Factory Applications: Turn Up the Wi-Fi
Image via WikipediaWireless Fidelity, or Wi-Fi, technology is proliferating in the factory, but it’s not the best answer for everything. Will Wi-Fi take over the industrial world? How about wireless Ethernet? The second question is easy to answer: there is no wireless Ethernet. Ethernet, IEEE 802.3, runs on wires. Yes, you will see the term. The current generations of Wi-Fi, or Wireless Fidelity—IEEE 802.11a, 802.11b, 802.11g and 802.11-2007 (which rolls up -a, -b and -g with the lesser-known -h, -i, and -j)—define wireless local area networks (LANs) that have become so inextricably linked with Ethernet that many call Wi-Fi, “wireless Ethernet.”
Wi-Fi is taking over a range of factory applications. Part of the reason might be called peer pressure: outside of industrial settings, there is a huge installed base of IEEE 802.11 LANs—based on the Institute of Electrical and Electronics Engineers standard—at work literally everywhere. A second driver is the direct link to Ethernet, both for environments that use industrial Ethernet and for communication with Ethernet-based enterprise IT systems.
The reasons for the widespread usage of Wi-Fi are many. First, the silicon investment is minimal on the commercial or consumer side. Chips and circuits are commodity items at commodity prices, driving equipment prices down to less than a single meal at a moderate restaurant.
Second, people like Wi-Fi and demand it in their solid-state goodies. Name any reason from sternly practical to frivolously air-headed and someone around you will be trying to connect using 802.11(x). The result is that every new laptop computer—in fact, any new device that will reach into e-mail or Web addresses—includes wireless, and the lines between cell phones, personal data assistants (PDAs), MP3 music players and wireless computers are increasingly blurred.
The upshot is that, while Wi-Fi was once a struggling new technology, it is now literally easier to log on to a wireless LAN anywhere than to avoid logging onto a LAN. In fact, the 802.11 airwaves are now so crowded that many of us (especially those on the road) spend appreciable time figuring out just which LAN we are using at a given locale. It can take many minutes to ensure that you are on the LAN you want amid all the LANs around you.
Traffic flowing on 802.11 highways is likely to be in the air around you, especially if your facility is anywhere near office buildings or family residences, or if your corporate IT embraces wireless connectivity (most do).
So, Wi-Fi is beckoning to production. Broadly speaking, there are only three responses to its siren call. The first is to simply hold off while the current recession blows chill winds through every kind of technology, especially those committed to silicon chips. It is unclear who might benefit from this approach (if anybody). For a while, there will be fewer changes to keep up with. In the vendor community, the survivors will be smaller, leaner and hungrier than last year’s (or last decade’s) boom-time participants. Unfortunately for manufacturing, at the same time, the availability of resources for custom installation will be greatly diminished—and manufacturing absolutely depends on customization.
The second is to hold off until the next generation of Wi-Fi specification, IEEE 802.11n, becomes mainstream. A new generation, 801.11n may reach finalization in November of this year. Its promise—less interference, more data throughput, possibly enhanced security—provides a rosy glow for the future, a glow that will almost certainly invite industrial needs into its warmth. More on that later.
The third is to evaluate current Wi-Fi in relation to factory needs. Then if the technology is appealing, the next steps are familiar from any network implementation: study, strategize and install.
But these are not the only responses. “Wi-Fi and Ethernet are solidly entrenched technologies, but there are better choices for applications such as sensor networks,” says Cliff Whitehead, manager of strategic applications at Rockwell Automation Inc., the Milwaukee-based automation vendor. Whitehead is co-chair of the factory automation study group of the International Society for Automation’s ISA100 standards committee, which is developing an industrial wireless standard. “Remember, radios were used in manufacturing long before computers or 802.11, or any comprehensive set of standards, for that matter. The result is that there are many point solutions involving licensed and unlicensed radio bands, cellular or any number of media for sending this or that kind of data without wires. They all work, and for some needs, many of them work better than Wi-Fi.”
If Wi-Fi is having trouble reaching into control networks, one reason is performance. Whitehead points out that performance on existing 802.11a/b/g technology is not as fast as wired. “For periodic monitoring, say every second or so, Wi-Fi works fine,” Whitehead says, “but for high-speed motion control in microsecond time frames, wireless is not there in a/b/g, and it pushes the envelope in [802.11]n. On the other hand, for peer-to-peer data sharing, or for mobile workers with a laptop doing program adjustments and troubleshooting, Wi-Fi is an excellent alternative.”
Hesh Kagan, managing consultant, enterprise architecture and integration, for automation supplier Invensys Process Systems, in Foxboro, Mass., and president of the Wireless Industrial Networking Alliance (www.wina.org), agrees that Wi-Fi is far from the answer to everything. “There are two major divisions in the industrial wireless world,” he says. “The first applies to workstations or devices in enterprise-wide or secondary implementations using 802.11 Wi-Fi. These are not directly involved in control. The second revolves around field sensors as part of operational control. In this arena, Wi-Fi unfortunately has a big footprint and requires huge amounts of power compared to the far less power-hungry equipment designed to meet ISA100 and 802.15.4. Battery life is extremely important in the field sensor world, and Wi-Fi would suck batteries dry quickly.”
