Cable into the Future: Industrial Ethernet with 10 Gb/s
A White Paper presented by
Bernd Horrmeyer, Industrial Network Cabling Specialist, Phoenix Contact GmBH & Co. KG

Today's machines and plants generally communicate using Ethernet with 100 megabits per second (Mb/s). However, many applications, such as cameras for quality inspection, servers to document quality data, and scanners that identify components, demand higher data rates. Frequently, communications also must be established with the factory control system. While data transmission rates of 1 gigabit per second (1 Gb/s) are standard, 10 Gb/s will be necessary in the near future (Fig. 1)

Classic fieldbuses and generic cabling can no longer meet the requirements of these networks. Automation-related applications are subject to the same demanding environmental conditions as fieldbus communication. To reliably transmit data in this environment, the components must be able to cope with the mechanical effects as well as the high electromagnetic load.

Figure 1. Today, Cat6_A components allow 10 Gb/s Ethernet to be
reliably used in an industrial environment.

Many different organizations have attempted to establish their own Ethernet-based system. These solutions range from transferring generic communication wiring schemes to industrial applications, to the use of special components and topologies, which are similar to established fieldbus systems. The International Electrotechnical Commission (IEC) has taken responsibility for standardizing these (see Figure 1). In addition to generic, application-neutral networks based on IEC 11801/24702, today's company communication networks are typically designed for specific production applications on automation islands, as defined in IEC 61918. 

Harsh Environments

Industrial Ethernet is often used in harsh environments. When selecting components, users should take the application conditions into account as well as the data transmission properties. The surrounding conditions can be described systematically using a Mechanical Ingress Climatic Electromagnetic (MICE) model in accordance with IEC TR 29106 for mechanical loads, exposure to foreign matter, weather, and electromagnetic fields, as well as test standards 1, 2, and 3 for offices and light and heavy industrial environments. On the other hand, fieldbus organizations have their own definitions, such as how to define the inside and outside of a control cabinet. Furthermore, the use of shielded cables and a grounding/potential equalization system improve the network reliability significantly. The shield connection for symmetric cable must be connected - preferably meshed - to the potential equalization system on all sides. Potential differences between the grounding points generate equalizing currents, which then cause interference in the cabling. If there is no functional potential equalization system in place, use optical cable instead.

Generic Cables

The generic cabling developed for industrial applications based on the IEC 24702 standard uses a reference installation as a model. Since the planning for this type of cabling is straightforward, it is often used for installations in buildings. The reference installation model demonstrates how a given level of quality can be achieved by installing specific components in a definite manner.

For example, installing Category 5 components with balanced cabling makes for a Class D channel, which is suitable for Fast and Gigabit Ethernet. In this example, the flexible cords can have a maximum span of 10 meters, permanently installed lines can be 90 meters in length, and channels can connect any two active devices separated by maximum of 100 meters. Since the cords offer inferior transmission properties to permanently installed cables, it is essential to comply with the stipulated lengths.

Theoretically, one can compensate by using higher quality components, such as Category 6 components, or reducing the channel length, but in practice this can be cumbersome to calculate. Therefore, this type of cabling is only really suitable for application-specific infrastructures in production facilities. It is not appropriate for communication lines between machines and production systems.

Also, it is important to note that Cat6_A is not the same as Cat6_A. Different standards exist to implement a channel for 10 Gb/s Ethernet. The American Telecommunications Industry Association (TIA) 568B standard describes a Cat6_A channel that is achieved with category Cat6_A components. Cable configurations according to Cat6 should still be used if at all possible.

Figure 2. Lower signal clearances for Gigabit Ethernet with Pulse Amplitude Modulation (PAM) increase
the danger of disturbances when compared to Fast Ethernet with Multi Link Trunk (MLT).

Because Cat6 is defined only up to 250 MHz, only a reduced transmission-related quality is defined for the frequency range from 250 to 500 MHz (Fig. 3). The incorrect interpretation of a signal occurs far more frequently. This means that it is necessary to repeat the Ethernet packet. Office applications can tolerate this, since the only effect is slower data transmission. However, this is not acceptable in the industrial area, with its real-time requirements. Each signal must be reliably transmitted to avoid having to repeat packets. As a consequence, designing a channel according to standard TIA 568B is insufficient for the industrial environment.

Standard ISO/IEC TR24750 shows how an existing network can be qualified for 10 Gb/s Ethernet. This standard can be used for existing cable sections where measurements can prove that it is suitable for 10 Gb/s Ethernet transmission. This can often be achieved with good Cat6 components, careful cable routing, and short channel lengths. However, it is not possible to configure new channel types. Several components on the market, with attributes such as "suitable for 10 Gb/s Ethernet," refer to the standard, but they are not Cat6 or Cat6_A components.

