How Ethernet technology advances can help process manufacturers
Ethernet Advanced Physical Layer (E-APL), an enhanced physical layer for single-pair Ethernet (SPE) based on 10BASET1L, could help process manufacturers move on from 4-20 mA technology.
To understand why the process industry has traditionally struggled with Ethernet solutions, a detailed look at the complexity of the industry is necessary. In process plants, Ethernet has so far been used mainly at the higher levels of the automation pyramid and rarely at the field level. Ethernet offers many advantages in the context of digitalisation and Industry 4.0, especially the large bandwidth and high speed, which enables access to a great deal of data. Indeed, modern and innovative diagnostic concepts would not be possible without access to this data. However, conventional Ethernet solutions do not meet the requirements of the process industry, such as intrinsic safety and line lengths of up to 1km on a shielded 2-wire line.
This is why 12 industry partners and four user organizations – FieldComm Group, ODVA, OPC Foundation, and Profibus International – have worked together to develop a 2-wire Ethernet solution that meets these needs of the process industry. The concept, titled ‘Ethernet-Advanced Physical Layer’ (now known as Ethernet-APL) was established in 2015. Since then, IEEE and IEC standards have been established and the technology has been fully developed.
Using technology with intrinsic safety in potentially explosive environments presents a challenge for the process industry. The Fieldbus Intrinsically Safe Concept (FISCO) was introduced to address this and has proved very successful. To ensure that Ethernet-APL supports intrinsic safety in hazardous areas, the IEC PT60079-47 working group developed a technical specification for 2-wire intrinsically-safe Ethernet, known as 2-Wire Intrinsically Safe Ethernet or ‘2-WISE’. This approach was confirmed by successful tests at DEKRA Testing and Certification GmbH.
From a formal point of view, nothing now stands in the way of Ethernet technology entering the process industry. However, as is always the case when a new technology is introduced, a great deal of detailed work awaits users and manufacturers before it can finally be used in practice.
It is not just the technology that has to be considered – and this is more than demanding in view of electromagnetic compatibility (EMC) requirements, explosion protection, dust or high temperatures – but also international standardization, the extremely long service life of the systems, the development of engineering guidelines and test scenarios for devices. Any new technology has to be considered from the outset and adapted to the new requirements: connectors have to be reviewed and checked for compatibility on the part of the manufacturer, housings for small temperature sensors have to be designed, the limited power supply has to be considered, and the necessary test procedures have to be developed.
In 2019, Bilfinger Engineering & Maintenance launched an initial test of Ethernet-APL with Pepperl+Fuchs. The goal was to examine the technology and the associated technological leap. In the test setup, the available Ethernet-APL infrastructure prototypes from Pepperl+Fuchs were connected to a current process control system via Profinet. This setup ran various use cases from the entire lifecycle of an automation system, including assembly, commissioning of the devices, and the robustness of communication in the event of faults on the Ethernet-APL layer. For this purpose, the setup had to undergo several stress tests. In addition, the general handling of the new infrastructure components such as field and power switches or existing cable types was examined on the new physical layer. Overall, the test setup was a success.
Making a change
In process plants that have been in operation for decades, it is important that devices of different generations work well together. Therefore, a pilot application investigated these types of generational issues, for example, when Ethernet-APL field devices and Profibus PA field devices are connected to a switch, or whether different Profinet devices, such as APL switch, proxy, or remote I/O from different manufacturers can communicate with each other in a ring.
In addition, the effort required for migration projects from Profibus to Profinet was investigated. For example, it was shown that a PA device can be easily exchanged via PA Profile 3.02, since the ports on an APL switch speak Profibus PA and Profinet. In addition, the permanent joint operation of Profibus PA and Profinet in one infrastructure was demonstrated to be possible.
This makes device replacement easy and also makes upgrades from fieldbus to Ethernet-APL during operation easy too. To list just a few practical examples – the exchange is accomplished in a few minutes if a device is no longer available for purchase or if users would like to obtain additional information through a more modern interface, for example, if a life image of the echo curve of a level sensor is to be made available more quickly. Generally, commissioning can be completed more quickly because addressing can be performed automatically through means of Ethernet-based communications. Furthermore, Ethernet offers the opportunity for new applications, such as the connection of web server functions or for applications within the framework of the Namur Open Architecture (NOA) concept via OPC UA. Even the changes in the control technology required for this are manageable due to the similarity of the Profibus PA and Profinet protocols and are therefore easy to implement.
The verdict of the testers was positive. They concluded that Ethernet-APL with Profinet has the potential to finally replace 4-20 mA technology.
Faster and simpler
The advantages are undisputed. Thanks to Ethernet-APL, data can be transported more securely and easily, allowing more intelligent tools to be used. This means that work processes can be simplified considerably, starting with installation and commissioning. The high level of data integration ensures a higher degree of automation and thus faster implementation. For example, new field devices register ‘personally’ during the loop check.
Furthermore, the data is always available in the right place, such as on a handheld in the field. The current data exchange increases the consistency of this data – a perhaps banal problem, but one that crops up again and again in practice. Thanks to Ethernet-APL, continuous data exchange between the project planning, control or asset management system and the instrumentation is possible. Inconsistencies due to changes that have not been transferred, for example when replacing devices, are now a thing of the past.
In addition, fast and easy data access provides deeper insights into the process and thus offers the opportunity for process optimization, such as through intelligent data analysis. In addition, new maintenance concepts are possible because, among other things, the field devices can independently report a need for maintenance.
Undeniably, 4-20 mA technology has served industry well thanks to its robustness and simplicity, but it is no longer adequate for future digital tasks. It should always be kept in mind that Ethernet in itself is not a new technology on the market. Rather, it has been tried and tested – as four-wire technology – in many industrial control rooms for years. Ethernet-based protocols such as Profinet or EtherNet/IP are widely used, for example to control controllers, frequency converters or analyzers. Ethernet-APL is merely the physical layer, which can now be used in the field of the process industry and can unfold its benefits there.
In other words, Ethernet-APL not only makes processes safer, but also avoids data inconsistencies and thus increases the quality and delivery reliability of the end products. Many manufacturers are therefore already evaluating the implementation of Ethernet-APL in their products, so that users can benefit from a wider choice of devices. Join the leap into the digitalisation of the process industry.