Friday, November 24, 2017

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PROFInet

PROFInet is a comprehensive automation concept that has emerged as a result of the trend in automation technology towards modular, reusable machines and plants with distributed intelligence. With its comprehensive design (uniform model for engineering, runtime and migration architecture to other communication systems, such as PROFIBUS and OPC) PROFInet fulfills all the key demands of automation technology for
  • consistent communications from field level to corporate management level using Ethernet,
  • a vendor-independent plantwide engineering model for the entire automation landscape,
  • openness to other systems,
  • implementation of IT standards and
  • integration capability of PROFIBUS segments without the need to change them.

PROFInet is available as a specification and as an operating system-independent source software. The specification describes all aspects of PROFInet: the object and component model, the runtime communication, the proxy concept and the engineering. PROFInet software covers all runtime communications. This combination of specification and software as source code enables simple and efficient integration of PROFInet in the broadest range of device operating system environments. The chosen path of preparing a source software upon which all product implementations are built presents an outstanding opportunity to ensure the consistent quality of the PROFInet interface in products. The procedure ensures that any interoperability problems are reduced to a minimum.

 

10.1 The PROFInet Engineering Model

A vendor-independent engineering concept has been defined to enable user-friendly configuration of a PROFInet system. It is based on an engineering object model which enables the development of configuration tools as well as the specification of manufacturer/ customized functional expansions.

Creation and interconnection of components

Fig. 34: Creation and interconnection of components


The PROFInet engineering model distinguishes between the programming of the control logics of the individual technological modules and the configuration of the overall plant for an application.

As previously, programming of the individual devices and their configuration and parameterization is carried out by the manufacturer with manufacturer-specific tools. The software created during programming is then encapsulated in the form of a PROFInet component using the component editor interface that is also to be integrated in the tool. The component editor interface generates the component description in the form of an XML file whose configuration and contents are defined in the PROFInet specification.

The plant is configured by interconnecting the PROFInet components to an application using the PROFInet engineering tool (connection editor). To do this, the generated PROFInet components are transferred to the connection editor by importing their XML files and the relationship is established over graphical lines. This allows plantwide combination of distributed applications (of different manufacturers) to an overall application (see Fig. 34). The decisive advantage of this is the fact that the communication no longer needs to be programmed. Instead, the communication relationships between the components are established over lines, called interconnections.

The interconnection information is then downloaded to the device with a simple mouse click. This means that each device knows its communication partners and relationships and the information to be exchanged.

 

PROFInet components

The basic approach of PROFInet is the application of the object model, already tried and tested in the software world, on automation technology. For this purpose, machines, plants and their parts are divided into technological modules, each of which comprises mechanical, electrical/electronical and application software. The functionality of the technological module is encapsulated in PROFInet components, which can be accessed over universally defined "interfaces". The components can be combined over their interfaces according to the modular principle and interconnected to applications.

In this context "components" means an encapsulated, reusable software unit. For the implementation of this component model, PROFInet uses the model most common in the PC world, the Microsoft Component

Object Model (COM), in its expansion for distributed systems (DCOM). In this case, all the objects of a system are equal and, to all outward appearances, identical.

This type of distributed automation system enables the modular design of plants and machines and supports reusability of plant and machine parts.

 

10.2 The PROFInet Communications Model

The PROFInet communications model defines a vendor-independent standard for communication on Ethernet with conventional IT mechanisms (runtime communications). It uses TCP/IP and COM/DCOM, the most common standards of the PC world. It provides direct access from the office world to the automation level and vice versa (vertical integration).

With PROFInet, the DCOM wire protocol, together with the aforementioned standards, defines the data exchange between the components of different manufacturers over Ethernet. Alternatively, there is also an optimized communication mechanism available for application areas with hard real time requirements.

Devices that are operated on Ethernet require the implementation of communication mechanisms in accordance with the PROFInet-standard (see Fig. 35). The connection technology required for the link to Ethernet is available in protection classes IP 20 and IP65/67.

Device structure of PROFInet

Fig. 35: Device structure of PROFInet

 

10.3 The PROFInet Migration Model

The integration of PROFIBUS segments in PROFInet is implemented using proxies (see Fig. 36). These assume a proxy function for all the devices connected to PROFIBUS. This means that when rebuilding or expanding plants, the entire spectrum of PROFIBUS devices, including products of PROFIdrive and PROFIsafe can be implemented unchanged, thus providing users with maximum investment protection. Proxy technology also allows integration of other fieldbus systems.

PROFInet migration modelFig. 36: PROFInet migration model


10.4 XML

XML (EXtensible Markup Language) is a flexible data description language based on a simple ASCII code. XML documents can be exchanged with applications in a number of ways, for example on diskette, by e-mail, using TCP/IP or with HTTP over the Internet.

XML is important in automation technology for, among other things, parameter descriptions in FDT, as import and export format for field device parameters in engineering tools or as a means of vertical integration (data exchange independent of the operating system used).

 

10.5 OPC and OPC DX

OPC is a standard interface introduced in 1996 for access to Windows-based applications in automation. The implementation of OPC enables the flexible, manufacturer-independent selection of components and their interconnection without the need for programming. OPC is currently based on the Microsoft DCOM model.

Since 2000, OPC data and OPC services are mapped in XML, which means that OPC data can even be exchanged between non-Windows platforms by means of readable XML documents.

OPC DX (Data EXchange) is being developed within the framework of the OPC Foundation with the goal of developing a protocol for the exchange of non-time-critical user data between automation systems of different manufacturers and types (PLC, DCS, PC).

OPC DX is based on the existing specification OPC DA (Data Access). At the same time an engineering interface has been defined, which enables configuration of the connected systems. In contrast to PROFInet, OPC DX is not object-orientated, but tag-orientated, i.e. the automation objects do not exist as COM objects but as (tag) names.

OPC DX will enable the connection of different automation systems in a plant at the Ethernet level. However, it is not possible to access field level, so that existing fieldbus systems and PROFInet are not influenced in any way.

Go back to the header article PROFIBUS Technology and Application


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