大卫·卡勒联合创始人兼首席技术人员cer of Arch Rock, a San Francisco-based wireless sensor network technology provider says, “IEEE 802.15.4 is a very significant advance in the technology. It’s here to stay, but it will continue to evolve. Prior to 2004, we had to deal with any radio. But now, the standard link layer allows a lot of different companies to line up to drive up quality and drive down price. Industry protocol says ‘Here’s the option for each piece of the stack,’ but Internet protocol says that each needs to be there, but they need to be decoupled so we can use the same higher protocols on different lower protocols. The big question is whether engineers will have to know all seven or eight different protocols or whether there will be a convergence. There is beginning to be a common sense of network protocols with Internet Protocol task forces within other groups such as the IEEE 1451.5 sensor standard group. In a sense, this is like the beginnings of Ethernet and token ring when there was an initial proliferation of networks, and then a convergence into layers.”
Adds Rob Conant, vice president of marketing for Dust Networks, Hayward, Calif., wireless sensor network technology provider, “In the past 12 months, wireless mesh networking technology has matured. There is a lot of product development going on. Hart Communication Foundation has made a ton of progress. BP (the London-based energy company) has identified it as a game changing technology. Emerson Process’ John Berra says his customers are excited by the possibilities. With fewer people operating plants and increasing safety and environmental regulations requiring more monitoring, here comes a technology to help.
“There are a couple of approaches to the solution. One is a tightly engineered solution for specific applications. This requires site surveys and installing the entire system at once. The second is to build intelligence into the environment and make the network robust enough to survive in a variety of industrial environments. There’s a lot of activity around Hart because it’s already used for continuous process diagnostic information. This protocol can be transported wirelessly. Another area of broad interest is machine health monitoring. This is an area of potentially huge energy savings. The lower cost of installing wireless monitoring can enable monitoring of smaller motors to increase the savings.”
Wireless hurdles
Tom Phinney, senior researcher at Honeywell Process Systems, takes note of potential problems with mesh networking, and especially with wireless sensors—those not connected to power supply wiring as well as communication wiring. “We’ve heard from users that mesh is not deterministic enough for some applications. Also, access points are usually good for 150- to 500-meter distances. Since many sensors are close to the ground, you may get many interferences. The major problem is with battery life. You may have to hire a contractor for a year, eight years after installation to replace all the batteries. Users want to install, then forget about it for 20 years. Security is another problem that must be addressed in mesh networks.”
Phinney is active with the ISA SP100 committee working on an industrial wireless network standard. “ISA is unique among standards organizations in that it requires a strong end user voice. Vendors tend to say ‘Please accept mine so that I can sell more,’ while small companies say ‘Pick mine so I can live.’ End users don’t care about the technology. They just want compatibility with tools such as EDDL (Electronic Device Description Language), asset management software, training and so on. The fieldbus thing standardized how to describe all protocols. Now, any grad student could write a protocol converter. That’s important for a wireless world where there isn’t a wire for each protocol (e.g. Profibus, Foundation Fieldbus) but all protocols converge in a common backbone. Most users say they’re nervous about control on wireless. The future may be small wired clusters with wireless transmitter devices. Radio and MAC (Media Access Control) neutral is the only way to go for a standard. A low power 802.11 chip is coming that may put an end to the 802.15 world, since users are already familiar with it.”
Finally, there are other wireless technologies widely used in the world. One is Bluetooth. Dave Wisniewski, product specialist for Rockwell Automation Inc., in Milwaukee, describes how it uses this wireless technology in its drives division. “We have a wireless input module (WIM) that the customer can install on the drive in place of the standard Human Interface Module. In fact, one WIM could be installed on the door of an enclosure. A technician with a PocketPC with PocketDrive Explorer could have access from up to 32 feet away to every drive in the enclosure without being exposed to high voltage within it. One customer has a drive lineup on a mezzanine about 50 feet up. They had to rent a boom every time they wanted to go up and check the drives. Now, they just stand on the floor underneath and access them all. Some would ask why add a Bluetooth access at the drive since we already have Ethernet access. With one WIM, a user could have access to all the drives on the system through EtherNet/IP. You do have to implement some security. We have ‘pairing,’ that is, a PocketPC is paired once, then no one else can access or even see the devices.”
