HART: benefits for today and into the future
Today, the HART (Highway Addressable Remote Transducer) Communication Protocol is the global standard for sending and receiving digital information across analogue wires between smart devices and control or monitoring systems. In addition, the introduction of WirelessHART has significantly expanded the capabilities of the technology while maintaining compatibility with existing HART devices, tools and systems.
“Despite digital fieldbus technologies such as Foundation Fieldbus and Profibus entering the market over ten years ago, HART is still the market leader today, with more than 90% market share,” said Frank Fengler, head of device integration management at ABB Automation Products.
HART was originally created to superimpose digital communication onto a 4-20 mA signal. “Primarily, it was intended to access remote or dangerous applications, where the superimposed communication could be used to configure devices,” explains Frank Hils, director projects and solutions at Endress+Hauser. “Originally it was considered to be a fit-and-forget solution for device configuration and, thereafter its digital communication capabilities were not often used.”
However, when digital fieldbus communications became more widely used and accepted in the industry the use of HART Communication also increased. When users became aware of the valuable intelligent information in their installed HART devices, they were able to make better use of the HART capabilities.
Added to this came an increasing demand for optimization of asset management capabilities using the available digital information. “This led to more host systems becoming HART-enabled, allowing them to read HART digital information in their application,” said Fengler. “The benefits were two-fold. On one side, because the equipment was already installed, very little additional investment was required – maybe just a HART-compatible I/O device. Secondly, the information that came from the device could help to optimise their systems, especially useful for maintenance purposes and to help increase productivity.
“With HART, there is also a synergy for device development design. Having a data highway between the device and the system makes it possible to bring more functionality into the device without the need for additional wires, especially for non-time critical computed values. Today, although more people are now making use of HART capabilities, there are still many users with legacy HART-enabled devices in their plant who are not doing so, which means that there is a huge, untapped potential waiting for many plant operators.”
So, if you are reading this article and wondering how you could possibly meet the ever increasing demands from management for greater productivity, less downtime and better management of energy consumption, you may already have the solution installed. You just need to look at how you could better utilize your installed base of HART-enabled devices.
Engineering practices need to be considered to get the most from a system. “When designing a control loop, the HART capabilities should always be taken into consideration,” advised Fengler. “It could even help to reduce capital expenditure. For example, if you do not know that a device produces three values and you apply three devices instead of one to achieve the required tasks, it is not a cost-efficient design.”
Unlocking hidden potential
Dr. Juergen Spitzer, head of process instrumentation, Siemens Industry Automation Division in Nuremberg, believes that the HART protocol can still offer potential to unlock hidden value of the plant. “A typical example is the replacement of a legacy control system by a modern HART-enabled system. By maintaining the installed smart field devices with 4-20 mA/HART and installing an infrastructure to add WirelessHART devices for increased future flexibility, the user can realize several benefits,” he said.
“The new communication infrastructure with ‘HART integrated’ allows easier access to the existing field devices from all levels of the automation pyramid ‘HART integrated’ automation solutions can increase the transparency of the plant. WirelessHART can also be seamlessly integrated into the control strategy in the same way as wired HART devices by using HART-IP to communicate with the WirelessHART gateway. This standardizes the communication to HART components and devices using Ethernet. It is an important benefit for users because, in addition to wired connections, they could also use industrial wireless LAN (IWLAN), which may save time and costs through reduced cabling and communication components.”
HART-IP was added to the specifications to aid system integration. It serves as a high bandwidth connection between host applications and HART enabled I/O such as multiplexers and gateways, combining the HART network and application protocol layers with the Internet Protocol to provide connectivity with existing IP infrastructure.
Commenting on the future for the HART protocol, Fengler sees a parallel path emerging. “Traditional thinking has dictated that field level data can only be brought to the management or business level by being first pulled through the control system which creates a bottleneck. However, increasing digital capabilities offer a parallel path, allowing information to move directly from the device level into the business system, eliminating the need for direct involvement of the control loop or affecting the integrity of the control system. One of the strengths of HART is its ability to separate 4-20 mA and digital.”
Achieving this goal will, of course, depend on the age of the installation but most installations that have been put in place within the last 10 years will almost certainly already include this digital extraction capability.
A role in the Internet of things
In the future, Fengler predicts higher communication speeds for HART. He also predicts that there will be a migration of even more IT capabilities and Internet protocols down to the field level. “Devices are becoming more powerful and I believe that HART-based technology will play an important role in ‘the Internet of things’ too,” he said. “A HART device is not just a device, it is an internet server with multiple users and subscribers to the information it provides.
“I also believe that, in the future, there will not be a big difference between a data concentration unit, such as an HMI, and a field device, as devices become ever more powerful. The value and hierarchy of the field devices will become higher, and the overall architecture will become more flattened with the HART device acting as an information server.”
Jim Cobb, senior marketing manager, temperature, at Emerson Process Management, believes that one of the major evolutions of HART instrumentation has been the advancement in diagnostic capability. He said: “Traditionally, diagnostics only reported on the operational status of the device itself. Today instruments can report on external conditions that may affect the measurement or operational ability of a valve controller.
Devices can have the ability to monitor the signal loop for proper voltage which can indicate poor wiring, water in the housing or a malfunctioning power supply allowing the situation to be remedied before the process is affected. Flow meters can automatically verify their reading, reducing the frequency of calibrations. The ability to detect ‘on-scale’ errors when the reading looks good, but is not consistent with past measurements, can prevent unnecessary shutdowns and improve safety.”
Sergio Diaz, product marketing manager at Emerson, believes that one of the biggest benefits of HART is its simplicity. “It uses 4-20 mA so is very reliable and users are comfortable with it. It is also compatible with legacy systems, which makes it very flexible. The HART Communication Foundation continues to add new functionality which helps with the growth of the technology. Recently, for example it has added support for NAMUR NE 107 to HART.”
NAMUR created a set of recommendations on device status reporting to achieve greater consistency from installed field device networks. Many plants utilize a variety of technologies for different applications, yet traditionally, diagnostic information has been represented in different ways. NE107 provides a standard way to report an event to a whole system.
“I would expect that device manufacturers will now start to provide NE 107 functionality and that host systems will also be enabled to leverage this functionality to improve predictive diagnostics and improve all the information available for device diagnostics. It should provide a standardized way to look a the alerts coming from the devices, regardless of the manufacturer – it will all be reported in the same way, providing a more consistent approach,” said Diaz, concluding that Emerson will soon be adding support for NAMUR 107 recommendations in HART.
Since its inception, HART technology has remained cost-effective because of its simplicity, reliability, and interoperability. So, if your plans call for an upgrade, expansion or new construction, look to HART Communication. HART delivers valuable benefits today and into the future.
Suzanne Gill is editor of Control Engineering Europe.