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Unfortunately, the detailed content of discussions around technicalities in industrial control networks is a different matter vis-à-vis intrinsic interest, at least to anyone outside the disciplines involved. Digital signal processing and the ramifications of control timing are not light dinnertime discussions. Engineering development in these arenas resembles development in every complex technical project: participants slog through a painstaking process of examining alternatives and weighing trade-offs.

Each person who has the knowledge, experience and skills needed for this kind of close technical examination, and who has made selections of one or two alternatives from among hundreds, usually comes away from the encounter with strong opinions. The upshot is, in any standards building process, there will be roomfulls of bright people, each initially leaning toward a specific and probably unique solution. Hammering out the differences can generate much heat while a standard is being born. We draw the curtain around this aspect of standards development, not for lack of importance, but for lack of space.

{mosimage}More easily discussed at a high level is the history and methodologies. WirelessHart began with Emerson Process Management, an Austin, Texas-based automation controls vendor. “We saw a huge potential for wireless automation,” says Bob Karschnia, director of technology for Emerson Process Management. “After several years of joint research and development with Dust (Dust Networks Inc., a Hayward, Calif., wireless networking technology provider), and a year-and-a-half of installation experience, we decided to open up the technology through the Hart Foundation. We felt that a WirelessHart standard would be the best way to proliferate the technology.” That was in late 2004.

The first group meeting was in March, 2005, involving some 15 companies, including Emerson Process Management, Honeywell, Siemens and Yokogawa.

“We began the process of an open standard for industrial wireless by looking at existing standards,” says Ron Helson, executive director of the Hart Communication Foundation. “We tried to find an existing standard that fit the various needs of Hart users. ZigBee was a natural choice, and the IEEE 802.15 (a standard promulgated by the Institute of Electrical and Electronics Engineers) specification that we chose to build on is almost certainly the result of ZigBee.”

However, ZigBee-based radios, although relatively low in power requirements, proved to be too power hungry. “We asked ourselves if we could mold some of the ideas behind ZigBee into a less power consuming technology. It had a lot of good things—mesh networking being a key one—but in addition to unwanted levels of current consumption, it didn’t have frequency agility, the ability to frequency hop automatically.”

The WirelessHart committee, made up of automation equipment suppliers, also looked at other existing wireless protocols with the objective of creating a network for wireless measurement via field devices. “Dust Networks then came forward,” Helson says. “Their technology became a starting point—the mesh network, frequency hopping and gateway communications control fit our needs. The committee extended and molded the basic infrastructure, adding to and enhancing the original concepts.”

The key objective was functionality. “We wanted an interoperable standard,” Helson says. “Devices from vendors A, B and C should drop seamlessly into a network controlled by a system from D, via a gateway from vendor E. On top of this, the WirelessHart standard is designed to hide the complexities and make for a familiar and easy transition from wired to wireless. Process users have enough on their plates—they don’t have the time to assimilate revolutionary new things.”

With its roots in Emerson, Dust, IEEE and a universe of other technologies, WirelessHart can be seen as an amalgam of both proprietary and standard elements. Far more of this kind of amalgamation characterizes ISA100.11a (a standard in development by the Instrumentation, Systems and Automation Society), with its broader focus. The increased number of constituent elements is, of course, consistent with the wider scope of the ISA100 wireless objectives, including standards for systems for discrete manufacturing as well as closed-loop control.

Among the many contributing standards to ISA100.11a are—prepare yourself for many a dot and many an
acronym—IEEE 802.15.4-2005 wireless personal area network (WPAN) radio specifications, 6LoPAN (Internet protocol 6 low power personal area network) specifications adopted by the Internet Engineering Task Force (IETF), and UDP (user datagram protocol), a message-oriented Internet transport layer. “Yes, there are a lot of available technologies, but we focus on what users need, and that simplifies the job of picking the best technologies to adapt to industrial needs,” ...