Emerson 1420 Reference Manual

Reference Manual
00809-0200-4420, Rev HC
Appendix D: Redundancy
July 2015
75
Redundancy
D.4.4 Dual RS-485
A Dual RS-485 host connection support Modbus RTU protocol. When using this architecture,
connect the secondary Ethernet port on Gateway A directly to the secondary Ethernet port on
Gateway B. Then wire the RS-485 ports for both Gateways separately to dual serial cards at the
host system. See Figure D-6 Dual RS-485 Architecture.
Figure D-6. Dual RS-485 Architecture
Note
By default, only the active Gateway in a redundant system will respond to Modbus polling
requests. If simultaneous polling is desired, login to the Gateway web interface, navigate to
Setup>Modbus>Communications and set “Respond when running as redundant standby?” to
Yes. Only use this setting in a dual RS-485 architecture.
D.4.5 Power
Power for the redundant Gateways should be applied after all primary and secondary Ethernet
and RS-485 connections have been made. Using separate uninterruptable power supplies (UPS)
is recommended to ensure availability of the redundant Gateway system.
A. Engineering Station
B. Process Control Network
C. Controller and I/O
D. Dual Serial Card
E. RS-485 Bus
F. Secondar y Ethernet
AA
B
C
D
E
F

Emerson 1420 Specifications

General

Brand	Emerson
Model	1420
Category	Gateway
Language	English