Most industrial controls are wired solutions that are developed for reliability and safety purposes, as well as economic reasons. For instance, 802.11 Wi-Fi can be used with industrial Ethernet protocols that don't require specialized hardware or synchronization. Yet they do have one problem—collisions—that can be overcome with wired switches.
An Ethernet switch can buffer incoming traffic because each connection is independent of the other connections on the switch. However, wireless communication drops back to Ethernet's roots, where collisions are commonplace. Collisions aren't conducive to deterministic communication. Nonetheless, as a higher-level coordination system, wireless has a great deal to offer. It's also equally suitable for non-time-critical communication.
The other area where wireless is becoming more important on the plant floor, and in arenas such as building management, is low-speed wireless that uses standards like 802.15.4. Speed and low-latency determinism aren't among its highlights, but it does offer low cost, convenience, and mobility. Along with RFID, low-speed wireless is cropping up in product tracking, environmental monitoring, and non-time-critical controls. Now the products on the production line can communicate with the product line itself.
ZigBee is one protocol built on top of 802.15.4. Profiles are being created for ZigBee to address a number of different environments, including production systems that would employ industrial Ethernet. As a result, wireless systems can coexist with their wired counterparts.
The low-speed wireless infrastructure structure is in its infancy, but it's growing quickly. There's no clear winner for industrial use yet, making the next couple of years very interesting in industrial automation.
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