SYSTEM ARCHITECTURE
SNAP PAC Redundancy Option User’s Guide
2
NOTE: The SNAP-PAC-SRA arbiter and the SNAP-RPSW redundant power switch can be purchased
together in the SNAP PAC Redundancy Option Kit, part number SNAP-PAC-ROK.
•
One or more Opto 22 SNAP PAC Ethernet brain-based I/O units on the same Ethernet network
as the controllers
•
A PAC Control Professional strategy for use on the system’s two redundant controllers that
includes special features such as
sync blocks
and
persistent/redundant variables
. (See
on
.) Included with PAC Control Pro is the
PAC Redundancy Manager
, a software utility
you can use to configure and monitor the redundant PAC S-series controllers and the
SNAP-PAC-SRA arbiter.
Ethernet Link Redundancy
This guide describes only how to set up redundant controllers for your system, not Ethernet link
redundancy, which is also offered by Opto
22. Using PAC Project Professional, Ethernet link
redundancy allows you to configure redundant networks for your control system. This is achieved in
part by assigning a primary IP address to one Ethernet interface on a PAC S or PAC R controller, and a
secondary IP address to the controller’s other Ethernet interface. If communication to the primary
address fails, the secondary address takes over.
There are two basic ways to use Ethernet link redundancy:
•
HMI-to-controller link redundancy, which
is not
supported when using redundant controllers.
For more information, see form 1700, the
PAC Control User’s Guide
, and form 1702, the
PAC
Display User’s Guide
.
•
Controller-to-I/O link redundancy, which
is
supported when using redundant controllers. For
more information, see form 1700, the
PAC Control User’s Guide.
NOTE: When using controller-to-I/O link redundancy, you must connect ENET 2 on the controllers and
I/O units to a switch. No other devices can be connected to that switch.
System Architecture
In the following simplified illustration of the redundancy architecture, two SNAP-PAC-S2 controllers
are connected via Ethernet to the same I/O. A SNAP-PAC-SRA arbiter is connected to both
controllers with dedicated RS-485 links. An Ethernet crossover cable connected to the ENET 2
Ethernet ports enables communication between the controllers. A SNAP-RSPW redundancy power
switch connected to the arbiter controls power to the controllers. Separate power supplies for the
arbiter and each of the controllers are not shown.
