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“HART is the de facto standard in this industry and will remain so for a significant time. It is standard in all our devices,” says Hans Georg Kumpfmüller, Siemens AG, Germany. Not only a de facto standard, HART technology also is established in IEC global standards. In IEC61804, HART EDDL technology is established in cooperation with Fieldbus Foundation and Profibus Nutzerorganization (PNO). In IEC 61158, the HART Application Layer and Services are part of the standard. IEC 61784-1 establishes the HART Communication Profile.
“I see HART 7 as the reliable, low-cost solution for users to use more of the power in their installed HART-enabled devices,” says Thomas Holmes, CEO of MACTek Corporation, a manufacturer of HART modems. “The additional features included in HART 7 step up the game, opening opportunities for improved asset management, lower operating cost, and less downtime.”
HART technology is one of the most widely used fieldbus communication standards in the world. Seventy percent of the process measurement and control devices shipped worldwide each year use HART communication, adding to the over 41% of installed devices that already use HART communication—for a total of over 26 million devices shipped and installed worldwide.
As devices have changed, applications have changed, and requirements have changed, HART has also changed to keep pace. All the things you knew and loved about HART Communication before are still true, but with the new capabilities of HART 7, there’s a whole lot more. HART Communication is not your daddy’s protocol!
“The HART protocol was originally a hybrid analog-digital technology,” says Peter Zornio, Chief Strategic Officer, Emerson Process Management. “By contrast, WirelessHART (part of HART 7) is an all-new, all-digital mesh networking technology. What’s been retained in WirelessHART and enhanced in HART 7 for both wired and wireless are the tools, technologies, and practices used to configure devices from multiple vendors in a standard manner and integrate their data into host systems.”
The current generation of the HART Communication Protocol is HART 7. The HART 7 feature that has already received the most interest publicly since its release in September 2007, is WirelessHART, an evolutionary extension to the HART Protocol. According to Sean Ireland, wireless product manager for Siemens Energy and Automation, “This would be rated extremely high in importance, both to us and our customers. Wired and wireless products must work together in a common network.”
But HART 7 is significantly more than WirelessHART. There are significant differences and improvements between HART 5 and HART 6, the most commonly installed and used versions of HART, and HART 7—and not just wireless, either.
“There will be increased diagnostic capability built into the instrument,” says ABB’s Gareth Johnston, “and the ability to report by exception, based on time or event.” But in keeping with the HART Communication Foundation’s long-standing commitment to the users of the HART protocol, HART 7 is fully backward-compatible with all the HART versions that came before it.
The fact that WirelessHART is simply part of the HART 7 standard shows off an important characteristic. Wired HART and WirelessHART are intended to be used together seamlessly, as integral parts of a digital field sensor and control network. They operate the same way, program the same way, and are useable interchangeably, wired and wireless.
ABB’s Johnston says, “WirelessHART is the logical migration of the current HART technology to a wireless environment.” He continues, “Customers now have the capability to maintain their current legacy 4-20 mA loops and unlock the power of HART instrument data via HART wirelessly.”
What do the HART users get? Johnston continues, “This will enable customers to obtain real-time asset monitoring data. This data will permit them to better manage the health of their instruments, thus insuring a reliable measure of their process.”
The HART protocol is enshrined in several IEC global standards, and the WirelessHART portion of HART 7 has been submitted for ballot as an additional IEC standard. HART has become both an IEC and de facto global standard because it is easy to use, simple to understand, flexible, and adaptable, and it can be used anywhere in the world. WirelessHART, because it uses the 2.4 GHz band, can also be used almost everywhere in the world without licensing challenges.
In Table 1, you can see what’s been added to HART 7: new capabilities for increased intelligence and communication throughput efficiency, with new features such as enhanced data publishing for process variables, configuration change and device diagnostic status alerts, with support for “Publish by Exception” and “Automatic Event Notification.” Another exceptionally valuable new feature: “Time-Stamped Data,” applies to device process variables, diagnostics status, and configuration change events. This new feature supports broader use of multivariable device capabilities in control systems and permits users to employ better forensics in the event of problems. Measurements or actions can be triggered at a specific time, and HART 7 allows synchronized operation across multiple devices.
In HART 7, Process Variable Trends can now be sent as 12 sequential time-stamped data points of the same process variable in a single packet, effectively multiplying communication throughput for the selected process variable. “This makes it easy to setup a plant-wide asset management system,” says Endress + Hauser vice president Victor Wolowec.
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