UFC 4-021-02NF
27 September 2006
change 1, 23 October 2006
4-2
DIGITAL VIDEO RECORDER (DVR)
4-2.1
In current CCTV systems, the digital video recorder (DVR) has become the
"heart" of the CCTV system. The DVR is used principally for the download of camera
images onto a hard-drive for recording and storage of historical information. Older
systems used VHS tapes, but are largely phased out. DVRs currently have memory
storage capability of 80 gigabytes to 240 gigabytes with options to expand using
additional hardware to increase storage. Most DVRs are provided with self-contained
CD burners for archiving or removal of stored data. Most specifications call out for a
CCTV system to be able to retain 30 days of camera images. The amount of storage
required for 30 days is dependent on a number of factors to include: number of
cameras, compression ratio, resolution, and frame rate. This subject of storage space
as it relates to the above factors is developed in additional detail later in this chapter.
4-3
SYSTEM DISPLAYS
4-3.1
Display Technologies. ESS displays for CCTV images make use of three
general technologies: cathode ray tube (CRT), liquid crystal display (LCD), and plasma
display units. LCD and plasma display can be grouped as large format display units. A
general overview on each technology follows:
4-3.2
CRT. CRT displays are an older technology and have been used in the
security industry for a long time. A CRT works by moving an electron beam back and
forth across the back of the display screen. Each time the beam makes a pass across
the screen, it lights up phosphor dots on the inside of the glass tube, thereby
illuminating the active portions of the screen. By drawing many such lines from the top
to the bottom of the screen, it creates an entire screen full of images. Since individual
phosphors are illuminated, the CRT technology offers a high-resolution image. There
was a historic problem of a static image being "burned in" permanently on the CRT
screen. Most current CRT manufacturers provide a "screen saver" image or feature to
avoid this problem and extend the life of the monitor. The ESS designer should specify
or verify that a screen saver feature is available for CRT displays. With a long term
pedigree of security applications, security CCTV vendors offer a variety of standard
CCTV monitor display sizes to include: 9, 10, 12, 14,15, 17, 19, 20, and 21 inch
displays. Note that displays are described in terms of their diagonal dimension as
shown in Figure 4-2. Since there has been a strong history of using CRT displays in
security projects, manufacturing economies of scale have resulted in commensurate
favorable COTS prices and inventory availability. While initially more cost effective as a
display component, CRTs take up desk space, could require a custom built console,
consume more power, and generate more heat.
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