the focal length of the lens (Wide lens), the better the close-up images are.
Its viewing angle is wider. For example, the focal length of the human eye lens is 17 mm and its viewing angle is 30 degrees. While a lens with a focal length of 4 mm and a viewing angle of 62 degrees.
The IRIS is responsible for determining the amount of light passing through the lens into the camera.
In the dark, the aperture should be larger to allow more light to enter the camera
In bright environments, to prevent the image from turning white, the aperture should be reduced to allow less light to pass through.