Wireless?

By Walt Boyes, Editor in chief

It's been nearly a decade since low-power field devices appeared using Zigbee as their mesh protocol. A consensus that Zigbee was not robust enough led to the formation of the ISA100 standard committee. A desire to extend the HART protocol to the wireless realm created the push toward what became WirelessHART. So, where have we come in the past few years?

Well, for one thing, WirelessHART has become IEC Standard IEC62591. There's a new standard from China. ISA100.11a is undergoing a rework, and is expected to be released again later this year. Zigbee has been strengthened, and is being positioned for use in smart-grid applications. So there are still four competitive standards, as we discussed last year. (See Control. Aug. '08, www.controlglobal.com/articles/2008/271.html.)

A Convergence of Standards?

There is an active "convergence" dialog between WirelessHART supporters and ISA100 supporters that's been pushed by some end users and vendors including Honeywell and Emerson. Hesh Kagan, technology innovation director for Invensys, says, "It's not a technology issue. Convergence can work if the key players want it to work." 

Pat Schweitzer of ExxonMobil and co-chair of ISA100 agrees from an end user's point of view. "Technically there is no issue. Both base specs were developed under the same premise. One is constrained only by the applications layer that was adopted. The base networking is almost the same. The better question is can the supplier community ever come together to meet the users' expectations."

David Land, field instrumentation network lead from ConocoPhillips agrees. "I hope so! Not sure it can be done at this point." But, another engineer with a consumer products company, who asked for anonymity said, "I don't care."

The ISA100.12 committee, which was set up to manage the convergence, hopes to include Zigbee and the new Chinese standard, as well as WirelessHART in a converged ISA100 standard. However, a survey of many ISA100 committee members shows them divided into two basic camps. The first, mostly comprised of end users, feel that convergence must work.

The other group feels that convergence is a chimera, and we'll be stuck with competing standards. "Full convergence (meaning coexistence of WirelessHART, ISA100 and ZigBee products within the same sub-net) is not realistic and not really useful," says Jean-Pierre Hauet of KB Intelligence. "These subnets will comprise no more than 100 field devices. The development of backbone routers allowing the transparent communication between sub-nets should suffice." Lou DiSilvio of IndustrialTelemetry Inc. is quite blunt. "Yes, ultimately it may be made to work. Octagonal tires would work on cars if you could stand the ride." From the end-user and EPC point of view, Scott Sommer of Jacobs Engineering says, "I don't need wireless standards to converge; I need them to play nicely together in the same airspace! To me, this is a silly concept. Did we ever need 4-20ma, 24VDC and 120VAC to converge? No, we just let them play nicely in the same space by providing each with their own connections and making sure they stay separated."

Sommer and Hauet have a point. Real convergence is already happening in the network layer behind the field sensor network gateway. Roy Freeland, CEO of Perpetuum, a U.K.- based manufacturer of energy-harvesting devices, put it well; "Most plants will just connect into whatever backhaul system is already there."

According to a recent ControlGlobal.com survey (www.controlglobal.com/wirelesssurvey2010.html), while 46% of respondents say it is just a nuisance, 54% say that competing standards are keeping them from deciding on implementing a wireless field device network or making them look for alternatives to wireless.

Alternatives to Wireless??

In an ironic twist, because of the delays in producing wireless field devices and agreeing on a common standard, wireless sensors may have missed their window. For WirelessHART, one of the chief arguments has been that the "stranded data" (diagnostics, other PVs, time stamps, etc.) in the over 25 million installed HART transmitters needed to be extracted. Our survey indicates that 62% of end-user respondents seriously question the utility of that data. Our survey of ISA100 members bears this out as well. Our anonymous engineer from the consumer products company is very clear. "No! We don't use HART data now, so getting stranded diagnostics is of almost no value to us."

Dick Caro, a wireless consultant with CMC Inc., agrees. "If it was really important, a HART multiplexer could have been used long ago." And Peter Fuhr, formerly CTO of Apprion, says, "Discussions with individuals at multiple industrial facilities reveal that 'stranded data' is more valuable to the vendors than the end users. This feeling may change over time, particularly as maintenance costs rise."

It Costs HOW Much?

And, in another twist, wireless sensor pricing appears to be having negative effect on the adoption rate of wireless sensor networks in process plants. Our survey indicated that over 70% of respondents thought that pricing currently is either "way overpriced" or "moderately overpriced." Only about 28% of respondents seemed satisfied with current pricing. Art Sampson, a product manager with Hach Co., is emphatic about what he's seeing in the market. "With a HART wireless adapter costing around $800, the price will need to drop 75% to be viable in municipal markets," Sampson says.

The argument is that prices will come down as soon as more competition arrives on the scene. Invensys' Kagan says, "There will be a coming together of supply and demand—there always is. The largest cost associated with wireless sensors is packaging. The radio is very low-cost. The gateway is hopefully amortized over a large number of sensors. The real issue around price is competition. As more vendors enter the sensor market, the price will come down and the utilization will go up."

Emerson's vice president of wireless, Bob Karschnia, has a slightly different view. "The cost of a wireless measurement point needs to be compared to the total cost of wiring the same point," he says. "Several studies have shown that the installed cost is reduced by 50%-80%. Time savings are also a huge factor, not only the actual billable hours that are saved, but also the longevity of the overall project. So if you just ask the question in one direction, you get one answer, and if you ask in another, you get a different answer. The best way to evaluate pricing is through some sort of conjoint where tradeoffs are made, because those are the decisions that customers really make. At this point in the adoption curve, lower prices would not increase the adoption rate at all. Additionally, economies of scale will kick in as volumes rise, and this will help with pricing."

Prices had better come down, as ControlGlobal.com blogger and industrial networking theorist Ian Verhappen noted in a recent blog post (http://tinyurl.com/22lcyue). "Wireless is being proposed as the easiest and lowest cost way to install additional infrastructure between a field device and the control system when the home-run cable is 'full.' Unfortunately, this is not true since, as the title implies, another alternative exists and that alternative can be used in any area classification. The solution is fieldbus," Verhappen wrote.

In a ControlGlobal.com survey done in March 2010 in cooperation with Apprion, Inc., 41% of respondents identified cost of wireless devices and infrastructure as the number one barrier to wireless device deployment at their plants.

Current wireless field device pricing is based on the theory that it will be total installed cost that determines the application. In the case of extracting the "stranded data" from HART transmitters, which is the largest single potential application, the new ISA100-based HART wireless adapter from Honeywell and WirelessHART adapter products from Emerson, ABB, Siemens, Pepperl+Fuchs and others are priced at very close to the same cost as putting in wired HART multiplexers and modems.

One member of the ISA100 committee who requested anonymity noted that the pricing needs to be significantly less than it currently is, or plants will just wait for shutdowns and put in HART modems. Worse, they may decide that the "stranded data" isn't worth it anyway and do nothing.

And What About Those Batteries?

The supposition has always been made, since the early days of Zigbee, that wireless sensors are supposed to be low-power consumption, and that battery operation is desirable. But in nearly all process automation applications, line voltage ("mains" power) is usually closer than the closest marshalling cabinet.