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22/05/2009
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Emerson Process Management has been installing wireless mesh networks for device monitoring since October 2006, and Wireless HART (the plant standard, where digital communications are superimposed on the 4—20mA signal) since last September.
 Speaking at this year's mtec exhibition at the NEC, Andy Wallace, Emerson's business manager for so-called 'smart wireless solutions', described how wireless transmitters can now be screwed into the back of existing hard-wired devices to enable remote instrument diagnostics.
Systems work over distances of more than 400m with good line of sight, despite only running at 1mW. As a demonstration, members of the audience were invited to commission six ATEX-compatible Rosemount instruments, fitted with the wireless units.
Despite interference in the hall, the network set itself up in less than a second. Wallace explained that the instruments identify themselves and, in the event of network problems, quickly find new paths, via other instruments that act as repeaters.
Battery life is typically five to 10 years; communications are 128-bit encrypted for security and use multiple time slots to avoid data 'collisions'. In fact, there are five levels of security if the4re are problems with interference or jamming, the units can even frequency hop, like military radios.
Wallace expects the power industry to show biggest uptake, although, to date, the biggest implementations have been on offshore oil rigs, BP's Wytch Farm (where the system monitors 40 pressure transmitters), an oil storage terminal and a power station in East London.
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Author
Tom Shelley
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