Making Sense of Wireless from www.automationworld.com

Making Sense of Wireless
November 2006

Written by By Gary Mintchell, Editor in Chief

Discussions of wireless technologies in manufacturing sometimes take on a religious fervor among adversaries, leaving engineers scratching their collective heads. But indicators of resolution are positive.
Today, when discussions turn to industrial wireless networking, one often hears a curious mix of successful application stories combined with promises of much to come in the future. The field is new enough to generate a whole series of unfamiliar buzzwords that can leave managers and engineers scratching their heads in bewilderment when trying to decide which direction to go in their plant automation designs.
Wireless technology is not totally new to the factory. Remote supervisory control and data acquisition (SCADA) sites have used specialized radio telemetry for many years. Also, the growth of the network popularly called WiFi (from wireless fidelity) for personal computer (PC) networking based on the 802.11 standard of the Institute of Electrical and Electronics Engineers (IEEE) has bled over into industrial applications.
Now, however, a recent series of new sensor network products—especially for process plants—is showing promise for helping engineers achieve better plant performance. To be sure, continued bickering among technology suppliers regarding which technology is best suited to industrial performance clouds this promise. But there are signs that the situation is beginning to sort itself out, and now may be the ideal time for manufacturing professionals to take the deep dive into the promise of wireless.
Wireless pump control
The Coca-Cola Co. purchased a plant in southern Missouri to bottle its Dasani brand of drinking water. The facility would draw water from the nearby Roubidoux Formation—the source of some of the purest water in North America. What Coca-Cola officials didn’t know, however, was that the plant was not equipped to pump the roughly 1,000 gallons of water per minute needed to meet demand. At best, the plant would be able to pump only half that amount.
Now, though, the plant is pumping more than 1,500 gallons of water per minute, thanks to a new control and data acquisition system provided by Opto 22, of Temecula, Calif. “We used Opto 22 hardware and software to build this system primarily for the sake of simplicity,” says Barrett Davis, owner of The Automate Company LLC, the Pacific, Mo., control systems integrator that designed and installed the system for Coca-Cola. “We typically build the panels for our control systems from scratch, and the Opto 22 hardware and software makes it easy to do that.”
The system includes a pump on each of the three wells, each controlled by a variable frequency drive (VFD). The three drives must work in coordinated fashion to ensure that the storage tank does not overflow. “Any of the well pumps can be designated as the lead,” Davis explains. “That pump will have a set point for moving water at a certain level of pressure, say 60 psi (pounds per square inch). Once that point is set, the pump will work to provide that level of pressure to the plant at all times. The VFD works to speed the pump up or slow it down, as necessary, to keep the pressure at that level.”
An Ethernet network for the system connects an OptoTerminal—the primary operator interface—and Snap Ultimate input/output (I/O) controller and I/O systems, many of which are connected to the network wirelessly. The system continually monitors pumping activity. It detects when a VFD is operating at maximum speed and can no longer make the lead pump push enough water to keep up the required level of pressure. When that happens, an additional pump is called into action. This new “lag” pump begins moving water at a preset minimum speed.
“Having an Ethernet-based system and running it over a wireless network means that all of the communication takes place very quickly and efficiently,” Davis says. “When the Snap Ultimate unit sends out a request for information, the response arrives within three milliseconds, as opposed to five to 10 seconds with traditional radio telemetry equipment.” This fast response time means that the plant is always operating at maximum efficiency and never pumping too much or too little water.
Possible applications
While there are already SCADA and some control applications such as this one using wireless technologies, many possible applications are awaiting the outcome of standardization efforts. There are two organizations working on standards—the Hart Communications Foundation and the SP100 committee of the Instrumentation, Systems and Automation Society (ISA). Davis Mathews, regional business unit manager for interface at Phoenix Contact, a Harrisburg, Pa.-based automation supplier, reflects the opinions of many when he notes that the SP100 committee seems to be divided on technology into two groups driven by vendors Emerson Process Management and Honeywell Process Solutions, respectively.
“One thing I noticed was SP100 trying to emulate the IEEE 802.11 wireless local area network,” says Mathews. “That will be popular. We sell about $5 million per year now of 802.11 products with a proprietary-based product. But customers are looking for a standards-based product so that they can use more devices. Meanwhile, the Hart group decided to move quickly and develop its own wireless standard. It is agreeing on the IEEE 802.15.4 mesh standard for radios. In this area, technology innovation comes from suppliers, but needs to come from users. So, Hart put together a demo with products from eight suppliers for the ISA Expo (Oct. 17-19, in Houston) to enable customers to see a direction and provide feedback.”
Mathews sees major customer applications starting in the sensing world. The technology is so new in manufacturing that customers are hesitant to move to continuous monitoring or control right now. “The technology’s evolving,” says Mathews. “Customers are already sending data. It’s only a matter of time before they apply wireless to other needs. Look at the evolution of wired Ethernet use.”
How big could wireless networking become? Senior Analyst Harry Forbes, of ARC Advisory Group Inc., the Dedham, Mass., analyst firm, writes in a research report titled “Wireless Technology in Process Manufacturing” that the worldwide market for wireless technology for manufacturing is expected to grow at a compound annual growth rate of 26 percent over the next five years—from $325.7 million in 2005 to more than $1 billion in 2010.
Sean Keeping, vice president, technology, for ABB Instrumentation, St. Neots, England, also points to the two standards under development from the process industries point of view. “Hart has been discussed for some time and is reasonably well developed. We have some prototypes for testing by the industry. It’s not something that is device vendor-proprietary, it’s an industry standard. SP100 is slightly less developed than Hart, but many key players are looking at this. These two emerging standards are likely to succeed. I think the industry does not want a device specific or vendor specific solution.”
Keeping believes customers will develop confidence in the technology as the suppliers prove that the newer products are both reliable and secure. Adds Gareth Johnseon, fieldbus communications specialist at ABB, “Users are using some proprietary products now, and they are asking for more information. It’s not like when the fieldbuses came in. We’re seeing a lot of inquiries about setting up pilots or field trials.”
A matter of vision
What are the important factors that standards bodies should consider? Hesh Kagan, director, new ventures, for automation supplier Invensys Process Systems, in Foxboro, Mass., says, “The function that comes to mind most is interoperability. But that may not be most important to users. That may be coexistence—that is, will the various radios interfere with each other, be immune to lightning or other radiation and the like? Interoperability will come with a bit-level standard.”
Where will wireless technologies find a home in industry? Says Kagan, “Every customer has an application that’s most important to them. I see applications like field data logging from satellites and voice over Internet (VoIP) replacing some currently used radios, perhaps adding a little remote I/O to make remote control easier. I expect to see incremental video over the network for physical plant security. Another application is the mobile operator concept with tablet PCs where an operator can still be in touch with the operation even while stepping away from the main console to check out a problem somewhere else.
“Coming down the pike, I see expanded condition monitoring with low-cost sensors. It’s going to be a whole new model of doing maintenance based on those sensors and model-based predictive maintenance. The dollars that can be saved in continuous process are enormous. In the longer term, an interesting thought is to consider what happens when these low-cost condition monitors take hold. They will be very inexpensive compared to today’s process measurement. What if at some point someone takes a look and thinks, ‘That condition monitor may be good enough for process measurement.’ I may have two excellent measurements now. But there’s a lot of math being developed that would say, ‘What if I have 20 to 30 not-so-excellent measurements but I can develop a profile that would give me better information overall?’ This is at least five to seven years out, but think of the potential.”
Someone else thinking long term about the philosophy of process control is John Berra, president of Emerson Process Management. He says, “Plant knowledge is the key to improving business performance. No wires means no limits. We can put more sensors in plants at a tenth of the cost with wireless technologies. More eyes and ears in the plant means added intelligence.”
Products now
Emerson announced the availability of several wireless sensor products and a gateway at its Users Exchange Conference Oct. 2-4 in Nashville. The technology uses IEEE 802.15.4 mesh radios with technology from Dust Networks. Says Bob Karschnia, vice president of technology for the Rosemount division of Emerson Process, “We did three years of field trials to test out various technologies. We looked at the CDMA (code division multiple access) tree structure, which uses direct sequence spread spectrum technology built on IEEE 802.11 WiFi, but then we switched to mesh networks built on IEEE 802.15.4 with frequency hopping. It coexists with WiFi in a plant, but doesn’t require a site survey to install nodes. Reliability of a mesh network actually increases with the number of nodes installed.”
Dave Kaufman, director of integrated field solutions at Honeywell Process Systems, in Phoenix, says, “As we looked at plant requirements, we saw different classes of applications, including safety, closed loop control, open loop control and monitoring. Customers told us they wanted to do them all, and if they could go wireless, they’d like to do that. So as we looked at architectures, the question we asked ourselves was, ‘How can we do this efficiently and effectively.’ Even if customers may not go directly to control applications right away, we wanted to provide a single infrastructure to handle everything. So, we went after a robust architecture with the performance to meet all requirements.”
Robert Jackson, product marketing engineer at Austin, Texas-based test and automation systems vendor National Instruments (NI), sees the current state of wireless as the market “long tail” effect, citing a book by Chris Anderson, titled “The Long Tail: Why the Future of Business is Selling Less of More.” The long tail effect describes a curve with the quantity of each item sold on the y axis and individual products on the x axis. Mass marketers sell a few items of huge quantities each, while other companies—Amazon.com being a good example—sell only a few each of a very large number of products, which in total add up to a large quantity—the long tail of the curve.
Jackson reports that NI typically uses 802.11 wireless technology and is partnering with many wireless technology companies, including Accutech, Alcatel, Crossbow, Oceania and Phoenix Contact. “We have drivers within LabView, our programming software, to each of these wireless providers with virtual instruments (software function blocks) defining each driver to make it easy for our integrator partners to develop applications. Right now, typical applications are for monitoring and communication. We aren’t always sure what our partners and integrators will do next, but we’ll have the technical foundation for them to do it.”
Adds NI Senior Product Strategist Dave Potter, “Just looking at the companies that we have drivers for shows how fragmented the wireless market is right now. Different technologies fit different applications. The way we look at it, LabView provides a common interface to all of these largely proprietary networks. The benefit of 802.11 is the huge number of developers working with it, especially for security. There is growing momentum for 802.15.4 currently.”
Nobuaki Konishi, general manager at Yokogawa, the big Tokyo-based automation supplier, says his company recognizes “field wireless” and WiFi. “Wifi is already established as a technology, but it assumes much power supply. It can be used with PCs (personal computers) and other handheld devices, though. ‘Field wireless’ is what we call technology at the sensor level. This requires devices in the field that require little power supply. Standardization here is still under development. Our intention for this standard is one radio and network management in order to avoid the many protocols of the wired fieldbus solutions.”
Jeremy Bryant, automation marketing network specialist at supplier Siemens Energy & Automation, in Alpharetta, Ga., sees many applications for wireless in manufacturing. “Wireless networking gives ease of access to the automation system without the need to plug in. So, if you physically can’t get to a panel easily, you can still get at the information. Another application is remote monitoring and control. Some applications like airplane hanger doors require complicated cable festooning, where wireless makes much more sense.”
Eric Marske, product manager for wireless modem provider Electrical Systems Technology-ESTeem, Kennowick, Wash., says, “The biggest thing in designing an application is picking which direction to go. There’s a lot of excitement around wireless right now. This is good. Ten to 15 years ago, wireless was a black box. Now there are purposes for it. Right now, the best-selling systems are in water/wastewater SCADA over long distances. Implementations have come to be based on Ethernet. There’s enough bandwidth now to add video as well.

