Distributed Control System (DCS) Migration Best Practices

By Dick Hill

Industry Trends

A simple definition of Distributed Control System (DCS) Migration is upgrading a legacy or installed control system to a current system while:

  • Preserving as much of the intellectual properties as possible from the legacy system
  • Leveraging the capabilities of the new system
  • Minimizing the impact on operations
  • Minimizing cost
  • Enabling future business value

Many choices are available when evaluating specific methodologies for a control system migration.  For many distributed control system end users, migration represents a significant step change to warrant a complete review of all the supplier offerings in the marketplace.  ARC advocates that you take the same approach to control system migration that you would to overall control system selection, all in the context of a six-sigma style continuous improvement process.  One thing end users should consider when evaluating a supplier for a migration project is their ability to provide you with a solution that minimizes downtime and risk, while providing you with a tangible business value proposition that will have a real economic impact on your business.  If you end up with a like for like functional replacement, you have failed in your migration project. 

When Is the Best Time for Distributed Control System Migration?

All too often, an impending crisis drives the need for a company to initiate a control system migration.  This may result from a supplier removing a product from the market; forcing the end user to buy a different model or even turn to a new supplier.  The crisis may also involve sudden urgency to replace an obsolete system; a decision that had been postponed until there is no other option except an often-massive replacement project.​

Due to the possible threat of an impending shutdown, these decisions must often be made quickly, without adequate time to consider how well the replacement choice meets all current and future projected needs and how to smoothly perform the changeover process to the new technology.Distributed Control System Migration Strategy

ARC always encourages our technology user clients to think in strategic, rather than tactical terms.  When it comes to replacing Operational Technologies (OT) such as process control systems, it’s best to have an ongoing strategic plan in place for a variety of scenarios.  In this manner, companies can turn a potential crisis situation into a strategic business opportunity.   

This strategic plan for all OT including process control systems should align with the company’s business strategy.  ARC recommends that the multi-disciplinary team of stakeholders tasked with creating the OT strategic plan should first look at the “current situation,” followed by a determination of the “desired situation.”  Then, a list of criteria must be defined to identify the characteristics and capabilities that would be required to help the company close the gap between the current and desired situation.  This requires an “OT strategy,” that might involve more than one possible scenario. 

Developing a strategic plan for operational technology is not a one-time project.  Each time a company does this, it will surely uncover some new opportunities because the exercise will include the observations and insights of a new mix of internal stakeholders, plus the observations and insights of a new mix of OT suppliers and the new technology capabilities they bring to the table.

Distributed Control System Migration Options Available

Many automation suppliers are well known for supporting their systems for a very long time, probably longer than they should reasonably be supported when you compare the automation / OT business to the world of IT.  Eventually, however, availability of spare parts and support for legacy platforms must end. 

Although, ARC recommends that the process control system be well integrated from the plant floor all the way up to business systems, for the purpose of this discussion, the fundamental control system migration options available are outlined below.

Total System vs. Phased Migration

The hardware infrastructure, including wiring and I/O, can become embedded in the plant, making it very difficult and cost prohibitive to do a wholesale replacement of the system.  If this is the conclusion of the OT Strategy phase, then a phased migration could be the direction selected.  In a phased migration, only those components that need to be replaced are upgraded. 

There are cases, however, where the user may want to consider a single total replacement approach.  Primary factors driving this approach include availability of a time window during the regularly scheduled turnaround, the type of manufacturing process involved, and the experience of the supplier and/or the system integrator partner involved in the project.  When the circumstances are right, a single total replacement can be the fastest and possibly the least costly option because there is less downtime and less redundant labor compared to the aggregate cost of system evolution or migration in multiple phases.  Another potential benefit of single total replacement is that it ensures a single, current generation of system and the associated reduced total cost of ownership (TCO).

Hot Swap vs. Downtime Migration

Changing DCS components while the production process is running (Hot Swap) can minimize the amount of time the process is not producing product.  It is however potentially a higher risk if not carefully planned and executed.  Hot Swap involves significant preparation, planning, and testing.  Tasks like database and graphics conversion should be as automated as possible, and the supplier should offer both tools and services that speed the task of conversion as much as possible.  The conversion of legacy sequence code is a more problematic issue and needs to be addressed on an individual supplier basis. 

For many production facilities the other option, Downtime migration also presents advantages and risk.  If the entire control system hardware and software can be successfully migrated while the process is not operating, then there is no chance of an accidental shutdown of production. The control system must be replaced and fully functioning within the downtime window that meets the plant’s overall plan.  If the new system is not fully functioning, then there is typically no turning back and product delays may be the result.

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