ABB AC 800F Mounting And Installation Instructions Manual page 141

4
With RS422 transmission one pair of wires serves for differentially transmitting the
transmit data. A second wire pair transfers the receive data. As a result, the fieldbus
module can simultaneously transmit and receive data (full-duplex operation).
The GND connections are not needed when cabling the module in the field, they are
only used for measuring and testing in the commissioning phase. Please note that the
offset voltage between GND and the signal lines is less than ± 7 V. Observe the max.
permissible cable length of 1200 m. Fig. 4-50 shows how to cable fieldbus module
FI 820F with an RS422 device. Connect the signal wires to the device to be linked. If
you want to connect several slaves, follow the instructions for cabling via RS485. Note
that the bus must be terminated at the last node.
Fig. 4-50 Cabling FI 820F via RS422 interface on channel 0
Terminate the two signal pairs on the AC 800F side and on the device to be
connected. There are three possible terminations on the AC 800F side:
•
•
•
Only use one of the possible terminations. Using two terminations at
one bus end will cause communication problems.
Internal termination
External termination with internal supply
External termination with external supply
Cabling the AC 800F
4-75