Control Systems: Don’t Get Misled by Modernization Misconceptions

Six fallacies often undermine control system upgrades

By Mike Alsup, Emerson Process Management

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Consider extending the life of an existing system to help address short-term plant reliability during the planning and execution of a modernization but not as a long-term solution. While spending money to upgrade an existing system will cut upfront costs, the plant undoubtedly will face expenses for future repairs and upgrades unnecessary with a new system and may suffer unplanned shutdowns. More importantly, this approach also incurs “lost opportunity costs” because the legacy system lacks many capabilities to increase a plant’s return on investment. A new system will provide improved control strategies, capabilities to take advantage of smart field devices, including more accurate instruments and better performing valves, as well as advanced control and abnormal situation prevention — bolstering plant performance and safety. It will enable better sharing and integration of data with business systems and thus will enhance business opportunities.

Misconception No. 3: I should stay with my current vendor because I don’t want to support two systems. This is false because migrating with either a new vendor or the current one still entails having two systems in place until the modernization is complete and the legacy system is decommissioned.

Misconception No. 4: Every vendor offers the same migration options. Not true. Vendors differ in their capabilities both in migration tools and expertise in areas like field instrumentation and control valves as well as in implementing fieldbus and wireless. It’s important to match the needs of the migration project to the capabilities of the candidate vendors.

Misconception No. 5: “One button” conversions eliminate coding concerns. Some people put great faith in a vendor’s promise of “one button” software conversions. The problem is that conversion tools are automated to various degrees and automated code conversion often can lead to errors and omissions.

Online language translators exemplify the drawbacks of such automated procedures. Try typing “The quick brown fox jumped over the lazy dog” into an online translator and then having it convert the text to another language and that result back into English. yielded the results in Table 2. Even though this was a simple two-step translation, only one of the “back into English” phrases was even close to the original.

On a more serious note, “as found” migrations that copy code from the legacy system will include a great deal of “dead code” — code that has been superceded by upgrades and other changes over the years but still exists in the system. A migration is an excellent opportunity to purge that dead code.

In addition, the converted legacy code doesn’t capitalize on advances in control technology over the past 20 to 30 years. Indeed, an end user at the modernization workshop at the 2012 ARC Forum advised that only about 70% of the legacy control strategy should be converted and warned: “Any more than that and you aren’t taking advantage of the new system capabilities.”

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