Connecting the IIoT: an introduction to single-pair Ethernet

By Martin Keenan   |   February 17, 2021

Industrial Internet of Things gathers momentum

There is no doubt that the Industrial Internet of Things (IIoT) trend coupled with process improvement initiatives such as Industry 4.0 are leading a profound and transformative change in manufacturing. Initially slow to catch on, many automation service providers and manufacturing operations are immersed in deployments.

Key to improving overall operational effectiveness is analysing, and interpreting data collected from vast numbers of sensors attached to production assets such as pumps and motors. Many of these sensors function to determine an asset's operation status by monitoring key parameters such as vibration. Likewise, control of the production assets is communicated back from the enterprise production control system.
 

Data communications methods

Deciding the best method to provide the bidirectional data communication link has been the subject of much debate. In many cases, the amount of data is relatively small. A lot of attention has been given to low power, low bandwidth wireless protocols. However, that then forces the decision to either wire power to the IIoT device or assume that it will be battery powered. In any sizeable IIoT deployment, the through-life costs of regularly changing hundreds or possibly thousands of batteries are daunting, making a wired connection desirable. A wired data connection adds the benefit that cabling data and power could be achieved using a single cable.
 

Ethernet evolution

Ethernet has long been the preferred wired connectivity method for IT, computing and data centre connectivity. Over the years the IEEE Ethernet 802.3 standard has continued to evolve, and more recently find new markets. Ethernet has also been adapted for specific applications such as Industrial Ethernet to incorporate low latency and determinism. Automotive manufacturers also sought to embrace Ethernet's resilience and robustness.

One of the few challenges in the way that Ethernet has evolved is that to achieve the multi-gigabit throughputs it uses four cable pairs, making the cable dimensions and associated connectors sizeable. Cable and connector size has never been an issue for most commercial applications, but they are limiting for automotive applications, as is the cable weight and the maximum bending radius. The possibility of accommodating a higherdata transfer rate using just a single twisted pair led to the development of a set of single-pair Ethernet (SPE) standards.
 

Single-pair Ethernet

The use of a single twisted pair is not new, and by no means is it supposed to replace the existing four-pair Ethernet standard. The characteristics of single-pair Ethernet include thinner and lighter weight cables making them more space efficient, simpler to assemble, and easier to install. Compared to a four-pair Cat 6A cable with AWG 23 conductors, a single-pair version is 60 % lighter. 

In keeping with the concepts of Power over Ethernet (PoE), single-pair Ethernet includes the 50 watt / 48 V Power over Data Line (PoDL) capability. These benefits offer significant advantages to a broad range of building automation and IIoT applications. Many IIoT devices do not require large amounts of power or access to significant bandwidth, so SPE is quickly becoming favoured as the communication infrastructure of choice for IIoT.

Figure 1 highlights a typical implementation scenario where conventional four-pair Ethernet and single-pair Ethernet are deployed. SPE is also an ideal candidate for replacing legacy Fieldbus proprietary industrial automation protocols.

The initial 802.3 SPE 'T1' standards - see Figure 2 - provide capabilities of link distances of 15 m (unshielded) or 40 m (shielded) with up to a multi-gigabit bandwidth. Current bandwidths are indicated in green, with planned future standards evolution in grey.

Figure 2: Current and future IEEE 802.3 standards for single-pair Ethernet

Automotive system manufacturers drove the initial 100 Mbits/s IEEE 802.3bw 100BASE-T1 standard. Compared to Cat 6 Ethernet IEEE 802.3ab, which operates at 125 MHz bandwidth and uses all four pairs, the 802.3bp needs to operate at 600 MHz to achieve the same 1000BASE-T1 1 Gbit/s data transfer rate.
 

Power over Data Line (PoDL) capability

The IEEE 802.3bu-2016 specification stipulates ten classes (0 - 9) of power delivery capability up to a maximum of 50 watts (Class 9) at the connected device - see Figure 3. Each class provides a range of working voltages and maximum current to deliver a maximum power rating.

Figure 3: PoDL power classes for single-pair Ethernet

The IEEE 802.3cg-2019 standard published on 5 February 2020 added six additional PoDL classes (10 - 15) to support new use cases and a slightly revised maximum power of 52 watts at the device. The conductor diameter needs to increase accordingly to meet the higher power ratings.
 

Connector standards for single-pair Ethernet

Unlike the ubiquitous RJ45 connector used for four-pair Ethernet, a series of connector standards have been proposed or published for SPE. Based around the IEC 63171 standard, variants exist to accommodate different power transfer, ingress protection, data rates, and cable types - see Figure 4.

Figure 4: Single-pair Ethernet connector standards 

For IIoT applications, the possibility that the device, hence the connector, may be used in the proximity of fluids, moisture or dust is highly likely. IP65/67 connectors offer protection against contaminant ingress. Shielded connector assemblies - specified at Type B - cater for link segments up to 40 m using a single shielded twisted pair. Type A denotes unshielded link segments up to 15 m.
 

Single-pair Ethernet: The IIoT's network

SPE is the ideal data networking, and power delivery method for any IIoT deployment. Lighter, smaller and providing various data rates and connectivity configuration options make it the perfect choice. Ethernet now provides the single common protocol for connecting everything from the compact, low power IIoT sensor device to enterprise data centres and production management systems.

To  find out more about single-pair Ethernet, request a sample kit, or learn about the leading suppliers that have joined us on the SPE alliances, click here. Alternatively, if you would like to discuss your requirements in detail, get in touch with our technical specialists in your local language.

About Author

Martin Keenan

As Technical Director, Martin is responsible for technical marketing strategy across IP&E, power and...

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