ROHS EVC422, Manual

Page: 19 / 24

19
Addendum
- The system must be grounded with equal potentials. The earth
ground connection must satisfy the anti-interference and electrical
safety requirements and must not short circuit with the high voltage
electricity connection. When the system is grounded separately, the
resistance of the down conductor should be <4 Ohms and the
sectional area of the down conductor should be <25mm
2
.
2. RS485 bus basic knowledge
2.1 Characteristics of the RS485 Bus-
As specified by RS485 standards, the RS485 Bus consists of half
duplexed data transmission cables with characteristic impedance of
120 Ohms. The maximum load capacity is 256 unit loads (including
main controller and controlled equipment).
2.2 Transmission distances of RS485 Bus-
When the user selects the 0.56 (24AWG) twisted pair wires as the
data transmission cable, the maximum theoretical transmitting
distances areas follows:
Baud Rate Maximum Transmitting Distance
1200 Bps 2400 metres
2400Bps 1800 metres
4800Bps 1200 metres
9600Bps 800 metres
19200Bps 200 metres