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From the inception of the HART Communication Protocol, two of the technology's critical capabilities have been interchangeability and interoperability. That is, any HART transmitter must work interchangeably in the same application with any other HART transmitter, regardless of manufacturer, and any HART transmitter must work with all other HART transmitters, again regardless of manufacturer. This has permitted the huge growth of the HART protocol—with now more than 30 million devices installed worldwide. With HART technology, you can have ten transmitters from Vendor X, add three from Vendor Y and expect that they will communicate the same way, operate the same way and use the same handheld communicator or PC program through a HART modem.
Because HART requires interchangeability, you can mix manufacturers and products in the same network. Controllers use the same commands with all devices. Standardized diagnostics are in every device. The same tool works with all manufacturers, and one EDD (Electronic Device Description) works on all EDD-enabled Hosts.
Interchangeability means that you have the freedom to use any revision of the protocol or of the device without mandatory upgrades of tools or applications.
The HART Protocol has expanded and evolved over the past 20 years. HART 5, the most widely used version of the protocol, was released in 1989. In 2001, the HART Communication Foundation released HART 6, which was adopted by some, but not all, of the manufacturers of HART devices. In 2007, HART 7, which includes WirelessHART, was released, and was immediately adopted by vendors around the world. In 2010, the WirelessHART portion of HART 7 was approved as the first international standard for wireless communication for the process industries (IEC 62591).
HART has always been built upon standards. The IEC recognizes HART as part of its Industrial Communication Networks and Device Description Language (EDDL) standards. WirelessHART is built upon the IEEE 802.15.4 standard for low-power mesh radio networks.
Because of the huge installed base of HART wired transmitters and field devices, it is very well known that HART devices are all interchangeable and interoperable. They all are also backward-compatible. This means that while you can ADD features in subsequent revisions, you cannot remove features or change the meaning of diagnostics or data from a previous revision. This commitment to backward-compatibility and protection of installed assets is what made possible the incredible adaptability of WirelessHART.
There are over 240 vendors who produce HART devices—transmitters, actuators, analyzers, valve positioners and other field devices. Because of the interoperability and interchangeability built into the HART specifications, some of these vendors are building devices on HART 5, some on HART 6, and many are upgrading to HART 7 and WirelessHART. These 240-plus vendors and the owners of the 30 million-plus installed HART devices form a robust ecosystem.
Honeywell Process Solutions has upgraded to HART 7 because of the new features available for wired HART devices. It has chosen to use wired HART because the Experion DCS automatically takes the diagnostics and alternate PV information off the standard 4-20 mADC wiring. Honeywell has produced an adapter to provide older HART transmitters access to its One Wireless plant infrastructure network. "Most of our devices are currently based on HART 6 and will support HART 7, says John Yingst, a Honeywell product manager. "Our Field Device Manager asset management software can currently configure HART 7 devices with additional HART 7 support enhancements planned."
Emerson Process Management was first to market with HART 7 and WirelessHART devices, and now has over a dozen devices including a gateway, network manager software, a WirelessHART adapter (called the THUM because of its shape), several wireless transmitters (pH, flow, temperature, wet chemistry) and smart valve actuators that are wirelessly enabled using WirelessHART.
"We have a complete wireless portfolio," says Bob Karschnia, Emerson's vice president of wireless. "People are solving problems, not just collecting data. THUM adapters make additional data points available that would otherwise remain stranded and provides easy access to information that will enable improved performance. For example, standard Coriolis meters using 4-20mA output often need to be verified to ensure accurate custody transfer and top fiscal performance. A Smart Wireless THUM adapter enables measurement verification in an easy and scheduled way."ABB has also brought out a new suite of wireless transmitters, including a WirelessHART adapter and a temperature transmitter that can be powered by a power-harvesting device instead of a battery. "While many WirelessHART devices are intended to be battery-powered, we believe that the majority of applications to retrofit existing HART transmitters need no batteries. We have therefore produced a simpler WirelessHART adapter that takes its power directly from the already existing 4-20 mADC loop connection," says ABB CTO Peter Terwiesch.
ABB is also proving that the vaunted interoperability and interchangeability of the HART specification extends to WirelessHART. Instead of developing its own gateway, ABB is using one produced by Pepperl+Fuchs.
Gerrit Lohmann, Pepperl+Fuchs' wireless product manager also points out that the extension of HART to wireless also works in the other direction. "I feel that the interest in WirelessHART will also have a positive affect on wired HART multiplexers," he says. "With all of the talk regarding WirelessHART, people are rediscovering the benefits of HART. As the pressure continues to grow to optimize in a cost-effective manner, the stranded HART data contained in legacy instruments will be extracted via the customers' existing hardware, through a HART multiplexer or by the latest WirelessHART solution."