Wireless Pioneers from www.automationworld.com

Wireless Pioneers Tell All
October 2007

Here's a look at some of the trials, tribulations and challenges faced by two early end-users of industrial wireless networking technology, along with some lessons learned and benefits gained.
There’s an old adage about pioneers: They’re the ones who take the arrows in their backs. In the best cases, however, the pioneers who successfully dodge the arrows—or even survive a few hits—are the ones who also gain the advantages of being out in front. And when it comes to industrial wireless networking technology, some of today’s pioneering end-users believe that their efforts will pay off for their companies in just such a way.

Leading The Charge
Take the case of David Runkle, production manager at Lost Pines Power Park, an electric power generating complex about 40 miles southeast of Austin, Texas. When Runkle led the charge last year to install a wireless infrastructure at the facility for a new wireless public address system to boost staff efficiency, he faced heavy opposition from his corporate information technology (IT) department. One IT staffer, concerned about security, even hired a third-party hacker to try to break into the system as it was being launched.Runkle also took flak from some plant personnel when he and a wireless vendor formed a “core team” of employees to test a set of wireless Voice over Internet Protocol (VoIP) paging devices. Their mistake was distributing the devices too soon, before all of the system bugs were worked out. Some workers had already been skeptical of the technology. And when the wireless system would suddenly stop working due to intermittent problems, those suspicions were reinforced.The cause of the problem was minor, and has since been corrected. But by moving too soon with the tests, the Lost Pines wireless team lost the chance for some “early buy-in” for the project from key plant personnel. In retrospect, says Runkle, “we probably should have waited until we knew what all the issues were.”
Today, however, Runkle is “still standing” after surviving the early problems. The wireless system is up and running, and working well. And the infrastructure put in place for the public address system—installed at cost of about 25 percent less than that of a comparable hard-wired system—includes a “wireless umbrella” over the Lost Pines complex that can cost-effectively accommodate other industrial wireless applications.

What that means is that the Lost Pines Power Park is now well-positioned to use its new wireless infrastructure to cash in on a broad range of other cost-saving industrial wireless applications, Runkle says. “The project was justified on the communications piece alone, and now we’ve got a number of future applications that are already on the drawing board.” These range from remote wireless monitoring of Internet protocol (IP) video cameras, to wireless tank level sensing, leak detection and wireless systems for stress wave analysis-based equipment monitoring.


