Wireless Sensor Network Standards: On the Road to Convergence

Oct. 1, 2011
Two similar wireless standards—WirelessHart and ISA 100.11a—are competing for dominance as the enabler of smart instrumentation and all its promised benefits. Some users, however, are seeking convergence rather than competition.

Process industry users have been walking the path toward wireless communications for a number of years now. They are building confidence in wireless technologies one step at a time. They may have embraced smart wired instrumentation and seen process improvements. They understand the potential cost- and time-saving benefits of wireless communications, and maybe even have freed up money for a pilot project to investigate it for themselves. But faced with the need to get specific—to pick devices for their applications, commit to a trial, and the like—they find that a tough choice has to be made: Two similar wireless protocols—WirelessHart, promulgated by the Hart Communication Foundation (www.hartcomm.org) and ISA 100.11a, promulgated by the International Society of Automation ( www.isa.org)—are competing for dominance as the enabler of smart instrumentation in Europe and North America. And these two de facto standards don’t work together. A third standard, WIA-PA, exists in China and further complicates the task for those with Asian operations.

“Unlike with wired instrumentation, if you want to mix brands of wireless field devices to get an optimum mix of measurements, you can’t. You have to have two separate host systems to talk to two different types of field devices. And they have to come from different vendors,” explains Herman Storey, who retired from Shell Oil as a senior consultant in 2009 after 42 years with the company. “If you want to use the two types, you have to stock both types and remember which goes where. With the wired standards, I only have to stock one type of pressure transmitter and I can use it as a substitute for one of the others. I can buy the best product for the best application, I can switch vendors, and I can control my pricing and cost.”

The German Association NAMUR (representing some 120 users and vendors involved in process automation) published a very strong requirements document last year asking vendors for a single wireless sensor network for use in utility substations. In his blog, News on IEC 61850 and Related Standards, consultant and trainer Karlheinz Schwarz said, “NAMUR requires to get coexistence, interoperability and interchangeability for wireless based technologies…. The far too many IEC standardized protocol stacks of the Field Busses (comprising some 12,000 pages) are causing still a lot of headaches and pain.” IEC is the International Electrotechnical Institute, a European standards setting organization.

Can’t we all get along?

In many ways, WirelessHart and ISA 100.11a are alike. They are designed to serve the same market in the same way. At an application level, they perform the same function and have the same benefits.  Brian Neal, a senior controls engineer and project manager at Wunderlich-Malec Engineering in Las Vegas, says: “I see two remarkably similar wireless standards for instrumentation. Both ISA 100.11a and WirelessHart implement IEEE 802.15.4 radio hardware. Both protocols use DDL and Device Description files. Both would eliminate a lot of PLC I/O hardware, wiring and associated schematics. I could go on and on with the similarities,” he says. “It would be a huge win-win for the manufacturers and the consumers if the standards would converge,” Neal adds.

Now an independent consultant and co-chair of the non-profit ISA100 Wireless Systems for Automation standards committee, Herman Storey has been active both in the development of ISA100 wireless standards and in the discussions to converge ISA100.11a with WirelessHart. He and 119 other people sit on a convergence committee that is part of ISA100, called Working Group 12 (WC12). According to this group, a convergence of the WirelessHart and ISA100.11a protocols is urgent and essential. The effort, says Storey, is also “way down the road toward an impasse. I think we can break the impasse, but it isn’t a given.”

The obstacles seem to be commercial rather than technical. There are two similar protocols. Investments have been made, vendors and early adopters are lined up on either side, and product certification processes have been established. The two protocols have been developed into products for sale. Marketing programs designed to win over additional customers and vendor partners are in high gear. Both sides believe their approach is “right” and others should just come over to their way of thinking.  

ON THE WEB: The Race is On. Follow the intense developments of these two, wireless standards. See who’s jumped on board with what standard and what’s next. Visit bit.ly/related_026.

