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I have encountered a difficulty using Produced and Consumed tags over ControlNet. Our customer has a network of 7 Controllogix PLCs connected by ControlNet and Ethernet. We were using message instructions over Ethernet to pass data from one PLC to another. We considered converting to Produced and Consumed tags over ControlNet to improve performance. When using Produced and Consumed tags, the consuming PLC must have the producing PLC entered in its IO configuration. IO configuration changes must be performed off line and then downloaded.
Here is the problem. The Controllogix processors are not all the same model. If one were to fail the replacement may be a different model or firmware revision. To make the produced tags work it would require revising the “consuming” program in each PLC off line and downloading. Then the ControlNet network would have to be re-scheduled.
This application is mission critical. Putting a single PLC in program mode for more than a few minutes is a problem. Putting all PLCs in program mode to reschedule the network during production would be a catastrophe.
Rockwell does a good job of marketing its product features but unfortunately the Devil is in the details. As in this case, they need to be more mindful of the shortcomings of their designs and build in more tolerance for the consequences of failure. Designing the products to allow these changes to be made on-line would be solve a lot of problems.
Has anyone encountered a similar experience? I am interested in any comments the PLC community may have.
Here is the problem. The Controllogix processors are not all the same model. If one were to fail the replacement may be a different model or firmware revision. To make the produced tags work it would require revising the “consuming” program in each PLC off line and downloading. Then the ControlNet network would have to be re-scheduled.
This application is mission critical. Putting a single PLC in program mode for more than a few minutes is a problem. Putting all PLCs in program mode to reschedule the network during production would be a catastrophe.
Rockwell does a good job of marketing its product features but unfortunately the Devil is in the details. As in this case, they need to be more mindful of the shortcomings of their designs and build in more tolerance for the consequences of failure. Designing the products to allow these changes to be made on-line would be solve a lot of problems.
Has anyone encountered a similar experience? I am interested in any comments the PLC community may have.