World Library  
Flag as Inappropriate
Email this Article

Profibus

 

Profibus

Profibus electrical connector

PROFIBUS (Process Field Bus) is a standard for fieldbus 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 openly published as part of IEC 61158.

Contents

  • Origin 1
  • Technology 2
    • Application layer 2.1
    • Security layer 2.2
    • Bit-transmission layer 2.3

Origin

The history of PROFIBUS goes back to a publicly promoted plan for an association which started in Germany in 1986 and for which 21 companies and institutes devised a master project plan called "fieldbus". 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 (Decentralised 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 (Decentralised Peripherals) is used to operate sensors and actuators via a centralised 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

PROFIBUS Protocol (OSI reference model)
OSI-Layer PROFIBUS
7 Application DPV0 DPV1 DPV2 Management
6 Presentation --
5 Session
4 Transport
3 Network
2 Data Link FDL
1 Physical EIA-485 Optical MBP


Application layer

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

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

Security layer

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
SD1 DA SA FC FCS ED

Variable length data:

SD2 = 0x68

SD2 LE LEr SD2 DA SA FC DSAP SSAP PDU FCS ED

Fixed length data:

SD3 = 0xA2

SD3 DA SA FC PDU FCS ED

Token:

SD4 = 0xDC

SD4 DA SA ED

Brief acknowledgement:

SC = 0xE5

SC
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
SAP (Decimal) SERVICE
Default 0 Cyclical Data Exchange (Write_Read_Data)
54 Master-to-Master SAP (M-M Communication)
55 Change Station Address (Set_Slave_Add)
56 Read Inputs (Rd_Inp)
57 Read Outputs (Rd_Outp)
58 Control Commands to a DP Slave (Global_Control)
59 Read Configuration Data (Get_Cfg)
60 Read Diagnostic Data (Slave_Diagnosis)
61 Send Parameterization Data (Set_Prm)
62 Check Configuration Data (Chk_Cfg)

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

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┬ákm. 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
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
 
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
 
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.
 


Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.