Huitt Manering, project engineer with BC Hydro, in Vancouver, British Columbia, Canada, had an unenviable problem. Three of his power generation boilers had old Bailey Infi-90 distributed control systems (DCSs), and three others were due to get new controls.
Tearing out all the existing DCSs would mean a lot of work when re-wiring all the input/output (I/O) points and re-programming the entire control logic. So, Manering decided to review all of his options, and asked several suppliers for possible solutions. The first task would be to upgrade the three Bailey systems. This would be followed with installation of controls on the remaining three systems.
“When the bids came in,” says Manering, “Foxboro (an Invensys company based in Foxboro, Mass.) was the low bidder—even lower than Bailey, which would be retrofitting its own equipment. In fact, during the bidding process, Bailey was bought by ABB, so they had not only the Bailey platforms, but all their other ones as well.”
Another factor in the equation, according to Manering, was BC Hydro’s wish to have the operator terminals running on the Unix operating system, and engineering workstations running Microsoft Windows NT. Foxboro’s new I/A Series DCS could do that.
Five options
According to analysts at ARC Advisory Group, a Dedham, Mass., manufacturing industry analyst firm, there are five ways to replace existing DCS systems. As shown in the table, the I/O Substitute method is very cost effective. They note that should something go wrong with the upgrade, the process is easily reversed using the old cards. The challenge, they note, is that not many companies can do it.
The process is quite simple in concept, but carrying it out requires engineering and project management expertise. Foxboro manages it by manufacturing its controller and I/O cards in the size and form factor of different competitive DCS suppliers.
ARC analyst Dick Hill, states, “Invensys’ largest installed base of distributed control systems is by far its Foxboro I/A Series. Introduced in the late ‘80s, I/A has consistently evolved to incorporate new technologies. The Foxboro solution was originally developed to include migration from the company’s Spectrum and SPEC-200 systems to the I/A Series system. Invensys was one of the first suppliers to offer a comprehensive migration path from a competitors’ control system with purpose-built hardware. It leveraged the same principles applied in its Spectrum/SPEC-200 migration plan and applied it to competitor systems from ABB (Bailey Net 90 and INFI 90), Emerson (PROVOX and WDPF), and Honeywell (TDC 2000 and 3000).”
Betty Naylor-McDevitt, Invensys Migration Program director, says, “The time, cost and risk associated with a system replacement have been due to the need for rewiring, and retesting of the new system while the process is shut down. Every supplier’s I/O equipment has a different signature size, shape and I/O capacity. I/O modules from different suppliers cannot plug into the existing termination assemblies and leave the wiring intact.”
The process starts with the manufacture of I/A Series I/O modules (FBMs) to be a form fit replacement for the original I/O modules. Original cabinets, termination assemblies, power supplies and racks are reused. Foxboro I/O modules are substituted for the legacy ones without modification to the wiring or termination assemblies. New controllers are added, completing an entirely upgraded control system.
Card lineup
No custom software is required. The new cards line up exactly with the original legacy I/O wiring terminations. Automated conversion tools are used to ensure correct conversion. Where appropriate, opportunities for optimization are identified and implemented.
Full system factory acceptance testing is performed ahead of time to ensure that all database conversion work was done correctly and to the satisfaction of the customer.
On the day the switchover to the new system is to occur, the process is shut down, the legacy I/O modules are taken out and replaced with I/A Series FBM modules, and the network connector is put in place. Loop checkout is performed to ensure that all is working correctly, and the process is re-started.
Manering reports, “Implementation issues were really minor. For instance, the way Bailey does I/O channels is to skip number 8. It counts 1 through 7, skips 8, and then continues. We had to make sure we caught that. We had a little learning curve getting used to the I/A Series controllers, but it really was simple.”
Engineering was all done off-site at Foxboro during the fall of 2001. Two Invensys engineers were on site for the startup and final check out. “It was one of the smoothest starts we’ve done,” he continues. “An added bonus was that the logic was much simpler than we had. The original system had different sequences with multiple steps in each sequence. They designed the code as if for a more complicated boiler. This greatly aided start-up.”
Sometimes, a project that looks good to the engineers is a nightmare for operations. The first system was installed in late 2001. Now, two years later, Manering says plant personnel appreciate the simpler logic. The new system has 10 percent of the logic sheets of the old system, and graphics sheets are reduced from 12 to two. This simplicity leads to improved operations and troubleshooting.
“It’s still working,” Manering states. “In fact, after the first unit was working, we decided to install the migration package in the last two units and install the new I/A 200 series DCS in the other three units.”
Bring ‘em over
Manering’s experience at BC Hydro reflects the promise of the new business model within Invensys’ Foxboro business unit. Says ARC’s Hill, “Migrating users from their competitor’s installed base is a major initiative for Invensys now, and the company plans to make migration a key to its market share growth strategy over the next several years.
Naylor-McDevitt concludes, “Our solution is non-destructive. Because we do not touch any of the field wiring or alter the existing nests and termination assemblies, the original legacy system can easily be put back in place in the event that a problem is seen. We can take the problem and its resolution off-line without impacting the production schedule. Our experience shows that with careful planning, the switchover can be done in hours, not days or weeks.
Certainly the BC Hydro experience reflects this optimistic outlook.