PPG Industries' Lake Charles, La., plant is using Emerson's Smart Wireless self-organizing mesh network technology at its A Caustic Unit. Shown at left is a Rosemount wireless temperature transmitter, which is being used as a repeater for wireless temperature and level sensing applications. The mesh technology has worked well in tests, and PPG plans to expand use of the technology, says PPG Senior Design Engineer Tim Gerami (right).
IT buy-in

Another pioneer in the industrial wireless space is Tim Gerami, senior design engineer at the Lake Charles, La., plant of PPG Industries Inc. The plant, which comprises more than 20 operating units on about 765 acres, manufactures chlorine, caustic soda and chlorine hydrocarbons.Unlike Lost Pines’ Runkle, Gerami says he hasn’t suffered any slings and arrows from his company’s corporate IT staff. One key is that Gerami and his fellow Lake Charles engineers got the corporate IT department involved early; they invited IT people from PPG’s Pittsburgh corporate headquarters to join the initial, multi-discipline team formed in 2005 to investigate use of wireless technology at the Louisiana plant. As a result, says Gerami, “it’s a very free and open exchange [between IT and process controls departments] and we all get along very well.” IT involvement at each step of the way also ensures that the wireless team doesn’t run afoul of any corporate IT policies, he adds.That’s not to say that the Lake Charles wireless team didn’t encounter its share of early problems and setbacks. Some setbacks had nothing to do with wireless technology. Shortly after the PPG team received approval for its first wireless pilot project in late summer 2005, Hurricane Rita roared through, knocking out power and leaving standing water in the Lake Charles plant, which was shut down for 2½ weeks. Then, beginning in late May 2006, the plant suffered a 110-day strike, which had an equally debilitating effect on the team’s ability to install and test wireless technology. That’s life in the real world.Despite those obstacles, the PPG team was able to successfully complete testing on a variety of wireless technologies and applications at the plant throughout 2006, and is continuing its testing in 2007, says Gerami. And not everything has gone without hitches, or turned out as expected.Wireless Fiber In the early going, PPG tested both IEEE 802.16 WiMAX technology (for Worldwide Interoperability for Microwave Access) and IEEE 802.11 Wi-Fi technology (for Wireless Fidelity). Both are wireless standards promulgated by the Institute of Electrical and Electronics Engineers (IEEE). Wi-Fi is the familiar and increasingly ubiquitous technology that allows wireless connection through “hotspots” in homes, offices, airports and retail establishments such as coffee shops. WiMAX is a longer-range, higher-bandwidth wireless technology that can be used for long-distance, backhaul applications, and also can also provide a wireless “umbrella” over a facility. Compared to a typical Wi-Fi range of a few hundred feet, WiMAX supports a coverage range of 30 miles, along with significantly higher data rates.WiMAX is “sort of like wireless fiber,” observes Steve Lambright, chief executive officer at Apprion, a Moffett Field, Calif.-based vendor that offers a WiMAX-based product family for industrial use. The company’s ION product platform is designed to provide broadband wireless capability on a vendor-agnostic and standards-agnostic basis. Video data from remote security cameras, along with Wi-Fi-based VoIP traffic, for example, as well as data from an IEEE 802.15.4 wireless mesh sensor network, could all be backhauled together on the same WiMAX network, Lambright explains.
Invensys Process Systems, the Foxboro, Mass.-based automation supplier, has partnered with Apprion to provide wireless application services. And because the PPG Lake Charles plant uses distributed control systems (DCS) from Invensys Foxboro, the PPG wireless team at the plant worked with the Invensys/Apprion team—along with various other vendors—for some of its early wireless tests. The PPG plant also uses Rosemount transmitters from Emerson Process Management, the Austin, Texas-based process control vendor, so the PPG team also began work early-on with Emerson as a beta site for some of that vendor’s Smart Wireless mesh networking technology.
WiMAX Intentions On the WiMAX front, PPG began beta testing in early 2006 on the wireless transmission of video data from an inexpensive IP video camera, says Gerami. “At the time, our intent was to have WiMAX blanketing the whole plant in umbrella fashion, and security cameras that had WiMAX connections would send the video back.” The PPG team was also considering WiMAX for the transport of bar code- or radio frequency identification (RFID)-scanned data that would be used to track forktruck delivery of products and materials to some 150 delivery stations throughout the plant.Another WiMAX link-up would handle long-haul voice communication between the Lake Charles plant and two salt water brine feedstock facilities that are about eight and 21 miles away. That system would replace the unreliable telephone connections to the brine fields, which are in remote, rural locations.But a couple of things happened that altered the PPG team’s thinking about WiMAX. One was the failure of WiMAX technology to take off in the market. “We had heard that there would be a wealth of WiMAX appliances coming out, because of the Intel Rosedale chip, which is WiMAX enabled,” says Gerami. “We thought there would be WiMAX laptops coming out, and WiMAX VoIP, WiMAX PDAs (personal digital assistants) and other things.” But so far, despite the introduction of the Rosedale chip by microprocessor supplier Intel Corp., Santa Clara, Calif., “that just hasn’t occurred,” Gerami observes.As a result, the PPG team began taking a closer look at the capabilities of Wi-Fi, which it was also testing in the Lake Charles plant. The team discovered that it could use an indoor industrial Wi-Fi access point, priced at about $300, and enclose it in a National Electrical Manufacturers Association (NEMA) 4X box for outdoor use at a cost of only about $200 more, says Gerami. “So for less than $1,000, we can get a 54-megabit/second (Mb/s) Wi-Fi access point,” he notes, “whereas it might cost $6,000 to maybe $20,000 for a WiMAX base station.”A Better OptionGranted, says Gerami, the Wi-Fi technology can’t match the throughput or range of WiMAX. “But once we started studying it, we decided it was better to just blanket the plant in Wi-Fi, by having hundreds of access points, instead of covering the plant with one, two or maybe three WiMAXs,” Gerami explains.The second thing that happened involving WiMAX was that one contractor used by the PPG team apparently installed the wrong radio for one of the test applications. Instead of deploying a point-to-point WiMAX radio for the brine field communication tests beginning in mid-2006, the contractor installed a point-to-multipoint unit. The result was that the system didn’t work correctly. And PPG now has decided to replace the long-haul WiMAX connection with a dedicated 5.9 Gigahertz non-WiMAX radio from another vendor, Gerami says.Neither has PPG’s Wi-Fi testing progressed without providing some learning experiences. “In early 2006, we installed several Wi-Fi access points and had some issues with them dropping in and out,” Gerami relates. “We finally figured out what was wrong, with a consultant, and got those pretty stable, with some firmware upgrades.”The PPG team also learned that even though a Wi-Fi access point may be labeled “industrial,” that doesn’t necessarily make it so. PPG has done much of its wireless testing in its A Caustic unit, one of three caustic soda production units at the Lake Charles plant. This included the installation of nine Wi-Fi access points for testing with VoIP, as well as with wireless handheld computers used for operator rounds, along with tablet personal computers (PCs) for use by technicians in wireless equipment calibration.Wi-Fi Failures Despite the “industrial” rating for the early Wi-Fi access points used, the PPG team found that the units couldn’t withstand the rigors of the outdoor A Caustic environment, which includes chlorine, caustic soda and acids. “They’ll say it’s industrial, but it’s just Class 1. It will meet explosion proof ratings, maybe Class 1, Div. 2, but it won’t meet NEMA 4X corrosion resistance ratings, which is what we need,” Gerami says. By about April of this year, some of the Wi-Fi access points were experiencing failures due to gasket erosion and corrosion on portions of the device that were aluminum, instead of stainless steel, he notes.After researching the issue, Gerami says the PPG team determined that that no vendor at the time was making a true industrial Wi-Fi access point. The PPG team solved that problem by purchasing lower-priced indoor Wi-Fi access points and enclosing them in NEMA 4X enclosures. At least two vendors—Apprion and Cisco Systems—have since introduced Class 1, Div. 2 NEMA 4X Wi-Fi access points, says Gerami. But for now, PPG is moving ahead with tests using indoor access points enclosed in NEMA boxes. The team hopes to make a decision soon on which approach and which vendor's access points to use, and then to move ahead with a plan to blanket the entire plant with Wi-Fi during 2008, Gerami says. Including the plant’s 20 operating units and various non-production areas, that may require about 300 Wi-Fi access points, he estimates.As part of his advice to other industrial end-users who may want to get started with wireless, Gerami recommends working with as many vendors as possible, and then to “test, test, test and test some more. If any salesman wants to bring you something to try out, go ahead and try it,” he says. “It’s worth it because you learn so much.” And even though PPG has decided to move away from use of WiMAX technology for now, Gerami says the PPG team is still in talks with Apprion and Invensys “to see their latest offerings. They have a really good solution, and we’re still considering them,” he says.PA Upgrade Indeed, Lost Pines’ Runkle says that his company’s successful wireless implementation and infrastructure is based upon the Invensys/Apprion technology. The Lost Pines Power Park, which is operated by the Lower Colorado River Authority (LCRA), is made up of two adjacent power producing facilities—the Sim Gideon power plant, which began commercial operation in 1965, and the newer Lost Pines Power Project built in the 2000/2001 timeframe.When the two operations merged in February 2005, Runkle, who had been production manager at Sim Gideon, took over the job for the combined operation. It quickly became apparent that an upgrade of the combined plants’ communication system would be needed, he says. Sim Gideon’s 42-year-old Public Address (PA) system was rapidly reaching obsolescence. And because the newer plant had no PA system, it was extremely inefficient to try to page and otherwise locate plant mechanics and technicians, who could be working on either of the two sites.A request for proposals for a hardwired PA system produced “sticker shock,” as Runkle puts it. But through a 12-year-old LCRA alliance with Invensys, Runkle heard about the Invensy/Apprion approach to wireless, and inquired about its possible use to meet Lost Pines’ communication needs. A July 2006 site assessment by Apprion and Invensys showed that “it was very doable,” says Runkle, despite the preponderance of large steel structures at the Lost Pines facilities.The project proceeded, albeit with various issues and challenges, including those described at the top of this story. But in the end, says Runkle, Lost Pines ended up with a highly effective system that includes a 360-degree WiMAX backhaul system, creating a wireless umbrella over the facility. A total of 51 Wi-Fi access points were installed throughout the plants for local area network access, and the common infrastructure enabled VoIP to support wireless communication using a voice-activated pendant that workers wear around their necks. Wireless speakers were installed throughout the facility, and the system integrates with the private branch exchange (PBX) system and personal cell phones for enhanced connectivity.The entire infrastructure was put in for a cost of “a little over $400,000,” says Runkle, compared to a $560,000 price tag quoted for a hard-wired PA system, prior to any cost adders. And now, given the vendor- and standards-agnostic nature of the WiMAX backhaul system, says Runkle, “any future wireless applications that we choose to purchase can be easily added to the foundation that’s already in place. So the return on investment will just continue.”
Mesh Tests Beyond Wi-Fi and WiMAX, one of the most discussed technologies today in the industrial space is wireless mesh sensor networking. Runkle, for one, has been working with Emerson regarding future testing of some of that vendor’s forthcoming products in this arena. And the PPG Lake Charles plant has been working with Emerson as a beta test site for the vendor's emerging Smart Wireless mesh networking family since late 2005, Gerami says.As with other wireless technologies, PPG has done its wireless mesh testing in its A Caustic unit. “We brought our 900 Megahertz (MHz) Elpro technology there [to A Caustic], our 900 MHz wireless mesh Emerson technology there, our Wi-Fi, and we also had WiMAX there for a little while, just to make sure that coexistence wasn’t an issue,” Gerami explains. “And they seemed to work very well, all together, and are still working very well.”PPG’s initial Smart Wireless tests involved eight wireless sensors to provide redundant tank level measurements for some existing radar level systems. “With the radar only, we were strapping, or measuring, the tanks by hand every four hours,” Gerami says. “But now, with the radar and the Emerson wireless level sensors in place, we strap it only on Sundays.”Subsequent Smart Wireless tests involved 10 additional sensors to measure steam pipeline temperatures. “Those pipelines had no temperature measurements on them at all before,” notes Gerami. The mesh technology has worked so well that PPG’s long-term plan now is to install Smart Wireless-based temperature profiling across the entire plant, says Gerami. “I think we’ll have that running by the end of the year, if not before.”PPG is continuing to work with Emerson for beta testing of additional Smart Wireless product technologies. The list includes wireless vibration monitors, wireless corrosion monitors, instrument health monitors and a wireless device manager for Emerson’s AMS Suite of predictive maintenance applications.Benefits Galore So far, PPG’s total cost to purchase, install and test the full range of Wi-Fi, WiMAX and wireless mesh technologies has been in the neighborhood of $400,000, Gerami says. But the savings in conduit and wiring costs from use of the wireless mesh technology alone has already amounted to $216,000 in 2006, he notes, with an additional anticipated savings of $343,000 in 2007 and 2008. That’s not to mention anticipated benefits ranging from improved productivity of workers equipped with wireless tablets and handheld devices, to the elimination of telephone lease lines and the ability to gather data wirelessly that was previously unavailable in the wired world.Despite some of the problems and challenges encountered, neither Gerami or Runkle have any regrets about being early movers in the wireless space. Both feel the efforts have given their operations an advantage going forward.
“I do feel like we’re really trying to be cutting edge with wireless,” Gerami observes. “I wish we were further along than we are. Rita and the strike really hurt us. But we’re trying to get it together and move forward, because there are a lot of savings here. This is really good stuff, and we’re excited.”Lost Pines’ Runkle is no less effusive. “We’re going to be ready for whatever comes along in wireless,” he says. “I think we’re ahead of the game. And there’s no doubt in my mind that wireless is going to be the next big thing in the process world,” he declares, “because it works.”

