Installation Manual

RS-485 Cable 14
RS-485 Cable
General
RS-485 industrial buses are half-duplex communication buses whose characteristic impedance
is 120Ω. Its maximum load is 32 payloads (including drivers and receivers).
RS-485 Transmission Distance
When using 0.56 mm (24AWG) twisted pair, depending on different baud rates, the maximum
theoretical transmission distances are listed. See Appendix table 2-1.
Appendix table 2-1 Theoretical maximum transmission distance
Baud rate
Maximum transmission distance
2400 bps 1800 m
4800 bps
1200 m
9600 bps 800 m
The maximum transmission distance might be reduced in the following conditions; otherwise,
maximum transmission distance will be increased.
 When thinner communication cables are used;
 The camera is used in places with intense electromagnetic interference;
 Too many devices are connected to the RS-485 cable.
Frequently Occurred Problems
Customers tend to connect devices as the way displayed in Appendix figure 2-1. In this
condition, the terminal resistance must be connected to the two devices whose cable length is
the largest among all the devices (in Appendix figure 2-1, cable length between 1# and 15# is
the largest). However, this connection manner dose not comply with the RS-485 industrial bus
standard. As a result, problems like signal reflection and anti-interference capability reduction
might occur. Due to the above mentioned problems, the camera can be out of control.