Quantum Hot Standby Operation Modes

Operating Modes Overview

In a normally operating Quantum Hot Standby system, there are two PLCs running, one as the Primary PLC and one as the Standby PLC. Consequently, a Quantum Hot Standby system requires additional states to reflect the system status. The redundant nature of the system means that the relationships between operating modes changes. The following provides a quick summary of the Quantum Hot Standby operating modes and states.

WARNING

UNINTENDED EQUIPMENT OPERATION

Verify the PLC operating mode before installing, operating, modifying, or servicing it.

Failure to follow these instructions can result in death, serious injury, or equipment damage.

Before acting on a PLC, positively confirm the operating mode of both Hot PLCs by viewing their LCD displays, LEDs or System Status Words.

Before running a Quantum Hot Standby system that uses an Ethernet I/O Head, ensure that a least one CRA Drop has established communication with CRP Head module.

This information is accessible through:

%SW172 and %SW173
Mod Status LED of the CRP module, for more information refer to the “Quantum Ethernet I/O Ethernet Modules Installation and Configuration Guide”

Without communication established, the CPU goes to RUN OFFLINE instead of the PRIMARY RUN or STANDBY RUN mode.

For a more detailed description of the Quantum Hot Standby operating modes, including a state transitions diagram, refer to Operating Modes.

STOP Mode

In the STOP mode the PLC has both:

received a Stop command
successfully stopped

RUN Mode

There are 2 Hot Standby states in the RUN mode:

Primary state

The PLC has both:
- received a RUN command
- assumed the Primary role because either it did not detect another Primary PLC or, if both PLCs were started simultaneously, it is PLC A
Standby state

The PLC has:
- received a RUN command
- assumed the Standby role because either it detected a Primary PLC or, if both PLCs were started simultaneously, it is PLC B

NOTE: For information about A/B PLC assignment, refer to Distinguishing Between Controllers.

OFFLINE Mode

In the OFFLINE mode the PLC has:

received a Run command
responded to a detected error by either changing either from Primary Run or Standby Run to the Offline mode
received an Offline command

Non-Configured State

In certain circumstances, such as when no valid application is loaded on a PLC, a Hot Standby controller enters (and report itself) as being in a "Non-Conf" (non-configured state), which is not considered as an operating mode.