Fieldbus & Industrial Networking

Realising the fully digital process plant

July 2023 Fieldbus & Industrial Networking

The world of digital communication is an Ethernet world. Ethernet drives the internet, it connects computers at home and it has become the communication backbone of just about any organisation. Cloud-based solutions rely on Ethernet. Manufacturing processes are automated with Ethernet. Even the Internet of Things uses the Ethernet protocol to link to computers and systems. It is therefore not surprising that Industry 4.0 and similar initiatives rely on this omnipresent communication standard that has conquered the world.

The process industries, however, are confronted with very specific situations, and Ethernet is only now becoming the enabling technology for a digital future. The new buzzword is Ethernet-APL, and describes a new Ethernet Physical Layer that is tailored to the requirements of process plants while seamlessly integrating into the omnipresent Ethernet world. Ethernet-APL (Advanced Physical Layer) is a joint development and standardisation project of the four major user groups in the process world: the FieldComm Group, ODVA, the OPC Foundation and PROFIBUS/PROFINET International. Ethernet-APL is supported by Pepperl+Fuchs and leading PCS and hardware vendors.

What has made Ethernet so successful is primarily its inherent simplicity. You plug in a device and it is automatically detected by the network. You need to configure it only once and it will always work as intended. In process automation such simplicity is still wishful thinking for many plant operators. But with Ethernet-APL it is close to becoming a reality.

Ethernet simplicity adapted to the process world

For the process industries, standard Ethernet communication has serious drawbacks. Firstly, the length of Ethernet cables is limited to 100 m. Widespread process plants, however, often require to cover distances of up to 1000 m. There are also issues when it comes to providing power to devices via an Ethernet line. Plus many process plants also require reliable hazardous area protection and resilience to electromagnetic interference.

Process plant operators therefore had good reasons for sticking to well proven two-wire cabling. At least until now, because Ethernet-APL is able to integrate fully into existing communication infrastructures while providing considerably higher data throughput for the unlimited use of device data.

There were four main requirements on the way to adapting Ethernet to the process world: a reliable data path for fast communication, a suitable power supply for field devices via the data lines, efficient explosion protection, and significantly simplified installation and connection.

More data communicated at higher speeds

For Ethernet communication over two wires, IEEE 802-3 distinguishes between different variants of the BASE-T1 cabling standard, which allow different speeds and cable lengths.

For example, two wires will soon enable the high-speed networking of computers within a data centre. This will enable speeds of up to 10 GB/s over relatively small distances. In contrast, 10BASE-T1L is the alternative for communication over long distances. Speeds of up to 10 Mbit/s are possible via shielded cables with a length of up to 1000 m. This will be the new communication standard for process engineering plants, requiring two-wire cabling for plants with a large area.

All protocols, all installation standards

Ethernet-APL does not require any special wiring, but uses standard Type A cables which are already well known in the process industries. As a consequence, installation methods conform to the well-established procedures. There are both clamp and screw-type connectors for switches and field devices. Standard M12 connectors are also possible. In other words, migration to Ethernet-APL will protect investments in the process plant infrastructure by simply using existing cables.

Another aspect of Ethernet-APL is this that as a physical layer standard for two-wire Ethernet communication it works completely independent from the protocols used. This gives the system operator the freedom to always opt for the communication protocol which is best suited for the respective application.

Intrinsic safety easier than ever before

A common feature of process plants is hazardous areas. This aspect must be considered for any system that supplies power to field instruments. Ethernet-APL includes intrinsic safety according to the new 2WISE standard (two-wire Intrinsic Safety Ethernet), which is based on FISCO. It is defined in IEC TS 60079-47 currently available as community draft, and describes all values and requirements that Ethernet-APL-capable field devices must meet.

This device-based solution not only guarantees the interoperability of the devices, it also frees the system planner from the need to perform complex calculations for each individual loop. This makes planning and verification of explosion protection safer, faster and easier than ever before. The procedure for this follows three very simple steps: select the parameter set for your hazardous area; select a suitable cable; document.

Simplicity meets speed and versatility

Ethernet-APL requires only two types of infrastructure components: power switches and field switches:

The APL field switch for direct Ethernet connection is suitable for process plants that are smaller or with a smaller footprint, such as those typically found in the food and pharmaceutical industries. It is designed for DIN-rail mounting and supplies power to the connected spurs and enables data exchange between the devices and the control system. Made for control cabinet mounting in Zone 2/Div 2, it offers intrinsic safety on the spur for Ex ic IIC or Ex ia IIC. Ring redundancy is ensured via the Ethernet backbone. The switch can be connected to an external power supply to feed the field devices.

The APL Power Switch from Pepperl+Fuchs feeds electrical energy to the trunk to supply the field devices with the required power. It is designed for control cabinet mounting in Zone 2/Div 2, allows the connection of an external power supply, and provides ring redundancy for the connection to higher level systems.

The APL Field Switch for the trunk is the power supply and communication component that connects several spur lines to the trunk line. It is designed for field installation in Zone 1/Div 2 and can operate devices in Zone 0/Div 1. This trunk-powered component provides intrinsically safe power supply on all spurs up to Ex ia IIC.

In large process plants, Ethernet-APL is typically used as a trunk and spur topology over distances up to 1000 m. For smaller process plants star topologies are preferred. Both topologies can fully replace any existing fieldbus infrastructure. Communication is very robust, as Ethernet-APL defines point-to-point connections only so that crosstalk between segments is practically impossible.

The top level of any Ethernet-APL-based process control system can consist of controllers as well as systems for process visualisation, engineering, and plant management. A completely new aspect for process automation is the barrier-free access to any system in the network and the added possibility to include cloud-based systems. Such a structure not only enables access

to practically all process data regardless of the user’s location, it also enables process-independent long-term data storage for the analysis of large amounts of data.

Migration made easy

An Ethernet-APL communication infrastructure is very similar to present Fieldbus-based solutions based on FieldConnex Power Hubs, FieldBarriers, and Segment Protectors. This allows an easy migration path to a fully Ethernet-based process control system.

For some 20 years, many process plants were equipped with digital communication to the field devices, for example via PROFIBUS PA. For such plants, migration to Ethernet-APL is especially easy. The only thing that needs to be done is to replace the existing field barriers or segment protectors with APL Field Switches. These are able to automatically detect the fieldbus or Ethernet interface of the field device.

Ethernet-APL also opens the opportunity to fully integrate available safety concepts into an overall communication infrastructure. For this purpose, safety data communicates via a ‘black channel‘ that basically rides piggyback on any of the standard communication protocols. Solutions of this type are already well established in the manufacturing industries and can eventually become part of any Ethernet-APL based plant. Utilising this concept will not only greatly simplify design and implementation of safety systems, it will also reduce costs, while maintaining a superior safety level to protect both employees and the plant itself.

In summary, it can be said that Ethernet-APL will not only lead process automation into the omnipresent world of digital communication. It will also greatly simplify design, installation, commissioning and maintenance of the communication infrastructure. Plus it will pave the road to completely new applications that are presently often prevented by heterogeneous systems imposing restrictions on the availability of process data.


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