IEEE 802.15.4

To get the detailed description of 802.15.4 go to:

http://standards.ieee.org/getieee802/download/802.15.4-2006.pdf

Wikipedia on IEEE 802.15.4

IEEE 802.15.4
From Wikipedia, the free encyclopedia

IEEE 802.15.4 is a standard which specifies the physical layer and medium access control for low-rate wireless personal area networks (LR-WPAN's). As of 2007, the current version of the standard is the 2006 revision. It is maintained by the IEEE 802.15 working group.
It is the basis for the ZigBee specification, which further attempts to offer a complete networking solution by developing the upper layers which are not covered by the standard.
Contents
1 Overview
2 Protocol architecture
3 Network model
4 Data transport architecture
5 Reliability and security
6 See also
7 References
8 External links
//

Overview
IEEE standard 802.15.4 intends to offer the fundamental lower network layers of a type of wireless personal area network (WPAN) which focuses on low-cost, low-speed ubiquitous communication between devices (in contrast with other, more end user-oriented approaches, such as Wi-Fi). The emphasis is on very low cost communication of nearby devices with little to no underlying infrastructure, intending to exploit this to lower power consumption even more.
The basic framework conceives a 10-meter communications area with a transfer rate of 250 kbit/s. Tradeoffs are possible to favor more radically embedded devices with even lower power requirements, through the definition of not one, but several physical layers. Lower transfer rates of 20 and 40 kbit/s were initially defined, with the 100 kbit/s rate being added in the current revision.
Even lower rates can be considered with the resulting effect on power consumption. As already mentioned, the main identifying feature of 802.15.4 among WPAN's is the importance of achieving extremely low manufacturing and operation costs and technological simplicity, without sacrificing flexibility or generality.
Important features include real-time suitability by reservation of guaranteed time slots, collision avoidance through CSMA/CA and integrated support for secure communications. Devices also include power management functions such as link quality and energy detection.
802.15.4-conformant devices may use one of three possible frequency bands for operation.

Protocol architecture

IEEE 802.15.4 protocol stack
Devices are conceived to interact with each other over a conceptually simple wireless network. The definition of the network layers is based on the OSI model; although only the lower layers are defined in the standard, interaction with upper layers is intended, possibly using a 802.2 logical link control sublayer accessing the MAC through a convergence sublayer. Implementations may rely on external devices or be purely embedded, self-functioning devices.
The physical layer (PHY) ultimately provides the data transmission service, as well as the interface to the physical layer management entity, which offers access to every layer management function and maintains a database of information on related personal area networks. Thus, PHY manages the physical RF transceiver and performs channel selection and energy and signal management functions. It operates on one of three possible unlicensed frequency bands:
868-868.8 MHz: Europe, allows one communication channel (2003), extended to three (2006).
902-928 MHz: North America, up to ten channels (2003), extended to thirty (2006).
2400-2483.5 MHz: worldwide use, up to sixteen channels (2003, 2006).
The original 2003 version of the standard specifies two physical layers based on direct sequence spread spectrum (DSSS) techniques: one working in the 868/915 MHz bands with transfer rates of 20 and 40 kbit/s, and one in the 2450 MHz band with a rate of 250 kbit/s.
The 2006 revision improves the maximum data rates of the 868/915 MHz bands, bringing them up to support 100 and 250 kbit/s as well. Moreover, it goes on to define four physical layers depending on the modulation method used. Three of them preserve the DSSS approach: in the 868/915 MHz bands, using either binary or offset quadrature phase shift keying (the second of which is optional); in the 2450 MHz band, using the latter. An alternative, optional 868/915 MHz layer is defined using a combination of binary keying and amplitude shift keying (thus based on parallel, not sequential spread spectrum, PSSS). Dynamic switching between supported 868/915 MHz PHY's is possible.
The medium access control (MAC) allows the transmission MAC frames through the use of the physical channel. Besides the data service, it offers a management interface and itself manages access to the physical channel and network beaconing. It also controls frame validation, guarantees time slots and handles and node associations. Finally, it offers hook points for secure services.
Other higher-level layers and interoperability sublayers are not defined in the standard. There exist specifications, such as ZigBee, which build on this standard to propose integral solutions.

Network model
The standard defines two types of network node. The first one is the full-function device (FFD). It can serve as the coordinator of a personal area network just as it may function as a common node. It implements a general model of communication which allows it to talk to any other device: it may also relay messages, in which case it is dubbed a coordinator (PAN coordinator when it is in charge of the whole network).
On the other hand there are reduced-function devices (RFD). These are meant to be extremely simple devices with very modest resource and communication requirements; due to this, they can only communicate with FFD's and can never act as coordinators.
Networks can be built as either point-to-point or star networks. However, every network needs at least an FFD to work as the coordinator of the network. Networks are thus formed by groups of devices separated by suitable distances. Each device has a unique 64-bit identifier, and if some conditions are met short 16-bit identifiers can be used within a restricted environment. Namely, within each PAN domain, communications will probably use short identifiers.

IEEE 802.15.4 cluster tree
Peer-to-peer networks can form arbitrary patterns of connections, and their extension is only limited by the distance between each pair of nodes. They are meant to serve as the basis for ad hoc networks capable of performing self-management and organization. Since the standard does not define a network layer, routing is not directly supported, but such an additional layer can add support for multihop communications. Further topological restrictions may be added; the standard mentions the cluster tree as a structure which exploits the fact that an RFD may only be associated with an FFD at a time to form a network where RFD's are exclusively leaves of a tree, and most of the nodes are FFD's. The structure can be extended as a generic mesh network whose nodes are cluster tree networks with a local coordinator for each cluster, in addition to the global coordinator.
A more structured star pattern is also supported, where the coordinator of the network will necessarily be the central node. Such a network can originate when an FFD decides to create its own PAN and declare itself its coordinator, after choosing a unique PAN identifier. After that, other devices can join the network, which is fully independent from all other star networks.

Data transport architecture
Frames are the basic unit of data transport, of which there are four fundamental types (data, acknowledgment, beacon and MAC command frames), which provide a reasonable tradeoff between simplicity and robustness. Additionally, a superframe structure, defined by the coordinator, may be used, in which case two beacons act as its limits and provide synchronization to other devices as well as configuration information. A superframe consists of sixteen equal-length slots, which can be further divided into an active part and an inactive part, during which the coordinator may enter power saving mode, not needing to control its network.
Within superframes contention occurs between their limits, and is resolved by CSMA/CA. Every transmission must end before the arrival of the second beacon. As mentioned before, applications with well-defined bandwidth needs can use up to seven domains of one or more contentionless guaranteed time slots, trailing at the end of the superframe. The first part of the superframe must be sufficient to give service to the network structure and its devices. Superframes are typically utilized within the context of low-latency devices, whose associations must be kept even if inactive for long periods of time.
Data transfers to the coordinator require a beacon synchronization phase, if applicable, followed by CSMA/CA transmission (by means of slots if superframes are in use); acknowledgment is optional. Data transfers from the coordinator usually follow device requests: if beacons are in use, these are used to signal requests; the coordinator acknowledges the request and then sends the data in packets which are acknowledged by the device. The same is done when superframes are not in use, only in this case there are no beacons to keep track of pending messages.
Point-to-point networks may either use unslotted CSMA/CA or synchronization mechanisms; in this case, communication between any two devices is possible, whereas in “structured” modes one of the devices must be the network coordinator.
In general, all implemented procedures follow a typical request-confirm/indication-response classification.

