A field bus is a bus system that connects field devices such as measuring probes ( sensors ) and actuators ( actuators ) in a plant for the purpose of communication with an automation device . If several communication participants send their messages over the same line, it must be specified who (identifier) says what (measured value, command) when (initiative). There are standardized protocols for this .
The first generation of fieldbus technology was developed in the 1980s in order to replace the parallel wiring of binary signals and analog signal transmission with digital transmission technology, which was common up until then . Today there are many different fieldbus systems with different properties established on the market. Fieldbuses have been standardized worldwide in the IEC 61158 standard ( Digital data communication for measurement and control - Fieldbus for use in industrial control systems ) since 1999 . The second generation of fieldbus technology is based on real-time Ethernet .
If the automation is electrical, the question arises as to how the sensors and actuators should be connected to the automation device. Two basic variants are possible:
- A pair of cables is drawn from the automation device to each sensor and actuator (parallel wiring, star topology).
- Only a single pair of cables is drawn from the automation device: The pair of cables is routed to each sensor and actuator (serial wiring, bus topology).
With the increasing degree of automation of a system or machine, the cabling effort increases with parallel wiring due to the larger number of input / output points. This is associated with great effort in planning , installation, commissioning and maintenance.
The demands on the cables are often high, e.g. B. special cables must be used for the transmission of analog values.
The parallel field wiring becomes a serious cost and time factor in automation technology . In comparison to this, the serial networking of the components in the field area using so-called field bus systems is much cheaper.
The fieldbus replaces the parallel bundle of cables with a single bus cable and connects all levels, from the field to the control level. Regardless of the type of automation device, e.g. B. Programmable logic controllers (PLC) from different manufacturers or PC-based controllers, the transmission medium of the fieldbus networks the components in the field.
The advantages of a field bus:
- less cabling saves time in planning and installation
- Cables, distribution boxes and the size of the control cabinet are reduced
- Self-diagnosis by the system possible
- Higher reliability and better availability thanks to short signal paths
- Protection against interference increases, especially with analog values.
- Open fieldbuses standardize data transmission and device connection across manufacturers. Components from different manufacturers are easier to exchange, at least with regard to basic communication.
- Extensions or changes are easy to carry out and guarantee flexibility and thus future security.
- It is not necessary to define measuring ranges for transmitters. The (visual) display scale in the control system can be changed at any time.
The disadvantages of a fieldbus:
- more complex system - more qualified employees necessary
- higher price of components with fieldbus functionality
- complex measuring devices
- slightly longer response time
- The smallest exchangeable unit becomes more expensive.
- Due to the large number of different field buses, sensor / actuator manufacturers are forced to support several field buses, which causes additional costs. In addition, it is very difficult to predict which fieldbuses will gain or lose importance in the future. As a result, there is a risk of bad investments in the development of fieldbus connections.
- Due to the central connection principle, the control system can be cut off from all sensors and actuators in the event of a bus fault. Therefore redundant bus systems may be required.
Fieldbuses for industrial applications have been standardized worldwide in the IEC 61158 standard ( Digital data communication for measurement and control - Fieldbus for use in industrial control systems ) since 1999 . The individual field buses are listed in the IEC 61784-1 standard as Communication Profile Families (CPF). The new real-time capable Ethernet- based fieldbuses are compiled in the IEC 61784-2 standard. Each protocol family can define further fieldbuses. The following protocol families are listed in the standard:
|CPF1||FOUNDATION Fieldbus (FF)|
|CPF1 / 1||FF-H1 (Low Speed)|
|CPF1 / 2||FF-HSE (High Speed Ethernet)|
|CPF1 / 3||FF-H2 (high speed)|
|CPF2||CIP ( Common Industrial Protocol )|
|CPF2 / 1||ControlNet|
|CPF2 / 2||EtherNet / IP|
|CPF2 / 3||DeviceNet|
|CPF3||PROFIBUS and PROFINET|
|CPF3 / 1||PROFIBUS DP|
|CPF3 / 2||PROFIBUS PA|
|CPF3 / 3||PROFINET CBA|
|CPF3 / 4||PROFINET IO Conformance Class A|
|CPF3 / 5||PROFINET IO Conformance Class B|
|CPF3 / 6||PROFINET IO Conformance Class C|
|CPF10||VNET / IP|
|CPF14||EPA (Ethernet for Plant Automation)|
|CPF15 / 1||Modbus / TCP|
|CPF15 / 2||RTPS|
|CPF16 / 1||SERCOS I|
|CPF16 / 2||SERCOS II|
|CPF16 / 3||SERCOS III|
Common field buses
- ARCNET Deterministic, real-time capable fieldbus, used in the fields of automotive, industrial automation (especially printing machines) and medical technology
- ARINC 629 Fast avionics bus from Arinc , used in the Boeing 777
