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Ethernet for the Field – Two-Wire Ethernet products for the process industry have arrived

11 April 2023

Users of process automation currently have high expectations for Single Pair Ethernet (SPE) to enable end-to-end digital communication without gateways or protocol conversions in the field of process plants. There is no discussion about connectors in the process industry because rugged terminals are preferred. This article explains the minor differences between Ethernet-APL and SPE, and the impact that Ethernet-APL is having.

Process and factory automation differ in virtually all key features. In the process industry, the paths are longer, the environments are harsher, the requirements for continuous operation are higher, and explosion protection with intrinsic safety is required. This also results in a very strong need for extremely rugged technologies and products. Ethernet-APL has been specifically developed for the field of process plants.

Ethernet specifically for the process industry

Single Pair Ethernet describes a physical transmission path for Ethernet, for example based on 10-BASE T1L with a 10 Mbit transmission rate. The advantages of SPE include the reduced number of wire pairs, as only one is required for communication. The transmission technology therefore supports all Ethernet-based protocols, which enables continuous communication from the cloud to the sensor in factory automation and, with Ethernet-APL, in the process industry as well.

For the power supply, Ethernet-APL offers defined, broadly differentiated performance classes in IEC standards, which can also be used in hazardous areas for long cable routes with the associated voltage drop in the cable. Explosion protection via intrinsic safety and very rugged installation technology are also included.

A two-wire cable, plug-in terminals, and devices with reverse polarity protection ensure ease of use and installation. Compliance testing, which manufacturers submit to as part of device certification, guarantees a high degree of interoperability. The switch transmits the power supply and communication through point-to-point connections. This topology has a simple design and is therefore easy to use and maintain. The network infrastructure is highly resistant to interference—even during connection and disconnection processes, which are often required when performing maintenance or replacing devices.

Protection for hazardous areas

The "intrinsic safety" type of protection is an integral part of Ethernet-APL. Intrinsic safety is simply a method of limiting electrical energy to a level that does not generate ignition sparks significant enough to ignite the surrounding potentially explosive atmosphere. This type of protection is mainly used for circuits with relatively low power ratings. This makes it ideal for safely operating measuring instruments and other field devices such as sensors and actuators.

Ethernet-APL borrows the FISCO concept from fieldbus technology, but allows higher power and greater distances between the switch and the field device. A chapter has been added to the established IEC standard (IEC 60079) which details the methods used to verify intrinsic safety. This intrinsic safety concept for Ethernet-APL connections is known as "2-WISE", which stands for two-wire intrinsically safe Ethernet.

The legally required verification of intrinsic safety is very simple for users. The designer selects the devices according to the desired zone, takes care to use a suitable cable up to 200 m long, and documents the installation. Time-consuming calculations to prove intrinsic safety are no longer required. Suitable devices show the "2-WISE" marking and the explosion-protection class for which the Ethernet-APL device is approved.

Clear network structures

The FieldConnex Ethernet-APL rail field switch provides the transition by establishing the connection to the instrumentation and translating the data transparently and without barriers from fast Ethernet or Gigabit to Ethernet-APL. The switch protects the field devices, which have very little power available for computing power, from unnecessary data traffic.

The expected traffic determines the design of Ethernet networks. The instrumentation in the process plant represents a large number of participants, each of which only needs to transmit very small amounts of data – the measured values, diagnostics, and alarms. These prerequisites enable network architects to plan clear structures.

This means that an APL network never has to withstand a 500 MB download from Singapore. Definitions from leading industrial protocols for implementation, such as PROFINET over APL and EtherNet/IP over APL, take these special requirements into account.

End-user expectations

The promise of a network in the field of processing plants with Ethernet-APL as the underlying technology is raising high expectations among users. They expect a network in the field of processing plants to be the platform of the future: the basis for digitalization and the seamless integration of all plants into a single system. End users want to simplify device diagnostics and integrate functional safety, all with the goal of creating a good user experience when using complex devices. Plant engineers are looking for cross-system data migration to help them link the actual device tags to the master tag list, thereby increasing the speed and quality of loop checks. Exchanging devices is easier than with the current best-practice solution of 4–20 mA and HART technologies.

Ethernet-APL is the physical layer – the data highway – to the field of process plants. Ethernet-APL is based on over 30 years of experience in digital communication, combined with today's most modern digitalization and explosion-protection concepts. This provides users with what is currently the most powerful tool for modern plants. The experts who have helped to standardize Ethernet-APL have also pooled their expertise into a set of engineering guidelines (free to download at The simplicity of the design has the potential to convince owners and operators to use Ethernet-APL, reducing both their investment costs and operating costs while maintaining maximum availability and plant performance. Now is the time to familiarize yourself with Ethernet-APL. Switches, infrastructure, and the first field devices are now available to users.

This is creating a market potential that will enable additional suppliers to likewise equip their products with interfaces and protocols via Ethernet-APL.

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