The Future of Field Device Infrastructure

By Guadalupe Chalas | April 11, 2023

Industrial communications strategies are shifting in favor of real-time communications at the field device level, with automation engineers and installers preferring single-pair Ethernet-enabled devices to collect field data.

Figure 1: SPE enables IP connectivity for field devices in various applications.

SPE enables IP connectivity for field devices in various applications.

Industrial field device infrastructure trends

Industrial communications strategies are shifting in favor of real-time communications at the field device level, with automation engineers and installers preferring Ethernet-enabled devices to collect field data. IP-based communications from and to field devices play a fundamental role in supporting modern automation trends. The goal is to not only track asset performance, but also to couple field device information with artificial intelligence for preventive and predictive maintenance. This shift toward accessing device performance data in real time using IP-enabled infrastructure at the field level is advantageous, as it supports process optimization and could eventually limit downtime and increase process autonomy.

Manufacturing and process plants have long used field instruments for process monitoring and for the automation of production and process lines (sensors, actuators, vision systems, etc.). The information collected in the field can be used to increase output yield, monitor process quality, and reduce downtime, thus optimizing production. Widespread digitalization efforts are changing the way field devices communicate in favor of seamless Ethernet communications from the field device to the upper levels of the communication ecosystem. While Ethernet has been the preferred communication protocol between the control and enterprise levels, Ethernet-enabled field devices and Ethernet field communication infrastructure are not widespread. This is because of several factors, including the need for long deployment distances at lower transmission rates than traditional Ethernet, Ethernet wiring (four or eight wires) versus fieldbuses, and existing cabling infrastructure.

Seamless Ethernet communications all the way to the field require an upgrade in the infrastructure for industrial communications, as traditional communication pathways do not support seamless communications between devices and from devices to the upper levels. While industrial Ethernet is widely used in industrial communications, its compatibility with field device communication requirements is limited. Industrial Ethernet transmission rates are above those required by most field devices, while transmission distances fall short. Additionally, industrial Ethernet infrastructure requires more wiring than traditional legacy communications protocols, eliminating the possibility for cable reuse and miniaturized connector solutions.

Single-pair Ethernet (SPE) is a two-wire physical layer specification for Ethernet communications in industrial applications that support field device infrastructure by enabling real-time data transmission over long distances. SPE is ideal for field applications, as it enables higher transmission rates to, from, and between field instruments and devices than previously possible using traditional field communication protocols such as HART and fieldbus. Additionally, SPE extends the reach of traditional Ethernet with distances that can reach over one kilometer for transmission rates up to 10 Mb/s, 100 meters for rates up to 100 Mb/s, and 40 meters for rates up to 1 Gb/s. It also supports power delivery via Power over Data Line (PoDL) up to 52 W. The two-wire interface provides miniaturized connectivity options for IP communications and power delivery to sensors, actuators, vision systems, and other field devices and instruments.

SPE Connector Standards for Field Devices in Harsh Environments

Industrial and process automation field devices often operate in environments with high vibration, dust, moisture, EMC, etc. As such, suitable connectors and/or cabling terminations for data transmission in the field should be rated for harsh environments. The IEC (International Electrotechnical Commission) has released several specifications for single-pair Ethernet connectors, including IEC 63171-2 for IP20 applications and IEC 63171-5, which supports connectivity in harsh environments.

This is the second SPE connector specification to be published by the IEC from the Single Pair Ethernet System Alliance (SPESA) partnership, of which Phoenix Contact is a founding member. IEC 63171-5 is a part of IEC 63171, which describes two-way shielded or unshielded circular connectors with IP65/67 rating on an M8 or M12 locking interface. It has provisions for use with alternative locking mechanisms, such as push-pull and bayonet locking. These connectors are intended for balanced single-pair data transmission with frequencies up to 600 MHz. The connectors also feature a current-carrying capacity of up to 4 A.

Figure 2: SPE variants

SPE variants, including IP20, M8, M12, and M12 Hybrid (counterclockwise)

While all the connectors within the IEC 63171 specification can provide Ethernet transmission over a single pair of wires, different interfaces are specified to comply with the specific application requirements of their intended markets. The connector interfaces defined in IEC 63171-5, also known as “Type 5” SPE Connectors, are designed for areas with harsh environmental conditions, and where ingress protection is needed. This specification represents a change in the landscape of connectivity available for SPE, in which it helps enable a new technology using a connector interface that fits within known M-type connector panel cutouts that are widely used in sensor and other field device communications.

IEC 63171-5 compatible products are released and available with PCB panel-mount options for M8 and M12 standard housings and their respective mating cable assemblies. The cable assemblies are available with two cable options: 20 MHz cable for lower speed applications (up to 10 Mb/s) and 600 MHz cable for applications up to 1 Gb/s. Additionally, the Type 5 connector interface is fully compatible with the Type 2 interface (IEC 63171-2), a feature that allows IP20 and IP67 variants to be intermateable for testing and diagnostics purposes. In the case of applications that use existing wiring infrastructure, or for long deployments, a field-wirable version of the SPE connector can be used for a termination that does not require any tooling.

Standardization Benefits and Challenges

The benefits of SPE connector standardization are many. From the early stages of specification development, connector manufacturers have offered several variants of SPE connectors with a portfolio that includes IP20 jacks and cable assemblies, an IP20 field-wirable interface, and IP67 jacks and cable assemblies with M8 housings. And, although the products have been available for a while, the publication of a standard such as IEC 63171-5 further assures users that these products meet IEC requirements, and that the new connector technology is approved for implementation and deployment.

