Ethernet-APL addresses the challenges of linking field devices with automation systems over long distances in hazardous environments. Christian Johansson, global product manager for ABB process automation explains how this open, high-speed physical layer standard lets plant owners unlock more value from their process data, optimise performance and promote safer operations.
In a relentlessly competitive market, industrial customers are looking to achieve gains in efficiency, resilience and sustainability by digitalising their process operations. Plants are becoming smarter and more connected as they grow in scale and complexity, with increasingly intelligent field devices producing and consuming masses of process and diagnostic data. This flood of information informs a range of valuable activities, from remote monitoring and optimisation to preventive maintenance, advanced analytics and fleet-wide asset management.
With more devices, more data and more applications come greater operational challenges. A typical mid- to large-sized plant may be home to sensors, actuators and other field devices from multiple vendors of varying ages and capabilities. Hundreds or thousands of these end points are connected to controllers and automation systems via a range of different control standards and communication protocols. From a plant owner’s perspective, this diversity of devices and standards can blunt efforts to manage data efficiently and share it smoothly with enterprise applications and systems for analysis, insight and action.
Serving as a highway for these multiple types of process, control, configuration and diagnostic data is the underlying physical layer that connects the distributed control system (DCS) to sensors and other field devices scattered across a large refinery or processing plant. Long-established technologies, notably the widely-used 4-20 mA signalling standard, are progressively giving way to faster, more flexible and resilient solutions for transporting bidirectional data in what can be highly challenging environments.
Over the last decade, Ethernet-based networking technology has been rapidly gaining traction with industrial users. A mainstay of the enterprise IT world since the 1990s, Ethernet is an increasingly popular option for exchanging data between controllers and field devices, where it sits as the physical layer beneath higher-level control protocols such as Modbus TCP and PROFINET that feature in tens of thousands of industrial plants worldwide.
Ethernet’s intrinsic speed, proven reliability and near universal adoption are of obvious appeal to the needs of today’s industrial automation users. Balancing these attractions is the limited suitability of regular Ethernet for use as a physical networking layer in hazardous process automation environments. Conceived to link computer systems in the relatively benign surroundings of offices and research labs, the original suite of Ethernet standards did not envisage transporting high-speed digital data in a chemical plant or oil refinery, where electrical sparking can have catastrophic consequences in flammable and explosive atmospheres. Nor was Ethernet envisioned for point-to-point connections between field devices and their controllers, where cable runs may extend over many hundreds of metres in a large industrial site.
A purpose-built standard
The desire for a safe, robust, cost-effective and high-speed connectivity solution based on open standards for the process industries has been reflected in the recent development of Ethernet-APL. The result of close collaboration between international standardisation organisations and leading vendors including ABB, Ethernet-APL augments the foundational set of specifications for wired Ethernet, adding specific capabilities to meet the current and future needs of digital instrumentation users.
Baseline capabilities of Ethernet-APL start with ultra-reliable bidirectional data transmission at speeds of up to 10 Mbps. Several orders of magnitude quicker than HART and digital serial fieldbus protocols, this speed boost allows Ethernet-APL to effortlessly carry large volumes of real-time process, configuration and diagnostic data that are common to today’s smart plant operations.
Equally appealing to plant owners is Ethernet-APL’s ability to carry high-speed data as well as electrical power for field devices over a familiar shielded single twisted pair cable. With no need to rip out and replace existing fieldbus Type A cabling, the time, costs and complexity of migrating legacy control and automation infrastructures to Ethernet-APL in brownfield sites are minimised.
Intrinsic safety is another key part of the new standard. Reflecting Ethernet-APL’s intended use in hazardous environments such as petrochemical sites, a range of power classes are defined for different applications. These include a specific port profile that limits maximum supply voltage and current. By restricting levels of electrical energy within a physical connector that might allow a spark to occur, this gives the reassurance of safe operation in flammable or explosive atmospheres.
The new physical layer standard meanwhile tackles another issue that hampers the appeal of regular Ethernet, a practical limit to the length of point-to-point cable connections. Progressive degradation in transmission speeds and reliability with cable runs beyond 100 metres limits Ethernet’s suitability for linking field devices in large industrial sites. Ethernet-APL, by contrast, enables reliable connections for data and device power over distances of up to a kilometre. Similarly, it can support mixed trunk and spur network topologies that feature prominently in modern process plant operations, with shorter spurs off the main trunk carrying lower power over distances up to 200 metres with optional intrinsic safety.
Ethernet-APL also affords the designers of automation systems considerable flexibility and resilience when addressing the increasingly sophisticated needs of today’s industrial plant operations. A notable example of this is ring redundancy, where each Ethernet-APL switch has at least two connections to other switches. This robust network topology provides high levels of fault tolerance, supporting uninterrupted operations in environments where uptime is critical.
Ethernet-APL provides an exceptional robust and reliable foundation, supporting a wide range of higher-level industrial communication protocols used with new and legacy automation systems such as PROFINET, Open Platform Communication Unified Architecture (OPC UA) and Ethernet/IP. Migrating from analogue 4-20 mA HART or conventional fieldbus infrastructures to Ethernet-APL can also be readily accomplished without additional investment in hardware gateways or protocol conversion solutions, simplifying plant owners’ transition with reduced costs and system complexity.
The ability to be readily deployed in combination with Field Device Integration (FDI) technologies also makes Ethernet-APL a particularly attractive fit for high-speed data communications in industrial plants. The result of cooperation between leading automation industry groups and vendors, including ABB, FDI provides a suite of standardised software tools that streamline integration of FDI-compliant devices with similarly equipped DCS or other host systems. This in turn reduces the engineering effort needed to install and configure fleets of field devices supporting a mix of protocols including PROFIBUS, PROFINET and HART.
Opening a new path for managing industrial data
As plant owners look to realise greater operational efficiencies and unlock fresh sources of value from their instrumentation assets, Ethernet-APL provides a compelling alternative to ageing fieldbus technologies, accelerating the efficient exchange of control and diagnostic data between today’s intelligent field devices and the automation systems controlling them.
Bringing the benefits of reliable, high speed networked communications to devices in the field, Ethernet-APL simplifies interworking between different field instrumentation technologies and communication protocols, allowing plant owners to reinforce the continuity of their operations while delivering more from their precious data.
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