Nowadays, the term “Industrial Ethernet” is so commonly used that one could easily become confused and startthinking that it must be different from the Ethernet that is used in consumer and computing installations. This blog aims to review the evolution of this networking technology and explain the differences between consumer and industrial Ethernet. It also presents a range of components from Nexperia that can be used to protect Ethernet networks against the damaging effect of electrostatic discharge (ESD), regardless of whether they are deployed in everyday consumer or industrial applications.
A brief history of Ethernet
Since it was first developed at Xerox’s Palo Alto Research Centre (PARC) 1972, the flexibility of Ethernet has helped it become the most popular computer networking interface. It can be implement in various logical topologies (star, ring, bus and others), transporting data using the Internet Protocol (IP). Originally designed to carry data at speeds of up to 10 Megabits per second (Mbps) over coaxial cable, over the decades since its standardization, it has continuously evolved to operate at ever increasing speeds - 100Mbps, 1Gbps and most recently MG (multi-gigabit). Various types of media, rangingfrom unshielded twisted pair (UTP) copper cables to fiber-optic cables are supported. While initially intended for computer networks in academic and business premises, its flexibility helped it to quickly be adapted for use in homes and industrial networks. Some of the main (non-fiber) versions of the Ethernet standard and their target markets are shown in Table 1.
What is ‘Industrial Ethernet’ and is it different to ‘normal’ Ethernet?
The term ‘Industrial’ Ethernet only indicates the location in which a network is operating – namely an industrial environment. At the physical layer, there is no difference in how a home/office Ethernet network and an ‘industrial’ Ethernet network operates i.e. it uses the same medium (cables), 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 a higher OSI layer (the Network layer) which is outside the scope of the Ethernet specification. Industrial Ethernet uses different Network layer protocols like Profinet and Ethernet/IP which better serve the real-time requirements of industrial operations than the internet protocol. 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 (better mechanical and electrical shielding) 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 in Figure 1. The PHY (abbreviation for physical layer) 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 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:
- 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 center 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 to via a capacitor to ground. Then, both unidirectional and bidirectional devices can be used. As shown in Figure 1, 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 here, need to be placed on the PHY side of the transformer.
Nexperia offers ESD protection for all Ethernet implementations
To provide designers with maximum flexibility, Nexperia offers a broad range of ESD protection devices for every implementation of magnetic components (Table 2) 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 the highest 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. Find out more about Nexperia’ s flexible portfolio of ESD protection devices for industrial and consumer Ethernet network installations here.
