ProfiNet IRT

PROFINET IO IRT (Isochronous Real Time) is a type of clocked commu­nication that is optimized for maximum performance. It is often used for motion control applications.

ProfiNet IRT

STANDARDS BODY, TITAN AND PHILOSOPHY

PROFINET (“Process Field Network”) is differentiated into different performance classes to address various timing requirements: PROFINET RT for soft real-time, or no real-time requirements at all, and PROFINET IRT for hard real-time performance. The technology was developed by Siemens and the member companies of the PROFIBUS user organization, PNO. The Ethernet-based successor to PROFIBUS DP, PROFINET I/O specifies all data transfer between I/O controllers as well as the parameterization, diagnostics, and layout of a network.

ARCHITECTURAL PHILOSOPHY: OPEN SOFTWARE/MODIFIED ETHERNET

In order to cover the different performance classes, PROFINET makes free use of the producer/consumer principle and resorts to various protocols and services. High-priority payload data sent directly via the Ethernet protocol travels in Ethernet frames with VLAN prioritization, whereas diagnostics and configuration data, for instance, is sent using UDP/IP. That enables the system to achieve cycle times of around 10ms for I/O applications.

Clock-synchronized cycle times below one millisecond, as required for motion control applications, are provided by PROFINET IRT, which implements a time multiplex mode based on specially managed, hardware-synchronized switches. So-called dynamic frame packing (DFP) will in the future give users a new PROFINET variant designed to optimize cycle times, making use of the summation frame principle for a certain set of devices in the network.

PROFINET IRT for hard real-time also uses a time slot mechanism. Accordingly, a certain bandwidth is reserved for the real-time data traffic (IRT = isochronous real time), and the remaining bandwidth is available for asynchronous communication. The stations are interfaced via special switches integrated into the field devices rather than by standard Ethernet switches. These special integrated switches comprise a special ASIC controlling two or four ports at a data rate of 100Mbps.

PROFINET is widely used industrial Ethernet by Siemens and GE, and since it is embedded in their controllers and equipment, the market share is slightly inflated. Not many drive vendors support PROFINET IRT so it has not been broadly adopted by machine builders outside of Siemens and GE.

Talk to us. We speak industrial data communications.

---