How Profinet over Ethernet-APL brings value to process industries

Profinet technologies provide users with the digitalization tools and infrastructure to manage the instrument fleet during commissioning, startup and plant upkeep. This article provides users with insights on the ruggedized Ethernet physical layer for the process industries. Profinet features such as proxy bridging technology, the PA Profile, dynamic reconfiguration, and redundancy concepts all enable instrument orchestration with levels of automation yet to be achieved in today’s process plants.

Use cases for increased plant performance using Ethernet diagnostics

Process plants strive for higher efficiency and increased plant performance. One of the major challenges in plant operation is device replacement since subject matter experts are often needed to do so. Furthermore, maintenance people struggle with diagnostic information from field devices because it is supplier dependent, can be difficult to decipher, and often does not provide useful remedy information. This leads to inefficiency in plant operations.

In the context of NAMUR Open Architecture in NE 176, several use cases were defined which bring added value to the life cycle of a process plant. Examples are “Unique identification,” “Device dimensioning,” “Read multivariable process values” and “Health monitoring and diagnosis.”

To fulfill such use cases, a high-performance connection to the field level is crucial to ensure data availability from smart instrumentation up to higher level applications and digital services.

Figure 1: Classical automation pyramid with Ethernet gap in the field level. Courtesy: PI North America

Today’s technologies in the field level and their limitations

Most plants today use the 4 to 20mA current loop as communication technology between sensors and actuators and the process control system. This technology seems to many plant operators to be sufficient for pure process control and has therefore proven and established itself over the last decades. 4 to 20mA analog technology is supported by all important process instruments and provides simple installation and maintainability. The limitation of 4 to 20mA technology comes in the context of extended data access, be it for more process values or for reading out diagnostic information or for configuring a device. However, to fulfill these use cases, more extensive data access to the intelligent field instrumentation is required. In other words, a lot of additional untapped information is available that can increase efficiency and performance.

With the HART protocol, which provides a digital communication signal over the current signal, it is possible to retrieve much of this additional information. However, the HART protocol is used primarily for configuration purposes. Regarding comprehensive data access, the HART protocol is not suitable as the data transfer speed is quite slow.

With fieldbus technologies such as Profibus PA, a real digital communication technology is available. While technically sound, the adoption rate in process industries has not yet reached the level of 4-20mA analog technology. One reason might be the relative complexity of fieldbus networks compared to simple analog technologies. Another reason might be that even though fieldbus technologies are much faster than HART, this speed is still insufficient for transferring large amounts of data.

In summary, these traditional technologies have many limitations regarding digitalization and fulfilling new use cases for efficient process plants.

As Ethernet technology is already widespread for data communication on the upper layers of the automation pyramid, the question arises as to why Ethernet can’t be used at the field level as well. In many other industries, the success of Ethernet technology at the field level is proven for many years already. By comparing the characteristics of Industrial Ethernet with the requirements of process plants, the answer to this question is quite simple: Ethernet standards today do not fulfill the challenging requirements of process industries:

• Process plants need a technology which can be deployed in explosion hazardous areas including intrinsic safety.
• Process plants aim for a two-wire technology similar to 4 to 20mA and Profibus PA with power and data over the same cable.
• Process plants must bridge cable distances over several hundred meters.

A physical layer which fulfills the requirements of process plants – Ethernet-APL

The advanced physical layer (APL) for Ethernet enables network infrastructures to extend all the way to field instrumentation including those in explosion hazardous areas. Ethernet-APL combines the advantages of the well-known 2-wire technology with the high performance of Ethernet technology.

To create Ethernet-APL, a group of vendors in the process automation area collaborated over the last four years with major standards organizations to work on an Ethernet solution which meets the requirements of the process industries. This one network can be adopted by any other standards organization for any industrial Ethernet-based protocol. Work packages of the APL project go well beyond standardization and conformance testing; they include insights into best-in-class knowledge:

• The basis is the latest IEEE 802.3 specification 10BASE-T1L which specifies a 10 Mbps Ethernet solution over a twisted-pair cable for long distances.
• Profiles standardize power transmission levels allowing for long cable reach. Choosing the right profile for the application is easy and ensures interoperability in a diverse environment.
• A new chapter in IEC TS 60079-47 standardizes intrinsically safe protection as an integral design. “2-WISE,” short for 2-wire intrinsically safe Ethernet, defines simple verification of protection without any calculations. The electrical parameters are derived from fieldbus intrinsically safe concept (FISCO) and is well-known by many fieldbus users.
• With mandatory APL conformance tests, operators can assure all APL interfaces in switches or instruments are certified according to the specifications and thus are interoperable with each other.
• The Ethernet-APL engineering guideline provides best-in-class knowledge and designs supporting end users during planning, installation, and commissioning of an APL network. It’s the perfect guide to get familiar with this new technology.

How Profinet enables process control communication

With Ethernet-APL, a new physical layer for Ethernet is available which fulfills the requirements of process plants.

Profinet is a well-established Industrial Ethernet protocol with tens of millions of installed devices worldwide. The protocol and related standards are specified by PI, an organization with more than 1700 member companies. Most of the common distributed control systems (DCSs) are already able to operate with this protocol.

Profinet is standardized in IEC 61158 and IEC 61784 and supports other standard Ethernet protocols like address resolution protocol (ARP) for identifying IP addresses in the network, device configuration protocol (DCP) for assigning device names, link layer discovery protocol (LLDP) for neighborhood detection, or simple network management protocol (SNMP) for observing network components. Besides these standard mechanisms, many further features are part of Profinet to enable the use of Ethernet in industrial environments. With different redundancy concepts the high availability of process plants is ensured. Both for failures of controllers and for cable breaks, an appropriate solution is available from Profinet to guarantee the process is not interrupted. Even for specific measurement tags which are not Profinet-capable yet, available dedicated proxies allow for the integration of legacy fieldbus instruments into a Profinet network. Even traditional technologies like 4-20mA can be integrated into such a network via Profinet-capable remote input/output (I/O).

On top of that, Profinet allows for the reconfiguration of a device during plant operation. This provides the openness needed for future flexibility like electronic/virtual marshalling.

Figure 2: Ethernet-APL eliminates wiring cabinets and enables flexible topologies with redundancy easily engineered. Courtesy: PI North America

A standardized solution for device integration and diagnostics

With PA Profile 4, workflows can be implemented for automatic device replacement, even across suppliers. Therefore, the new device needs to be installed in place of the former device. The new device is recognized and configured and basic function can resume. Further configuration can then be performed to increase performance with common tools when convenient.

Troubleshooting is simplified for maintenance staff with PA Profile 4 via harmonized diagnostic messages according to NE107. It increases efficiency in plant operations and reduces training effort.

All use cases described in NE176 will be supported by PA Profile 4 in a standardized, supplier-independent way with all the data required from field devices.

Enable value optimization for process industry plants

Future process industry plants require robust technology to fulfill use cases around digitalization or increased efficiency in daily work. Profinet and PA Profile 4 are the perfect solution for easy integration and operation. With Ethernet-APL, the physics is now also ready for use in explosion hazardous areas. With the combination of these technologies, endless possibilities are achievable in terms of digital services, higher performance, and any kind of value optimization.

Michael Bowne is executive director, PI North America, the organization for Profinet, Profibus, and other networking technologies. Profibus & Profinet International (PI) Process Automation Working Group is a CFE Media and Technology content partner. Edited by Chris Vavra, web content manager, Control Engineering, CFE Media and Technology, cvavra@cfemedia.com.

Keywords: Profinet, ethernet, industrial networks

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