Profinet gains another major PLC supporter
05 September 2009
It’s not hard to see why there is such a strong trend toward adopting Ethernet-based systems for virtually every type of data communication installation, including those associated with industrial automation.
Omron Electronics has launched two Profinet products. One module (PNT21, left in photo) is for the CJ1 programmable controller, which is Omron’s main PLC range. Setup and monitoring is supported using FDT configuration tools. Right: Omron’s SmartSlic
—Opinion by Karl Walker, Marketing Manager, Automation, Omron Electronics Ltd.
It’s important to remember, however, that Ethernet was originally developed for office-type applications where, in particular, timing was not critical. This is clearly not the case in automation, where virtually instant response is needed to inputs such as the sensing of objects.
For this reason, various types of ‘industrial Ethernet’ protocols have been developed. One of these is Profinet, which is already gathering so much support that, in Europe at least, it looks set to become a de-facto standard. Several leading European manufacturers are enthusiastic proponents of Profinet, and they have now been joined by Omron.
Unlike some other industrial Ethernet systems, Profinet-IO can share the network infrastructure with other Ethernet communications.
This means, for example, that the same network can be used for plant I/O connections and for transferring data and files between PLCs or between PLCs and the site computer. In many applications, this leads to big savings on network cabling and network components such as switches and routers.
Profinet-IO has been designed to give dependable real time operation, even with shared infrastructure. The fast cyclic I/O data bypasses the conventional TCP/IP layers, and priority flags in the Ethernet frame ensure that I/O messages can jump queues in network switches.
A particular benefit of the Omron implementation of Profinet-IO is that the SmartSlice remote I/O stations incorporate integral Ethernet switches. This makes it possible to implement field wiring systems that use a conventional linear fieldbus topology, rather than the star and tree topologies more usually associated with Ethernet, without having to install additional hardware switches to interconnect devices.
Profinet-IO is in itself inherently reliable. However, for critical applications reliability can be further enhanced by closing the line structure of the network to form a ring. When this is done, a failure or malfunction in any one of the connected devices will leave communication with other devices on the network unaffected. The MRP (media redundancy protocol) specified by Profinet-IO assures much faster recovery than traditional ring protocols.
Omron builds the MRP client function into the SmartSlice communication interface as standard. Creating a highly secure ring topology requires the addition of only one extra device—an Ethernet switch acting as MRP manager – to the network. The manager collects status data from all clients and, in the case of a media failure, activates the alternative communication path.
The ancestral links
Profinet also benefits from its ancestral links to Profibus-DP, Europe’s most widely used non-Ethernet fieldbus system. Because of this heritage, Profinet can be configured in a very similar way to Profibus-DP. For the many existing Profibus-DP users, the transition to an Ethernet-based system is, therefore, no more than a small step.
As the basis for the software tools for Profinet-IO, Omron uses its established FDT (Field Device Tool) network-independent framework. This framework works in conjunction with Device Type Manager (DTM) plug-ins that are produced by field device vendors to characterise the functions of their devices.
These DTMs give the user the same GUI for a device, irrespective of the type of network in use. This means, for example, that the configuration of a SmartSlice I/O station on Profinet-IO is virtually identical to the existing plug-in for Profibus-DP.
This approach eliminates the need to learn how to use new software tools when changing bus systems, while allowing full access to the specific features of each vendor’s devices. Of course, conventional text-based GSD (ML) files are also supported for the set up of third-party devices.
Recent market figures show that the number of Profinet-IO nodes currently installed is already over one million. This may be fewer than some of the longer established fieldbus systems, but the growth rate of Profinet-IO is far higher. In fact, it is expected that the installed base will reach the same level as Profibus (20+ million nodes) in less than five years.
There is no doubt that Ethernet is fast becoming the dominant force in every area of data communication, and that the industrial applications of Ethernet are gradually taking the place of conventional fieldbus systems in the automation sector.
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