What is Single-Pair Ethernet?

16-11-2020 |   |  By Robin Mitchell

One connection technology, single-pair ethernet, has been showing up lately as the connection technology for the future. What is single-pair ethernet, what technologies can it allow, and how can it potentially be a critical technology for future IIoT systems?

What is IIoT?

One of the biggest changes to technology has been the rise of the Internet of Things (IoT), but the term IoT can be somewhat misleading. While internet-connected devices have existed for decades, IoT is generally reserved for devices that would otherwise not have internet capabilities such as sensors, appliances, and everyday household devices. The advantage of integrating IoT technologies into everyday life stretches far beyond simple convenience and data gathering; IoT has enabled the development of AI systems which are now helping to create adaptive systems that can change and learn to improve themselves over time. 

However, the concept of individual devices and sensors having internet capabilities has also emerged in the industrial market giving rise to IIoT, or Industrial Internet of Things. In IIoT, all aspects of an industrial process are connected to the internet whether it is a machine tooling station, a temperature sensor on a motor drive, or safety sensors detecting the presence of workers. Just like IoT, IIoT, when fully utilised, will usher in a new era of industrial processes which can intelligently communicate with each other, improve their performance, and provide valuable data for industrial AI systems. While some devices and sensors can be connected wirelessly to a network, others may benefit from a wired connection, whether it be for providing power or for creating a secure system. When it comes to developing a wired network, there are many different protocols on the market available to industrial systems, all with their own advantages, and many of these protocols cannot communicate with each other. 

What is Single-Pair-Ethernet?

Traditional ethernet connections use RJ45 connectors, and these include four pairs of wires, creating a total of 8 wires. While these cables can provide high-speed connections, the maximum speed and length depend on factors such as the quality of the cable, if the cable is shielded, and what environment the cable is in. Thus, standard ethernet connections offer communication up to 100 meters at (100mbps), but gigabit ethernet cables are also available which too operate up to 100 meters. The capability of the cable can be determined by its category numbers such as CAT5 and CAT6. Single-pair ethernet, as the name suggests, reduces the total number of wires to just two (i.e. one pair), and this can be used for both communication and power. Currently, single-pair ethernet allows for data speeds up to 10Mbps (with plans for 1Gbps), can provide up to 52 watts of power, and provide power and data up to distances of 1,000 meters. 

How can single-pair ethernet change industrial systems?

Single-pair-ethernet is an industrial solution to overcome challenges provided by traditional ethernet systems specifically aimed at industrial applications. 

The first advantage to a single twisted pair is the increased reliability in mechanical connectors. Instead of needing 8 different conductors to carry signals, only two conductors are used, and only two physical contacts are required for the system to work. This also allows for the use of more robust connectors that require stronger mechanical links, such as Mx connectors which can provide environmentally sealed connections. 

The second advantage to a single twisted pair is the significant decrease in the size of the cable. A reduced cable size allows for an increase in cable density when routing networks, thus allowing for more devices to be connected simultaneously (as a result of laying more cable in the same cable ducts). Reduced cable size also reduces the weight of the cable, and thus allows for easier installation when compared to thicker, heavier cables. This also makes it easier for operates to make adjustments to the network as the cable is easier to move and manipulate.

The third advantage to a single twisted pair is cost; reducing the number of conductors in a cable reduces its price. Cheaper cables allow for lower-cost installations, thus incentivising industrial facilities to upgrade their networks. Since a cable cannot become simpler than a single-twisted-pair, such a cable installation will most likely be compatible with future changes to the network.

The fourth advantage of a single twisted pair is the simplicity in connectivity. While such a cable can be fitted with strong, dedicated connectors, the use of just two wires allows for a designer to choose any connection type they want with ease. If, for example, a sensor system that requires power and a network connection were incredibly small, then an installer could connect a twisted pair using directly soldered connections. Failing that, terminal blocks can also be implemented with ease. An installer could also use a cable crimping system to attach their own custom connector that fits with the hardware in question.

Overall, a single twisted pair ethernet may not currently provide the needed speed for networking in offices and homes. Still, in industrial environments where only sensory and command data is being transmitted, 10Mbps is more than enough. Considering that a single twisted pair is expected to support 1Gbps in the future, the case that SPE may become the cable for future industrial systems is strong.

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By Robin Mitchell

Robin Mitchell is an electronic engineer who has been involved in electronics since the age of 13. After completing a BEng at the University of Warwick, Robin moved into the field of online content creation developing articles, news pieces, and projects aimed at professionals and makers alike. Currently, Robin runs a small electronics business, MitchElectronics, which produces educational kits and resources.

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