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What makes Ethernet ‘industrial’?

13 June 2024

Nexperia reviews the evolution of the now ubiquitous Ethernet networking technology and explains the differences between consumer and Industrial Ethernet.

Since it was first developed at Xerox’s Palo Alto Research Centre (PARC) in 1972, the flexibility of Ethernet has helped it become the most popular computer networking interface. It can be implemented in various logical topologies – star, ring or bus, for example – transporting data using the Internet Protocol (IP). 

Originally designed to carry data at speeds of up to 10 Megabits per second over coaxial cable, over the decades since its standardisation, it has continuously evolved to operate at ever increasing speeds – 100Mbps, 1Gbps and most recently MG (multi-gigabit). Various types of media, ranging from unshielded twisted pair (UTP) copper cables to fibre-optic cables are now supported. While initially intended for computer networks in academic and business premises, its flexibility helped it to be quickly adapted for use in homes and industrial networks. 

The term ‘Industrial’ Ethernet really only indicates the location in which a network is operating. At the physical layer, there is no difference in how a home/office Ethernet network and an ‘industrial’ Ethernet network operates. It uses the same medium, signal voltage levels and rules for when and how fast network nodes transmit or receive data. This means that at the physical layer, they are electrically compatible. 

The difference between the two occurs at the network layer – the Open Systems Interconnectivity (OSI) layer, which is a conceptual model created by the International Organization for Standardization which enables diverse communication systems to communicate using standard protocols – which is outside the scope of the Ethernet specification. 

Figure 1: Simplified Ethernet interface circuitry.
Figure 1: Simplified Ethernet interface circuitry.

Industrial Ethernet uses different network layer protocols, such as Profinet and Ethernet/IP, which better serve the real-time requirements of industrial operations. Other differences relate to the types of connectors used to join cables to interfaces. The Ethernet standard specifies the use of RJ45 connectors but sometimes these can be susceptible to damage by dirt and moisture in harsh industrial environments where there are high voltages/currents and lots of heavy equipment. Some manufacturers have designed connectors with a higher degree of robustness to help them survive these conditions, but these are not included in any of the Ethernet specifications. 

In addition to different connectors, Industrial Ethernet-based equipment often uses components that can be mounted on a 35mm DIN rail and can operate from the 24V DC supply that is commonly used in industrial applications.

Protecting Ethernet circuitry

At its simplest, the circuit in an Ethernet interface looks like Figure 1. The physical layer (PHY) is the integrated circuit that manages Ethernet’s rules for transmitting and receiving data. Transformers provide Galvanic isolation while enabling signaling to take place, despite differences in voltage potential at both ends of the cable. They also provide some protection against transient surge and ESD events. Common-mode chokes (CMCs) are used to reduce electromagnetic interference (EMI) between twisted pairs in the cable – this is especially important for unshielded twisted pairs.

There are several different options for how the transformer and CMC circuits can be implemented:

Figure 2: Magnetic component implementation affects ESD device placement.
Figure 2: Magnetic component implementation affects ESD device placement.

• Integrated magnetic module which includes the transformer and CMC.

• Integrated connector which includes the RJ45 connector, the transformer and the CMC.

The way in which the magnetic components are implemented determines the placement and product options for the ESD protection devices. In case the centre tap on the PHY side of the transformer is connected to ground, bidirectional devices need to be used. The most common case is that it is kept floating or connects via a capacitor to ground. Then, both unidirectional and bidirectional devices can be used. As shown in Figure 2, there are two options for placing ESD protection devices. Firstly, it can be placed between the PHY and the magnetic components, which works also for all forms of integrated magnetic components. In case CMC and transformer are separate components, the ESD protection device can be placed between the CMC and the transformer – which is, from the ESD protection perspective, the preferred position. In any case, the ESD protection devices shown in Figure 2 need to be placed on the PHY side of the transformer. 

To provide maximum flexibility, Nexperia offers a range of ESD protection devices for every implementation of magnetic components in an Ethernet interface. Key features of these devices include multiple package options – both leadless and leaded – and they are available in capacitance values appropriate for the required operating speed of the Ethernet specification into which they are designed. The higher the data rate, the lower the capacitance while still offering high levels of protection in harsh industrial environments.

Conclusion

Industrial Ethernet is electrically identical to standard Ethernet, but industrial environments are more rugged, with a greater chance of voltage surges and ESD events occurring. 


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