Single Pair Ethernet Explained: 802.3bp, 802.3bw, 802.3cg

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As the name indicates, Single Pair Ethernet, SPE is a version of Ethernet that uses a single twisted pair cable to reduce costs and simplify installations.

Single Pair Ethernet it aimed at low data rate applications such as industrial control and automotive applications for sensors and remote controls that only require very low data rates.

The concept of single pair Ethernet is aimed at the growing number of building automation installations, “smart” systems and the Internet of Things, IoT where wired rather than wireless links are needed for greater reliability and security.

With remote sensors, actuators and switches requiring just a few bytes of data when they are polled or triggered, the full bandwidth of Ethernet is simply not needed.

A host of applications are ideal for the Single Pair Ethernet systems: sensors for lighting, HVAC, access control, occupancy monitoring and a host of other smart systems.

Advantages of single pair Ethernet

Within modern manufacturing and other organisations Ethernet is already widely used, and with the growing need to connect remote sensors, actuators and other devices used for general control and automation, single pair Ethernet provides a very easy addition.

The fact that single pair Ethernet only uses two wires, the cables are simple, low cost and much thinner than the Cat 5, Cat 6 and other cables and this makes them much easier to install. Standard Ethernet cables have either two or four twisted pairs and this makes them much thicker, heavier and less flexible. In fact single pair Ethernet cables are around 60% lighter than the more common Cat 5, Cat 6, etc cables.

Naturally there is a trade-off between data rate achievable and the range with single pair Ethernet. Speeds of 10 Mbps are often achieved and top data transmission speeds up to 1 Gbit/second are now available with some SPE systems, and this is more than enough for all but the most data hungry industrial monitoring and control applications.

SPE & Power over Data Line, PoDL

For many industrial sensors and remote nodes, it is necessary to be able to send power over the single twisted pair data line to power the remote devices. This is the SPE equivalent of the standard Ethernet Power over Ethernet, PoE functionality

Using Single pair Ethernet, a power over data line capability is available. There are fifteen different classes of PoDL available offering regulated and unregulated power supplies of 12V, 24 V, etc with a maximum of 50W power transmission but with distance limitations.

It is also possible to accommodate higher levels of power transmission, but thicker cables are required than the standard cables to achieve the length required and without excessive resistive voltage drops along the line.

The details of the power supply limitations and specifications are contained within the IEEE 802.3cg standard.

Single pair Ethernet specifications

SPE connectors

One of the areas that has seen ongoing work is the standardisation of the connectors. Although Single Pair Ethernet and the standards including IEEE 802.3cg are well established, the connectors that are used are causing a problem.

What is clear is that there is a move away from the familiar RJ45 style connector to types that are more suited for the environments in which Single Pair Ethernet will operate.

Currently two different connector types are on the market and both of them are standardised, and each type is supported by different manufacturers. As a result both types are likely to be widely used, but it is possible that the different connectors may be used in different areas.

The SPE Industrial Partner Network has adopted the T1 interface defined in IEC 63171-6, and the focus for this connector type tends to be for industrial applications.

The other connector type is the IEC 63171-2 and this is supported b the SPE System Alliance for which the focus tends to be automotive and smart buildings.

Both types of connector are smaller and more robust than the RJ45 which almost become synonymous with Ethernet systems and cabling.

What SPE means for industrial plant

The concept of Single Pair Ethernet is ideal for many manufacturing operations. Wit the increase in the level of automation, control and monitoring, many links are needed to provide the required connectivity. Single Pair Ethernet provides the answer to many industrial automation and monitoring demands.

SPE is an ideal partner to the IIoT (Industrial Internet of Things). As wireless links are not as reliable as wired ones, especially in an environment where RF noise levels can be high, a simple low cost solution is required and this is exactly what SPE provides.

In addition to the options for expanding or substituting SPE in classic sensor and industrial Ethernet cables, SPE 1000Base-T1 can work with CAN bus with ranges up to 50 metres.

For process automation, 10BASE-T1L SPE offers significant advantages for process automation, where data rate transmissions have been 31.25 kBit via RS232, etc for many decades. Using SPE 10BASE-T1L the 10 Mbit data rate could be used for video transmissions from security cameras and the like.

Single pair Ethernet vs Industrial Ethernet

Single pair Ethernet may appear to address the same market as Industrial Ethernet, but it is really in name only.

Industrial Ethernet requires high reliability, high speed communications with very high reliability, with the equipment and cables being designed to be able to operate in a more harsh environment.

The Ethernet switches, and cables and other equipment are designed to operate over wider temperature ranges and in environments where IP ratings may be required.

The Single Pair Ethernet, whilst needing to be robust, is aimed at providing lower data rate links to communicate with actuators, sensors and the like where low cost, ease of installation, low data rate are needed along with possibly a much lower cable weight.

Although the two schemes are aimed at industrial environments, they are intended for different types of applications.

Accordingly there is no conflict between the single pair Ethernet and Industrial Ethernet.

Single Pair Ethernet, SPE is a standard that is already being used widely in a number of areas. As the number of remote control, monitoring and automation systems grows, and the need for wired solutions is required for security and reliability, then the requirement for SPE will only grow.

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