When will wireless be ready for control functions?
Today, wireless technology is fine for level measurements on a tank farm, vibration readings on a compressor and other low-criticality monitoring operations. But what will it take for companies to feel confident enough to recommend it for actual control functions?
“Before users will become fully comfortable with the idea of using wireless technology for closed-loop process control, their comfort level will have to gradually increase in stages,” says Hesh Kagan, director of technology marketing with Invensys Process Systems. “The first stage is for users in industrial process plants to become confident that they can effectively manage wireless networks to provide industrial-grade availability, robustness and security for open-loop process monitoring applications.
“Once the management issue is behind them, the next step is for users to be confident that the wireless standards, such as ISA SP-100, have evolved enough so that device interoperability and coexistence are no longer issues. This will set the stage for users to truly feel comfortable with the idea of relying on wireless technology to do closed-loop process control. This can take the form of wireless fieldbus (to valves and actuators) or wireless communication at the control bus level between loosely coupled controllers (with limited peer to peer) or both.”
Bob Karschnia, vice president of technology for the Rosemount division of Emerson Process Management, believes the issues of control depends on three basic components: high-quality measurements, reliable communications and robust control systems.
“A robust control system needs to be in place that can handle the data and communicate it to the final control element,” he says. “Process control has performed all of these functions over wire for many years. Since the new piece of the puzzle is the wireless communications, the hurdle that must be overcome is the reliability of the communications in light of unplanned physical and environmental changes. This is the key to robust communications and the key to wireless control.”
Honeywell Process Solutions has designed its OneWireless system deliberately with control capabilities in mind. “It’s not a question of if, but rather a question of when,” says Dave Kaufman, director of business development. “Remember when no one would run a plant with a PC? General wireless control will come with time as users get more comfortable with the security, availability and reliability designed into these solutions. Given this, it’s important to install a wireless network already designed for the possibility of control.”
Gene Chen, Honeywell’s product marketing manager for wireless, adds, “The control application also has to make sense. End users will not rip out perfectly good wires just to use wireless. They will use wireless control where it is too difficult to use control wiring, such as in harsh environments and remote areas.”
The HART Foundation has been developing its wireless protocol, and during discussions of that, its engineers have been very cautious about the idea of actual control functions. “In a traditional chemical plant environment, where the risk of failure of a particular control function could result in catastrophic consequences to people or even communities, I don’t think we’ll be doing wireless closed loop control of those functions any time soon. Perhaps never,” says Ron Helson, executive director. “Safe and effective plant operation is No. 1 always. Control functions in those applications are done over wire today, and I believe they will be done over wire for the foreseeable future.”
Wally Pratt, chief engineer for the HART Foundation, doesn’t expect a defining event. “Process control with wireless will be a quiet revolution,” he suggests. “The hype and market posturing will fade as significant sales of wireless field devices begin. Market leaders care more about selling boxes than whether wireless is used for control or not. User education and reliable, continuous, consistent operation will, over time, give the industry confidence. Experimentation will then begin with wireless-based control. However, success will be masked by users perceiving their success as a competitive advantage.”
|Peter Welander is process industries editor for Control Engineering. He can be reached at PWelander@cfemedia.com .|