One of today's hottest technology topics is wireless: wireless Web, wireless cellular, wireless LAN. A wireless local area network (wireless LAN or WLAN) offers businesses a valuable and natural extension of their existing Ethernet LANs, making data on their wired network available to mobile users with handheld computers and wireless laptops.
One of today’s hottest technology topics is wireless: wireless Web, wireless cellular, wireless LAN. A wireless local area network (wireless LAN or WLAN) offers businesses a valuable and natural extension of their existing Ethernet LANs, making data on their wired network available to mobile users with handheld computers and wireless laptops.
Accurate business decision-making requires real-time inventory and process data. Integrating shop floor data with business applications on the Ethernet network is no longer a rarity. With a wireless LAN, real-time data cannot only be delivered to mobile users but also gathered from mobile sources.
Inventory control can be more timely when warehouse employees using handheld computers scan items as they pick them up. With a wireless LAN, data is sent directly from the handheld computer into the system. WLAN “access points,” placed at strategic locations in the warehouse and wired to the network, connect with the existing Ethernet LAN.
Two standards
Wireless LANs follow one of two IEEE standards. The original standard defined in 1997 was IEEE 802.11, which describes transmission requirements to achieve a 1- to 2-Mbps data rate via radio using frequency-hopping spread spectrum (FHSS) or direct sequence spread spectrum (DSSS) transmission in the 2.4-GHz ISM band. IEEE 802.11b, a higher-speed standard defined in 1999, describes requirements for 5.5 Mbps and 11 Mbps data rates, both using DSSS. DSSS might be subject to additional interference in some applications, but FHSS is unavailable at higher data rates due to current FCC regulations that restrict the bandwidth of subchannels.
Combined with TCP/IP standard protocols, these new wireless standards provide a solid basis for extending the boundaries of the traditional control network. Using a standard Ethernet network with TCP/IP transport to control manufacturing processes breaks from limitations of proprietary buses and systems.
Opto 22 (Temecula, Calif.) introduced pure TCP/IP Ethernet I/O to the industrial automation field in 1998. The company’s SNAP Wireless LAN I/O system networks most electrical, mechanical, and electronic devices. SNAP Wireless LAN I/O connects analog, digital, and serial devices to existing wired Ethernet networks so any authorized PC on the network can monitor, control, and collect data from those devices.
The advent of SNAP Wireless LAN I/O for wireless LAN, combined with a wireless access solution such as Spectrum24 from Symbol Technologies, means the same secure monitoring and controlling can now be extended to mobile devices. On the factory floor, for example, mobile test equipment must move wherever the product being tested is located. With a SNAP Wireless LAN I/O system on the cart, test data can be directly tied into the factory’s quality control databases through Spectrum24 access points.
Companies interested in using wireless LAN usually begin with a radio frequency (RF) survey of the area to be covered, to determine placement and type of WLAN access points and antennas. Access points must be positioned so that signals—and data—aren’t dropped as users of the wireless system move about. Access point antennas fall into two broad categories: omni-directional and directional. Omni-directional antennas are generally used in square areas such as a shop floor or warehouse. Directional antennas provide coverage in a focused beam and are more suitable for point-to-point applications, such as tank farms.
The convergence of Internet and wireless technologies brings new opportunities to the factory floor. Products such as Spectrum24 and SNAP Wireless LAN I/O can help businesses leverage standard Ethernet technologies and existing systems for more efficient manufacturing and control operations.
For information, visit www.controleng.com/freeinfo .
| Author Information |
| Gary A. Mintchell, senior editor, [email protected] |
