How many times do you walk around your facility and visually look upon every control system that is currently in operation?

If you are anything like me, it may be months in between the times I see some control panels.

Image By Brandon Cooper

Along the same line, how often do you “go online” with many of your control systems?

For some systems, it may be nearly every day, while others, it can again be months in between the time spent on this equipment.

For all the equipment that is running in your facility, who notices when a PLC module fails and is running on the backup module or chassis?

I have found myself in situations where there was little to no monitoring in place for controller batteries, remote I/O chassis faults, DLR faults and even redundant controller system faults.

You heard me correct, the redundant system you thought you had in place has been un-synchronized for three weeks and no one noticed. So how can we, as control system engineers, keep this from happening?

I submit to you that implementing alarming for every redundant controller pair, will be worth the effort.

Add PLC Code to monitor both the Primary and Secondary Redundancy Modules:

Parameters for first GSV Instruction:

  • Class Name: Redundancy
  • Attribute Name: ChassisRedundancyState
  • Dest: RedundancyStatus (“INT” Data Type tag that you create)

Parameters for second GSV Instruction:

  • Class Name: Redundancy
  • Attribute Name: PartnerChassisRedundancyState
  • Dest: RedundancyStatus_Partner (“INT” Data Type tag that you create)
Image by Brandon Cooper

Add PLC Code to monitor the correct status from each chassis:

  • The primary chassis redundancy state should return a value of “2”. If not, set an alarm.
  • The secondary chassis redundancy state should return a value of “8”. If not, set an alarm.
Image by Brandon Cooper

Image by: Brandon Cooper-REDALM.PNG

What to do with the alarm:

  • Implement an alarm that operations will notice with an urgent or audible indication. Chances are, they will call you as it will not be something they recognize.
  • If you have a historian available, have the historian send you an email alert that the event has taken place.

Reference: “1756-um535-EN-P from Rockwell Automation for further parameter information and monitoring capabilities of redundancy systems


Lack of knowing when a redundant controller pair is not synchronized and ready for a failover is a great liability to the production of your facility.

Keeping these systems at the highest level of availability and performance is important to maintaining any facility and helping achieve its production goals.

The “little things” make a big difference when it comes to facility up-time.

Written by Brandon Cooper
Senior Controls Engineer and Freelance Writer

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Brandon Cooper


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