Legacy distributed control system migration strategy

You face two key control system migration strategy decisions: whether to migrate in phases or replace in step and how to time what you want to do. These decisions are almost always intertwined in ways that might not be apparent initially. And there are plenty of side issues.

How do you resolve these issues? With a good planning process and thorough DCS migration methodology.

Common legacy DCS migration issues

  • Should you rip and replace? Or migrate your consoles now and logic later?
  • Can or should you re-use field wiring, even the old terminations?
  • Should you simply replicate existing capabilities? Or take advantage of the opportunities to gain new efficiencies and other benefits?
  • Should you delay all migration activities and costs, instead propping up your current system for as long as you can?

Replicate current capabilities or do more?

Many companies start considering a straightforward replacement of their existing control capabilities with a supportable and more reliable modern system. This can be a valid objective. Legacy screen features can even be recreated in modern HMI.

Depending on the age of your system, you might find that even basic modern controls include additional features from which your operation might benefit. There is no requirement that you use these features.

We recommend reviewing the potential features. Benefits in productivity, efficiency and ease of operation may be available to you at no additional cost.

With HMI, for example, operators who initially preferred replicating legacy screens often find themselves attracted to the possibilities and additional feedback possible with modern configurations.

The bottom line: Expose yourself to the possibilities.

DCS migration strategy considerations

Among other things, you should consider:

  • How much downtime can your operation tolerate?
  • When is the window?
  • How modular and robust are your subsystems and other processes?
  • What’s the budget?
  • What system capabilities do you want to have when the migration is complete?

Migrate in phases or rip and replace

Many migration teams begin with the idea that moving forward in phases is less risky than a complete system replacement. But a complete replacement eliminates a potentially complex step: interaction between elements of the old and new system.

A phased migration can be the right step. If you have tens of thousands of I/O points, it would be an extreme challenge to engineer a one-step replacement, as one example. Or budget constraints might dictate phases.

In other circumstances, it can be less involved—the total dollar outlay can be less to completely replace the old system with new in one step. In many cases, you might still be able to retain field wiring.

The bottom line: do a thorough capabilities and site audit and consider all factors in your planning.

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