Characteristics of means of visual control. Scheme, description

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Characteristics of means of visual control. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Security and safety. Audio and video surveillance

Main technical characteristics of television cameras

1. Resolution depending on the number of elements of the CCD matrix.

2. Sensitivity - the ability of the camera to work efficiently in conditions of minimal illumination (illuminance is measured in lux).

3. Signal-to-noise ratio, measured in decibels. For high-class equipment, this ratio is 58 dB, and for ordinary equipment - no higher than 40 dB. Possible voltage fluctuations in the network can be negatively perceived by some cameras, especially color cameras, therefore, in order to avoid such a nuisance, it is better to install a special power supply.

Lenses

Focal length as the main characteristic of the lens can be fixed or variable. It affects the field or angle of view of the lens.

Characteristics of means of visual control

When choosing a lens, it must be taken into account that they are calculated on a CCD-crystal of a certain size. If this condition is not met, the image will be distorted. It should be noted that many foreign-made cameras have a lens with a standard C-mount thread (diameter 25 mm).

Protective cases

Used outdoors. At low temperatures, they can be equipped with heaters. In our climatic conditions, as a rule, it is impossible to use imported heaters, which are characterized by increased frost sensitivity.

Guidance devices

Pointing devices are used for TV cameras with remote control. They make it possible to rotate the camera in the horizontal plane by 175°, and in the vertical plane by 90°.

Monitors

Monitors are available in color and black and white. The diagonal screen size can be 7, 9, 12, 15, 21 inches or 17, 22, 30, 36, 53 cm, respectively. The resolution can be from 240 to 1000 lines in the center of the screen. Some monitors can connect multiple cameras. The choice of the necessary channel is made through the switch.

Switches

Designed to connect multiple cameras to one monitor. The number of channels can be from 4 to 16, and when using several switching units, their number can reach 64. Cameras are switched manually or automatically.

Motion detectors

If there are more than 4 cameras, then the attention of the operator and the effectiveness of surveillance are reduced. When protecting large objects - such as a bank or an enterprise - it is necessary to install a large number of cameras, and with them the installation of motion detectors that will attract the operator's attention if any movement occurs in the camera's field of view.

Motion detectors process the image received from the cameras and, if necessary, can turn on the video recorder to record the image or give an alarm if the appearance of the object has changed. In this case, the image from the camera is distributed to the zones and the sensitivity of the reaction of the motion sensor is set. For example, it is configured in such a way that it does not react to small birds and animals when installed outdoors. The detector has a built-in LED alarm indicator and a loudspeaker. There is also an "alarm" output for connecting an external audio amplifier.

Specialized VCRs

Designed for long-term recording. When protecting an object, they are successfully used to record and document all ongoing events or only certain moments recorded on film. Recording is documented using a date/time generator.

To obtain black-and-white or color images of various sizes from a television signal, use video printers.

Important parameters of the VCR are the resolution when recording an image and the reliability of operation.

The high resolution recording capability captures fine details, and reliability is important due to the fact that such a VCR is capable of continuous operation for several years.

On the front panel under the cover are the controls. With their help, it is possible to set any mode of operation: recording, playback, reverse playback, freeze frame, fast rewinding of the tape in two directions, placement of time and date information anywhere on the screen, correction of time and date indicators.

Specialized VCRs operate in "start-stop" mode. Recording frames on videotape will depend on the recording time set.

Connecting a specialized video recorder to the general security system of the facility makes it possible to program it to change the recording speed in case of an alarm. It is for this purpose that the VCR has a timer. When viewing recorded frames on the monitor, you can restore events to analyze the current situation.

TV signal transmission

A television cable is used as a connector between a video camera and a monitor, and its length can be several hundred meters. At a distance of several kilometers, video signal amplifiers must be used to transmit a television signal.

The transmission of a television signal can be carried out through telephone wires. To convert information, special blocks are installed at both ends of the wire (transmitting and receiving). In this case, the range is not limited. The image can be transmitted in analog or digital mode with different resolutions. The transmission time will depend on the specified requirements for image quality (it can be from tenths of a second to a minute). When using mobile and portable surveillance systems, radio communication is usually used, and then the cameras are connected to the transmitter. The image is received on a conventional TV. With a high power of the transmitting device, the range can reach several kilometers. When using stationary surveillance systems in the area of high electromagnetic interference, communication via fiber-optic lines is used.

Such a long cable allows you to increase the range up to hundreds of kilometers. Image transmission by laser beam is the most resistant to external interference, but it is difficult to implement and therefore rarely used.

Author: Korshevr N.G.

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