- AS-Interface ( Actuator-Sensor-Interface ) for connecting sensors and actuators
- BACnet Building Automation and Control Networks for building management systems, but can also be used in some cases down to the field level
- CAN z. B. in the automotive sector
- CANopen (CAN-based, higher protocol) standard for elevator technology, automation technology, vehicle bodies, medical technology, ship electronics. Maintained by CAN in Automation (CiA)
- CC-Link bus widely used in Asia for industrial applications
- DALI for lighting in building automation
- DeviceNet (CAN-based, higher protocol)
- EIB European installation bus Mainly house installation, predecessor of KNX
- EtherCAT Ethernet-based fieldbus in automation technology
- Ethernet Powerlink Ethernet-based fieldbus for machine and plant construction
- EtherNet / IP (Ethernet-based, higher protocol), at least the former, especially in the USA
- FAIS-Bus , a Japanese fieldbus standard
- Foundation Fieldbus (FF) of the Fieldbus Foundation (process automation)
- FIP bus , French and Italian field bus standard, competitor to Profibus
- FlexRay bus in the automotive sector ( X-by-Wire )
- Hart Communication for industrial field devices
- INTERBUS mechanical engineering, plant engineering in special designs for safety technology
- KNX standard for building automation, successor to EIB
- LCN Local Control Network Universal building management system
- LIN bus in the automotive sector
- LocoNet for model railways
- LON mainly for building automation
- M-Bus (fieldbus)
- MIL-STD-1553 mainly used in military aviation
- Modbus industry
- MOST bus In the automotive multimedia sector
- MVB (Multifunction Vehicle Bus) rail vehicles IEC 61375
- P-NET The P-NET fieldbus
- PROFIBUS (variants: DP & PA), PROFINET : robots, mechanical engineering, plant engineering, process automation
- SafetyBUS p safety-related applications
- SERCOS interface Motion Control, CNC, robots, mechanical engineering, plant engineering
- SmallCAN integrative low-cost / low-power system, mainly for building automation (but also general automation technology)
- SMI Standard Motor Interface for controlling electronic drives, e.g. B. for blinds or shutters
- T-Bus Mainly used in agriculture, irrigation technology and environmental monitoring
- Time-Triggered Protocol (TTP)
- VARAN Ethernet-based fieldbus for the automation of machines and systems
Safety properties of field buses
If field bus systems are to be used in systems that have to withstand a test according to safety standards such as IEC 61508 or EN 954-1 , the bus system has to meet certain special requirements. These requirements are satisfied, for example, through the redundant structure of software and hardware in the end devices and, depending on the bus protocol, measures such as running counters, CRCs , acknowledgments, timeouts , identifiers for sender and receiver or redundancy with cross-comparison. See also safety requirement level , safety concept , safety . The internationally valid international standard IEC 61784-3: Industrial communication networks - Profiles - Part 3: Functional safety fieldbuses defines nine different protocols for safety-related fieldbuses in the CPF 1, 2, 3, 6, 8, 12, 13 and 14 families .
Another safety function of field buses relates to occupational safety if people are threatened by dangerous movements. For this purpose, emergency stop actuations, locking of safety doors for machines and robots, light grids and light curtains as well as optical scanners and the like are used. a. deployed and networked. Such facilities are subject to acceptance (e.g. Institute for Occupational Safety and Health of the German Social Accident Insurance in St. Augustin and TÜV ). The realization takes place without additional conventional wiring increasingly through innovative fieldbus solutions that do without the redundancy concepts mentioned above and can be implemented on a normal sensor-actuator fieldbus. More information about a system with "Safety at Work" and its creation can be found in the articles AS-Interface , Horst Saalbach and Werner Kriesel .
- Udo Enste, Jochen Müller: Data communication in the process industry . Oldenbourg Industrieverlag, Munich 2007, ISBN 978-3-8356-3116-8 .
- NP Mahalik: Fieldbus Technology . Springer Verlag, Berlin 2003, ISBN 978-3-540-40183-4 .
- Gerhard Schnell: Bus systems in automation and process technology . Basics, systems and trends in industrial communication. Ed .: Bernhard Wiedemann. 7th edition. Vieweg + Teubner Verlag, Wiesbaden 2008, ISBN 978-3-8348-0425-9 .
- Werner Kriesel , Tilo Heimbold , Dietmar Telschow: Bus technologies for automation . Networking, selection and application of communication systems. 2nd Edition. Hüthig, Heidelberg 2000, ISBN 3-7785-2778-9 .
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- Frithjof Klasen, Volker Oestreich, Michael Volz (eds.): Industrial communication with fieldbus and Ethernet . VDE Verlag, Berlin, Offenbach 2010, ISBN 978-3-8007-3297-5 .
- Werner Zimmermann, Ralf Schmidgall: Bus systems in vehicle technology - protocols, standards and software architecture. 5th edition. Springer Vieweg, 2014, ISBN 978-3-658-02418-5 .
- Werner Kriesel , Frank Sokollik , Peter Helm and Ralph Seela: KNX / EIB for building system technology in residential and functional buildings. Hüthig Jehle Rehm Verlag, Heidelberg, 5th edition 2009, ISBN 978-3-7785-4054-1 .