Jim Montague is the executive editor for Control. Email him at [email protected].
Once end users and integrators become convinced that wireless can substantially benefit their equipment and applications, they can get giddy. The savings in cabling, hardware, labor, maintenance and all the new signals and data can be downright intoxicating. Recent converts to romance, religion or other ways of thinking are often similarly infatuated, but their euphoria can cause them to miss some crucial details and risk losing the blessings that love or wireless can give them. Or, as Marvel Comics' sightless superhero, Daredevil, once said when some villain knocked him for a loop, "From despair to overconfidence in one easy lesson."
Well, I was reminded while researching this issue's Bandwidth column, "Wireless Builds Ties That Bind," that the most important detail about wireless is that it can be accomplished by multiple avenues and devices. However, because they're invisible, wireless methods can appear to be a single concept, and this can obscure the importance of doing a site assessment for each facility and determining the appropriate wireless components for each application.
"Wireless is not one monolithic thing, so all the different types of wireless should not be lumped together and treated as one," says Carl Henning, deputy director of PI North America, which supports the Profibus and Profinet communication protocols. "I see four main types of wireless used in industrial automation, each with its own capabilities, benefits and requirements."
First, traditional long-distance radios bring data in from faraway sources, such as remote terminal units (RTUs) at wellheads and deliver it to a central control facility. These radios tend to be proprietary, so users generally must employ the same brand at both ends.
Also Read: Infographic: Do You Deploy Wireless in Your System?
Second, process instrument networks implement wireless via WirelessHART and ISA 100.a standards, and related suppliers specify their respective protocols and radios. Henning adds that the HART Communication Foundation has been working with PI and the Fieldbus Foundation on their Wireless Cooperation Team for several years to ensure better interoperation.
Third, discrete sensors and actuators don't use much wireless yet. Henning reports that, while process instruments have slow cycle times (seconds or fractions thereof), discrete devices operate much faster (milliseconds). "PI has worked with leading discrete vendors to develop a wireless standard for discrete sensors and actuators," Henning adds.
"The specification is complete, and the working group is developing a software base that will expedite adoption. Coexistence with the other wireless technologies is assured."
Fourth, wireless backbone is how Henning characterizes Wi-Fi and Bluetooth when they're implemented in conjunction with industrial Ethernet. "Any plain old Ethernet should run just as well on wireless standards like 802.11a-n," Henning says. "Of course, Profinet does this well."
Likewise, Bill Conley, machine-to-machine applications manager at B&B Electronics, agrees that users never will have just one wireless protocol because their applications will rely on different combinations of WirelessHART, ZigBee, ISA 100, Wi-Fi proprietary radios, cellular and other communication methods. "The real pain point today is getting away from the mindset that wireless must emulate a former piece of wire," Conley says. "It can't do it because wireless still has some latencies compared to hard wiring, even though those latencies are decreasing. So in applications that need fast data turnaround, those latencies still must be taken into account. Similarly, Wi-Fi isn't a full duplex radio that's able to receive and transmit at the same time, so that limit has to be addressed. Each application's required data volume, speed, latency, security and other issues must be considered. For instance, is your IT department going to let you bump into its wireless network, and if not, what cellular carrier are you going to use?"
So as the Lord High Executioner sings in Gilbert and Sullivan's Mikado, "Let the punishment fit the crime." Or, in this case, let the wireless fit the application. I believe that wireless can be as good or better than hard wiring, but only with a thorough site assessment, comprehensive layout design, careful implementation, complete testing and ongoing maintenance. Of course, you were already doing all those things for your hard-wired systems, so doing it for wireless shouldn't be an added strain, right?
