Ethernet Reaches Down to Field Devices

Ethernet, and the reliable internet connectivity it offers, has unlocked greater automation of industrial processes. The following article dives deep into this technology’s broad efficacy, from typical process plants with requirements for explosion-hazardous areas to automating workflows for routine safety procedures.

Ethernet-APL brings two-wire Ethernet, including power supply, into the field.

Ethernet technology is used in industrial plants only at the higher levels of the automation pyramid, hardly at the field level. However, Ethernet has many advantages that could be used, especially in the context of digitalization and Industry 4.0. So, what are the obstacles to using Ethernet in the field of process plants? What does a solution for integrated network technology look like?

This article focuses on answering these questions and shows how Ethernet technology can also open up the field of process plants in standard applications and in areas of functional safety, both in plants with requirements for hazardous areas and in plants without these requirements. Ethernet-APL (Advanced Physical Layer) brings two-wire Ethernet, including power supply, into the field—for all plant areas and applications.

Digitalization in process plants

Digital transformation is increasingly being driven in the process industry to produce products with ever-higher efficiency and quality. Digitization can support these efforts. New digital technologies make it possible to network all the components of a process plant, so plantwide information can be centrally recorded, consolidated, and evaluated. The devices in the field of process plants have long been smart enough to provide detailed information about themselves and about the process. Based on this data, digital services, such as recording the installed base, detailed device diagnostic information, or predictive maintenance, can be provided. The only problem is the lack of or the costly access to this data. Although the currently established technologies in the field of process plants already support remote access to the field level, the available bandwidth is not sufficient for data-driven use cases. In addition, various technologies along the automation pyramid require additional hardware and protocol conversion, which increases the complexity of the plant design.

Ethernet technology is established as the de facto standard for data transmission at the upper levels of the automation pyramid, from the office network to the control room. Furthermore, Ethernet-based communication in factory or building automation is already widely available in the field. In process automation, Ethernet technology has so far hardly been used at the field level. The reasons for this are the existing Ethernet specifications, which do not yet meet the high requirements of the process industry.

Figure 1. Safety applications architecture


Ethernet-APL for future field-level connectivity 

To work on this gap, an industrial alliance of device vendors worked out the general requirements for an Ethernet solution for process automation. These requirements were discussed with the representatives of NAMUR. From these discussions, NAMUR developed the recommendation NE168, which describes the requirements for the use of Ethernet in process plants from the point of view of the end user. NE168 was then also the basis for the development of detailed technical requirements, which were adopted within the industry group. The basis for further work was thus created.

In summary, the following objectives for the Ethernet-APL project resulted in the development of a standardized Ethernet-based solution for process automation, with these specific requirements and objectives:

  • It must be a standardized solution embedded in the IEEE 802.3 family.
  • The specific requirements of process automation must be met. These include in particular:
    • bridging long distances, up to 1000 m
    • support of typical topologies in process automation (e.g., trunk and spur)
    • a two-wire cable for data transmission and power supply of the connected devices
    • use in potentially explosive areas of a process plant, including intrinsic safety
    • verification of the intrinsic safety of the field devices according to the Fieldbus Intrinsically Safe Concept (FISCO) model
    • sufficient power supply of field devices in one segment with a target of up to 60 devices
  • There must be a uniform procedure for the certification of the Ethernet-based solution.
  • It must have a supporting documentation for engineering and installation.

Based on these goals, 12 industry partners are cooperating to support the development of a solution. Well-known companies from process control systems, system infrastructure, and instrumentation are represented. Since the results are not intended to be proprietary, the work is being carried out together with the four major user organizations PROFIBUS & PROFINET International, ODVA, FieldComm Group, and OPC Foundation. This ensures that there will only be one technical solution and that this solution will be jointly maintained into the future.

Because one of the main requirements and thus also one of the main project goals is to develop a standardized Ethernet solution that fits seamlessly into the IEEE 802.3 family, cooperation with the Institute of Electrical and Electronics Engineers (IEEE) was necessary at an early stage. At the end of 2019, the technical solution in IEEE 802.3cg-2019 for 10BASE-T1L was approved.

