INDUSTRIAL
that conventional Ethernet cabling was too bulky for it to be implemented into certain scenarios. With SPE, it is now possible to support simultaneous bi-direction operation across just one pair of conductors. The result is a connectivity solution that is substantially thinner, weighs less and is more flexible than the Cat 5/6 cabling used in conventional Ethernet. Also, the implementation costs involved are significantly lower, since single twisted pair arrangements are much more straightforward to install.
So that particular circumstances can be addressed, the IEEE has introduced several different SPE specifications. With all supporting full-duplex communication, they each have their own distinct plus points in terms of data rate and transmission length. Through these different options, the breadth of possible applications addressed by SPE is certainly extensive. Table 1 gives details of each of the current SPE specifications and outlines their respective capabilities.
Adding power into the equation As well as the standards specifications just mentioned, there are also specifications in respect of power delivery across SPE. The IEEE 802.3bu and IEEE 802.3cg specifications define SPE’s Power over Data Line (PoDL) capabilities, which are analogous to the PoE capabilities of conventional Ethernet.
IEEE 802.3bu can deliver up to 50W of power, which will be easily more than adequate for most IIoT related applications. It should, of course, be noted that in situations where there are large cabling distances involved then the size of the power losses could be substantial. The more recent IEEE 802.3cg specification is for multi-drop topologies where there are several nodes (up to 8) all being powered via one SPE
cable over a short distance (normally around 15m).
Standardising the connector face Although the actual link aspect of SPE remains constant, there are several different prospective connector face versions to choose from, with each being supported by numerous interconnect manufacturers. The two important ones from an industrial perspective are:
IEC 63171-5 - backed by vendors like Weidmüller and Phoenix Contact plus all the other members of the Single Pair Ethernet System Alliance. This relies on M8/M12 connector types and offers 2.5GHz bandwidth. IP65/67 protection against liquid ingress is supported. IEC 63171-6 - adapted for the M8 format, this is the connector face favoured by Harting, Hirose and TE Connectivity, which are among the members of a consortium called the SPE Industrial Partner Network. Like IEC 63171-5, this conforms with IP65/67 requirements. Furthermore, the SPE contacts are accompanied by two additional power contacts, allowing it to handle up to 8A of current and thereby enhancing its power delivery capabilities.
Fully IEC 63171-6 compliant, TE Connectivity has introduced an SPE Sample Kit. This enables engineers to validate the use of SPE connectors in their IIoT designs and create basic prototypes. The kit contains multiple board connectors and cable connectors.
Enhancing performance and providing protection
As well as connectors that conform with SPE specifications, passive components will also need to be sourced. In order to ensure that acceptable levels of signal integrity are
attained across SPE cabling, it will be necessary for passive filtering to be incorporated. This will allow electro-magnetic interference (EMI) effects to be mitigated (which will be particularly problematic over long cable lengths), as well as safeguard sensitive semiconductor devices within the system from surges or spikes. Likewise, defence against the risk of electro-static discharge (ESD) strikes is required.
The SPE sample kit from TE Connectivity
Housed in DFN6 packages, the Bourns CDDFN6-3312P transient voltage suppressor (TVS) diode arrays meet IEC 61000-4-2 ESD requirements. Thanks to their ultra-low capacitance values between I/O lines (just 0.04pF being typical), they can be specified on SPE infrastructure transmitting at up to Gbps speeds. These components have a 3.3V maximum reverse voltage, along with a 4.5V minimum breakdown voltage. Bourns’ surface-mount SM453229 series LAN transformers provide the galvanic isolation necessary to protect Ethernet-based infrastructure, while being far more compact than competing solutions. These differ from conventional LAN magnetics comprised of multiple toroidal core transformers and common mode chokes. Each has a discrete, centre-tapped arrangement with windings on a drum core. This is capped with a ferrite plate that emulates the magnetic path of a toroid core. The compactness of these components means that they are highly applicable to space-limited SPE deployments. They are available in inductance values from 120µH to 380µH, and have 1500V (AC) insulation resistance levels. An operational temperature range of -40°C to +85°C is supported. Leveraging a bifilar winding arrangement, the Bourns SRF3216A series of chokes are able to combat the issues caused by common-mode interference. Impedance values from 90Ω to 2.2kΩ at 100MHz are covered and currents from 200mA through to 400mA. These components exhibit a 125VDC withstand voltage. It is end-to-end networking, based on Ethernet protocols, that will be responsible for much of the digital transformation that is set to happen within the industrial space. Through SPE, there will no longer need to be any dependence on the multitude of different incompatible fieldbus technologies previously used here. Adequate data rates for the functionality involved can be delivered while keeping the cost, size and weight of cabling infrastructure down. There is also provision to go beyond just carrying data, and adding power - further simplifying cabling requirements.
Avnet Abacus
www.avnet-abacus.eu
28 NOVEMBER 2022 | ELECTRONICS TODAY
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