Articles and Reports

New article by Dr. Michael Hilgner, Lukas Bechtel, Cornelia Eitel for Belden

For the first time, Single Pair Ethernet is being standardized through projects that take industrial environmental requirements into account.

Single Pair Ethernet (SPE) technology may have gained traction by enabling connected cars, but it’s now being used to extend Industrial Ethernet communications to field-level devices on the plant floor.

While standard Ethernet uses two or four pairs of wires, SPE uses a single twisted pair of wires.

Early SPE projects, such as IEEE 802.3bw for 100 Mb/s (published in 2015) and IEEE 802.3bp for 1 Gb/s (published in 2016), were focused on the automotive industry and its need for space-saving, lightweight and cost-effective Ethernet cabling to transmit data from wireless sensor networks in new vehicles.

Recent Single Pair Ethernet standardization projects have focused on industrial requirements, but there other industrial sectors have different requirements.

Slow But Steady SPE Progress

While IEEE 802.3bp was released in 2016 and included a segment with a reach up to 40m to support industries beyond automotive, such as discrete manufacturing and other types of transportation, chip manufacturers continued to focus their efforts on the automotive industry since demand was the highest there.

Industrial environments may not have been top of mind for SPE at the time, but progress still continued.

For example, IEEE 802.3cg for 10 Mb/s was published in 2019, featuring a shielded 1,000 m segment (10BASE-T1L) for the process industry. (It also included an unshielded 15 m automotive segment [10BASE-T1S].)

By defining two signal levels, 10BASE-T1L enables Ethernet use in potentially explosive atmospheres, forming a suitable base for Ethernet Advanced Physical Layer (Ethernet-APL), which was developed in 2021 specifically for process industry requirements.

The combination of the 1,000 m segment length and bandwidth of 10 Mb/s, plus the power supply scheme via the data line defined by Ethernet-APL, bridges the distance between instruments (between sensors and an aggregation point or control room, for example) while transmitting data with higher bandwidth than traditional fieldbuses. This enables capabilities like predictive maintenance.

The ongoing IEEE 802.3dg 100 Mb/s project, which is expected to be completed in 2025, is also driven by applications beyond automotive. For the process industry, for example, a 500 m segment with 100 Mb/s is a good complement to 10BASE-T1L for instruments with high bandwidth requirements.

For discrete manufacturing, which traditionally focuses on 100 Mb/s, a 100 m segment would be sufficient to provide an alternative to existing Multi-Pair Ethernet solutions.

How Network Requirements Differ for Industrial Automation

In addition to different ranges, process and transportation industry requirements also differ in another way: permissible latency.

Latency must be low, especially for motion-control applications in discrete manufacturing. This requirement has an influence on the essential specification in IEEE 802.3dg as to whether FEC (forward error correction) can be provided to achieve the required bit error rate as defined for 10BASE-T1L.

FEC is necessary for process automation, since sufficient transmission quality cannot be guaranteed over a distance of 500 m due to electromagnetic interference. Because it increases latency, however, it should be avoided in discrete manufacturing. This is possible by reducing the distance to 100 m and selecting a suitable coding method.

Whether FEC will be specified as an optional feature, or whether there will be two segment definitions, is not yet known. What is certain, however, is diversification by sector.

SPE in the Process Industry

Ethernet-APL enables the development and market access of end devices—from instruments to switches. Cable requirements are specified for new and existing cabling via IEC 61156, with diameters ranging from 26 AWG to 14 AWG. Cables with diameters between 18 AWG and 14 AWG are primarily intended for implementing the trunk (connecting APL field switches to APL power switches).

Ethernet-APL also contains specifications for connectors and screw and clamp terminals. Corresponding specifications can be adopted or adapted for the 100 Mb/s segment from IEEE 802.3dg.

SPE in Hybrid Manufacturing

Ethernet-APL combines the communication requirements of the process industry with the challenges posed by potentially explosive environments.

In non-hazardous environments, such as food and beverage manufacturing, intrinsic safety requirements do not apply. As a result, PoDL (Power over Data Line) in the form specified by IEEE 802.3cg (also referred to as SPoE, or Single Pair Power over Ethernet) can be used.

Depending on the connected device’s power consumption and SPoE class, wire diameters of up to 16 AWG are required for longer distances.

SPoE, according to IEEE 802.3cg, is directly applicable to the 100 Mb/s segment from IEEE 802.3dg due to its reference to maximum loop resistances.

SPE in Discrete Manufacturing

For connecting sensors and actuators, the 10 Mb/s segment from IEEE 802.3cg represents an alternative to IO-Link.

It’s up to you to decide which is best for your application based on a comparison of the advantages of SPE (Ethernet-to-sensor range, bandwidth, etc.) and IO-Link (unshielded cables, lower purchase costs, etc.).

With the 100 Mb/s segment from IEEE 802.3dg, assuming the realization of acceptable latency, SPE forms an alternative to Multi-Pair Ethernet in Industrial Ethernet.

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