In addition to the 4-20 milliAmp (mA) analog control channel in every Hart device, a second, all-digital channel provides access to real-time device status, diagnostics and multivariable information that resides within the device. When continuously monitored, this digital Hart data can provide valuable process information, such as advance warning that a device is about to fail.

But in today’s plants, most of this valuable data remains trapped. According to the Hart Communication Foundation (HCF), about 85 percent of some 25 million Hart devices in the field are connected to legacy, analog-only input/output (I/O) systems that can’t understand the Hart digital data.

Wireless rescue

The coming generation of WirelessHart adapters, based on the new WirelessHart standard, will enable users to rescue this stranded data and put it to use. When attached to installed Hart devices, or anywhere on the control loop, WirelessHart adapters will extract the digital data and transmit it wirelessly for use in asset management systems and other applications.

“We’ve got a lot of people asking for them,” says Steve Ekblad, director of global wireless sales and marketing for Emerson Process Management, regarding his company’s forthcoming WirelessHart-compliant Smart Wireless Thum Adapter. Ekblad doesn’t believe the adapter market will be as large as that for new WirelessHart-compliant instruments. “But I think it will unleash a lot of things that people have always wanted to do but couldn’t do in the past,” says Ekblad, who is based in Chanhassen, Minn.

Emerson is one of more than a half dozen vendors that are planning near-term introductions of WirelessHart-compliant products, including adapters. Emerson will focus first on new WirelessHart products, says Ekblad. Rollouts will begin this month on a range of WirelessHart entries including pressure, temperature and vibration transmitters, he says. The Thum Adapter will come slightly later, “probably early in 2009.”

Likewise at Pepperl+Fuchs Inc., Twinsburg, Ohio, Product Manager Robert Schosker says that P+F’s first WirelessHart adapters will be available during next year’s first quarter. Pepperl+Fuchs plans to offer battery-powered, loop-powered and line-powered adapter versions, with an emphasis on the battery-powered units, says Schosker. “By keeping it battery-powered, it eliminates any fear from the customer’s standpoint that the unit has any chance of interfering with the 4-20 mA signal,” he notes.

Emerson is taking a different approach. The Emerson Smart Wireless Thum Adapter will come only in a loop-powered version, and Emerson has no plans currently for a battery-powered version, Ekblad says. A loop-powered version can be attached without affecting the intrinsically safe approval rating of a device, he points out. “If you use a battery, you can’t hook it up to a device in an explosion-proof area, so that’s a really big deal.”

What’s the price?

Some industry watchers believe that a strong WirelessHart adapter market will depend on pricing being set at $500 or less. “Even $500 might be a little pricey,” opines Wil Chin, a research director at ARC Advisory Group Inc., in Dedham, Mass. Some Hart devices such as temperature transmitters are priced as low as $500 for the whole device, Chin says, so a $500 adapter might give some users pause. On the other hand, he notes, a $500 adapter price wouldn’t seem so bad as an add-on for a $5,000 to $10,000 Coriolis flowmeter.

At Pepperl+Fuchs, Schosker says he hasn’t yet received final WirelessHart adapter pricing from the company’s European parent. “But I’m guessing it will be in the range of $250 per loop,” he says. At Emerson, Ekblad indicates that initial pricing for the Smart Wireless Thum Adapter will fall between $500 and $1,000 per unit.

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