Why Not Wireless?
Several forms of wireless communication, data acquisition, monitoring, networking and control are making inroads into control and automation. Wireless, like most new technologies, is fueled by the only force stronger than corporate inertia—the constant search for cost savings, efficiency, and competitive advantage.
Several forms of wireless communication, data acquisition, monitoring, networking and control are making inroads into control and automation. Wireless, like most new technologies, is fueled by the only force stronger than corporate inertia—the constant search for cost savings, efficiency, and competitive advantage. A natural target for savings is the 50% of new control system usually spent on cabling, labor, materials, testing and verification.
Because of this driving force, wireless isn’t likely to replace hardwire, but rather supplement it in hybrid applications where wireless can demonstrate efficiencies and savings—without sacrificing reliability and security.
“Wireless is possible, desirable, and can solve key problems, but this isn’t going to be black and white. Wire and wireless will coexist,” says Michael Evensen, NetSilicon’s (Waltham, Mass.) vp for Europe. “We’re seeing small islands of wireless today, but we expect it to move more into the mainstream over the next two or three years.” For instance, wireless monitoring of remote water/wastewater, tanks, and mining operations could evolve into almost real-time monitoring and control of process applications.
Wireless has many cousins among traditional and emerging radio frequency (RF) communication, networking and control technologies, and can often extend them, as well as receive aid from them. These ties will no doubt hasten wireless’ acceptance in the long run.
For example, Mr. Evensen says increasing use of distributed, intelligent control architectures and intelligent devices able to make decisions about input/output signals in the field are leading to more autonomous situations. This means less end-to-end network traffic, which can make wireless connections more practical and fuel their adoption. Local area networks (LANs), DeviceNet, Ethernet, and the Internet also have wireless connection strategies that can further their reach, and subsequently increase applications with wireless capabilities.
With a number of technologies able to claim some wireless capabilities, it’s helpful to look at where each began, which type is most appropriate for an application, and how to implement them. Environmental factors to consider include speed, distances, compatibility and interference. (See “Types of wireless” sidebar.)
Stripes of wireless
Similar to other control-related communications, different wireless protocols and methods arose from and are still associated with different RF technologies. These include traditional radio transceivers, cellular telephones and, more recently, laptop PCs, personal digital assistants or other mobile web browsers enabled by personal area networks, most notably Bluetooth.
Most wireless methods considered for control arise from decades-old spread-spectrum technology and digital packet switching. Spread-spectrum smears one transmission over many channels on one portion of bandwidth, which prevents interference, jamming, and congestion. The original signal is then reassembled, or “correlated,” from identical, aligned portions of apparent noise. Packet switching also organizes signals more efficiently, allowing faster, higher-volume data transmission.
Some wireless protocols are defined and administered by the Institute of Electrical and Electronic Engineers (IEEE) as part of its 802 standards, which are multiplying as developers achieve increased speeds and add new functions.
Several wireless standards have grown out of the cellular telephone industry. These include Bluetooth, Wireless Application Protocol (WAP), and Third-Generation (3G). A few wireless efforts, such as Wireless DeviceNet, are extending traditional fieldbus standards, while others are assisting more specific industries, such as Wireless autoID enabling RF identification (RFID) and bar-code applications.
Enabled by Ethernet
While it has close ties to many networking technologies, wireless is likely to be aided most by Ethernet. In fact, Rockwell Automation’s wireless strategy is to run its control information protocol (CIP) over wireless Ethernet, IEEE’s 802.11b standard. This is expected to allow Rockwell’s wireless equipment to accomplish the same tasks as its wired systems, according to Kenwood Hall, architecture and systems technology vp, Rockwell Automation Advanced Technology Group (Mayfield Heights, O.).
Benson Hougland, technical marketing director, Opto 22 (Temecula, Calif.), says “Interest in 802.11b is substantial because, like Ethernet, it’s prominent in the IT environment, costs are lower, it has mainstream awareness, interoperability, and infrastructure in place.”
For instance, Grupo Antolin (Hopkinsville, Ky.) recently began using Opto 22’s Snap Wireless LAN I/O in water jet robots from Robotic Production Technology (RPT, Auburn Hills, Mich.) that Grupo uses to trim 96 versions of its automobile headliners (interior ceilings). Snap Wireless LAN I/O communicates via RF data collection terminals, a 2.4-GHz signal, and Symbol Technologies’ access point network between RPT’s robot and PowerNet ControlLinc software from Control Inc. (Woodridge, Ill.). Identification, glue pattern, wiring harness and other information all flow over this wireless network, while Grupo reports increased production, improved accuracy, and reduced labor costs, specifically a move from three to two and a half shifts per day.
Though Mr. Hall maintains wireless is still more expensive than wired in many cases, he adds that wireless Ethernet allows users to work in the same way as if they were physically hooked up to their network. They can program processors; debug, monitor and maintain equipment; create multiple mobile operator interfaces for large machines; and enable wireless I/O devices or add sensors in places where traditional cabling, conduit and downtime would be too costly.