WirelessHart supporters say their protocol has numbers and momentum on its side: 15 vendors committed to making products and thousands of working networks established around the world. ISA100.11a supporters say that their protocol is a layered, adaptable standard that is the first of a suite of wireless standards necessary for addressing the entire plant, and therefore is the better long-term choice.

Storey says the differences between the protocols add a lot of unnecessary cost to use of the technology, and present barriers to users’ ability to freely pick vendors for systems and field devices, because the differences lead to differences in implementation, system integration, and field procedures. “The differences lead to engineering preferences, advantages, and disadvantages—much like VHS and Beta,” he says. “It is worth noting,” he adds, “that neither of those technologies is around today.”

Two organizations

The ISA100 committee runs a major wireless standards initiative for the International Society of Automation (ISA). Its initial focus is on the field level devices in process manufacturing applications and its first deliverable is ISA100.11a. Planned additions to the family of standards include support for backhaul functionality, factory automation and other key use cases. The ISA100 Wireless Compliance Institute (WCI) was formed to deliver compliance certification services for the work of ISA100. Its website lists 10 vendors, numerous large users and others as members.

Last year, an ISA100Wireless Plugfest demonstrated the interoperability of ISA100.11a field devices, provisioning devices and gateways. Last month, the IEC approved it as a publicly available specification. “There has been a great deal of interest to move ISA100.11a into the IEC process, and I am very pleased this has been accomplished,” said Tony Capel of Comgate Engineering, who is the chair of IEC SC65C, the committee that will oversee the standard.
Phoenix-based Honeywell Process Solutions is one of the key vendors associated with ISA100.11a. Phillip Ng, global senior product manager, says end users should consider their future needs as well as their current needs when choosing a standard to follow: “It’s not just the field instruments you need to worry about. ISA100 is all about the wireless infrastructure. The use of IPv6 (the latest version of internet protocol addressing) allows for every field device to be individually addressed and accessed.” By using IP addressing, NG explains, ISA100.11a can accommodate thousands of devices on a single wireless network.

The main thing that’s different about WirelessHart, according to Robert Schosker, product manager with Twinsburgh, Ohio-based Pepperl+Fuchs, is that it specifies Hart as the Application Layer while ISA100.11a leaves that layer undefined. “As a result, data in the Application Layer of SP100.11a can be transferred using Foundation Fieldbus, Profibus, Modbus, Hart or other protocols. While this makes SP100.11a highly flexible, the customer must decide which protocol to use,” he says. Schosker , whose company has worked with WirelessHart since its inception, says the decision to specify only Hart in the Application Layer delivers simplicity: a single data communication specification through the network. “While this may limit its perceived flexibility… data communication is well-defined and understood,” he says. 

ON THE WEB: IPv4 and IPv6 Developments. ISA 100.11a utilizes IP addressing, so what’s the future of IPv6 and IPv4 in the coming years? Click here to find out.

The Austin, Tex.-based Hart Communication Foundation is the technology owner and standards organization for the Hart Communication Protocol, and WirelessHart is defined in the latest version of the Hart specification—Hart 7, says Chuck Micallef, spokesperson for the foundation. It’s been approved as standard by the IEC as IEC 62591, and Emerson Process Management was the key vendor behind the development of the technology early on.

According to an ARC Advisory Group market study, 46 percent of all field devices installed worldwide at year-end 2010—32 million devices—communicate using the Hart Communication Protocol. Says Wil Chin, ARC research director, this is the largest market share of any field communications protocol—larger than all other fieldbus devices, proprietary protocols and 4-20mA combined. However, Micallef says the majority of installed Hart devices use Hart 5, rather than Hart 7.

Regardless, says Micallef, “WirelessHart is Hart and is therefore interoperable with all Hart-enabled control, programmable logic controllers (PLCs), safety and asset management systems. No existing Hart-enabled devices, control valve or control system needs to be replaced in order to implement WirelessHart alongside of the existing Hart assets.” As of Sept. 1, 2011, he also says that 27 vendors are building or intend to build WirelessHart products.  

