AGI Security SYS-HC0451 HDCVI DVR User Manual - Manual (Page 280)

HDCVI Standalone DVR User’s Manual
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 Signal lightning arrester: This device is mainly used in the PC network,
communication system. The connection type is serial connection. Once you
connected the signal lightning arrestor with the signal port, it can cut the channel of
the thunderstorm to the device, and on the other hand, it can discharge the current to
the ground to guarantee the device proper work. The signal lightning arrester has
many specifications, and widely used in many devices such as telephone, network,
analog communication, digital communication, cable TV and satellite antenna. For all
the input port, especially those from the outdoor, you need to install the signal
lightning arrester.
 Antenna feed cable lightning arrester: It is suitable for antenna system of the
transmitter or the device system to receive the wireless signal. It uses the serial
connection too.
Please note, when you select the lighting arrester, please pay attention to the port type
and the earthing reliability. In some important environment, you need to use special
shielded cable. Do not parallel connect the thunder proof ground cable with the ground
cable of the lightning rod. Please make sure they are far enough and grounded
respectively.
2. The earthing modes
We all know the earthing is the most complicated technology in the electromagnetism
compatibility design since there is no systematic theory or module. The earthing has many
modes, but the selection depends on the system structure and performance. The
following are some successfully experience from our past work.
One-point ground: In the following figure you can see there is a one-point ground. This
connection provides common port to allow signal to be transmitted in many circuits. If
there is no common port, the error signal transmission occurred. In the one-point ground
mode, each circuit is just grounded only and they are connected at the same port. Since
there is only one common port, there is no circuit and so, there is no interference.
Multiple-point ground: In the following figure, you can see the internal circuit uses the
chassis as the common point. While at the same time, all devices chassis use the
earthing as the common port. In this connection, the ground structure can provide the
lower ground resistance because when there are multiple-point grounds; each ground
cable is as short as possible. And the parallel cable connection can reduce the total