Control Logix Redundancy and Produced and Consumed Tags

Hello and thank you for taking the time to view my post!

First of all, I've attached an image as reference.

What I am trying to accomplish is exchanging data between two control logix processors via produced and consumed tags. Simple right? Not this time.

What I have is two systems in question. The first is a simple, single processor setup with an ENBT ethernet card. The other, however, is an enhanced redundancy system with two processor/communication racks and two I/O racks.

Some more specifics regarding each system:

• Panel A (from reference image)
• 17 slot rack
• Slot 0 - 1756-L71 Rev. 20.13
• Slot 1 - ENBT/A Rev. 6.3

• Panel B (from reference image)
• Identical 7 slot racks
• Slot 0 - 1756-L71 Rev.20.55
• Slot 1 - RM2/A Rev. 20.004
• Slot 2 - EN2TR/C Rev. 10.007
• Slot 3 - EN2T/D Rev 10.6

Each rack in panel B is connected via an internal panel network (192.168.1.0/24) via the EN2TR. The two identical racks are connected via fiber between the RM2 modules. Also, the identical racks are both connected to the plant scada network (172.16.0.0/16) via the EN2T. There is also a panelview plus connected to the ETAP.

Everything within Panel B functions as intended. The problem is when trying to produce and consume tags on the plant network.

Configuration Details
The PLC in Panel A is configured to consume data from the PLC in Panel B. I've configured a produced tag in the PLC in Panel B, set it to "Allow Unicast Consumer Connections". I've added the PLC in Panel B to the project on the PLC in Panel A. I've configured the module with no rack connection and no time sync. All is well at this point. The problem arises when I attempt to consume that produced tag in Panel A. I get an error in PLC A from PLC B saying "(Code 16#000c) Service Request Error: Invalid mode or state for service request."

I read the documentation for enhanced redundancy and found a system configured with enhanced redundancy disallows unicast consumption but will still allow unicast production. As a test, I disabled unicast on both PLC A and PLC B to no avail.

If I've left anything out, please let me know and I will provide more info as needed.

Thank!

Welcome to the Forum!

Have you assigned the same IP address to the two EN2TR modules? These need to be set the same for Produce/Consume to work properly with Enhanced Redundancy systems.

It is possible to set them differently and the system will still SYNC, so it's not so obvious to spot.

Regards,
George

Short answer, yes. They were configured the same.

Here's some more info.

Within the redundant system:
Rack 1
-EN2TR IP: Configured - 192.168.1.2; Actual - 192.168.1.2
-EN2T IP: Configured - 172.16.6.2; Actual - 172.16.6.2

Rack 2
-EN2TR IP: Configured - 192.168.1.2; Actual - 192.168.1.3
-EN2T IP: Configured - 172.16.6.2; Actual - 172.16.6.3

I believe that is intended as the redundancy module will assign the secondary controller the ip of the primary + 1.

Stupid question: Why not just use MSG?

harryting said:

Stupid question: Why not just use MSG?

Click to expand...

I disagree, that is a great question. Ultimately, I did use a MSG instruction because it was part of a critical process at the plant. I'm seeking to expand my arsenal of knowledge for later projects so I'm not caught off guard in the future.

I prefer produced/consumed over msg. My reason is simple: It's harder for someone that doesn't know what they're doing to alter and potentially break a connection using produced/consumed than MSG simply because produced/consumed can't be changed while online.

I've only personally designed and implemented three plant wide SCADA systems. There may be other pros and cons to both that I am not aware of.