Blog: Single-pair Ethernet – Deployment and characteristics
Part 2: Transition paths in different industries
Hilscher expects an early adoption and deployment of SPE in the process automation sector starting around 2021. The reason is that the installations are based to a large extend on HART, PROFIBUS PA and similar fieldbuses that are not in the necessary extend supporting digital business models. The Namur Organisation and specially the FieldComm Group together with the PROFIBUS International (PI) and ODVA strongly drive the move to APL for process automation industries. The applications in these areas have usually lower performance and cycle time requirements and the deployment of diagnosis and parameterization through the network has not yet happened as much as in factory automation applications. On the other side, the deployment of SPE in factory automation might take a bit longer. Organization such as the ODVA, PI including the IO-Link group have started activities to evaluate the integration of SPE into their respective standards looking at positioning and the benefit in their applications. In parallel, there are two very active groups on their way to propose different plugs, connectors and cabling for the installation. Looking at all these very productive initiatives and the numerous open questions they address, a field deployment in factory automation would rather start around 2024.
As a conclusion we believe that those areas in the manufacturing industry, where equipment is still non-transparent to the upper layers in terms of status, diagnosis and parameterization, the overall system performance lacks and the advantages of digitization such as machine up time increase, availability, predictive maintenance etc. will not materialize. Therefore, the pressure in the process industry is expected to be much higher to act and move forward as quickly as possible.
Single-pair Ethernet at a glance
The question might come up why people have not moved much earlier towards a single twisted pair as the basic idea appears comparably simple and potential benefits appear also quite obvious. However, the change versus an existing Ethernet network is not so quite simple as the exchange of a cable implies. In addition, a number of requirements need to be added to enable the expected benefits for the different industries.
Different physical layer
The current Industrial Ethernet 10Base-T/100Base-TX that is the most deployed and adapted standard in industry, uses two twisted pair cables for unidirectional transmit and receive data. Therefore, in change to this, a single-pair Ethernet transmits and receives via in the same twisted pair and therefore requires a different physical layer as well as different coupling and transducers.
Various requirements for SPE
Long distance transmission
Especially the targeted sensors, actuators and other peripheral field devices in industrial automation require on top a much larger cable length between them. Hence, a strong demand came to enhance the cable distance between stations up to 1000m, versus the specified 100m that are available in 100Base-TX today.
Intrinsically safe
Another aspect came from the process automation field. Next to the long distance requirement, an intrinsically safe transmission is needed, to support the Ex and hazardous areas.
Power transmission
In many of the actual sensor communication fieldbuses, a power transmission over the communication cable is possible. Hence, the single twisted-pair cable needs to also carry the necessary power to enable the powering of remote sensors and actuators.
Application specific bandwidth demand
Next to field level devices and sensors that are well covered from their bandwidth demand with 10Mbit transmission speed, the idea was to also roll-out SPE into higher bandwidth applications. Therefore, the IEEE also defined standards suitable for vision, motion or HMI including the physical layers.
IEEE Standardization and related applications
PHY connection to upper layer host system
Although the physical layer differs to some details, that connection to the upper layers is the same. The IEEE has taken effort to make sure that any actual system with a MAC and an MII connection can interface to the actual new PHY so that the major change remains in only one OSI layer. The following picture shows the set-up:
System set-up of a point-to-point connection with power distribution
On top of this, the 802.3bu standard has defined a standardized transmission of power over the data line and it is capable to transmit up to 50W to the single endpoint. This feature allows backward compatibility to several existing sensor network standards that also power the connected sensor from a central power controller. The set-up in SPE is as follows:
Related Links
Learn more about SPE in our whitepaper from Niels Trapp! Click on the Link for download.
Part 3 of our blog series about SPE: Factory automation networks are already largely based on Ethernet standards today. However, the adoption of Ethernet in the process automation field is still in progress. How does SPE affect these two industrial areas?
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