Rugged fieldbus modules with IRT for time-critical tasks

Profinet is a popular fieldbus system that is now open for even more applications thanks to the integration of IRT Isochronous Real-Time) for time-critical applications. With the MVK Metal fieldbus modules, Murrelektronik offers new components that not only meet the conformance class C requirements, but can even be used in demanding industrial environments because they are very rugged.

Profinet is a comprehensive fieldbus system with a large number of functions and options. However, not all applications require all functions and maximum speed. Therefore, the PNO defined three conformance classes, A, B and C, that include the minimum requirements according to plant operators.

Conformance Class A (CC-A) is designed to use the infrastructure of an existing network and includes basic Profinet functions such as real-time communication (with cycle times from 2ms) as well as alarm and diagnostic functions. In this class, it is possible to use unmanaged switches and wireless communication without any problems. Murrelektronik's fieldbus modules meet all the requirements to use in this class. Murrelektronik's unmanaged TREE switches are also suitable.

Next, the concept for Conformance Class B (CC-B) includes network diagnostics and collecting information with the topology. All configured devices are assigned names. That way, defective devices can easily be changed with a new device that may even have factory settings. The configuration data stored in the control will automatically be used. Cycle times starting from 2ms are typical for installations based on Conformance Class B. Murrelektronik's MVK Metal MPNIO fieldbus modules meet the requirements of this class. The unmanaged TREE switches are also transparent for the information of the LLDP protocol. If switches are to be included in the topology of the control - regarding diagnostics and topology recognition - it is necessary to use Profinet-managed switches. A Media Redundancy Protocol (MRP) can be included to increase data security. This protocol is integrated in the MVK Metal MPNIO from software version 3.5.

Highly precise and synchronous data transfer is also possible in applications according to Conformance Class C (CC-C). When implementing Isochronous Real Time (IRT) in Ethernet controllers, it is possible to reach update times of 250us and a jitter accuracy (time offset) of less than 1us. This requires a special IRT chipset in the Ethernet Switch in the Profinet device. With Dynamic Frame Packing (DFP) technology, the cycle times can be reduced from 250s to 31.25us - which is exactly one-eighth of the time. An IRT network with this highly precise cycle accuracy requires that all devices are equipped with an IRT Ethernet chipset. If a standard Ethernet chipset is used, synchronicity would get lost. Another advantage of IRT Ethernet chipsets is that they keep the packet switching time short. It does not wait for the whole frame to be received, as opposed to the technology known from CC-A and CC-B. The complete data packet is instead directly routed to the output port already after the first bytes (including the MAC address) have been verified. This considerably reduces the latency, especially of big packets (1500 bytes). This is the reason why it is preferable to use cut-through Ethernet switches that enable this fast data flow in big industrial plants where often 20 up to 80 Profinet devices are installed in one segment.

MVK Metal series fieldbus modules with IRT

With the new fieldbus module MVK Metal Push-Pull Profinet IRT, Murrelektronik presents a digital I/O fieldbus device with IRT function that is suitable for Conformance Class C applications. These devices support fast forwarding and real-time data transfer according to Profinet specification 2.3. Profinet push-pull connectors with RJ45 copper, according to the AIDA standard, or SC-RJ-POF connectors are suitable to connect the modules. This makes the MVK Metal Push-Pull Profinet IRT excellent for all applications with real-time sensors, and for integrating motion drives. This fieldbus module is designed for consistent Profinet systems, especially in 'fast' areas.

The mechanical features of the fieldbus module make it capable of withstanding harsh industrial environments. It has a one-piece zinc die-cast housing with surface finishing and is vibration-resistant (vibration 15 'g' and shock 60 'g'). The push-pull connection technology enables fast installation of power and data cables without requiring tools. The module's inputs and outputs are galvanically separated. The integrated Fast Start Up function (FSU) allows the shortest tool changing times - a top feature for robot applications. The outputs can supply 2A, which makes it possible to connect even powerful loads, for example solenoid valves.

Follow the link for more information about the new MVK Metal series fieldbus modules with IRT from Murrelektronik.