SPE Ethernet will replace RS-485 bus

In 2019, the SPE (Single Pair Ethernet) standard was adopted for industrial applications. It is expected to replace various implementations of the RS-485 fieldbus and current loop with protocols: Profibus, Modbus RTU, CC-Link, CAN, FlexRay, HART and others.

SPE was originally developed for transport applications. In 2015, a 100-megabit version of the standard was released, which allows data transmission over a distance of up to 15 meters. But in industrial automation and robotics, equipment can be located over long distances. So in 2019, the IEEE 802.3cg standard was introduced, which allows data transmission at a speed of 10 Mbps over up to 1 km.

In this article, we will take a look at 10Baset-T1L and 10Baset-T1S standards for industrial automation.

SPE location on OSI model

The SPE standard refers to the physical layer of the OSI model, which allows transferring over it any industrial protocols, such as PROFINET, EtherNet/IP, HART/IP, OPC UA, MODBUS TCP and the protocol for IoT devices MQTT.

To connect an SPE device to a regular Ethernet switch, you need a media converter that converts the physical media without converting protocols and data packets. No additional software is needed to work with SPE devices. Communication with SPE devices will proceed as usual in TCP/IP networks via IP address.

A diagram of corporate Ethernet bus organization:

10BASE-T1L

The SPE 10Baset-T1L standard uses one twisted pair (two wires) to connect devices over long distances instead of four pairs. The maximum distance for data transmission has increased from 100 to 1,000 meters (1 km). And the end devices can also be powered over the same twisted pair. The data transfer rate can be up to 10 Mbps.

· Operating range up to 1 km

· Conductor cross section 18 AWG or 0.8 mm2

· Supports up to 10 intermediate connections and two end connections

· Point-to-point mode

· Full duplex

· Symbol rate 7.5 Mbaud

· PAM-3 modulation, 4B3T coding

· Signal with an amplitude of 1 V (1 Vpp) or 2.4 V

· Energy Efficient Ethernet (“quiet/refresh” EEE) support

Once powered up, the 10BASE-T1L standard can start data transfer in less than 100ms. To reduce errors and noise and improve the signal-to-noise ratio, 10BASE-T1L can switch the signal amplitude from 1 V to 2.4 V.

EEE (Energy Efficient Ethernet) technology saves energy by turning off the transmitter when it is not needed while the receiver remains on.

10BASE-T1S

This standard is for connecting devices over short distances.

· Operating range up to 15 m in point-to-point mode

· Duplex or half duplex

· Conductor size 24–26 AWG or 0.2–0.13 mm2

· Symbol rate 12.5 Mbaud

· DME modulation, 4B5B coding

· Signal with an amplitude of 1 V (1 Vpp)

· Support for up to four intermediate connections and two end connections

· No EEE support

· Operating range up to 25 m in multipoint mode (up to 8 knots)

· Collision avoidance mode PLCA RS (PHY-Level Collision Avoidance Reconciliation Sublayer)

PoDL power supply works only in point-to-point mode. In multipoint mode, power has to be supplied separately.

PLCA RS technology in multipoint mode allows using one environment for multiple devices. The first node becomes the network coordinator and separates the data transmission from different devices in time. This allows to get rid of collisions and reduce network latency.

Transferring data and power over two wires

Ethernet has PoE (Power over Ethernet) technology, which allows not only transferring data, but also supplying power to the end device. PoE uses four wires to transmit power. Another standard, IEEE 802.3bu Power over Data Lines (PoDL), had to be developed to adapt PoE technology for two wires.

· PSE (Power Sourcing Equipment) is a power source

· PD (Powered Device) is a power consumer

The IEEE 802.3bu PoDL standard includes several power classes that differ in voltage, current, and maximum power consumption. The maximum power consumption of the end device can vary from 0.5 W to 52 W.

The coordination of power classes between the PSE source and the PD consumer takes place through a special protocol SCCP (Serial Communications Classification Protocol). It is 1-Wire based and has a speed of 333 bps. SCCP works only when the line is not connected to the main power supply (including in sleep mode).

SPE connectors and cables

Two types of connectors were chosen for the SPE standard.

CommScope’s IEC 63171–1 LC connector was chosen for normal operating conditions.

For harsh environments, there is the HARTING IEC 63171–6 (former 61076–3–125) connector family with an ingress protection rating of IP20 to IP67.

Among cables that can be used, there are UTP cables without shielding or STP cables with shielded twisted pairs.

Ethernet-APL standard for hazardous areas

Ethernet-APL (Advanced Physical Layer, meaning extended or enhanced Ethernet physical layer) describes an Ethernet physical layer that is specifically designed for the processing industry. Ethernet-APL provides high-speed communication over long distances, allows data transmission and power supply over a single twisted pair (two wires), and provides safe use in hazardous areas.

Ethernet-APL is based on the physical layer of the OSI model and the 10BASE-T1L (IEEE 802.3cg) standard with additional intrinsic safety requirements.

Main characteristics of Ethernet-APL:

· Data transfer rate up to 10 Mbps;

· Power supply up to 60 W;

· Supports major network topologies, including backbone and branches;

· Maximum line length 1,000 meters in Zone 1, Class 1, Division 2;

· Maximum branch length 200 m in Zone 0, Class 1, Division 1;

· Supports transferring industrial Ethernet protocols, including OPC UA.

The future of Ethernet and SPE

The modern era of Industry 4.0 and the Internet of Things places increasing demands on data transmission channels and device connectivity to Ethernet networks and the Internet. The outdated RS-485 bus and current loop do not allow transferring a large amount of data, and they require specialized interface converters to work. On the other hand, SPE technology will allow organizing a continuous Ethernet bus from end devices to the Cloud. A united Ethernet network will simplify equipment installation, commissioning, configuration, and equipment replacement.

Sensors and end devices using SPE will be smarter. The SPE bus will allow transferring more information about processes and device state and receiving archived data directly from the device itself. Sensors can be powered through the same wire that carries the data. Cloud or Edge solutions for Machine Learning, Artificial Intelligence and Predictive Equipment Maintenance will be able to get data directly from devices and sensors without additional gateways.

If SPE is backed with TSN (Time-Sensitive Networking) and OPC UA technologies, it will allow organizing an integral data transfer structure according to uniform standards, both within a company and outside it.