Reliability and security
The physical medium is accessed through a CSMA/CA protocol. Networks which are not using beaconing mechanisms utilize an unslotted variation which is based on the listening of the medium, leveraged by a random exponential backoff algorithm; acknowledgments do not adhere to this discipline. Common data transmission utilizes unallocated slots when beaconing is in use; again, confirmations do not follow the same process.
Confirmation messages may be optional under certain circumstances, in which case a success assumption is made. Whatever the case, if a device is unable to process a frame at a given time, it simply does not confirm its reception: timeout-based retransmission can be performed a number of times, following after that a decision of whether to abort or keep trying.
Because the predicted environment of these devices demands maximization of battery life, the protocols tend to favor the methods which lead to it, implementing periodic checks for pending messages, the intensity of which depends on application needs.
Regarding secure communications, the MAC sublayer offers facilities which can be harnessed by upper layers to achieve the desired level of security. Higher-layer processes may specify keys to perform symmetric cryptography to protect the payload and restrict it to a group of devices or just a point-to-point link; these groups of devices can be specified in access control lists. Furthermore, MAC computes freshness checks between successive receptions to ensure that presumably old frames, or data which is no longer considered valid, does not transcend to higher layers.
In addition to this secure mode, there is another, insecure MAC mode, which allows access control lists merely as a means to decide on the acceptance of frames according to their (presumed) source.

Streamline Data Distribution

Wireless Sensors Streamline Data Distribution
With applications ranging from home automation and remote meter reading to industrial sensor networks, low-power, low-cost wireless devices are set to reshape the control and data-distribution landscape.
By Tod Riedel, Sokwoo Rhee, and Sheng Liu
CommsDesign Jul 21, 2003



Self-organizing, wireless sensor networks have immediate utility in a variety of industrial, medical, consumer and military applications. As a result, a new IEEE wireless standard, IEEE 802.15.4 (Callaway), has been proposed that aims to derive the optimum power, transmission distance and data rate requirements for devices that would best suit this space. With a lower-power profile and lower data rate than Bluetooth, this technology presents a number of interesting hurdles to its implementation, such as battery use and size of device. The networking protocol presents another challenge, encompassing latency, node acquisition time, route discovery and message confirmation. While a full understanding of the physical- and data-link-layer parameters of this technology is essential for its proper use, the potential impact depends also on the real-world implementation.

