PAC Control Pro with Redundancy Manager
Arbiter
RS-485
RS-485
Ethernet crossover
cable connects the
PAC
S2s on ENET 2
2 PAC S-series
controllers
Redundant power switch
Power
Power control
SNAP PAC brain and I/O
N-TRON Switch
CHAPTER 1: WELCOME
SNAP PAC Redundancy Option User’s Guide
3
3
Redundancy Option Components
The Redundancy Option components—S-series PACs, SNAP-PAC-SRA arbiter, and SNAP-RPSW
redundant power switch—are described below.
SNAP-PAC-SRA Arbiter
The SNAP-PAC-SRA arbiter is a stand-alone unit that monitors the
operation of the PAC S-series controllers connected to it via a
dedicated RS-485 link. If the arbiter detects improper operation of
the primary controller, the arbiter switches control to the secondary
controller. The SNAP-PAC-SRA arbiter is responsible for:
•
Maintains the active/backup status of each controller in a
redundant Opto 22 system
•
Sends heartbeat requests at regular intervals to each controller
in order to receive status information
•
Based on the status information, sends messages that make
one controller active and put the other controller in backup
mode
•
Signals the backup controller to
qualify
itself to be ready to take over as the active controller.
The qualification process includes matching the firmware and strategy to those on the active
