Single Pair Ethernet—or SPE for short—is currently one of the mega-trends in industrial data transmission. If you want to understand the applications and advantages of reducing data cabling to a single wire pair, you must learn the history of Ethernet and industrial automation.
As a non-standardized software protocol, Ethernet was developed in the 1970s for the internal and locally limited transmission of data packets in wired computer networks (LAN or Local Area Network). The Institute of Electrical and Electronics Engineers (IEEE) defined the software protocol and the physical layer—including physical interfaces such as connectors and cables—in the following two decades and laid the foundation for the modern internet with the introduction of various protocols such as 802.4 (Token Bus), 802.5 (Token Ring), and finally 802.11 wireless LAN (WLAN).
Parallel to this, the increased use of electrical automation technology drove the development of fieldbus technology in the 1980s. The basic idea was the same: Different communication participants should communicate with each other in an orderly manner using a common system. However, the various fieldbus protocols, such as Interbus, DeviceNet, and Profibus, were not used for networking computers at the company level but serial or parallel connection of sensors and actuators to the control and management level.
Ultimately, the parallel development of the two transmission protocols established the form of the automation pyramid that is still valid today. The highest levels represent locally limited computer networks that are used for rough and detailed production planning. The lower levels comprise the signal, data, and power transmission for recording, controlling, and regulating the physical production process (Figure 1).
Figure 1: Paradigm shift: SPE turns the conventional automation pyramid upside down. (Source: Phoenix Contact)
The shape of the pyramid resulted primarily from the hierarchical-logical arrangement of the different levels. However, it also represents the previously valid framework conditions for industrial data transmission: High transmission rates and short distances via Ethernet, low transmission rates, and long distances via fieldbus.
So why this digression? Industrial Ethernet and especially Single Pair Ethernet (SPE) are turning this automation pyramid upside down. With the development of Ethernet-based protocols, such as EtherNet/IP, Profinet, or EtherCAT, real-time data transmission from the company level to the field level was introduced.
The physical interfaces became more powerful and more complex in electrical terms because data transmission had to be protected from interference, such as dirt, vibrations, and electromagnetic radiation. Manufacturers of connection technology, therefore, developed special, IP6x-protected Ethernet interfaces to meet these increased requirements at the field level. At the enterprise and operational levels, IP20 solutions were still sufficient for the top of the automation pyramid.
So far, standardization efforts have been limited to ever-higher data rates and higher demands on cabling technology. These requirements were defined by ever-higher performance classes in copper-based cabling categories.
The Single Pair Ethernet does not again define higher bandwidths or transmission distances but forms the normative framework for reduced cabling to suit the application. The IEC 63171-2 (IP20) and IEC 63171-5 (IP67) standards focus on lower transmission rates of 10Mbps to 100Mbps. The data cabling with only one pair of wires enables transmission distances of up to 1000 meters (Figure 2). Thus, for the first time, SPE allows areas of application and applications that conventional Ethernet had not allowed, for example, in-process technology. The advantage for plant operators: Data cabling can be carried out continuously based on the Ethernet protocol, such as identical interfaces, and pin connector patterns can be used in different environments.
Figure 2: Standardization: The data transmission rates at the field level and in data centers are successively standardized. (Source: Phoenix Contact)
Another advantage is that single-pair interfaces are considerably more compact than two- or four-pair device and cable connectors. Thus, SPE supports the continuing trend towards compact, decentralized devices in industrial automation, process technology, building automation, and telecommunications and infrastructure applications. SPE can therefore turn application-neutral into the DNA of the Industrial Internet of Things (IIoT).
To ensure consistent compatibility of all interfaces, the IEEE has formed working groups for the normative description of different applications with transmission rates of 10Mbps, 100Mbps, and 1000Mbps. Standards for 10-Base-T1, 100-Base-T1, and 1000-Base-T1 have been adopted.
Phoenix Contact is a major driving force behind the standardization of the corresponding interfaces. With market partners, Reichle & De-Massari and Weidmüller, the connection technology specialist develops protected and unprotected pin connector patterns for single-pair and four-pair cables. The MICE model describes their mechanical robustness (M1 or M2/3), IP protection (I1 or I2/3), chemical and climatic resistance (C1 or C2/3), and electromagnetic safety (E1 or E2/3).
The compact pin connector patterns are ideal for efficient cabling of numerous communication participants—either via a single wire pair or via four wire pairs for four participants sharing a common line and interface (Figure 3). Because of the common interface, single- and four-pair cabling concepts can be mixed as well as IP20 and IP6x solutions. Possible applications are splitting eight-wire cabling concepts into four individual SPE strings for four different communication participants or the dimensioning of individual pairs within the eight-wire device interfaces. The two-wire technology permits the application-specific supply of terminal devices with outputs of up to 60 watts via the same pair of wires (Power over Data Line or PoDL).
Figure 3: Efficiently wired: Single-pair and four-pair MICE interfaces are used for cabling IP20 and IP6x applications. (Source: Mouser Electronics)
SPE cannot be seen as a mega-trend in industrial data transmission independent of other standardization efforts. The basic framework for the future of industrial communication technology is being created in parallel in various committees and projects. New communication standards such as the Open Platform Communications Unified Architecture (OPC UA), Time-Sensitive Networking (TSN), and 5G form the basis for continuous networking from the sensor via the machine and higher-level systems into the cloud.
The new standards will outperform existing protocols and interfaces in terms of cost, data throughput, latency, and deterministics. Phoenix Contact is active in all the relevant standardization committees with over 30 years of experience in industrial communication. The goal: nothing less than a new, manufacturer-independent communication standard for automation.
Today, OPC UA already serves as a superimposed communication standard in plants. OPC UA is now being expanded by standardized application profiles in the field—for I/O, safety, or drive applications. In addition, standardized device models are defined for uniform configuration and diagnostics of the network devices (Figure 4).
Figure 4: Information (IT) and operating technology (OT): New communication standards form the basis for integrated networking from the sensor to the machine and higher-level systems to the cloud. (Source: Phoenix Contact)
Single Pair Ethernet (SPE) connects the IP20 world of the enterprise and operating level with the IP6x world of the control and field level—and thus opens up new areas of application. The goal is the seamless connection of all communication participants based on the same protocol language and uniform interfaces. Because of the reduced cabling with only one or four individual wire pairs, users can build efficient network and cabling structures from the sensor to the control and company level right up to the cloud. And in addition to data rates of up to 1000Mbps, the SPE cabling also allows the end devices to be supplied with power of up to 60W.
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