Redundant Operating Characteristics; Overview; Start-Up; Modes Of Operation (Figure 100) - Honeywell 900U02-0100 User And Installation Manual

9. Redundant Operating Characteristics

9.1.

Overview

This section describes operating characteristics specific to redundant controllers.
In a redundant ControlEdge HC900 system, the Lead Controller performs all primary tasks including
interfacing with remote I/O racks, communicating with a local HMI, exchanging data with peer
controllers, interfacing with Modbus slave devices, and communicating with a Host PC application.
Detection of a fault or removing power from a Reserve Controller will initiate a diagnostic prompt in the
Lead Controller, but will have no impact on the process under control. The detection of a fault or
removing power from a Lead Controller will initiate failover, that is, transfer all primary tasks to the
Reserve Controller, establishing this controller as the new Lead. Following a failover, the new Lead
Controller will remain the Lead, even if the condition that caused the failover is corrected.
9.2.

Start-Up


Assignment of Lead and Reserve status is determined at start-up

First available C75 assumes Lead

In case of a tie, CPU mounted in the left position of the rack will Lead

No user configuration or manual operations required to establish Lead / Reserve status

Lead Controller assumes control of I/O and all external communication interfaces.
 Reserve Controller receives the configuration from the Lead Controller
9.3. Modes of operation (Figure 99)
The modes of operation are:

Run
 Run/Program

Program
You can change modes with:

key-switch on the redundancy control module

HC Designer software

HC Utilities software
 900Control Station.

a command from a supervisory host
Both Lead and Reserve Controllers maintain the same mode. Placing the Lead Controller into the
Program mode will also place the Reserve Controller in the Program mode.
Revision 10 ControlEdge HC900 Process & Safety Controller User and Installation Manual
May 2019
179