The most likely options for such alternative power supplies center on so-called energy harvesting or scavenging devices that turn either vibrational or thermal energy recovered from plant sources into sufficient electrical power to drive the wireless devices — or at least a capacitor that can store enough power for their intermittent use. Roy Freeland, CEO of Perpetuum, a Southampton, U.K.-based company, whose new PMG17 vibrational microgenerator (Figure 3) has attracted a lot of interest since its showing at last October’s ISA Expo in Houston (see Wireless devices may get a shake up), says that since IEEE 802.15.4-based systems are specifically designed for low power, the microgenerator “can more than meet those requirements.”
Figure 3. Microgenerator transforms vibration from equipment into electrical power.
Typically located on or near AC synchronous motors — although Freeland says, “What’s surprising is just how far from the source of vibration you can go and still pick up enough vibration” — devices like the PMG17 obviously lend themselves to condition monitoring (CM) of such equipment. Perpetuum is currently installing a complete explosion-proof system at a grassroots site of a major oil company. “It’s a plant where traditional hard-wired condition monitoring systems are being installed on the major parts of the plant, compressors and so on,” explains Freeland, “but it was too expensive, even on a greenfield site, to do such monitoring on the hundreds of smaller pumps and motors. They were left with the option of going round with handheld monitoring devices, or using our system to acquire the CM data wirelessly.”
Taking control — eventually
CM is certainly one way wireless is coming to the plant. And monitoring, rather than control, is what most automation companies anticipate in the near term. “We’re not pushing anyone to do control,” says Emerson’s Karschnia, “although we have set up our system so we are ready to do it, integrated with our PlantWeb architecture. But I don’t believe customers are going to broadly deploy wireless control right away. They will first need to get comfortable with wireless in monitoring applications, but then we should see it moving relatively easily into control.”
IPS’ Kagan shares that view of a gradual move towards wireless control. “Having a valve or actuator, say, wirelessly communicating with a control system may take a little longer, but within a year or two I think we’ll see a greater acceptance of more distributed ‘islands of control’ communicating on a wireless link.”
As to when wireless will wend its way onto the plant, that obviously depends upon how rapidly products come to market. And that, in turn, might depend upon how long it takes to gain agreement on industry standards, Emerson’s pre-emptive move notwithstanding. At the field device level, next month’s anticipated Wireless HART specifications could be approved “by mid-year,” says Helson, “and we would expect to see [compliant] products follow very quickly thereafter.” The ISA SP100 Committee is faced with a broader, “more holistic” in Karschnia’s words, brief and one that Kagan thinks will end up in more of a quality or functional specification, “as opposed to a bit-level specification.”
Whenever a standard does emerge, however, it should help consolidate what is shaping up to be one of the more significant shifts in control and instrumentation technology since the move from analog to digital communications.