Dahua HCVR5204A Series, Руководство пользователя, Страница: 263 / 268

254
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.
Mixed ground: The mix ground consists of the feature of the one-point ground and
multiple-point ground. For example, the power in the system needs to use the one-point
ground mode while the radio frequency signal requires the multiple-point ground. So,
you can use the following figure to earth. For the direct current (DC), the capacitance is
open circuit and the circuit is one-point ground. For the radio frequency signal, the
capacitance is conducive and the circuit adopts multiple-point ground.
When connecting devices of huge size (the device physical dimension and connection
cable is big comparing with the wave path of existed interference), then there are
possibility of interference when the current goes through the chassis and cable. In this
situation, the interference circuit path usually lies in the system ground circuit.
When considering the earthing, you need to think about two aspects: The first is the
system compatibility, and the other is the external interference coupling into the earth
circuit, which results in system error. For the external interference is not regular, it is not
easy to resolve.
3. Thunder proof ground method in the monitor system

The monitor system shall have sound thunder proof earthing to guarantee personnel
safety and device safety.

The monitor system working ground resistance shall be less than
1Ω.