Four-Pair Solution for the Future: Profinet Cabling for Extended Plant Concepts
Industrial Ethernet is very successfully used in the automation environment to establish communication between devices. Now, technology like the new four-pair Profinet cables can 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 10 years (Figure 1). One reason for its success is the high data transfer performance of Ethernet according to IEEE 802.3. Another factor is rugged cabling technology specifically designed for industrial applications. This leverages know-how gained in the fieldbus area. An important requirement is cabling technology optimized for easy installation on-site. The determining features of fieldbuses and Industrial Ethernet include the conductor cross-sections, number of conductors, and color-coding.
Data Transfer Rates on the Increase
Like other Industrial Ethernet systems, Profinet is based on the 100Base-TX standard according to IEEE 802.3 with a data transfer rate of 100Mb/s. It uses four cores arranged in two pairs or in a star quad. Special protocol or hardware extensions, such as IRT (Isochronous Real-Time), have also been implemented 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 100Mb/s for this system. In fact, in some cases, this might even prove disadvantageous.
For this reason, Profinet Guideline 2713 defines components according to Cat5, including four-core cables and four-pin connectors. These components offer the required technical performance coupled with simple installation technology. Consequently, cost-effective installation, fast commissioning, and high reliability in operation can be simply fulfilled, which is why Profinet has such a good reputation in the automation technology segment (Figure 2).
On the other hand, state-of-the-art automation solutions integrate more than just the classic devices. For instance, industrial facilities employ cameras 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, these applications require data transfer rates of at least 1 Gb/s. Here, devices and communication structures cannot operate separately. Instead, they must function logically and physically as integral components of the overall automation solution.
PNO Extends the Cabling System 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 (Figure 3). 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 employ the usual two-pair Profinet cabling infrastructure while also 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 had the challenging task of developing a cabling system that, at a minimum, transfers Ethernet according to 1000Base-T with 1Gb/s. At the same time, it must be sufficiently rugged for the industrial environment and, on top of that, ensure simple installation. The results are impressive.
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 real-time data transfer (Figure 4, below).
All applications that previously relied on two-pair cables can now use four-pair cables. The rugged component design also ensures 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, color coding according to the well-established TIA568 Standard, and harmonized cables and connectors simplify the work of planners and installation technicians. As a consequence, now more demanding plants and systems can 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 (Figure 5).
Criteria for Selecting Either Two- or Four-Pair Profinet Cabling
RJ45 and M12 Plug Connectors
Also, the plug connectors must fulfill 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. This ensures that this technology is fit for the future. The same does not hold for M12. According to IEC 61076-2-101, the four-pin, D-coded M12 plug connectors currently 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 future-proof solution for four-pair Profinet cabling (Figure 6).
Key Parameters of the Two- and Four-Pair Profinet Cables
New challenges in automation technology demand new communication solutions. Four-pair Profinet cabling provides the basis for state-of-the-art solutions. As a consequence, high-performance devices can be used in complete automation solutions, and the rugged and simple installation technology for industrial environments can be employed. Based on the extensive portfolio of plug connectors and additional components from Phoenix Contact, today’s automation solutions and those of tomorrow can be simply planned and installed as well as reliably operated.
By Bernd Horrmeyer, Industrial Network Cabling Consultant, Phoenix Contact GmbH & Co.
Visit Phoenix Contact online.
Gigabit Ethernet in the Industrial Environment:
IEEE 802.3 defines the electrical characteristics of Gigabit Ethernet. The standard also specifies the signal coding, which is implemented according to PAM 5 and PAM 16 (PAM = Pulse Amplitude Modulation). Contrary to binary signals, where the information is only transferred using the upper and lower voltage levels, with PAM the voltage range from 1V up to +1V is split up into five or 16 levels that carry the information. This means that the voltage difference between two information levels can be as low as 133 mV (Figure 7).
Even the smallest disturbances can induce a voltage that destroys the original signal information. IEEE accounts for standard defined disturbances in the office environment that still allow the correct signal content to be identified. Generally, disturbances in the industrial environment are more significant, and real-time requirements do not allow for repeat transmission of data packages. As a consequence, when transferring Gigabit Ethernet in industrial settings, significantly higher protective measures are required than those defined in IEEE for the office environment. The quality of the components, which must guarantee the lowest possible signal attenuation over the complete frequency range, is crucial here. High-quality shielding is also required to prevent external disturbances from being introduced. This is why it is all the more important to use shielded components and maintain the highest possible system safety margin. The coupling attenuation is a measure of the shield quality, which should reach a value of 80dB. This also ensures that separation class D according to EN 50174-2 is met, allowing for communication cables to be routed directly next to power cables. This is an important criterion where space is restricted and when there are cable bundles, as is common in robot applications. The combination of these measures represents a solid foundation for taking Gigabit Ethernet into the industrial arena.