An additional standard to consider is ISO/IEC 11801. Amendment 1 defines the requirements placed on a channel. Class EA is specified for 1 to 500 MHz without reducing the quality (Fig. 3). This avoids the risk of a high-frequency signal transmission error and the resulting repetition of the Ethernet frame packet. Real-time systems, as well as systems with a high data rate, can also be reliably configured. Amendment 2 describes the requirements of Cat6_A components used in the Class EA channel.

Figure 3. The TIA and IEC committees assume different NEXT values
(near end crosstalk) across the frequency range.

The planned configuration of a new channel - without incurring the risk of a data transmission error - is possible only when Cat6_A components are used. Only this channel (signified by the "A" as subscript) permits reliable data transmission in the industrial environment, with its wide range of disturbance sources.

Cabling Standards

The communication-related infrastructure of buildings, with their ISDN telephone communication and Ethernet applications, is based on generic cabling. ISO/IEC 11801 describes the structure and quality of the components.

ISO/IEC 24702 is a supplemental standard for industrial buildings. It considers the specific conditions, such as temperature and the environment, which can affect an industrial application.

Cat, Channel, and Class

Under the ISO/IEC 11801 and 24702 standards, the channel includes all of the cabling between two active devices. The various quality stages are designated with the Class and the associated component qualities with the Cat. The table shows these interrelationships and, therefore, the maximum number of possible Ethernet versions.

Table 1.

Standard Cable Cross Section

The voltage differences between signals for 1 Gb/s and 10 Gb/s Ethernet are minimal, according to IEEE 802.3, and even slight disturbances can reduce the information content (Fig. 2). IEEE assumes disturbances that are applicable for the office environment. Disturbances in an industrial environment are generally more extreme and demand the appropriate protective measures.

Figure 4. Low NEXT values increase the level of disturbance coupled in
from adjacent pairs, and are added to external disturbances.

This means that shielded components, which correspond to standard Cat6_A, are that much more important. The coupling attenuation (a measure of the shield quality) should reach 80 dB. This results in a rating of separating class d according to EN 50174-2, which allows communication cables to be routed with almost no clearance to power cables (Fig. 4).

For generic cabling with its reference implementation, a channel length of 100 meters is achieved with a rigid system of horizontal and patch cables. In the industrial environment, for the various subsections, cables with varying quality and cross sections are used. The reference implementation model is not sufficient here. Using the appropriate formulas, a check must be made as to whether the transmission section maintains the values required for the channel. This method is complex and inflexible. If this method is not to be applied, then a horizontal cable with AWG 24 must be routed in the complete channel.

These considerations apply only up to 20 degrees Celsius. Higher temperatures - typical for industrial applications - can also be taken into consideration from a theoretical perspective. As a consequence, the user can calculate a channel with several subsections with different temperature profiles. This calculation is not required if a cross section of AWG 22 is used throughout the system being considered.

Plug Connectors Must Remain User-Friendly

The plug connectors are just as important as the cables. Cables with cross sections of AWG 24 or AWG 22 require special versions. Cables sold by the meter are generally used in industry. This requires simple connection of plug connectors without the use of special tools. Cables must be routed so that the data transmission quality is automatically maintained. Quick connection technologies (such as Phoenix Contact's Quickon and Piercecon) allow a high-quality connection in compliance with the requirements of Cat6_A. The assembly of plug connectors in the field, generally used in industry, is therefore now also possible for 10 Gb/s Ethernet. This means it is no longer necessary to rethink planning and installation - a decisive advantage.

Plug connectors can be roughly classified according to their use in the control cabinet or in the field. In the first case, the usual RJ45 mating face can be used up to Cat6_A. An especially good 360-degree shielding is necessary to minimize the EMC effects of neighboring devices, such as frequency converters. High-quality surfaces will prevent gases from causing contact corrosion, thereby preventing a creeping aging process, which can result in the connection failing due to higher transition resistances. Over the long term, the usual patch cables from the office environment do not fulfill the reliability requirements that industrial applications call for.

For use in the field, RJ45 plug connectors with a special protective housing and M12 plug connectors have established themselves on the market. Also in this case, Cat6_A is already possible with the new M12 plug connectors, according to IEC 61076-2-109 (International Electrotechnical Commission). The same is true for RJ45 connectors.

Sophisticated and demanding tasks that require the extended use of automation technology can now use cabling solutions that are fit for the future. 10 Gb/s Ethernet can be transmitted via a class EA channel in line with industrial requirements using Cat6_A components. With well-designed, industrial-grade components, planning and installation can become routine.