WirelessHART was designed so it could be used to retrofit wired HART devices with a wireless adapter that is a native HART device and can be located either at the device or anywhere along the current loop. Thus, any HART device can be upgraded to act as a WirelessHART device, within the capabilities of its native HART version.
Because the HART protocol was designed for multiple vendors, many HART commands are universal and must be adhered to by all vendors for any device. This forms the backward-compatibility to other previous versions of HART, so that any installed HART device can be used with any other HART device, completely interoperably. Other commands, such as Common Practice, include calibration and PV range, while a third set of commands includes device-specific commands such as Linearization Tables.
HART, whether wired or wireless, uses EDDL (Enhanced Device Description Language), with all the information needed by the host to communicate with a field device. The DD (Device Description) is a binary file which cannot be read as a text file. This enhances the cyber security of field devices.
The DD is generated via a tokenizer during the development and testing of the instrument. The DD contains all of the information required by a connected host, either a handheld communicator or a PC, for an engineer to be able to support the instrument. More complex instruments have been able to benefit from a backward-compatible upgrade to the DD that allows a more graphical user interface, much the same as that offered by the Device Type Manager.
HART data can be transmitted using a multiplexer (available from several vendors), connected to many field instruments with a single connection to a host system. The multiplexer is often incorporated during the design phase of the project, but can also be added as a retrofit due to the backward-compatible and interoperable nature of the HART protocol. Recent control systems have been able to take advantage of I/O cards that can pass HART commands over a fieldbus network such as Profibus DP. HART data can also be transmitted via OPC to the control system or the asset management system.
What People Use HART For
Most users use HART for calibration and routine diagnostics. This is changing rapidly. More HART devices are being connected directly to the process control system or asset management system now than previously. Endress+Hauser's Robinson says, "This depends on the individual's perspective of how that process device impacts the profitability of the plant. Even though a process asset isn't connected to the plant controls does not minimize its importance to the process. We all know that the right information in the right hands at the right time always yields positive results."
Phoenix Contact's Schmidt says, "Being able to use HART has a lot of benefits; I think one of the most overlooked uses is for getting off of preventative maintenance schedules and being able to predict device failure with the HART data—especially for valves. Partial stroke testing (PST) and positioning feedback data is extremely valuable."
HART and the future
Users discover more ways to use HART Communication to make their plants competitive and sustainable; suppliers offer more intelligent HART products; and the use of HART technology grows globally.
The ARC Advisory Group reports about half the worldwide installed base of process measurement and control devices is HART enabled. ARC forecasts the number of installed HART devices will surpass 37 million by year end 2012 .
ARC says, "HART continues to have the largest share of the market. We see strong, continued growth (for HART) ."
The HART Communication Foundation continues to enhance the HART Protocol. HART technology developments support changing industry requirements and preserve investments, to provide new opportunities for both users and suppliers. Backward compatibility ensures that an investment made in a HART device is protected into the future.
IEC 62591-WirelessHART, designed to bridge the gap between wired and wireless, is the first international wireless standard for process monitoring and control. WirelessHART benefits both existing and new monitoring and control applications. The development of wireless capabilities and other enhancements for the functionality of the HART Protocol preserves the viability of the technology's future indefinitely.
And more enhancements will come to extend, amplify and improve your HART assets for the future.
HART technology for today and the future
Planning an automation solution requires many considerations, including technology risks mitigation, funding, resources capability, team agreement, leveraging of installed assets, system integration and real-world needs assessment. From point-to-point to multi-drop to wireless, HART technology enables real answers. HART Communication is the most robust, most versatile fieldbus protocol, and positioned to carry the industry well into the future.