Managing the DCS upgrade

The right process can take out the guesswork and lead to a successful migration.

02/13/2014


The goal in most DCS migrations today is incremental improvement in the system. Courtesy: OptimationAs distributed control system manufacturers evolved and their products and solutions became less attractive due to their proprietary nature, cost, and most importantly, lack of support and availability, customers began to look for viable replacement strategies. Many “hybrid” DCS platforms and advanced process controllers began to market replacement programs for legacy, monolithic DCS systems in manageable and cost-effective slices.

Today one can choose to replace only the I/O, or only the processors or only the HMI, or combinations of the aforementioned, without full-scale demolition and fabrication of a new system. This may reduce the actual installation timeline and costs of each phase of a DCS upgrade.

Proper planning, definition of project team roles, and testing are vital to take the headache out of a DCS migration project. 

Make it more manageable

I/O migrations can be accomplished by providing an upgrade to the I/O structure and devices which would leverage the current I/O termination points, eliminating the need to disturb or rewire the existing field connections. Several manufacturers offer I/O and terminations that are simply a “bolt-on” upgrade and provide backplane or native communications to the original processors. Little or no software changes are needed, and the field wiring and installation requirements are minimal.

Because I/O modules and devices are typically still available from the OEM, and unless there is a shortage or the OEM no longer exists, this upgrade is not critical.

Although replacing the processing units usually is done at the same time as I/O migration, it’s not absolutely necessary. Some manufacturers offer processor upgrades that will still continue to communicate to the original I/O structures, even if those structures are from another manufacturer.

Software services are required for this upgrade, which can vary from automatic control program upgrades (usually requires some manual verification and tweaking) to complete rewrites of the control programs. An experienced systems integrator can determine the proper approach.

A processor upgrade may require an HMI upgrade, as the processor may now have a different communications protocol and naming structure for the tags or control blocks being used at the HMI.

Typical DCS communications are proprietary and serial (such as Modbus), but usually do not cover any recent (past 20 years) protocols like Fieldbus or various Ethernet protocols.

Most plants today are looking for fractional improvements to current systems. From a controls perspective, the DCS does a great job in handling various control loops and other control schemes, but original DCS tools make advanced data mining and manufacturing intelligence unavailable or difficult to obtain and analyze.

The tools best suited for these tasks run on open architectures (like Windows) and require robust connectivity to the SCADA/HMI, I/O services, or databases.

Additional considerations

Most typical DCS installations contain additional controllers, consisting of a variety of PLCs and single loop devices, which currently possess limited or no connectivity to the DCS. This produces an HMI environment that may be blind to some portion of the plant and may require additional HMI products to view those data types.

Some DCS manufacturers no longer exist, or their product line has been discontinued for many years. In these cases, customers have relied on third-party electrical repair houses, surplus and reclaimed electronic stores, or even eBay for replacement parts. Software upgrades are virtually nonexistent and may not be a required purchase, but support of those products is spotty at best.

Most DCS legacy HMI screens are visualized as 2-dimensional vector-based graphics. In today’s world of high definition, realistic animation, and video games, these old HMI systems truly show their age and antiquated level of technology. Although most operators of these systems have grown accustomed to their generally flat colorless interface, far more information can be displayed through new high-definition graphics, increasing operator comprehension without producing information overload. 


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