IC Realtime Combo Series: 8 Channel DVR with built-in 19 LCD monitor - Manual (Page 139)

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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
z The monitor system shall have sound thunder proof earthing to guarantee personnel safety
and device safety.
z The monitor system working ground resistance shall be less than 1Ω.
z The thunder proof ground shall adopt the special ground cable from the monitor control room
to the ground object. The ground cable adopts copper insulation cable or wire and its ground
section shall be more than 20mm2.
z The ground cable of the monitor system can not short circuit or mixed connected with the
strong alternative current cable.
z For all the ground cables from the control room to the monitor system or ground cable of
other monitor devices, please use the copper resistance soft cable and its section shall be
more than 4mm2.