The Case for Single-Pair Ethernet in Industrial Applications

By Guadalupe Chalas | August 10, 2021

An update on activities related to SPE standardization and implementation in industrial and automated applications.

Single-pair Ethernet (SPE) promises to revolutionize industrial applications with speeds up to 1 gigabit per second (Gb/s) over a single pair. Yet there are still questions surrounding standardization and the benefits of SPE when compared to industrial RJ45 and other standard products.

Phoenix Contact SPE Type 2 and Type 5 connectors

SPE Type 5 and Type 2 connectors from Phoenix Contact

SPE enables 10 megabits per second (Mb/s), 100 Mb/s, and 1 Gb/s transmission speeds using a single pair of wires and allows for both point-to-point and multipoint communications. At 10 Mb/s over long distances (up to 1,000 meters), SPE finally brings the internet protocol to field devices. This enables full duplex communication and power up to 50 W over a single wire pair with existing M8 and M12 interfaces.

At 1 Gb/s over shorter distances (up to 40 meters), SPE is a miniaturized solution with high-speed performance. Because SPE uses a single pair for data transmission and can deliver enough power to field devices without the need for specialized cables, it is a cost-effective and compact alternative for implementing industrial Ethernet in the field with a portfolio that includes field-wireable connectors.

Moreover, SPE represents an upgrade from existing industrial protocols, as it enables higher speeds of full-duplex communications over longer distances. Some traditional communication technologies allow for only half-duplex communications at much lower speeds and shorter distances. As we look at the industrial-rated SPE proposals defined in the standards and compare them with existing industrial Ethernet and other industrial protocols, we discover that SPE is the future-proof solution that enables high-speed communication from the field to the cloud.

Single-pair Ethernet Specifications

IEC 63171 specification status and description

The International Electrotechnical Commission (IEC) has published various standards for shielded and unshielded SPE connectors under IEC 63171. Each of these standards addresses a specific application area for SPE based on solutions proposed by industry manufacturers and intended to address a specific market segment. As such, there are six different specifications derived from the basic standard IEC 63171 that cover circular or rectangular connectors for balanced single-pair data and power transmission. The specifications, denoted with a “dash” symbol and a number after “IEC 63171,” may differ in ingress protection (IP) rating, port density, end application, as defined by IEC. For simplicity, we will refer to the variants as “Type 1” through “Type 7.” Table 1 details the status of the IEC connector specifications.

IEC 63171 interfaces for single-pair Ethernet

Type 2, Type 5, Type 6, and Type 7 have been identified as suitable for industrial applications. Type 2 and Type 5 (Figure 2) meet requirements for mechanical robustness, vibration, EMC compatibility, and various pollution degrees. Among the connector features that differentiate the connector variants, it is worth mentioning that Type 2 and Type 5 connectors are the only specifications within the list to feature a consistent mating face that is intermateable and interoperable for IP20 (unsealed applications) and IP67 (harsh environment applications).

Type 2 connectors are also approximately 38% more compact than Type 6 connectors, and 50% more compact than standard and industrial RJ45. Type 2 also has the smallest interface available for IP20 industrial SPE applications, which allows for a high packaging density with the ability to accommodate four Type 2 connectors within a single M12 housing (Figure 3).

The SPE interface from Phoenix Contact with M12 housing allows for a four-chamber system.

The Institute of Electrical and Electronics Engineers (IEEE) is also working on specifications for single-pair Ethernet, and unlike IEC, IEEE does not specify the connector interface. The scope of IEEE standards for SPE, as described on the IEEE website, is to specify the physical layer and management parameters, as well as associated power delivery over a single twisted-pair copper cable, published under IEEE 802.3cg for 10 Mb/s (10Base-T1), IEEE 802.3bw for 100 Mb/s (100Base-T1), and IEEE 802.3bp for 1 Gb/s (1000Base-T1). Currently, IEEE is working on enhancing the 10Base-T1 specification for multidrop applications through working group IEEE 802.3da. The goal is to define larger topologies, as many industrial applications begin to transition from legacy non-Ethernet networks to Ethernet.

