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Suzanne Gill finds out what role the now ubiquitous HART protocol might have to play in factories and processing plants of the future, as more enterprises look to reap the benefits promised by Industry 4.0.
With over 40 million installed field instruments and support from leading instrumentation suppliers, the HART Communication Protocol (Highway Addressable Remote Transducer) is the largest digital communications technology deployed in the process industry today. Beyond its original ability to communicate over 4-20 mA analogue instrument current loops, which helps preserve existing investments in legacy analogue instrumentation, today the technology can offer many additional capabilities and it has huge potential when it comes to plant digitalisation and the move towards smarter factories and Industry 4.0.
Even if the HART signal is predominantly used for parameterisation, with the appropriate tools it can enable continuous device monitoring, real-time device diagnostics and multi-variable process information for both new and old devices. If collected and turned into actionable information, this data has value throughout the plant lifecycle – from design and installation right through to operation and maintenance.
According to Ted Schnaare, director engineering, Rosemount Wireless at Emerson Automation, the HART protocol is well positioned to help realise the vision of Industry 4.0. “While the protocol has been in existence for some time, it was designed around the basic concepts that have become the pillars of Industry 4.0. The WirelessHART protocol was designed to provide reliable, secure and ultra-low power wireless communication for field measurement and control instruments,” he said.
HART instruments themselves are key maintenance tools within plants. One important element of the HART protocol is its ability to effectively communicate instrument and measurement health information to operators and maintenance technicians. The protocol allows for the right status information to be delivered to the right person at the right time.
HART was also designed to strike a balance between the benefits of standardisation and the need for customisation for certain types of instruments. This ensures interoperability while providing the flexibility to support new and innovative instruments – including instruments such as wireless ultrasonic monitors used for state and event detection in critical plant assets. “The HART protocol is being used by many of our customers as they move into the next industrial revolution and it has been proven to be very well suited for this task,” continued Schnaare.
The WirelessHART protocol has enabled users to improve the safety and efficiency of their operations at much less cost than with traditional wireless solutions. Examples include monitoring and optimising the performance of critical assets such as steam traps, safety showers, pressure relief valves, heat exchangers, and pumps. “Using WirelessHART-enabled monitoring solutions allows users to gain critical insight into aspects of their operation that were either not possible or cost-prohibitive in the past. This insight is one of the key aspects of the Industry 4.0 vision,” continued Schnaare.
Bastian Engel, team leader technology marketing for Endress+Hauser Process Solutions, agrees. “With industry moving forwards to Industry 4.0, the importance of wireless communication is also increasing. If measurement points are distant or difficult to access, WirelessHART is particularly useful,” he said. “It can add wireless functions to the HART protocol transmitting the measured value and additionally supports all specific HART functions, especially diagnostic information and can be easily retrofitted into existing infrastructures.”
The importance of data
An example of how important the data provided by HART-enabled field devices is for processes can be demonstrated by a simple valve. Often, it is not only a question of how often the valve is operated, but also how long it takes to open. If the time period is longer, it may be an indication of wear. The correct times for maintenance or replacement are also relevant. Whereas premature replacement increases costs, a date scheduled too late can lead to a total system failure.
Sabrina Weiland, product marketing manager at Pepperl + Fuchs, agrees that HART is also an important element for Industry 4.0 projects. She said: “When modernising a plant towards Industry 4.0, for example, a remote I/O system is the ideal solution, as a new control system works with bus protocols such as PROFIBUS, PROFINET, MODBUS RTU or MODBUS TCP. The remote I/O system replaces the point-to-point connection between field devices and control levels, enabling migration to a bus protocol. However, only the connection from the control system to the remote I/O is a bus; the existing cabling from the remote I/O to the field devices remains. The benefit of this is that plant operators can retain the existing structure with HART and 4-20mA, with all of its advantages.
“In parallel to PROFINET or MODBUS TCP, there is an Ethernet-based communication with the control system, such as HART IP via PROFINET. Direct access to the field device is also possible via HART IP. In addition, an OPC UA server can be implemented into a remote I/O gateway.” OPC UA offers standardised communication according to IEC 62541 with a high data throughput for connecting different systems. The operator is then able to choose whether data is accessed via HART or other protocols.
Weiland continues. “If the operator only requires more information from the field devices for Industry 4.0, without plant modernisation, this can be very conveniently implemented via a HART multiplexer connected to the control system via an RS485 interface. The multiplexer can be integrated in up to 32 different loops in the field and can request HART data from the devices.” This, says Weiland, can offer a very economical solution, as a loop currently costs less than 100 euros. “The multiplexer also ensures that a request from the asset management system is forwarded. This variant can be used with OPC UA to access data via the serial interface and distribute it as needed.”
“Today, instruments and asset management systems are being designed to simplify diagnostic alerts and ensure that the right people get the right information at the right time.”
Making life easier
Some time ago an end-user called on device vendors to make life easier for end users of HART devices in three particular areas – Simplified and unified device integration software; reduced device complexity for basic functionality; and simplified device diagnostics capabilities in line with NAMUR NE 107. Vendors are now addressing these issues with many demonstrating their commitment to making their products easier to configure, use, and maintain by investing in initiatives such as Field Device Integration (FDI) whose primary goal is to produce consistent, easy to use tools that simplify the management of field devices over their entire lifecycles.
Weiland explains more about FDI. “Previously, when a new measuring instrument or an actuator was integrated into the process, the user deployed EDDL or FDT. This meant either a text-based parameter description or a standardised, multi-vendor software interface that allowed the programming and description of complex functions and displays. However, neither variant alone meets the current requirements when it comes to integrating functions of field devices. In contrast, FDI provides the full description of a device in an FDI device package. This is supplied by the device manufacturer and contains all the essential information for an integration.
“The device parameters are described via an EDDL interpreter and supplemented by complex graphic elements in freely programmable user plug-ins, just as with FDT. A further advantage of FDI is that it can be easily integrated into existing system architectures. An FDI-enabled host must therefore be available for new plants. In the case of existing plants with FDI devices in the field, the control systems must be able to understand EDDL and FDT.”
Endress+Hauser is also actively working on the FDI standard as the new integration standard with a unified EDDL specification as a base. “FDI is seeking to provide the same look and feel for all devices within the FDI host, independent of device type, manufacturer and communication protocol. Endress+Hauser focuses on the most important customer demand – meaningful diagnostics according to NE 107,” said Engel.
So, next generation field measurement and control devices are being designed with ease of use as a primary objective. While some devices can be extremely complex by necessity, manufacturers are going to greater lengths to make sure that these complexities are hidden from users. Emerson, for example, has invested in the area of human centered design (HCD), with reviews being a standard part of all of its new product development programmes. “These reviews address all aspects of a product and all phases of its lifecycle including ease of ordering, installation, configuration, and maintenance,” said Schnaare.
Attention has also been paid in recent years to the problem of diagnostic alert flooding. This condition results from a single instrument health issue generating numerous diagnostic alerts which can distract or overwhelm operators. “Today, instruments and asset management systems are being designed to simplify diagnostic alerts and ensure that the right people get the right information at the right time. For example, operators don’t need to know the details of a particular diagnostic such as a detected memory failure, they just need to know if the data they are using to control critical processes can be trusted,” said Schnaare. “Instrument maintenance resources, however, need the details so they can investigate and solve problems. This is being achieved by applying the basic principles defined in NAMUR NE107 which recommends classifying alerts and using that classification to determine how to communicate with operators and maintenance people. Indeed, the latest version of the HART protocol has revisions that align it with the recommendations of NE107,” he said.