A further essential component of a standardized Ethernet solution for process automation is intrinsic safety and its verification according to the FISCO model. For this purpose, a technical solution from the project group was incorporated into IEC TS 60079-47 under the name 2-WISE (Two-Wire Intrinsically Safe Ethernet), which is on the path to be adopted as a technical specification.

Ethernet-APL technology

The Ethernet-APL project needs to overcome several technical challenges. To ensure intrinsic safety, low power transmission is required. This contrasts with the requirements of high bandwidth, long cable distances, and robustness against electromagnetic interference. In addition, the reference cable “Fieldbus Cable Type A” is designed for a data transmission of 31.25 kbps. These challenges for the Advanced Physical Layer for Ethernet are processed and defined in various standards and documents:

  • 10BASE-T1L: IEEE 802.3cg-2019 defines full-duplex data transmission with 10 Mbit/s over a two-wire cable for long cable distances. As a result, cable distances of up to 1000 m can be used. This standard is the basis for the PHY components, which will be part of the Ethernet-APL devices.
  • 2-WISE: The concept for 2-WISE is based on FISCO. A migration of existing fieldbus installations is simplified by compatible Ex-i parameters. The project team 60079-47 prepared the concept for standardization. The 2-WISE concept ensures easy installation without extensive validation in Ex areas. 
  • Port profiles: The APL port profile specification defines further Ethernet-APL-specific specifications. After completion, this specification will also be converted into an IEC standard. In this standard, port profiles are defined for use in both hazardous and nonhazardous areas. In addition, a distinction is also made between power transmission via the same two-wire cable and no power transmission. The functional and electrical requirements are defined in port profiles with several power concepts. This definition allows different topologies in APL networks, such as the common trunk and spur concept, with up to 1000 m on the trunk and a maximum of 200 m on the spur line. 

The port profile specification also includes installation rules, such as cable usage, connection technology, shielding, and grounding.

The supported cable in APL segments is a shielded two-wire cable with a resistance of 100 ohm ± 20 percent. The permissible cable cross sections are in the range between AWG26 and AWG14. The Fieldbus Cable Type A fulfills the necessary cable requirements from 2-WISE for intrinsic safety and also supports the cable distances mentioned. For the connection of APL components, terminal connections and M8/M12 connectors are defined in the specification.

  • Engineering guideline: To support the process of engineering an APL network in an optimal way, an engineering guideline is created. This guideline has detailed information for the planning, installation, and commissioning of APL networks and thus simplifies the corresponding phases of a process plant.
  • Conformance test specification: To ensure that an APL device conforms to the above specifications, an appropriate test specification is created. These tests are the basis for the certification of APL devices at accredited test laboratories of the involved user organizations. This ensures the interoperability of APL devices for the end user.

All mentioned specifications and additional documents are on track. The goal is to have all work completed by mid-2021 so that the technology will be officially launched at the Achema 2021 trade fair. It is expected that the first APL infrastructure and APL devices will be available soon afterward.

In a first evaluation in practice, BASF in Ludwigshafen successfully tested the APL technology. In a test setup, the company installed APL prototypes from various manufacturers and carried out many tests, from installation to commissioning to the transfer of data parallel to the process control system. BASF presented the promising results at the NAMUR Annual Meeting 2019. This test setup identified many advantages of the APL technology, such as:

  • easy and flexible installation due to connectors and different topologies
  • simple and fast commissioning through remote access and fast data transmission
  • stable Ethernet communication via the two-wire fieldbus cable
  • data extraction from the smart instrumentation via the second channel according to NAMUR Open Architecture (NE175), in parallel to the process control system.

Ethernet-APL in functional safety applications

With Ethernet-APL there is now a solution for the conventional operation of a process plant. However, chemical plants are increasingly subject to safety-related requirements. The number of safety devices in a plant is constantly increasing.

Currently, this part of a plant still uses conventional 4–20 mA analog technology. In the course of digitalization, it is becoming increasingly apparent that this part of the plant can no longer benefit from the advantages of digitalization with such solutions—more information, in particular diagnostic information from the devices, greater flexibility for changing requirements, easier engineering in the overall context of the plant, homogeneous network structure, etc.

The logical next step is to use Ethernet-APL also for such plants. Figure 1 shows an example architecture for safety applications with Ethernet-APL.

