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5.5
Transmission distances of RS485 Bus
The 0.56mm (AWG#24) twisted pair or higher grade wires are recommended for
data transmission cable
The maximum theoretical transmitting distances, for the AWG#24, are as follows:
Baud Rate
2400 Bps
4800 Bps
9600Bps
If user selects thinner cables, or installs the dome in an environment surrounded by
strong electromagnetic interference, or connects lots of equipment to the RS485
bus, the maximum transmitting distance will decrease. To increase the maximum
transmitting distance, do the opposite way, i.e. use thicker wire and keep the cable
away from the interference.
Connection and terminator resistor
The RS485 requires daisy-chain connection among the equipments. There must be
terminator resistors for impedance matching (typically 120 ohms, within the range
from 90 to 250 ohms). Terminators are to be located at both ends of each RS-485
net.
120O
1#
D
120£ [
1
Impedance setup for the speed dome
Vidia Srl – Via Vasanello 23, 00189 Roma – Tel +39 0630316333 Fax +39 0630350231 www.vidia.it
RS485 Network and Impedance
2#
A+
B-
A+
B-
#
2
Maximum Transmitting Distance
1800m
1200m
800m
3#
4#
3
. . . . .
120O
32#
. . . . .
. . . . .
120£ [
32
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