What are the Benefits of Ethernet for Industrial Users?

The initial push towards Industrial Ethernet was motivated by two factors: for one, increasing the performance of distributed automation control systems on the network, and secondly, to achieve greater cost efficiency by integrating office hardware in these systems. Although this sparked a veritable Ethernet euphoria, the main thrust quickly departed from the original objective of distributed automation. The focus was now set on aspects such as a universal protocol, shared both by automation and office applications. In theory, this universality seemed to be an impressive, simple form of vertical integration. Ethernet TCP/IP was aggressively advanced as sole standard in communication applications. In the process, the fact was disregarded that countless application profiles were developed for field bus automation systems. In the meantime, these represent the actual value of the field bus system. The large number of application profiles should be maintained to the benefit of users.

The importance of vertical integration has over long been accepted. This includes the integration of all information acquired from field level into the office networks, with the focus set on the optimized control of production, preventive maintenance, easy global networking, etc. This state-of-the-art integration may also be implemented on field level, on the basis of field bus systems with gateways / proxies, and independent on Ethernet.

The result of an analysis of the motivation for using Ethernet in machines shows that users expect two core benefits:

• Existing field bus systems have by now reached a complexity which requires an increase in the bandwidth of communication systems. Ethernet may form a future-proof basis for expected increases in performance.

• Specialized network systems cover specialized tasks. This requires adequate user competence in handling numerous networks and functions: automation, vertical communication, image processing, drive control, and safety.

A universal field bus system which can be represented by Ethernet also is considered an appropriate means in meeting the most extensive level of convergence.

Demands of automation systems on networks

Regarding the world of manufacturing from the viewpoint of the IT department, we can see that the factory contains terminals which are connected to a central IT system. Machines are handled as PC workstations, with each one being assigned to a TO(= Telecommunication Outlet), in compliance with international standards for application-independent structured cabling to ISO/IEC 11801. Compared to the office, the requirements of automation technology do not allow the unmodified integration of machines into existing office networks.

The following core requirements in industry have been identified:

• Permanent availability of the network on a time scale < 10 ms

• Network areas secured by means of suitable devices (security, safety)

• Creation of physical subnet within individual machines

• Installation of diverse topologies (line, ring, for example) / flexible cascading options

• Definition of real-time areas (ms and μs ranges)

• Alternative and combined use of different transfer media (fiber optic cable, copper cable, wireless)

• Direct connection of two IP67 devices (transfer segments without patch cables)

• Transfer segments with different media (for cable carriers, for example) and a large number of connectors

Where the office network is only used for integrated communication, rather than for control tasks within the plant or machine, the situation is the same as in a field bus subsystem which controls all vital parameters of the process. The integration of data required for production control is implemented via network node. This integration of the machines can be implemented via the standard office network, and takes place in current systems at a layer above the field bus subsystem in a separate network infrastructure.

How office networks can now be used

An obvious approach is the physical separation by forming two network hierarchies:

• Industrial building networking: networking of the plant building for bidirectional, vertical integration of production data.

• Unit networking: networking within a unit for the purpose of process control.

The separation of these two networking applications as such does not fully solve the problem of heterogeneous networks from the user perspective, but nevertheless represents starting point to solutions providing an expedient application-specific structure.

Industrial building networking

By comparison with the office world, industrial buildings differ in terms of their ambient conditions. The differences may seem less weighty as long as the new factory floor does not yet contain any machinery. The aim is also to create an infrastructure which is optimally suited to meet future requirements of the shop floor. This requires a global pre-wired system which is suitable for all applications.

Production cell networking

In contrast to the office network, an automation network does not consist of identical units, but rather of diverse devices which are distributed within the plant according to their application. There, the switch cabinet of a tooling machine may accommodate up to ten nodes on a single square meter, in contrast to only one node on an area of 100 m2 in a sewage plant, for example. This requires a certain flexibility of the network, and the topology must be adapted to the relevant application. In addition to the line, star and ring topologies, complex tree structures are also implemented in these areas. Automation applications require a cascading depth of 20 nodes (layers) or more, as are usual in a line topology. Such conditions are not encountered in the three layer model of the office building.

Which topology needed for cell structures?

A production unit in the automation system requires structures with a significantly higher flexibility and complexity, rather than the rigid, horizontal hierarchy model to ISO/IEC 11801.

The integrated network called for in office networking combines with the demand for a uniform, repetitive application for the computer connections.