If sensor networks and control applications are not ideal for Wi-Fi, Kagan suggests several layers of applications that are well-suited, ranging from least complex to most. In general, the applications are adjuncts to (rather than direct participants in) process instrumentation or machine control—that is, they provide overview and management functions rather than operational control.
The first of this kind of adjunct or helper application is wireless video: “Remote visualization provides the easiest application,” Kagan says. A read-only application, Wi-Fi-based video takes advantage of a broad array of low-cost products. “There are highly capable cameras for low light and external applications,” he explains. “They are easily set up and provide a dead simple way to gather images of whatever needs to be watched, whether that be perimeters for intruders, or tanks for leaks, or any number of safety-related needs. You can even focus on dials and indicators if you want to lighten the load on a roving clipboard-carrier.”
Neil Peterson, services marketing manager for the wireless plant network, at vendor Emerson Process Management, Austin, Texas, agrees: “Video monitoring offers cost-effective visualization of things like emissions, perimeter control and safety needs. Because Wi-Fi shares resources with a variety of network configurations, it can share much of existing infrastructures. That makes installation relatively painless.”
Similar applications include Wi-Fi-enabled motion detection, ambient heat or carbon monoxide sensors and similar devices with radios. All of these devices are well established as commercial security and safety units.
Slightly more complex is wireless enablement of mobile operators, who can benefit from two-way hookups. Here, specific operational information is channeled to end-users, giving them access to data or information that in a non-wireless world would be locked away in printed manuals or fixed-station computer terminals. At the same time, operational or maintenance data can travel from the mobile resource back to the control rooms, enterprise systems or remote resources via the Web.
“There is value in untethering people from the control room,” Kagan says. “Inter-process measurements, operator access to set points or remotely acknowledging alarms—any number of mobile applications—are ideal for Wi-Fi-enabled handhelds or computers. A degree of security is involved, but it’s easy enough to allow or disallow specific changes to specific operators.”
“[Wi-Fi] access points are a means to an end, and the end in this case is mobility,” says Emerson’s Peterson. “Wi-Fi offers a cost-effective way for an operator to run things from a hand-held while performing manual steps in the field. In small plants especially, Wi-Fi allows people to break the chains to their desks.”
“The next layer up, control over mobile assets, is gaining a lot of interest,” Kagan says. “RTLS (real-time location services) benefits from Wi-Fi-enabled tags on equipment or badges on people. Setting up mobile asset tracking this way has no impact on the processes or controls, and it allows you to add important capabilities with very little outlay.”
“With wireless RFID [radio-frequency identification] tags, you can know exactly where your personnel are,” Peterson points out. “This can be valuable for teams entering hazardous areas—you can keep an eye on exposure time. More importantly, in a safety-related mustering, RFID tags let you know exactly who has exited dangerous areas and who has not.”
Note that it is easy enough to avoid intrusive tracking, simply by deactivating the system except for those moments when safety demands require a clear, accurate picture of where people are.
A final touch is the ability to use Wi-Fi to send relevant information to maintenance teams. “You can codify a repair procedure into step-by-step tasks,” Kagan says. “Then, wherever they are, they can positively identify a piece of equipment, then download the exact procedures for a given fix. And you can do more than that. You can collect machine data and repair information and send it back up to the server, again, from anywhere within reach of [a Wi-Fi] access point. The result is a maintenance database that reflects reality.”
As part of this vision, last August, the Wonderware business unit of Invensys acquired the Houston-based SAT Corp., with its IntelaTrac Enterprise Suite set of mobile offerings. They include configurable software and mobile hardware for workflow, procedural and general task management. Originally focused on maintenance, IntelaTrac is expanding into broad-based production and compliance applications.
Looking for more complexity? Thanks to the tight integration of Wi-Fi and Ethernet, the most widespread LAN technology, there should be no limit on application areas for which the latter offers advantages. Ironically, Ethernet’s original inspiration was radio broadcasting, enhanced by the capability to detect data collisions better in wired connections than in radio frequency connections.
Once data is gated over to Ethernet, the first gain is the ability to communicate with a huge array of devices running a broad range of applications. Enterprise information technology (IT), in particular, depends on Ethernet, so a Wi-Fi bridge to Ethernet makes many an IT practitioner feel more comfortable around production data. The second gain is direct connectivity to the growing application base running on Ethernet’s rough-and-tumble sibling, industrial Ethernet (IE). IE as a link-layer protocol offers increased bus speed compared to serial buses, as well as access to relatively low-cost, standard devices. (For more detail, type “industrial Ethernet” into the search box on AW’s Web site, www.automationworld.com. You’ll find a goodly store of features, white papers and product information on the technology.)
