ABB REM 610 Technical Reference Manual page 105

1MRS 755537
Motor protection Relay
Technical Reference Manual
The RS-485 communication module follows the TIA/EIA-485 standard and is
intended to be used in a Daisy-chain bus wiring scheme with 2-wire, half-duplex,
multi-point communication. The maximum number of devices (nodes) connected to
the bus where REM 610 is being used is 32, and the maximum length of the bus is
1200 meters.
When connecting REM610 to the bus, a quality twisted pair shielded cable is to be
used. The conductors of the pair are connected to A and B. If signal ground is being
used for balancing potential differences between devices/nodes, a quality dual
twisted pair shielded cable is to be used. In this case, one pair is connected to A and
B, and one of the conductors of the other pair to signal ground. When connecting
one device to another, A is connected to A and B to B.
The cable shield is to be connected directly to ground (shield GND) in one point/
device of the bus. Other devices connected to the bus should have the cable shield
connected to ground via a capacitor (shield GND via capacitor).
Note!
Signal ground can only be used for balancing potential differences between devices/
nodes if all devices connected to the bus have isolated RS-485 interfaces.
The RS-485 communication module is provided with jumpers for setting bus
termination and fail-safe biasing. The bus is to be terminated at both ends, which can
be done by using the internal termination resistor on the communication module.
The termination resistor is selected by setting jumper X5 to the ON position. If the
internal termination resistor of 120 Ω is used, the impedance of the cable should be
the same.
The bus is to be biased at one end to ensure fail-safe operation, which can be done
using the pull-up and pull-down resistors on the communication module. The
pull-up and pull-down resistors are selected by setting jumpers X3 and X4 to the ON
position.
The jumpers have been set to no termination (X5 in the OFF position) and no biasing
(X3 and X4 in the OFF position) as default.
REM 610
105