Unlike the myriad profiles of the now emerging Bluetooth devices, there are three general application classes that have been derived for these devices: periodical sampling, event driven and "store and forward." There are also three basic topologies in which this technology can be deployed: star, mesh and star-mesh hybrid. Each of these implementation modes has relative advantages and disadvantages that must be properly understood in order to match the application requirements to the appropriate wireless sensor network.
Why now?That low-power, self-organizing networks are becoming a reality is largely a result of significant advances in microelectromechanical systems, low-power radio and digital circuit design. Wireless sensor networks are now capable of operating with submilliampere power consumption, allowing a 3-volt dc coin battery to power the sensor node for periods of up to five years and beyond, depending on the sampling rate. Such sensor nodes, when integrated with a coin battery, are portable, unobtrusive and easily designed into small devices. Low-power, low-data-rate applications include aiding digital precision instruments on the factory floor, collecting water and gas meter readings, monitoring shipments through the supply chain and reporting on the vital signs of individual wearers. All of these applications share three common requirements: small form factor, long battery life and a robust, efficient network protocol. Proper implementation starts, however, with the basic choice of topology.
Topology optionsThe basic star topology is a single-hop system in which all wireless-sensor nodes communicate bidirectionally with a base-station or gateway (Figure 1a). The basestation can be a PC, PDA, dedicated building-control device, embedded Web server or other gateway to a higher-data-rate device. The nodes are identical and the basestation serves both to communicate data and commands among endpoints, and to transfer data to a higher-level system like the Internet. The nodes do not pass data or commands to each other; they use the basestation as a coordination point. Among wireless-sensor networking topologies, the star system is the lowest in overall power consumption but is limited by the transmission distance between each node and the basestation (Figure 2). That distance is typically 10 to 30 meters in the ISM band.
Mesh topologies are multihopping systems in which all wireless sensor nodes are identical and communicate directly with each other to hop data to and from the basestation and to pass commands to each other (Fig. 1b). A mesh network is also highly fault-tolerant because each sensor node has multiple paths back to the gateway or to other nodes. The multihop system allows for much longer range than a star topology, but consumes more power since nodes need to always "listen" for messages or for changes in the prescribed routes through the mesh.
A star-mesh hybrid seeks to take advantage of the low power and simplicity of the star topology, as well as the extended range and self-healing nature of a mesh network topology (Fig. 1c). A star-mesh hybrid organizes sensor nodes around routers or repeaters which, in turn, organize themselves in a mesh network. The repeaters serve both to extend the range of the network and to provide fault-tolerance. Since wireless-sensor nodes can communicate with multiple routers or repeaters, the network will reconfigure itself around the remaining routers if a repeater fails or if a radio link experiences interference.
Form factorA typical node configuration for wireless sensor networks has two main components: an RF transceiver, which is primarily analog and runs in the high-frequency, 300-MHz to 2.4-GHz ISM bands, and the MCU, which is digital and runs in a relatively low-frequency band in the kilohertz to several-megahertz range. Typically, the RF transceiver must be accompanied by a number of external components such as inductors, capacitors or surface acoustic wave filters. Because these external components are bulky and expensive, it has been challenging to integrate RF circuitry that can meet the size and cost requirements. With rapid advances in CMOS process technology, several small, low-cost, highly integrated RF transceivers are now available.
Meanwhile, the performance and integration level of off-the-shelf industrial microcontrollers are also improving rapidly. More and more peripheral devices are being embedded in the MCU without significant cost additions.
For example, some microcontrollers come with built-in voltage supervisor/ regulators, which have been traditionally considered key external components for the MCU. Many microcontrollers even include an on-chip, low-power, real-time clock and hardware encryption block, both of which help reduce the size and cost of digital circuitry.
The emergence of "combo" chips is even more encouraging. Currently, several companies are introducing the RF transceiver and the MCU in one silicon unit. Previously, this was difficult due to interference and noise issues between RF and digital circuitry. But as CMOS RF technologies improve, it has become possible to design integrated RF-digital chips, further reducing the size and cost.
Battery lifeOne critical advantage of wireless sensor networks is their independence from the wiring constraints and costs of traditional networks. This advantage will not materialize unless an adequate wireless power source is available, so power efficiency is a critical design factor. If the battery must be replaced often (every week or every month), the labor cost for battery replacement will overwhelm the initial wiring cost savings. Therefore, long battery life (typically from five to 10 years) is essential. In addition, since the philosophy of the sensor networks is "wireless anywhere," the size of a sensor node must also be considered. In many cases, even AA batteries are too bulky to power the sensor node, so coin cell batteries are the only option.
Typically, RF components consume more than 70 percent of the total power in full-operation mode, sometimes consuming even more while receiving than transmitting. The RF components also burn significant amounts of power during switching or waking up. Consequently, many scenarios must be considered in the power budget.
The power the RF circuitry consumes is highly dependent on the modulation scheme. Wideband RF chips, like those for Bluetooth, consume much more power than typical narrowband radios because of the complex baseband processing. Although wideband radios offer better immunity to interference, for many sensor network applications narrowband radios remain a practical and more power-efficient choice. Currently, several companies offer RF chip solutions that can achieve data rates of up to 1 Mbit/second with less than -85-dBm sensitivity in receive (Rx) mode, and draw no more than 10 mA of current at 3 Vdc. A few state-of-the-art RF chips have been developed that operate in the 2.4-GHz band with a current drain at 15 mA. Given the advantage of the 2.4-GHz band in terms of worldwide regulatory compliance and coverage, these RF chips are certainly viable candidates for wireless sensor network systems.
Impressive progress has also been made in the area of microcontroller power savings. Until recently, the typical power consumption of 8-bit microcontrollers has been 4 mA per Mips. With advanced chip fabrication processes and new microcontroller architectures, however, this number has recently decreased to 0.5 mA per Mips in certain new devices, helping to reduce the overall power consumption of the wireless nodes.
Network protocolA typical network protocol stack, following the Open System Interconnect model, for self-organizing, wireless sensor networks is shown in Figure 3. In general, each layer in the reference model can be designed independently, as long as interfaces between layers are consistently defined. To establish a reliable, ad hoc sensor network with a tight power budget, however, all layers in the protocol stack should be designed to meet the same set of system-level requirements, such as energy constraint, bandwidth efficiency, adaptability and robustness. To achieve a viable solution, design trade-offs must be made at all layers, while taking into account intrinsic limitations of channel capacity, device processing speed and variations in RF link quality.
Physical layerFrom radio signal path loss models, it is well-known that required output power varies exponentially with radio range, with an exponent of 2 in free space and 4 in cluttered areas. For the same end-to-end distance, forwarding information over multiple links, with limited transmit power for each link, can result in power consumption much lower than directly transmitting signals over one long link. To operate on small batteries for extended periods, sensor networks must employ radios with extremely low transmit and receive power and rely on multihopping for long-range connectivity. Popular radios such as cellular phones, IEEE 802.11 and Bluetooth, with typical current drain at 30 mA or higher, are not suitable here.
As discussed above, low-power chip radios fabricated with advanced CMOS process technology are now available that offer 100-foot line-of-sight range with 10-mA current drain at 3 Vdc. When these radios operate with less than 0.1 percent duty cycle, a coin cell battery with 220-mA-hr capacity can last for more than two years in a suitable environment.
