How to Use Single Pair Ethernet to Save Space and Weight While Improving Industrial IoT Performance
Contributed By Digi-Key's North American Editors
Ethernet is the most popular wired networking standard for Industrial Internet of Things (IIoT) networks, providing solid performance and proven reliability. In addition, Power over Ethernet (PoE) reduces wiring by providing power to sensors and IIoT endpoints over the same Ethernet cable. Ethernet has also become a standard in passenger cars, in many cases replacing the Controller Area Network (CAN) serial protocol. This provides noticeable advantages for autonomous driving and advanced driver assistance systems (ADAS) because of Ethernet’s reliability and high data rate.
However, in large IIoT networks, Ethernet cable bundles can become so large, heavy, and cumbersome that the cable bundles can become obstructions that weigh down equipment, requiring extra reinforcement. This is particularly problematic for automotive applications where the extra weight and space reduce capacity and mileage. In industrial transportation applications such as trucks, passenger and cargo trains, and aircraft, the extra size and weight of the cables can be large enough that it must be compensated for in the system design, increasing costs and slowing setup times.
To address these issues, manufacturers have introduced single pair Ethernet (SPE) connectors and cables that also support power over data lines (PoDL). SPE provides high-speed data transmission as well as power over only one twisted pair of conductors. This article will explain the advantages of SPE for industrial and transportation applications. It will then discuss two SPE connectors from Phoenix Contact as well as two SPE cables that are suitable for SPE applications.
SPE versus conventional Ethernet
Ethernet is the most popular wired networking standard for commercial and industrial local area networks (LAN). The most widely used versions are 10/100Base-T Ethernet which uses two twisted pairs of wires to transmit data and Gigabit Ethernet which uses four twisted pairs. As industrial automation systems demand faster speeds, Gigabit Ethernet with PoE has become more popular for connecting computers to sensors. Commonly, 24 AWG copper wire is used for the twisted pairs. These eight wires are usually encased inside an industrial-grade CAT5e cable covered with foam tape and a foil shield. In a large industrial facility, hundreds of these cables can be seen routed all over the building. These cable bundles can become heavy, and rather than route them across the floor where someone can trip over them, they are bundled into harnesses that are attached to walls and equipment. These bundles can weigh 50 pounds (lb) or more, and if the added weight of additional cables is not accounted for, they can strain or break the cable support system or even topple equipment.
In addition, conventional Ethernet cables have a length limit of 100 meters (m). For larger industrial facilities and for building automation systems, repeaters must sometimes be used to extend the reach of Ethernet cables in order to reach remote sensors. This increases the complexity of the system and introduces another point of maintenance. With the extra time and added expense of routing these thick, heavy cables, it’s clear that an alternate cabling method is needed.
SPE provides bidirectional data and transmits power using one twisted pair cable. It supports cable lengths up to 1000 m, extending the reach to networked sensors without using repeaters. This significantly lowers weight and eases installation by simplifying layout, providing maximum power efficiency, a smaller footprint, and lower setup and maintenance costs compared to conventional Ethernet. While industrial systems can use shielded jackets to prevent cable bundles from interfering with each other, lightweight unshielded cables are also supported. This is an advantage in automotive applications, allowing for lightweight cables that can be routed more easily in space-constrained areas such as under seats and beneath running boards. With the combined advantages of a smaller and lighter cable, along with providing high-speed data alongside power delivery in a single cost-effective pair of wires, SPE is expected to become a popular, if not dominant, industrial communications standard.
The formal IEEE specification for 10 megabit per second (Mbit/s) SPE is 802.3cg. It supports full duplex data communication up to 1000 m.
IEEE 802.3bw supports full duplex data communication up to 100 Mbits/s for cables up to 50 m. It targets high-speed sensors in industrial applications and some automotive applications.
IEEE 802.3bp supports full duplex data communication at up to 1000 Mbits/s for a cable length of up to 15 m. At this cable length, it is applicable for some industrial sensor applications but is especially suited for high definition video, as well as small aircraft and commercial automotive applications where high-speed sensor data must be transmitted over a relatively small distance.
At present, IEEE 802.3ch supports up to 10 gigabits per second (Gbps) with a cable length of up to 15 m. It is similar to 802.3bp but includes the physical layer (PHY). This is primarily focused on commercial automotive and industrial transportation applications where high data rates, smaller cable diameter, and especially lower weight are very important system design considerations.
SPE with PoDL provides power to the Ethernet sensor or endpoint over the same twisted pair, with the amount of power delivery determined by the length of the cable and the wire gauge. At a maximum length of 1000 m using 14 AWG wire, the IEEE specification allows for 60 volts and 13.53 watts of power at the endpoint.
Industrial SPE hardware
Industrial SPE connections do not use RJ45 connectors but instead, use the new IEC 63171 T1 connector standard. Phoenix Contact supplies a family of SPE connectors and cables that target industrial applications.
For industrial SPE applications that need IP67 robustness, Phoenix Contact offers a true M8 connection using the 1163793 SPE M8-2 insert with the 1412502 M8 shell (Figure 1). The combination of the shell and insert assembly provides IP67 protection which is appropriate for harsh industrial environments. The lightweight assembly is also appropriate for aviation and transportation systems.
