Wireless proponents take HART

More chemical plants are expected to go wireless with the introduction of the new wireless protocol for HART devices.

By C. Kenna Amos, contributing editor

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Many chemical plants are abuzz with talk about using wireless technology. The noise is apt to get louder now with the launch of a new wireless protocol for HART devices. After all, 23 million to 25 million HART devices are installed globally, with about 40% used by the process industries, notes Ron Helson, executive director of the HART Communi-cation Foundation, Austin, Texas. The new WirelessHART protocol is backward-compatible with existing HART devices and applications.

Helson understandably applauds the wireless-mesh-network communications pro-tocol. “It represents a major step for the industry,” he says. “We’ve defined it in terms of what users know and love about HART devices.” The new specification, a key part of the HART Field Communications Protocol Revision 7, was approved June 15 by the HART Users Group.

“With proper installation, I would think WirelessHART would be quite successful in doing its job,” believes Hesh Kagan, president of the Wireless Industrial Networking Association and also director of technology development and new-business development for Invensys Process Systems, Foxboro, Mass. “By definition, it’s a process measurement tool,” he says. “Now the question is: How many process measurements are going to be incremental, based on wireless sensors or WirelessHART?”

Figure 1. Working prototypes of this gateway have been released.
Figure 1. Working prototypes of this gateway have been released.

For process automation, it represents wireless communication’s future, believes Guido Stephan, director of technology and processes within Siemens’ Research & Devel-opment’s Technology & Processes group, Karlsruhe, Germany. “Our conclusion is that WirelessHART will become a standard.”

Pepperl+Fuchs (P+E) is “very excited” about the new protocol, says Robert J. Schosker, product manager for intrinsic safety, HART, at the firm’s Process Automation Division, Twinsburg, Ohio, calling it “the first standard for a wireless network in the process automation area.” “I believe WirelessHART now gives the user added flexibility in installation and helps give those riding the fence that extra push to get them to use HART,” he adds.

Key features

Wireless HART comprises three distinct parts, explains Kagan. One is the radio, which many manufacturers can provide. The second is the stack, which handles the physical, data-link and network layers. Finally, there’s the protocol, which he calls “the handshake between the applications and the systems — a data frame out of the HART 7.0 standard.”

Helson cites two particularly noteworthy attributes. The physical and data-link layers adhere to the 2.4-GHz IEEE 802.15.4 Low-Rate Wireless Personal Area Network standard, and wireless mesh networking forms the network layer. The specification has a full-mesh topology, meaning each device connects to all others, directly or through other devices.

Stack definition owes a lot to Dust Networks, Berkeley, Calif. It includes much of the firm’s proprietary Time Synchronized Mesh Protocol (TSMP), used in ultra-low-power wireless sensor networking, notes Joy Weiss, Dust Networks’ CEO. TSMP helps the protocol “provide wire-like reliability in a harsh environment on which the devices will have to operate in, but in a wire-free economy,” Weiss explains.

WirelessHART also includes several features that are essential for wireless of any type to take hold, adds Robert Shear, Dust Networks’ director of market development. Those include channel hopping, self-organizing mesh and time synchronization. The lat-ter unlocks the economics for the new specification, he says. “You end up with the ability to have battery-powered routers allowing frequency hopping.”

“The fact that there are batteries contributes to the low initial cost,” explains Weiss. “The highest cost element [in wired automation systems]: It’s still cable and con-duit and the time associated [with installation] and the disruption associated with a plant [through that installation].”

Potential users certainly will value two attributes highly, notes Martin Zielinski, director of HART and Fieldbus Technology for Emerson Process Management, Austin, Texas — reliability and coexistence, or the capacity of the wireless bands to carry traffic from various transmitters.

Immediate value

Many plants in the huge installed base of control systems using wired HART’s 4-20-mA loop lack the economic justification or technical capability to access HART devices’ in-telligent information. WirelessHART will significantly change that, Helson predicts.

“We tried to make it as easy as 4–20 mA, by extending the protocol with a view to allowing use of similar tools: self-building, self-healing networks and minimal engi-neer input,” explains Gareth Johnston, fieldbus-communications specialist with ABB, St. Neotts, U.K., who helped develop it.

End-users who understand the benefits of asset management will embrace Wire-lessHART, believes Dave Smith, manager, plant-network-technology systems marketing for Yokogawa of America, Newnan, Ga. It’s a “solution adding digital communication for device configuration and/or various prognostic/diagnostic functions provided by intel-ligent field devices — with minimum or no changes to control configuration.”

“It fits well with maintenance and asset management strategies,” adds his col-league Nobuaki Konishi, senior general manager of IA Marketing Division, Yokogawa Electric, Tokyo. He foresees a definite role for the new protocol for monitoring and alarming.

Two early asset-management applications come to mind to Siemens’ Stephan. One is transport of field-device diagnostic data. That’s because in the installed base, “precious diagnostic data. . . is lost in about 20 million devices, or must be read manually due to a lack of HART functionality in the remote I/Os (inputs/outputs),” he notes. The other: “complete wireless integration of process values and diagnostic data of field devices.”

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