Emerson, for example, might have taken the market by surprise in September 2006 with the launch of its Smart Wireless solutions and a Wireless SmartPack starter kit, but these innovations follow three years’ development work that included extensive field trials at BP’s Cherry Point refinery in Blaine, Wash., mainly for monitoring of process variables, maintenance and environmental conditions.
What Emerson’s field experiences demonstrated, however, was a 99.9% reliability level for its self-organizing wireless mesh network (Figure 1). “When we looked at was available [before],” recalls Karschnia, “we found wireless in niche applications. It was costly and complicated, and it was certainly not reliable — not even for the basics, and certainly not for control.”
Figure 1. Mesh approach avoids the need for direct line-of-sight between device and gateway.
Meshing into the plant
Unlike many wireless installations that generally require a line of sight between the instrument and the communications gateway, Emerson uses the time-synchronized mesh protocol (TSMP) of Dust Networks, Hayward, Calif., running on the low-power IEEE 802.15.4 standard, for Smart Wireless. This enables devices to communicate with each other. If a direct connection between instrument and gateway isn’t available, the network automatically reroutes the signal to an adjacent device to make the connection. If that unit can’t make a connection, the signal passes to another and so on — in theory, the more devices in place, the more reliable the network. “Instead of worrying that you have to put your [wireless] transmitter in just the right spot to get it to work, all of a sudden those problems just disappear,” Karschnia says.
Rather than wait for the upcoming process standards (the draft Wireless HART specification is due out at the end of next month, but the ISA’s SP100 Committee isn’t expected to be at a similar stage until mid-2008, although both are favoring the 802.15.4 standard for their respective physical layers), Emerson has arguably stolen a march on its rivals with its new products — while guaranteeing “an upgrade path to the future industry standard.”
Initially available for 900-MHz operations in the U.S., with 2.4-GHz global systems launching early this year in Europe and Asia, the starter kit consists of from five to 100 wireless Rosemount temperature, pressure, flow or level transmitters, a 1420 wireless gateway, and a 25-tag license for Emerson’s AMS Device Manager asset-management software application.
The relatively low cost kit (starting at $15,000) also includes “SmartPack Services” to help with installation, although anyone familiar with Rosemount HART devices probably should have few problems. “Our goal,” says Karschnia, “is to make products like users have had in the past, with only minimal added knowledge required.” Some, if not all, of that extra knowledge is now available on Emerson’s PlantWeb University website.
With their respective field trials, IPS and Emerson have shown just how reliable modern mesh networking can be, assuaging one major concern of potential users. However, as all suppliers can attest, customers also worry about security. Not in the sense of ensuring their networks are secure — Kagan says security issues are manageable as “the technology behind it is really very good” — but more in convincing corporate IT departments that the networks really are secure. Kagan notes this can “extend the sales cycle, but once IT understands our security model it speeds implementation.”
Emerson’s approach was to start its wireless product development from scratch with security in mind. Using a “threat model” methodology, developers looked at every possible way they could think of attacking the network and then worked out mitigation strategies for each one. The result “is a very sound security system that’s been checked out by security experts, including the Department of Homeland Security,” says Karschnia.
FHSS systems are the most secure, according to Gary Mathur, senior applications engineer at Moore Industries-International, North Hills, Calif., which offers radio-frequency transmitters using that technology (Figure 2).
Figure 2. This module broadcasts a 900-MHz FHSS signal to maximize security.
“For an intruder to successfully tune into a FHSS system, he needs to know the frequencies used, the hopping sequence, the dwell time, and any included encryption,” Mathur explains. “Given that for the 2.4-GHz band the maximum dwell time is 400 ms over 75 channels, it is almost impossible to detect and follow a FHSS signal if the receiver is not configured with the same information.”
Customers also cite battery life as a concern, and progress also is being made here. Claims of battery life of up to 10 years are commonplace, but, as Kagan says, “the trouble with battery life is that there is no standard nomenclature on this.” Karschnia agrees: “It’s a complicated question that you always answer with ‘it depends’ — on where you’re using the products, how often you use them and what level of accuracy you want.”
The inherently low power systems likely to be based around IEEE 802.15.4 (including those of Wireless HART and ISA SP100) should go some way towards allaying that concern for all but the most critical applications. But for these, and users that won’t accept batteries under any circumstances, vendors either are offering or considering alternative ways of powering their wireless devices.