Meeting standards for the next generation

13 May 2019

Uwe Widmann asks whether single-pair Ethernet (SPE) technology herald a breakthrough for Ethernet right down to sensor connection at field level? And does single-pair Ethernet have what it takes to supplant conventional field bus systems?

Digitalisation is continuing to gain pace and is expected to have implications across a wide range of application areas. 

One element of digitalisation is the creation of a cyber-physical system (CPS) which enables information and software to be linked together with electromechanical components. Implementing a CPS requires a powerful and robust data infrastructure and this can be built using Ethernet technology in accordance with the IEEE 802.3 standard.

The IEEE 802.3 working group has pushed Ethernet technology forward at a tremendous pace since the introduction of the first Ethernet 10BASE-T standard in the 1990s. The first Ethernet CAT 5 cable, based on TIA-568 A/B and with a transfer rate of 10 Mbps, was unveiled as early as 1995, followed by publication of the 1000BASE-T standard in 1999. Today CAT 6A cables for 10GBASE-T are standard products.

Running alongside the technical development of the Ethernet technology – driven principally by the IEEE 802.3 (Institute of Electrical and Electronics Engineers) and the TIA (Telecommunications Industry Association) – the IEC (International Electrotechnical Commission) and the affiliated national committees have worked on compiling uniform standards for cables and connectors. Examples of successful efforts in this area are the IEC 60603-7 series of standards for the RJ45 detail specification for shielded 8-pin connectors up to 2,000 MHz and the ISO/IEC TR 11801-9901 guideline for balanced cabling to support transmission speeds of at least 40 Gbps.

To fulfill the stringent environmental and IP-protection requirements demanded for industrial environments, D-coded M12 data connectors for Fast Ethernet with two pairs of wires were included in the IEC 71076-2-101 standard for circular connectors in 2008. For higher data speeds up to 500 MHz, an X-coded 4-pair M12 standard conforming to IEC 61076-2-109 was published in 2014.

The PROFIBUS & PROFINET International (PI) user organisation included these standards, and its PROFINET specification in its PROFINET Cabling and Interconnection Technology guideline.

Time Sensitive Networking
More recently Time Sensitive Networking (TSN) in accordance with IEEE 802.1 and IEEE 802.3, enables urgent and business-critical messages to be transmitted parallel to other data traffic. This permits defined response times – which is a prerequisite for use in industrial environments.

In order to implement end-to-end Ethernet technology from the cloud right through to the sensor, and to replace existing field bus systems such as Profibus at process level, new technologies with cost-effective, miniaturised and standardised components are needed.

The new single-pair Ethernet cables from Belden will play a crucial role in transmission technology. As well as being significantly compacter and lighter, these single-pair cables are cheaper to manufacture.

SPE cables are suitable for use in offices as well as harsh and dirty industrial environments – as permanent or flexible connections. Belden’s LSZH (low smoke zero halogen) cables provide enhanced safety in cases of fire and comply with the requirements laid down in the EU Regulation No. 305/2011. SPE cables with a PUR sheath are available for industrial applications. Thanks to its 80% shield coverage, Belden’s shielded SPE cable is said to be suited to use in applications where there is severe electromagnetic interference.

The combination of foil shielding and braid shielding brings a significant increase in overall shielding quality and ensures that the cable can withstand the stresses and strains encountered in industrial environments. 

To reconcile the opposing requirements of high data speed and long transmission links specified by IEEE 802.3, new cable standards are needed. The IEC subcommittee SC 46C is currently working on 4 new standards for SPE cables (IEC 61156-11/-12/-13/-14) for permanent and flexible installation. These include:

• Balanced shielded SPE cables with transmission properties of up to 600 MHz at a transmission distance of up to 40m; suitable for the IEEE 802.3bp standard:
– Permanent installation: IEC 61156-11 CDV; scheduled publication: July 2019.
– Flexible installation: IEC 61156-12 CD; scheduled publication: December 2020.

• Balanced shielded SPE cables with transmission properties of up to 20 MHz at a transmission distance of up to 1000m; suitable for the IEEE 802.3cg standard:
– Permanent installation: IEC 61156-13 NP; scheduled publication: July 2020.
– Flexible installation: IEC 61156-14; currently being drawn up.

Coupled with ISO/TR 11801-9906, the requirements defined in the SPE cable standards place high demands on the quality and construction of single-pair Ethernet cables. SPE cables conforming to the IEC 61156-11/-12 standard require wire diameters of between 0.4  and 1.0mm. SPE cables conforming to IEC 61156-13 must have wire diameters of between 0.64 and 1.7mm. The cables are suitable for use in temperature ranges between -20 and +60°C.

Single-pair Ethernet connectors are needed to connect up SPE cables to devices. IEEE 802.3 has instructed ISO/IEC JTC 1/SC 25 WG 3 to come up with proposals and standards for such connectors. The selection process must take the different requirements in office and industrial environments into account, with connector types appropriate to the environmental classifications specified in ISO IEC TR 29106 for M1I1C1E1 (IP 20) and M2I2C2E2 / M3I3C3E3 (IP 67).

Due to the importance of SPE technology for a whole range of application areas, a large number of manufacturers are participating in the selection process. The IEC SC 48B – PT 63171 project team is working on the specifications for connector variants 1 to 6.

In addition to pure single-pair cabling configurations, it is also possible to set up a four-pair structure in order to simultaneously integrate four single-pair channels into one single cable. This enables simpler cabling, particularly in industrial environments where large numbers of sensors are frequently located in small spaces.

Tried and tested in industrial environments, the design of the M8 and M12 connectors, described in variant 3; IEC 48B/2653/NP – IEC 63171-5, enables the implementation of this type of cable structure.

All SPE connector variants need to comply with the fundamental single-pair Ethernet specifications defined in the SPE connector basic standard IEC 63171 ‘General Requirements and Test’.

Manufacturers of connectors and cables are working together in national and international standardisation bodies to meet the market’s demands for standardised components. Belden collaborates closely with other experts within these projects, and late in 2018 the company was able to present SPE cables conforming to the IEC 61156-11 and IEC 61156-13 standard at electronica and SPS/IPC/Drives. 

However, more standardisation work is still needed. In the context of Industry 4.0, the need for higher data speeds and for robust and cost-effective connectors and cables demands further development and standardisation efforts. In IEEE P802.3ch, a working group titled the Multi-Gig Automotive Ethernet PHY Task Force was set up to refinethe IEEE 802.3 standard for speeds greater than 1 Gbps for Automotive Ethernet.

Combined with a simple connection technology, the advantages of SPE technology with regard to miniaturisation and weight reduction make it attractive across many industry  sectors.

Uwe Widmann is a technology & standardisation expert for Belden Deutschland. 

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