Profibus

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Current Profibus logo
First version of the Profibus logo from 1989, used until 2010

Profibus ( Pro cess fi eld Bus ) is a standard for field bus -Communication in the automation technology and was initially (1989) from the Federal Ministry of Education and Research funded. It should not be confused with the Profinet standard for Industrial Ethernet .

Emergence

The history of Profibus goes back to a publicly funded joint project launched in Germany in 1987, for which 21 companies and institutes had drawn up a project framework plan " Fieldbus ". The aim was to implement and distribute a bit-serial field bus, for which the standardization of the field device interface should create the basic requirements. To this end, the relevant member companies agreed to support a joint technical concept for production and process automation. In a first step, the complex communication protocol Profibus FMS (Fieldbus Message Specification) was specified, which was tailored to demanding communication tasks. In further steps from 1993 the specification of the more simply structured and therefore much faster protocol Profibus DP (Decentralized Peripherals) was carried out.

commitment

variants

Profibus exists in three variants, with DP being the most used:

  • Profibus DP ( decentralized periphery ) for controlling sensors and actuators through a central control in production technology. The main focus here is on the many standard diagnostic options. Further areas of application are the connection of "distributed intelligence", ie the networking of several controllers with one another (similar to PROFIBUS FMS). Data rates of up to 12 Mbit / s are possible on twisted two-wire cables or fiber optic cables. Use with drive devices is defined in the PROFIdrive profile .
  • Profibus PA ( P rozess- A utomation) is used for communication between measuring and process equipment , actuators and the process control system or PLC / DCS in the process and process technology used. Profibus PA is a Profibus variant with a physical layer ( transmission layer ) suitable for process automation , in which several segments (PA segments) with field devices can be connected to Profibus DP via so-called couplers. The two-wire bus line of these segments not only takes over the communication, but also the energy supply of the participants ( MBP transmission technology ). Profibus PA is a digital alternative to the classic analog connection of devices (4 to 20 mA technology) and offers additional functions through bidirectional communication. Profibus PA is also suitable for potentially explosive areas thanks to its power limitation. Different types of explosion protection are used depending on the area of ​​application . The intrinsic safety degree of protection is particularly well established . It allows access to the field device during operation without a hot work permit ( FISCO specification ). The data transfer rate of Profibus PA is 31.25 kbit / s, which ensures high immunity to electromagnetic interference and enables long cable runs. This speed is completely sufficient for process engineering applications. Another special feature of Profibus PA is the widespread device profile "PA Devices" (PA profile), in which the most important functions of the field devices are standardized across manufacturers, which is of considerable benefit for the user.
  • Profibus FMS (Fieldbus Message Specification) was primarily intended for use in complex machines and systems. This protocol variant was replaced by DP and is no longer part of the international fieldbus standard.

Application scenarios

In the manufacturing industry , Profibus DP is used for fast communication between controls and sensors / actuators of all kinds in machines and systems.

The further development in the manufacturing industry is clearly moving towards higher speeds through the use of Industrial Ethernet ( Profinet ) as communication technology. Investments made are largely protected by z. B. Mapping of existing Profibus device profiles (such as PROFIdrive ) on Profinet.

In the process industry there is a twofold relationship between

  • conventional technology (4–20 mA, mostly with HART technology), especially with existing systems and the
  • Fieldbus technology (Profibus PA and Foundation fieldbus H1) for newly built systems.

Since, however, larger amounts of data will have to be transmitted in the coming Industry 4.0, systems are already being equipped with Profinet to ensure that they are compatible.

The benefits of fieldbus technology with regard to z. B. simple and cost-saving topology, bidirectional communication, extensive information options and standardization of the device functions (device profile) is welcomed by the user without reservation. Further developments are expected in the direction of easier handling of the field devices in operation and maintenance.