Another advantage of a published specification is the ability for connector manufacturers to submit their approved standard interfaces for consideration at user groups’ standardization committees as those seek to further standardize connector selection for their specific applications. This creates synergy among markets, applications, and standards, and drives manufacturers to innovate and build new products that address specific requirements.

Standardization also has its challenges. As application requirements continue to evolve and more industries start considering SPE for their field infrastructures, additional requirements are uncovered. These requirements often make their way into physical layer specifications and operation parameters, as well as connector specifications that address a specific market. One example is the need for updated SPE transmission distances for applications in industrial automation and process control industries as they begin to transition legacy networks to Ethernet, which has led to a new IEEE working group. The project, known as IEEE 802.3dg, intends to amend physical layer specification parameters to support lengths up to 500 meters for 100 Mb/s operation and up to 100 meters for 1 Gb/s operation.

Example of synergy among markets, applications, and standardization in a sensor application.

Markets, Application, and Standardization Example: Ethernet-APL  

With its origins in the automotive industry in the 2010s, and based on IEEE standards, SPE is in the early adoption stages in the process industry as Ethernet-APL enables long cable length and explosion protection in intrinsically safe areas while providing communication and power to end devices. Ethernet-APL is one of the first use cases for SPE in an industrial application and is the result of the collaboration among several process industry stakeholders with the goal of bringing Ethernet communications to field devices. The goal of Ethernet-APL is to bring the broadly accepted industrial standard that is Ethernet into the field device ecosystem along with its existing tools for installation, troubleshooting, and diagnostics. Because current Ethernet standards do not address specific requirements for harsh environment deployments, the new Ethernet physical layer ideally would support explosion protection via intrinsic safety and surge protection and allow for potential cable reuse.

SPE use case in process automation: An Ethernet-APL switch and flow meter.

Ethernet-APL takes 10Base-T1L, the SPE physical layer for reach, and adds provisions for intrinsic safety in explosive environments. Full-duplex data communications and power transmission can happen simultaneously over a single pair of wires, enabling much faster transmission speeds than current field device communication methods, such as HART and fieldbus. Because Ethernet-APL is an Ethernet physical layer, it can support EtherNet/IP, HART/IP, OPC-UA, PROFINET, and other IP transmission protocols. Ethernet-APL is compatible with existing SPE connector standards that specify Ethernet transmission over shielded connectors with IP20, M8, and M12 variants. Ethernet-APL is also compatible with spring-clamp and screw-type terminals with three positions: two positions for the data pair, and one position for the shield for simple installation over a wide range of cable gauges (26-14 AWG).

The Ethernet-APL project has created a series of documents to aid in implementation. One of the documents is an engineering guideline for Ethernet-APL with planning, commissioning, and installation details to help users with deployment. There are also drawings for device vendors and users that detail a system concept two-wire intrinsically safe Ethernet or two-wire with detailed information for powered systems, including voltage source and other parameters that need to be used. These documents serve to highlight the commitments of user group organizations and stakeholder companies in the advancement of this technology by going a step beyond releasing products for an application. Ethernet-APL infrastructure is becoming available, with the first switches set for release in Q2 2023 and some manufacturers already implementing early devices. Field device manufacturers are also catching up with the technology and have promised to have devices in 2023.

The Road Ahead

A versatile Ethernet connection to the field with SPE M8.

As of March 2023, several specifications for SPE connectors have been published. These include IEC 63171-2, which defines the requirements for the smallest of the IP20 connector interfaces, and IEC 63171-5, which defines the requirements for transmission using M8 and M12 frames. Additionally, IEC 63171-7 is a new draft specification for hybrid M12 connectors for SPE and power for applications with high power requirements where PoDL is not a viable option. The new connector specification uses an M12 frame to house one SPE port and additional power contacts for power transmission. The IEC specification further defines interface coding and voltage ratings to match the coding. While still in its draft phase, the specification defines pin assignments for seven types of connectors to support voltage ratings up to 600 V AC and DC. While the power contacts will vary by connector type/coding, the data pair will comply with IEC 63171, which specifies transmission speeds of up to 1 Gb/s.

The IEEE also continues to revise the physical layer standards for SPE to increase transmission lengths. These enhancements aim to address high-speed applications such as motor communications, which require speeds higher than 10 Mb/s over long distances by increasing transmission lengths from 100 meters to 500 meters for 100Base-T1 (100 Mb/s), and from 40 meters to 100 meters for 1000Base-T1 (1 Gb/s) over shielded cabling. This is an example of how a specific application is driving enhancements to an existing specification. Other use cases for SPE in industrial communications will drive further enhancements to the specifications, which can benefit early adopters as their need for data transmission increases. Because the SPE connector interfaces were designed with scalability in mind, they are expected to support future changes to the point-to-point standards as a single connector interface can support transmission speeds ranging from 10 Mb/s to 1 Gb/s.

IEEE and IEC standards for SPE are an important addition to the physical layer specifications that support industrial ethernet communications as they define the infrastructure for field device Ethernet communications, enabling compatibility between the field and the control and network levels. Smart factories can move along the path of digitalization with communication infrastructures that support Ethernet-based protocols for seamless data transmission throughout the entire manufacturing process. Some industrial user groups are also considering SPE as a viable technology and are starting to develop additional standards to address niche applications as they accelerate toward digitalization.

Phoenix Contact and the SPE System Alliance are responsible for three out of the seven specifications for SPE connectors. Phoenix Contact is an important collaborator in the Ethernet-APL project and is responsible for some of the first switching infrastructure to deploy the technology in the process industry and the connectors to support field devices in harsh environments.

Learn more about single-pair Ethernet at

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