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PROFIBUS at a Glance

PROFIBUS is an open, digital communication system with a wide range of applications, particularly in the fields of factory and process automation. PROFIBUS is suitable for both fast, time-critical applications and complex communication tasks.

PROFIBUS communication is anchored in the international standards IEC 61158 and IEC 61784. The application and engineering aspects are specified in the generally available guidelines of the PROFIBUS User Organization. This fulfills user demand for manufacturer independence and openness and ensures communication between devices of various manufacturers.

2.1 History

The history of PROFIBUS goes back to an association venture project supported by the public authorities, which began in 1987 in Germany. Within the framework of this venture, 21 companies and institutes joined forces and created a strategic fieldbus project. The goal was the realization and establishment of a bit-serial fieldbus, the basic requirement of which was the standardization of the field device interface. For this purpose, the relevant member companies of the ZVEI (Central Association for the Electrical Industry) agreed to support a mutual technical concept for factory and process automation.

A first step saw the specification of the complex communications protocol PROFIBUS FMS (Fieldbus Message Specification), which was tailored to demanding communication tasks. A further step in 1993 saw completion of the specification for the more simply configured and faster PROFIBUS DP protocol (Decentralized Periphery). This protocol is now available in three functionally scaleable versions DPV0, DP-V1 and DP-V2.


2.2 Market Position

Building on these two communications protocols, coupled with the development of numerous application-oriented profiles and a fast growing number of devices, PROFIBUS began ist advance, initially in factory automation and, since 1995, in process automation. Today, PROFIBUS is the fieldbus world market leader with more than a 20% share of the market, approx. 500,000 equipped applications and more than 5 million nodes. Today, there are more than 2000 PROFIBUS products available from a wide range of manufacturers.


2.3 Organization

The success of PROFIBUS stems in equal measures from its progressive technology and the success of its non-commercial PROFIBUS User Organisation e.V. (PNO), the trade body of manufacturers and users founded in 1989. Together with the 22 other regional PROFIBUS associations in countries around the world, and the international umbrella organization PROFIBUS International (PI) founded in 1995, this organization now boasts more than 1,100 members worldwide. Objectives are the continuous further development of PROFIBUS technology and increased acceptance worldwide.

As well as sponsoring the wide range development of technology and its acceptance, PI also undertakes additional tasks for the worldwide support of members (users and manufacturer) with advice, information and procedures for quality assurance as well as the standardization of technology in international standards.

PI forms the largest fieldbus user association in the world. This represents future opportunities and responsibility in equal measure, opportunity to continue creating and establishing leading technologies that are useful to users and responsibility for those at the head of these user associations to be unwavering in their endeavors to target openness and investment protection for PROFIBUS in the future. This commitment (see introduction) serves as the guiding principle for all concerned.

Technical system structure PROFIBUS

Figure 3: Technical System Structure of PROFIBUS

2.4 The PROFIBUS “Tool Box”

PROFIBUS has a modular design and offers a range of communication technologies, numerous application and system profiles, as well as device management tools. Thus PROFIBUS covers the diverse and application-specific demands from the field of factory and process automation. The number of installed PROFIBUS plants are proof of the high acceptance of this fieldbus technology.

From the technological standpoint the lower level (communications) of the system structure of PROFIBUS (see Fig. 3) is based on the aforementioned ISO/OSI reference model. This intentionally gave an abstract description of the communication steps without providing details of content/practical implementation. Fig. 3 contains the implementation of the OSI model (layers 1, 2 and 7) in PROFIBUS with details on how the layers are individually implemented/specified.

Specifications agreed between manufacturers and users on specific device applications are arranged above layer 7 in application profiles I and II.

Across several layers, the modular system as shown in Fig. 3 has the following:

  • Functions and tools for device description and integration (umbrella term: Integration Technologies, see Chapter 7) and
  • A range of standards (interfaces, master profiles; umbrella term: system profiles) that primarily serve the realization of uniform, standardized systems, see Chapter 6.

 

From the user standpoint PROFIBUS presents itself in the form of different typical-application main emphases that are not specifically defined but have proven useful as a result of frequent applications. Each main emphasis results from a typical (but not specifically defined) combination of modular elements from the groups "transmission technology", "communications protocol" and "application profiles". The following examples explain this principle using the best known PROFIBUS versions (Fig. 4).

PROFIBUS DP is the main emphasis for factory automation; it uses RS485 transmission technology, one of the DP communications protocol versions and one or more application profile(s) typical of factory automation, such as Ident Systems or Robots/NC.