Profibus is the only fieldbus that can be used in the manufacturing industry and in the process industry and has meanwhile become the world market leader. Over 43.8 million devices with Profibus are in use worldwide.

technology

Profibus protocols ( OSI model )

OSI layer English Profibus
7th application Application DP-V0 DP-V1 DP-V2 management
6th presentation Presentation -
5 meeting session
4th transport transport
3 network Network
2 connection Data link FDL
1 medium Physical EIA-485 Optically MBP


Application layer

The DP application layer was defined in three steps. The DP protocol originally stipulated in 1993 is now colloquially known as “DP-V0”, the two extensions correspondingly “DP-V1” and “DP-V2”. The following functions were defined in the individual stages:

  • In DP-V0 the cyclical exchange of data and diagnoses . Devices that support this range of functions are mainly used in general automation technology and machine control.
  • Acyclic data exchange and alarm handling in DP-V1 . Devices that support these expansions are mainly found in process engineering.
  • In DP-V2 the isochronous data exchange, the slave cross-traffic and the time synchronization. With this expansion, requirements from manufacturing technology and robot control were taken into account.

The PA protocol was defined as part of the DP-V1 development stage.

Data link layer

Exemplary topology to illustrate the combination of token passing with a master-slave method

The data link layer FDL ( F ieldbus D ata L ink) works with a hybrid access procedure that combines token passing with a master-slave procedure. In a Profibus network, the controls or process control systems are the masters and the sensors and actuators are the slaves.

Different telegram types are used, which can be differentiated by the start delimiter (SD) (Profibus DP):

Telegram type Coding Telegram structure
No data SD1 = 0x10
SD1 THERE SA FC FCS ED
Variable length data SD2 = 0x68
SD2 LE LEr SD2 THERE SA FC PDU FCS ED
Fixed length data (rare) SD3 = 0xA2
SD3 THERE SA FC PDU FCS ED
Token SD4 = 0xDC
SD4 THERE SA
Short acknowledgment SC = 0xE5
SC

Abbreviations:

The FCS is calculated by simply adding up the bytes within the specified length. An overflow is ignored. Each byte is secured with an even parity and transmitted asynchronously with start and stop bits .

The individual bytes of a telegram must be slip-free, i. H. without a pause between the stop and the next start bit. The master signals the start of a new telegram with a SYN pause of at least 33 bits (logical "1" = bus idle state).

With Profibus-PA there is the same division of the telegram types, they have a different telegram frame which, in contrast to DP, is the same for all telegram types (except SD), etc. a. with special bit symbols of the Manchester code and a preamble for synchronization. A 16-bit long CRC replaces the checksum as FCS, but is used for every telegram type. The pause times between the telegrams are also set differently. With the signal level free of DC voltage, the bus idle state is determined by the absence of a signal (no signal level change).

Physical layer

Three different procedures are defined for the physical layer:

  • For electrical transmission according to EIA-485 , twisted two-wire cables with a wave impedance of 150 ohms are used in a bus topology . It can bitrates s s be configured up to 12 Mbit / 9600 bit / s. Depending on the bit rate used, the cable length between two repeaters is limited to 100 to 1200 meters. This transmission method is mainly used with Profibus DP and FMS. Two different cable types are specified for electrical transmission (type A and type B). The most popular cable is the purple type A.
  • In the optical transmission via optical fibers come star , bus and ring topologies are used. The distances between the repeaters can be up to 15 km. The ring topology can also be implemented redundantly .
  • With MBP ( Manchester Bus Powered) transmission technology, data and the power supply for the field devices are transmitted over the same cable. The power can be limited so that it can also be used in an explosive environment. Then one speaks of a so-called intrinsically safe area. The use of the FISCO concept is recommended. For this area, the bus cables, which have a different specification than cable type A (EIA-485), have a blue jacket. The bus topology can be up to 1900 meters long and allows branches to the field devices with a maximum length of 120 meters. The bit rate is fixed at 31.25 kbit / s. This technology has been specially defined for use in process automation for Profibus PA.

Products from several manufacturers are available for data transmission via sliding contacts, for mobile users or for optical or radio data transmission in free space, but these are not specified in any standard ( wireless Profibus ).

