What is Single Pair Ethernet (SPE) and how is it used in industrial applications?

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Single-pair Ethernet was originally developed to meet the needs of the automotive industry - smaller, lighter cables and connectors for transmitting data from the numerous sensors involved in adaptive cruise control, parking assistance, autonomous driving and other in-vehicle systems. In fact, the lower data loads and shorter distances required by automotive applications were well suited to early SPE development.

But as the technology developed, companies began to see its potential in other applications—particularly manufacturing and building automation—and developed the SPE Industrial Partner Network. The manufacturers’ association advocates for single-pair Ethernet as “a foundation on which to build the IIoT” and supports standards for transmission protocols, cabling and equipment components.

The interface (connection) of SPE in industrial applications is governed by the IEC63171-6 standard, and the data speed and transmission length are covered by the Ethernet protocol standard established in IEEE802.3. Image source: SPE Industrial Partner Network

Traditional Ethernet requires two pairs of wires to achieve a data rate of 100Mbps, or four pairs of wires to achieve a transmission rate of 1Gbps. Single-pair Ethernet uses only one pair of wires to transmit data at a rate of 1Gbps over a distance of up to 40m, or up to 1000m at a transmission rate of 10Mbps—significantly reducing cable size, cost, and complexity. Although traditional Ethernet has been implemented throughout the automation pyramid, devices at the lowest level (the field level) are still often controlled by fieldbus protocols. SPE provides an Ethernet solution that can be implemented at all levels, from the cloud to the field, eliminating the need for gateways and other hardware required for various networks to "talk" to each other.

Single-pair Ethernet supports Ethernet communications from the top to the bottom of the automation pyramid. Image source: MIAC Automation

Smaller cables also use smaller connectors – another benefit of SPE in space-constrained applications or those with numerous small devices at the field level. Thinner cables have tighter bend radii, making installation, routing and management easier and more flexible, both literally and figuratively.

SPE's ability to transmit both power (up to 50W) and data positions it as an ideal solution for IIoT applications, where many field-level devices require power as well as fast, real-time communications with higher-level controls or to the cloud. For applications requiring more than 50W of power, a hybrid solution using four conductors is available, delivering up to 96W at 24V or 392W at 48V.

How does SPE achieve Fast Ethernet communication with only one pair of wires when traditional Ethernet requires four pairs of wires?

Classic 1Gbps Ethernet uses Cat5 cable with four pairs of wires and operates at frequencies up to 100MHz. Each pair can send and receive data, allowing transfer rates of up to 1Gbps. Single-pair Ethernet uses only one pair of wires but operates at frequencies up to 600MHz. Within this wide frequency band, some frequencies send data and other frequencies receive data, allowing transfer speeds of 1Gbps to be achieved with just one pair of wires.