“Wireless is useful where there isn’t a good wired alternative,” says Mr. Hall. “This could include an application where you would otherwise be replacing festoon cable every six months.”
Obstacles, reliability, security
Both wired and wireless networks are subject to signal and throughput degradation, as their communication paths become crowded with devices, higher-speed data, or new interference sources. However, wireless equipment can often overcome these and a few additional physical hurdles.
Walls, machines, moving metal and other objects common on factory floors can interrupt, reflect or even cancel original signals, and so users must install and maintain clear physical paths between transmitters’ and receivers’ antennas. To help with these and other unseen issues, engineers often hire wireless experts to perform site surveys, which determine access points, service arms, and other capabilities needed by an application in its particular environment.
“A network site survey will map out any issues a widespread wireless application is likely to face, such as concrete walls, attenuation, and physical and electromagnetic obstacles,” says Opto 22’s Mr. Hougland. “However, those considering wireless should also reexamine what they want their application to achieve, and use that perspective to help decide if wireless would be useful.”
Using more secure broadcast frequency methods can also improve reliability. For example, spread-spectrum with frequency hopping is faster than traditional modulated signals because many frequencies process its packets, and these frequencies make any intercepted signal sound like noise. Also, because spread-spectrum now operates at 2.4 GHz, it no longer risks interference from microwave, variable-frequency drives, welding equipment, and ac motors that generate noise at the MHz and kHz levels, according to Bill Arnold, I/O and networks product marketing manager, Omron Electronics (Schaumburg, Ill.).
Though its unseen connections usually inspire security concerns based on fear of outside access, Mr. Hall adds that wireless Ethernet will soon accept encryption using extremely secure 128-bit keys. These will accompany existing required log-ins and other security measures.
|For more suppliers, go to www.controleng.com/buyersguide; for more information, use the following circle numbers, online at www.controleng.com/freeinfo.|
|Actis Computer |
|Analog Devices |
|Bluetooth Special Interest Group |
|Connect Inc. |
|Control Chief |
|Control Systems International |
|Crossbow Technology |
|DAP Technology |
|Digi International |
|Data Comm for Business |
|Data-Linc Group |
|ECS Engineering |
|Enea OSE Systems |
|International Telecommunication Union |
|Microwave Data Systems Inc. |
|National Instruments |
|Omron Electronics |
|Phonetics Inc. |
|Psion Teklogix |
|Robotic Production Technology |
|Rockwell Automation |
|Symbol Technologies |
|TeleRadio Remote Control |
|Techkor Instrumentation |
|Ward Systems |
|Weigh Systems South |
Coal handling line saves big with wireless Ethernet
While replacing obsolete controls on a two-mile, eight-section coal conveyor line at the D.B. Wilson 440-MW power generating station in April 2001, engineers from owner Western Kentucky Energy (WKE, Henderson, Ky.) and integrator ECS Engineering (Elberfield, Ind.) decided to go wireless.
Their evaluation found that joining the line’s remote I/O sections and its control system with fiber-optic cable would have cost $368,000 or 60% more than the $425,000 eventually budgeted and spent on its new wireless Ethernet-based solution. They estimated that a fiber-optic project would also have taken four to six weeks, while the wireless version only required a week and a half.
The line starts at the nearby Green River, where a “clam shell” unloader moves 80-100 tons of coal per barge onto the line. The system unloads 10-12 barges per day.
Vince Wooldridge, D.B. Wilson’s resource leader/instrument and electrical supervisor, says the conveyor’s transition to wireless was easier because it already uses Rockwell Automation’s Allen-Bradley ControlLogix PLC-based controls, and simply added wireless Ethernet/IP functionality to its existing system. Engineers were also confident because they’d had no problems implementing ControlLogix wireless Ethernet in 1998 on a 1,000-1,200-ft stacker and reclaimer application at the station.
The two-mile conveyor’s new controls include two radio antennas, a three segment-plus-control room sub-network, and BreezNet Ethernet-based radio transmitters. These are rated at 3 Mbps, though they usually operate at 2 Mbps, which is still faster that the line’s previous Data Highway network. The radios are as trustworthy and durable as the old hardwired system, according to Greg Midkiff, ECS’ sales and marketing representative.
“A lot of people fear radio because they associate it with Grandpa’s CB shop down the road, but that isn’t what radio is anymore,” says Mr. Midkiff. “Radio equipment available now is as reliable as a hardwired system.”
Mr. Wooldridge adds the line’s wireless controls transmit digital and analog signals to control the conveyor’s starts and stops. “This new system handles as well as before with more reliability and less downtime. We’re getting better motor amp and switchgear information, which is helping us with preventive maintenance and troubleshooting. Run times and weights are accumulating historically, which we didn’t have before. Previously, we had to go read the scales,” he says.
“In fact, the only problem that we’ve had is that we had to cut down a tree between two of the antennas. However, weather hasn’t affected our wireless system—not even the lightning that moved through with some thunderstorms.”