Vendors speak out

Some vendors have been reluctant to commit to a direction until ISA100.11a gets further along. Memories of the “fieldbus wars” are still fresh, and no one wants that level of acrimony to exist. Sallyanne Ofner, president of Denver-based Levelese, Inc., a maker of wired and wireless liquid level sensors, says “When watching the discussions about [the] SP100 committee and WirelessHart, I felt thrown back into the late ‘80s when SP50 was extending into digital communications to bring some kind of order to product-to-product interfaces. It seems normal and healthy, though sometimes confusing and difficult to accommodate [the conflict], while the competing technologies are shaken out.” Levelese instruments use Hart and other communication methods, and the company resells Phoenix Contact gateways.

Flowserve Corp., manufacturer of pumps, valves, seals and other components, announced in April that it had joined ISA100 WCI as a supplier member. Senior Product Portfolio Manager Scott Wilkerson tells Automation World, “We have considered all protocols currently on the market and review opportunities according to customer demand. Joining ISA100 WCI gives us access to a technical and user ecosystem that enables us to accelerate our ISA100.11 product offerings. We look forward to offering our customers products based on the global ISA100.11a wireless standard.”

Schosker said Pepperl+Fuchs, which makes WirelessHart gateways and adapters, is “currently monitoring the activities of ISA SP100 and have chose to delay R&D investment in this particular standard. Pepperl+Fuchs supports SP100 and expects to develop products based on this specification once economic justification has been met and we have customer support to move forward with investment and R&D resources.”

Siemens is involved with both standards. It released WirelessHart products last year in Europe, and this year in the U.S., said Michael Cushing, process instrumentation manager. Siemens also supports other wireless protocols more commonly found in discrete operations such as packaging. On the German product development side, he says, “we’re active members of the ISA100 standard, and from a product perspective, it’s on the roadmap.”

Martin (“Marty”) Zielinski, who represents Emerson on the WC12 convergence committee, says, “Emerson Process Management has over 5,100 operating WirelessHart networks at sites around the world today [so] backward compatibility with the large installed base of IEC 62591 based devices is increasingly important. Emerson Process Management supports convergence, provided that this backward compatibility can be achieved.”

Status of convergence

Storey sums it up: “A lot of money has been invested in the two technologies. We have reached a point where the act of converging will cost a lot of money and possibly result in stranded investments.  The costs associated with having a fragmented market, however, have driven groups to discuss ways to accomplish convergence. ” From the standpoint of the market, standards convergence is important because it enables more rapid market growth, says Harry Forbes of the ARC Research Group. “From a technical standpoint, the challenges to converge even two standards are very difficult, and trying to combine three global standards [counting China’s WIA-PA] is even harder. The challenge is more difficult because the ‘voice of the end user’ is not a single voice by any means. Most importantly though, [users] have stated their highest priority is to achieve a single standard going forward in order to minimize total cost of ownership.” According to Ian Verhappen, director of system integrator Industrial Automation Networks Inc. in Wainwright, Alberta Canada, “End user involvement will be required if resolution of the three-part standard is to be resolved. Like anything, ‘money talks’ and until end users are comfortable that they will have life-cycle (20+ years) support for anything they install for permanent use, the next step will be some form of gateway that will ‘translate’ from one wireless protocol to another.” Vanhappen adds, “We all know this isn’t going to be over quickly but it will be the end users that decide.”Renee Robbins Bassett[email protected], is Managing Editor of Automation World.See also: Wireless Choices Abound: Ford and Rockwell Speak Out Visit www.automationworld.com/feature-9448Hart Communication Foundation (www.hartcomm.org)ISA100 Committee ( www.isa.org/ISA100)ISA Wireless Compliance Institute (www.isa100wci.org)

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