Legacy technology: How much control and I/O infrastructure can (and should) survive a migration?


After publishing the first legacy technology discussion in March , I received an e-mail from an end user (name withheld) describing his experiences and some frustrations working with older systems and what can happen to the existing control strategy and I/O infrastructure when it’s time to upgrade. Since Honeywell was named specifically, I asked the folks at Honeywell Process Solutions (HPS)

Original letter:

“I read with interest your Control Engineering article on legacy DCSs and the speed at which companies are transitioning over to the latest fieldbus / networked systems. One thing that may not get much press is the difficulty in translating programming / application / control strategies from the old to the new. In many cases, the support of programming structures is non-intuitive, leading to a re-engineering of how to meet the objective.

“This leads to a review of how important the old programs are and if the same objectives can be met more efficiently. It is my experience that the DCS vendor / system integrator managing the hardware switch-out may not have the right personnel who can evaluate and "re-code" the DCS applications. The customer must determine if the vendor is supplying the right talent for the job and must take a very active role in defining what stays and what goes. Nail down the scope before signing contracts.

“I’m speaking from experience transitioning from an internal company legacy system layered on top of Foxboro Spec200/Taylor MOD 3 to a Honeywell TDC 3000 system across an entire processing facility. There will be a future project to replace the legacy Honeywell TDC 3000 system to a Yokogawa CS-3000 fully fieldbus networked system.”

Jason Urso, systems marketing manager for HPS, responded:

“To maximize your return on investment, Honeywell recommends that manufacturers seek solutions that retain their legacy technology, particularly related to control and I/O infrastructure. It’s difficult to provide a financial justification for the significant effort required to translate those point databases, control strategies, control applications, displays, history, etc., and then to retrain your operators and maintenance techs. And, many times you will end up with new controllers and new I/O modules and no new benefits (replacing PID loops with equivalent PID loops). Ultimately, replacing the controller and I/O is a tough proposition unless the equipment is obsolete and unsupported by the supplier.

“Honeywell protects these investments, like expecting our TDC 3000 control and I/O infrastructure released in 1984 to be supported for at least another 15 years. In fact, many previous generation TDC 2000 controllers are still operating reliably and supported after 30 years. So, I would encourage you to look for ways that you can capture added business benefits in a way that is more cost effective than replacing real time controllers responsible for base level regulatory control.

“The most common recommendation is a solution that preserves your intellectual property but also lets you embrace next generation technology. In the Honeywell case, customers can add a modern human interface like our Experion Station on top of their existing network and TPS/TDC system to achieve new benefits to improve operator effectiveness, reduce incidents, drive more throughput, and increase asset reliability. This technology brings a modern alarm infrastructure and opens the door to advanced applications that increase profit. This means that your operators don’t need to be retrained and you can retain your display, control, and applications intellectual property. And, this way, you can achieve 90% of the business benefits at nearly 20% of the total cost.”

Thanks, Jason. The ultimate answer is that you should be able to retain everything that makes sense to retain. Sometimes networking infrastructure, control devices, and even instrumentation should be upgraded, but not in every case. Retaining too much legacy technology might limit more sophisticated capabilities of a new system. On the other hand, don’t be too anxious to throw out systems that work well and economically. It’s all about balance.

—Edited by Peter Welander, process industries editor, PWelander@cfemedia.com , Control Engineering Weekly News (Register here and scroll down to select your choice of eNewsletters free.)

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