By contrast, industrial applications have good reason to set the focus on topologies deviating from the horizontal hierarchy. Reduced wiring effort, for example, forms a vital criterion in the user‘s assessment. The decisive factor is not the aspect of saving cable material, but rather the reduced space requirements in the switch cabinet. The benefits of an increase in installation space by discarding the installation of large cable ducts are apparent.

This result is guaranteed by the interconnection all network nodes with a central switch that supports the connection to 24 V power supply units and to 400 Volt mains. A layout consisting of several hierarchy layers also supports an electrical segmentation, resulting in autarchic distributed units which remain operational in the event of disturbances and failures.

Such a structure allows the conversion and expansion of the installation in one plant section, while the other section continues production. In this way the installation reflects the automation topology.

The modular layout of automation units has become widely accepted. Various function groups are merged to form complex plants. This trend continues within stand-alone machines. Here too, users benefit from the cost-effective and efficient implementation of a modular structure of high granularity. Expansions are possible by simply adding on modules. This aspect is of particular importance in the assembly area, for example, in the automotive industry, in view of the necessary, continuous adaptation of the infrastructure to plant requirements due to the production of new models.

Demands made on industrial network components

The demands made on network components are structured according to function and mechanical design. As office components are not able to cope with the mechanical conditions of an industrial environment, network components must be adapted to withstand tough ambient conditions. This also involves the adaptation of connectors and housings, and their combination with the functionality of network components which are suitable for industrial utilization.

Industrial networks can only be operated if they are safely isolated from the office network. Such separate networks, and also networks of the same type, always require the implementation of defined gateways or network nodes.

In this way, the user can easily integrate a new machine into the network system by cascading the various machine modules and creating more than ten additional layers in the hierarchy. However, network management may argue that such actions require the integration of ten distributed switches, in addition to the master switch, the assignment of corresponding IP addresses, and the local replacement of faulty switches.

However, troubleshooting network problems definitely requires a local unit diagnosis. Although manageable SNMP-compatible switches would support such operations using a central network utility, maintenance staff usually does not consider this an acceptable approach. Industrial users therefore demand extended diagnostics capabilities.

How to handle highly complex applications in the field of cell networking

Practical experience would suggest orienting the selection of network components to specific applications, rather than to the complex parameter configuration of universal network components. This calls for the definition of typical applications in unit networking.

Network components contain a pre-selection of parameters that are optimally attuned to application requirements. These parameters cannot only be requested from network diagnostics or web-based management, but may also be read locally at the device. In this way users are assured of the integration of basic functionalities in the operation of a given machine.

International standardization aspects with regard to the existence of two networks

If networks are expediently structured from the viewpoint of industrial buildings and also that of automation units, the current standardization topics can be easily assigned accordingly. IEC 11801 represents the international standard for application-independent, structured IT wiring. The high level of acceptance of this standard is based, for one, on the three networking levels (primary, secondary, tertiary), and secondly on its application-independent approach which has enabled communication of diverse services on the network. In practical applications, this has evolved into a „quasi standard“ in communications. Ethernet is now deployed in over 90 % of the LAN topologies.

Transferring this standard to the conditions of an industrial environment yields a standard for industrial buildings. This process was already initiated in the year 1999 by German standardization institutes. A draft dealing with industrial wiring will be available shortly under ISO/IEC 24702.

ISO/IEC 24702 sets the focus on networks in industrial buildings, rather than on unit networking. This subnet is part of the building and supports vertical integration within this building. The production units contain autarkic areas which are individually adapted to the production process. These areas cannot be forced into the rigid structure of a building network. Consequently, the various field bus organizations have developed their own directives which usually preserve he installation character of field bus. An international standardization is developing in IEC SC 65 which will produce a standard describing installation within automation units.

These two worlds are merged at the TO. This outlet, referred to as Apparatus Outlet (AO) in the industrial arena, segments the networks.

The existence of these autarkic networks is confirmed within international standardization by the current trends in standardization. Both networks, however, must be interconnected via defined interfaces.

Summary

Users benefit from the targeted deployment of Ethernet in the industrial arena which enables significant innovation gains based on synergies with office technologies. Network convergence is given by the performance and integration of field bus profiles. In this way, Ethernet forms a high-performance field bus system.

In order to make such added value available to industrial users, the focus must be set on defined applications. As a result, only specially developed components can be integrated into applications for a product cell network. Expert IT know-how should not, however, represent the prerequisite for the utilization of such components. At HARTING, this aspect sets the benchmark for the current and future development of new products.