Konig SEC-CON22, Руководство пользователя, Страница: 15 / 18

15
●
Distance of RS485 bus transmission
While use the 0.56mm (24AWG) twisted cable as the communication, the farthest distance it can reach as
follow based on the different Baud rate:
Baud rate Farthest Distance
2400bps 1800M
4800bps 1200M
9600bps 800M
19200bps 600M
If user selects thinner cables, or installs the dome in an environment with strong electromagnetic
interference, or connects lots of equipment to the RS485 Bus, the maximum transmitting distance will
be decreased. To increase the maximum transmitting distance, do the contrary.
● Connection and termination resistance
The RS485 standards require a daisy-chain connection between the equipment. There must be termination
resistance with 120 impedance at both ends of the connection (refer to picture 4-1.1).Please refer to picture 4-1.2
for simple connection But “D” should not exceed 7m.
………..
1# 2# 3# 4# 32#
Picture 4-1.1
A+
…………
D B-
A+ B-
…………
1# 2# 3# 4# 32#
Picture 4-1.2
●Problems in practical use
In some circumstances user adopts a star configuration in practical connection. The termination
resistors must be connected to the two equipments that are father away from each other, such as
equipment1# and 15# (refer to picture 4-1.3). As the star configuration is not in conformity with the
requirements of RS485 standards, problems such as signal reflections, lower anti-interference
performance arise when the cables are long in the connection. The reliability of control signals are
decreased with the phenomena that the dome dose not responds to or just responds at intervals to the
controller, or dose continuous operation without stop.
In such circumstances the factory will recommends the usage of Rs485 distributor. The distributor
can change the star configuration connection to the mode of connection stipulated in the
120
Ω
120
Ω
120
Ω