ABB Relion 670 Series Installation Manual page 77

1MRK 514 026-UUS F
1
EIA Standard RS-485 - Electrical Characteristics of Generators and Receivers for Balanced
Digital Multipoint Systems
2
RS-485 differential bipolar signaling
2.1
Two differential signal levels are defined:
2.2
The RS485 circuit shall be isolated from ground by:
Three isolation options exist:
2.3
2.3.1
2.3.2
The termination network below required at each end of each Bus Ph-segment.
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670 series
Installation manual
Normative references
Transmission method
Differential signal levels
A+ =line A positive with respect to line B
A- =line A negative with respect to line B
Galvanic isolation
Riso ≥ 10 MW
Ciso ≤ 10 pF
a) The entire node electronics can be galvanically isolated
b) The bus interface circuit can be isolated form the rest of node electronics by
optoisolators, transformer coupling or otherwise.
c) The RS485 chip can include built-in isolation
Bus excitation and signal conveyance
Requirements
a) The RS485 specification requires the Signal A and Signal B wires.
b) Each node also requires (5 V) Excitation of the RS485 termination network.
c) Vim - the common mode voltage between any pair of RS485 chips may not exceed
10 V.
d) A physical ground connection between all RS485 circuits will reduce noise.
Bus segment termination network
Section 6
Connecting
71