Distributed intelligence stands alone

This works best if the hardware and software are not proprietary to a vendor or, as Stauffer puts it, “Being open is absolutely critical. Openness allows users to realize the benefits of distributed intelligence. If intelligent field devices from different vendors cannot coexist and effectively communicate their full set of data, then the potential benefit of distributed intelligence is lost.”

Kennedy and others say that OPC – although far from perfect – is a good answer: “OPC as it stands has fueled a geometric increase in the amount of information that is available in real time – nearly 50% of the interfaces we sell today are OPC,” says Kennedy.

Raether agrees: “Engineers and technicians in charge of choosing and integrating products from hundreds of vendors providing hardware and software are challenged with making sure that they all and play nice and talk to each other. There have been multiple efforts in the industry to make equipment from different vendors compatible with each other. One such very successful standard is OPC.”

And then there is fieldbus. "Foundation fieldbus is a vendor-neutral DCS,” says Rezabek. “Function blocks are not as extensive as what may be available on the DCS or PLC level, but that's mainly because too few of us are making extensive use of it. Once users catch on, I think suppliers are likely to respond to the demand for more ‘blockware’."

Distributed vs Standalone
We’ve concentrated on distributed systems here, but standalone control systems still have a place in the sun. Some engineers stand by their traditional standalone control systems. “For our relatively simple process control needs, we have discouraged distributed control, believing that it is better to have a central PLC-based master control that can be monitored and modified as needed,” says Doug Rhodes, manager, electrical power & automation group at Dayton & Knight, North Vancouver, B.C. D&N is a consulting engineering firm that specializes in water and wastewater.

“We want to maintain control of the control system,” continues Rhodes. “Since a loss of communication with the PLC can usually be tolerated for a short period, distributed systems are not deemed necessary.”

Standalone systems can take advantage of all the modern hardware that makes distributed control possible. They can operate unattended as easily as a distributed system can, communicate to far-away enterprise servers, and take advantage of device diagnostics, wireless networking, web servers and redundant architectures. An unattended remote distributed system is a standalone system when communications fail, so the distinction between standalone and distributed is getting blurred.

What is clear, however, is that the face of control is changing. There are many challenges remaining – getting systems from various vendors to talk to each other, making sense out of equipment diagnostics, and managing alarms – but true remote control is becoming more practical every day.