Types of wireless
Wireless communications and networking methods are based on digital packet switching, spread-spectrum, cellular telephone, and other technologies. Some of the most well-known include:
Two primary Wireless Local Area Network (LAN) standards exist. The first, 12-year-old IEEE 802.11b, operates at 2.4 GHz and 11 Mbps for a maximum distance of 100 meters. The second, two-year-old IEEE 802.11a, operates at 5 GHz and 54 Mbps, also for a maximum distance of 100 meters. Recent costs are reportedly dropping from $1,000 per node to $120 per node range. Several other 802 standards have been drafted, and more are expected soon. For more on IEEE’s 802 standards, visit
Bluetooth, managed by the multi-company Bluetooth Special Interest Group, is designated as IEEE 802.15. It also operates at 2.4 GHz and 722-784 kbps at a maximum of about 10 meters. Approximately $100 per node, but prices are also expected to drop here. Visit www.bluetooth.com for more information.
Third-generation (3G) wireless is a cellular telephone-based standard managed by the multi-company International Telecommunication Union (ITU). It reportedly functions at 2 Mbps for stationary applications and at 384 kbps in mobile situations.Visit ITU at www.itu.int.
Wireless Application Protocol (WAP) is another cellular telephone-inspired standard, this time based on wireless markeup language (WML). Visit WAP Forum at
Wireless assists intelligent pallet traffic
Instead of shutting down an entire conveyor for hours every time a belt or gearbox fails, what if you could pull the faulty component and let the overall system continue to run? After all, one broken cart doesn’t shut down a whole golf course. This is the simple logic behind Generation 1 and 2 PowerPallets from Ward Systems Inc. (Grass Valley, Calif.).
Rather than producing a traditional, inflexible, bolted-to-the-floor, motorized conveyor, founder Glen Ward reversed his system, and made its active ingredient a squad of semi-autonomous, motorized, battery-powered, RFID-enabled pallets that move like miniature automated guided vehicles (AGVs) and can be switched off track as needed. This not only reduces downtime, component wear, and power use, but it also allows more flexible maintenance scheduling.
However, to handle resulting traffic among the 25 pallets used in a PowerPallet application at Hexcel Manufacturing (Stamford, Conn.) Ward Systems employs on-board PLCs and a central PLC that communicate via Omron’s (Schaumburg, Ill.) Wireless DeviceNet solution. Power Pallets can travel at 250 ft/min on the track because RFID capabilities help slow them to 7 ft/min before they reach assigned destinations. Meanwhile, the main controller approves routes, coordinates timing, and mediates traffic conflicts at track intersections.
Bill Arnold, Omron’s I/O and networks product manager, says Wireless DeviceNet not only saves on cable, but it allows far more flexible layout of production lines and factories because it’s easier to deploy than the usual wire bundles that run back to a central processor. Its 34 channels can accommodate 34 devices or 34 wireless masters, each with 32 slaves.
“Wireless DeviceNet allows users to have a main trunk and traditional topology, and then supplement or replace it using wireless linkages to smart DeviceNet nodes that can perform intelligent processes,” says Mr. Arnold. “This kind of ‘decentralized control’ allows users to meet frequently changing production requirements, use existing space more effectively, and react faster to customer orders. Reconfiguring this many wiring points would be cost prohibitive.”
RF-based data collection provides clarity in food processing
Many poultry processors want to use RF to aid weighing, help automate cutting, and other production efforts. However, most food-related facilities are metal-sheathed, motor-enabled, high-pressure washdown, USDA-compliant settings—in short, a potential nightmare of radio interference and harsh environments.
To help a large, Fort Smith, Ark.-based poultry processor improve its information gathering, automation use, and frequent reconfigurations, Weigh Systems South (WSS, Waldron Ark.) and Data Comm for Business (DCB, Champaign, Ill.) recently implemented a WSS SR-1W wireless data collection and communication system for up to 96 devices. The new system uses frequency-hopping, spread-spectrum technology, operates at 900 MHz or 2.4 GHz, and functions well inside or between buildings at up to 15 miles.
WSS initially tried RS-232 connections from each scale to a central data system, but continual line changeovers to handle varied products required constant rewiring. Experiments with infrared scanners, bar code readers, and transmission devices were similarly ineffective.
Finally, WSS tied 43 of DCB’s wireless devices to one host in a production room at the Fort Smith processor where chickens are cut up and de-boned. Device signals are sent and multiplexed almost instantaneously through one host RF transceiver. Forty-three scales were also linked via wireless to one Microsoft Windows NT-based server over a three-day weekend, and so far the spread-spectrum system has experienced virtually no interference. DCB’s devices are also doubled-boxed, which prevents failures due to washdowns with 2,000-psi water at the processor.
In addition, data from the wireless system has made order filling more accurate. For example, DCB’s wireless system visually alerts the plant’s cutters and tub handlers when they’re close to completing an order, so virtually no meat is wasted. Then the wireless system is simply reset for the next order, instead of possibly being rewired.
This added accuracy is expected to increase the plant’s yield by 2% for the 400,000 lb of chicken it processes during each shift. Likewise, the wireless system’s data transmission speed enables the cutters to process more meat during their shifts, which means more pay for pieceworkers. Also, the system can check each cutter’s production, which makes payroll accounting more accurate.
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