Dahua Technology DHI-XVR5108HS-4K, Руководство пользователя

Страница: 308 / 318

User's Manual
300

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.
Appendix 7.2 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 point to allow signal to be transmitted in many circuits. If there is
no common point, the error signal transmission occurred. In the one-point ground mode, each
circuit is just grounded only and they are connected at the same point. Since there is only one
common point, there is no circuit and so, there is no interference.
One-point ground

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
point. 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 conductance of the ground conductor. In the high-
frequency circuit, you need to use the multiple-point ground mode and each cable needs to
connect to the ground. The length shall be less than the 1/20 of the signal wavelength.