This article was printed in CONTROL's September 2009 edition.
You weenies. Despite your surface acceptance of wireless, you never really wanted to let go of good old, visible, solid, hold-in-your-hand hardwiring, did you? Too, too Freudian, dudes. Even though fieldbuses, Ethernet and wireless have proven repeatedly that they can replace point-to-point wiring in many applications and processes, it appears that most users remain suspicious and many are still unwilling to try them. Consequently, even though survey respondents to Industrial Networking's recent "Market Intelligence Report on I/O Networking" reported that they're using these newer networking methods in double-digital percentages, these results also indicate that most users continue to cling to their hardwiring. The report can be viewed at www.controldesign.com/multimedia/2009/MIR_IOsystems0908.html.
After years of covering these networking technologies, I've heard many users say they're reluctant to use fieldbus, Ethernet and wireless because they're not reliable and robust enough. However, I think what they're truly saying is that they're suspicious of these newer networks because they can't physically see and manipulate the traditional cables running from place to place, and so they don't really trust that their crucial communications can reliably happen on that twisted pair. And wireless makes them ever more nervous because there's no visible connection at all.
So, what's it going to take to let go? Not much. Just a tiny psychological shift—but one that no hardware module or line of software code can provide. It's easy to say that a lightbulb must go on over someone's head, but it can be very hard to make it happen.
Consequently, even though improved signaling, switching and layout have greatly reduced wireless' interference and obstruction issues, skeptics quickly fall back on their prejudices that's its unworkable even as they misapply it. To solve these problems, Ira Sharp, of Phoenix Contact (www.phoenixcon.com), reports that his firm conducts extensive training to help users select the most appropriate wireless tools for their application. They must first define their applications by inventorying the process and facility, determining whether they need to communicate to a PLC or collect signals from I/O points, and deciding whether they need to condition those signals for a PLC or bring those I/O points back as I/O points. "So a water treatment plant that wants to bring PLC data back to a host is a data application, but one that needs to get float and pump data to a master SCADA host is moving I/O signals," explains Sharp.
Subsequently, users must evaluate the speed and volume that their data needs and decide if they need bandwidth at kilobytes-per-second (kbps) for slower digital data from a few I/O points, or if they need megabytes-per-second (mbps) for data from an IP-based video camera. Then they need to check how far their data needs to go. For example, going 100 feet across a production line could use a simple wireless sensor network at 900 MHz, while traveling 1,000 feet across a plant might have to cope with slower data and more obstructions, and longer distances might best use UHF or licensed radios at 900 MHz or 2.4 or 5 GHz. Next, users must learn if local power is available for their wireless devices or if they can use batteries, and decide how many milliseconds, seconds, minutes, hours or days they'll need to poll those devices for updates data.
"Once all of these questions are answered, then users can confidently decide if they need a short-distance wireless sensor network using WirelessHART or ISA 100, or perhaps a higher-speed WiFi (IEEE 802.11) wireless local area network (WLAN) at up to 54 Mbps over 1,000 to 3,000 feet. Or, they may choose 900 MHz proprietary radios that can go up to 500 kbps and up to 20 miles, UHF that can go 40 miles, or a cellular method like GPRS that runs at 86 kbps worldwide," adds Sharp.
Wireless has come a long way to prove it can be trusted. Can you meet it halfway?