In sensor network applications that rely on cooperative channel sharing and distributed data routing, however, reducing the duty cycle of individual nodes directly impacts network-level performance. Therefore, higher layers in the protocol stack must be carefully designed with this mind in order to support physical-layer implementation with ultralow duty cycles.
Data link layerThe data link layer in the protocol stack generally provides two main services: media-access control (MAC) and error control. Among a variety of MAC schemes, carrier sense, multiple access (CSMA) is the most popular in ad hoc sensor networks, mainly due to its ease of implementation, but more importantly, for its efficacy in exploiting channel reuse in a large-scale network.
With CSMA, a network node always listens to the communicating channel and checks its availability before it starts transmitting a data packet. If the channel is busy, the node backs off for a random period of time before the next attempt. In most cases, such as IEEE 802.11, radios remain in listening mode even during a back-off period. However, radio circuits consume a significant amount of energy even if they're only listening. Therefore, radios should be turned off when each network node is in the back-off period or has no data to broadcast. Both listen period and back-off period are key design parameters for CSMA.
CSMA is well suited for networks with sporadic traffic, but its performance degrades dramatically when the channel is constantly occupied by long packets or streaming data. To improve the accessibility of busy channels, particularly for critical data packets, a noncontention-based mechanism should be established, in addition to the regular CSMA. Transmission scheduling based on a centralized beacon has been an effective scheme for contention-free channel access. Beacon-based scheduling can work well in a centralized system with a star topology. For general sensor networks with a decentralized topology, however, transmission scheduling that requires proper synchronization proves to be highly challenging (Goldsmith). Instead of offering guaranteed time slots, one effective way of improving channel accessibility to essential information is to prioritize data packets; packets with a high priority can occupy the channel with a low probability of collision when all listening nodes with lower-priority packets collectively back off for a longer period of time.
Further improvement on channel access can be achieved when higher-layer protocols are designed with a MAC objective. For instance, certain sensor network applications require periodical sampling of sensor data. If the application layer allows for dynamic adjustment of the sampling interval and phase shift of sampling sequence, the air channel can be effectively shared by a relatively large number of nodes with periodical transmission.
Due to the cost constraint on device hardware, CSMA with collision detection is not feasible in sensor network applications. The alternative, CSMA with collision avoidance, offers an effective approach to contention control. CSMA-CA introduces a considerable amount of overhead in network traffic, however. Without any explicit contention control, an error-control scheme must be incorporated into the data link layer to ensure an adequate transmission success rate. Common error-detection techniques such as cyclic redundancy check implemented with acknowledgment handshake prove to be effective in sensor networks. A flexible combination of data-link-layer acknowledgment (node to node) and network-layer acknowledgment (end to end) can offer an adequate transmission success rate and achieve the desired energy efficiency.
Network layerThe network layer is responsible for route discovery and data packet delivery. In ad hoc sensor networks, where large numbers of nodes are deployed randomly, discovery of multihop routes (self-organization) in a mesh topology is a difficult task. It is equally challenging to maintain and repair routes (self-heal) when nodes are relocated or fail. Numerous distributed-routing algorithms have been developed over the years that support ad hoc, multihop networks. In general, these routing algorithms can be divided into two categories: proactive and reactive (Goldsmith). In a proactive routing protocol, all nodes in the network constantly maintain tables for routes between certain source-destination pairs, regardless of whether these routes are needed.
Proactive routing can deliver data packets faster than reactive routing because no discovery time is needed. The routing table size grows exponentially with the network size, however, and maintaining these tables can quickly become impractical for typical sensor networks employing a high number of nodes. On the other hand, in a reactive routing protocol, routes are discovered based on the demands of source nodes initiating data for specific destinations. Once a route is discovered, the nodes will maintain the route information for a limited period. The routing table size can be relatively small and remains constant in relation to network size, but on-demand route discovery often leads to long latency, making it ineffective for real-time applications.
Most distributed-routing algorithms for ad hoc mobile networks, proactive or reactive, are developed based on a flat network architecture such as the mesh topology. Without any hierarchy, every node in an ad hoc network takes equal responsibility for relaying packets for other nodes. In a flat network implementing a fully distributed routing algorithm, every node not transmitting needs to actively listen to the channel in order to serve as relay for route-through traffic. As a result, power efficiency of distributed-routing algorithms in a mesh structure is intrinsically low. Using the star-mesh hybrid framework, intelligent routing can be developed that achieves high power efficiency, low latency and robust connectivity. Given limited code space for routing table storage on each sensor, reactive routing offers the more compact solution to sensor network applications. The latency issue associated with reactive routing can be effectively resolved by directing traffic to flow to a few nodes that are designated as data collection stations, with each station attracting traffic within a relatively local area.
Maintaining traffic to a local neighborhood is essential to ensuring scalability of ad hoc networks. It is observed (Gupta) that the per-node capacity in an ad hoc network decreases asymptotically as the network size increases. This result is based on the condition that the average path length between the source and destination grows in proportion to the network size. To avoid grinding the per-node capacity to a halt in a large-scale network, all traffic in the network should remain local-that is, the average hop count of data packets should be low compared with the network size.
Application classAmong various industrial, building and home applications, the following application classes represent the most common modes of acquiring and propagating sensor data:
· Periodic sampling. For applications where a certain condition or process needs constant monitoring, such as temperature in a conditioned space or pressure in a process pipeline, sensor data is acquired from a number of remote points and forwarded to a data collection center on a periodic basis. The sampling period mainly depends on how fast the condition or process varies and what intrinsic characteristics need to be captured. Since the duty cycle of a remote node varies in proportion to sampling rate, the application layer on the protocol stack should always seek to use a minimal sampling rate while fulfilling the monitoring requirement. In many cases, the dynamics of the condition or process to be monitored can slow down or speed up from time to time. Therefore, if the application layer can adapt its sampling rate to the changing dynamics of the condition or process, oversampling can be minimized and thus power efficiency of the overall network system can be further improved.
Another critical design issue associated with periodic sampling applications is the phase relation among multiple nodes. If two nodes operate with identical or similar sampling rates, collision between packets from the two nodes is likely to happen repeatedly. It is essential that the application layer detect this repeated collision and introduce a phase shift between the two transmission sequences to avoid further collision.
· Event driven. There are many cases that require the monitoring of one or more crucial variables and transmission occurs only when a threshold is reached. Common examples include fire alarms, door and window sensors, and instruments that are used intermittently. To support event-driven operations with adequate power efficiency and speed of response, the sensor node must be designed so that its power consumption is minimal in the absence of any triggering event, and the wake-up time is relatively short when the threshold is reached. These design requirements should be accounted for in all layers of the protocol stack.
· Store and forward. In many applications, sensor data can be captured and stored or even processed by a remote node before being transmitted to the basestation. Instead of immediately transmitting every unit of data acquired from a sensor, the aggregation and processing of data by remote nodes can potentially improve overall network performance in both power consumption and bandwidth efficiency. The application-layer protocol should provide proper application programming interfaces for effective integration of data aggregation and processing algorithms.