As with much of wireless technology, factory Wi-Fi applications are still in their infancy. Peterson points out that ramping up offers the greatest flexibility. “It’s easy enough to begin with a scattering of access points,” he says. “You might start with a single backhaul network or a wireless field network, maybe even funneled through a single access point to the control room. In this way, you gain a hot spot for mobile worker coverage or for any number of uses. Next year, another access point can be added for relatively low cost, then another. Each addition broadens Wi-Fi accessibility without drawing too much budget.”
“One emerging growth area is a potential for productivity gain through the reining-in of your engineering drive for pinpoint precision,” Kagan says. “Instead of a $1,500 temperature monitor that resolves to one tenth of a degree over its entire range, how about a relatively coarse wireless unit on a motor just to see if it is overheating? Surrounding a potential problem area with many casual monitoring sensors can prove more practical than employing one or two high-precision devices. Clearly, this kind of thing is reserved to situations where a few seconds lag time or a few degrees off true reading won’t make a difference, but there are a lot of these out there.”
Progress on IEEE 802.11n standards is adding a new layer of potential applications. Already there are “Draft n” devices in the marketplace. The developing standard promises to accelerate the rate at which Wi-Fi gains adherents. For one thing, 802.11n offers significantly higher throughput with significantly reduced latency compared to earlier 802.11 specifications.
“The biggest gain is increased reliability in transferring data quickly and completely,” says Whitehead. He cites a number of technical elements in 802.11n that enhance transmission, chief among them MIMO (multiple in, multiple out) technology that takes advantage of multipath signals and multiple antennas. The approach enables the transmission of significantly more information than is possible with single antennas.
“Conceptually, you’re transmitting simultaneously on multiple radios,” he explains. “In our testing with draft n Cisco equipment, we’re seeing 2,400 to 7,500 packets per second. That’s approaching rates consistent with discrete I/O (input/output) control. ‘Real time’ has many meanings in manufacturing, but this is near real-time for many uses.”
Additionally, while previous 802.11 standards focused on 2.4 gigahertz (GHz) frequency bands, 802.11n can use 5.8 GHz frequencies. “There’s less congestion in 5.8,” Whitehead says, “so there are fewer latency or error problems traceable to the coexistence of competing transmissions.”
Finally, 802.11n incorporates a number of other new approaches. Channel bonding (transmitting information on two non-overlapping channels) further speeds up data rates. Data encoding and aggregation algorithms help decrease overhead while increasing signal clarity and speeds. Through it all, the standards process has emphasized backward compatibility with earlier 802.11 specifications, though the overall throughput is necessarily reduced when in compatibility modes working with older Wi-Fi devices.
Meanwhile, to step from the future back into the present, any enablement or enhancement to factory life through Wi-Fi, regardless of how cutting-edge or exploratory it might be, depends on standard processes for technology planning and implementation.
“It boils down to the same three things, whether you’re dealing with Wi-Fi, wireless Hart, wired networks or a person with a clipboard,” says Whitehead. “The first is performance, the second is reliability and the third is security. Wireless doesn’t have the same inherent reliability as a bundle of cables in many an application. Plus, if you decide that wireless is the solution, you need to remember that performance and reliability are affected environmental factors. You need to know what other wireless co-exists with your installation, since existing radio traffic has the potential for radio frequency overlap. And you have to remember that if Wi-Fi drops packets, it will cycle through retries. While 30 seconds one way or the other won’t bother you if you’re downloading an MP3 audio file at home, in a control situation with time-outs built into the protocol, you risk nuisance trips or downright outages.”
Standard procedures are emphasized by Peterson as well. “Every solution involves software, hardware, services and customization, and each one has to be scrutinized,” he says. “What do you want to do? What will you want to do in the future? You need to involve the stakeholders first to see what needs to be done. Then you evaluate the site, and for Wi-Fi, you’ll want to do a radio frequency site survey to see what’s in the air, so to speak. Then it’s just a matter of installing the wireless, the applications, and checking it all out. A finished installation will include planning for after-install services—training, maintenance, ongoing evaluation. You can’t just say, ‘Here’s a box, have fun.’ ”
There are a range of questions around architecture, focusing first on the exact location of the radio, then on the transfer of data to whatever end-point is chosen.
“You’re looking at a virtually infinite number of ways to put systems together,” says Whitehead. “As the application space settles down and people share the basic concepts, these will no doubt resolve to a few different primary strategies. Right now, however, I doubt that anyone would feel comfortable starting from scratch, working on their own. Everyone in the space—suppliers, consultants, device makers, end-users, everyone—has the responsibility to make sure they are deploying things they understand. Standards are increasingly fleshed out with reference architectures that provide suggestions for deployment. Plus, as standards proliferate, more and more people will be comfortable with the technologies involved. Once that happens, you’ll find more and more people able to see both the capabilities and the shortfalls of a given approach.”
Wireless Industrial Networking Alliancewww.wina.org