A neat DCS migration solution

12 July 2011

CEE reports on the importance of upgrading aging process control systems, and looks at the options currently available.

Process plants today need to be able to react quickly to factors such as the demand for product customisation and shorter, more frequently changed production runs. Add to this the need to produce products faster and more cost-efficiently and it becomes clear that there is a growing need for the installation of more flexible processes solutions.

Many projects are not undertaken because of a belief that it will mean abandoning existing legacy systems. Instead, many companies have invested in top-level automation of the business process, but have been disappointed with their capabilities. In reality to release the maximum return from top-level investments requires real-time exchange of information with the plant floor, which is not achievable with many of the aging systems currently employed.
A classic DCS will have three main elements – operator console (HMI), distributed controllers with integral input/output (I/O) modules, and a proprietary communications protocol. Typically, it also includes an engineering station and an application processor. Non-DCS functions such as batch management or supervisory control are often linked via a gateway or computer interface.

There are three basic upgrade paths – Complete replacement of the system, transitional upgrade of elements of the system, or a ‘plug in’ system to obtain the required functionality.

Total system replacement
Total system replacement is, conceptually, straightforward. Once you find the system that meets your criteria. Find a system, shut down for an extended period of time, tear out the old system and wire in the one. Unfortunately, this approach nearly always represents the most expensive route.

The migration upgrade
In reality, such a drastic approach is rarely needed anyway. In most cases, it would be possible to save parts of the system such as racks and I/O wiring, as they will not hinder the performance of the upgraded system.

For legacy systems where the wiring is sound, basic control can often be migrated to new control system hardware. However, every vendor’s new I/O equipment has a different signature size, shape, and I/O capacity, it usually cannot plug into the existing termination assemblies without cutting and rewiring which will increase the risk of process downtime.

Migration via gateway
Another migration approach is to keep the old system and wiring intact while installing a new system in parallel, then integrating the two systems through a gateway. While this can be relatively low-cost and quick to implement, the underlying technology will still be obsolete and will continue to age.

The plug-in upgrade
An alternative to these migration approaches is available from Invensys Operations Management. By furnishing new I/O modules designed to mount into a legacy chassis, it can provide a new control system.

There is no need to cut any wires or add any racks or cables, and there is no risk of lengthy downtime, as it is possible to convert a rack back to the original system in the event of an unexpected problem arise during installation.

Most important, because the new system is set up, staged, and fully tested offline, the time delay before production is reduced to just hours.

Invensys has been tackling the challenges of migration for many years because of its solutions for users of its 1970s-1980s-era SPECTRUM system. A migration program was introduced in 1997 to provide the same answer to users of other DCSs. As with the SPECTRUM system, it was realised that replacement solutions would need to be cost-effective, low-risk, easy to install, and designed to minimise process downtime. Also, they would have to eliminate the need for rewiring and retesting while the process is shut down.

The solution? The award winning* Invensys Foxboro I/A Series I/O modules (FBMs) are manufactured to be form-fit replacements of the I/O modules in the legacy system. Plug-in migration solutions are currently offered for Honeywell TDC 2000 & TDC 3000; Emerson (Fisher) PROVOX Series 10 and Series 20; Westinghouse WDPF; Bailey Net90 & Infi90; Foxboro SPECTRUM & SPEC 200; Moore APACS; and Taylor MOD 300.

Replacement I/O modules are standard I/A Series FBMs. They are made with the same components as traditional I/A Series system FBMs. No custom software is involved and they are designed to line up with the original I/O wiring terminations.

*The Invensys Foxboro I/A Series won the Frost & Sullivan 2010 Award for Global Customer Value Enhancement Award for DCS systems because of its migration strategy.

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