The Wireless Factory Floor

ISA in the factory: Wireless networks, automation interest group meets
Control Engineering -- January 21, 2008

Burlington, MA — ISA, a organization originally for standards and best practices in instrumentation and process control, is aiming to help more in factory automation with launch of an interest group for factory automation and wireless issues. Second meeting of ISA’s Interest Group on factory and discrete automation is Jan. 25. On Jan. 11, Mark O’Hearne, vice president of business development & marketing at Millennial Net, called the first teleconference meeting to order with 21 attendees representing automation equipment vendors and users interested in understanding where wireless networks may be applied in different environments.The purpose of the teleconference was to determine if there was enough participation to form an interest group to explore opportunities and requirements distinct in nature from what is currently considered on ISA100.11a. O’Hearne set the context with respect to the ISA process toward forming a standards working group. Dan Sexton of General Electric and others helped to clarifying the role, deliverables, and governance of this process.The process begins with identifying a topic of interest with enough participation and proceeds through three stages:1. Interest Group surveys the “market” to define broad scope of interest among the community, who is interested, and what other organizations are doing in the space. If it finds sufficient interest, it then recommends to ISA formation of a Study Group.2. Study Group considers whether a standards effort led by ISA is warranted, describing use cases and investigates what other organizations are doing. If so, the group moves on to developing the scope, purpose, deliverables and schedule for a proposed working group, and recommends to ISA formation of a Working Group.3. Working Group defines a standard for ISA approval.
The effort grew out of discussions at the last ISA100 meeting in Houston, where support formed to understand the need for standards for wireless networks in different environments, recognizing that ISA100.11a is oriented toward process wireless applications. This effort will be oriented toward factory automation, discrete parts manufacturing, high-speed machines and other non-process applications. Jim Reizner of Proctor & Gamble (P&G) and O’Hearne agreed to champion a call to form an ISA Interest Group for “Factory/Discrete Automation.” The new group is reaching out to all interested parties. It seeks to determine the interest level in the industry around possible development of a standard for a wireless factory/discrete automation system to serve hybrid and discrete industries (such as consumer goods, electronics, automotive, aerospace, and other industries). In contrast to environments driving the ISA100.11a (release 1) and other emerging interest groups, this group will consider assembly, batch, blending, packing, robotics, shop floor data collection and other applications. These are likely to drive different demands for mobility, scalability, point density and lower latency.Participants Reizner, Larry Graham of General Motors, and Mike Read of Ford described end-user perspectives on how their environments are different from what is currently covered in ISA100.11a. P&G manufacturing includes many high-speed production lines, including lines producing Pampers diapers and boxes of Tide detergent. Such production lines involve many types of sensors, beyond process sensors (such as pressure, flow, and temperature) covered by ISA100.11a. At Ford there are many situations where it is inconvenient or impractical to run wires for sensor I/O. Eliminating high flexure forces associated with cables is higher priority for Ford than the environmental monitoring focus that drove SP100.11a.David Brandt of Rockwell Automation commented that when ISA100.11a was formed the working group had a taxonomy with a process bent. Discrete and factory automation may need a new taxonomy. Participants generally agreed that their companies want to use wireless to build automated production machines, as well as for assembly lines and material conveyors.

Wireless Encoders

Motion Control Research will be posting information regarding usage of wireless technology in the factory as well as those items important to the Optical Encoder Manufacturer and User to this site.

Please note our survey (available soon and will be posted here) that will request potential users to define their ideal wireless system, or at least tell us what won't work. The survey results are proprietary to Motion Control Research and will be revealed only to current clients who sign up for the final report.

Jon