The wireless realm is no longer confined to the world of cell phones and pagers. There’s a big push to use wireless communications in the industrial world for cost, flexibility, and reliability reasons. With the introduction of the IEEE 802.11 wireless Ethernet LAN standard, wireless LAN usage has only become more attractive.
However, some disagreement still exists about which version of the 802.11 wireless standard is best for the factory floor. Presently, there are three such versions–802.11a, 802.11b, and 802.11g. The first operates at 5 Gbits and can transmit data at 54 Mbits/s for distances up to about 100-150 feet. The latter two operate in the ISM (instrument, scientific, and medical) band of 902-928 MHz and can transmit data at 11 and 54 Mbits/s, respectively, for distances of up to about 300 feet. Many PC manufacturers also support the various forms of the 802.11 standard.
Additionally, there’s Bluetooth, a personal-area network (PAN) standard that allows devices like sensors to send signals up to about 30 to 40 feet at 10 Mbits/s, and the ZigBee standard, which has made its presence felt with two very desirable attributes for industrial automation: simplicity and low cost. It, too, operates in the ISM band, but transmits data at only up 240 kbits/s. Although its range is similar to Bluetooth, at least for indoor applications, Zigbee is proving attractive for industrial monitoring and control. Plus, its low data rate isn’t much of a problem because more plant sensors like thermocouples needn’t send data at very high rates.
Another standard proposed last year and now under development–the IEEE P1451.5 for wireless communications between a network-capable application processor (NCAP) and a transducer with a transducer electronic data sheet (TEDS)–should become an actual standard within the next couple of years. Once that happens, sensors and actuators on the plant floor can transmit wireless data to some sort of central location. At that point, the information is retransmitted to a host computer, making data monitoring, acquisition, and control instantaneous from a centralized computer controller.
In a wireless industrial environment, a wireless access point (WAP) is usually mounted in a plant’s ceiling or a wall to communicate with several wireless nodes on the factory floor. These nodes can be found in machines, PLCs, PCs, sensors, inventory control terminals, and handheld devices like bar-code readers.
No matter what standard prevails, the fact remains that a WLAN hooked up to wireless sensors can make an enormous impact on plant flexibility and productivity. As operators, materials, and equipment move around the factory floor, they will no longer be constrained by the availability of hardwiring for connections. An operator at a centralized computer console(s) can keep track of everything, in real time, and re-arrange plant operations on demand, as situations that demand instant action arise.
For more information, go to www.ieee.org/standards, www.bluetooth.com, or www.zigbee.org.