"There are lots of pieces of equipment in the 'wireless cloud' that surrounds a plant," says Dave Kaufman, Honeywell’s new business development director (See Figure 2 below). "So, you have to make sure that not only are all your pieces of wireless equipment compatible with each other, but also that you have some way of assuring that the next piece of wireless equipment you install won't bring down the existing networks."
FIGURE 2: THE WIRELESS CLOUD
There are lots of pieces of equipment in the "wireless cloud" that surrounds a plant.
Kaufman continues, "When you have wired networks, you’re most interested in making sure that every device on the wire is 'interoperable' with every other device, and that there are few if any incompatibilities. This is magnified in the wireless world."
What happens when you try to install too many wireless sensors in what Emerson Process Management's director of technology, Bob Karshnia, and John Berra, Emerson's president, call, "canyons of steel?”
According to Graham Moss, president of pioneering Australian wireless company, Elpro Technologies, what you get is increasing latency. Latency is the time lag between the time the message is sent, and the time it’s received at the address to which it was sent. Currently, as congestion or interference increases, latency also increases. So, if you want your signal to be received quickly (a critical alarm, perhaps), you may be in trouble. "This means that just installing a single, huge network with 10,000 sensors isn't likely to work," says Moss. He predicts "multiple networks, arranged in layers."
This is why the SP100 committee included coexistence and quality of service as two of its main goals. Some of the questions each responder to SP100's Call for Proposals must answer include:
- How does the system deal with poor quality RF links due to high noise, low signal due to long path lengths or obstacles, multipath fading, or interference?
- How does the system adapt to changing RF environments, and loss of key components such as routing nodes, gateways, and network managers? What components can be redundant?
- How does this system coexist with other systems operating in the same band, and how does it coexist with other systems within the facility?
- What is the throughput of the system? With many sensors? How scalable is the system?
- How does the system deal with quality of service (latency)? How does adding other services affect the latency of existing services in the network?
A Hacking We Will Go
And then there’s the problem of security. The only way somebody can enter bad data into a wired network is to hack that network. Assuming a competent firewall, this is hard to do from outside the plant. In addition, most process control systems aren’t directly connected to the Internet, making it even more difficult to intrude. However, a wireless network theoretically can be hacked by anybody who can pick up the signal.
At my house, I can pick up anywhere from 7 to 12 wireless networks, just in my neighborhood. Most of them aren't even encrypted with WEP (a basic security precaution). There’s more than one reported case of wireless tampering with process systems in water and wastewater plants. Any industrial wireless standard will have to have a significant security component. In addition, those wireless components will have to have some sort of certification that they won't keel over and die the minute somebody tries to attack them.
HART Wireless Update: Draft Spec by End of 2006?
For many reasons, Emerson's announcement in February (see the Process Automation Radio Network’s podcast with Karshnia, Gabe Sierra, Emerson’s product manager, and others, that it’s producing a system for Rosemount to market that’s intended to meet the HART Communications Foundation's draft specification threw its HART Wireless Working Group into confusion. Based on work done at its recent meeting in Minneapolis, however, most observers believe, along with WINA’s Kagan, that "HART Wireless is once again on track, and may very well meet your (Control editor-in-chief Walt Boyes') challenge to have a draft specification by the end of 2006."
Rumor has it that there might even be an interoperability demonstration of a HART Wireless specification at ISA Expo 2006 this coming October.
With approximately 20 million devices already installed, and the specification expected to be backward compatible with every device with HART installed, this is good news for people who want to start using their HART-enabled devices for more than just smart calibration.
SP100 Standard—Where Do We Stand?
ISA SP100 has split into several working groups. The most important of these groups are the SP100.11 and SP100.14 committees. SP100.11 is concentrating on Classes 1 through 5, with consideration for Class 0 applications. SP100.14 is concentrating on Classes 4 and 5, with consideration for the other application classes. There’s some overlap, but fundamentally SP100.11 is working with process measurement and control networks, while SP100.14 is working with long-term monitoring and asset management applications primarily.
Throughout this summer, SP100 member are working on the Calls for Proposal issued on July 14. A proposer conference is planned for early September, and final proposals for the standard are due in early December. Selection of the final proposal is scheduled by the end of January 2007, and draft specifications are expected to be written by August 2007. A period of comment and voting will take place with a standard recommended out of the committee by the end of June 2008.