Profibus electrical connector

PROFIBUS (Process Field Bus) is a standard for field bus communication in automation technology and was first promoted in 1989 by BMBF (German department of education and research) and then used by Siemens. It should not be confused with the PROFINET standard for Industrial Ethernet. PROFIBUS is not an openly published and royalty-free protocol as MODBUS.

Origin [edit]

The history of PROFIBUS goes back to a publicly promoted plan for an association started in Germany in 1987 and for which 21 companies and institutes devised a master project plan called "field bus". The goal was to implement and spread the use of a bit-serial field bus based on the basic requirements of the field device interfaces. For this purpose, member companies agreed to support a common technical concept for production (i.e. discrete or factory automation) and process automation. First, the complex communication protocol Profibus FMS (Field bus Message Specification), which was tailored for demanding communication tasks, was specified. Subsequently in 1993, the specification for the simpler and thus considerably faster protocol PROFIBUS DP (Decentralized Peripherals) was completed. Profibus FMS is used for (non deterministic) communication of data between Profibus Masters. Profibus DP is a protocol made for (deterministic) communication between Profibus masters and their remote I/O slaves.

There are two variations of PROFIBUS in use today; the most commonly used PROFIBUS DP, and the lesser used, application specific, PROFIBUS PA:

• PROFIBUS DP (Decentralized Peripherals) is used to operate sensors and actuators via a centralized controller in production (factory) automation applications. The many standard diagnostic options, in particular, are focused on here.
• PROFIBUS PA (Process Automation) is used to monitor measuring equipment via a process control system in process automation applications. This variant is designed for use in explosion/hazardous areas (Ex-zone 0 and 1). The Physical Layer (i.e. the cable) conforms to IEC 61158-2, which allows power to be delivered over the bus to field instruments, while limiting current flows so that explosive conditions are not created, even if a malfunction occurs. The number of devices attached to a PA segment is limited by this feature. PA has a data transmission rate of 31.25 kbit/s. However, PA uses the same protocol as DP, and can be linked to a DP network using a coupler device. The much faster DP acts as a backbone network for transmitting process signals to the controller. This means that DP and PA can work tightly together, especially in hybrid applications where process and factory automation networks operate side by side.

In excess of 30 million PROFIBUS nodes were installed by the end of 2009. 5 million of these are in the process industries.

Technology [edit]

Application layer [edit]

To utilize these functions, various service levels of the DP protocol were defined:

• DP-V0 for cyclic exchange of data and diagnosis
• DP-V1 for acyclic and cyclic data exchange and alarm handling
• DP-V2 for isochronous mode and data exchange broadcast (slave-to-slave communication)

Security layer [edit]

The security layer FDL (Field bus Data Link) works with a hybrid access method that combines token passing with a master-slave method. In a PROFIBUS DP network, the controllers or process control systems are the masters and the sensors and actuators are the slaves.

Various telegram types are used. They can be differentiated by their start delimiter (SD):

No data: SD1 = 0x10

Variable length data:

SD2 = 0x68

Fixed length data:

SD3 = 0xA2

Token:

SD4 = 0xDC

Brief acknowledgement:

SC = 0xE5

SD: Start Delimiter

LE: Length of protocol data unit, (incl. DA,SA,FC,DSAP,SSAP)

LEr: Repetition of protocol data unit, (Hamming distance = 4)

FC: Function Code

DA: Destination Address

SA: Source Address

DSAP: Destination Service Access Point

SSAP: Source Service Access Point

Note: SAP55 is optional and may be disabled if the slave doesn't provide non-volatile storage memory for the station address.

PDU: Protocol Data Unit (protocol data)

FCS: Frame Checking Sequence

ED: End Delimiter (= 0x16 !)

The FCS is calculated by simply adding up the bytes within the specified length. An overflow is ignored here. Each byte is saved with an even parity and transferred asynchronously with a start and stop bit. There may not be a pause between a stop bit and the following start bit when the bytes of a telegram are transmitted. The master signals the start of a new telegram with a SYN pause of at least 33 bits (logical "1" = bus idle).

Bit-transmission layer [edit]

Three different methods are specified for the bit-transmission layer:

• With electrical transmission pursuant to EIA-485, twisted pair cables with impedances of 150 ohms are used in a bus topology. Bit rates from 9.6 kbit/s to 12 Mbit/s can be used. The cable length between two repeaters is limited from 100 to 1200 m, depending on the bit rate used. This transmission method is primarily used with PROFIBUS DP.
• With optical transmission via fiber optics, star-, bus- and ring-topologies are used. The distance between the repeaters can be up to 15 km. The ring topology can also be executed redundantly.
• With MBP (Manchester Bus Powered) transmission technology, data and field bus power are fed through the same cable. The power can be reduced in such a way that use in explosion-hazardous environments is possible. The bus topology can be up to 1900 m long and permits branching to field devices (max. 60 m branches). The bit rate here is a fixed 31.25 kbit/s. This technology was specially established for use in process automation for PROFIBUS PA.

