October, 2003

• One customer cruises around his refrigerated warehouse on his Ethernet-connected forklift. A wireless laptop computer mounted next to the steering wheel tells him which pallet of product to pick up and where to put it.
• Another Superior Controls biotech customer enjoys sipping coffee in the cafeteria while monitoring real-time buffer prep, purification, and batch reactor data on his wireless laptop computer. He says "it provides the motivation" to review and approve the previous days quality reports, which are also invisibly transmitted to his computer.
  

These types of standard wireless Ethernet networks are rapidly gaining industrial acceptance with a growth rate in some areas of more than 100% per year. So it's worth explaining what they are and how they work.

At the heart of all wireless devices are a radio transmitter and a receiver. License-free radio frequency bands operating at 900 Megahertz MHz) and 2.4 Gigahertz (GHz) are used to transmit, via Spread Spectrum packets of data, to the receiver. Spread Spectrum means that the radio messages are not transmitted on fixed channels, but are spread over multiple channels. This anti-jamming technology came from the U.S. Department of Defense as a means to overcome enemy interference on fixed radio channels. It also enables many users to reliably share the same frequency band.

Both bands are from the line of sight RF spectrum i.e., they travel in straight lines and don't bounce off the ionosphere like low frequency RF waves. Over short distances they can penetrate through and around walls, buildings, vessels, and enclosures.

The two most common 2.4-GHz technologies are the IEEE 802.11 Wi-fi wireless LAN and Bluetooth. These are more popular because the 2.4 GHz band is license-free in most of the world and the use of the 900 MHz band is unique only to North America. The Federal Communication Commission (FCC) allows up to 1 Watt of RF transmitted power to be used to carry the signal. A 1W, 900 MHz device will communicate over a distance of 1/2 to 2 miles in an industrial environment. The 2.4 GHz signal will carry a shorter distance, but with a higher data throughput.

IEEE 802.11, wireless Ethernet is defined as an open standard with three different variations: 802.11a, 802.11b, and 802.11g. All three are 802.3 compliant (the 10 Base T Ethernet standard for communication with the wired network), but use different hardware and data rates for wireless service. IEEE 802.11b, for example, communicates at up to 11 Megabits per second (Mbps) while 802.11a reaches 54 Mbps.

Now to the radio transmitter and receiver. Manufacturers have combined both into units called transceivers that can communicate in both directions (full duplex). The advantage of a transceiver is that the receiver node can acknowledge receipt of the message back to the transmitter node (a standard part of Ethernet). If the message is not received correctly, it can be retransmitted. In an industrial environment, the probability of a single radio message not being successfully transmitted can often be up to 30%. But with retransmission for, let's say, five attempts, the probability of failure drops to 10.8 and five attempts will take only 1.2 seconds.

Another advantage is that the transceivers can be used as retransmitters or routers, receiving and sending messages onto the next transceiver and eventually onto its destination. Dead or black-spots can be reduced by strategically placing transceivers throughout an industrial facility and using auto routing. Just like the Internet, the system will work out the best route for each data packet and, if a transceiver were to fail, the system would automatically reroute the message. In addition, by reducing the distance traveled by 50% with a transceiver placed in the center of a data path, the power and clarity of the data increases by a factor of 4.

But what about security? Can an intruder purchase the same equipment and, by sitting under the Barberry Bush in your company's backyard, surreptitiously collect data or, worse yet, increase the temperature set point on your fermentor thus boiling off your $1M product? Fortunately, the IT industry has developed several defenses for this. Spread spectrum uses a form of frequency encryption that can be set for each user, thus preventing outside access. In addition, simple data encryption techniques are used to scramble or encrypt each data packet before sending it to the wireless system.

So back to our forklift operator cruising in his refrigerated warehouse with his laptop computer. He can be confident that the Superior Controls-configured wireless information that is telling him which product pallet is ready and where it should be moved is accurate and secure from outside interference. Likewise, the quality manager sipping his coffee in the cafeteria while electronically signing his approval of real-time batch reports through his wireless network can be certain that his electronic signature is logged and saved properly in the Superior Controls designed, plant-wide, 21CFR Part 11 compliant, database.