The June 2013 cover article in Control is going to be about migrating distributed control systems (DCSs). I originally thought it should be about upgrading all kinds of legacy equipment and systems, but I quickly found that, not only are there dozens of heroic examples of DCSs being revived, but they do branch out to embrace all kinds of devices from HMIs to I/O modules to simulation and business systems.
One sidebar in the story is going to be "Why and How to Upgrade a DCS," which will feature a summary of a whitepaper by Chad Harper of system integrator Maverick Technologies in Columbia, Ill. The whitepaper, "Upgrading Your DCS: Why You May Need to Do It Sooner Than You Think," lays out some reasons for migrating DCSs, and describes how to approach it.
Signs Your DCS Needs Upgrading
- Staff resources supporting the existing DCS are close to retirement;
- Vendor plans to end support for the product;
- Control problems are causing unplanned outages and increased downtime;
- Latest technologies are not compatible with your DCS; and
- Spare parts and technical support are becoming hard to find.
Why Not to Wait Too Long to Upgrade
- Present staff don't know your legacy DCS;
- Waiting until support for DCS ends will make migration harder
- Old systems often can't use new technologies;
- Old DCSs only allow for configuration of certain types of controls; and
- Cost of maintaining an old system will outgrow the cost of migration
Approaching a DCS Upgrade
Because upgrading a DCS can be a monumental and expensive project, it’s important to evaluate whether it makes more sense to migrate all at once, or conduct a partial or phased approach, which most DCS suppliers offer. A phased upgrade can be less risky, spread out costs, and minimize downtime. Two common phased-migration methods are:
Upgrade HMIs first. Most newer DCS HMIs can be configured on top of legacy control systems. This can be done on a running plant with little impact to production. By upgrading the HMI first, you ensure that toperators know the new technology before the complete system is installed. Changes in presentation and interaction with new controls are some of the biggest hurdles that operators face. Many new HMI packages also support extra connectivity, such as OPC. HMI software can serve as an interface that allows for development of MES and ERP projects without needing a full DCS revamp.
Replace the controllers and HMI, but leave the existing I/O modules. Most of the latest DCSs can connect to I/O devices at the backplane of old DCS controllers.
Most I/O and field wiring can be left in place and upgraded as needed. This approach allows for easier hot cutovers and the ability to change out I/O as plant shutdown schedules permit. It also reduces labor costs for electrical and wiring work and associated documentation updates, such as wiring diagrams.
