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Industrial Ethernet Book Issue 70 / 39
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A four-pair Profinet cabling solution for extended plant

Dipl. Wirt. Ing. Bernd Horrmeyer of Phoenix Contact says that new challenges in industrial automation technologies are repeatedly demanding new communication solutions. He shows how four-pair Profinet cabling can provide the basis for the latest industrial Ethernet solutions. Using this system, high-performance devices, plus a strong, simple installation technology for industrial environments, can be used with confidence in complete automation systems, he claims.

TODAY, INDUSTRIAL ETHERNET is being very successfully used in the automation environment to establish communications between devices. The new four-pair Profinet cables are now available to address more demanding plant and system concepts and provide a technology that is fit for the future.

Industrial Ethernet has been successfully used in automation technology for about ten years now (Fig. 1). One reason for its success is the high data transfer performance of Ethernet according to IEEE 802.3. Another one is the tough cabling technology specifically designed for industrial applications, which uses know-how gained in the fieldbus area. An important requirement is cabling technology optimised for easy installation on site. The determining features of fieldbuses and industrial Ethernet include the conductor cross-sections, number of conductors and colour coding.


Fig. 1: Company-wide communication. Automation networks are created using two-pair Profinet cables and subordinate fieldbuses, which are linked with the building network.

Data transfer rates increase

As with other Industrial Ethernet systems, Profinet is based on the 100Base-TX standard according to IEEE 802.3 with a data transfer rate of 100 Mbps. Four cores are used, arranged in two pairs or a star quad. Special protocol or hardware extensions, for example Isochronous Real-Time (IRT), have also been implemented in order to facilitate the real-time properties demanded in the automation environment.

This is why there is no reason to use Ethernet with data transfer rates higher than 100 Mbps for this system - in fact, in some cases this might actually prove disadvantageous. For this reason, components according to Cat5 are also defined in Profinet Guideline 2713, including four-core cables and four-pin connectors. These components offer the required technical performance, coupled with simple installation technology, so cost-effective installation, fast commissioning and high reliability in operation can be simply fulfilled (Fig. 2).


Fig. 2: Assembling an industrial RJ45 plug connector. In this simple procedure, prepare the cable and insert the cores (left), cut the cores (centre), close the latch key and snap on the housing (right).

On the other hand, state-of-the-art automation solutions integrate more than just the classic devices. For instance, cameras are employed to inspect quality, servers to document quality data and scanners to identify components. Generally, these devices require higher data transfer rates.

Many systems also need to link automation technology with factory and supervisory control systems to transfer orders and the corresponding processing state. Frequently, data transfer rates of at least 1 Gbps are required.

Here, devices and communication structures cannot be operated separately; instead, they must function logically and physically as integral components of the overall automation solution.

Extending cabling for Profinet

This task cannot be addressed using traditional industrial Ethernet network structures and generic cabling used in the office environment. Profinet does not provide the demanded data transfer rate, and a generic cabling system focuses more on the building infrastructure than on the ability to be flexibly adapted for use in plant and machinery construction. In this case, an additional cabling infrastructure level must be introduced between Profinet and generic cabling (Fig. 3).


Fig. 3: Additional cabling infrastructure level. Four-pair Profinet is installed between two-pair Profinet and the building network to integrate devices that require high data transfer rates.

This level must connect all of the classic networks of an automation solution with one another, integrate additional devices in the automation application, and establish communication to the corporate network.

This model makes it possible to use the usual two-pair Profinet cabling infrastructure while facilitating a professional solution that can address demanding industrial applications.

Given this backdrop, the PNO decided to extend the cabling system for Profinet. The experts therefore had the challenging task of developing a cabling system that, as a minimum, transfers Ethernet according to 1000Base-T with 1 Gbps while being sufficiently rugged for the industrial Environment. In addition to that, the solution had to ensure simple installation.

The result is that the four-pair installation technology is completely compatible with Profinet according to 100Base-T. This has been achieved by applying key two-pair cabling parameters to the four-pair cabling design - for instance, a low delay skew (difference in the signal propagation times) to guarantee IRT real-time data transfer.

Four-pair cables can be used for all applications that relied on two-pair cables up until now. The component design was also adopted so that both of these cabling systems are equally applicable in harsh industrial environments. Cable cross-sections that do away with the tedious calculation of data transfer lengths, colour coding according to the well-established TIA568 standard, as well as harmonised cables and connectors, simplify the work of planners and installation technicians. As a result, more demanding plants and systems can now be seamlessly equipped with Profinet cabling. Depending on the particular part of the plant or system, two- or four-pair cabling can be used in the channel.

RJ45 / M12 plug connectors

What also needs to be ensured is that the plug connectors fulfil the demands relating to the number of pins and the appropriate signal integrity. Today, RJ45 plug connectors are available in versions extending from Cat5 up to Cat6A, which ensures that this technology is fit for the future.

The same does not hold for M12. Four-pin, D-coded M12 plug connectors according to IEC 61076-2-101, which today are used in many automation systems, are only suitable for 100Base-TX as they only have four pins. Eight-pin M12 connectors with X-coding according to IEC 61076-2-109 are suitable for 1000Base-T and 10GBase-T. They comply with Cat6A, therefore also representing a futureproof solution for four-pair Profinet cabling.

In conclusion

The latest automation technologies put pressure to develop suitable communication solutions. Four-pair Profinet cabling can provide stateof- the-art solutions, so high-performance devices can be used in complete automation solutions, and the simple industrial installation technology can be employed.

Based on extensive portfolios of plug connectors and other parts, today's automation solutions and those of tomorrow can be simply planned, installed, and reliably operated.

Bernd Horrmeyer is Industrial Network Cabling Consultant at Phoenix Contact GmbH & Co. KG, Blomberg, Germany.

www.phoenixcontact.com


Source: Industrial Ethernet Book Issue 70 / 39
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