Pin assignment 9-pin D-Sub

The standards recommend using a D-Sub connector for connecting the Profibus . The connection assignment for this is:

Profibus pin assignment DF PROFI 2 (COMSOFT). Connections in brackets are optional

Pin SUB-D Profibus
9-pin D-Sub connector
1 NC (shield)
2 NC (M24)
3 BUS B
4th NC (CNTR-P)
5 DGND
6th +5 V
7th NC (P24)
8th BUS A
9 NC (CNTR-N)


  • Various Profibus connectors

  • Cable routing in the plug

  • Cable for Profibus DP in characteristic color

Application profiles

For the bus participants involved in an automation solution to work together smoothly, they must match in terms of their basic functions and services. The standardization is achieved through "profiles" with binding specifications for the functions and services. The possible functions of the communication with the Profibus are restricted and additional specifications about the function of the field device are prescribed. This can involve properties across device classes such as safety-relevant behavior (Common Application Profiles) or device class-specific properties (Specific Application Profiles). A distinction is made between these

  • Device Profiles for e.g. B. Robots, drives ( PROFIdrive ), process devices, encoders, pumps
  • Industry profiles for e.g. B. laboratory technology or rail vehicles
  • Integration profiles for the integration of subsystems such as B. HART or IO-Link systems

Process devices

Modern process devices have their own intelligence and can take over part of the information processing or the overall functionality in automation systems. The PA Devices profile defines all functions and parameters for various classes of process devices that are typical in process devices for the signal flow from the sensor signal from the process to the preprocessed process value that is read out to the control system together with a measured value status. The PA Devices profile contains device data sheets for

  • Pressure and differential pressure
  • Level, temperature and flow
  • Analog and digital inputs and outputs
  • Valves and actuators
  • Analyzers

The current version 3.02 of the PA device profile is a novelty in the process industry: Classified diagnostic information, device-neutral configuration or self-adapting field devices (when devices are replaced with an earlier device version) are some examples.

Drives

PROFIdrive is the modular device profile for drive units. It was developed jointly by manufacturers and users in the 1990s and has since covered the entire range from the simplest to the most sophisticated drive solutions in conjunction with Profibus and later also with Profinet .

functional safety

PROFIsafe defines how safety-related devices ( emergency stop button , light grids , overfill protection, ...) communicate with safety controllers via Profibus so safely that they can be used in safety-related automation tasks up to SIL3 ( Safety Integrity Level ). It implements secure communication via a profile, i. H. via a special format of the user data and a special protocol. PROFIsafe is specified for Profibus and Profinet in the IEC 61784-3 standard.

Normalization

Profibus was 1991 / 1993 in DIN defined 19245, is 1996 in EN been transferred 50170 and since 1999 in IEC 61158/ 61784 IEC fixed.

organization

The Profibus User Organization eV (PNO), in which manufacturers and users in Germany have come together, has existed since 1989 . The first regional Profibus Switzerland organization was founded in Switzerland in 1992. Further RPAs (Regional Profibus & Profinet Association) were added in the following years. Today Profibus is represented by 27 RPAs around the world. In 1995 all RPAs merged to form the international umbrella organization Profibus & Profinet International (PI).

literature

  • Max Felser: PROFIBUS Manual: A collection of explanations for PROFIBUS networks . Epubli, ISBN 978-3-7375-5470-1
  • Manfred Popp: Profibus-Dp / DPV1 basics, tips and tricks for users . Hüthig, ISBN 3-7785-2781-9
  • Christian Diedrich: PROFIBUS PA - instrumentation technology for process engineering . Oldenbourg, ISBN 3-8356-3056-3
  • Josef Weigmann, Gerhard Kilian: Decentralization with PROFIBUS-DP / DPV1. Structure, configuration and use of the PROFIBUS-DP with SIMATIC S7 , 3rd edition, 2002, ISBN 3-89578-189-4
  • Christian Diedrich, Thomas Bangemann: Profibus PA , Oldenbourg Industrieverlag, ISBN 978-3-8356-3125-0
  • Gerhard Schnell and Bernhard Wiedemann: Bus systems in automation and process technology, Vieweg + Teubner Verlag, Wiesbaden 2008, ISBN 978-3-8348-0425-9 .

Web links

Technical information:

Organization:

Individual evidence

  1. ↑ http://www.profibus.com/community/regional-pi-associations/germany-new/presse-aktuelles-presse/single-view/article/pi-technologien-durchdringen-die-maerkte/ ( Memento from 30. June 2013 in the web archive archive.today )