Though they are vital cogs in any automation system, programmable logic controllers and distributed control systems have always been strange bedfellows.

DCS systems for the last 20 years have controlled regulatory and some batching schemes, focused largely in areas that employed analog controls. PLCs, by contrast, controlled the discrete systems such as motor control and high-speed material handling applications.

The problem is, together, DCS and PLC systems communicated slowly and inconsistently as a result of low-bandwidth serial protocols.

Dwayne Robbins, an engineering manager for Weyerhaeuser, one of the largest pulp and paper companies in the world, remembers the two systems requiring completely different engineering tools, along with additional hardware and software, only to result in a clumsy quality of communication.

But the last decade has seen something of a renaissance for automation control systems, such as programmable logic controls and DCS systems. Automation vendors have begun designing more open control systems, allowing easier communication due to system protocols, Ethernet networks and the use of PC computer platforms.

"As time has gone on, as we've seen with every desktop computer that's out there, the processing capability has improved dramatically and these systems are able to communicate much easier," says Weyerhaeuser's Robbins. "They have tools that make every element of the facility able to talk together."

Implementing industrial control systems has historically been a daunting process. Simply getting them to interface with signals from sensors and actuators has been a starting point, followed by incorporating advanced control features, network connectivity, device interoperability and enterprise data integration.

According to Mike Vernak, DCS program manager for Rockwell Automation, the capabilities of these newer control platforms evolved to include easier analog control for PLCs and better discrete control capabilities for DCS systems. Ultimately, the two systems have meshed into programmable automation controllers (PACs), which combine the features of PLCs, motion controllers, DCS systems and PCs in a single platform.

When automation controls were first developed nearly 40 years ago, their primary task was turning nozzles on and off and opening and closing loops. Today, a standard cell phone has all the computing capability to run such a function. Instead, technology is being asked to leverage knowledge to make smarter decisions.

"We're at the cusp where it goes from PLCs to DCS to PAC to really an enterprise controller, where it's not so much about opening and closing loops, but how to reach the next level of efficiency," says Rick Morse, vice president of Invensys' controls and safety portfolio. "I see it as bringing in the economics and other aspects of productivity into what an automation controller does that is the next step."

Weyerhaeuser has instituted a migration toward a single plantwide control platform throughout its facilities in North America, starting with its Columbus, Miss., plant. Like many manufacturers in recent years, Weyerhaeuser was having difficulties in maintaining its legacy DCS and PLC systems due to shortages and other obsolescence issues.

But according to Rockwell Automation's Vernak, the migration is also being dictated by the loss of technical resources to maintain legacy systems. Mass layoffs and early retirements, for instance, have resulted in a loss of technical expertise on older platforms.

An operator at one of Pepsi's bottling facilities interacts with PLCs on the bottling line in real-time using Wonderware HMI and System Platform from Invensys Operations Management.
"That's one of the reasons we've selected this path," says Robbins. "We feel it improves our existing training and experience if we move more of our applications into this technology."

In many ways, the evolution of automation controls reflects the different role of process engineers, who decades ago worked in plants using tweaking tools to run machines. Machines today are instead run by controls.

"Automation has evolved so that's not what they need to be worrying about," says Invensys' Morse. "What we have now is the shift from manual automation to knowledge automation, where the worker has to understand the process and instead of thinking about how to do the job, use information to be more productive. It's a fundamental shift."

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