01 July 2004
Wireless automation gaining ground
By Rick Pierro
A forklift operator cruises around a refrigerated warehouse on his Ethernet-connected forklift. A wireless laptop mounted next to the steering wheel tells him which pallet of product to pick up and where to put it.
A biotech company quality control manager sips coffee in the cafeteria while monitoring real-time buffer prep, purification, and batch reactor data on his wireless laptop.
These are just two examples of how standard wireless Ethernet networks are rapidly gaining industrial acceptance, with a growth rate in some areas of more than 100% per year. In its report entitled, "Worldwide Industrial Markets for Ethernet Infrastructure Components and Network Software," Venture Development Corp. projects high adoption rates for wireless Ethernet in industrial facilities. This is reflected by the forecasted increase in shipments of wireless Ethernet infrastructure access point/networking components for use in industrial facilities from $62 million in 2003 to $152 million in 2006, a 34.8% compound annual growth rate.
At the heart of all wireless devices are a radio transmitter and receiver. License-free radio frequency bands operating at 900 megahertz and 2.4 gigahertz transmit packets of data to the receiver, using spread spectrum technology. Spread spectrum means that the radio messages do not transmit on fixed channels, but spread over multiple channels. It enables many users to reliably share the same frequency band.
Both bands are from the line-of-sight radio frequency (RF) spectrum. Over short distances they can penetrate through and around walls, buildings, vessels, and enclosures.
The two most common 2.4-gigahertz technologies are the IEEE 802.11 Wi-Fi wireless local-area network and Bluetooth. These are more popular because the 2.4-gigahertz band is license free in most of the world, and the use of the 900-megahertz band is unique only to North America.
The Federal Communication Commission allows up to 1 watt of RF transmitted power for use in carrying the signal. A 1.0-watt, 900-megahertz device will communicate over a distance of 1/2 to 2 miles in an industrial environment. The 2.4-gigahertz signal will carry a shorter distance but with a higher data throughput.
IEEE 802.11 wireless Ethernet is an open standard with three different variations: 802.11a, 802.11b, and 802.11g. All three are 802.3 compliant, but use different hardware and data rates for wireless service. IEEE 802.11b, for example, communicates at up to 11 megabits per second, while 802.11a reaches 54 megabits per second.
Manufacturers have combined the radio transmitter and receiver into transceivers, which communicate in both directions. The big advantage here is that the receiver node can acknowledge receipt of the message back to the transmitter node. If the receiver does not receive the message correctly, the transmitter can then retransmit.
In an industrial environment, the probability of a single radio message not being successfully transmitted is often as high as 30%. But with retransmission for, say, five attempts, the probability of failure drops to 10-8 and takes only one to two seconds.
Transceivers can also see use as retransmitters or routers, receiving and sending a message to the next transceiver and eventually on to its destination. You can reduce dead spots by strategically placing transceivers throughout an industrial facility and using auto routing. Like the Internet, the system works out the best route for each data packet, and if a transceiver fails, the system automatically reroutes the message. By reducing the distance traveled by one-half, with a transceiver placed in the center of a data path, the power and clarity of the data increases by a factor of four.
Meanwhile, no one has ignored security issues surrounding use of wireless Ethernet networks. Can an intruder purchase the same equipment and surreptitiously collect data or, worse yet, increase the temperature set point on your fermentor, for example, thus boiling off your $1 million product?
Spread spectrum itself uses a form of frequency encryption that can be set for each user, thus preventing outside access. In addition, simple data encryption techniques can scramble or encrypt each data packet before sending it to the wireless system.
Behind the byline
Rick Pierro is president of Superior Controls, Inc., an N.H.-based systems integrator and a member of the Control and Information System Integrators Association. Rick has an M.S. in chemical engineering and is on both the board of directors of ISPE-Boston and The New Hampshire High Tech Council. His e-mail is email@example.com.
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