Here, Ethernet-APL provides the technical transmission basis. With PROFIsafe and CIP-Safety, communication solutions for safety applications already exist that have been used in production automation for many years. These are TÜV-certified solutions based on the “Black Channel” principle for transmission. On this basis, a solution with Ethernet-APL would also be possible. For the user, this has several advantages:

  • simple engineering, one technology for all applications
  • increased measurement accuracy due to fewer conversions
  • online diagnosis avoids unnecessary “plant shutdowns”
  • uniform network infrastructure reduces maintenance effort
  • increased flexibility and easier adaptation to new safety requirements.

A possible use case is described below, which very impressively illustrates the possibilities when using Ethernet-APL. During the planning phase, i.e., when designing a system, the parts for safety-related systems are specified. These result partly from legal regulations, but also from the technical requirements. During the construction of the system, changes often occur, either through extensions or other changes. In this case, a redesign is necessary, and the network must be reengineered. In some cases, this involves considerable effort, since the plant was not designed in this way from the beginning.

If the devices support safety and nonsafety requirements and if one network technology is used, adaptation is relatively easily done.

Figure 2. Ethernet-APL and types of single-pair Ethernet defined in IEEE 802.3


Ethernet-APL as SPE solution in nonhazardous areas

Ethernet-APL brings Ethernet into the field of process plants, even for use in explosion-hazardous areas including intrinsic safety and for long cable distances. The underlying IEEE 802.3 standard for 10BASE-T1L joins a series of already available single-pair Ethernet (SPE) standards. These differ in terms of data transmission speed and the cable distances that can be achieved (figure 2).

SPE describes the transmission of Ethernet over a single cable pair. In addition to the data transmission via Ethernet, an optional parallel power supply via Power over Data Line (PoDL) is possible according to IEEE. The usage of so-called PoDL chips is not an option for hazardous areas, because lower voltage levels and safety concepts for ignition protection cannot be fulfilled. The APL project is therefore developing port profiles for the APL power concept as mentioned above.

From the point of view of manufacturers of field devices, whose devices are installed in industries with hazardous areas as well as in industries without hazardous areas, a technical solution that avoids hardware variance is needed. For this reason, the APL port profiles also define a power class for use in standard areas, i.e., without requirements for ignition protection. The parameters defined in this power class, such as the higher available energy, are compatible with the defined PoDL power classes 10–12.

From the specification side, two different implementation concepts are therefore conceivable with regard to the power supply. The decisive factor is that compatibility is ensured, regardless of which concept is implemented in the field device: Use of a PoDL chip or implementation according to APL port profile for nonhazardous areas.

The requirement for an SPE field switch is therefore that it supports both types of power supply. This requires an automatic detection of the required power concept and the automatic power supply of the connected two-wire Ethernet devices.

From a specification point of view, the compatibility of a switch with PoDL as a power concept with a field device without a PoDL chip is ensured; the correct implementation is decisive. To ensure this compatibility, the next step is to adapt the specifications and tests at the standard organizations. Parallel to this, first implementation tests between field switches and field devices are running.

From the user’s perspective, this compatibility has decisive advantages. As the APL technology is about to be launched and first products are expected, a corresponding portfolio for use in nonhazardous areas will be available at the same time. This increases the number of field devices that can be used and at the same time shortens the time to market for SPE.

For manufacturers of field devices, the electronic hardware variance is also avoided, meaning that the same hardware can be used for devices with and without Ex requirements. This in turn reduces costs and shortens time to market.

Noticeable advantages

“Ethernet in the field of process plants”—this vision is now becoming reality thanks to the availability of Ethernet APL. The use of this technology is not limited to individual applications, but ranges from typical process plants with requirements for explosion-hazardous areas, to applications in plant areas of functional safety, to plants without requirements for explosion-hazardous areas.

The advantages of Ethernet-APL will be noticeable in all life-cycle phases of a plant: from simplified engineering thanks to the homogeneous network structure with only one technology across all levels, to simple two-wire installation with less manual effort and reduced susceptibility to errors, to efficient maintenance thanks to high performance and real-time data transmission and detailed diagnostic information. Particularly in the context of Industry 4.0, Ethernet APL ensures the connectivity that is necessary for digitalization.


This article was written by Benedikt Spielmann from InTech and was legally licensed through the Industry Dive publisher network. Please direct all licensing questions to