For data transfer via sliding contacts for mobile devices or optical or radio data transmission in open spaces, products from various manufacturers can be obtained, however they do not conform to any standard.

PROFIBUS DP It runs over two core screened cable that is violet sheathed and its speed varies from 9.6Kbps to 12Mbps. A particular speed can be chosen for a network to give enough time for communication with all the devices present in the network. If systems change slowly then lower communication speed is suitable and if the systems change quickly then effective communication will happen through faster speed. The RS485 balanced transmission that is used in PROFIBUS DP only allows 32 devices to be connected at once but more devices can be connected and network can be expanded with the use of hubs or repeaters.

PROFIBUS PA It is slower than PROFIBUS DP and runs at fixed speed of 31.2Kbps via blue sheathed two core screened cable. The communication may be initiated to minimise the risk of explosion or for the systems that intrinsically need safe equipment. The message formats in PROFIBUS PA are identical to PROFIBUS DP.

Note: PROFIBUS DP and PROFIBUS PA should not be confused with ProfiNet. ProfiNet is an Ethernet communication standard and it is used for process control and process measurement. It is basically used to link computer systems in an office or a network.

Profiles [edit]

Profiles are pre-defined configurations of the functions and features available from PROFIBUS for use in specific devices or applications. They are specified by PI working groups and published by PI. Profiles are important for openness, interoperability and interchangeability, so that the end user can be sure that similar equipments from different vendors perform in a standardised way. User choice also encourages competition that drives vendors towards enhanced performance and lower costs.

There are PROFIBUS profiles for Encoders, Laboratory instruments, Intelligent pumps, Robots and Numerically Controlled machines, for example. Profiles also exist for applications such as using HART and wireless with PROFIBUS, and process automation devices via PROFIBUS PA. Other profiles have been specified for Motion Control (PROFIdrive) and Functional Safety (PROFIsafe).

Standardization [edit]

PROFIBUS was defined in 1991/1993 in DIN 19245, was then included in EN 50170 in 1996 and, since 1999, established in IEC 61158/IEC 61784.

Organization [edit]

The PROFIBUS Nutzerorganisation e.V. (PROFIBUS User Organization, or PNO) was created in 1989. This group was composed mainly of manufacturers and users from Europe. In 1992, the first regional PROFIBUS organization was founded (PROFIBUS Schweiz in Switzerland). In the following years, additional Regional PROFIBUS & PROFINET Associations (RPAs) were added.

In 1995, all the RPAs joined together under the international umbrella association PROFIBUS & PROFINET International (PI). Today, PROFIBUS is represented by 25 RPAs around the world (including PNO) with over 1400 members, including most if not all major automation vendors and service suppliers, along with many end users.

See also [edit]

	Computer networking portal
	Computer Science portal

• Fieldbus
• List of automation protocols

References [edit]

• [1] PROFIBUS system description
• J. Weigmann, G. Kilian: Decentralization with PROFIBUS DP/DPV1, ISBN 978-3-89578-218-3
• M. Felser: PROFIBUS Manual, A collection of information explaining PROFIBUS networks assembled by Prof. Max Felser, ISBN 978-3-8442-1435-2

External links [edit]

• PROFIBUS & PROFINET International

v t e Computer bus official and de facto standards (wired) General System bus Front-side bus Back-side bus Daisy chain Control bus Address bus Bus contention Plug and play List of bus bandwidths Standards S-100 bus Unibus VAXBI MBus STD Bus SMBus Q-Bus ISA Zorro II Zorro III CAMAC FASTBUS LPC HP Precision Bus EISA VME VXI VXS NuBus TURBOchannel MCA SBus VLB PCI PXI HP GSC bus CoreConnect InfiniBand UPA PCI Extended (PCI-X) AGP PCI Express (PCIe) RapidIO Intel QuickPath Interconnect HyperTransport Portable PC Card ExpressCard Embedded Multidrop bus AMBA Wishbone Storage ST-506 ESDI SMD Parallel ATA (PATA) DMA SSA HIPPI USB MSC IEEE 1394 interface (FireWire) Serial ATA (SATA) eSATA eSATAp SCSI Parallel SCSI SAS Peripheral Apple Desktop Bus HIL MIDI Multibus RS-232 RS-422 RS-423 RS-485 DMX512-A IEEE-488 (GPIB) IEEE-1284 (parallel port) UNI/O ACCESS.bus 1-Wire I²C SPI Parallel SCSI Profibus USB IEEE 1394 (FireWire) Camera Link External PCIe Thunderbolt Note: interfaces are listed in speed ascending order (roughly), the interface at the end of each section should be the fastest Category