Good Wireless Design Smoothes Path to Benefits

Despite Limitations, Wireless Fits the Bill in Many Industrial Applications

By Jim Montague

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Wireless can save cabling and installation costs, deliver previously unreachable signals and data, and reduce infrastructure and maintenance expenses. But many potential users are still hesitant to evaluate and implement it, according to Rob Snyder, Rockwell Automation, product manager, for Stratix 5100 wireless access points, and Scott Friberg, senior applications engineer in Cisco's Internet of Things (IoT) group.

To help answer users' questions and alleviate their concerns, the pair walked attendees of this week's TechED conference in Orlando, Florida, through a comprehensive application manual recently published by Rockwell Automation and Cisco. Wireless Design Considerations for Industrial Applications is a free, 97-page guide intended to help users apply wireless appropriately, safely and securely in their machines, applications and production processes. It includes details of wireless local area network (WLAN) implementations, test details and results, and links to Cisco documentation.

"The main advantages of wireless are that it can reduce installed costs due to less cable and labor; reduce operations costs by eliminating cable failures; allow connections to hard-to-reach and remote areas; and improve productivity by making equipment and people more mobile. However, these savings sometimes aren't enough because there are some challenges to using wireless, such as dealing with interference and other issues," said Snyder. "For instance, one of the main ways wireless is different is that wireless is a half-duplex, shared medium. So, while wired can communicate in both directions simultaneously, only one wireless device can communicate at a time. Also, wireless signals can vary with time and direction; wireless coverage areas can't be precisely defined; wireless signals may reach beyond intended area; wireless can lose more data packets than wired Ethernet; and wireless is less protected from interference."

Wireless 802.11 Complements Ethernet

Though there are several major wireless technologies, Snyder stressed his and Friberg's presentation focused primarily on those governed by the IEEE 802.11a/g/n standard, which covers I/O components, peer-to-peer and safety controls, and mobile HMIs.

"IEEE 802.11 has many benefits for industrial automation control systems (IACSs), such as widely adopted, standard-based technology, convergence with the enterprise wireless local area networks (WLANs), WLAN mobility and fast-roaming capabilities, high throughput and reliability for real-time applications, 5-GHz spectrum availability with more bandwidth and less interference, and direct transmission of Ethernet protocols such as EtherNet/IP," explained Snyder. "There are many types of wireless access points (APs), including embedded adapters, universal bridges and work group bridges (WGBs) that are very useful for adding wireless to machines. They can handle multiple wired clients, but are viewed as one wireless client on the network. For example, our Stratix 5100 can handle up to 19 devices."

Meanwhile, Friberg reported that WLANs come in two main flavors: autonomous WLAN that has lower initial costs, requires less expertise and allows more control of some parameters, and unified WLANs that centralize management and control, support larger deployments and offer enhanced security and services.

"There are WLANs in most plants today, and they probably extend from the business to the plant," said Snyder. "We typically think of wireless being used to monitor and control large gantry cranes, but smaller and smaller machines and devices are using wireless because it's so capable. In fact, wireless is enabling new manufacturing techniques, such as allowing newly mobile machines to move around products they're working on, connecting formerly separate islands of automation and securing big data to aid optimization."

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