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        Digital Video Recorder records video pictures digitally. DVR, Digital Video Recorder, records       video pictures digitally on a hard disk drive(HDD). This HDD, usually built-in, has capacity of 20 Gb, 30 Gb or 60Gb to store the records. You can program the picture resolution and recording time according to the application; real-time or time-lapse recording also available. Overwriting the oldest pictures is programmable. Event alarm recording that records, only when a movement is captured within the image frame, is easier to program and more reliable than the Time Lapse VCR's alarm recording function. You just assign dots over the screen where you want to detect the movement. As DVR records digitally, the image quality remains the same regardless of how many times the images are stored or rerecorded. And, you can select images quickly by using time/date or alarm search, or just browsing through.

2 Electronic Shutter

       Electronic Shutter, one of the major features of CCD camera, is not really a moving shutter, but a clever piece of signal processing.

Under low light conditions, the CCD is allowed to gather signal at the electronic shutter speed of full 1/60th of a second.

Under brighter lighting conditions, the video processing chip automatically responds by reading the CCD and then immediately "early purging" it, resulting in precise control over the video level. Even at a shutter speed of 1/100,000th of a second, the CCD camera is still delivering 60 images per second, but each image is gathered over a much shorter period of time. The end result is a fantastic picture, with no fading, no adjustments, and best of all, unbelievable reliability.


Closed Circuit Television
      It does not broadcast TV signals but transmits them over a closed circuit through electrically conducting cable or wireless transmitter and receiver.


4. CCD 
      Charge Coupled Device.
A video image sensor chip
      CCD (charge coupled device) consists of several hundred thousand individual picture elements (pixels) on a tiny 1/2", 1/3", or 1/4" chip. Each pixel responds to light falling on it by storing a tiny charge of electricity. The pixels are arranged on a precise grid, with vertical and horizontal transfer registers carrying the signals to the camera's video processing circuitry. This transfer of signals occurs sixty times per second. The 1/3" CCD chip is the most widely used sensor format these days; its size is 5.5mm (diagonal), 4.4mm (horizontal) and 3.3mm (vertical). The 1/4" sensor format, recently being used in color cameras, is 4mm (diagonal), 3.2mm (horizontal) and 2.4mm (vertical).


5. AC Adapter

       Alternating Current Adapter; when plugged to AC Power (usually 117VAC/60Hz in the United States) it produces 12VDC, 24VAC or others. "UL Listed" and "Regulated" recommended. It is also called Power Transformer.

      Most board cameras, mini cameras and about one third of the professional cameras work with 12V DC 100mA to 200mA for B/W cameras and 150mA to 300mA for color ones.

      About two thirds of the professional cameras work with 24VAC, 20VA to 40VA. The cameras usually have screw type connections and you don't need to worry about the polarity. This power is usually supplied with AC Adapter and you need to prepare separate power cable for the connection. Unlike 12VDC, this power can be transmitted to a long distance up to 450ft and is proper for the cameras that are to be installed out-door or when you don't have the power outlet near the camera.


6. TV System

1..CCIR/EIA is for B/W system

(1)CCIR is made the technical recommendation for the European 625 line standard for video signals.

(2)EIA is American standard for B/W camera system.

    2..PAL/NTSC is for color system.

      PAL is a color television system, which is used in Europe, Australia , parts of Africa and the Middle East . It has 625 horizontal scan lines and 25 frames per second. (Frame: A whole video image; is composed of two interlaced fields. A CCD chip produces 30 frames per second at NTSC system and 25 frames at PAL. )

     NTSC formulates standards for American color television system. NTSC system has 525 horizontal scan lines and 30 frames per second.


      The Radio Corporation of America; conveniently used to describe phono jack and plug, one of the audio/video connectors.

8. Resolution
      Expressed by TV lines or pixels, it indicates the quality level of video images.
<Camera Resolution>
      The industry of CCD video camera sensor uses pixels (picture elements) as its quality parameter. Medium resolution of B/W camera in EIA system is 510 horizontal pixels by 492 vertical pixels and is equivalent to 380 TV lines. High resolution is 768(H) x 492(V) pixels and equivalent to 570 TV lines. Color camera's medium resolution means 330TV lines and high resolution needs more than 460 TV lines.

<Monitor Resolution>
      The monitors in NTSC system have 525 vertical scanning lines regardless of their size. The horizontal 700 TV lines of B/W monitors represents medium level and more than 900 TV lines means high resolution in EIA system. The color monitor's horizontal resolution of 300 TV lines means medium quality and that of more than 450 TV lines means high resolution.

9. Infrared Light

      Invisible light beyong the 750 nanometers (red end of the visible lights)


Cathode Ray Tube

      The vacuum tube part of a monitor or television

11. BLC

      According to special area of measuring light and adjust the electrical shutter, the exposal value will be normal in the measuring area.





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