PROFINET

PROFINET is the open industrial Ethernet standard of PROFIBUS&PROFINET International (PI) for automation. PROFINET uses TCP/IP and IT standards, is real-time Ethernet, and allows investment protection through seamless integration of fieldbus systems.

The PROFINET concept features a modular structure so that users can select the cascading functions themselves. They differ essentially because of the type of data exchange to fulfill the partly very high requirements of speed.

In conjunction with PROFINET, the two perspectives PROFINET CBA and PROFINET IO exist.PROFINET CBA is suitable for the component-based communication via TCP/IP and the real-time communication for real-time requirements in modular systems engineering. Both communication options can be used in parallel.

PROFINET IO was developed for real time (RT) and isochronous real time IRT (Isochronous Real Time) communication with the decentral periphery. The designations RT and IRT merely describe the real-time properties for the communication within PROFINET IO.

PROFINET CBA and PROFINET IO can communicate at the same time on the same bus system. They can be operated separately or combined so that a PROFINET IO subsystem appears as a PROFINET CBA system from a system perspective.

Technology

To achieve these functions, three different protocol levels are defined:

* TCP/IP for PROFINET CBA and the commissioning of a plant with reaction times in the range of 100ms
* RT (Real-Time) protocol for PROFINET CBA and PROFINET IO applications up to 10 ms cycle times
* IRT (Isochronous Real-Time) for PROFINET IO applications in drive systems with cycles times of less than 1ms

The PROFINET protocol can be recorded and displayed using any Ethernet analysis tool.In the current version, Wireshark/Ethereal also decodes the PROFINET message frames.

PROFINET component model (PROFINET CBA)

A PROFINET CBA system consists of various automation components. One component covers all mechanical, electrical and IT variables. The component can be generated using the standard programming tools.A component is described using a PROFINET Component Description (PCD) file in XML. A planning tool loads these descriptions and enables the logical interconnections between the individual components to be generated for implementing a plant.

This model was largely inspired by the IEC 61499 standard.

The basic idea of CBA is that an entire automation system can in many cases be divided into autonomously operating subsystems, thereby arranging them very clearly. The design and the functions can actually end up in identical or slightly modified form in several systems. These PROFINET components are usually controlled by manageable number of input signals. Within the component, a control program written by the user executes the required function within the component and passes the corresponding output signals to another controller. The engineering that is associated with it is manufacturer-neutral. The communication of a component-based system is only configured, instead of being programmed. The communication with PROFINET CBA (without real time) is suitable for bus cycle times of approx. 50 ... 100 ms. The parallel running RT channel allows for data cycles similar to PROFINET IO (a few ms).

PROFINET and the decentral periphery (PROFINET IO)

Interfacing the decentral periphery is implemented by PROFINET IO. It defines the communication with decentrally connected peripheral devices. Its basis is a cascading real-time concept. PROFINET IO defines the entire data exchange between controllers (devices with "master functionality") and the devices (devices with "slave functionality"), as well as parameter setting and diagnosis. PROFINET IO is designed for the fast data exchange between Ethernet-based field devices and follows the provider-consumer model. Field devices in a subordinate PROFIBUS line can be integrated in the PROFINET IO system without any effort and seamlessly via an IO-Proxy (representative of a subordinate bus system). A device developer can implement PROFINET IO with any commercially available Ethernet controller. It is well-suited for the data exchange with bus cycle times of a few ms. The configuration of an IO-System has been kept nearly identical to the "look and feel" of PROFIBUS. PROFINET IO always contains the real-time concept.

A PROFINET IO system consists of the following devices:
* IO Controller controls the automation task.
* IO Device is a field device, which is monitored and controlled by an IO Controller. An IO Device comprises several modules and submodules.
* IO Supervisor is an engineering tool typically based on a PC for parameterizing and diagnosing the individual IO Devices.

An Application Relation (AR) is established between an IO Controller and an IO Device. These ARs are used to define Communication Relations (CR) with different characteristics for the transfer of parameters, cyclic exchange of data and handling of alarms.

The characteristics of an IO Device are described by the device manufacturer in a General Station Description (GSD) file. The language used for this purpose is the GSDML (GSD Markup Language) - an XML based language. The GSD file provides an engineering system with a basis for planning the configuration of a PROFINET IO system.

PROFINET and real time

Within PROFINET IO, process data and alarms are always transmitted in real time (RT). Real time in PROFINET is based on the definition of IEEE and IEC, which allow for only a limited time for execution of real-time services within a bus cycle. The RT communication represents the basis for the data exchange for PROFINET IO. Real-time data are treated with a higher priority than TCP(UDP)/IP data. How small this window should be selected is dependent upon the real-time implementations. RT provides the basis for the real-time communication in the area of decentral periphery and for the PROFINET component model (PROFINET CBA). This type of data exchange allows achieving bus cycle times in the range of a few hundred microseconds.

PROFINET and isochronous communication

The isochronous data exchange with PROFINET is defined in the isochronous real-time (IRT) concept. PROFINET IO field devices with IRT functionality have switch ports integrated in the field device. They can be based e. g. on the Ethernet controllers ERTEC 400/200. The data exchange cycles are usually in the range of a few hundred microseconds up to a few milliseconds. The difference to real-time communication is essentially the high degree of determinism, so that the start of a bus cycle is maintained with the highest precision. The start of a bus cycle can deviate up to 1 µs (jitter). IRT is required, for example, for motion control applications (positioning control processes).

Additional highlights of the PROFINET concept:

Engineering: By supporting the Tool Calling Interface, every manufacturer of field devices can latch onto any TCI-capable engineering system and parameterize and diagnose "his" field devices without having to leave the engineering system.

The proximity recognition and device replacement: All PROFINET field devices determine their neighbors. This allows replacing field devices without additional tools and prior knowledge in case of a fault. By reading this information, the system topology can be graphically represented in a very clear way.

Parameter server: Individually set data can be loaded manufacturer-neutral (e.g. via TCI) and automatically archived in a parameter server. Reloading is also done automatically when replacing a device.

Determinism: PROFINET supports the deterministic data traffic, for example, for high-precision control tasks.

Redundancy: The redundancy concept defined in PROFINET significantly increases system availability.

Benefits of PROFINET

Due to the continuous further development of PROFINET, users are provided with a long-term perspective for the implementation of their automation tasks. For system or mechanical engineers, the use of PROFINET minimizes the costs for installation, engineering and startup.

The system operator profits from the simple expandability of the system and high degree of availability from autonomously running subsystems.

Organization

PROFINET is defined by PROFIBUS&PROFINET International (PI) and backed by the INTERBUS Club and, since 2003, is part of the IEC 61158 and IEC 61784 standards.

External links

* [http://www.profinet.com/pi PROFIBUS&PROFINET International (PI)]

Books

* Raimond Pigan, Mark Metter: "Automating with PROFINET", 2nd rev. and enl. edition. 2009, ISBN 978-3-89578-294-7