Figure 1: The Phoenix Contact 1163793 M8-2 insert (left) and the 1412502 M8 shell (right) provide a true SPE M8 solution with IP67 protection when assembled. (Image source: Phoenix Contact)
The connector assembly can supply PoDL up to 72 volts at 4 amperes (A) and is rated for temperatures ranging from -40°C to +85°C, making it appropriate for powering IIoT endpoints and sensor nodes in outdoor environments. The popular M8 connector format makes it easy for systems manufacturers to refit existing sensors and equipment with M8 connectors to SPE. The SPE connector assembly uses a standard SPE M8-2 connector pattern with D-coding to ensure only SPE cables are inserted into the connector assembly.
Enterprise SPE hardware
SPE is also appropriate in enterprise systems, including office environments, where the lighter and smaller diameter cables are easier to build and route. IP67 industrial applications can easily interact with these enterprise systems using the same SPE network. For enterprise applications that typically require IP20 protection, an appropriate solution is the Phoenix Contact 1163797 SPE modular jack, a through-hole soldered IEC 63171 jack with a locking clip to ensure a solid cable connection (Figure 2).
Figure 2: The Phoenix Contact 1163797 modular SPE jack is compatible with all current SPE standards. It is rated to supply up to 72 volts at 4 A. (Image source: Phoenix Contact)
The M8-2 insert is keyed to prevent misconnections. The jack has two gold plated, copper alloy plugs that keep contact resistance to a minimum, allowing it to deliver PoDL up to 70 volts at 4 A. The M8 shell is brass with nickel plating to provide corrosion resistance.
The 1163797 supports all current SPE connector specifications of 802.3cg/bu/bw/bp. It is built to withstand rugged environments, with insertion and withdrawal cycles specified at greater than 750, is rated at IP20, has an operational temperature range of -40°C to +85°C, and measures 5 x 8.35 x 14.2 mm. This makes it appropriate for solder mounting on single board computers (SBCs) as well as programmable logic controllers (PLCs), where cables are occasionally swapped. Example scenarios where this proves useful include manufacturing facilities that may need to be reconfigured for different product assemblies.
SPE cables for IIoT
For short SPE connections, Phoenix Contact supplies the 1183808 2 m SPE cable. This cable supports PoDL up to 72 volts at 4 A and has two SPE receptacles at each cable termination (Figure 3). While conventional Ethernet has jacks on the cable ends and receptacles at the endpoints, SPE hardware is reversed.
The cable jacket is made of polyurethane which is resistant to ultraviolet (UV) light, abrasion, and most solvents. Polyurethane cables are also resistant to shrinkage and cracking caused by exposure to sunlight and water, as well as the abuse commonly found in industrial environments. The cable is protected from electromagnetic interference (EM) by a tinned, copper-braided shield that is wrapped in plastic-coated aluminum foil. This makes it appropriate for electrically noisy environments, especially when bundled with other high-speed cables.
Figure 3: The Phoenix Contact 1183808 SPE cable is 2 m long and has a protective polyurethane jacket. It is shielded from EMI and supports data rates of up to 1000 Mbits/s. (Image source: Phoenix Contact)
The cable receptacle contacts are copper alloy and support 802.3cg compliant 10 Mbit/s data transmission, as well as 100 Mbit/s 802.3bw speeds. The highest transmission rate is 802.3bp 1000 Mbits/s, making this appropriate not only for sensors but also for high definition (HD) video surveillance equipment.
While the cable jacket is immune to water and dust, as well as being flame resistant to UL94V0, the cable assembly is rated IP20 because of the cable termination connectors. Each connector has a locking clip to securely connect the cable to the jack endpoint. This locking mechanism is part of the SPE connector standard to prevent accidental removal in busy environments. The cable is rated at -40°C to +85°C operation and up to 750 insertion and removal cycles. It is suitable for indoor use with patch panels, as well as connections between IIoT sensors and SPE junction boxes.
For applications requiring a longer cable, Phoenix Contact offers the 1183811 5 m SPE cable, which has the same specifications as the 1183808.
The move to SPE in applications such as IIoT, automotive, and the enterprise, helps designers meet the need for high-speed connectivity solutions that are lighter, smaller, and easier to use, while also lowering cost. However, designers must be careful in selecting the connectors and cables they use when deploying SPE-based networks to ensure reliable connectivity in physically harsh and electrically noisy environments.
As shown, connector variations are available that allow IP20 rated enterprise systems to easily interconnect to IP67 industrial control systems with true M8 SPE connectors, providing seamless connectivity and power delivery in both environments. With the added capability of PoDL, SPE connectivity makes it easy to provide both power and data to IIoT endpoints in both enterprise and industrial environments without running extra wiring, greatly simplifying and streamlining deployments.
Disclaimer: The opinions, beliefs, and viewpoints expressed by the various authors and/or forum participants on this website do not necessarily reflect the opinions, beliefs, and viewpoints of Digi-Key Electronics or official policies of Digi-Key Electronics.