PROFIBUS PA is the main emphasis for process automation, typically with MBP-IS transmission technology, the communications protocol version DP-V1 and the application profile PA Devices.

Motion Control with PROFIBUS is the main emphasis for drive technology using RS485 transmission technology, the communications protocol version DPV2 and the application profile PROFIdrive.

PROFIsafe is the main emphasis for safety-relevant applications (universal use for allmost all industries), using RS485 or MBP-IS transmission technology, one of the available DP versions for communication and the application profile PROFIsafe.

2.4.1 Transmission Technologies

There is a whole range of transmission technologies available for PROFIBUS.

RS485 is the most commonly used transmission technology. It uses a shielded twisted pair cable and enables transmission rates up to 12 Mbit/sec.

The newly specified version RS485-IS has been recently specified as a 4-wire medium in protection type EEx-i for use in potentially explosive areas. The specified levels of voltage and current refer to the safety-relevant maximum values that must not be exceeded in either individual devices or during interconnection in the system. In contrast to the FISCO model (see Chapter 3.1.2), which only has one intrinsically safe source, in this case all stations represent active sources.

The MBP transmission technology (Manchester Coded, Bus Powered, previous designation "IEC 1158-2 -

Physics", see Chapter 3.1) is available for applications in process automation with a demand for bus powering and intrinsic safety of devices. Compared to the previously used procedure, the "Fieldbus Intrinsically Safe Concept“ (FISCO, see Chapter 3.1.2), which was specially developed for interconnection of intrinsically safe fieldbus devices, considerably simplifies planning and installation.

Fiber-optic transmission is suitable for use in areas with high electromagnetic interference or where greater network distances are required (see chapter 3.1.3).

2.4.2 Communication Protocols

At the protocol level, PROFIBUS with DP and its versions DP-V0 to DP-V2 offers a broad spectrum of options, which enable optimum communication between different applications. Historically speaking, FMS was the first PROFIBUS communications protocol.

FMS (Fieldbus Message Specification) is designed for communication at the cell level, where programmable controllers, such as PLCs and PCs primarily communicate with each other. It was the forerunner of PROFIBUS DP.

DP (Decentralized Periphery) is the simple, fast, cyclic and deterministic process data exchange between a bus master and the assigned slave devices. The original version, designated DP-V0, has been expanded to include version DP-V1, offering acyclic data exchange between master and slave. A further version DP-V2 is also available, which provides for direct slave-to-slave communication with an isochronous bus cycle.

The Bus Access Protocol, layer 2 or the data-link layer, defines the master-slave procedure and the token passing procedure for coordination of several masters on the bus (Fig. 5). The tasks of layer 2 also include functions, such as data security and the handling of data frames.

The Application Layer, Layer 7, defines the application layer and forms the interface to the application program. It offers various services for cyclic and acyclic data exchange.

Technical system structure PROFIBUS

Figure 4: Technical system structure PROFIBUS

2.4.3 Profiles

Profiles are the specifications defined by manufacturers and users regarding specific properties, performance features and behavior of devices and systems. Profile specifications define the parameters and behavior of devices and systems that belong to a profile family built around to profile-conformance development, which facilitate device interoperability and, in some instances, device interchangeability on a bus. Profiles take into account application and type-specific special features of field devices, controls and methods of integration (engineering). The term profile ranges from just a few specifications for a specific device class through comprehensive specifications for applications in a specific industry. The generic term used for all profiles is application profiles.

A distinction is then drawn between general application profiles with implementation options for different applications (this includes, for example, the profiles PROFIsafe, Redundancy and Time Stamp), specific application profiles, which are developed for a specific application, such as PROFIdrive, SEMI or PA Devices, and system and master profiles, which describe specific system performance that is available to field devices.

PROFIBUS offers a wide range of such application profiles, which allow application-oriented implementation.

2.5 PROFIBUS - The keys to success

The success of PROFIBUS, its world market leadership is determined by many factors:

  • PROFIBUS offers plant manufacturers and operators an industry-wide, universal, open technology.
  • PROFIBUS is a key factor in noticeably reducing costs in the field of machine and plant engineering.
  • PROFIBUS has consistently and logically expanded its application area while taking into account the demands of the respective application fields. This ensures optimum support of industry-specific applications.
  • PROFIBUS means optimum integration in many automation and engineering systems for users due to its overall acceptance and widespread use.
  • PROFIBUS has pursued the stabilization and broad acceptance of communication platforms, the further development of application profiles and the connection of industrial automation to the IT world of corporate management.

PROFIBUS configuration with active masters and slaves

Figure 5: PROFIBUS configuration with active masters and slaves

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