The HART Protocol: A Brief Overview
HART is an acronym for “Highway Addressable Remote Transducer”. The HART Protocol became an open communications technology in 1990. Today the HART Communication Protocol is the global standard (IEC 61158) and the leading communication technology for smart instruments with more than 30 million HART-enabled devices installed worldwide. No other process communication protocol comes close—in size or scope of installation and overall effectiveness.
During the past 20 years, the technology has been enhanced to serve process industry needs while remaining true to its key principles of backward compatibility and interoperability. Today industry suppliers continue to manufacture and ship HART products in record numbers—75% of the smart devices installed each year are HART-enabled.
HART Basics
HART Communication is a backward-compatible enhancement for 4-20mA instrumentation equipment that enables remote, two-way digital communication with smart microprocessor-based field devices.
Primary characteristics include: two simultaneous communication channels for exchange of process variables, device status and diagnostics information between field devices and process automation systems; an extensive application layer with standard commands for real-time transfer of standardized data; and standard operating procedures for efficient device commissioning and calibration.
The HART digital communication channel transmits simultaneously on the same wire and without disruption to the 4-20mA analog channel. This bi-directional communication channel provides real-time access to the rich set of data items available in all HART smart devices. Simultaneous and complementary real-time use of both communication channels provides a high level of control security and loop integrity far beyond what is achievable by using either channel alone.
Device Description Language (IEC 61804-3) has been a key element of HART technology since 1990. Today it remains the most important and widely used digital communication descriptive language, providing a stable platform for suppliers to define and document the capabilities of HART-enabled products in a single, open and consistent format.
DDL programs toward the standardization of device configuration provide a platform for future enhancements to DD technology as a whole and enable wider spread global access to DD technology.
The Smart Part of HART
All HART-enabled field devices, regardless of manufacture, contain 35 to 40 data items of rich information for improving plant operations and managing assets. The inherent intelligence of these devices allows them to perform internal diagnostic checks and communicate information regarding their status continuously.
The extensive array of device status, diagnostic and process related data items in every HART device are continually updated and readily available for real-time use by plant control, safety and asset management systems. Standard HART Universal and Common Practice Commands make it easy for systems to access the real-time data in HART devices.
Getting Connected
Real-time HART integration with plant control, safety and asset management systems unlocks the value of connected devices and extends the capability of systems to detect any problems with the device, its connection to the process or interference with accurate communication between the device and system. Choosing HART integration reduces costs by improving operations and increasing efficiency and helps to avoid the high cost of process disruptions and unplanned shutdowns.
Technology Enhancements
In addition to major enhancements to the HART technology that address industry needs for enhanced device communication, product development tools have been created. These tools include: the HART Server, a standardized, OPC-compliant software component that provides the backbone for systems to communicate using HART technology; and the HART Device Description Integrated Development Environment with Smart Device Configurator (SDC-625), an integrated set of tools that supports development, testing and maintenance of DDs for HART devices.
HART Goes Wireless
The latest step in the evolution of the HART Protocol, HART 7, released in September 2007, moves the technology into the world of wireless communication. HART 7 includes the new WirelessHART standard (IEC 62591Ed. 1.0) and addresses the critical needs of the process industry for a secure, reliable, and simple technology in the real world industrial plant environment that provides a common sense and industrial strength network solution to wireless communication.
WirelessHART is a complementary enhancement to the HART Protocol, providing an additional capability that can benefit both existing and new monitoring and control applications. WirelessHART is a wireless mesh network communications protocol for process automation applications that adds wireless capabilities to the HART protocol while maintaining compatibility with existing HART devices, commands, and tools.
WirelessHART includes several features to provide reliable communications in all industrial environments, including a self-organizing and self-healing network. WirelessHART employs robust security measures to protect the network and secure the data at all times including the latest security techniques to provide the highest levels of protection available.