As non-Ethernet networks using legacy connectors and protocols start to migrate into Ethernet networks, IEEE has also worked to address two different configurations for 10 Mb/s SPE. 10Base-T1L addresses longer distances, up to 1,000 m, and 10Base-T1S addresses shorter distances, up to 50 m and potentially 16 multidrop nodes. These specifications also address Power over Data Line (PoDL) requirements for both long- and short-range applications with multiple power classes up to 50 W.

SPE versus RJ45: What are the differences?

Standard Ethernet solutions currently available in the market can support 10 Mb/s, 100 Mb/s, and 1 Gb/s, often using the RJ45 interface, known as 10Base-T (legacy), 100Base-TX, and 1000Base-T. The RJ45 interface consists of either four or eight poles (contacts) used for full-duplex communication. With 10 Mb/s and 100 Mb/s variants, known as Fast Ethernet, two pairs are used: one pair for transmitting and another pair for receiving. One Gb/s variant, known as Gigabit Ethernet, use all four pairs, and each pair is used for transmitting and receiving.

An industrial SPE solution like Type 2 or Type 5 can also support 10 Mb/s, 100 Mb/s, and 1 Gb/s Ethernet, but unlike Fast and Gigabit Ethernet, it can do so with a single pair configuration. Type 5 connectors are available in either an M8 or an M12 housing with Ingress Protection (IP) rating IP67 and have been designed with the mechanical robustness and reliability required for industrial applications, also known as M3I3C3E3. While there are Ethernet solutions on the market for Fast and Gigabit Ethernet within the M12 interface and Fast Ethernet on M8 housings, SPE is the first solution to enable Fast and Gigabit Ethernet on both M8 and M12 housings, with the possibility of having multiple SPE ports (up to four) within one single M12.

Left: RJ45 next to Type 2 header from Phoenix Contact. Type 2 IP20 (first row) and Type 5 IP67 (second row) connector solutions from Phoenix Contact.

SPE is a much more compact solution for both Fast and Gigabit Ethernet and uses less cabling than standard solutions for both speeds, which can translate into cost savings and shorter termination times. In addition, the SPE Industrial interface is also specified for slower speeds (10 Mb/s). This is ideal for devices that do not require Fast Ethernet speeds, but could benefit from switching over to the Internet Protocol.

Single-Pair Ethernet: Upgrading Existing Industrial Applications

Besides standard Industrial Ethernet solutions on the market, other protocols for industrial applications can also benefit from SPE deployment. IO-Link and PROFINET are both communication standards for connecting digital field devices to controllers in industrial applications.

IO-Link works over an unscreened three-wire cable and features speeds up to 321 Kb/s over no more than 20 meters using M5, M8, and M12 connectors. PROFINET, on the other hand, is an implementation of 100Base-TX featuring two pairs for data transmission and reaching up to 100 Mb/s over distances up to 100 meters. Figure 5 shows a comparison between IO-Link, PROFINET, and SPE cables featuring an M8 housing.

IO-Link, PROFINET, and SPE cables from Phoenix Contact

SPE supports a wide range of speeds within a single connector solution, so it can be the ideal upgrade to IO-Link, PROFINET, and other industrial communication standards. Specifically, 10 Mb/s SPE could become the logical progression from IO-Link and other lower speed standards by increasing data transfer over much longer distances (up to 1 km) and less cabling (two wires). Likewise, 1 Gb/s SPE has the potential to upgrade 100Base-TX PROFINET by delivering much higher transmission speeds, going from 100 Mb/s to 1 Gb/s over half the amount of cable.

As application areas begin to transition to Ethernet protocols and field devices continue to require increased transmission capacities, SPE can deliver both Fast and Gigabit Ethernet combined with power over a simple two-wire interface, making it easier to implement Ethernet from the field to the cloud. We already see end users, vendors, system integrators, and component manufacturers coming together to publish specifications (IEC, IEEE) that address SPE implementation for their specific market areas. Such collaborations and partnerships highlight the importance of single-pair Ethernet for industrial applications.

SPE has the advantage enabling high-speed communications over a single pair of wires and allows for the use of standard industrial-grade housings proven to withstand the harshest environments. These factors make SPE the ideal upgrade for both low-speed and high-speed protocols with a single connector interface.

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